A Fairhurst, UK, Environment Agency – Comments for input to meeting

(DRAFT Ver.3)DISPOSAL FACILITIES FOR INTERMEDIATE

LEVEL RADIOACTVE WASTE

Drafted atCS in Vienna, 15-19 September, 2014

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Table of ContentsFOREWORD ......................................................................................................................................................7

1 Introduction ..............................................................................................................................................8

1.1 Background .......................................................................................................................................8

1.2 Objectives and scope ........................................................................................................................9

1.3 Structure ...........................................................................................................................................9

2 Definitions and Timescales .....................................................................................................................11

2.1 Definitions associated with ILW classification .................................................................................11

2.2 Definitions and timescales associated with disposal options ..........................................................11

3 Application of Safety Requirements and Guides to ILW disposal ...........................................................13

3.1 Legal and Organisational Infrastructure .........................................................................................13

3.2 Safety Approach .............................................................................................................................13

3.3 Design Concepts for Safety .............................................................................................................14

3.4 Framework for disposal of radioactive waste .................................................................................15

3.5 Demonstration of safety ...............................................................................................................15

3.6 Assurance of safety .........................................................................................................................16

4 ILW characteristics ..................................................................................................................................18

4.1 Radionuclide content and activity concentration ...........................................................................18

4.2 Waste volume and geometry ..........................................................................................................18

4.3 Physical, chemical and biological properties ...................................................................................19

4.4 Criticality .........................................................................................................................................20

4.5 Heat Generation .............................................................................................................................20

4.6 Chemotoxicity .................................................................................................................................20

4.7 Preparing ILW ..................................................................................................................Gas Generation 20

5 Preparing ILW for Disposal .....................................................................................................................22

5.1 Treatment .......................................................................................................................................22

5.2 Conditioning ...................................................................................................................................22

5.3 Storage ............................................................................................................................................23

5.4 Identification and compliance with waste acceptance criteria for disposal ...................................23

6 Disposal Options .....................................................................................................................................24

6.1 Principal safety functions ................................................................................................................24

6.2 Available Disposal Options ..............................................................................................................24

6.2.1 Near surface options ...............................................................................................................25

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6.2.1.1. Landfill disposal ...................................................................................................................25

6.2.1.2. Trench disposal ...................................................................................................................25

6.2.1.3. Engineered surface vault ....................................................................................................25

6.2.1.4. Near surface underground disposal facilities ......................................................................26

6.2.2 Geological disposal options ....................................................................................................26

6.2.3 Other disposal options ............................................................................................................27

6.2.3.1. Boreholes ............................................................................................................................27

6.2.3.2. In-situ immobilization .........................................................................................................27

6.3 Factors for the selection of a disposal option .................................................................................27

6.3.1 Safety related factors ..............................................................................................................27

6.3.2 Waste volume related factors .................................................................................................28

6.3.3 Economic and technical resources ..........................................................................................28

6.3.4 National policy and social aspects ...........................................................................................28

7 Siting .......................................................................................................................................................29

7.1 Site natural properties ....................................................................................................................29

7.2 Site evolution ..................................................................................................................................31

7.2.1 Precipitation and recharge ......................................................................................................31

7.2.2 Permafrost and glaciation .......................................................................................................31

7.2.3 Sea level change ......................................................................................................................32

7.2.4 Weathering .............................................................................................................................32

7.2.5 Uplift/erosion, faulting/folding and subsidence/sedimentation .............................................32

7.2.6 Other tectonic related processes ............................................................................................32

7.2.7 Impact of geodynamic evolution on the consideration of human intrusion ...........................33

The likelihood of human intrusion may be impacted by site evolution processes including glaciation, sea level change, and uplift/erosion. This issue needs to be considered over the timescale relevant for the radiological content of the ILW, especially for near-surface disposal. ...................................................33

7.2.8 Natural and social environment ..............................................................................................33

8 Disposal Facility Design for ILW ..............................................................................................................34

8.1 Design process ................................................................................................................................34

8.1.1 Requirements on the disposal facility .....................................................................................34

8.1.2 Design solution development .................................................................................................35

8.1.3 Verification of compliance ......................................................................................................35

8.2 Safety considerations for ILW disposal facility design ....................................................................36

8.2.1 Construction phase .................................................................................................................36

8.2.2 Operational phase ...................................................................................................................36

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8.2.3 Post-closure phase ..................................................................................................................37

8.3 Design considerations for ILW ........................................................................................................38

8.3.1 Disposal volumes ....................................................................................................................38

8.3.2 Layout .....................................................................................................................................39

8.3.3 Access ways ............................................................................................................................39

8.3.4 Operating systems ..................................................................................................................40

8.3.5 Backfilling, capping and sealing ...............................................................................................40

8.3.6 Monitoring and retrievability ..................................................................................................41

8.3.7 Management of concurrent construction and operation .......................................................41

9 Safety Case Development .......................................................................................................................42

9.1 Iterative Approach of the Safety Case ............................................................................................42

9.2 Demonstration of safety .................................................................................................................43

9.3 Aspects of safety assessment .........................................................................................................43

10 Institutional Control and Record Keeping ...........................................................................................45

10.1 Institutional control ........................................................................................................................45

10.2 Record keeping ...............................................................................................................................45

REFERENCE .....................................................................................................................................................46

APPENDIX I: National Examples ......................................................................................................................47

APPENDIX II: IAEA publications relevant to this document ........................................................................48

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FOREWORDThe IAEA safety standards have been developed in order to serve as the global reference for protecting people and the environment from harmful effects of ionizing radiation, providing a robust framework of fundamental principles, requirements and guidance to ensure safety.

In the field of disposal of radioactive waste, a specific Safety Requirement SSR-5 has been developed to cover all disposal concepts. As supporting documents of SSR-5, several Safety Guides have been developed, such as Specific Safety Guide SSG-14 and SSG-29 for near surface disposal facilities and geological disposal respectively.

Since 2008, there have been discussions on the need for the development of additional safety guides or guidance documents on the disposal of intermediate level waste (ILW).

In 2008, the Workshop on Intermediate Depth Disposal of Radioactive Waste: the Safety Basis and its Realization was held in Korea. The workshop covered disposal of the broad range of wastes termed as ILW under the recognition that disposal options for the broad range of materials in the middle of this spectrum (ILW) have been developed at the national level but have not so far been the subject of as much attention from the perspective of international activities. At the workshop, it was concluded that existing IAEA Safety Standards for near surface disposal and geologic disposal provide the needed foundation for addressing ILW disposal. The safety case for ILW disposal facilities would reflect a graded application of existing IAEA Safety Standards to address issues such as the wastes included for disposal, the specificities of the natural and engineered barriers, and operational considerations. However, conclusions of the workshop also mentioned that additional guidance in existing IAEA draft guides may be needed to address ILW disposal.

This issue was followed by further discussion at several other IAEA meetings between 2011 and 2013. As a result, it was decided to develop a Safety Report focusing on the specific nature of ILW disposal as a supplemental document of existing Safety Standards, and this report was prepared by 5 consultancy meetings and technical meetings in 2013 and 2014.

The IAEA officer responsible for this publication was Y. Kumano of the Division of Radiation, Transport and Waste Safety.

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1 Introduction1.1