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Date: 8 September 2021
IAEA SAFETY STANDARDS
STATUS: STEP 8
for protecting people and the environment
Draft
for
review
by
the
Member States
Borehole Disposal Facilities for Radioactive
Waste
DRAFT SAFETY GUIDE
DS512
Draft Safety Guide
CONTENTS
CONTENTS ............................................................................................................................................ ii
1.
INTRODUCTION ........................................................................................................................ 1
Background ................................................................................................................................... 1
Objective ....................................................................................................................................... 2
Scope ............................................................................................................................................ 2
Structure........................................................................................................................................ 3
2.
OVERVIEW OF BOREHOLE DISPOSAL AND ITS IMPLEMENTATION ........................... 4
Borehole Disposal of Disused Sealed Radioactive Sources ......................................................... 4
Other Borehole Disposal Concepts ............................................................................................. 11
3.
LEGAL AND ORGANIZATIONAL INFRASTRUCTURE ..................................................... 11
Responsibilities of the Government............................................................................................ 11
Responsibilities of the Regulatory Body .................................................................................... 15
Responsibilities of the Operating Organization .......................................................................... 19
4.
SAFETY APPROACH ............................................................................................................... 22
Importance of Safety in the Development and Operation of a Disposal Facility ....................... 22
Passive Means for the Safety of a Disposal Facility ................................................................... 25
Understanding of a Disposal Facility and Confidence in Safety ................................................ 26
Multiple Safety Functions........................................................................................................... 28
Containment of Radioactive Waste ............................................................................................ 29
Isolation of Radioactive Waste ................................................................................................... 30
Surveillance and Control of Passive Safety Features ................................................................. 31
Step by Step Development and Evaluation of Disposal Facilities .............................................. 32
5.
SAFETY CASE AND SAFETY ASSESSMENT ...................................................................... 33
Preparation, Approval and Use of the Safety Case and Safety Assessment ............................... 34
Scope of the Safety Case and Safety Assessment....................................................................... 36
Documentation of the Safety Case and Safety Assessment ........................................................ 47
6.
APPROACH TO THE DEVELOPMENT OF A BOREHOLE DISPOSAL FACILITY .......... 50
Predisposal Management of Radioactive Waste for Borehole Disposal..................................... 50
Site Characterization for a Borehole Disposal Facility .............................................................. 53
Design of a Borehole Disposal Facility ...................................................................................... 56
Construction of a Borehole Disposal Facility ............................................................................. 59
Commissioning of a Borehole Disposal Facility ........................................................................ 62
Operation of a Borehole Disposal Facility ................................................................................. 62
Closure of a Borehole Disposal Facility ..................................................................................... 70
7.
ASSURANCE OF SAFETY ...................................................................................................... 70
Monitoring Programmes at a Borehole Disposal Facility .......................................................... 70
The Period After Closure and Institutional Controls .................................................................. 73
Accounting for, and Control of, Nuclear Material...................................................................... 75
Managing Interfaces Between Safety and Security .................................................................... 76
Management Systems ................................................................................................................. 77
Preparedness and Response for a Nuclear or Radiological Emergency ..................................... 78
8.
EXISTING DISPOSAL FACILITIES ....................................................................................... 79
Existing Disposal Facilities ........................................................................................................ 79
Appendix I. SITING AND SITE CHARACTERIZATION FOR BOREHOLE DISPOSAL
FACILITIES ......................................................................................................................................... 81
Appendix II. SAFETY ASSESSMENT FOR BOREHOLE DISPOSAL FACILITIES ...................... 93
REFERENCES ..................................................................................................................................... 97
ANNEX I. OTHER BOREHOLE DISPOSAL CONCEPTS ............................................................. 103
ANNEX II. ISOLATION AND DISPOSAL DEPTH ........................................................................ 107
CONTRIBUTORS TO DRAFTING AND REVIEW ........................................................................ 109
1. INTRODUCTION
BACKGROUND
1.1.
This Safety Guide provides recommendations and guidance on the development, operation,
closure, institutional control and regulation of borehole disposal facilities for radioactive waste to fulfil
the safety principles and requirements contained in the IAEA Safety Standards, particularly in IAEA
Safety Standards Series No. SF-1, Fundamental Safety Principles [1], IAEA Safety Standards Series
No. GSR Part 3, Radiation Protection and Safety of Radiation Sources: International Basic Safety
Standards [2], IAEA Safety Standards Series No. GSR Part 5, Predisposal Management of Radioactive
Waste [3], and IAEA Safety Standards Series No. SSR-5, Disposal of Radioactive Waste [4]. The
radioactive waste considered in this Safety Guide comprises disused sealed radioactive sources 1 that
have been declared radioactive waste, and low level waste and intermediate level waste generated
during their management.
1.2.
This Safety Guide supersedes IAEA Safety Standards Series No. SSG-1 2. Since SSG-1 was
published in December 2009, relevant safety requirements have been revised, and significant further
research and development has been conducted on borehole disposal of disused sealed radioactive
sources in preparation for its implementation by Member States. In addition, borehole disposal of
disused sealed radioactive sources has been licensed in one Member State and pilot borehole disposal
projects are underway. Several other Member States are actively interested in developing their own
borehole disposal facilities for disused sealed radioactive sources. It is timely, therefore, to provide
revised guidance that properly reflects the current safety standards and the state of knowledge regarding
borehole disposal for these types of radioactive waste.
1.3.
The modifications incorporated into this Safety Guide reflect recent research and development,
research studies and pilot projects on borehole disposal of waste as described in para. 1.1. The Safety
Guide has also been updated for consistency with current IAEA safety standards. The Safety Guide is
consistent with the Joint Convention on the Safety of Spent Fuel Management and on the Safety of
Radioactive Waste Management – (the Joint Convention), Ref. [6] and the supplementary guidance to
the Code of Conduct on the Safety and Security of Radioactive Sources (the Code of Conduct) on the
Management of Disused Sealed Radioactive Sources, Ref. [7].
A radioactive source, comprising radioactive material that is permanently sealed in a capsule or closely bonded
and in a solid form (excluding reactor fuel elements), that is no longer used, and is not intended to be used, for the
practice for which an authorization was granted, Ref. [5].
1
INTERNATIONAL ATOMIC ENERGY AGENCY, Borehole Disposal Facilities for Radioactive Waste, IAEA
Safety Standards Series No. SSG-1, IAEA, Vienna (2009).
2
1
OBJECTIVE
1.4.
The objective of this Safety Guide is to provide recommendations and guidance on the
development, operation, closure, institutional control and regulation of borehole disposal facilities for
disused sealed radioactive sources that have been declared radioactive waste and small amounts of low
level waste and intermediate level waste generated during the management of the disused sealed
radioactive sources, to fulfil the safety requirements contained in GSR Part 3 [2], GSR Part 5 [3] and
SSR-5 [4]. This Safety Guide can also be used as a basis for reassessing and where appropriate
upgrading the safety of existing borehole disposal facilities.
1.5.
This Safety Guide complements IAEA Safety Standards Series No. SSG-29, Near Surface
Disposal Facilities for Radioactive Waste [8] 3 and IAEA Safety Standards Series No. SSG-14,
Geological Disposal Facilities for Radioactive Waste [9].
SCOPE
1.6.
This Safety Guide provides recommendations and guidance on borehole disposal facilities for
disused sealed radioactive sources that have been declared radioactive waste, and low level waste and
intermediate level waste generated during their management as described in para. 1.1. This Safety Guide
does not provide recommendations and guidance on the predisposal management or disposal of other
radioactive waste; in particular high level waste is not addressed 4.
1.7.
There is a potential to develop safe borehole disposal facilities with various designs and
different methods for conditioning waste for disposal. For example, borehole disposal facilities could
include different numbers of boreholes and boreholes with different diameters. Further information on
such concepts and facilities is provided in Annex I. The waste could, for example, comprise disused
sealed radioactive sources that have been encapsulated in concrete within steel drums – a previously
recommended, but now obsolete practice. The recommendations in this Safety Guide are relevant to all
borehole disposal facilities for radioactive waste as described in para. 1.1. However, in providing
recommendations on borehole disposal, this Safety Guide focusses on a recommended borehole
disposal concept that involves the conditioning and disposal of radioactive waste as identified in
para. 1.1 using cement-based and stainless steel engineered barriers and narrow diameter boreholes –
see paras 2.12 to 2.18. Furthermore, in light of experiences in various States, this Safety Guide focuses
on the disposal of radioactive waste at depths that are sufficient in conjunction with other factors to
surface disposal facilities include disposal facilities at the surface and at depths of up to a few tens of meters
underground – SSG-29 [8]
3 Near
In IAEA Safety Standards Series No. GSG-1, Classification of Radioactive Waste [10] spent fuel that has been
declared radioactive waste is included in high level waste.
4
2
make adverse effects on safety due to inadvertent human intrusion improbable (see paras 4.33 to 4.37
and Annex II) 5.
1.8.
The Safety Guide assumes that all transport of radioactive material as defined in IAEA Safety
Standards Series No. SSR-6 (Rev. 1), Regulations for the Safe Transport of Radioactive Material [11]
is conducted in accordance with SSR-6 (Rev. 1).
1.9.
This Safety Guide addresses the safety of the predisposal management of waste as described in
para. 1.1 and its disposal. This Safety Guide addresses both operational safety and post-closure safety
at borehole disposal facilities. This safety guide addresses the interdependencies between the
predisposal management steps for the radioactive waste in question and its disposal in borehole disposal
facilities.
1.10.
It is recognized that radioactive waste disposal is carried out within a wider process that, for
example, includes consideration of financial, economic and social issues, as well as issues of
conventional safety, security, planning and aspects of environmental protection not related to protection
from exposure to ionizing radiation. These ‘wider’ issues are not specifically addressed in this Safety
Guide.
1.11.
This Safety Guide is intended for those persons whose prime interest is in the regulation and
implementation of the safe disposal of radioactive waste in borehole disposal facilities.
STRUCTURE
1.12.
Following this Introduction, Section 2 provides an overview of borehole disposal and describes
a recommended borehole disposal concept for waste as identified in para. 1.1. Section 3 provides
recommendations and guidance on fulfilling the requirements on the legal and organizational
infrastructure. Sections 4 and 5 focus on how an adequate level of safety may be achieved and
demonstrated. Section 6 describes the process of developing a borehole disposal facility. Section 7
provides recommendations and guidance on measures to give additional assurance of safety. Section 8
addresses existing borehole disposal facilities. Two Appendices complement the main text with respect
to (a) siting and site characterization for borehole disposal facilities and (b) safety assessment for
borehole disposal facilities. Two Annexes address (a) other borehole disposal concepts and (b) the
relationship between disposal depth and isolation of waste from people and the environment.
Radioactive waste disposal facilities comprising rock caverns, silos and tunnels at depths of up to a few tens of
meters underground are near surface disposal facilities and are addressed in SSG-29 [8].
5
3
2. OVERVIEW OF BOREHOLE DISPOSAL AND ITS IMPLEMENTATION
BOREHOLE DISPOSAL OF DISUSED SEALED RADIOACTIVE SOURCES
2.1.
Para. 1.6 of SSR-5 [4] states:
“The preferred strategy for the management of all radioactive waste is to contain it (i.e. to
confine the radionuclides to within the waste matrix, the packaging and the disposal facility)
and to isolate it from the accessible biosphere”.
2.2.
The safety standards recognize three options for the disposal 6 of radioactive waste: near surface
disposal, borehole disposal, and geological disposal. From a safety perspective, borehole disposal is not
conceptually different from either near surface disposal or geological disposal. In all cases, safety is
achieved through a combination of natural and engineered barriers that provide sufficient containment
and isolation of the waste to fulfil the safety requirements and, thereby, ensure an adequate level of
protection for people and the environment.
2.3.
In borehole disposal, containment and isolation should be provided by a multi-barrier system,
each element of which fulfils one or more safety functions over different timescales. The host geological
environment and the depth of disposal should be chosen so that the disposal facility provides the
necessary containment and isolation. Isolation should be provided inter alia by reducing the probability
of inadvertent human intrusion.
2.4.
Borehole disposal facilities have to comply with the requirements and standards of safety that
apply to all disposal facilities. It is a requirement that the operating organization7 develops a site-specific
safety case, including safety assessments, to evaluate and demonstrate facility safety, and to determine
the types and amounts of radioactive waste that can safely be disposed of at the facility – see SSR-5 [4].
The safety assessments have to comply with the requirements in SSR-5 [4] and in IAEA Safety
Standards Series No. GSR Part 4 (Rev. 1), Safety Assessment for Facilities and Activities [13].
2.5.
Borehole disposal offers flexibility concerning the possible depth of waste disposal; the range
of depths that may be accessed by boreholes can reach from the surface (but see paras 4.33 to 4.36)
down to and beyond the depths typically associated with geological disposal facilities – see SSR-5 [4].
The depth chosen for the disposal of radioactive waste in a particular facility should be determined by
the need to reduce the probability of inadvertent human intrusion (as discussed further below in paras
6
Disposal is the emplacement of waste in an appropriate facility without the intention of retrieval [5].
The operating organization is “any organization or person applying for authorization or authorized to operate an
authorized facility or to conduct an authorized activity and responsible for its safety. This includes, inter alia,
private individuals, governmental bodies, consignors or carriers, licensees, hospitals, self-employed persons.
Operating organization is synonymous with ‘operator’” [5]. The licensee is “the holder of a current licence. The
licensee is the person or organization having overall responsibility for a facility or activity” [5]. The operating
organization may not be the holder of the licence (e.g. the operator could be a supply chain organization). In
practice, for an authorized facility, the operating organization is normally also the registrant or licensee. However,
the separate terms are retained to refer to the two different capacities [5].
7
4
4.33 to 4.36) and by factors including the nature of the waste and the suitability of the host geology and
the associated hydrogeological and hydrogeochemical conditions, and the possible influence of climatic
and other surface related processes (e.g. erosion).
2.6.
A borehole disposal facility at a specific site should include one or more boreholes. The number
of boreholes and the depths of waste disposal should be determined by taking into consideration the
inventory of waste to be disposed of, the probability of inadvertent human intrusion, the geology of the
site, and the results of safety assessment. Each borehole should be fitted with a casing which is sealed
at the bottom of the borehole to provide a dry and well-defined disposal volume. The spacing between
boreholes should be optimized taking account of the practicalities of drilling and operations, the
potential for interactions between boreholes, and the results of safety assessment.
2.7.
The operating organization should use waste packages that are suitable for the borehole disposal
facility. The size of the waste packages for disposal should be compatible with the diameter of the
borehole and the length of the disused sealed radioactive sources. The waste package is the product of
conditioning the waste. The waste package should include one or more waste containers. Backfill
material should be used to fill any spaces in the waste package. Backfill material should also be used to
fill the spaces in the boreholes outside the waste packages, and the spaces between the borehole casing
and the host geology. All these components together with the surrounding rocks should provide a multibarrier system that ensures a safe and sustainable management solution for the radioactive waste.
2.8.
To the fullest extent possible, the safety of a disposal facility is required to be ensured by
passive means, and the need for actions to be taken after closure of the facility is required to be
minimized (Requirement 5 of SSR-5 [4]). The operating organization should design a borehole disposal
facility so that safety is provided by passive means through the inherent characteristics of the
components of the facility itself; the waste package, backfill materials and the host geological
environment, and there should be no need for actions to be taken to ensure safety after release of the
site from regulatory control 8.
2.9.
Borehole disposal facilities are constructed by drilling and, therefore, have a characteristic
geometry. The geometry of a borehole disposal facility is such that it is generally suitable for relatively
small volumes of radioactive waste as compared with the volumes that can be disposed of in near surface
or geological disposal facilities. When planning waste disposal, consideration should be given to the
volumes of waste that need to be disposed of and to the volumes of existing and planned disposal
facilities and their capacities to receive safely the radioactive waste that needs to be disposed of,9.
8
Monitoring at a borehole disposal facility is discussed in Section 7.
The volume capacity of borehole disposal facilities to receive conditioned radioactive waste is limited by the
diameter and length of borehole in host rocks suitable for safe disposal – see main text; the term ‘small volumes’
here refers to volumes that are significantly less than the thousands to hundreds of thousands of cubic meters of
9
5
2.10.
The operating organization should optimize the design a borehole disposal facility so that in
combination with appropriate facility siting (see paras 6.16 to 6.23 and Appendix I) and disposal of
waste at sufficient depth, it is improbable that radioactive waste disposed of in a borehole would be
affected by inadvertent human intrusion or other potential causes of the waste returning to the surface.
2.11.
This safety guide focusses on the disposal of disused sealed radioactive sources and describes
a concept that involves one or more vertical boreholes drilled using widely available drilling
technology; this concept differs from some other borehole disposal concepts (see para. 2.26 and
Annex I). The concept for borehole disposal on which this safety guide focusses is described in the
following subsection - more detail is provided in Refs. [14], [15] and [16] and the safety of the concept
is considered in Refs. [17] and [18].
Concept for borehole disposal of disused sealed radioactive sources
2.12.
A concept for the disposal of disused sealed radioactive sources in boreholes was described in
Ref. [14]. The concept was designed to assist IAEA Member States that have hazardous disused sealed
radioactive sources in storage, recognizing the associated security issues and the obligations under the
Joint Convention, Ref. [6] and the recommendations of the Code of Conduct, Ref. [7] to implement a
disposal solution. While there have been improvements to details of the design since Ref. [14] was
published - see Refs [15] and [16] - the concept remains essentially the same and has become a
recommended concept. It entails the emplacement of disused sealed radioactive sources that have been
declared radioactive waste, and possibly some small amounts of low level waste and intermediate level
waste generated during their management, in borehole disposal facility drilled and operated from the
surface.
2.13.
In the recommended borehole disposal concept, the borehole is assumed to be vertical and
straight, and to have a minimum diameter of around 260 mm - this diameter is large enough to
accommodate borehole casing, backfill and reasonably sized waste packages 10. 260 mm is also a
diameter for which drilling rigs are widely available because boreholes of this size are often used for
water abstraction. In the concept, the borehole is cased to full depth using high-density polyethylene
(HDPE) tubing whose purpose is to facilitate operations such as emplacement of the waste packages
into the borehole. The bottom of the casing should be sealed with a cement-based plug, and the gap
between the casing and the borehole wall is filled with cement-based backfill. The plug and backfill
should prevent the ingress of groundwater and allows the waste emplacement operations to be
waste that are disposed of in near surface disposal facilities. It cannot necessarily be assumed that radioactive
waste created as a result of an accident with disused sealed radioactive sources, such as the accident that occurred
at the Goiânia in Brazil and which generated approximately 3,500 m3 of radioactive waste Ref. [12], could be
disposed of by borehole disposal.
Note that the dimensions provided are for the recommended concept, but they can and should be varied to meet
the safety requirements for a particular implementation.
10
6
conducted in essentially dry conditions. The cement-based material in the recommended borehole
disposal concept comprises principally a sulphate-resistant Portland cement and sand with a maximum
particle size of 4 mm. The operating organization should justify the choice of the materials to be used
in the disposal facility, taking account of their intended purposes, safety functions and performance in
the conditions of the disposal system.
2.14.
In the recommended borehole disposal concept, disused sealed radioactive sources should be
placed inside a 3 mm-thick stainless steel disposal capsule which should be closed by welding on a
3 mm-thick stainless steel lid. The weld should be tested for leaks. The thickness of the weld should be
at least as thick as the disposal capsule walls. The sealed disposal capsule containing the radioactive
sources should then be placed inside a pre-cast cement-based insert inside a 6 mm-thick stainless steel
disposal container. The cement-based insert should comprise two pieces, a larger body part and a lid.
The lid of the insert should be fixed to the insert body using a small amount of liquid grout, which will
set and solidify. The disposal container should be closed by welding on 6 mm-thick stainless steel lid.
The thickness of the weld should be at least as thick as the disposal container walls. Disposal capsules,
cement-based inserts and disposal containers should be made in diameters and lengths to accommodate
the sizes of the sources to be disposed of and taking account of the diameter of the borehole and casing.
2.15.
The composition of the stainless steel used for the disposal capsules and containers and their
lids should be the same to avoid the possibility of processes such as galvanic corrosion. The stainless
steel described in Ref. [14] is a 316L stainless steel. The choice of stainless steel and other materials
for the disposal capsules and containers should be appropriate for the disused sealed radioactive sources
to be disposed of (e.g. in terms of their potential to generate heat and to cause radiolysis of water – see
Appendix II).
2.16.
In the recommended borehole disposal concept, the waste packages should be emplaced into
the borehole and the spaces around the waste packages in the borehole should be backfilled using
cement-based backfill. The number of waste packages and the size of the spaces between them, which
will be filled by backfill, should be assessed to determine the total length of disposal zone needed. The
total length of disposal zone needed should be considered together with the characteristics of the host
rocks to determine the number of boreholes and disposal zones needed and the locations and depths of
the disposal zones.
2.17.
Fig. 1 illustrates a disposal facility for disused sealed radioactive sources with two boreholes;
the inset highlights the components present in the disposal zone.
7
FIG. 1. Main components of a borehole disposal system for disused sealed radioactive sources –
modified from Ref. [17].
2.18.
When the final waste package has been emplaced and any temporary casing above the disposal
zone has been removed, a steel deflection plate should be inserted into the borehole above the waste.
This deflection plate should prevent a drill bit from running into the waste packages in the event that
someone drilled into the borehole. The borehole above the deflection plate should be backfilled with
concrete to a depth of five metres from the ground surface. The top five metres of the borehole should
be filled with crushed rock and local soil so that the borehole is undetectable without specialist
equipment.
Periods in borehole disposal of disused sealed radioactive sources
2.19.
A step by step approach should be followed in developing a borehole disposal facility –
SSR-5 [4]. It is probable that a programme for developing a borehole disposal facility (including inter
alia site characterization and selection, safety case development, interactions with interested parties,
and authorization) will take several years to a decade. It is probable that once the necessary authorization
processes are completed, the operation and closure of a disposal borehole 11 would not last more than a
few months or a year. The step by step approach should include formal stages at which the programme
is reviewed, and evaluations of safety are undertaken before decisions are made to progress. Such a step
by step approach allows confidence in safety to be increased gradually and helps to ensure that decisions
are well-founded. The regulatory body should undertake reviews at each major decision point. These
11
8
A small borehole disposal facility might have only one disposal borehole.
reviews also provide opportunities for independent technical review and involvement of interested
parties.
2.20.
The operating organization should design the step by step process of facility development so
that there is flexibility for the disposal programme to be adapted in response to new scientific and
technical information that becomes available. Throughout the development, operation, closure and
institutional control of a borehole disposal facility, the operating organization and the regulatory body
should follow a graded approach so that the effort expended, and the controls applied, are commensurate
with the hazard and the level of risk associated with the waste. Guidance on how a graded approach can
be taken to post-closure safety assessment for borehole disposal is provided in Ref. [18].
2.21.
It is convienient to identify three periods in the development, operation, closure and
institutional control of a radioactive waste disposal facility, namely the pre-operational period, the
operational period and the post-closure period – SSR-5 [4]. Various activities take place during the
three periods depending inter alia on the disposal concept. The following applies for borehole disposal:
The pre-operational period
2.22.
The pre-operational period includes all of the activities before waste is received at the site. The
extent of these activities should reflect the situation in the State and can include the characterization of
waste in the country and the definition of the inventory of waste for disposal, disposal site investigation,
characterization and selection, site-specific disposal facility design, development of the safety case and
security plan, and regulatory review and authorization. Waste processing for storage and disposal could
occur at authorized facilities at other sites in the State. In this period, the operating organization should
develop its management system and those aspects of the safety case for the disposal facility site
necessary to obtain an authorization for the borehole disposal facility. The operating organization
should conduct environmental impact assessment studies as necessary and should develop a safety case
for the facility that includes appropriate safety assessments (e.g. operational and post closure safety
assessments) in accordance with the national legal and regulatory framework.
The operational period
2.23.
The operational period begins after an authorization has been obtained when waste is first
received at the site. During this period waste management activities could result in radiation exposures
– hence these activities are required to be authorized by the regulatory body and subject to controls in
accordance with the requirements for radiation protection and safety – see GSR Part 3 [2] and
GSR Part 5 [3]. The operating organization should conduct predisposal management activities in
accordance with the guidance and recommendations contained in IAEA Safety Standards Series Nos
WS-G-6.1, Storage of Radioactive Waste [19] and SSG-45, Predisposal Management of Radioactive
Waste from the Use of Radioactive Material in Medicine, Industry, Agriculture, Research and
Education [20].
9
(a)
In some cases, waste received at the site may already have been processed, meaning that
following successful passage through applicable waste acceptance procedures, and any
necessary period of buffer storage, waste emplacement can proceed directly;
(b)
In other cases, the operating organization should process the waste so that it is ready for disposal
using appropriate facilities and following appropriate procedures for the necessary predisposal
management activities (e.g. dismantling of devices containing disused sealed radioactive
sources, removal of the disused sealed radioactive sources, conditioning). The operating
organization should design and conduct the waste processing activities so that there are no
discharges 12. If discharges cannot be avoided, the operating organization should ensure that
they meet established standards and requirements. Processing facilities may be fixed or mobile.
IAEA Safety Standards Series No. RS-G-1.9, Categorization of Radioactive Sources [21]
recognizes five categories of radioactive sources. Hot cell facilities, such as the one described
in Ref. [22], typically have sufficient shielding to be used for processing all categories of
disused sealed radioactive sources. Processing of Category 3 to 5 disused sealed radioactive
sources can be done safely with relatively less shielding and can be performed using a facility
such as the one described in Ref. [23]. Whichever facilities are used, the operating organization
should provide sufficient shielding to ensure protection of workers appropriate to the nature of
the waste – the operating organization should consider the possible need to provide shielding
for both gamma and neutron sources. The operating organization should provide appropriate
storage facilities at the site to facilitate the waste management process;
(c)
The operation of a borehole disposal facility includes handling of waste packages, emplacement
of waste packages in the disposal facility, emplacement of engineered barriers (e.g. borehole
backfill, seals, anti-intrusion barriers) and facility closure. The operating organization should
conduct disposal activities in accordance with the requirement in SSR-5 [4] and the guidance
and recommendations contained in this safety guide.
2.24.
All operations should be conducted in accordance with an appropriate management system by
suitably qualified and experienced personnel, trained in accordance with clear operating procedures –
see IAEA Safety Standards Series No. GSR Part 2, Leadership and Management for Safety [24] and
IAEA Safety Standards Series No. GSG-16, Leadership, Management and Culture for Safety in
Radioactive Waste Management [25]. Traceable records should be created that describe and
characterize the site, the facilities, the radioactive waste and the waste management activities
undertaken. The range of information and the level of detail to be recorded should be specified in the
management system, taking account of the graded approach. All important safety-related information
Discharges are planned and controlled releases of (usually gaseous or liquid) radioactive substances to the
environment [5].
12
10
concerning radioactive waste management should be retained and controlled – GSG-16 [25]. Facilities
other than the borehole that were used during operations should be decommissioned in accordance with
IAEA Safety Standards Series No. GSR Part 6, Decommissioning of Facilities [26].
The post-closure period
2.25.
The post-closure period begins immediately after the borehole disposal facility has been closed.
After facility closure, the safety of the borehole disposal facility is required to be provided by passive
features inherent in the characteristics of the site and the facility. Some forms of institutional control
can continue after closure; initially these may be active controls (such as maintenance of site security
and monitoring – see para. 7.15), but active controls cannot be maintained indefinitely and so, later,
passive institutional controls may become more relevant. Passive institutional controls may, for
example, include administrative restrictions on land use that provide additional assurance that
inadvertent human intrusion would be improbable. The authorization for the disposal facility should be
terminated when the necessary technical, legal and financial requirements have been fulfilled – see
IAEA Safety Standards Series No. WS-G-5.1, Release of Sites from Regulatory Control on Termination
of Practices [27].
OTHER BOREHOLE DISPOSAL CONCEPTS
2.26.
Several other concepts have been proposed involving the use of boreholes for radioactive waste
storage or disposal, and some of these have been implemented for various types of radioactive waste
(Annex 1). In accordance with the objectives and scope of this safety guide, the disposal concepts
described in Annex 1 for waste types other than those identified in para. 1.1 are not considered further
in any detail, although the guidance provided may be of general interest. The guidance in this safety
guide, and particularly that in Section 8, should be considered as a basis for reassessing and, where
appropriate, upgrading the safety of existing borehole disposal facilities that contain waste of the types
identified in para. 1.1.
3. LEGAL AND ORGANIZATIONAL INFRASTRUCTURE
3.1.
The development, operation, closure and institutional control of a borehole disposal facility
necessitates the assignment of responsibilities among three types of organization: the national
government, the appointed regulatory body (or bodies) and the operating organization of the facility.
Recommendations on the responsibilities of each of these are provided in this section.
RESPONSIBILITIES OF THE GOVERNMENT
3.2.
General safety requirements for the establishment of national policies and strategies for safety
and for radioactive waste management are set out in Requirement 1 of GSR Part 1 (Rev. 1) [28] and
Requirement 2 of GSR Part 5 [3]. Requirement 2 of GSR Part 5 [3] states:
“To ensure the effective management and control of radioactive waste, the government
shall ensure that a national policy and a strategy for radioactive waste management are
11
established. The policy and strategy shall be appropriate for the nature and the amount
of the radioactive waste in the State, shall indicate the regulatory control required, and
shall consider relevant societal factors. The policy and strategy shall be compatible with
the fundamental safety principles and with international instruments, conventions and
codes that have been ratified by the State. The national policy and strategy shall form the
basis for decision making with respect to the management of radioactive waste.”
3.3.
In establishing national policies and strategies for radioactive waste management, the
Government should ensure the following:
(a)
Development and maintenance of a comprehensive national register of radioactive sources –
see para 4.63 of GSR Part 1 (Rev. 1) [28];
(b)
The establishment and implementation of a decision-making process for declaring disused
sealed radioactive sources radioactive waste – see Ref. [7];
(c)
Development and maintenance of a comprehensive national inventory of radioactive waste
(including disused sealed radioactive sources declared radioactive waste);
(d)
That the preferred options for radioactive waste management are identified – see para 3.5 of
GSR Part 5 [3];
(e)
That due consideration is given to interdependences between the various steps in waste
management;
(f)
That long-term storage of disused sealed radioactive sources that have not been declared
radioactive waste is avoided;
(g)
That a disposal programme is developed for disused sealed radioactive sources that have been
declared radioactive waste which is compatible with the State’s overall radioactive waste
management programme 13 – see Ref. [7];
(h)
That consideration is given to the need nationally for one or more disposal facilities, depending
on the inventory of disused sealed radioactive sources and other radioactive waste for disposal
in the State. For example, in some States a national strategy for the disposal of disused sealed
radioactive sources might include the use of one or more borehole disposal facilities, in other
States it might include near surface disposal for low level waste and borehole disposal for
disused sealed radioactive sources, while in yet other States it might include near surface
disposal for low level waste and some short-lived disused sealed radioactive sources, and
geological disposal for other disused sealed radioactive sources and waste;
In a radioactive waste management programme, a group of related waste management projects is
managed in a coordinated way and with a particular long-term aim, in order to obtain benefits and control
not available from managing the projects individually.
13
12
(i)
That safety is paramount amongst the factors considered when selecting appropriate types of
disposal facilities for disused sealed radioactive sources that have been declared radioactive
waste and other radioactive waste. Other factors that should be considered include the inventory
of disused sealed radioactive sources and other radioactive waste for disposal in the State, the
potential need for transport of radioactive materials, and relevant socio-economic factors;
(j)
That the resources devoted to safety by the licensee, and the scope and stringency of regulations
and their application, are commensurate with the magnitude of the radiation risks and their
amenability to control – para. 3.24 of SF-1 [1]. The numbers of disused sealed radioactive
sources in States varies from just a few sources in some small States, to well in excess of
100,000 sources in some States. The volumes of packaged radioactive waste envisaged to result
from conditioning of disused sealed radioactive sources are estimated as varying from less than
ten m3 in typical small States to several hundred m3 in some large States. Although these
volumes are relatively small in comparison to the volumes of other waste types present in some
States, the hazard associated with some disused sealed radioactive sources can be very high.
3.4.
In addition to the development of national policies and strategies, the Government is required
to establish and maintain an appropriate governmental, legal and regulatory framework, including
relevant laws and regulations, an effective regulatory body that is independent of the operating
organization, and a regulatory process that defines the steps to be taken in the licensing and
development, operation, closure and institutional control of the facility. Requirement 1 of SSR-5 [4]
states:
“The government is required to establish and maintain an appropriate governmental,
legal and regulatory framework for safety within which responsibilities shall be clearly
allocated for disposal facilities for radioactive waste to be sited, designed, constructed,
operated and closed. This shall include: confirmation at a national level of the need for
disposal facilities of different types; specification of the steps in development and licensing
of facilities of different types; and clear allocation of responsibilities, securing of financial
and other resources, and provision of independent regulatory functions relating to a
planned disposal facility.”
3.5.
In accordance with Requirement 1 and para. 3.7 of SSR-5 [4], the Government should in the
governmental, legal and regulatory framework:
(a)
Confirm at the national level the need for disposal facilities of different types (including where
appropriate borehole disposal facilities);
(b)
Establish or identify organizations for the development, operation, closure and institutional
control of disposal facilities (including where appropriate borehole disposal facilities);
13
(c)
Set clearly defined legal, technical and financial responsibilities for organizations that are to be
involved in the development, operation, closure and institutional control of disposal facilities
(including where appropriate borehole disposal facilities);
(d)
Ensure the adequacy and security of financial provisions, for example by requiring the operating
organizations of borehole disposal facilities to establish funds for facility closure and any
subsequent controls for which they are responsible;
(e)
Define the overall process for the development, operation, closure and institutional control of
disposal facilities (including where appropriate borehole disposal facilities), including the legal
and regulatory requirements at each step, and the processes for decision making and the
involvement of interested parties;
(f)
Define legal, technical and financial responsibilities and, if necessary, provide for any
institutional arrangements that are envisaged after disposal facility closure, including
monitoring and arrangements that may be required for ensuring the security of the disposed of
waste;
(g)
Establish a regulatory body with appropriate responsibilities for oversight of predisposal waste
management facilities and disposal facilities (including where appropriate borehole disposal
facilities);
(k)
Ensure that the necessary scientific and technical expertise is available to both the operating
organization and the regulatory body (e.g. from national institutes for health and radiation
protection, geology and hydrology, and other relevant disciplines).
3.6.
The government should ensure that the regulatory body is independent of the generators of the
waste and operating organizations. The regulatory body should possess the expertise to provide proper
oversight and objectivity in evaluating predisposal waste management and disposal activities.
Individuals working within the regulatory body should be sufficiently independent of influence from
waste generators and from operating organizations. The government should perform periodic reviews
to evaluate the effectiveness of the regulatory body and its ability to fulfil its mission.
3.7.
In accordance with national laws and preferences, the government should ensure that interested
parties that are directly or indirectly affected by radioactive waste management facilities and activities
are involved in making decisions at appropriate stages. A clear, formal process identifying interested
parties and decision makers should be established to facilitate a meaningful exchange of information
and viewpoints. The ways in which interested parties are involved in decision making processes
concerning the borehole disposal of radioactive waste will vary according to national laws, regulations
and preferences. The involvement of interested parties in the development of frameworks for decision
making can encourage public confidence in government actions, make the regulatory body more
effective and improve the safety performance of operating organizations.
14
RESPONSIBILITIES OF THE REGULATORY BODY
3.8.
Requirement 3 of GSR Part 5 and Requirement 2 of SSR-5 establish the responsibilities of the
regulatory body for radioactive waste management facilities and activities. Requirement 2 of SSR-5 [4]
states:
“The regulatory body shall establish regulatory requirements for the development of
different types of disposal facility for radioactive waste and shall set out the procedures
for meeting the requirements for the various stages of the licensing process. It shall also
set conditions for the development, operation and closure of each individual disposal
facility and shall carry out such activities as are necessary to ensure that the conditions
are met.”
3.9.
The regulatory body should develop and implement a process for establishing regulatory
requirements. The regulatory body should involve interested parties in the process for establishing
regulatory requirements. Regulatory requirements should be established well in advance of any licence
application. The regulatory arrangements should cover all stages in the development, operation, closure
and institutional control of facilities and activities, specifying the principles, requirements and criteria
that will be used to regulate the facilities and activities, and requiring the operating organization to
establish arrangements for what should happen in the event of non-compliances, events and accidents.
The safety objective and relevant criteria are provided in paras 3.23 to 3.26. Model regulations for
borehole disposal are provided in Ref. [29].
3.10.
The regulatory body should provide guidance on how it will implement the regulatory
arrangements, on the procedures that the operating organization is to follow in making applications for
authorization and safety case submissions, and on the probable timescales required for regulatory
review and assessment of safety cases and applications for authorization. The regulatory body should
ensure that the regulatory arrangements are both comprehensive and commensurate with the scale and
potential hazard of the facilities and activities under regulatory control.
3.11.
The regulatory body should define and follow a step by step approach to authorization. At each
step, the operating organization should as far as is possible describe in its application for authorization
and safety case the totality of the disposal programme so that early steps in the disposal programme can
be seen to be compatible with later ones, and the regulatory body is informed of the potential long-term
safety of the facility when it reviews applications for initial steps in the facility development process.
3.12.
The regulatory body should not grant an authorization for facility construction, commissioning
or operation until regulatory review and assessment of relevant applications for authorization and the
safety case have been completed and the regulatory body considers that the application is complete and
the safety case presents sufficient evidence to provide reasonable assurance that the safety requirements
will be fulfilled and that funds are, or will be, available to finance the waste disposal programme through
15
all of its steps (i.e. construction, commissioning, operation, closure and any planned period of postclosure active institutional control).
3.13.
The regulatory body should ensure that the authorization has sufficient flexibility to
accommodate changes (e.g. in disposal facility design) through a change control process. The regulatory
body should specify in the authorization, conditions under which the operating organization can make
changes to the disposal system without needing to apply to the regulatory body for a new authorization.
The burden imposed by the change control process should be commensurate with the scale and potential
hazard of the facilities and activities.
3.14.
The regulatory body should develop and implement processes and procedures through which it
sets conditions for the development, operation, closure and institutional control of each disposal facility.
These processes and procedures should include regulatory review and assessment of the safety case for
the facility, and authorization with appropriate conditions.
3.15.
The operating organization of a borehole disposal facility should submit the safety case to the
regulatory body for independent review and assessment. The regulatory body should review and assess
the safety case for the facility. The regulatory body should consider critically the available evidence
and the level of confidence that can be held, in each aspect of the safety case, for example, in the
effectiveness of the institutional controls assumed in the safety case.
3.16.
General guidance on regulatory review and assessment is provided in IAEA Safety Standards
Series No. GSG-13, Functions and Processes of the Regulatory Body for Safety [30]. GSG-13 indicates
that the scope of a regulatory review and assessment should not be restricted solely to the documented
safety case, but should consider a wide range of aspects, including whether:
(a)
The operating organization has the necessary competences and resources;
(b)
The site is suitable;
(c)
All aspects of the facility design and the limits and controls are adequate;
(d)
The operating organization uses an appropriate safety management system;
(e)
The safety assessments are adequate;
(f)
There are any additional requirements (or conditions) that should be imposed and, if these were
imposed previously, whether they have been complied with.
3.17.
The regulatory body should develop a plan for managing the regulatory review and assessment
process; this plan should cover staffing and resourcing, the objectives and scope of the review and
assessment, timescales and scheduling, the allocation of responsibilities, the training of personnel, the
processes and procedures to be followed, monitoring of progress, meetings with the operating
organization, the role of technical advisors, and interactions with the public and other interested parties.
Guidance for the regulatory body on interacting with interested parties is contained in IAEA Safety
16
Standards Series No. GSG-6, Communication and Consultation with Interested Parties by the
Regulatory Body [31].
3.18.
Regulatory reviews and assessments of facility safety cases should reflect the scale and
potential hazard of the facilities and activities. The regulatory body should focus on issues, review
comments and findings according to their importance to safety.
3.19.
The regulatory body should ensure that it has an independent capability to carry out reviews
and assessments of facility safety cases in order to determine whether the facility is and will be safe and
what conditions of authorization should be specified and attached to the authorization. Regulatory
review and assessment of the safety case and licence application may be undertaken in various ways,
and may include the use of independent external experts in accordance with the guidance provided in
IAEA Safety Standards Series No. GSG-12, Organization, Management and Staffing of the Regulatory
Body for Safety [32].
3.20.
The regulatory body should check that the operating organization exercises adequate control of
the borehole disposal facility. The regulatory body should carry out activities to ensure that the
conditions of authorizations are met. This should include checking that the operating organization is
properly developing and complying with waste acceptance criteria and conducting appropriate
regulatory inspection and enforcement activities.
3.21.
The regulatory body should develop a regulatory inspection plan for activities important to
safety, such as construction, operation and closure - see GSG-13 [30]. The regulatory inspections should
examine the operating organization’s compliance with the authorization, safety case and operating
procedures, and the safety culture of the operating organization’s staff and contractors – GSG-16 [25].
3.22.
The regulatory body is required to establish appropriate requirements for radiation protection.
Radiation protection in the operational period
3.23.
The following key requirements apply in the operational period:
(a)
Justification: Requirement 10 of GSR Part 3 [2] states: “The government or the regulatory body
shall ensure that only justified practices are authorized.” Radioactive waste management is part
of the ‘practice’ giving rise to the waste, and as such does not require separate justification [3].
(b)
Optimization: Requirement 11 of GSR Part 3 [2] states: “The government or the regulatory
body shall establish and enforce requirements for the optimization of protection and safety, and
registrants and licensees shall ensure that protection and safety is optimized.”
(c)
Dose limits: Requirement 12 of GSR Part 3 [2] states: “The government or the regulatory body
shall establish dose limits for occupational exposure and public exposure, and registrants and
licensees shall apply these limits.”
17
(d)
Dose and risk constraints: para. 3.120 of GSR Part 3 [2] states “The government or the
regulatory body shall establish or approve constraints on dose and constraints on risk to be used
in the optimization of protection and safety for members of the public.” Dose and risk
constraints are established at levels below those of the corresponding limits because exposures
could be received from more than one source. Risk here refers to the risks of all cancers and the
risks of hereditary effects.
3.24.
Predisposal radioactive waste management activities may lead to planned exposures.
Radioactive waste disposal may lead to planned exposures of workers and the public in the operational
period and planned potential exposures of the public in the post-closure period – planned potential
exposures are not certain to occur. Schedule III of GSR Part 3 [2] sets out dose limits that apply to
radioactive waste management; the key criteria are:
“For occupational exposure of workers over the age of 18 years, the dose limits are:
an effective dose of 20 mSv per year averaged over five consecutive years (100 mSv
in 5 years) and of 50 mSv in any single year;”
(a)
“For public exposure, the dose limits are:
(a)
an effective dose of 1 mSv in a year;
In special circumstances, a higher value of effective dose in a single year could apply,
provided that the average effective dose over five consecutive years does not exceed 1 mSv per
year;”
(b)
Radiation protection in the post-closure period
3.25. The fundamental safety objective is to protect people and the environment from harmful
effects of ionizing radiation – SSR-5 [4] and this requires the operating organization to site, design,
construct, operate and close a disposal facility so that protection after its closure is optimized, social
and economic factors being taken into account. Reasonable assurance also has to be provided that doses
and risks to members of the public in the long-term will not exceed the dose constraints or risk
constraints that were used as design criteria.
3.26.
The following key criteria apply in the post-closure period:
(a)
The dose limit for members of the public for doses from all planned exposure situations is an
effective dose of 1 mSv in a year, GSR Part 3 [2]. This and its risk equivalent are considered
criteria that are not to be exceeded in the future;
(b)
To comply with this dose limit, a disposal facility (considered as a single source) is so designed
that the calculated dose or risk to the representative person who might be exposed in the future
as a result of possible natural processes affecting the disposal facility does not exceed a dose
constraint of 0.3 mSv in a year or a risk constraint of the order of 10-5 per year – para 2.15(b)
of SSR-5 [4];
18
(c)
In relation to the effects of inadvertent human intrusion after closure, if such intrusion is
expected to lead to an annual dose of less than 1 mSv to those living around the site, then efforts
to reduce the probability of intrusion or to limit its consequences are not warranted;
(d)
If human intrusion were expected to lead to a possible annual dose of more than 20 mSv (see
Table 8 of Ref. [33]) to those living around the site, then alternative options for waste disposal
are to be considered;
(e)
If annual doses in the range 1–20 mSv (see Table 8 of Ref. [33]) are indicated, then reasonable
efforts are warranted at the stage of development of the facility to reduce the probability of
intrusion or to limit its consequences by means of facility design;
(f)
The ICRP considers that a dose rising towards 100 mSv will almost always justify protective
action (para. 241 of Ref. [33]);
(g)
Exposures above 100 mSv incurred either acutely or in a year would be justified only under
extreme circumstances, either because the exposure is unavoidable or in exceptional situations
such as the saving of life or the prevention of a serious disaster. No other individual or societal
benefit would compensate for such high exposures (para. 236 of Ref. [33]).
RESPONSIBILITIES OF THE OPERATING ORGANIZATION
3.27.
Requirement 4 of GSR Part 5 and Requirement 3 of SSR-5 establish the responsibilities of the
operator for the safety of radioactive waste management facilities and activities. Requirement 3 of
SSR-5 [4] states:
“The operator of a disposal facility for radioactive waste shall be responsible for its safety.
The operator shall carry out safety assessment and develop and maintain a safety case,
and shall carry out all the necessary activities for site selection and evaluation, design,
construction, operation, closure and, if necessary, surveillance after closure, in
accordance with national strategy, in compliance with the regulatory requirements and
within the legal and regulatory infrastructure.”
3.28.
The operating organization has prime responsibility for the safety of facilities and activities;
this responsibility cannot be delegated. This responsibility extends throughout all stages in the lifetime
of facilities and the duration of activities, until the end of regulatory control. If the operating
organization employs contractors to perform work, the operating organization retains the prime
responsibility for safety and ensuring compliance with legal and regulatory requirements. – see paras
2.14 and 2.15 of GSR Part 1 (Rev. 1) [28].
3.29.
The operating organization is responsible for preparing and maintaining a safety case, including
relevant safety assessments, on which decisions on the authorization and development, operation,
closure and institutional control of the disposal facility should be based. The operating organization is
responsible for submitting the safety case to the regulatory body for review and assessment. The
19
operating organization should include in the safety case information on site selection and evaluation,
design, construction, operation, closure and, if necessary, surveillance after closure. General guidance
on the safety case and safety assessment for the predisposal management of radioactive waste is
contained in IAEA Safety Standards Series No. GSG-3, The Safety Case and Safety Assessment for the
Predisposal Management of Radioactive Waste [34]. General guidance on the safety case and safety
assessment for the disposal of radioactive waste is contained in SSG-23 [35]. More detailed information,
specific to post-closure safety at borehole disposal facilities for disused sealed radioactive sources, is
contained in Section 5 and in Refs [17] and [18].
3.30.
The operating organization is responsible for conducting or commissioning investigations of
sites as necessary to evaluate their suitability to host a borehole disposal facility and to inform decisions
on site selection. The operating organization should use the safety case to plan site investigations and
integrate results from site investigations into the safety case.
3.31.
The operating organization should seal site investigation boreholes before commissioning the
disposal facility; sealing should be done in a timely manner and in accordance with the authorization
and the safety case. Site investigation boreholes should be sealed to prevent them from acting as
pathways for groundwater or gas flow and radionuclide migration. The operating organization should
seal site investigation boreholes so that the permeability of the sealed boreholes is no worse than that
of the surrounding intact rocks. Further guidance on site characterization is contained in Section 6 and
Appendix I.
3.32.
The operating organization should take full responsibility for radioactive sources and
radioactive waste at the site. The operating organization should verify that the radioactive sources and
radioactive waste are described correctly and sufficiently in the accompanying documentation. For
disused sealed radioactive sources, the information should at least include the following:
(a)
The radionuclide, its half-life and activity at a specified date;
(b)
The nature of radiation emitted; dose rate at contact and 1 m distance;
(c)
The size of the sources to be disposed;
(d)
Whether the source is known to be leaking or not.
(e)
The physical and chemical form of the sources and the materials of the containers and their
thickness.
3.33.
Where possible, the information recorded for each disused sealed radioactive sources should
include the following:
(a)
Manufacturer, serial number and the dates of manufacture, import and receipt by the operating
organization;
20
(b)
Previous owners, the name and type of device in which it was used and the use to which was
put.
3.34.
The operating organization should attempt to fill any gaps in the information available. The
operating organization should as appropriate consult with the manufacturers and users of disused sealed
radioactive sources, with the waste generators and the IAEA sealed source catalogue and other
information sources.
3.35.
The operating organization is responsible for processing of the radioactive sources and
radioactive waste, for producing waste packages suitable for disposal, and for waste disposal. The
operating organization should:
(a)
Provide the facilities and equipment necessary for the activities and develop and follow
appropriate operating procedures;
(b)
Provide radiation shielding appropriate to the nature of the radioactive sources and radioactive
waste to be processed;
(c)
Remove the sources from the devices in which they were used and place them in appropriate
capsules for temporary storage;
(d)
Retrieve the sources from temporary storage and condition them for disposal;
(e)
Condition waste for borehole disposal and dispose of the waste packages.
3.36.
The operating organization is responsible for safety throughout all of the activities and should
ensure that the activities are optimized and performed by suitably qualified and experienced personnel
that have been trained in the procedures to be followed. The operating organization should ensure that
interdependencies in the waste management process are taken into account (e.g. that the disposal
capsules and waste packages are suitable for emplacement in the disposal facility).
3.37.
The operating organization is responsible for all steps in the disposal of radioactive waste. The
operating organization should not begin construction of disposal borehole(s) or any other activities that
could significantly affect baseline (e.g. hydrogeological) conditions at the site (see SSG-31, [36]) until
an authorization has been granted. The operator should engage with the regulatory body beginning at
an early stage in the process leading to authorization and the development of a borehole disposal facility.
The operating organization should ensure that all construction and disposal activities are performed in
accordance with the approved safety case.
3.38.
The operating organization is responsible for establishing limits, controls and conditions (e.g.
technical specifications), from the safety assessments and the safety case, to ensure that the borehole
disposal facility is constructed and operated in accordance with both the safety case and the
authorization conditions. The operating organization should exercise due control over the receipt,
processing and emplacement of waste and implement and maintain appropriate security measures.
21
3.39.
The operating organization should assess the implications for safety of changes to the types or
amounts of wastes or to the design or operation of the facility as part of a change control process.
3.40.
The operating organization is responsible for all steps necessary for the safe and sustainable
decommissioning of predisposal management facilities and activities at the site. Decommissioning
should be conducted in accordance with GSR Part 6 [26].
3.41.
The operating organization should record and retain all information relevant to the safety of the
disposal facility, including inspection records and other assessments of compliance with regulatory
requirements, the operating organization’s management system and the operating procedures. If
responsibility for the facility is transferred between organizations, the operating organization should
hand over to the newly responsible organization all information relevant to the safety of the facility.
The operating organization is required to cooperate with the regulatory body and supply all the
information that the regulatory body may require to fulfil its responsibilities.
4. SAFETY APPROACH
IMPORTANCE OF SAFETY IN THE DEVELOPMENT AND OPERATION OF A DISPOSAL
FACILITY
4.1.
Principle 5 of SF-1 [1] states that: “Protection must be optimized to provide the highest level
of safety that can reasonably be achieved”. Demonstrating that doses and risks will be below the
relevant dose and risk criteria set by the regulatory body is a necessary, but not sufficient objective. The
operating organization should seek to reduce doses and risks to levels that are as far below the relevant
dose and risk criteria as can be reasonably achieved, taking account of economic and social factors.
Decisions on whether protection has been optimized will be judgemental because of the needs to
consider what is reasonable and to balance information on a wide range of quantitative and qualitative
factors, including present-day and potential future doses and risks, costs, uncertainties, and the views
of interested parties. The optimization of protection should be considered at every step and discussed
with interested parties in the light of the particular situation.
4.2.
The operating organization should consider the following in optimizing protection at a borehole
disposal facility:
(a)
Arrangements for above-ground operations (e.g. waste handling and transport);
(b)
Providing appropriate radiation shielding;
(c)
Controlling working environments;
(d)
The design of predisposal waste management facilities and activities (e.g. waste processing);
(e)
Designing facilities and activities so that the need for any discharges is avoided;
(f)
Separating facility construction activities (e.g. drilling) from waste emplacement operations;
22
(g)
Procedures for operating the disposal facility (e.g. waste emplacement, borehole backfilling);
(h)
Using remote techniques as necessary (e.g. for waste handling and emplacement);
(i)
Reducing the potential for accidents and minimizing their potential consequences;
(j)
Minimizing the need for maintenance activities in radiation and contamination areas.
4.3.
The operating organization should determine how to place radioactive sources and waste into
disposal capsules and containers by considering the radionuclides present, the sizes of the sources, and
the volumes of the waste to be disposed of. The operating organization should in general avoid mixing
dissimilar sources (such as those containing short-lived radionuclides and those containing long-lived
radionuclides) in disposal capsules and containers. The operating organization should consider using a
software tool such as, SIMBOD, to help refine plans for the placement of sources into disposal capsules
and containers; SIMBOD is described in Ref. [37].
4.4.
The following are examples of aspects that the operating organization and the regulatory body
should consider when optimizing the protection that will be provided in the post closure period at a
borehole disposal facility or when judging whether optimization has been achieved:
(a)
That due attention has been paid during the facility development process to the post-closure
safety implications of possible options, including the design and siting related issues discussed
in paras 6.16 to 6.23 and Appendix I - in particular:
i)
selecting a suitable site for the borehole disposal facility;
ii)
designing the facility so that it is appropriate for the volume of waste to be disposed of
(e.g. by choosing the number and diameter of the boreholes to be used);
iii)
locating the disposal zone(s) appropriately within the geological environment, taking due
account of the geology, hydrogeology and geochemistry;
iv)
providing sufficient isolation of the waste to keep the probability of inadvertent human
intrusion low.
(b)
The assessed potential doses and risks fall below the relevant dose and risk criteria.
(c)
The probability of events that might give rise to potential doses or risks above the relevant dose
and risk criteria has been reasonably reduced by means of siting or design.
(d)
The siting, design, construction, operation and closure programmes have been conducted in
accordance with a suitable management system to ensure the necessary level of quality in safety
related aspects of the project. Guidance on the management system for radioactive waste
management is contained in GSG-16 [25].
23
4.5.
Requirement 4 of SSR-5 [4] states:
“Throughout the process of development and operation of a disposal facility for
radioactive waste, an understanding of the relevance and the implications for safety of the
available options for the facility shall be developed by the operator. This is for the purpose
of providing an optimized level of safety in the operational stage and after closure.”
4.6.
An option for the safe, secure and sustainable management of waste of the types identified in
para. 1.1 (including long-lived and high-activity disused sealed radioactive sources and their shielding
materials) is isolating the waste from the surface environment in a borehole disposal facility at depths
greater than 100 m (see Annex II). Another safe, secure and sustainable management option for these
waste types is geological disposal.
4.7.
Options for the safe, secure and sustainable management of some short-lived disused sealed
radioactive sources might be provided by borehole disposal at depths shallower than 100 m or by near
surface disposal together with low level waste, but this is conditional on there being sufficient
confidence in the ability to maintain effective active institutional control at the disposal facility site until
the hazard has reduced to safe levels by radioactive decay. In the case of waste disposal at depths
shallower than 100 m, even if the post-closure safety assessment suggests that assessed potential doses
and risks will be below relevant dose and risk criteria, this alone might not provide sufficient confidence
that the disposal facility will be safe in the long-term (as was noted in para. 4.1). The operating
organization should in the safety case complement the results from safety assessment with other types
of argument to show that the disposal facility will provide a safe, secure and sustainable (permanent)
solution for the waste.
4.8.
In developing a borehole disposal facility, the operating organization should address questions
such as the following:
(a)
Where should the facility be sited?
(b)
How can the facility layout be designed to take advantage of the natural characteristics and
barrier potential of the host environment?
(c)
How should predisposal waste management operations be performed?
(d)
How many boreholes should be constructed?
(e)
In what depth range should waste be disposed of?
(f)
What type of borehole casing should be used?
(g)
What materials should be used as engineered barriers?
(h)
What institutional controls should be put in place?
24
4.9.
In addressing and coming to decisions on such questions, the operating organization should
conduct safety assessments and demonstrate that a range of available options has been considered and
that the safety implications of the available options have been assessed and are understood. The
operating organization should document these assessments of the available options clearly with the aim
of increasing confidence in the disposal system. Complying with the safety requirements in SSR-5 [4]
will ensure adequate levels of operational and post-closure safety. At all stages, the operating
organization should provide reasonable assurance of safety to the regulatory body and other interested
parties.
4.10.
For the recommended borehole disposal concept, much of the documentation needed to satisfy
the requirement to demonstrate an optimized level of protection and safety is already available, for
example:
(a)
A generic design including the use of stainless steel and cement-based engineered barriers –
Section 2 (see also Refs [38] and [39]);
(b)
Procedures for, and a demonstration of, operational safety, Refs [40] and [41];
(c)
A generic safety assessment, Ref. [17] – although this does not remove the need for a sitespecific assessment, the generic safety assessment does provide reasonable assurance that the
disposal concept is capable of providing the necessary levels of safety in a wide range of
environments.
4.11.
In all cases, the operating organization should follow a graded approach in addressing the safety
requirements. The operating organization should expend effort to comply with the safety requirements
in a way that is commensurate with the hazard and the level of risk associated with the waste – further
guidance on this aspect is provided in paras 5.28 to 5.47.
PASSIVE MEANS FOR THE SAFETY OF A DISPOSAL FACILITY
4.12.
Requirement 5 of SSR-5 [4] states:
“The operator shall evaluate the site and shall design, construct, operate and close the
disposal facility in such a way that safety is ensured by passive means to the fullest extent
possible and the need for actions to be taken after closure of the facility is minimized”.
4.13.
The operating organization should develop, operate and close a borehole disposal facility so
that after closure, the safety of the facility does not depend on active systems or on actions by future
operating organizations, government or future generations.
4.14.
The operating organization should promote passive safety by:
(a)
Siting the facility at a location that benefits from stable geological conditions, has low potential
for the abstraction of water and or the extraction of minerals, oil and gas and other resources (a
25
site that has a low probability of inadvertent human intrusion) and that has groundwaters that
will be chemically unreactive to the structures, systems and components of the facility;
(b)
Designing the disposal facility so that it includes solid, unreactive waste forms, chemically and
physically stable waste packages, and other structures, systems and components, and that
facilitates waste disposal at depths greater than 100 m;
(c)
Keeping the operational period short and avoiding keeping a borehole open for an extended
period; this should be achieved by drilling and constructing a borehole and emplacing waste
and backfill only when sufficient waste has been collected to allow this sequence of activities
to be conducted as a reasonably sized disposal ‘campaign’. The operating organization should
provide sufficient storage capacity for waste prior to and between disposal campaigns. During
predisposal management, waste is required to be processed into a safe and passive form for
storage or disposal as soon as possible (para. 4.13 of GSR Part 5 [3]). The processing is required
to be consistent with the type of waste, the possible need for its storage, the anticipated disposal
option, and the limits, conditions and controls established in the safety case and in the
assessment of environmental impacts;
(d)
Closing the facility in a way that does not require subsequent maintenance of the structures,
systems and components of the facility that are designed to provide barriers to the migration of
radionuclides;
(e)
Implementing passive institutional controls, such as the archiving of records of the disposal
facility, controls on land ownership, and restrictions on land use. Such passive institutional
controls should be designed to reduce the possibility of future inadvertent human intrusion and
provide additional assurance and confidence in the safety of the facility.
UNDERSTANDING OF A DISPOSAL FACILITY AND CONFIDENCE IN SAFETY
4.15.
Requirement 6 of SSR-5 [4] states:
“The operator of a disposal facility shall develop an adequate understanding of the
features of the facility and its host environment and of the factors that influence its safety
after closure over suitably long time periods, so that a sufficient level of confidence in
safety can be achieved.”
4.16.
The operating organization should develop and demonstrate to the regulatory body and, as
appropriate, to other interested parties, an adequate understanding of the disposal system and of the
factors that could affect safety. The operating organization should define a logical and reasoned strategy
for the development of this understanding that includes the conduct of systematic safety assessments in
accordance with the requirements and guidance provided in GSR Part 4 (Rev. 1) [13], SSG-23 [35] and
in this publication. The operating organization should develop safety assessments covering the
predisposal management activities, the disposal operations and the post-closure period that are based
26
on a systematic and as comprehensive as possible analysis of the features events and processes that
could affect the disposal system and analyses of the safety functions of the structures systems and
components of the disposal facility.
4.17.
The operating organization should use the safety assessments to develop an understanding of
how the borehole disposal facility and its surrounding environment may behave and evolve in future
under different conditions or scenarios. A generic list and analysis of features events and processes
relevant to the post-closure safety of borehole disposal facilities are contained in Ref. [17]; the operating
organization should consider this information when identifying features events and processes and
scenarios for a borehole disposal facility at a specific site.
4.18.
To demonstrate reasonable assurance of safety the operating organization should develop a
safety case that includes safety assessments which show that the system’s features events and processes
and their possible interactions have been identified and are sufficiently well understood, and analyses
of uncertainties. The operating organization should perform structured uncertainty analyses to identify
the range of possible disposal system behaviours. The operating organization should consider
conducting more detailed modelling and sensitivity studies for parts of the disposal system that are
significant to safety. Further discussion of the analysis of uncertainties through the use of scenarios and
features events and processes in safety assessment is contained in GSR Part 4 (Rev. 1)[13], GSG-3 [34],
SSG-23 [35] and Refs [17] and [18].
4.19.
The operating organization should acknowledge openly the uncertainties that exist at any stage
in the development, operation, closure and institutional control of the disposal facility, and should
develop and apply an approach to the management of uncertainties that ensures that the facility is
developed and managed in a manner that will be safe. The existence of uncertainties is not a reason for
not proceeding to the next step in facility development and management.
4.20.
The operating organization should update the safety case and the safety assessments as the
disposal programme proceeds to reflect new data and lessons learned from the experience. The level of
understanding of the behaviour of the disposal system will evolve as more data are accumulated and as
scientific knowledge develops. Early in the development of the disposal concept, the data and
understanding should be sufficient to give the confidence necessary to commit the resources to further
investigation. Before the start of construction, during emplacement and at closure, the understanding
gained from safety assessment and compiled in the safety case should be sufficient to give reasonable
assurance of safety and that the relevant regulatory requirements will be satisfied.
4.21.
Confidence-building should be an integral part of safety assessment and the safety case
development process. The operating organization should present in safety case documents a series of
arguments that is intended to build confidence in the safety of the disposal system. The operating
organization should seek to build confidence in safety of the disposal system by, for example:
27
(a)
Showing that the safety assessment is as comprehensive as possible and is based on good
science and engineering practice and high-quality data;
(b)
Showing that the disposal system is robust (i.e. its performance is not unduly sensitive to
individual detrimental events and processes);
(c)
Providing evidence regarding the appropriateness and effectiveness of controls such as waste
acceptance criteria – see paras 6.58 to 6.66;
(d)
Providing information to demonstrate the feasibility and build confidence in the effectiveness
and durability of the engineered components of the facility.
4.22.
The operating organization should develop further confidence building arguments as
appropriate related, for example, to defence in depth, multiple lines of reasoning, institutional control,
monitoring, information from natural analogues, and the use of conservative approaches.
MULTIPLE SAFETY FUNCTIONS
4.23.
Requirement 7 of SSR-5 [4] states:
“The host environment shall be selected, the engineered barriers of the disposal facility
shall be designed and the facility shall be operated to ensure that safety is provided by
means of multiple safety functions. Containment and isolation of the waste shall be
provided by means of a number of physical barriers of the disposal system. The
performance of these physical barriers shall be achieved by means of diverse physical and
chemical processes together with various operational controls. The capability of the
individual barriers and controls together with that of the overall disposal system to
perform as assumed in the safety case shall be demonstrated. The overall performance of
the disposal system shall not be unduly dependent on a single safety function”.
4.24.
The operating organization should develop a safety strategy for the facility that includes
multiple safety functions. A safety function is a specific purpose that must be accomplished for safety
- IAEA Safety Glossary, Ref. [5]. Safety functions are usually attributed to particular structures, systems
and components. A safety function could be provided by a physical or chemical quality of a structures,
systems and components.
4.25.
The operating organization should ensure that safety functions are provided by a combination
of engineered and natural barriers. The operating organization should design the disposal system so that
the number and complexity of the barriers and safety functions in in accordance with the hazards
associated with the waste.
4.26.
28
Examples of barriers and safety functions in borehole disposal systems include the following:
(a)
Host rocks with low permeability and where the rate of groundwater movement and the degree
of radionuclide sorption onto the rocks together ensure that the radionuclides would take many
thousands of years to migrate to the biosphere;
(b)
Waste containers that are resistant to corrosion under the conditions in the disposal system.
Ref. [15] suggests the use of containers made of particular stainless steels for the disposal of
different types of disused sealed radioactive sources;
(c)
Solid waste forms that are insoluble and release radionuclides only slowly;
(d)
Engineered barrier materials that retard radionuclide migration. For example, a cement-based
backfill placed between the container and the borehole casing can create high-pH conditions
that limit solubility and promote sorption and so provide containment.
4.27.
The operating organization should ensure that the performance of the disposal system is not
unduly dependent on one safety function or barrier, and that the barriers are not unduly dependent on
each other. The operating organization should provide reasonable assurance that, if one barrier does not
perform as expected, or if one safety function is not fulfilled, then the disposal system will still be safe.
The operating organization should design the disposal facility so that the loss of performance of one
barrier does not lead directly to the loss of performance of other barriers.
4.28.
The operating organization should design the engineered components of the disposal system so
that they are compatible with each other and with the natural barriers. Examples of components that are
probably incompatible include the following:
(a)
The use of ordinary Portland cement when the surrounding groundwater or geology has high
levels of sulphate; a situation which is common in some types of clay;
(b)
The use of swelling clays (e.g. bentonite) for containment in highly saline environments or in
groundwater with high levels of potassium.
CONTAINMENT OF RADIOACTIVE WASTE
4.29.
Requirement 8 of SSR-5 [4] states:
“The engineered barriers, including the waste form and packaging, shall be designed, and
the host environment shall be selected, so as to provide containment of the radionuclides
associated with the waste. Containment shall be provided until radioactive decay has
significantly reduced the hazard posed by the waste. In addition, in the case of heat
generating waste, containment shall be provided while the waste is still producing heat
energy in amounts that could adversely affect the performance of the disposal system”.
4.30.
Containment is defined as methods or physical structures designed to prevent or control the
release and the dispersion of radioactive substances, Ref. [5]. In the context of waste disposal, the
29
containment of the radionuclides associated with the waste is through the provision of engineered
barriers and natural barriers, Ref. [5].
4.31.
The operating organization is required to design the engineered barriers and select the host rock
so as to provide containment of the radionuclides in the waste, especially during the initial period after
disposal when the level of activity is most intense and radioactive decay can significantly reduce the
hazard. The operating organization should provide sufficient containment to allow the vast majority of
radionuclides to decay without reaching the biosphere. The operating organization is not required,
however, to provide absolute containment of all radionuclides for all time, as this cannot be
demonstrated and is not necessary for safety. The operating organization should demonstrate in the
safety assessment that potential doses and risks arising from any radionuclide releases that do occur are
below the relevant dose and risk criteria.
4.32.
Some disused sealed radioactive sources generate significant amounts of heat as a result of
radioactive decay. The operating organization should pay special attention to the need to provide
sufficient containment for such wastes by selecting or designing suitable waste containers and waste
packages. The operating organization should take particular account of the characteristics of, and
processes associated with, high-activity disused sealed radioactive sources, including heat generation,
the emission of neutrons and the radiolysis of water. The operating organization should design the waste
package so that it includes suitable barriers which are compatible with other barriers in the disposal
system (e.g. the borehole backfill, the host rocks) and which will work together with the other barriers
to contain the radionuclides through a combination of physical and chemical functions.
ISOLATION OF RADIOACTIVE WASTE
4.33.
Requirement 9 of SSR-5 [4] states:
“The disposal facility shall be sited, designed and operated to provide features that are
aimed at isolation of the radioactive waste from people and from the accessible biosphere.
The features shall aim to provide isolation for several hundreds of years for short-lived
waste and at least several thousand years for intermediate and high level waste. In so
doing, consideration shall be given to both the natural evolution of the disposal system
and events causing disturbance of the facility”.
4.34.
Isolation is defined as the physical separation and retention of radioactive waste away from
people and the environment, Ref. [5]. Isolation is a requirement for safe waste disposal and is also
important in providing and maintaining nuclear security over certain types of disposed waste.
4.35.
When siting a borehole disposal facility, the operating organization is required to provide
sufficient isolation and should give due consideration to processes and events that might lead to a loss
of isolation. Such processes and events might bring disposed waste closer to the surface environment
and cause people to become exposed to radiation, and include erosion, tectonic uplift, glaciation,
30
permafrost melting and inadvertent human intrusion. In order to minimize the probability of inadvertent
human intrusion, the operating organization should site borehole disposal facilities away from areas
with resources, including mineral, oil, gas, geothermal energy and water resources. Further information
on the siting of borehole disposal facilities is contained in Appendix I.
4.36.
In designing a borehole disposal facility, the operating organization should select an appropriate
depth range for the waste disposal zone(s), taking account of the characteristics of the waste and the
requirements for isolation and nuclear security. For waste that will have significant activity at the end
of the period of active institutional control 14 (e.g. long-lived disused sealed radioactive sources that
have been declared waste and intermediate level waste generated during their management), the
operating organization should locate the disposal zone(s) in a borehole disposal facility below 100 m
(Annex II). Disposal at depths shallower than 100 m could be a safe option for short-lived disused
sealed radioactive sources and low level waste that are not subject to safeguards (see paras 7.23 to 7.29),
but the operating organization has to demonstrate that such facilities would provide sufficient isolation
and nuclear security. In addition to providing sufficient isolation and nuclear security, the operating
organization should take account of the characteristics (e.g. permeability) of the host rocks and the
geochemistry of the groundwaters when deciding on the depth of the disposal zone(s) in a borehole
disposal facility (see Section 6).
4.37.
In designing a borehole disposal facility, the operating organization should give due
consideration to further enhancing confidence in the isolation provided by the selection of the site and
the design of the facility, including the choice of disposal depth, by including mechanically strong and
heavy engineered anti-intrusion barriers (e.g. concrete slabs).
SURVEILLANCE AND CONTROL OF PASSIVE SAFETY FEATURES
4.38.
Requirement 10 of SSR-5 [4] states:
“An appropriate level of surveillance and control shall be applied to protect and preserve
the passive safety features, to the extent that this is necessary, so that they can fulfil the
functions that they are assigned in the safety case for safety after closure.”
4.39.
In the context of a disposal facility for radioactive waste, surveillance is used to mean physical
inspection of the facility to verify its integrity and the capability to protect and preserve passive barriers
[5]. The operating organization should inspect the disposal system periodically throughout the period
of authorization to check that there have not been unexpected changes to conditions or human activities
at or near the site that could affect the structures, systems and components of the facility. The operating
organization should update the safety case for the facility if changes to conditions or human activities
For example, Figure 3 of Ref. [14] shows that some sealed radioactive sources containing Cs-137 will not decay
to exemption levels for more than 1,000 years and that Ra-226 sources can remain potentially dangerous for tens
of thousands of years.
14
31
at or near the site have occurred that could significantly affect the structures, systems and components
of the facility. The regulatory body should check periodically that any passive institutional controls
implemented remain in place and are adequate.
STEP BY STEP DEVELOPMENT AND EVALUATION OF DISPOSAL FACILITIES
4.40.
Requirement 11 of SSR-5 [4] states:
“Disposal facilities for radioactive waste shall be developed, operated and closed in a series
of steps. Each of these steps shall be supported, as necessary, by iterative evaluations of
the site, of the options for design, construction, operation and management, and of the
performance and safety of the disposal system.”
4.41.
The development, operation and closure of a borehole disposal facility could take place over a
shorter period than typical programmes for the development, operation and closure of near surface and
geological disposal facilities. Nonetheless, the operating organization should follow a step by step
approach to the development, operation, closure and institutional control of a borehole disposal facility
that includes iterative evaluations (assessments) of the site and the options for the facility.
4.42.
The most important steps in the development, operation, closure and institutional control of a
borehole disposal facility should coincide with regulatory or governmental decision points. These
decision points are typically the selection of a site, the approval of the design concept for the disposal
facility, authorization of the start of construction of the disposal facility, authorization of commissioning
and operation, authorization of facility closure, and the decision to release the site from regulatory
control. The regulatory body should establish and follow a step by step approach to the authorization
of a borehole disposal facility – see Section 3.
4.43.
The operating organization should engage with the regulatory body at the start of the
development process in order that there is clarity on the direction of the disposal programme and to
facilitate legitimate decision making.
4.44.
Decisions on the selection of a site, the design of the facility, the start of construction,
commissioning and operation, closure and release of the site from regulatory control should be made as
the project proceeds on the basis of the information available at the time and the confidence that the
borehole disposal facility will fulfil the requirements and provide acceptable safety and security.
Organizations making decisions on whether to proceed from one step to the next should also take
account of factors such as national policies and strategies, and the views of interested parties.
4.45.
The operating organization should follow an iterative approach to assess the safety of the
disposal system and should update the safety case as needed before a decision is made to progress to,
and commit resources for, the next step. By following a step by step approach, the operating
organization should progressively develop and build confidence in the safety of the disposal facility as
the disposal programme progresses.
32
4.46.
The iterative approach to safety assessment and safety case development should include the
collection, analysis and interpretation of relevant scientific and technical data, the development of
designs and operational plans and procedures, and should cover both the operational and post-closure
periods – SSR-5 [4]. The operating organization should use, the step by step approach as a framework
in which to develop and demonstrate sufficient confidence in the technical feasibility and safety of the
disposal facility. For each step in the process, the operating organization should identify the decision
that needs to be made and the information that is necessary to make the decision. The operating
organization should also identify the appropriate interested parties and determine when and how to
include them in the decision-making process.
4.47.
As information becomes available it should be used to update the safety case and inform
decisions regarding facility design and further data gathering to reduce uncertainties. The operating
organization should introduce additional iterations as appropriate to facilitate management of the
disposal facility development project.
4.48.
The operating organization and the regulatory body should conduct or commission independent
technical and regulatory reviews at appropriate steps and decision points. The nature of these reviews
and the degree of involvement of interested parties at each step and decision point will depend on
national practices and the facility in question.
5. SAFETY CASE AND SAFETY ASSESSMENT
5.1.
The safety case is the collection of scientific, technical, administrative and managerial
arguments and evidence in support of the safety of a disposal facility, covering the suitability of the site
and the design, construction and operation of the facility, the assessment of radiation risks and assurance
of the adequacy and quality of all of the safety related work associated with the disposal facility. Safety
assessments are an integral part of the safety case. Safety assessment involves quantification of radiation
dose and radiation risks that may arise from the disposal facility for comparison with dose and risk
criteria, and provides an understanding of the behaviour of the disposal facility under normal conditions
and disturbing events, considering the time frames over which the radioactive waste remains hazardous
(para. 1.3 of SSG-23 [35]).
5.2.
In addition to safety assessments, the collection of arguments and evidence compiled in an
operating organization’s safety case should include:
(a)
Descriptions of the safety case context, the safety strategy and the disposal system;
(b)
Demonstrations of optimization and the management of uncertainty;
(c)
Evidence of independent review and the involvement of interested parties in the development
of the safety case;
(d)
A statement of the limits, controls and conditions to be applied during facility development;
33
(e)
The management system and evidence that it has been applied to ensure the quality of all safety
related work and activities – see Section 4 of SSG-23 [35].
PREPARATION, APPROVAL AND USE OF THE SAFETY CASE AND SAFETY ASSESSMENT
5.3.
Requirement 12 of SSR-5 [4] states:
“A safety case and supporting safety assessment shall be prepared and updated by the
operator, as necessary, at each step in the development of a disposal facility, in operation
and after closure. The safety case and supporting safety assessment shall be submitted to
the regulatory body for approval. The safety case and supporting safety assessment shall
be sufficiently detailed and comprehensive to provide the necessary technical input for
informing the regulatory body and for informing the decisions necessary at each step”.
5.4.
The operating organization has the prime responsibility for safety and is required to develop a
safety case for the facilities and activities and to provide it to the regulatory body for approval. The
operating organization should start to develop the safety case, including appropriate safety assessments,
early in the development of the disposal facility. The operating organization should include the safety
case in the information provided to the regulatory body to request authorization.
5.5.
The operating organization should develop and use the safety case and safety assessments to
guide all steps and decisions in the development, operation, closure and institutional control of a
borehole disposal facility and as a basis for communication with interested parties – SSG-23 [35]. The
safety case should be regarded as a “living document”. The operating organization should update the
safety case to take account of new information at each step and as required in the authorization issued
by the regulatory body. Fig 2, from Ref. [42], illustrates the progressive updating of the safety case
during the development, operation, closure and institutional control of a disposal facility and the typical
sequence of decisions that are made. The operating organization should use the safety case to guide the
activities undertaken in the development, operation, closure and institutional control of the borehole
disposal facility, including research and development, site characterization, facility design, and
optimization.
5.6.
For a small borehole disposal facility, some of the periods in the step by step development
approach could be significantly shorter than would be the case for near surface and geological disposal
facilities. For example, at a small borehole disposal facility the operational period could be just a few
months to a year long. The regulatory body should define its requirements for information and updating
of the safety case taking account of the national regulatory approach, the size of the facility and the
hazard posed by the disposed waste.
34
FIG. 2 The typical sequence of decisions made in the development, operation, closure and institutional
control of a disposal facility for radioactive waste - Ref. [42]
5.7.
When preparing the safety case, the operating organization should consider the regulatory body
to be the primary audience but also take account of the needs of other interested parties. The operating
organization should make safety case information available to the public except where this is prevented
for legal reasons, or for reasons related to security or commercial confidentiality. The safety case
developed to support authorization may be highly-technical and so the operating organization should
also provide a description of the safety case that is readily understandable by the general public.
5.8.
The operating organization should make the safety case sufficiently detailed and
comprehensive so that it provides the information needed by the regulatory body for deciding whether
regulatory requirements have been fulfilled or have the potential to be fulfilled and, therefore, whether
the project can proceed from one step to the next. Early in the disposal programme, the safety case may
have weaknesses or gaps in some areas due to incomplete knowledge; in such cases, the operating
organization should acknowledge the lack of data or information in the safety case, should describe the
potential significance of the uncertainties, and describe how the uncertainties will be addressed and
managed.
5.9.
The operating organization should use the safety case to guide decisions concerning, for
example, the objectives and allocation of resources for research and development, site characterization,
disposal facility design, optimization, the development of waste acceptance criteria and the operation,
closure and institutional control of the borehole disposal facility.
5.10.
The operating organization should follow a graded approach in preparing the safety case and
conducting safety assessments. A programme for the development, operation, closure and institutional
35
control of a small borehole disposal facility ought to be significantly smaller than is typically needed
for a near surface or geological disposal facility. In developing a site-specific safety case for a borehole
disposal facility, the operating organization should consider the available information, including that in
Refs [14], [17], [18], [22], [23] and [37].
SCOPE OF THE SAFETY CASE AND SAFETY ASSESSMENT
5.11.
Requirement 13 of SSR-5 [4] states:
“The safety case for a disposal facility shall describe all safety relevant aspects of the site,
the design of the facility and the managerial control measures and regulatory controls.
The safety case and supporting safety assessment shall demonstrate the level of protection
of people and the environment provided and shall provide assurance to the regulatory
body and other interested parties that safety requirements will be met”.
Safety case
5.12.
The structure and main components of the safety case are illustrated in Fig. 3 from SSG-23
[35]. The operating organization should in the safety case describe and assess all of the safety relevant
aspects of the site, the facility and the activities, both during operations and following the closure of the
disposal facility, and demonstrate that appropriate and effective management controls will be applied.
The operating organization should work in accordance with the management system throughout the
development of the safety case and the facility and its operation, closure and institutional control –
GSG-16 [25]. Paras 5.15 to 5.26 address the safety case components identified in FIG. 3.
5.13.
The operating organization and the regulatory body should engage in appropriate formal
dialogue starting at an early stage in the programme leading to development of a borehole disposal
facility – this dialogue should include discussion of regulatory requirements, guidance and expectations
of the safety case and its scope and content. Detailed technical discussion may also be needed on the
safety assessments and on all other aspects relating for example to the design of the facility and plans
for its operation, closure and monitoring. The programme of dialogue should be broadly framed so that
it can include aspects other than those relating to radiological safety, such as environmental protection,
which may lead to requirements or constraints on facility development.
5.14.
The operating organization should establish and lead a programme of dialogue with interested
parties on the disposal facility. This programme of dialogue should be appropriate to the situation in the
State and local to the site. As part of this programme of dialogue, the operating organization should use
information from the safety case to provide assurance that safety requirements will be met. In addition
to discussing the plans for the disposal facility and its safety, the benefits resulting from use of the
radioactive sources should be described. Further guidance on interactions with interested parties on
radioactive waste management is provided in – GSG-16 [25]. Guidance on the role of the regulatory
body in such dialogue is provided in GSG-6 [31].
36
FIG 3 Components of the safety case, Ref. [35].
5.15.
The operating organization should describe in the safety case the safety case context comprising
the high-level framework, or boundary conditions, applicable to the development of the safety case.
The operating organization should include a description and discussion of aspects including the
following:
(a)
The legal and regulatory framework for the management of the waste, which may include
international commitments (e.g. the Joint Convention – Ref. [6] and the Code of Conduct –
Ref. [7]) and national laws, regulations, policies and strategies for radioactive waste
management, and their relationships to the use of borehole disposal;
(b)
The purpose of the safety case at this stage within the context of the step by step approach to
the development of the facility (e.g. predisposal management of waste, site characterization,
facility design, construction, commissioning, operation, closure, cessation of active institutional
control, safety reassessment, safety upgrading), possibly supplemented with specific supporting
objectives (e.g. relating to proposed changes to operations);
(c)
The scope of the safety case at this stage (e.g. which features, events and processes are included
in the safety case and which are excluded); this should be accompanied by justifications and
arguments to support the inclusions and exclusions. Aspects that may influence the scope of the
safety case include, the site selection process for the implementation of borehole disposal,
public engagement and acceptance, environmental and social impact assessment, the
operational and post-closure timeframes, and the application of the graded approach to safety
case development;
(d)
The target audience(s) for the safety case and how interested parties will be involved during the
development of the safety case.
37
5.16.
The operating organization should document in the safety case a safety strategy which
comprises the high-level integrated approach adopted to achieve safety of borehole disposal. The
operating organization’s safety strategy should describe the approach that will be taken to comply with
the safety objective, principles, protection criteria and other regulatory requirements as defined in the
safety case context, and to ensure that good science and engineering practices are adopted. The
operating organization’s safety strategy should describe:
(a)
How the waste is to be contained and isolated from the biosphere using borehole disposal;
(b)
The inclusion in the borehole disposal system of passive safety features;
(c)
The robustness and the defence in depth provided by the borehole disposal system;
(d)
The approach to management of uncertainties, interdependencies and the application of the
graded approach.
5.17.
The safety strategy should be defined at an early stage in the safety case development process.
5.18.
The operating organization should document in the safety case a system description. The system
description should include detailed information on:
(a)
The inventory of waste and how it was derived and the level of confidence in the inventory;
(b)
The characteristics of the site and its surrounding environment;
(c)
The predisposal facilities and activities (e.g. a hot cell or other facility for conditioning of
waste);
(d)
The operating procedures to be used;
(e)
The disposal facilities and activities (e.g. of the waste packages and borehole(s) and their
configuration and construction, commissioning activities, waste emplacement operations) and
the closure activities;
(f)
The safety functions associated with the engineered and natural components in the disposal
system and how these are expected to be fulfilled over time to provide safety.
5.19.
The operating organization should include in the safety case, safety assessments as necessary
to address all aspects relevant to the safety of the predisposal management facilities and activities, and
to the development, operation, closure and institutional control of the borehole disposal facility. The
operating organization should in the safety case for a radioactive waste disposal facility address both
operational safety and post-closure safety. The operating organization should in the operational safety
assessment show that, in conjunction with application of the management system, the facility will be
safe during operation. The operating organization should in the post-closure safety assessment provide
reasonable assurance that the facility will be safe after it is closed. In these assessments, the operating
organization should consider potential impacts on humans and the environment. The operating
38
organization should include other safety assessments in the safety case as appropriate to address, for
example, transport, non-radiological hazards (e.g. non-radiological hazardous substances such as
asbestos, lead), and ‘conventional’ health and safety hazards (e.g. hazards to workers during
construction of the borehole repository).
5.20.
To demonstrate the level of protection of people and the environment provided, the operating
organization should in the post-closure safety assessment take account of all waste disposed of at the
site (e.g. all waste in disposal boreholes and waste in any other disposal facilities at and neighbouring
the site). For example, where it is proposed to create a borehole disposal facility at or next to the site of
an existing near surface disposal facility, the operating organization(s) should assess the impact of the
borehole disposal facility on the safety of the near surface facility and vice versa.
5.21.
Further guidance on post-closure safety assessment for borehole disposal facilities is provided
in paras 5.27 to 5.46 and in Appendix II.
5.22.
The operating organization should in the safety case propose limits, controls and conditions on
how the facilities and activities will be developed, operated, closed and controlled. The regulatory body
should review and approve the limits, controls and conditions proposed by the operating organization.
The regulatory body should as appropriate include the approved limits, controls and conditions as
authorization conditions, together with any further conditions that the regulatory body considers
necessary. The limits, controls and conditions may relate to radiological and or non-radiological
parameters (e.g. the amount of activity that may be placed in a waste package, restrictions on the mixing
of radionuclides in a disposal capsule, a condition on the minimum thickness of a certain engineered
barrier, the timing of a backfilling operation, prohibitions on powdered, pyrophoric and or putrescible
wastes).
5.23.
The operating organization should ensure that iteration and design refinement occur throughout
the safety case development process and that they are properly documented in the safety case. Iteration
and design refinement involve multiple interactions between data gathering activities (e.g. research and
development, site characterization), safety assessment and disposal facility design. As new data and
knowledge are acquired relating to the site and the performance of the disposal system for a given
inventory and facility design, the design of the facility should be refined as necessary, and the safety
assessment and the data gathering programme should be updated. Many cycles of iteration and design
refinement may be necessary to achieve the desired result. Further discussion of iteration and design
refinement is provided in paras 4.1 to 4.11 and para. 6.35;
5.24.
The operating organization should ensure that the management of uncertainties occurs
throughout the safety case development process and that it is properly documented in the safety case.
There are and will always be uncertainties, including when considering the safety of radioactive waste
disposal, and particularly when considering long time frames and disposal systems that include natural
environmental systems. Some uncertainties relate to a lack of knowledge and can potentially be reduced
39
by gathering more data. Other uncertainties cannot be reduced because, for example, they relate to
intrinsic randomness or to aspects that are inherently unknowable, such as future human behaviour.
When developing a borehole disposal facility there will often be alternative ways of managing
uncertainties. For example, if results from a post-closure safety assessment suggest that it is uncertain
that the disposal of a certain inventory of waste in a proposed borehole disposal facility would lead to
potential doses and risks below the relevant dose and risk criteria, it might be possible for the operating
organization to increase confidence by gathering more data, by reducing conservatism in the models,
by changing the design of the facility, or through some combination of such actions. The operating
organization should set out and apply an approach to the management of uncertainties and should
document this in the safety case. Many uncertainties in borehole disposal of waste relate to the site and
the potential pathways by which radiation exposures could occur in future. The operating organization
should show in the safety case that the key uncertainties have been identified, quantified where possible,
and managed, for example, by appropriate site selection and appropriate location, depth and design of
the disposal borehole(s), and or by gathering more data and or improving assessment models, and that
having made these strategic management choices and taken such actions, the safety assessments give
confidence that potential doses and risks will be below the relevant dose and risk criteria;
5.25.
The operating organization should ensure that the management system is applied throughout
the safety case development process and that its application is properly documented in the safety case.
The operating organization should ensure that all safety case development activities, including those
performed by the supply chain, are conducted in accordance with an appropriate management system.
The operating organization’s management system should ensure that independent peer reviews of the
safety case for waste management facilities and activities are conducted and that peer review findings
are appropriately considered and acted upon. The regulatory body should ensure that activities related
to regulatory review and assessment of the safety case, including those performed by the supply chain,
are conducted in accordance with an appropriate management system – see GSG-16 [25] and paras 7.38
to 7.40.
5.26.
The operating organization should present in the safety case an integration of safety arguments.
The safety case should synthesize of all the available evidence, arguments and analyses conducted and
these must lead logically to the conclusion that the proposed activities can be safely and securely
managed. The operating organization’s synthesis should explain how relevant data and information
have been collected, quality assured and considered, how models have been tested, and how rational
and systematic procedures for safety assessment have been followed. The operating organization’s
synthesis should address all relevant aspects and requirements, including the importance of safety, the
requirement for passive safety, the level of confidence that exists in the understanding of the disposal
system, disposal system design principles (e.g. multiple safety functions, containment, isolation), the
steps in the disposal facility development process (site characterization and facility design, construction,
operation, closure) and assurance measures (e.g. monitoring and surveillance, institutional controls).
40
The operating organization’s synthesis should acknowledge any limitations of the currently available
evidence, arguments and analyses, and should highlight the principal grounds on which a judgement
has been made that the planning and development of the waste management and disposal system should
nevertheless be continued.
5.27.
The operating organization should define clearly and justify the scope of the safety case and
the safety assessments so that they are appropriate to the stage in the development, operation, closure
and institutional control of the disposal facility. For example, initial assessments of disposal concepts
and feasibility will differ from later assessments for regulatory approval, commissioning, operation and
closure. The operating organization should consider available information which may be of assistance
in developing the safety case and safety assessments appropriate to the situation in the State and the
stage that the disposal programme has reached.
Safety assessment
5.28.
The operating organization is required to undertake safety assessments to evaluate the
performance of the disposal system and quantify its potential radiological impacts on human health and
the environment – see para. 2.5 of SSG-23 [35]. The operating organization should undertake safety
assessments to develop and demonstrate an understanding of the behaviour of the disposal facility under
normal conditions and following disturbing events – SSG-23 [35]. The operating organization should
use safety assessment to guide site characterization studies and to guiding the design of the facility –
SSR-5 [4]. The operating organization should use safety assessment throughout the development,
operation, closure and institutional control of the facility to evaluate the prevailing level of
understanding of the disposal system and assess uncertainties – SSR-5 [4]. The following paragraphs
in this section address; post-closure safety assessment, operational safety assessment, and other
assessments.
5.29.
The IAEA has undertaken various studies to assess, and provide tools for assessing, the post-
closure safety of borehole disposal of disused sealed radioactive sources. A series of models at different
levels of complexity has been developed that can be used when applying a graded approach to assessing
post-closure safety, Ref. [18]. These models include a detailed generic safety assessment – see Ref. [17]
– which can be used as a basis for the development of a site-specific post-closure safety assessment that
could form part of the information needed for authorization. These studies – Refs [17] and [18] –
focussed initially on the disposal of Category 3 to Category 5 disused sealed radioactive sources – see
RS-G-1.9 [21] –, but were later extended also to allow consideration of the safety of the disposal of
Category 1 and Category 2 disused sealed radioactive sources – e.g. see Ref. [15] and Appendix II.
Although Refs [17] and [18] provide much useful information, the operating organization is still
required to develop a safety case for the disposal facility that is specific to the site and the waste
inventory to be disposed of.
41
5.30.
In accordance with para. 3.15 of SF-1 [1], the operating organization has to assess safety in a
manner that is consistent with a graded approach so that the effort expended, and the controls applied,
are commensurate with the hazard and the level of risk associated with the waste, Appendix II and Ref.
[18]. The operating organization should consider using the tiered assessment approach presented in
Ref. [18] to establish the scope, complexity and level of conservatism in post-closure safety assessment:
(a)
Tier 1 assessment (least complex, extremely conservative) in which the toxicity of the
radionuclide inventory for borehole disposal is assessed;
(b)
Tier 2 assessment in which the activity concentrations in the radionuclide inventory for
borehole disposal are compared against predefined waste acceptance criteria (e.g. as defined in
Ref. [18], for example) and clearance level values as defined in GSR Part 3 [2];
(c)
Tier 3 assessment in which the Borehole Disposal Concept Scoping Tool – Ref. [43] is used to
perform conservative scoping calculations for borehole disposal;
(d)
Tier 4 assessment (less complex, more realistic) in which a screening model is used to assess
the performance of the disposal system;
(e)
Tier 5 assessment (most complex, more realistic) in which the models developed for the generic
safety assessment – Ref. [17] are applied to assess the post-closure performance of the disposal
system.
5.31.
The operating organization should use these models or similar models to assess the safety of a
borehole disposal system following the graded approach by working systematically from simpler, more
conservative models (e.g. Tier 1) to more complex, more realistic models (e.g. Tier 5). By following
such a graded approach, the operating organization should gradually define and refine the scope of what
to consider and include in the safety assessments – for example:
(a)
The Tier 1 and Tier 2 assessments can be used to exclude some radionuclides from further
analysis. If the models in Tier 1 and Tier 2 show that the potential radiation exposures from
certain radionuclides are insignificant, even under very conservative assumptions, then there is
no need to consider those radionuclides in more detailed modelling at a later stage;
(b)
The use of relatively simple models can provide indications regarding the ease of making a
convincing safety case for the disposal of a certain waste inventory at a particular site. Such
models can also help to identify which properties of the disposal system and which uncertainties
are the most important to safety, and which of these may need to be addressed and quantified
in greater detail;
(c)
By comparison, a lower tier assessment model is simpler than a higher tier model and, therefore,
requires fewer input data and less modelling effort. The operating organization should define
its data gathering and site characterization efforts so that they focus on aspects that are
significant to safety.
42
5.32.
The operating organization should define clearly and justify the assessment approach to be
followed, including aspects such as the following: the use of probabilistic and or deterministic
assessment methods, conservative versus realistic assumptions, the approach to the assessment of
uncertainties, the assessment time frames to be considered, the assessment endpoints to be calculated
e.g. potential doses, risks, radionuclide fluxes (e.g. from engineered barriers or from the geosphere to
the biosphere).
5.33.
The operating organization should make a systematic assessment of the uncertainties associated
with the safety and the performance of the disposal system. The operating organization should use the
safety assessments to identify and, where possible, quantify uncertainties. The operating organization
should include in the safety assessments appropriate treatments of scenario, model, and data and
parameter uncertainty. Fig. 4 shows a general structure for analysing uncertainties in this way.
FIG. 4 Structure of uncertainty analysis, showing the treatment of scenario, model, and parameter
uncertainties – modified from Ref. [44]
5.34.
The treatment of uncertainty in post-closure safety assessment for disposal facilities is
discussed in general in SSG-23 [35]. More specifically, experience gained during the development of
the generic safety assessment for borehole disposal – Ref. [17], during development of the graded
approach to post-closure safety assessment for borehole disposal – Ref. [18] and during pilot projects
for the implementation of borehole disposal – Refs [45] and [46] – has shown that the operating
organization should consider a range of scenarios and potential radionuclide transport and exposure
pathways, as appropriate to the facility and site, including the following:
(a)
Scenarios representing the expected evolution of the disposal system, including the disposal
facility as designed and as constructed;
(b)
Scenarios including initial defects in engineered barriers;
43
(c)
Scenarios that address uncertainties in, and potential changes to, environmental conditions
(e.g. climate, hydrogeology);
(d)
Scenarios including radionuclide transport along a disposal borehole or in any zone of damaged
rock adjacent to a disposal borehole;
(e)
Scenarios including radionuclide transport in groundwater to a water abstraction well and to
other groundwater discharge points (e.g. a river);
(f)
Scenarios including radionuclide transport in groundwater and potential exposures via
pathways that include irrigation of crops, watering of livestock, and drinking;
(g)
Scenarios including inadvertent human intrusion.
5.35.
In considering human intrusion, the operating organization should focus on inadvertent human
intrusion and on the potential effects on the protection of people (including intruders and members of
the public) and of the environment at the time of the intrusion and afterwards caused by disruption of
the waste, engineered and natural barriers in the disposal system. In general, the probability of
inadvertent human intrusion decreases with depth because fewer human activities disturb systems at
greater depths.
5.36.
In cases where waste has been or is to be placed in boreholes at depths shallower than 100 m,
the operating organization should consider scenarios including the following:
(a)
The construction of building foundations, cuttings for roads and railways, ‘cut and cover’
tunnels, and standard tunnels;
(b)
Drilling.
5.37.
Where waste has been or is to be placed in boreholes at depths shallower than 100 m, the
operating organization should assess inadvertent human intrusion as a probable event. In such cases,
the operating organization should implement effective active institutional controls during the period
until the activity of the waste has decayed sufficiently so that it is no longer of concern; for waste
containing long-lived radionuclides or large initial amounts of radionuclides such as 137Cs, the period
of active institutional control should extend into the post-closure period as needed. The operating
organization should specify the institutional controls envisaged, justify the period over which they are
assumed to be effective and provide financial assurance for implementation of the institutional controls
envisaged. The regulatory body should include the provision of these institutional controls as conditions
of the authorization.
5.38.
For borehole disposal facilities in which waste has been or is to be disposed of at depths greater
than 100 m, the operating organization should consider scenarios that include drilling, but need not
consider the activities in para 5.36(a). Where the depth of waste disposal is greater than 100 m, the
operating organization should assess inadvertent human intrusion as an event of low probability.
44
5.39.
In assessing the risks associated with scenarios, the operating organization should take account
of scenario probability.
5.40.
The operating organization should use results from the assessment of plausible “what-if”
scenarios to help in demonstrating that the performance of the disposal system is robust and includes
defence in depth, and to help in optimization.
5.41.
In assessing potential doses and risks associated with waste disposal, the operating organization
should assume that humans will be present at the site and that they will make use of local resources that
could contain radionuclides originating from the waste. As it is not possible to predict future human
behaviour with any certainty, the operating organization should avoid undue speculation regarding
future human habits. The operating organization should, however, take account of probable changes at
the site, such as expected changes in land use, population and climatic conditions, and the effects of
such changes on potentially exposed groups. Given that many borehole disposal facilities for disused
sealed radioactive sources would be small facilities (as compared with near surface and geological
disposal facilities) and have small footprints, the operating organization should take account of the
agricultural capacity or productivity of the site, as this may limit the size of potentially exposed groups
that could receive exposure.
5.42.
The operating organization should use uncertainty and sensitivity analyses to demonstrate
robustness and defence in depth, i.e. that the safety of the disposal system does not rely unduly on any
single:
(a)
Feature of the design or the site;
(b)
Assumption made in the safety assessment;
(c)
Safety function.
5.43.
The operating organization should show that if one barrier were to fail prematurely or otherwise
not perform as intended, or one safety function were not fulfilled, safety would still be provided.
5.44.
The operating organization should build confidence in the safety of the disposal system by
presenting multiple lines of reasoning. These lines of reasoning should include, but not necessarily be
limited to, arguments related to robustness, defence in depth, institutional control, monitoring, the use
of good science and engineering, information from research and development work, safety assessment,
and peer review. The operating organization should highlight conservatisms in the safety assessments
and should use uncertainty and sensitivity analyses to further support the development of multiple lines
of reasoning that the disposal facility will be safe. The operating organization should identify the main
factors that contribute to the safety of borehole disposal (e.g. Fig. 5) and explain how these factors
combine to provide confidence in safety. The operating organization should show that peer review
comments have been addressed in a logical and scientifically reasonable manner.
45
5.45.
The operating organization is required to assess the safety of operations at a borehole disposal
facility in accordance with the requirements for the predisposal management of radioactive waste in
GSR Part 5 [3] and the requirements for the disposal of radioactive waste in SSR-5 [4]. At a borehole
disposal facility for the disposal of disused sealed radioactive sources, the principal predisposal waste
management activities involved are processing of the disused sealed radioactive sources, including
conditioning them for disposal. These activities are then followed by waste disposal in the borehole(s)
– more detail is provided in Section 6. Procedures and operational safety assessments for these activities
have been developed in support of concept development and as part of pilot projects on borehole
disposal – see Refs [23], [40], [41] and [47]; the operating organization should consider the available
information when developing assessments and procedures for use at a particular facility.
FIG. 5 Factors that contribute to confidence in the long-term safety of borehole disposal of disused
sealed radioactive sources – modified from Ref. [18].
5.46.
The operating organization should, in accordance with national laws and regulations, undertake
further assessments as necessary to address non-radiological risks. The operating organization should,
as appropriate, assess the impacts on people of non-radiological components of the waste, the impacts
on the environment of facility operations, and the safety of workers during operations (e.g. lifting
operations). The operating organization should, as appropriate, consider factors including the content
of chemically or biologically toxic materials in the waste and in the engineered materials, the protection
of groundwater resources, and the ecological sensitivity of the environment into which contaminants
could be released. For example, if disused sealed radioactive sources were to be disposed of together
with their lead shielding, the operating organization should undertake assessments to evaluate the
potential exposure of humans and other species to lead migrating from the facility.
46
5.47.
With regard to the protection of non-human species, it is often the case that the system of
radiation protection also provides sufficient protection for non-human species – IAEA Safety Standards
Series No. GSG-8, Radiation Protection of the Public and the Environment [48]. Furthermore, even
though the natural environment is complex, and radiation is only one of several types of impact, the
optimization of protection provides a means for integration across the different impacts – IAEA Safety
Standards Series No. GSG-10, Prospective Radiological Environmental Impact Assessment for
Facilities and Activities [49]. Notwithstanding these assurances, the regulatory body should consider
requesting the operating organization to undertake assessments of present day and potential future
impacts of the facility on flora and fauna, in addition to assessing the environmental impacts of noise,
traffic, dust and possibly other factors.
DOCUMENTATION OF THE SAFETY CASE AND SAFETY ASSESSMENT
5.48.
Requirement 14 of SSR-5 [4] states:
“The safety case and supporting safety assessment for a disposal facility shall be
documented to a level of detail and quality sufficient to inform and support the decision
to be made at each step and to allow for independent review of the safety case and
supporting safety assessment.”
5.49.
The operating organization should document the safety case as a hierarchy of documents; Fig. 6
illustrates a possible hierarchy of safety case documents. At the lowest, most detailed level are
documents containing the data and information gathered through research and development work, site
characterization studies, experiments, literature reviews and other studies covering a wide spectrum of
scientific, engineering and other disciplines, as well as records of activities during the development
programme. The operating organization should use these data and information to prepare various
scientific, engineering and other reports that support the safety assessments. The operating organization
should use the reports and safety assessments as a basis for preparing the higher-level safety case
documentation that addresses directly the safety requirements. Even for a small borehole disposal
facility, the hierarchy of safety case documentation may be quite extensive.
5.50.
The operating organization should present in the safety case documents arguments, reasoning
and supporting evidence (models, parameters, data) in a convincing, traceable and transparent way. The
operating organization should prepare the safety case and safety assessment documentation to facilitate
understanding of the disposal system and its behaviour and performance, of the models, data and
assumptions used in safety assessment, and of the basis for and veracity of the arguments that show that
the facility is or will be safe.
5.51.
The operating organization should present the results of safety assessment in a manner that
illustrates both the performance of the entire disposal system, and the performance of individual
structures, systems and components of the waste management system. The operating organization
should identify and document any weaknesses in the design that should be improved and should
47
implement appropriate design refinement activities to increase confidence in the performance of the
waste management system.
5.52.
The operating organization should update the safety case periodically, for example to take
account of; the conduct of iterative cycles of design and safety assessment work, increases in scientific
understanding, changes to the disposal system (e.g. receipt of new waste types, addition of further
disposal boreholes) and in accordance with regulatory requirements (e.g. for periodic safety reviews).
FIG. 6 Possible hierarchy of documents comprising a safety case.
5.53.
Safety cases for near surface or geological disposal facility are typically developed gradually
over a period of several years or more throughout the step by step facility development process. In
contrast, the potentially short period between construction and closure at a small borehole disposal
facility means that the operating organization should make the safety case documentation as complete
and as detailed as reasonably possible at the time of applying for authorization of construction.
5.54.
The operating organization should develop the safety case documentation taking account of the
audiences for the documents, including the regulatory body and other interested parties. The operating
organization should consider preparing safety case documents with various levels of technical detail
and in different styles for different audiences and purposes, but all safety case documentation should be
consistent in terms of the main conclusions and messages presented.
5.55.
The operating organization should include in the safety case documentation a ‘Level 1’
synthesis, or executive summary, that provides an overview of the safety case using relatively simple
and as far as possible non-technical language intended to be understandable by non-specialists who may
include elected representatives and officials within government and members of the public. Such a
‘high-level’ document should convey the main messages from the safety case (e.g. that the disposal
facility is safe and will be safely managed during operations and will remain safe in the long-term).
48
5.56.
The operating organization should support the Level 1 synthesis by developing more detailed,
‘Level 2’, documents as necessary and appropriate to the facility and the decision-making step in
question. The Level 2 documents supporting the synthesis should address the main components of the
safety case, as illustrated in Fig. 3.
5.57.
The operating organization should provide yet more detailed, ‘Level 3’, documents as
appropriate that record various studies, work and peer reviews conducted during safety case and facility
development, operation, closure and institutional control, such as reports on the waste inventory, from
engineered barrier studies, from hydrological and geochemical interpretation work, reports on software
development and verification, plans for monitoring, plans relating to emergencies and for
decommissioning and, where relevant, studies on options for remedial actions at existing facilities.
5.58.
The operating organization should develop and compile Level 4 documents as necessary
comprising detailed records, for example, of laboratory and field studies, of tests, inspections and
operations, and of the scientific literature cited in the safety case that collectively provide the basis for
the parameter values used and assumptions made in the safety assessments.
5.59.
The regulatory body should provide guidance on the expectations of the safety case
documentation, including as appropriate the scope, contents and level of detail of the documents, and
on arrangements for the provision of information.
5.60.
When documenting the safety case, the operating organization should ensure that:
(a)
The documents provide a complete record of (i) the decisions and assumptions made in the
development, operation, closure and institutional control of the disposal facility and (ii) the
models and data used in the safety assessments;
(b)
Information is presented in a traceable way so that that independent suitably qualified and
experienced personnel could go back to the original sources of information supporting the
various elements of the safety case and understand how these elements have been used in the
safety case and could, if necessary, reproduce the safety assessments;
(c)
The reasoning for decisions taken (e.g. regarding the siting, design and operation of the facility)
is recorded and is logical and clear. The operating organization should document reasons for
and against alternative options, and should explain why one option was chosen over another.
5.61.
The operating organization should include in the safety case documentation evidence of the use
of the management system, including processes and procedures for quality assurance and quality control
e.g. over data gathering, safety assessment modelling and document production. The operating
organization should include in the safety case documentation evidence of and results from internal and
external independent peer reviews of the safety case and responses to peer review comments.
5.62.
In accordance with the graded approach, the length and the depth of the safety case
documentation should be commensurate with the hazard and the level of risk associated with the waste.
49
Where it can be shown that, on the basis of verified data and information, assessed potential doses and
risks are orders of magnitude below the relevant dose and risk criteria, this should increase confidence
and allow the safety case to be simplified. How simple the safety case can be may depend on various
factors (e.g. national and local circumstances, regulatory requirements, the audiences for the safety
case), and be a matter of judgement that should benefit from dialogue between the operating
organization, the regulatory body and other interested parties.
6. APPROACH TO THE DEVELOPMENT OF A BOREHOLE DISPOSAL FACILITY
6.1.
The operating organization should establish and implement a management system (see paras
6.2.
Before operations commences, the operating organization should determine the needs for
7.38 to 7.40).
human resources in terms of numbers, responsibilities and expertise, and proceed to recruit and train
sufficient suitably qualified and experienced personnel to perform the operations. The operating
organization’s training programme should cover all activities that are significant for safety and should
provide the knowledge and practical experience necessary for conducting the activities safely. The
operating organization and the training programme should foster the development of a safety culture –
GSG-16 [25]. The training should provide staff with a high degree of awareness of the design features
of the borehole disposal facility that are significant for safety. The training programme should be
updated in the light of experience and staff should be retrained as necessary. The operating organization
should have access to technical expertise in various disciplines including; radiological protection,
handling of radioactive sources and waste, waste conditioning (including cement and concrete
technologies, and welding), waste transport, borehole construction, casing and backfilling, borehole
sealing, safety assessment and safety case development.
PREDISPOSAL MANAGEMENT OF RADIOACTIVE WASTE FOR BOREHOLE DISPOSAL
6.3.
The operating organization should conduct predisposal management activities in accordance
with the guidance and recommendations contained in GSR Part 5 [3] WS-G-6.1 [19] and SSG-45 [20].
This section provides further specific guidance on the predisposal management of radioactive waste, as
identified in para. 1.1, intended for disposal in narrow diameter boreholes as described in paras 2.12 to
2.18.
6.4.
Requirement 6 of GSR Part 5 [3] states:
“Interdependences among all steps in the predisposal management of radioactive waste,
as well as the impact of the anticipated disposal option, shall be appropriately taken into
account”.
6.5.
The operating organization should identify, plan and undertake predisposal management
activities for borehole disposal as appropriate to the situation. The operating organization should
consider the locations of the waste relative to the site for the disposal facility, the types of sources and
50
waste to be managed, the need for waste characterization, and the infrastructure available and that will
be needed for processing, transport and storage prior to disposal.
6.6.
In cases where disused sealed radioactive sources ultimately intended for disposal are located
at many locations across a State (e.g. at user’s sites), the Government should ensure that:
(a)
Short-term storage of a disused source always occurs in safe and secure conditions, with proper
authorization and periodic inspections – Ref. [7];
(b)
Short-term storage occurs in a manner that does not preclude future management options –
Ref. [7];
(c)
The regulatory body sets an appropriate time limit for short-term storage of a disused source,
contingent upon availability of other management options – Ref. [7];
(d)
Consideration is given to centralized storage - see WS-G-6.1 [19] and SSG-45 [20] 15.
6.7.
In cases where the waste is located in a centralized storage facility, the operating organization
should consider undertaking waste characterization and waste processing at the centralized facility. In
cases where it is not appropriate to process the waste for disposal at a centralized facility, the operating
organization should undertake waste characterization and processing to produce waste packages for
disposal at the disposal site using appropriate fixed facilities or mobile facilities.
6.8.
The operating organization is required to implement a radiological protection programme
throughout the management of radioactive sources and during the predisposal management of
radioactive waste - see GSR Part 3 [2], in particular, Requirements 19 to 28. Guidance on occupational
protection is provided in IAEA Safety Standards Series No. GSG-7, Occupational Radiation Protection
[50]. The radiological protection programme is an essential part of the safety case and, as such, is subject
to regulatory approval. The operating organization should use suitably qualified and experienced
personnel to implement the radiological protection programme – GSG-16 [25].
6.9.
The operating organization should determine the need for personnel in terms of numbers,
responsibilities and expertise, and proceed to recruit and train suitably qualified and experienced
persons to perform the operations. The operating organization’s training programme should cover all
activities that are significant for safety and should provide the knowledge and practical experience
necessary for conducting the activities safely. The operating organization and the training programme
Para 5.3 of WS-G-6.1 states: “The storage of waste in centralized facilities rather than in a multitude of on-site
facilities should be considered, since there will be opportunities to adopt more stringent safety standards and at
the same time to realize economies of scale.” Para. 4.80 of SSG-45 states: “In instances where the operator has
neither adequate storage facilities nor facilities or expertise for the conditioning of spent and disused sealed
sources by encapsulation, arrangements should be made to transfer the sources to another licensed operator with
proper and adequate facilities (e.g. a centralized conditioning or storage facility). A centralized facility should be
established for the safe long term storage of disused sealed radioactive sources containing 226Ra, 241Am and other
long lived radionuclides.”
15
51
should foster the development of a safety culture – GSG-16 [25]. The training should provide staff with
a high degree of awareness of the design features of the facilities and activities that are significant for
safety. The training programme should be updated in the light of experience and staff should be
retrained as necessary.
6.10.
In accordance with the management system, the operating organization should establish a set
of written procedures to ensure that facilities are operated and activities are conducted safely in
compliance with the conditions of authorization and consistent with the safety case – GSG-16 [25]. In
addition to operating procedures for normal operations, the operating organization should establish
written procedures for the detection of unexpected events and accidents and for the mitigation of their
consequences. Procedures for the protection of workers during the use of the Mobile Hot Cell described
in Ref. [22] for the conditioning and disposal of disused sealed radioactive sources in a borehole
disposal facility are described in Refs [40] and [41] and in Ref. [22]. Operating procedures ensuring the
protection of workers during the use of the Mobile Tool Kit Facility described in Ref. [23] are
summarised in Ref. [47].
6.11.
Waste and waste packages resulting from waste conditioning should be transported to the
disposal site for disposal in accordance with the requirements in SSR-6 (Rev.1) [11].
6.12.
Long-term storage requires ongoing regulatory control and associated resources, which cannot
be ensured indefinitely – Ref. [7]. Where disposal facilities are available, disused sources should be
processed and disposed of rather than stored in a long-term storage facility.
6.13.
Prior to appropriate processing, disused sealed radioactive sources are often kept or stored in
the shielding that formed part of the device that utilized the source. Common shielding materials in such
devices include depleted uranium, tungsten and lead. Disused sealed radioactive sources are also often
stored in transport containers (e.g. “lead bombs”). Experience has shown that disused sealed radioactive
sources can become difficult or impossible to remove from device shields (e.g. due to corrosion) if they
are kept or stored for too long under inappropriate conditions. Working in accordance with an
authorization from the regulatory body, the operating organization should remove radioactive sources
from the devices in which they were housed and place them in stainless steel capsules.
(a)
Where it is necessary to store the disused sealed radioactive sources temporarily before they can
be conditioned for disposal, the operating organization should consider using IAEA Standard
Source Conditioning Capsules – see Ref. [51]. IAEA Standard Source Conditioning Capsules
containing the sources should be stored inside storage containers that provide appropriate
shielding to protect workers. For some Category 2 sources and all Category 3, 4 and 5 sources –
see RS-G-1.9 [21] – , shielding with 100 mm of lead should be sufficient. For Category 1 and
some Category 2 sources, it will be necessary to provide greater amounts of shielding;
(b)
52
To condition disused sealed radioactive sources for borehole disposal, the operating organization
should transfer the sources into disposal capsules which should be sealed by welding and placed
and sealed inside a disposal container comprising a stainless steel outer with a cement-based
insert as described in paras 2.14 and 2.15. Other containers and packaging may be appropriate,
but in all cases the operating organization should justify in the safety case the use and
performance of alternative barriers and materials.
6.14.
The operating organization should keep records of all waste management activities and waste,
including records of any waste other than disused sealed radioactive sources generated during the
management of the sources to be disposed of. Such waste might include small volumes 16 of
contaminated materials (e.g. that might be generated during management of a leaking source), depleted
uranium and other waste. The operating organization should assess in the safety case whether this waste
can be disposed of safely in the borehole disposal facility.
6.15.
The operating organization is required to decommission predisposal waste management
facilities in accordance with the requirements of GSR Part 6 [26]. The operating organization is required
to prepare a decommissioning plan and to maintain it throughout the lifetime of the facilities. For each
facility the operating organization is required to prepare and submit to the regulatory body an initial
decommissioning plan together with the application for authorization to operate the facility. This initial
decommissioning plan is required to identify decommissioning options, to demonstrate the feasibility
of decommissioning, to ensure that sufficient financial resources will be available for decommissioning,
and to identify and estimate the types and quantities of waste that will be generated during
decommissioning. The decommissioning plan is required to be updated by the operating organization
and reviewed by the regulatory body periodically, or when specific circumstances warrant. Prior to the
conduct of decommissioning, the operating organization is required to prepare and submit a final
decommissioning plan to the regulatory body for approval. The final decommissioning plan is required
to cover: the decommissioning strategy; the schedule, type, and sequence of decommissioning actions;
the waste management strategy, the proposed site end state and how the operating organization will
demonstrate that the end state has been achieved; the timeframe for decommissioning; and financing
for the completion of decommissioning.
SITE CHARACTERIZATION FOR A BOREHOLE DISPOSAL FACILITY
6.16.
Requirement 15 of SSR-5 [4] states:
“The site for a disposal facility shall be characterized at a level of detail sufficient to
support a general understanding of both the characteristics of the site and how the site
At a small borehole disposal facility, the total volume of this waste should be less than ~1 m3; small enough
that it could be disposed of in the borehole within just a few disposal containers. This option to dispose in a
borehole disposal facility of waste generated during the management of the disused sealed radioactive sources to
be disposed of provides flexibility to a State having only a small inventory of disused sealed radioactive sources,
to dispose of all of its waste in a single disposal campaign and, thereby, avoid leaving the State with a potential
legacy comprising a small amount of waste with no disposal route.
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53
will evolve over time. This shall include its present condition, its probable natural
evolution and possible natural events, and also human plans and actions in the vicinity
that may affect the safety of the facility over the period of interest. It shall also include a
specific understanding of the impact on safety of features, events and processes associated
with the site and the facility”.
6.17.
The operating organization should document and implement a programme of site
characterization work to gain sufficient understanding of the geomorphology, geology, hydrogeology,
hydrology, geochemistry, climate, weather and ecology at and around the site. The operating
organization should document and implement a programme of work to gain sufficient understanding of
land use and human populations and behaviour at and around the site and how this affects the
environment. The operating organization should document the scientific basis and reasoning for the
contents of these site characterization programmes. The operating organization should develop and
implement these site characterization programmes in parallel with (to run at the same time as) the
programme for the development of the safety case and the conduct of safety assessments (see Section 5).
6.18.
The operating organization should use the results from the site characterization programmes to
inform the development of the safety case and the safety assessments. The operating organization
should use results from the safety assessments and the safety case development work to refine and focus
the contents of the site characterization programmes on issues of importance to safety. Although the
collection of site-specific data should focus on issues of importance to safety, the operating organization
should also collect other site-specific data and information for additional confidence building purposes;
while these data might not be absolutely necessary for demonstrating safety, they can nevertheless be
useful, for example, in helping to support multiple lines of reasoning in the safety case.
6.19.
The operating organization should apply a graded approach when establishing site
characterization programmes to support the development, operation, closure and institutional control of
a borehole disposal facility, so that the effort expended is commensurate with the hazard and the level
of risk associated with the waste. A small borehole disposal facility of the type considered in the generic
safety assessment, Ref. [17] is a relatively small-scale facility when compared to typical near surface
or geological disposal facilities and is expected to provide a safe disposal solution under a wide range
of site conditions. Ref. [18] describes a graded approach to post-closure safety assessment for a borehole
disposal facility and discusses how safety assessment models at different levels of complexity might be
used to guide site characterization (see Appendix I).
6.20.
Site characterization activities for a borehole disposal facility should include, but not
necessarily be limited to, investigating the following (see also Appendix I):
(a)
The geology and geological evolution of the area. This should involve various surface-based
and underground activities such as geophysical and borehole drilling investigations, and the
collection of rock samples for examination and characterization. Investigatory drilling may help
54
to establish drill penetration rates, determine the presence of resources, and establish the
geology at depth and the presence of faults or other geological features that may influence the
performance of the borehole disposal facility;
(b)
The geomorphology and geomorphological evolution of the area. This should involve various
studies to map and quantify the geomorphology and to investigate the potential for past, presentday and potential future erosive processes and land movements (e.g. landslips, faults,
earthquakes, volcanism);
(c)
The hydrogeological conditions of the disposal system and their evolution. This should involve
various studies to establish groundwater conditions at the site, including the presence of perched
water, the properties of the partially-saturated or ‘unsaturated’ zone, the depth to the water table
(i.e. the interface between the unsaturated zone and the saturated zone), the piezometric surface,
and results from tests to determine hydraulic parameters (e.g. hydraulic head gradient,
permeability, porosity, saturation);
(d)
The hydrological conditions of surface water bodies in the area and their evolution. This should
involve various studies to identify and establish the behaviour of surface water bodies in
response to local meteorological conditions (e.g. precipitation), including studies of
hydrological responses to adverse conditions (e.g. extreme rainfall events and flooding);
(e)
The geochemistry of the disposal system and its evolution. This should involve various studies
to identify the mineralogy and quantify geochemistry of the rocks and waters in the disposal
system. Particular attention should be focused on determining the chemical composition of
groundwaters and their oxidation and reduction (redox) potentials and speciation as these
parameters can strongly affect the mobility of radionuclides;
(f)
The meteorological conditions at present and its evolution, including the possible effects of
future climate states on landform development and site conditions (see e.g. Ref. [52]);
(g)
The ecology at and around the site. This should include studies to collect data on non-human
fauna and flora;
(h)
Human populations and behaviours at and around the site. This should involve the studies to
collect data on the size, locations and density of human populations and on human activities
including land uses (e.g. agriculture) and on human behaviours (e.g. food consumption rates
and sources of drinking water) that would be needed for dose assessments for past, present and
potential future conditions.
6.21.
The operating organization should use information gathered from these programmes and
studies to develop a credible scientific description of the natural system at the site, and demonstrate
understanding of the safety-significant features events and processes and their spatial and temporal
extent and variability (in the past, at present and potentially in the future). The operating organization
55
should use this information in determining the suitability of the site for a borehole disposal facility and
in evaluating the performance of a disposal facility at the site.
6.22.
The operating organization should use site characterization information to help demonstrate a
sufficient understanding of the potential effects of natural events and processes on the isolation of waste
and containment of radionuclides provided by the borehole disposal facility. The operating organization
should include in this demonstration assessments of the probability of occurrence and potential effects
on the borehole disposal system of disruptive events and processes. The operating organization should
use this understanding together with the site characterization data as part of the basis for the safety case
and safety assessments 17. The operating organization should use this understanding to select and
establish the location and design of the borehole disposal facility including, in particular, the depths of
the disposal borehole(s) and the depths of the disposal zone(s).
6.23.
The operating organization should conduct site characterization work in accordance with an
appropriate management system (see paras 7.38 to 7.40 and GSG-16 [25]). The management system
should include a process and procedures for dealing with spatially distributed information and timeseries data from site characterization and to support the establishment of a baseline for monitoring. The
operating organization should use the management system to control the work of suppliers undertaking
site characterization activities – see GSG-16 [25].
DESIGN OF A BOREHOLE DISPOSAL FACILITY
6.24.
Requirement 16 of SSR-5 [4] states:
“The disposal facility and its engineered barriers shall be designed to contain the waste
with its associated hazard, to be physically and chemically compatible with the host
geological formation and/or surface environment, and to provide safety features after
closure that complement those features afforded by the host environment. The facility and
its engineered barriers shall be designed to provide safety during the operational period.”
6.25.
Borehole disposal, particularly using narrow-diameter boreholes, is appropriate for the disposal
of relatively small volumes of waste (e.g. disused sealed radioactive sources that have been declared
waste). A reference design for a borehole disposal facility for such waste has been described and
assessed on a generic basis in Ref. [17]. Site-specific designs for this type of borehole disposal facility
for disused sealed radioactive sources have been developed and assessed for implementation in some
States – see Refs [45] and [46].
In addition to describing the present-day characteristics of a site, the operator should collate and interpret
information on the past and potential future evolution of the site. Such information should be used to support the
identification of scenarios for the site and for evaluating the relevance of features events and processes that could
affect the performance of the disposal facility. The timescale for consideration of past site evolution should be at
least comparable to the future timescale of interest in safety assessments.
17
56
6.26.
The operating organization should undertake a programme of work to develop and refine the
design of a borehole disposal facility that takes due account of the inventory of waste to be disposed of,
results from site characterization, results from safety assessment, and arguments in the safety case for
the facility. The operating organization should develop and refine the design for the disposal facility in
parallel with (at the same time as) the programme for the development of the safety case and the conduct
of safety assessments (see Section 5). The operating organization should use results from the design
work to inform the development of the safety case and the safety assessments.
6.27.
The operating organization should consider the following aspects in developing the design for
a borehole disposal facility:
(a)
The inventory of waste (waste types, quantities, physical and chemical properties, radionuclides
present) to be disposed of;
(b)
The number of boreholes, borehole dimensions (e.g. diameter and depth) and the suitability of
geological conditions at the site (e.g. geological stability, groundwater flow, and the chemical
compatibility of the rocks and groundwaters with the engineered barriers);
(c)
The engineered barrier system;
(d)
Plans for operation of the borehole disposal facility, including waste emplacement and
backfilling;
(e)
Plans for sealing of boreholes and closure of the borehole disposal facility;
(f)
Plans for the post-closure period.
Waste inventory
6.28.
The operating organization should identify and quantify the inventory of waste to be disposed
of in the facility at an early stage in the development process. In developing the design of a borehole
disposal facility, the operating organization should consider using the IAEA Source Inventory
Management for Borehole Disposal (SIMBOD) software – Ref. [37] to determine the total inventory of
radionuclides, the distribution of Category 1 to Category 5 disused sealed radioactive sources within
the total inventory, how many waste packages would be required, the length of disposal zone(s) within
the borehole(s) that would be required, and the number of boreholes that would be required for the
waste.
Disposal boreholes
6.29.
The operating organization should determine the number of boreholes and the borehole
dimensions taking account of the volume of waste to be disposed of, the drilling technology proposed
to be used, and the need for the borehole diameter to be consistent with the dimensions of the waste
packages. The operating organization should select the depth of the disposal zone(s) to reduce the
probability of inadvertent human intrusion and to ensure that the disposal zone(s) is (are) located in
57
suitable rocks (those having appropriate mechanical, hydrogeological and hydrogeochemical
properties). The operating organization should reduce the risk from inadvertent human intrusion by
keeping the footprint of the facility small and by disposing of the waste at sufficient depth. In selecting
the depth of the disposal zone(s), the operating organization should consider the time it would take for
radionuclides released from the disposed waste to migrate to the biosphere. In deciding on the number
of disposal boreholes, the operating organization should consider the total length of disposal zone
needed, which will depend on the number and lengths of the waste packages and their spacing, and the
geometry (e.g. thicknesses) of suitable strata within the host rock at depth. The operating organization
should consider various options for the design of the disposal facility and should document the
justification for the selected design. For example, it could be possible to dispose safely and securely of
a certain inventory of waste in either one borehole with a long disposal zone or in two or more boreholes
with shorter disposal zones; the operating organization should give reasons for such design choices as
part of the demonstration of optimization. The operating organization should assess whether different
waste types should be placed in different locations in the disposal facility. The operating organization
should assess the interactions that could occur between neighbouring boreholes and should justify the
chosen locations for disposal boreholes.
Engineered components
6.30.
The operating organization should design a system of engineered barriers that is consistent with
plans for predisposal management of the waste, with the design of the disposal borehole(s), and that
will contribute to the containment of the radionuclides in the waste.
6.31.
The engineered barriers should include a waste package that facilitates waste handling and
emplacement operations and that is compatible with geochemical conditions in the host rock and the
materials of the other engineered barriers. The engineered barriers should be designed to provide
containment of heat generating waste throughout the period while the waste is producing heat energy
in amounts that could adversely affect the performance of the disposal system – SSR 5 [4]. The
operating organization should consider using more than one containment barrier (e.g. by placing the
sources inside a disposal capsule within a disposal container). The operating organization should use
appropriate material(s) to fill the spaces that would otherwise exist (e.g. between the disposal capsule
and container, between and around disposal containers in the borehole, and between the borehole casing
and the surrounding rocks – see Fig. 1). The operating organization should decide on the design of the
waste package relatively early in the development process for the facility because this will affect both
the predisposal management of the waste and the disposal operations. The operating organization should
address factors such as the amount of shielding provided by the waste package (as this may affect the
need to handle the waste package remotely), the dimensions and weight of the waste package (which
will affect lifting, handling and emplacement operations), the corrosion and radiation resistance of the
materials to be used (further information is provided in Appendix II), and the method of waste package
emplacement in the borehole (this will influence operational feasibility and safety). The operating
58
organization should assess and consider the long-term performance of the waste package in the disposal
borehole as this may play an important part in the post-closure safety of the disposal system.
6.32.
The operating organization should design engineered barriers that will be used to seal boreholes
and close the borehole disposal facility. Borehole seals could, for example, comprise clay or cementbased plugs tens of metres long placed in the borehole above the disposal zone. Such seals or plugs
could also be placed at the bottom of the disposal zone).
6.33.
The operating organization should consider the need for borehole casing to ensure borehole
stability during the operational period, and whether some or all of the casing should be removed after
waste disposal. The operating organization should consider the type of backfill material to use at depth
and near the surface. The operating organization should consider the inclusion of engineered features
to reduce the probability of inadvertent human intrusion (e.g. a deflector plate).
6.34.
The operating organization is required to use a multiple safety function approach so that the
safety of the facility does not depend unduly on a single barrier or a single safety function – SSR-5 [4].
The operating organization should specify the safety function(s) of each of the components in the
disposal system and should justify the selection of materials for the engineered barriers and features by
providing evidence to support a reasonable expectation that they will fulfil these functions. The
operating organization should document analyses of features events and processes that could cause the
components to degrade and or stop fulfilling their safety functions.
Design refinement
6.35.
The operating organization should in the safety case and safety assessments examine alternative
design options to:
(a)
Assess whether the designs have the potential to fulfil the relevant dose and risk criteria;
(b)
Evaluate the performance of the disposal system and its components;
(c)
Inform decisions on the design and optimization.
6.36.
The operating organization should consider a range of factors (including safety, security and
socio-economic factors) in coming to decisions on the design of a borehole disposal facility. For
example, the expected performance of the natural barriers in containing radionuclides in a borehole
disposal system could have implications for the required level of engineered containment and for how
operations should be carried out, and these aspects could have cost and man-power implications.
CONSTRUCTION OF A BOREHOLE DISPOSAL FACILITY
6.37.
Requirement 17 of SSR-5 [4] states:
“The disposal facility shall be constructed in accordance with the design as described in
the approved safety case and supporting safety assessment. It shall be constructed in such
a way as to preserve the safety functions of the host environment that have been shown
59
by the safety case to be important for safety after closure. Construction activities shall be
carried out in such a way as to ensure safety during the operational period.”
6.38.
The operating organization is required to construct the disposal facility in accordance with the
disposal facility design presented and assessed in the safety case and approved by the regulatory body,
and in accordance with a valid authorization. As part of the safety case, the operating organization
should develop a written construction method and associated technical specifications and procedures.
6.39.
To support a decision on authorization, the regulatory body should review the safety case
prepared by the operating organization, including the safety assessments for both the operational and
post-closure periods and the construction method and associated technical specifications and
procedures. The regulatory body should consider, inter alia, whether the proposed method of
construction would be capable of delivering the proposed design (e.g. in terms of borehole dimensions,
borehole straightness, ability to provide suitably dry conditions for waste emplacement, methods for
emplacement and removal of casing, methods for backfilling and sealing of boreholes) without having
a significant detrimental effect on the host environment. The regulatory body should consider whether
the safety case adequately describes and justifies the actions to be taken in the event of abnormal events
during construction, such as the loss of a drill bit, excessive water ingress, unexpected failure of a
borehole wall.
6.40.
The operating organization should document and implement a programme of testing and
inspection work to confirm and demonstrate that construction of the facility is in accordance with the
design, the construction method, and associated technical specifications and procedures, and that any
features revealed during construction are consistent with the safety case.
6.41.
The operating organization should ensure that borehole construction is carried out by suitably
qualified and experienced personnel following the construction method, technical specifications and
associated procedures – Ref. GSG-16 [25]. The regulatory body should undertake inspections during
construction of the facility to verify that the operating organization has a sufficient number of suitably
qualified and experienced personnel available for the activities to be performed. The construction
method, technical specifications and procedures should be based on safe and successful prior practice
and should be updated as further experience is gained.
6.42.
The operating organization should ensure that the construction method is sufficiently flexible
for dealing with spatially variable rock conditions. The operating organization should monitor rock
conditions during drilling and should take appropriate timely actions to counteract unfavourable
conditions (e.g. fracture zones) or unexpected events (e.g. failure of the borehole wall). The operating
organization should specify in the construction method means either for remediating marginally
unsuitable boreholes or sealing such boreholes without emplacing any waste. The regulatory body
should consider whether the safety case adequately describes and justifies measures for sealing ‘failed’
boreholes (i.e. boreholes where waste emplacement proves to be impracticable).
60
6.43.
The operating organization should specify in the construction method means of avoiding
unnecessary disturbance to the geology, particularly where boreholes pass through different
hydrogeological regimes. The operating organization should not locate a waste disposal zone in an
aquifer. Where it is necessary to drill through an aquifer to reach a waste disposal zone, the operating
organization should case the borehole and isolate the aquifer from the waste and avoid the creation of
pathways between different strata.
6.44.
The operating organization should take measures to prevent the borehole and any disturbed
rock zone around it from providing pathways through which radionuclides could be transported in gas
or groundwater towards the surface or other relatively transmissive geological strata. The operating
organization should aim to ensure that the permeability of the backfilled borehole and any disturbed
rock around it are no worse than that of the surrounding intact rocks.
6.45.
The operating organization should specify in the construction method means for installing any
borehole casing to be used and, as appropriate, for the removal of borehole casing.
6.46.
The operating organization should at a site only construct and operate one disposal borehole at
a time. The construction of new boreholes at the site of an existing borehole disposal facility should
only be conducted after the previous disposal boreholes have been sealed and should be carefully
planned and authorized by the regulatory body.
6.47.
The operating organization should make and retain records of borehole construction to provide
a complete description of the history of construction, including when, how and by whom the borehole(s)
was (were) constructed and its (their) depth(s) and diameter(s), the geological formations encountered,
the rate of drilling, whether water was encountered and any occurrences of unexpected events and
accidents and non-compliances with construction procedures.
COMMISSIONING OF A BOREHOLE DISPOSAL FACILITY
6.48.
Before a borehole disposal facility can start to operate, the operating organization should
perform appropriate commissioning activities. Before waste emplacement, the operating organization
should test and confirm that the operations can be undertaken successfully and as planned in compliance
with the conditions specified in the authorization and the safety case. The operating organization should
pay particular attention to testing the processes for emplacing waste packages in the borehole and for
putting in place the engineered barriers. The operating organization should during commissioning and
after the emplacement of each waste package check that the borehole does not contain any obstructions
that might prevent the successful emplacement of the next waste package. In pilot studies this has been
done by lowering and then retrieving a non-radioactive, ‘dummy’ waste package down the borehole.
The operating organization should include an appropriate programme of commissioning tests to verify
that the backfill materials as prepared on site have appropriate characteristics (e.g. water content,
density, grain size, rheology, setting time).
61
OPERATION OF A BOREHOLE DISPOSAL FACILITY
6.49.
Requirement 18 of SSR-5 [4] states:
“The disposal facility shall be operated in accordance with the conditions of the licence
and the relevant regulatory requirements so as to maintain safety during the operational
period and in such a manner as to preserve the safety functions assumed in the safety case
that are important to safety after closure.”
6.50.
The operating organization is required to operate the disposal facility in accordance with a valid
authorization and the safety case approved by the regulatory body; the operating organization’s
management system should be compatible with the authorization and safety case and should include
written operating procedures.
6.51.
At a borehole disposal facility, the operational period should commence after appropriate
commissioning activities. Disposal operations include waste receipt and checking that the waste is
consistent with the waste acceptance criteria, waste emplacement (including the emplacement of
backfill between waste packages), and backfilling and sealing the borehole. Predisposal management
operations (including temporary storage of waste and waste conditioning) may be performed
immediately before waste emplacement (e.g. using a mobile hot cell such as the one described in Ref.
[22] or the Mobile Tool Kit Facility described in Ref. [23]). Decommissioning and closure are addressed
in paras 6.79 to 6.83.
6.52.
The operating organization should describe in the safety case how the facility is to be
commissioned and operated. The operating organization should describe in the safety case how doses
to workers are to be controlled under normal circumstances and what arrangements will be in place to
protect workers and members of the public in abnormal situations (e.g. events and accidents).
6.53.
The regulatory body should review and assess the safety case and inspect the operations to
satisfy itself that:
(a)
The operating organization is applying its management system to ensure safe operation of the
disposal facility;
(b)
The operations do not compromise safety functions on which the post-closure safety of the
facility depends;
(c)
Only waste that complies with the waste acceptance criteria is accepted for disposal in the
facility – see paras 6.58 to 6.66.
Radiological protection programme
6.54.
The operating organization is required to implement a radiological protection programme
throughout the operation of a borehole disposal facility – see GSR Part 3 [2] - see in particular
Requirements 19 to 28. The radiological protection programme is an essential part of the safety case
62
and, as such, is subject to regulatory approval. Guidance on occupational protection that should be
applied at disposal facilities is provided in GSG-7 [50]. The operating organization should use suitably
qualified and experienced personnel to implement the radiological protection programme – GSG-16
[25].
Operating procedures
6.55.
In accordance with the management system, the operating organization should prepare a set of
written procedures to ensure that the facility is operated safely and in compliance with the conditions
of the authorization and the safety case – GSG-16 [25]. The operating procedures should be derived
from the technical specifications for the operations which, in turn, should be consistent with the
operational safety assessment. In addition to operating procedures for normal operations, the operating
organization should establish written procedures for the detection of unexpected events and accidents
(e.g. receipt of waste that does not conform to the waste acceptance criteria, jamming of waste packages
in boreholes) and for the mitigation of consequences. The operating procedures should specify when
reports should be made to the regulatory body. The operating organization should train personnel in the
use of the procedures.
6.56.
The operating organization should verify that work is done according to the procedures, that
the work achieves the design aims for the operations, and that the work and operations are adequately
covered by the safety assessment and the safety case; the operating organization should demonstrate
this through appropriate programmes of inspection, auditing and record-keeping.
6.57.
The operating organization should apply formal change control procedures to proposals for
changes or modifications to operating procedures or equipment and should ensure that the implications
of such changes or modifications for safety are assessed, understood and taken account of.
Waste acceptance
6.58.
Requirement 20 of SSR-5 [4] states:
“Waste packages and unpackaged waste accepted for emplacement in a disposal facility
shall conform to criteria that are fully consistent with, and are derived from, the safety
case for the disposal facility in operation and after closure.”
6.59.
The operating organization is required to operate a borehole disposal facility in accordance with
the limits, controls and conditions specified in the authorization. Waste acceptance criteria are required
as a key component of the limits, controls and conditions. The operating organization should develop
waste acceptance criteria to ensure that waste packages accepted for disposal in a borehole facility are
consistent with the safety case. The waste acceptance criteria should be approved by the regulatory
body. The operating organization should use the waste acceptance criteria to control the types amounts
of waste that are disposed of in the disposal facility.
63
6.60.
The safety of a borehole disposal facility depends in part on the waste packages. The operating
organization should, therefore, develop specifications that the waste package have to fulfil. The
operating organization should subject proposals or requests (e.g. from waste generators) for changes to
the waste packages to a change control process that includes a safety review by the operating
organization and, as appropriate, regulatory scrutiny.
6.61.
When designing a waste package for borehole disposal, the operating organization should
consider all of the activities to be performed during the predisposal management and disposal of the
waste, and should take account of the conditions that could occur throughout the predisposal
management and disposal operations and after waste disposal. As an illustration, limits included in the
waste acceptance criteria on the activity of gamma emitters that may be put in a waste package will
probably be determined by consideration of predisposal management or operational safety (related to
issues such as waste package surface dose rates). The corresponding limits for the activity of alpha
emitters that can be put in a waste package, will probably be determined by consideration of issues
related to post-closure safety.
6.62.
The operating organization should develop and use the waste acceptance criteria to provide
confidence that the waste forms and waste packages will fulfil the safety functions attributed to them in
the safety case. The operating organization should consider establishing waste acceptance criteria such
as the following:
(a)
A limitation to accept for disposal only solid waste forms;
(b)
A limitation to accept for disposal only waste forms with stable chemical and physical
properties (e.g. no powders, no putrescible, reactive or explosive materials or waste);
(c)
Specifications regarding any waste types that may be accepted in unpackaged form;
(d)
Limits on the weight and size of waste packages;
(e)
Limits on the levels of surface contamination on a waste package;
(f)
Specifications for waste disposal containers (e.g. acceptable materials, manufacturing and
welding methods, testing protocols);
(g)
Specifications for backfill materials (e.g. acceptable materials, backfilling methods, testing
protocols);
(h)
A limit on the heat (thermal) output of a waste package;
(i)
Limits to prevent the release of gases from waste packages;
(j)
Limits on the total activity of each waste package, of the waste in each borehole and of the
waste that can be disposed of in the entire disposal facility;
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(k)
Limits on the radionuclide content of each waste package, of each borehole and of the entire
disposal facility;
(l)
Controls on the mixing of different types of disused sealed radioactive sources and or
radionuclides within disposal packages;
(m)
Controls on the location (e.g. depth, spacing) of the emplacement of certain waste packages
within disposal boreholes;
(n)
Limits on the fissile nuclide content of each waste package, of each borehole and of the entire
disposal facility.
6.63.
Experience from considering the reference borehole disposal system assessed in Ref. [17] for
the case of a single disposal borehole, includes the following:
(a)
The protection of workers during disposal operations could depend on the type of shielding that
is available, and this may in practice limit the activity of strong gamma emitters and neutron
sources that can be accepted for processing and disposal;
(b)
Post-closure safety could limit the activity of long-lived radionuclides that may be disposed of
in the borehole disposal facility;
(c)
To avoid excessive temperature rises in the disposal borehole, heat generation should be kept
below a few tens of watts per waste package. This need to limit waste package heat generation
may mean that the largest sources that can be accepted have activities of heat generating
radionuclides no more than tens of GBq – see Refs [15] and [53].
6.64.
The operating organization should ensure that waste intended for disposal is characterized
sufficiently and shown to comply with the waste acceptance criteria before the waste is accepted for
disposal. The operating organization is required to keep records of all pre-disposal waste management
activities and of waste accepted for disposal in accordance with the management system (see paras 7.38
to 7.40).
6.65.
The operating organization should, as far as possible, collate and retain records that provide a
detailed description of each disused sealed radioactive sources (including its physical, chemical and
radiological characteristics) and of the total inventory of disused sealed radioactive sources and other
waste accepted for disposal and disposed of. The operating organization should make appropriate
estimates to fill gaps in inventory information, e.g. due to the facts that disused sealed radioactive
sources sometimes fall out of regulatory control and are later found as orphan sources, and because
disused sealed radioactive sources are often collected from many different users and locations, and may
have been stored for considerable periods by persons or organizations other than those that originally
used the sources. The operating organization should make use of the national register of radioactive
sources – see RS-G-1.9 [21] – to fill gaps in inventory information.
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6.66.
The regulatory body should ensure that arrangements and procedures are put in place to define
and control the actions to be taken by the generator of the waste and by the operating organization of
the disposal facility to deal with any waste packages that do not conform with the waste acceptance
criteria. The operating organization should inform the regulatory body in a timely manner of waste
packages that do not conform with the waste acceptance criteria. Depending on the severity of any nonconformance, the actions to be taken may include remediation of the waste package, repackaging of the
waste, and investigation and refinement of the waste package production process.
Waste emplacement
6.67.
The operating organization should emplace waste packages in the disposal borehole(s) in
accordance with the authorization and the safety case. The operating organization should ensure that
waste packages are emplaced centrally in the borehole(s) and should use appropriate backfilling
materials to ensure that the waste packages are emplaced with appropriate spacing to provide for the
management of heat and interactions between waste packages. Pilot studies for the disposal concept
described in paras 2.12 to 2.18 have found it more effective, in terms of avoiding the formation of
unwanted voids in the disposal zone, to emplace each waste package into a measured amount of wet
cement-based backfill that has already been placed in the borehole; this approach necessitates use of a
backfill with appropriate rheology and setting time, and operating at a rate that allows for the waste
packages to sink into the wet backfill grout and then for the backfill to set before the emplacement of
the next waste package. The operating organization should conduct appropriate tests under realistic
conditions to demonstrate that the materials and processes to be used to manufacture the backfill provide
a mixture with the required properties (e.g. rheology and setting times).
6.68.
At a larger scale, the operation of a borehole disposal facility can be performed following a
continuous or a campaign approach. In the case of continuous operation, waste packages are emplaced
in the borehole disposal facility as they are generated and the operating organization may, therefore,
need to keep the borehole open and exercise control over the borehole for several years. Campaign
operation involves the accumulation of waste in storage facilities until there is sufficient waste to be
disposed of within a short period (e.g. weeks to a few months). Operating on a campaign basis allows
individual disposal boreholes to be constructed, receive waste and be sealed as a discrete project, and,
thus, reduces the chances of the borehole remaining open for a long time and degrading or being
mismanaged between individual waste emplacement operations. Continuous operation could be
appropriate in the case of larger capacity boreholes where operating on a campaign basis would require
more extensive waste storage facilities. In either case, the operating organization should prevent
rainwater, surface water and groundwater from entering the borehole while it is open. This can be
achieved by providing as necessary borehole casing, a borehole drainage system and a secure cover
over the borehole in periods between waste emplacement, backfilling and sealing operations. The
operating organization should provide in the safety case a justification for the proposed approach to
operating the disposal facility.
66
6.69.
In borehole disposal facilities where different types of waste are to be disposed of, it is
sometimes suggested that waste packages containing high-activity or long-lived waste should be placed
in the bottom part of the disposal zone and waste packages containing low activity short-lived
radionuclides at the top of the disposal zone. In theory this could improve post-closure safety and limit
the consequences of inadvertent human intrusion. However, considerable site characterization data and
detailed safety assessment modelling might be needed to justify such emplacement strategies and they
might also be difficult to implement in practice, as they might necessitate longer storage times, more
complicated storage arrangements, greater assurance regarding the location and management of
individual waste packages, and result in a greater total dose to the workforce. In general, therefore, the
operating organization should aim for a simple and robust disposal strategy in which any waste package
can safely be disposed of at any location in the disposal facility. In cases where this is not possible, for
example where there are large numbers of high-activity sources to be disposed of, more complex
disposal strategies should be considered. In all cases, the operating organization should provide in the
safety case a justification for the proposed waste disposal strategy.
Backfilling disposal boreholes
6.70.
After completing waste emplacement in a disposal borehole, the operating organization should
backfill the space in the borehole above the disposal zone up to the point at which a borehole seal will
be placed; backfilling should be done in a timely manner and in accordance with the authorization and
the safety case. Disposal boreholes should be backfilled to prevent them from acting as pathways for
groundwater and gas flow and radionuclide migration. The operating organization should backfill
boreholes so that the permeability of the backfilled boreholes is no worse than that of the surrounding
intact rocks. Materials that could potentially be suitable as backfills include mixtures of cement and
sand, bentonite and mixtures of bentonite and sand. The operating organization should implement
measures, such as backfilling in stages, to reduce the possibility of leaving voids in the backfill.
Sealing disposal boreholes
6.71.
After backfilling of a disposal borehole as described in para. 6.70, the operating organization
should seal the disposal borehole; sealing should be done in a timely manner in accordance with the
authorization and the safety case. The operating organization should document the approach to, and
design for, borehole sealing in the safety case. The operating organization should remove any borehole
casing from the section(s) of the borehole where the seal(s) is(are) to be placed so that the sealing
materials can form a hydraulically tight seal against the surrounding rocks. Disposal boreholes should
be sealed to prevent them from acting as pathways for groundwater and gas flow and radionuclide
migration. The operating organization should seal boreholes so that the permeability of the sealed
boreholes is no worse than that of the surrounding intact rocks.
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6.72.
The operating organization should specify the technique to be used for borehole sealing taking
account of the size of the borehole, whether the borehole is cased or not, and the geology. In the case
of narrow-diameter boreholes, standard borehole sealing techniques will probably be appropriate.
6.73.
The operating organization should specify how the very top of the borehole is to be closed.
Unless there are good reasons not to do so, the operating organization should fill the top two metres of
the borehole with native soil so that the precise position of the borehole cannot be determined without
specialist equipment.
Inspection and review
6.74.
Safe operation should be achieved through the application of recognized technical and
managerial principles – GSG-16 [25]. The regulatory body should require the operating organization to
conduct periodic reviews covering issues such as quality assurance audits, operating conditions,
environmental sampling and analysis, occupational health and safety, and maintenance of records. The
operating organization should submit the results of these reviews to the regulatory body for review.
6.75.
The regulatory body should conduct independent audits, inspections and reviews of any or all
of the disposal operations to satisfy itself that appropriate management controls are being applied and
appropriate technical work is being undertaken. The operating organization should when necessary
apply appropriate corrective actions in a timely manner.
Records
6.76.
Traceable records should be created that describe and characterize the radioactive waste and
the waste management activities undertaken. The records should include various types of information
including the following, as appropriate (para. 5.64 of GSG-16 [25]):
(a)
The origin of the waste and the processes by which it was generated;
(b)
The physical and chemical forms and properties of the waste (e.g. of the materials used in waste
conditioning and their radionuclide retention properties);
(c)
The activity concentration and total activity of radionuclide(s) in the waste;
(d)
The mass, activity concentration and total activity of fissile nuclides in the waste;
(e)
The type of waste package;
(f)
The radiation level at the surface of the waste package;
(g)
The level of surface contamination on the waste package;
(h)
The mass and weight of the waste or waste package;
(i)
The date(s) of waste processing;
(j)
The methods and instruments used to describe and characterize the waste.
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6.77.
Records should also be created and retained to describe the history of radioactive waste
management facilities, such as data obtained during facility design, construction, commissioning,
operation and closure. These records include the following, as appropriate (para. 5.66 of GSG-16 [25]):
(a)
Authorizations (e.g. licences, permits, amendments);
(b)
Commissioning records;
(c)
The safety case and safety assessments;
(d)
An environmental impact assessment;
(e)
Peer review reports;
(f)
Technical specifications and amendments;
(g)
Design options, concepts, documents, calculations and drawings;
(h)
Records of the facility actually constructed (‘as-built’ records);
(i)
Approved design changes;
(j)
Procurement records for structures, systems and components;
(k)
Operating procedures;
(l)
Records of the implementation, review, updating and maintenance of emergency preparedness
and response arrangements, including records of training, exercises, response to actual
emergencies, lessons identified, and corrective actions implemented;
(m)
Waste emplacement plans;
(n)
Records made during facility operation, including records of emplaced waste packages;
(o)
Records of assessments, inspections and verifications of processes and activities;
(p)
Records of any non-conformances and corrective actions;
(q)
Records of the training, experience and qualification of personnel;
(r)
Monitoring data;
(s)
Records of any incidents, including accidents, that have occurred;
(t)
Records of interactions between the operating organization and the regulatory body (e.g.
meetings, inspections).
6.78.
The range of information and the level of detail to be recorded should be specified in the
management system, taking account of the graded approach. Further information on records and their
maintenance and preservation is provided in GSG-16 [25].
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CLOSURE OF A BOREHOLE DISPOSAL FACILITY
6.79.
Requirement 19 of SSR-5 [4] states:
“A disposal facility shall be closed in a way that provides for those safety functions that
have been shown by the safety case to be important after closure. Plans for closure,
including the transition from active management of the facility, shall be well defined and
practicable, so that closure can be carried out safely at an appropriate time.”
6.80.
When any surface facilities at a borehole disposal facility have been decommissioned (see para.
6.15) and all boreholes used for waste emplacement have been backfilled and sealed, the operating
organization should close the disposal facility. The operating organization should close the facility in
accordance with the plan for facility closure included in the safety case that has been approved by the
regulatory body.
6.81.
To gain regulatory approval for disposal facility closure, the operating organization should
develop and provide the regulatory body with an updated safety case that is based on current data
(including records of the facility as built and operated) and that provides reasonable assurance that postclosure safety will be achieved.
6.82.
The closure plan should demonstrate that the closure activities will not impair the post-closure
performance of the facility. The closure plan should also describe any arrangements for the post-closure
institutional control period. The operating organization should undertake the closure activities and
demonstrate to the regulatory body that they have been satisfactorily completed.
6.83.
Any arrangements for the transfer of the site to a new organization after closure should be legal
and clearly documented. When the closure operations have been satisfactorily completed, the period of
post-closure institutional control can begin. Depending on the regulatory framework and the conditions
of the authorization, the transition to the period of post-closure institutional control may require separate
regulatory approval.
7. ASSURANCE OF SAFETY
MONITORING PROGRAMMES AT A BOREHOLE DISPOSAL FACILITY
7.1.
Requirement 21 of SSR-5 [4] states:
“A programme of monitoring shall be carried out prior to, and during, the construction
and operation of a disposal facility and after its closure, if this is part of the safety case.
This programme shall be designed to collect and update information necessary for the
purposes of protection and safety. Information shall be obtained to confirm the conditions
necessary for the safety of workers and members of the public and protection of the
environment during the period of operation of the facility. Monitoring shall also be
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carried out to confirm the absence of any conditions that could affect the safety of the
facility after closure.”
7.2.
Monitoring is the continuous or periodic measurement of radiological or other parameters or
determination of the status of a structure, system or component – Ref. [5]. The safety of a disposal
facility is required to be provided by passive means to the fullest extent possible and must not depend
on monitoring – SSR-5 [4]; monitoring should be for the assurance of safety.
7.3.
Guidance on monitoring of near surface and geological disposal facilities (and disposal
facilities for waste from mining and mineral processing) is provided in SSG-31 [36]. Monitoring
programmes at borehole disposal facilities developed, as recommended, with disposal zones at depths
greater than 100 m should have many characteristics that are similar to those for monitoring
programmes at geological disposal facilities.
7.4.
The operating organization should document and implement a programme of monitoring. The
operating organization should document the justification for the monitoring programme, including its
objectives and scope.
7.5.
The objectives of the operating organization’s monitoring programme should:
(a)
Be in accordance with applicable laws and regulatory requirements;
(b)
Be appropriate to the periods in facility development, operation, closure and institutional
control;
(c)
Include the collection and updating of information to help evaluate the behaviour of the disposal
facility and its structures, systems and components, and the impact of the waste disposal system
on the public and the environment;
(d)
Contribute to building confidence in the safety of the facility and the safety case by providing
measurements that can be used to demonstrate compliance and test assumptions;
(e)
Provide information that can be used to reassure interested parties, including the public, of the
safety of the facility.
7.6.
The scope of the operating organization’s monitoring programme should reflect the graded
approach and be commensurate with the hazard and the level of risk associated with the waste. The
operating organization should justify which parameters are to be monitored, how and where this is to
be done, at what frequency and for which duration. The operating organization should, as appropriate,
include in the monitoring programme the measurement of radiological, environmental and engineering
parameters; for example, background levels of radioactivity, water levels, flows and compositions, and
rock stresses. When deciding what to measure, the operating organization should note that the
concentrations of radionuclides that migrate from waste in the disposal facility and reach locations (e.g.
groundwater discharge points in the biosphere) where they could affect receptors (e.g. people) in the
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future are likely be so low that it would not be possible for them to be measured. For a small borehole
disposal facility, particularly one for waste containing short-lived radionuclides that are expected to
decay substantially while in the waste containers, the extent of the monitoring programme could be
quite limited, both in its spatial extent and duration.
7.7.
The monitoring programme should form part of the safety case. Monitoring should commence
before a disposal facility becomes operational, SSR-5 [4] e.g. during site characterization. As part of
site characterization, the monitoring programme should establish a baseline of environmental conditions
(e.g. groundwater levels) against which subsequent measurements and changes (such as might occur
due to drilling) can be compared and assessed. As the disposal programme moves from one period to
the next, the operating organization should update the objectives of the monitoring programme and the
monitoring activities.
7.8.
It is a requirement that monitoring programmes shall be designed and implemented so as not to
reduce the overall level of safety of the facility after closure SSR-5 [4]. The operating organization
should seal monitoring and other boreholes at or near the site that could reduce the safety of the facility
before commissioning the disposal facility; sealing should be done in a timely manner and in accordance
with the authorization and the safety case. Monitoring (and other) boreholes at or near the site that could
reduce the safety of the facility should be sealed to prevent them from acting as pathways for
groundwater and gas flow and radionuclide migration. The operating organization should seal
monitoring (and other) boreholes at or near the site that could reduce the safety of the facility so that
the permeability of the sealed boreholes is no worse than that of the surrounding intact rocks.
7.9.
The operating organization should document clearly and communicate to interested parties the
objectives, scope and results of the monitoring programme and take appropriate account of the results
and the views of interested parties.
7.10.
The operating organization should use results of monitoring to update and build confidence in
the safety case for the facility and to aid decisions on future steps. The operating organization should
use results of monitoring to gain and improve understanding of potential radionuclide transfer pathways,
and potential discharge locations. The operating organization should where possible use results from
the monitoring programme to assist in the development and calibration of the geosphere and biosphere
models used in safety assessment.
7.11.
The operating organization should include in the monitoring programme an approach for
responding to unexpected monitoring results. Unexpected monitoring results do not necessarily imply
that remedial actions or protective measures are necessary – SSG-31 [36]. The response may vary from
no action at all to increased sampling frequency for identifying or confirming spatial and temporal
trends, through to changes in design or procedures, all the way to significant remedial action or even
retrieval of emplaced waste. The operating organization should place emphasis on identifying trends in
monitoring results rather than assigning too much significance to individual measurements. Actions
72
such as retrieval of waste should be undertaken only after very careful study and justification, including
consideration of risks associated with the remedial action – SSG-31 [36].
7.12.
The regulatory body should provide guidance on the establishment of a suitable monitoring
programme in accordance with the national regulatory framework and should regularly review the
operating organization’s monitoring arrangements and results. The regulatory body should consider
conducting independent monitoring.
THE PERIOD AFTER CLOSURE AND INSTITUTIONAL CONTROLS
7.13.
Requirement 22 of SSR-5 [4] states:
“Plans shall be prepared for the period after closure to address institutional control and
the arrangements for maintaining the availability of information on the disposal facility.
These plans shall be consistent with passive safety features and shall form part of the
safety case on which authorization to close the facility is granted.”
7.14.
The operating organization is responsible for implementing and maintaining active institutional
control of the disposal site and facility throughout the period of its authorization. This responsibility
includes planning for the period after closure of a disposal facility. Institutional controls are generally
classified into ‘active’ and ‘passive’ controls.
7.15.
Active institutional controls include:
(a)
Operating the site and the facility in accordance with the authorization;
(b)
Maintaining signs, fences and guards at the authorized site, for example, to prevent
unauthorized access and unintended radiation exposures;
(c)
Providing nuclear security;
(d)
Undertaking monitoring and surveillance activities;
(e)
Performing any remedial work that may become necessary.
7.16.
Passive institutional controls include:
(a)
Archiving of records of the disposal facility;
(b)
Controls on land ownership;
(c)
Restrictions on land use.
7.17.
The period of active institutional control should be followed by a period in which passive
institutional controls contribute to an assurance of safety. The operating organization should propose in
the plan for closure and institutional controls which active and passive controls are to be implemented
and for how long active institutional control will be maintained.
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7.18.
The duration of the active institutional control period should be established through the
authorization process and approved by the regulatory body. The operating organization should provide
a justification for the proposed duration of the period of active institutional control based on the safety
case. The operating organization should use the safety case to take account of the specific characteristics
of the site and the hazard posed by the waste now and in the future (e.g. as a function of radioactive
decay, environmental change and the probability of inadvertent human intrusion). The timing of the
change from active institutional control to passive institutional control could coincide with the
completion of disposal facility closure or it could occur at a later date. The plan for the timing of the
change from active to passive institutional control should be reviewed periodically during the active
institutional control period and should be approved by the regulatory body.
7.19.
The safety of borehole disposal facilities in which waste has been disposed of at depths greater
than 100 m should not depend on active institutional controls and, depending on the safety case, quite
short periods of post-closure active institutional control could be justifiable. In such cases it might be
possible to convert the disposal site to other uses in just a few years, possibly with some ongoing passive
institutional controls, e.g. on land ownership.
7.20.
Depending on national laws and regulations, the institutional control period assumed for the
purpose of safety assessment calculations could be as long as a few hundred years (e.g. 100 to 300
years). This is not to say that institutional control would necessarily be needed at a site, or that if needed
and implemented it would necessarily be effective for as long as this, or indeed that it would necessarily
cease after this period. Rather, a few hundred years is the maximum period an operating organization
should claim in the safety case. Greater resources will be needed to maintain active institutional controls
for longer periods.
7.21.
The operating organization should propose and as far as possible initiate appropriate passive
institutional controls for the period after the authorization is terminated. At the end of the period of
active institutional control by the operating organization, the disposal facility might be transferred to
the regulatory body, or to the Government, or the site might be completely released from control by any
institution or organization. Before the site is transferred or released, the operating organization should
archive appropriate information related to the disposal facility. The arrangements for archiving of
records should be designed to maintain knowledge of the facility’s location and characteristics within
societal institutions. Information that should be archived for a borehole disposal facility should include
the following:
(a)
The location of the disposal facility;
(b)
Information on the geology, geochemistry and hydrology of the disposal facility site including
data derived from site characterization (see paras 6.16 to 6.23 and Appendix I);
(c)
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Details of the design of the facility, including descriptions of the borehole(s) and the associated
engineered structures systems and components (e.g. borehole backfill, casing and seals) (see
paras 6.24 to 6.27) and descriptions of the waste packages and the waste, including the origins
of the waste, the radionuclides present and their amounts, and the cement-based insert and
disposal capsules used, and the depths of disposal;
(d)
Descriptions of the construction and operation of the facility, including dates and details such
as measured water inflows to boreholes and any non-conformances and actions taken to rectify
them (see paras 6.37 to 6.47);
(e)
The facility safety case including a description of the arrangements for the post-closure period
and the monitoring programme and monitoring results (paras 7.1 to 7.12);
(f)
Authorizations (permits and licenses) issued by the regulatory body.
7.22.
The operating organization should make arrangements for the information to be retained for as
long as possible, and in doing so should consider making use of national archives.
ACCOUNTING FOR, AND CONTROL OF, NUCLEAR MATERIAL
7.23.
Requirement 23 of SSR-5 [4] states:
“In the design and operation of disposal facilities subject to agreements on accounting for,
and control of, nuclear material, consideration shall be given to ensuring that safety is not
compromised by the measures required under the system of accounting for, and control
of, nuclear material.”
7.24.
Systems for accounting for and control of nuclear material have been developed to provide for
the accountability of nuclear material so as to detect, in a timely manner, its diversion to unauthorized
or unknown purposes in the short and medium terms. The Government should facilitate the effective
implementation of for accounting for and control of nuclear material in a manner that does not
compromise safety.
7.25.
The borehole disposal facilities that are within the scope of this safety guide should only receive
waste of the types specified in para. 1.1. Most of this waste does not comprise or include nuclear
material and so does not fall within the system for accounting and control of nuclear material. Some
disused sealed radioactive sources contain fissile nuclides but do not fall within the system for
accounting and control of nuclear material because the content of fissile radionuclides is low. Some
disused sealed radioactive sources are contained in depleted uranium shields and this is usually present
in sufficient quantities that safeguards apply.
7.26.
Where nuclear material accountancy and control requirements need to be applied, they should
be considered at an early stage in the design of a disposal facility.
7.27.
Where IAEA nuclear safeguards requirements apply, they will apply for all three periods of
development, operation, closure and institutional control of a borehole disposal facility (see para. 2.21).
During the pre-operational period and during operation of a borehole disposal facility for waste that
75
includes nuclear material, surveillance for the purposes of IAEA safeguards is aimed at ensuring the
continuity of knowledge concerning the material and the absence of any undeclared activities at the site
in relation to such material. As presently organized, IAEA systems for accounting and control of nuclear
material, or safeguards, rely on active surveillance and controls.
7.28.
Where nuclear material accountancy and control measures are required for a closed borehole
disposal facility, then intrusive methods have to be avoided and safeguards should be applied by remote
means (e.g. satellite monitoring, aerial photography, micro-seismic surveillance and administrative
arrangements).
7.29.
Physical protection measures may also have to be taken for nuclear material and nuclear
facilities, and are addressed in IAEA Nuclear Security Series No. 13, Nuclear Security
Recommendations on Physical Protection of Nuclear Material and Nuclear Facilities [54].
MANAGING INTERFACES BETWEEN SAFETY AND SECURITY
7.30.
Requirement 24 of SSR-5 [4] states:
“Measures shall be implemented to ensure an integrated approach to safety measures and
nuclear security measures in the disposal of radioactive waste.”
7.31.
The government should adopt a graded approach to safety and security in the management of
disused sealed radioactive sources – Ref. [7]. Organizations with responsibilities for safety and security
of radioactive sources should promote appropriate safety culture and nuclear security culture – see Refs
[7], [24] and IAEA Nuclear Security Series No. 7, Nuclear Security Culture [55].
7.32.
The government should ensure that long-term storage facilities and disposal facilities for
disused sealed radioactive sources are subject to safety and security assessment prior to authorization
by the regulatory body and are located, designed, constructed, operated, and decommissioned or closed,
as appropriate, in conformance with regulatory requirements for safety and security – Ref. [7].
7.33.
The regulatory body should specify safety and nuclear security requirements for long-term
storage and disposal of disused sources – Ref. [7]. The operating organization is required to design and
implement safety measures and nuclear security measures in an integrated manner so that nuclear
security measures do not compromise safety and safety measures do not compromise nuclear security
– para. 2.40 of GSR Part 1 (Rev. 1) [28].
7.34.
Nuclear security recommendations on radioactive material and associated facilities, are
provided in IAEA Nuclear Security Series No. 14 [56]. Guidance on the security of radioactive sources
is provided in IAEA Nuclear Security Series No. 11-G (Rev. 1) [57]. The operating organization should
design and implement a nuclear security system to protect radioactive material through the
implementation of security measures to address deterrence, the three security functions of detection,
delay and response, and security management – Ref. [57]. The extent of nuclear security measures
should reflect the potential for damage to the facility and the assessed risk of unauthorized removal of
76
radioactive material or radioactive waste. The security system should include an integrated set of
nuclear security measures intended to prevent the completion of a malicious act during site operations,
closure and any period of post closure active institutional control. Cooperation is encouraged through
arrangements and appropriate liaison with relevant competent authorities to facilitate assistance in the
event of malicious acts. Nuclear security measures should be based on a risk informed graded approach
so that similar security is provided for material capable of resulting in similar potential radiological
consequences arising from use in a malicious act – Ref. [57].
7.35.
Borehole disposal of disused sealed radioactive sources in accordance with the
recommendation provided in this Safety Guide should result in radioactive waste being permanently
disposed of at depths greater than 100 m beneath the surface; a result that provides for both safety and
nuclear security. Where the waste in a borehole disposal facility is disposed of at a depth of more than
100 m, a site security presence will be required for as long as the borehole remains open. On sealing of
the boreholes and closure of the facility and site, the competent authority may consider removal of
security measures in relation to the disposal site in accordance with a risk informed graded approach.
7.36.
In general, waste that constitutes a significant nuclear security risk may need special security
consideration and further regulatory authorization. For example, a single source containing a large
amount of Cs-137 could still be quite small and would constitute a security risk if taken for malicious
purposes. If such waste were disposed of near surface, the proximity of the waste to the surface could
make it necessary for nuclear security measures to be continued to prevent human intrusion and
unauthorized removal of the waste. The nuclear security measures would need to remain in place until
the waste no longer constituted a potential nuclear security risk or hazard and would be a form of active
institutional control. To fulfil the requirement for safety to be provided by passive means, safety cannot
rely on the indefinite maintenance of active institutional controls.
7.37.
Where a borehole disposal facility is to be located at an existing nuclear site, the prevailing
nuclear security measures should consider the new activities in the site security plan.
MANAGEMENT SYSTEMS
7.38.
Requirement 25 of SSR-5 [4] states:
“Management systems to provide for the assurance of quality shall be applied to all safety
related activities, systems and components throughout all the steps of the development
and operation of a disposal facility. The level of assurance for each element shall be
commensurate with its importance to safety.”
7.39.
General requirements for the management system are established in GSR Part 2 [24] and
recommendations on how to fulfil the requirements during the predisposal management and disposal of
radioactive waste are provided in IAEA Safety Standards Series No. GSG-16 [25]. The regulatory body
and the operating organization should develop, implement, monitor and seek to continuously improve
77
management systems appropriate to the scope of their facilities and activities – GSG-16 [25]. The
management systems should be aimed at ensuring the protection of people and the environment, should
allocate clear responsibilities for safety, should address leadership for safety, should ensure that safety
is integrated into the management system, and should address culture for safety. The Appendix to GSG16 [25] provides a list of elements of the management system for organizations involved in the
management of radioactive waste or its regulatory oversight. The management system elements
included in an organization’s management system, and the level of detail contained in the processes and
procedures, should reflect the nature of the organization concerned, its role and situation, and be applied
according to the graded approach.
7.40.
The regulatory body should review the operating organization’s management system and audit
its application to activities related to the predisposal management and disposal of radioactive waste. In
the case of the borehole disposal system described in Section 2, key areas include:
(a)
The adequacy of the collection and interpretation of site characterization data, and their use in
safety assessment models;
(b)
The training of staff who will undertake predisposal management and disposal operations;
(c)
The capability of any contractor(s) employed, e.g. for borehole construction;
(d)
The proper management of waste emplacement and of events and incidents.
PREPAREDNESS AND RESPONSE FOR A NUCLEAR OR RADIOLOGICAL EMERGENCY
7.41.
Requirements for preparedness and response for a nuclear or radiological emergency are
provided in GSR Part 7 [58]. GSR Part 7 [58] applies the graded approach by placing the various types
of nuclear facility into categories: nuclear powers stations fall in Category I, research reactors into
Category II and some hospitals using powerful sealed radioactive sources are in Category III.
7.42.
A borehole disposal facility for disused sealed radioactive sources and low volumes of low
level waste and intermediate level waste generated during their management would fall in Category III.
7.43.
Para. 4.16 of GSR Part 7 [58] states:
“The operating organization shall establish and maintain arrangements for on-site
preparedness and response for a nuclear or radiological emergency for facilities or activities
under its responsibility, in accordance with the applicable requirements”.
7.44.
Para. 4.17 of GSR Part 7 [58] states:
“The operating organization shall demonstrate that, and shall provide the regulatory body with
an assurance that, emergency arrangements are in place for an effective response on the site to
a nuclear or radiological emergency in relation to a facility or an activity under its
responsibility”.
78
7.45.
Para. 6.19 of GSR Part 7 [58] states:
“The operating organization of a facility or for an activity in category I, II, III or IV shall
prepare an emergency plan. This emergency plan shall be coordinated with those of all other
bodies that have responsibilities in a nuclear or radiological emergency, including public
authorities, and shall be submitted to the regulatory body for approval”.
7.46.
Para. 6.17 of GSR Part 7 [58] states:
“Emergency plans shall specify how responsibilities for managing operations in an emergency
response are to be discharged on the site, off the site and across national borders, as
appropriate”.
7.47.
Where a borehole disposal facility is to be located on an existing nuclear site, the emergency
plan for that site should be modified to take account of the new facility – see para. 4.26 of GSR Part 7
[58].
8. EXISTING DISPOSAL FACILITIES
EXISTING DISPOSAL FACILITIES
8.1.
Requirement 26 of SSR-5 [4] states:
“The safety of existing disposal facilities shall be assessed periodically until termination
of the licence. During this period, the safety shall also be assessed when a safety significant
modification is planned or in the event of changes with regard to the conditions of the
authorization. In the event that any requirements set down in this Safety Requirements
publication are not met, measures shall be put in place to upgrade the safety of the facility,
economic and social factors being taken into account.”
8.2.
The regulatory body should require the operating organization of a borehole facility to reassess the
safety of the facility periodically throughout the period of authorization, taking account of new information
relevant to the site and facility, including monitoring results. It is probable that a project to develop a borehole
facility would take several years to a decade, and this period may be followed by a period of active
institutional control possibly lasting several decades to a few centuries. The operating organization should
assess the safety of the facility several times or more during the period of authorization to satisfy the
requirement for periodic safety assessment.
8.3.
The operating organization should assess the safety of any potentially significant modifications to a
borehole facility, such as the addition of an additional disposal borehole to the facility. Potentially significant
modifications to a borehole disposal facility might also include a proposal to accept a type of waste not
previously considered in the safety case. The regulatory body should make clear at an early stage the
requirements for periodic safety assessment and for assessment of modifications to facilities and the
approach to licencing of a borehole facility and any modification.
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8.4.
The government should ensure that arrangements are established and implemented for the safety of
borehole facilities for which there is no longer an operating organization to be reassessed periodically.
8.5.
Standards, procedures and practices change over time and therefore some existing borehole facilities
are not consistent with the safety requirements. For examples, see Ref. [59] and Section B.2.1 of Ref. [60].
Specifically, once active institutional control has ceased, exposures at some existing borehole facilities could
lead to doses at levels above those at which remedial action should be considered. Inadvertent intrusion at
some facilities could lead to annual doses exceeding 20 mSv, or even 100 mSv – a generic reference level
above which remedial action to upgrade safety should be considered almost always justifiable (see para
3.26).
8.6.
The purposes of reassessing the safety of an existing facility should be:
(a)
First, to assess whether the facility provides satisfactory protection from radiation for future
generations and the environment in accordance with the Fundamental Safety Principles [1] and
the requirements of GSR Part 3 [2] and SSR-5 [4];
(b)
Second, if satisfactory protection is not provided, to inform a judgement on whether it is
justified to take remedial action to upgrade the safety of the facility, for example, by adding
further physical and or administrative protection or by retrieving the waste.
8.7.
Any remedial action should be both justified and optimized – see GSR Part 3 [2] and the discussion
in Ref. IAEA Safety Standards Series No. GSG-15, Remediation Strategy and Process for Areas Affected
by Past Activities or Events [61]. Put succinctly, any remedial action should do more good than harm.
8.8.
In the context of borehole facilities, this means that the body responsible for taking such decisions
should identify, assess and compare options for remedial actions. When remedial actions have been
identified, they should be assessed and compared in order to provide input to a decision on the preferred
action (i.e. the remedial action that would do most good).
8.9.
Input into decision making should be obtained by comparing the various options on the basis of
their radiological and non-radiological impacts on people and the environment and a wide range of socioeconomic factors. Feasibility studies and demonstrations may support the decision-making process. Because
of the wide range of issues that need to be considered, interested parties (e.g. the local community) should
be involved in identifying, assessing and making comparisons of potential remedial actions.
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APPENDIX I. SITING AND SITE CHARACTERIZATION FOR BOREHOLE DISPOSAL
FACILITIES
Siting of borehole disposal facilities
I.1.
The Government is responsible for defining the overall process for the development, operation,
closure and institutional control of borehole disposal facilities, including siting – Requirement 1 of
SSR-5 [4]. In accordance with applicable laws and regulatory requirements, the Government should
ensure that interested parties are involved at appropriate stages in decision-making for radioactive waste
management facilities and activities, including borehole disposal facilities – para. 3.7 of SSR-5 [4]. The
operating organization is required to carry out all the necessary activities for site selection and
evaluation – Requirement 3 of SSR-5 [4]. In addition to reviewing the safety case, the regulatory body
should consider whether a site is suitable as part of its review and assessment processes – GSG-13 [30].
I.2.
When selecting a site for a disposal facility, the recommended approach is to select a site at
which a safe facility can be developed rather than, for example, trying to identify a conceptual ‘best’ or
‘safest’ site.
I.3.
Safety (i.e. protection of humans and the environment from undue radiation risks – Safety
Glossary [5]) should be the primary consideration in siting a borehole disposal facility. If a reasonable
assurance of safety can be provided for the development of a disposal facility at several candidate sites,
the operating organization should consider a range of other factors when selecting between the possible
sites.
Safety related factors
I.4.
When selecting a site for a borehole disposal facility, the operating organization should provide
reasonable assurance of safety; this should include giving due consideration to the following:
(a)
The geomorphology and geomorphological evolution of the site and the surrounding area, and
processes and events that might affect facility operations. The site should be
geomorphologically stable; this is generally consistent with there being an absence of features
such as mountainous terrane with steep gradients or areas with active subsidence. Processes and
events that might affect facility operations also include landslip and flooding and necessitate
consideration of climate and extreme weather;
(b)
The geology and geological evolution of the site and the surrounding area. The site should be
geologically stable. Geological stability should be evaluated based on evidence of relevant
events and processes (e.g. recent or historic tectonic events and processes, faulting and
seismicity, soil liquefaction, volcanism). Geological stability is generally consistent with there
being an absence of e.g. capable faults, diapirs, salt domes and volcanoes. The geology of the
site should include strata or horizons with characteristics that are suitable to be used as disposal
81
zones and which have sufficient thicknesses to accommodate the waste and separate the
disposed waste from any overlying or underlying zones with greater permeability;
(c)
The hydrological and hydrogeological conditions at the site and in the surrounding area and
their evolution. Information with which to evaluate hydrological and hydrogeological
conditions should include but not necessarily be limited to rock permeability, porosity,
groundwater flow rates and directions, hydraulic conductivity, hydraulic heads and gradients,
and the presence of groundwater wells. Characteristics that tend to be favourable for siting a
borehole disposal facility include rocks with low permeability, low hydraulic head gradients
and low rates of groundwater flow at depth; these characteristics are generally consistent with
low topography and the absence of aquifers and other rock types with high permeability
(e.g. karst). The generic safety assessment – Ref. [17] suggests that it is possible to develop safe
borehole facilities for the disposal of disused sealed radioactive sources in either hydrologically
unsaturated or saturated conditions, but it is recommended to avoid disposing of waste in a zone
through which the level of the water-table varies over time (for more information see para.
I.39). The operating organization should ensure through appropriate facility design that
disposed waste will be sufficiently isolated from any aquifers containing potable water that are
present at the site;
(d)
The geochemistry of the site and the surrounding area and its evolution. Information with which
to evaluate geochemical conditions should include but not necessarily be limited to rock types
and mineralogy, rock and groundwater compositions and ages. Characteristics that tend to be
favourable for siting a borehole disposal facility include the presence of old groundwaters,
which would tend to indicate low groundwater flows in the past, and groundwaters whose
geochemistry is and would be generally unreactive towards the rocks present and to the
materials of the engineered barrier system. It should not necessarily be assumed, however, that
it would not be possible to develop a safe disposal facility at sites with other characteristics,
such as the presence of saline groundwaters; this should be tested through safety assessment;
(e)
Geological setting. Some events and processes might bring disposed waste closer to the surface
environment, result in a loss of isolation and cause people to be exposed to radiation. Such
events and processes include erosion, tectonic uplift, glaciation, and permafrost melting. The
operating organization should site borehole disposal facilities away from areas where such
events and processes might occur (e.g. sites with resources including minerals, oil, gas,
geothermal and water resources) in order to reduce the probability of inadvertent human
intrusion.
I.5.
The recommended concept for disposal of disused sealed radioactive sources in narrow
boreholes has been assessed as being potentially safe to implement in a wide range of geological and
82
climatic conditions – see Ref. [17]; the expectation is therefore that, depending on the size of the waste
inventory to be disposed of, it should be possible to fulfil the safety requirements at many sites.
I.6.
Although very few of the factors identified above represent absolute exclusion criteria for the
siting of a borehole disposal facility, the selection of a site that combines favourable characteristics and
avoids unfavourable ones should allow safety to be demonstrated more simply and with fewer resources
than would otherwise be the case, and should be more convincing and acceptable to interested parties.
Other factors
I.7.
The operating organization should give due consideration to other (e.g. scientific, technical and
socio-economic) factors including; nuclear security, the views of interested parties, protection of
humans and the environment from non-radiological risks (including the possible contamination of
groundwater resources), the availability of information, costs, land ownership, infrastructure needs
(e.g. site accessibility and the provision of services such as water and electricity), transport, legal and
planning considerations, and the proximity of the site to population centres, national parks, nature
reserves, sites of special scientific interest, hazardous facilities, cultural and religious sites, disputed
boundaries and national borders. Siting a borehole disposal facility on the site of an existing nuclear
facility would provide an existing nuclear security infrastructure.
Process for site selection
I.8.
Working in accordance with applicable laws and regulations and relevant policies and
strategies, the operating organization should develop, communicate and lead a well-planned and
systematic site selection process that involves interested parties in making decisions at appropriate
stages. The operating organization should ensure that the steps in the process are clear, logical and
justified.
I.9.
IAEA guidance on the siting of near surface disposal facilities (Appendix I of Ref. SSG-29 [8])
suggests the adoption of a process in which, starting with a large area, possibly the whole country,
potential locations for a disposal facility are progressively narrowed down using a list of predefined
technical and socio-economic suitability or unsuitability (screening) criteria to yield a shortlist of
potential siting areas. Once potential siting areas have been located, the operating organization should
conduct more detailed investigations to identify potentially suitable disposal sites within the potential
siting areas. The operating organization should as part of the siting process consider whether there are
existing sites within the potential siting areas such as nuclear facilities, including radioactive waste
storage facilities and disposal facilities, and government-owned land that might be suitable for a
borehole disposal facility.
I.10.
Government may decide simply to nominate a site for development of a disposal facility, but
there have been several instances where such approaches to the siting of disposal facilities have failed
to gain societal acceptance and this approach is not recommended. Some programmes for the siting and
development of radioactive waste disposal facilities have, therefore, adopted approaches involving
83
partnerships with local communities. Partnership approaches involve collaborative working
relationships between communities and the operating organization. The key feature of the partnership
approach is the empowerment of local communities in decisions that affect their future. Such
partnership approaches may include seeking volunteer communities. A volunteer community is one that
has expressed interest in participating in a process to determine the suitability of a site for a radioactive
waste management facility. Such an expression of interest may be conveyed by appropriate
representatives of the community (e.g. from a local governing body) and may be made in response to
an invitation by the operating organization or by the government or may be an unsolicited offer. A
volunteer community should have either a formal or informal right to withdraw from the process and
may receive an appropriate community benefits package.
I.11.
Having established a shortlist of potentially suitable sites, the operating organization should
assess each site against the range of safety-related and other factors – for examples see paras I.4 to I.7
above. The relative ease of being able to develop a convincing safety case may also be a factor in
choosing between alternative sites. The operating organization should adhere to the pre-defined siting
process and should involve interested parties in the assessment of sites. The operating organization
should ensure that the process is clear and logical, and documented in a traceable manner. The operating
organization should ensure that the process followed includes appropriate arrangements for declaring
any conflicts of interest. The operating organization should document in a transparent way the reasoning
for the process followed, for the factors considered, for the ranking of sites against the factors, and for
the recommendation regarding which site is to be selected.
Site characterization for borehole disposal facilities
I.12.
The objective of site characterization for a disposal facility is to gain a general understanding
of both the characteristics of the site and how the site will evolve over time – see Requirement 15 of
SSR-5 [4]. The operating organization’s site characterization programme should include investigating
the geomorphology, geology, hydrogeology, hydrology, geochemistry, climate, weather and ecology
and land use and human behaviour at and around the site and how land use and human behaviour affects
the environment. The operating organization’s site characterization programme should include
characterization of the biosphere at and around the site and particularly in areas into which groundwater
contaminated with radionuclides from the facility could discharge. The operating organization’s site
characterization programme should collect information covering land use, habits of the local population
(especially data on the consumption of food) and sources of drinking water – the operating organization
should use such information to assist in identifying critical groups and potentially exposed groups for
use in assessing potential doses and risks.
Graded approach to site characterization
I.13.
In general terms the extent of the site characterization programme (including the number of site
investigation boreholes) and the amount of information needed from the programme will depend on
84
how complex the site is and on the margin of safety indicated by the safety assessments. A large margin
of safety may be indicated for various reasons, such as the following; a waste inventory that includes a
small amount of long-lived radionuclides, the absence of groundwater at the site, very arid conditions
on the surface. Where there is a large margin of safety, it may be possible for the operating organization
to provide reasonable assurance the disposal facility will fulfil the relevant dose and risk criteria despite
uncertainties introduced by a less extensive site characterization programme.
I.14.
The recommended borehole disposal concept for disused sealed radioactive sources has been
designed to provide a high level of isolation and it has been shown to be a safe disposal solution for
suitably small inventories of disused sealed radioactive sources under a wide range of site conditions –
Ref. [17]. In many States, the inventory of disused sealed radioactive sources to be disposed of is small
and includes a high proportion of short-lived radionuclides and the risks associated with borehole
disposal of such waste should be very low. Under these circumstances, the needs for site
characterization should be less extensive than for a near surface disposal facility or a geological disposal
facility for a large waste inventory.
I.15.
For a borehole disposal facility for a small inventory of disused sealed radioactive sources
containing mostly short-lived radionuclides, the operating organization should focus the collection of
site-specific data on parameters that are relevant to the assessment models used. Other site-specific data
and information may be collected for confidence-building purposes; although such data might not be
necessary for demonstrating the safety of the borehole disposal facility, this data can nevertheless be
useful, for example, in helping to demonstrate a general understanding of the site and for developing
multiple lines of reasoning in the safety case.
I.16.
The generic safety assessment Ref. [17] identifies the parameters that are expected to have the
greatest impact on safety of the recommended borehole disposal concept for disused sealed radioactive
sources; these lie in the fields of hydrogeology and geochemistry, which together determine the rate of
corrosion of the stainless steel disposal capsules and containers, and the rate of radionuclide migration
through the geosphere. Such insights are particularly valuable for defining the site characterization
programme and for using the understanding derived from the site characterization programme to inform
site-specific design.
I.17.
The identification of key parameters – the ones most important to safety – and, from that, an
ability to focus the site characterization programme was a key motivation for the development of the
tiered modelling approach presented in Ref. [18]. Ref. [18] describes an approach which involves the
gathering of site-specific information according to the needs of safety assessment models developed at
different levels of complexity. Five models are described, with the simplest model requiring the least
information and the most complex model requiring the most. Table A.1 indicates the list of site-specific
information needed by the different models.
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TABLE A.1. SUMMARY OF SITE-SPECIFIC PARAMETERS NEEDED FOR THE TIER 1 TO
TIER 5 MODELS IN REF. [18].
Tier
Near Field
Geosphere
1
Radionuclide inventory
-
-
2
Radionuclide inventory
Borehole disposal zone:
• inner diameter
• vertical length
-
-
3
Radionuclide inventory
Disposal capsule and container(b):
• outer diameter
• vertical length
• wall thickness
• weld thickness
Containment barrier(b):
• vertical length
• gap thickness
Hydrogeology:
• Percolation rate(a)
• Degree of saturation(a)
• Total porosity(a)
• Hydraulic conductivity
• Hydraulic gradient
• Water-filled porosity
Geochemistry:
• pH
• Eh
• Chloride concentration
• Sulphate concentration
• Total inorganic carbon
concentration
-
4
Radionuclide inventory
Diffusion coefficients
Sorption coefficients
Percolation rate(a)
Degree of saturation(a)
Total porosity(a)
Grain density
Hydraulic conductivity
Hydraulic gradient
Water-filled porosity
Failure times for disposal capsule
Diffusion coefficients
Sorption coefficients
Percolation rate(a)
Degree of saturation(a)
Total porosity(a)
Grain density
Hydraulic conductivity
Hydraulic gradient
Water-filled porosity
A fraction of water demand
supplied by contaminated water
Concentration factors
House dimensions
House ventilation rate
Soil total porosity
Soil degree of saturation
Percolation rate
Ingestion rates
Inhalation rates
House occupancy rate
Irrigation rates
Crop yields
5
Radionuclide inventory
Diffusion coefficients
Sorption coefficients
Percolation rate(a)
Degree of saturation(a)
Total porosity(a)
Grain density
Hydraulic conductivity
Hydraulic gradient
Water-filled porosity
Failure/degradation times for
near-field components
Diffusion coefficients
Sorption coefficients
Percolation rate(a)
Degree of saturation(a)
Total porosity(a)
Grain density
Hydraulic conductivity
Hydraulic gradient
Water-filled porosity
A fraction of water demand
supplied by contaminated water
Concentration factors
Garden dimensions
House dimensions
House ventilation rate
Soil total porosity
Soil degree of saturation
Percolation rate
Inhalable dust
concentration
Erosion rate
Ingestion rates
Inhalation rates
Occupancy rates
Irrigation rates
Crop yields
Notes:
(a) Only required if the disposal zone is in the unsaturated zone.
(b) Expected to be broadly similar for different systems.
86
Biosphere
Desk-based studies
I.18.
The operating organization’s site characterization programme for the development of a disposal
facility should generally begin with desk-based studies. The operating organization should aim to make
the maximum possible use of existing information on the disciplines within the scope of site
characterization (see para. I.12). The operating organization should consult relevant national and other
libraries, surveys, records and institutes (e.g. for geology, hydrology, hydrogeology and meteorology)
and local experts to gather detailed knowledge and information relating to the site. Where it is proposed
to create a borehole disposal facility at the site of an existing nuclear (or other) facility, the operating
organization of the borehole disposal facility should request and make use of information held by the
operating organization of the existing facility, including any safety case, safety assessment or similar
analysis that exists.
I.19.
The operating organization should gather long-term regional meteorological records and
demonstrate an understanding of the range of conditions that have occurred and assess the range of
conditions that are expected to occur in the future. The operating organization should assess the
susceptibility of a site to severe weather events (e.g. storms and flooding). The operating organization
should use meteorological data to estimate evapotranspiration rates and recharge at the site.
I.20.
The operating organization should gather information to characterize the geology, hydrology,
hydrogeology and geochemistry of the site and the surrounding area, particularly to identify and
characterize the source(s) of local groundwater (both deep and shallow) and areas where groundwater
from the vicinity of the facility could discharge. The operating organization should use this information
to identify potential pathways by which radionuclides from the disposal facility could lead to
radiological exposures.
I.21.
The operating organization should collect information on the size, locations and density of
human populations, on human activities, including land uses (e.g. agriculture), and on human
behaviours (e.g. food consumption rates and sources of drinking water) that would be needed for dose
assessments for present and potential future conditions. The operating organization should use
information on the nature of the current day biosphere to set the context for the models used in safety
assessment. The operating organization should use information on human populations and habits to
identify critical groups and potentially exposed groups for use in safety assessment.
Surface-based studies
I.22.
The operating organization should undertake surveys, fieldwork and surface-based
investigations to increase knowledge and information on the site and its surroundings. The operating
organization should undertake safety assessments to interpret and integrate available knowledge and
information on the disposal system and to focus further site characterization activities on issues that are
relevant to the safety of waste disposal.
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I.23.
The operating organization should conduct surface-based studies to gather information on the
geomorphology and hydrology of the site and its surrounding area (e.g. studies of landforms, evidence
of erosion and past land movements such as landslips, faults and earthquakes, lakes, rivers, sediment
burden, coastlines), including the effects of past climate states on landform development.
I.24.
The operating organization should conduct surface-based geological studies to gather
information on the rock types present, particularly those that may be present at disposal depths, and
understand their mineralogy, spatial distribution, variability and structure, including the presence of
faults, fractures and fabrics.
I.25.
The operating organization should conduct surface-based geophysical studies to gather
information on the geology, geological structure and hydrogeology at depth. Unless data of sufficient
quality and relevance are already available, the operating organization should undertake seismic
refraction surveys, scaled appropriate to the size of the site and proposed depth of the disposal facility
and with survey lines suitably arranged (e.g. to form a square or rectangular array surrounding the
disposal site). The operating organization should use appropriate computer-based techniques to interpret
the data gathered and should attempt to understand the spatial distribution of weathered and intact
bedrock and the position of faults and other geological structures. Even for complex sites, where
multiple interpretations may be possible, a seismic survey will usually be the most effective way of
understanding subsurface geology without drilling. The operating organization should consider
undertaking electrical resistivity surveys to complement results from seismic surveys and further
understand the geology and hydrology of the site.
I.26.
The operating organization should record and document the data gathered during the desk-
based and surface-based studies following the relevant procedures in the management system. The
operating organization should interpret the data in the form of preliminary conceptual models of the site
that extend from the surface down at least as far as the bottom of the deepest disposal zone. The
operating organization should document any significant inconsistencies between the conceptual models
and the data (e.g. aspects where the models do not explain the observations well), should recognize
these as uncertainties and should plan and undertake further studies as necessary to reduce the
uncertainties.
I.27.
The operating organization should use the data, models and the understanding gained from the
desk-based and surface-based site characterization studies to help decide on the locations of site
characterization borehole(s) and the potential locations of disposal borehole(s) and depths of disposal
zones.
Borehole-based studies
I.28.
The operating organization should conduct a programme of carefully planned borehole-based
site characterization studies in accordance with defined procedures. Unless suitable boreholes already
exist at the site, the operating organization should drill one or more site characterization boreholes. The
88
number and locations of site characterization boreholes should be in accordance with the needs of the
safety case for information and the graded approach. The operating organization should use a drilling
approach that minimizes disturbance to the disposal system that is to be characterized (e.g. the approach
should avoid the possibility groundwater becoming contaminated by the drilling activities and or
include methods for correcting for possible contamination).
I.29.
It is recommended that site characterization boreholes have a diameter of 100 mm or less.
Where possible, the operating organization should drill site characterization boreholes down to the base
of the formation in which it is proposed to dispose of waste and confirm the absence of features such
as high-pressure zones that could negatively and significantly affect the performance of the disposal
facility. If this is not feasible, perhaps because the base of the host formation is very deep, then the
operating organization should provide a justification for the chosen depth of the base of the site
characterization boreholes (which should, for example, be at least some tens of meters below the base
of the deepest disposal zone). Where it is proposed to dispose of waste in the hydrologically unsaturated
zone, the operating organization should drill site characterization boreholes down to at least the depth
of the water table.
I.30.
Where possible, the operating organization should design and drill site characterization
boreholes so that rock core is extracted for study. Where it is not practical to recover rock core, the
operating organization should collect and study rock fragments from the drilling. The operating
organization should use best practice to identify the locations and depths from which rock samples
(including rock core and fragments) are collected and make careful, detailed records. The operating
organization should use the rock core and or rock fragments to establish the geological sequence and
the mineralogy of the rocks. Rock samples should be kept and preserved for more detailed examination
(e.g. for use in assessing the radionuclide retardation properties of the rocks).
I.31.
The operating organization should in the drilling procedures instruct drillers to record water
strikes, water yields, drilling speeds, fractures and any unexpected events such as the loss of
compression air (possibly indicating the presence of joints or fissures), changes in penetration rate
(possibly indicating changes in lithology or structure), sharp changes in the colour of rock samples
(possibly indicating lithological changes or weathering), and sharp changes in the size of drill chips
(possibly indicating the presence of fractures). The operating organization should use the information
gathered (e.g. on the geological sequence and the depth of the water table) to calibrate the geophysical
surveys – see para. I.25.
I.32.
The operating organization should use geophysical wireline logging techniques to monitor the
shape and diameter of the boreholes, to detect fractures and breakouts, and to investigate the acoustic
and electrical properties of the rocks (which should be used to help interpret seismic and electrical
geophysical surveys) and their natural gamma radioactivity.
89
I.33.
The operating organization should consider undertaking further borehole-based studies to
support the safety case as appropriate. A list of probes and related parameters used during the pilot
project on borehole disposal of disused sealed radioactive sources in Ghana is provided in Table A.2.
TABLE A.2. DOWN-HOLE LOGGING PROBES AND RELATED PARAMETERS - Ref. [62].
Type of Probe
Related Parameter(s)
Optical borehole imaging probe
Optical borehole image
Borehole inclination
Natural gamma radioactivity
Acoustic borehole imaging probe
Acoustic borehole image
Borehole inclination
Natural gamma radioactivity
Dual induction conductivity probe
Medium and long-spacing induction conductivity
Natural gamma radioactivity
Focussed electric logging probe
Focussed resistivity
Natural gamma radioactivity
Three-arm calliper probe
Borehole diameter
Full-wave sonic probe
Acoustic travel time and speed
Flowmeter gamma temperature conductivity Vertical fluid flow (medium-high flow regimes)
probe
Fluid temperature and conductivity
Natural gamma radioactivity
Heat-pulse flowmeter probe
I.34.
Vertical fluid flow (low flow regimes)
Where the site investigation boreholes contain groundwater, the operating organization should
conduct hydrogeological investigations, including as appropriate measurements of water pressure,
hydraulic heads and gradients, and measurements of the rates of water inflows and outflows at different
horizons (these should be made using pump tests, flow recovery tests and cross-hole tests, as
appropriate, with the placement of packers, and the results should be used to establish the
hydrogeological properties of the rocks. If hydrogeological tests are conducted in open boreholes
(without packers), the values measured will tend to be strongly influenced by zones with high flow
rates, e.g. in the upper parts of the borehole.
I.35.
Where the site investigation boreholes contain groundwater, the operating organization should
conduct geochemical investigations, including the collection of water samples and the determination of
the chemical composition of the waters, including as possible their redox potentials (Eh), acidity (pH),
alkalinities and contents of solutes, colloids and particulates. The operating organization should
consider measuring the electrical conductivities of the waters to provide further information on the ionic
content and salinity of the waters. The operating organization should use best practice when collecting,
90
transporting and analysing samples (e.g. including the use of sealed containers with as little air space
as possible) to avoid artefacts (e.g. oxidation) and contamination.
I.36.
The operating organization should attempt to determine the concentrations in groundwater of
the following anions; chloride, sulphate, carbonate, bicarbonate and nitrate. Where possible, the
operating organization should use information on the chloride and sulphate contents of the
groundwaters to inform decisions on the materials of the engineered barrier system (chloride may affect
the rate of waste container corrosion; sulphate may cause undesirable reactions in some cement-based
materials). Where possible, the operating organization should measure Eh in situ, particularly in the
disposal zone(s) by using appropriate probes and packers (inflatable plugs) in the borehole to separate
the depth interval being measured from other parts of the borehole. In cases where it is not possible to
measure Eh in situ, the operating organization should estimate the in situ Eh by using Eh measurements
on water samples abstracted from the borehole and making corrections for changes in chemical
speciation, by using data collected in situ from adjacent depth intervals, and by using information on
the mineralogy of the rocks.
I.37.
At sites where the disposal zone(s) is(are) to be situated in saturated, low permeability rocks
(e.g. plastic clay), the rate of water ingress into site investigation boreholes may be very low or even
undetectable, and this may make the measurement of hydrogeological properties and the collection of
water samples difficult. In such cases, the operating organization should attempt to extract water
samples from extracted core. The operating organization may need to estimate the groundwater flow
rates based on the limit of detectability of water ingress to the borehole. The operating organization
should determine the permeability of the host rock and relevant diffusion coefficients using extracted
core samples. The operating organization should measure the thickness of the host rock layer and
establish the distances between the disposal zone(s) and more permeable rocks.
I.38.
At sites in some arid regions, groundwater may only be found at depth and disposal zone(s) can
be situated in an unsaturated environment. Locating the disposal zones(s) in unsaturated rocks may be
advantageous for post-closure safety because, in the absence of groundwater, interactions between the
radionuclides in the waste and groundwaters in the saturated zone are much delayed, allowing time for
radionuclides to decay and reducing potential doses and risks from groundwater pathways – Ref. [17].
At sites where the disposal zone(s) is(are) to be situated in unsaturated rocks, the operating organization
should provide reasonable assurance that the host rocks to the disposal zone(s) will remain unsaturated
over the assessment timescale by:
(a)
Gathering information and evidence on the amount and rate of percolation of water through the
unsaturated zone, on present-day and past groundwater levels, and on the characteristics of the
groundwaters in the underlying rocks, including details of groundwater chemistry, origin, age,
flows and pressures;
91
(b)
Making an assessment of possible future movements of the water table and the probability of
temporary saturation of the rock of the disposal zone(s), taking account of present and past
hydrogeological conditions, possible future climatic conditions, and rates of erosion.
I.39.
The operating organization should not situate disposal zones in rocks that might become
saturated periodically (e.g. seasonally or every few years) because such ephemeral groundwaters often
have oxidizing properties and may contain high concentrations of solutes, characteristics that can
greatly accelerate corrosion of steel waste containers.
92
APPENDIX II. SAFETY ASSESSMENT FOR BOREHOLE DISPOSAL FACILITIES
II.1.
Guidance on the development of the safety case and safety assessments relevant to all types of
radioactive waste disposal facilities is contained in SSG-23 [35]; that information is not repeated here
– the purpose of this Appendix is to address safety assessment issues that are specifically related to
borehole disposal facilities.
II.2.
While the information in this Appendix is applicable to borehole disposal facilities developed
in accordance with the concept for the disposal of disused sealed radioactive sources that have been
declared waste and other radioactive waste as described in para. 1.1 in narrow diameter boreholes as
described Section 2, some of the more general aspects of the guidance (e.g. relating to scenario
development) should be of interest to those involved with other borehole disposal concepts.
Generic safety assessment for borehole disposal of Category 3 to 5 disused sealed radioactive
sources and further studies
II.3.
In the context of this safety guide, a generic safety assessment is a preliminary safety
assessment for a disposal concept that is not based on a specific site. If a site has not been selected, the
operating organization should consider undertaking a generic safety assessment to assist planning in the
early stages of a disposal programme. For example, at the concept development stage and in support of
site screening and selection, a generic safety assessment can be used to help identify waste inventories
that are potentially suitable or unsuitable for disposal following a particular disposal concept, to
determine the need for engineered barriers and other aspects of disposal facility design, and to identify
potentially suitable and unsuitable sites. When a potentially suitable site has been selected for further
investigation, the operating organization should consider using generic safety assessment:
(a)
To help in identifying key data and parameters that will need to be gathered and evaluated in
order to develop a site-specific assessment;
(b)
To help in determining the extent of site characterization required;
(c)
As a basis for site-specific assessment.
Generic safety assessment for borehole disposal of Category 3 to 5 disused sealed radioactive sources
II.4.
A generic safety assessment for the disposal of disused sealed radioactive sources in narrow
diameter boreholes was developed over a period of several years and is presented in Ref. [17]. The
generic safety assessment presented in Ref. [17], considered the 31 most relevant radionuclides found
in disused sealed radioactive sources and assumed that they were disposed of in a borehole with stainless
steel and cement-based barriers as described in Section 2 under a range of different geosphere
conditions. Separate safety assessment calculations were undertaken for waste disposal in unsaturated
conditions and for waste disposal in saturated conditions. The rocks were assumed to be capable of
representation as either porous rocks or fractured rocks. A range of groundwater flow rates was
considered in the saturated zone and a range of safety assessment calculations was undertaken assuming
93
low, medium or high flow rates. Various groundwater geochemical conditions (e.g. Eh, pH, chloride
and sulphate content) were considered to investigate the influence of geochemistry on the performance
of the engineered components in the system.
II.5.
The generic safety assessment presented in Ref. [17], included a thorough features events and
processes analysis and this was used in scenario development. The following scenarios were identified
and defined:
(a)
‘The Design Scenario’. In this scenario it was assumed that the disposal facility was
constructed, operated and closed as designed and that it evolved during the post-closure period
as expected;
(b)
‘The Defect Scenario’. In this scenario it was assumed that not all of the components of the near
field performed as envisaged in the Design Scenario due either to defective manufacturing of
waste packages (e.g. welding defects), or defective implementation of the borehole disposal
concept (e.g. improper emplacement of backfill). Several variants of the Defect Scenario were
considered. These resulted in the earlier release of radionuclides from the near field;
(c)
‘The Unexpected Geological Characteristics Scenario’. In this scenario it was assumed that the
actual performance of the geosphere was worse than the expected performance (e.g. the
geosphere was subjected to an unexpected seismic event resulting in the reactivation of high
permeability fractures and modification of associated sorption properties);
(d)
‘The Changing Environmental Conditions Scenario’. In this scenario it was assumed that the
disposal system was affected by climate change resulting in modifications to certain geosphere
characteristics (e.g. groundwater recharge rates) and biosphere characteristics (e.g. water
demand, surface erosion rates);
(e)
‘The Borehole Disturbance Scenario’. In this scenario it was assumed that drilling of a water
abstraction borehole adjacent to the disposal borehole could result in the earlier exposure of
humans to radionuclides (e.g. due to the use of contaminated water from the abstraction
borehole).
II.6.
In the generic safety assessment – Ref. [17], it was argued that the potential consequences of
the Unexpected Geological Characteristics Scenario and the Changing Environmental Conditions
Scenario were bounded by the range of geosphere and biosphere characteristics that had been assessed
and the parameter sensitivity analyses undertaken for the Design Scenario.
II.7.
In the generic safety assessment – Ref. [17], the Borehole Disturbance Scenario was eliminated
(screened out) from more detailed consideration because of the depth of the disposal zone for the
reference design (>30 m), because of the small footprint of the disposal borehole, and because of the
facility’s location in an area with no natural resources that might lead to extensive surface excavation
94
or underground mining. All of these factors indicted that the probability of inadvertent human intrusion
directly affecting the disposal borehole was extremely low.
II.8.
The generic safety assessment presented in Ref. [17] showed that with a suitable combination
of inventory, disposal facility design and geological and hydrogeochemical environment, the borehole
disposal concept can provide a safe long-term management solution for the disposal of Category 3 to 5
disused sealed radioactive sources containing either long-lived or short-lived radionuclides.
II.9.
In the case of the borehole disposal system described in Ref. [14], all but the long-lived
radionuclides are expected to decay to negligible levels of activity in the disposal zone. Although it is
not possible to provide a demonstration of such containment over hundreds to thousands of years, the
extremely low corrosion rates measured for the stainless steel from which the disposal capsules and
containers are made imply such containment times; furthermore the mechanisms that might cause the
corrosion rate to increase are well understood and are considered to be of low probability (see
Appendix IX of Ref. [17]) providing reasonable confidence in the containment of the short-lived
nuclides within the near field.
II.10.
The generic safety assessment presented in Ref. [17] suggests that under non-fault conditions
(e.g. without any defects in the sealed disposal capsules or containers) even radionuclides with halflives as long as Ra-226 (half-life = 1,600 years) can be disposed safely in almost unlimited quantities.
For long-lived radionuclides such as 239Pu, 241Am and 237Np, the disposal capsules and containers will
delay their release into the geosphere surrounding the disposal zone, but will not prevent it altogether;
for these radionuclides the performance of the borehole disposal system also depends on containment
in the geosphere (which results from a combination of factors, including slow radionuclide diffusion, a
long groundwater travel time, radioactive decay and radionuclide sorption). Depending on the site and
the design of the disposal facility, it may be necessary to limit the inventory of long-lived radionuclides
that can be disposed of. As noted above (see Sections 4 and 5), the operating organization is required
to undertake a site-specific safety assessment and to establish and apply appropriate waste acceptance
criteria.
Further generic studies for borehole disposal of Category 1 & Category 2 disused sealed radioactive
sources
II.11.
Several further generic studies have been performed to assess the safety of the borehole disposal
of disused sealed radioactive sources. These studies have particular relevance to the disposal of
Category 1 and Category 2 disused sealed radioactive sources, and include:
(a)
The stainless steel corrosion models and backfill degradation models developed as part of the
generic safety assessment were incorporated into a Borehole Disposal Concept Scoping Tool –
Ref. [43]. The Borehole Disposal Concept Scoping Tool – Ref. [43] – allows the containment
provided by the disposal capsule and container in the post-closure period and the chemical and
physical degradation of the backfill to be evaluated. The Borehole Disposal Concept Scoping
95
Tool – Ref. [43] – also allows radionuclide transport and subsequent exposure of humans via
the drinking water pathway to be evaluated using a conservative model that takes no account of
the retardation of radionuclides during transport. The Borehole Disposal Concept Scoping Tool
has been extended to allow consideration of Category 1 and Category 2 disused sealed
radioactive sources;
(b)
The generic safety assessment – Ref. [17] did not explicitly consider radiolysis, criticality or
thermal effects because the effects of these processes are insignificant for typical Category 3 to
5 disused sealed radioactive sources to be disposed of. However, for the disposal of Category
1 and Category 2 disused sealed radioactive sources, the operating organization should assess
the potential effects of radiolysis, criticality and thermal processes. Ref. [15] addressed the
potential impacts of the disposal of Category 1 and Category 2 disused sealed radioactive
sources on the post-closure safety of the borehole disposal concept. The study described in Ref.
[15] was based on conservative assumptions and calculations, and indicated that, whilst there
are no criticality issues, the disposal of some Category 1 and Category 2 disused sealed
radioactive sources might result in higher temperatures and high radiation fields that could
significantly reduce the expected lifetime of the waste disposal packages. Consequently, lessconservative calculations were conducted to develop an improved understanding of the thermal
and radiation conditions in the borehole for representative Category 1 and Category 2, and
Category 3 to 5 disused sealed radioactive sources, respectively – Ref. [63]. The work described
in Refs [15] and [63] was supported by calculations using the CHEMSIMUL and Microshield
codes and led to the development of various specifications for the disposal capsules and
containers so that they could be used to contain Category 1 and Category 2 disused sealed
radioactive sources;
(c)
A review was made of the rates of general and localized corrosion of stainless steel in
cementitious environments – Ref. [39]. This review also considered the potential effects of
gamma radiation and galvanic corrosion between carbon and stainless steels in concrete. The
focus of the review was on 304 and 316 austenitic stainless steel. The work led to
recommendations for the use of super austenitic or super duplex stainless steel or a Pdcontaining titanium alloy for the disposal capsules and containers for heat-generating and
gamma-emitting Category 1 and Category 2 disused sealed radioactive sources;
(d)
The work described in Refs [15] and [63] highlighted a need for integration of the mobile hot
cell described in Ref. [22] into the conditioning and disposal operations for Category 1 and
Category 2 disused sealed radioactive sources. The integration work undertaken is described in
Refs [64] and [65].
96
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OFFICE, Occupational Radiation Protection, IAEA Safety Standards Series No. GSG-7, IAEA,
Vienna (2018).
[51] I-MECH Kft, Project Quality Assurance and Collaboration Plan for Manufacturing of Source
Conditioning Capsules and Disposal Containers to be Used by the International Atomic Energy
Agency (IAEA), Version #4, I-MECH Kft., Kertalja (2017).
[52] LINDBORG, T., THORNE, M., ANDERSSON, E., BECKER, J., BRANDEFELT, J.,
CABIANCA, T., GUNIA, M., IKONEN, A.T.K., JOHANSSON, E., KANGASNIEMI, V.,
KAUTSKY, U., KIRCHNER, G., KLOS, R., KOWE, R., KONTULA, A., KUPIAINEN, P.,
LAHDENPERÄ, A.-M., LORD, N.S., LUNT, D.J., NÄSLUND, J.-O., NORDÉN, M., NORRIS,
S., PÉREZ-SÁNCHEZ, D., PROVERBIO, A., RIEKKI, K., RÜBEL, A., SWEECK, L.,
WALKE, R., XU, S., SMITH, G., and PRÖHL, G., Climate Change and Landscape Development
in Post-Closure Safety Assessment of Solid Radioactive Waste Disposal: Results of an Initiative
of the IAEA, Journal of Environmental Radioactivity 183 (2018) 41–53.
[53] NECSA, Waste Acceptance Criteria for the Borehole Disposal Concept, Report No. GEA-1714,
NECSA, Pretoria (2006).
[54] INTERNATIONAL ATOMIC ENERGY AGENCY, Nuclear Security Recommendations on
Physical Protection of Nuclear Material and Nuclear Facilities (INFCIRC/225/Revision 5), IAEA
Nuclear Security Series No. 13, IAEA, Vienna (2011).
[55] INTERNATIONAL ATOMIC ENERGY AGENCY, Nuclear Security Culture, IAEA Nuclear
Security Series No. 7, IAEA, Vienna (2008).
[56] INTERNATIONAL ATOMIC ENERGY AGENCY, Nuclear Security Recommendations on
Radioactive Material and Associated Facilities, IAEA Nuclear Security Series No. 14, Vienna
(2011).
[57] INTERNATIONAL ATOMIC ENERGY AGENCY, Security of Radioactive Material in Use
and Storage and of Associated Facilities, IAEA Nuclear Security Series No. 11-G (Rev. 1),
Vienna (2019).
[58] FOOD
AND
AGRICULTURE
ORGANIZATION
OF
THE
UNITED
NATIONS,
INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL CIVIL AVIATION
ORGANIZATION, INTERNATIONAL LABOUR ORGANIZATION, INTERNATIONAL
MARITIME ORGANIZATION,INTERPOL, OECD NUCLEAR ENERGY AGENCY, PAN
AMERICAN HEALTH ORGANIZATION, PREPARATORY COMMISSION FOR THE
101
COMPREHENSIVE
NUCLEAR-TEST-BAN
TREATY
ORGANIZATION,
UNITED
NATIONS ENVIRONMENT PROGRAMME,UNITED NATIONS OFFICE FOR THE COORDINATION OF HUMANITARIAN AFFAIRS, WORLD HEALTH ORGANIZATION,
WORLD METEOROLOGICAL ORGANIZATION, Preparedness and Response for a Nuclear
or Radiological Emergency, IAEA Safety Standards Series No. GSR Part 7, IAEA, Vienna
(2015).
[59] INTERNATIONAL ATOMIC ENERGY AGENCY, Upgrading of Near Surface Repositories
for Radioactive Waste, IAEA Technical Report Series No. 433, IAEA, Vienna (2005).
[60] INTERNATIONAL ATOMIC ENERGY AGENCY, Safety Considerations in the Disposal of
Disused Sealed Radioactive Sources in Borehole Facilities, TECDOC-1368, IAEA, Vienna
(2003).
[61] INTERNATIONAL ATOMIC ENERGY AGENCY, Remediation Strategy and Process for
Areas Affected by Past Activities or Events, IAEA Safety Standards Series No. GSG-15, IAEA,
Vienna (in preparation).
[62] GHANA ATOMIC ENERGY COMMISSION, Site Description Report for Implementation of
the Borehole Disposal System, Draft 1.4, GAEC, Accra, (2018).
[63] THATCHER, K.E., PENFOLD, J.S.S., and METCALF, R., Further Calculations to Support the
IAEA's Borehole Disposal Concept, QRS-1668C-1 Version 2.0, Quintessa, Henley-on Thames
(2017).
[64] NECSA, Close-out Report on the MHC and BDC Integration, Report No. NLM-REP-15/216,
NECSA, Pretoria, [IAEA order 201306400-VAO] (year).
[65] NECSA, Procedural HAZOP Report on Mobile Hot Cell Borehole Disposal Container Welding,
Report No. SLD-HAZ2014-REP-0008. NECSA, Pretoria (year).
102
ANNEX I. OTHER BOREHOLE DISPOSAL CONCEPTS
I.1.
This annex provides several examples of borehole disposal concepts other than that described
in Section 2 which have been proposed or implemented for radioactive waste storage or disposal for
various types of radioactive waste. These examples are included in this Annex to distinguish them from
the recommended disposal concept for disposal of disused sealed radioactive sources. Their inclusion
in this annex does not imply that they necessarily meet the relevant safety requirements.
I.2.
Shallow boreholes have been used in the past in a number of States for the storage and disposal
of radioactive waste – Ref. [I.1]. In the Russian Federation, for example, there is experience of ‘RADON
wells’ dating back to the 1960s, Ref. [I.1]. These boreholes were originally designed for disposal of
disused sealed radioactive sources but have now been re-designated as storage facilities. More recent
designs can accommodate drummed waste and have depths of almost 40 m, although the uppermost
waste packages are just a few metres below the surface, Ref. [I.3]; these facilities are also designated
as storage facilities. Shallow boreholes have also been used for radioactive waste disposal at Mount
Walton East, a very arid location in Western Australia. Here, the ‘Intractable Waste Disposal Facility’
(IWDF) includes a pair of 2 m-diameter boreholes in which drummed low level waste and intermediate
level waste is stacked in layers that lie between 5.8 m and 28 m below the surface. The boreholes were
operational in 1992 and 1994; more recent disposals at the IWDF have been in near surface trenches,
Ref. [I.4].
I.3.
In the USA, at least two ‘Greater Confinement Disposal’ facilities have used 3 m-diameter
boreholes or shafts drilled with a large augur. At the Savannah River Plant, the Greater Confinement
Test Facility consists of a square array of eighty, 6 m-deep shafts that have been used for disposal of
US Class B wastes, Ref. [I.5]. A second type of Greater Confinement Disposal facility was used at the
Nevada Test Site (NTS) in the 1980s to dispose of ‘Greater-Than-Class-C’ (GTCC) low level waste,
which included disused sealed radioactive sources and some transuranic elements; here, the depth of
disposal was at least 21 m and was specified to be more than 120 m above the water table, Ref. [I.6].
I.4.
The Greater Confinement Disposal concept was re-evaluated in 2007 for another disposal of
GTCC low level waste, again at the NTS, Ref. [I.7]. The estimated total volume of the waste was 2,500
cubic meters, with an approximate activity of 7.8 million TBq. In this case, the waste was to be disposed
of at least 30 m deep because according to US regulations, Ref. [I.8], a shallower depth would require
it to be classified as a near surface disposal. A maximum depth of 300 m was envisaged, and 930
boreholes would have been needed, spread over an area of 44 hectares (implying a borehole spacing of
around 22 m). This proposal was eventually rejected in favour of an approach that utilized both
commercial disposal facilities and the Waste Isolation Pilot Plant (WIPP) – a geological disposal facility
in New Mexico, Ref. [I.9].
103
I.5.
Various studies have been made of concepts for the disposal of high level waste, including
spent fuel, in boreholes or bored drifts at depths associated with geological disposal, e.g. Ref. [I.10] 18,
or greater, e.g. Ref. [I.11]. The diameters of the disposal boreholes or drifts in these concepts vary in
the approximate range from 0.5 to 2 m. Very deep borehole disposal of radioactive waste (i.e. disposal
in boreholes deeper than a few hundred metres) was suggested in the 1970’s, e.g. Ref. [I.12] and the
idea has been studied intermittently since that time. Various different concepts have been described,
including concepts that involve using the heat produced by the radioactive waste to melt the surrounding
rock and, thereby, form a barrier to radionuclide migration e.g. Ref. [I.13], concepts that do not involve
rock melting and rely for safety principally on the great depth and high degree of isolation provided by
boreholes of up to 5 km deep, e.g. Ref. [I.14], and concepts that envisage the combined disposal of heat
generating radioactive waste and the production of ‘geothermal’ energy by pumping water through very
deep boreholes bored parallel to, but between, boreholes containing radioactive waste, Ref. [I.15].
I.6.
The various very deep borehole disposal concepts have been reviewed at different stages by
national radioactive waste disposal programmes in the UK, Ref. [I.16], in Sweden, Ref. [I.17], in
Germany, Ref. [I.18] and in the US, Ref. [I.19]. Ref. [I.19] noted various remaining uncertainties
(e.g. relating to rock heterogeneity and the ability to characterize the rocks at such great depths) and
concluded that very deep borehole disposal offers few clear advantages over conventional geological
disposal, including in terms of safety or the speed at which disposal could be implemented.
18
The disposal concept described in Ref I.10 is considered to be a form of geological disposal.
104
REFERENCES TO ANNEX I
[I.1]
INTERNATIONAL ATOMIC ENERGY AGENCY, Safety Considerations in the Disposal of
Disused Sealed Radioactive Sources in Borehole Facilities, TECDOC-1368, IAEA, Vienna (2003).
[I.2]
SOBOLEV, I.A., OJOVAN, M.I. AND KARLINA, O.K., Management of Spent Sealed
Radioactive Sources at Regional Facilities, ‘Radon’ in Russia”, 8th International Conference on
Radioactive Waste Management and Environmental Remediation, Bruges, (2001).
[I.3]
PROZOROV, L., TKATCHENKO, A., TITKOV, V. AND KORNEVA, S., Prospects of Large
Diameter Well Construction at ‘Radon’ Sites”, Waste Management ’01 Conference, Tucson, (2001).
[I.4]
GOVERNMENT OF WESTERN AUSTRALIA, DEPARTMENT OF FINANCE, BUILDING
MANAGEMENT AND WORKS, Intractable Waste Disposal Facility, Mount Walton East,
Information Handbook, 2017.
[I.5]
COOK, J.R., TOWLER, O.A., PETERSON, D.L., JOHNSON, G.M. AND HELTON, B.D,
Greater Confinement Disposal Program at the Savannah River Plant, Waste Management '84,
Conference, Tucson, (1984).
[I.6]
COCHRAN, J.R., CROWE, B.M., COLARUSSO, A., Results of the Performance Assessment
for the Classified Transuranic Wastes Disposed at the Nevada Test Site, Waste Management ’01
Conference, Tucson, (2001).
[I.7]
TONKAY, D.W., JAMES L. JOYCE, J.L. AND JOHN R. COCHRAN, J.R. A Fresh Look at
Greater Confinement Boreholes for Greater-than-Class C Low level Radioactive Waste Disposal, Waste
Management ‘07 Conference, Tucson, (2007).
[I.8]
UNITED STATES NUCLEAR REGULATORY COMMISSION, Code of Federal Regulations
10 CFR 61.2, 2017.
[I.9]
US DEPARTMENT OF ENERGY, Alternatives for the Disposal of Greater-than-Class C Low
Level Radioactive Waste and Greater-Than-Class C-Like Waste, Report to Congress, November 2017.
[I.10]
POSIVA OY AND SVENSK KÄRNBRÄNSLEHANTERING AB, KBS-3H System Design
Phase 2011−2016: Final Report, Posiva SKB Report 06, SKB ID 1538999, Posiva ID RDOC-104827,
Helsinki and Stockholm (2017).
[I.11]
FINSTERLE, S., MULLER, R.A., GRIMSICH, J., APPS, J. AND BALTZER, R. Post-Closure
Safety Calculations for the Disposal of Spent Nuclear Fuel in a Generic Horizontal Drillhole
Repository, Energies 13, 2599, (2020).
[I.12]
BATTELLE PACIFIC NORTH-WEST LABS., High level Radioactive Waste Management
Alternatives. In: Schneider, K.J. and Platt, A.M. (eds), Battelle Pacific North-West Labs., Report No.
BNWL-1900, BPNL, Richland, (1974).
105
[I.13]
GIBB, F.G.F., A New Scheme for the Very Deep Geological Disposal of High level
Radioactive Waste. Journal of the Geological Society of London, Vol. 157, pp. 27–36, (2000).
[I.14]
BRADY, P.V., FREEZE, G.A., KUHLMAN, K.L., HARDIN, E.L., SASSANI, D.C. AND
MACKINNON, R.J., Deep Borehole Disposal of Nuclear Waste: US Perspective, in: APTED, M. and
AHN, J. (eds) 2017, Geological Repository Systems for Safe Disposal of Spent Nuclear Fuels and
Radioactive Waste, 2nd Edition. Pages 89-112.
[I.15]
PUSCH, R. WESTON, R. AND KASBOHM, J., Deep Boreholes for Storage of Spent Reactor
Fuel and Use of the Heated Rock for Production of Electric Energy or Hot Fluid for Heating Purposes,
Journal of Earth Sciences and Geotechnical Engineering, Vol.10, No. 1, pp. 127-153 (2020).
[I.16]
UNITED KINGDOM NIREX LIMITED, A Review of the Deep Borehole Disposal Concept
for Radioactive Waste, Nirex Report No. N/108, Harwell (2004).
[I.17]
SVENSK KÄRNBRÄNSLEHANTERING AB, PASS – Project on Alternative Systems Study.
Performance Assessment of Bentonite Clay Barrier in Three Repository Concepts: VDH, KBS-3 and
VLH, Pusch, R. and Börgesson, L., SKB Report No. TR-92-40, SKB, Stockholm, (1992).
[I.18]
BRACKE, G., CHARLIER, F., LIEBSCHER, A., SCHILLING, F. AND RÖCKEL, T., Does
Deep Borehole Disposal of HLRW has a Chance in Germany? Decommissioning and Waste
Management, Vol. 62, Issue 1 (2017).
[I.19]
U.S. NUCLEAR WASTE TECHNICAL REVIEW BOARD. A Report to the U.S. Congress
and the Secretary of Energy: Technical Evaluation of the U.S. Department of Energy Deep Borehole
Disposal Research and Development Program, NWTRB, Arlington, 2016.
106
ANNEX II. ISOLATION AND DISPOSAL DEPTH
II.1.
The Safety Guide that this publication replaces (SSG-1) relied on a 1987 reference, Ref. [II.1]
for recommending a minimum depth at which waste should be disposed of in a borehole disposal
facility. This minimum depth was 30 m and was at that time regarded as a depth beyond which human
intrusion is limited to drilling and significant excavation activities, such as tunnelling, quarrying and
mining) Ref. [II.1]. In the 30 years since Ref. [II.1] was published, significant developments have been
made in the construction of high-rise buildings and other infrastructure and excavations deeper than
30 m have become common. For example, Ref. [II.2] presents data on the depths of underground
structures in Japan; the data for high-rise buildings, expressways and railways cluster in the approximate
range from 30 m to 50 m deep and extend to depths of approximately 80 m. Ref. [II.2] also shows that
the depths of underground structures in Japan increased significantly over the period from 1910 to 1980.
II.2.
In practice, there are many operating near surface disposal facilities for low level waste at
depths of up to several tens of metres, some of which also accept short-lived intermediate level waste,
and several disposal facilities are in operation for the disposal of low level waste and short-lived
intermediate level waste in vaults and silos at depths of up to approximately 120 m. For example, the
SFR repository in Sweden accepts low level waste and short-lived intermediate level waste for disposal
at depths between approximately 60 m and 120 m Ref. [II.3].
II.3.
For several reasons, including locating the waste below local topography and below the zone
of weathered rocks near the surface, which is often tens of metres thick in tropical environments, the
two pilot projects on borehole disposal of disused sealed radioactive sources in Malaysia and Ghana
have located disposal zones deeper than 100 m. In Malaysia the proposed disposal zone lies between
depths of approximately 115 m and 175 m, Ref. [II.4], in Ghana the proposed depth of the disposal zone
lies between approximately 135 m and 150 m, Ref. [II.5]).
II.4.
Experiences in several Member States (for examples, see Ref. [II.6] and Section B.2.1 of
Ref. [II.7]) have been that some existing shallow borehole disposal facilities have had later to be
reclassified as storage facilities from which the waste should be retrieved, or where safety should
otherwise be upgraded (see also Section 8).
II.5.
In light of these developments, practices and experiences, and given that it easy and inexpensive
(in comparison with the total cost of a waste disposal programme) to drill narrow diameter boreholes,
this publication recommends borehole disposal at depths below 100 m to increase confidence in the
safety of disposal and in the maintenance of nuclear security over the disposed waste.
107
REFERENCES TO ANNEX II
[II.1]
OECD NUCLEAR ENERGY AGENCY, Shallow Land Disposal of Radioactive Waste:
Reference Levels for the Acceptance of Long-lived Radionuclides, Report by an NEA Expert Group,
OECD, Paris (1987).
[II.2]
SAKAMOTO, Y., SENOO, M., SUGIMOTO, M., OHISHI, K., OKISHIO, M. AND
SHIMIZU, Survey of the Depth Distribution of Underground Structures for Consideration of Intrusion
into TRU Waste Repository, Atomic Energy Society of Japan, Volume 38, No. 6, pp. 442-447, (1996).
[II.3]
SKB, Safety Analysis for SFR Long-term Safety. Main Report for the Safety Assessment SR-
PSU. Report No. SKB TR-14-01 Revised Edition - Updated 2017-04, SKB, Stockholm (2017).
[II.4]
NUKLEAR MALAYSIA, Safety Case Synthesis Report for the Borehole Disposal Project,
Report No. NUKLEARMALAYSIA/L/2018/116(S), NMA, Bangi (2018).
[II.5]
GHANA ATOMIC ENERGY COMMISSION, Safety Case Report Required for the
Implementation of the Borehole Disposal System in Ghana, Draft 1.2, GAEC, Accra, (2018).
[II.6]
INTERNATIONAL ATOMIC ENERGY AGENCY, Upgrading of Near Surface Repositories
for Radioactive Waste, IAEA Technical Report Series No. 433, IAEA, Vienna (2005).
[II.7]
INTERNATIONAL ATOMIC ENERGY AGENCY, Safety Considerations in the Disposal of
Disused Sealed Radioactive Sources in Borehole Facilities, TECDOC-1368, IAEA, Vienna (2003).
108
CONTRIBUTORS TO DRAFTING AND REVIEW
D.G. Bennett
IAEA
J. van Blerk
Private Consultant, South Africa
G. Bruno
IAEA
I. Crossland
Private Consultant, UK
R. Little
Private Consultant, UK
109
| File Type | application/pdf |
| File Title | P1418.book |
| Author | BENNETT, David George |
| File Modified | 2021-10-12 |
| File Created | 2021-09-20 |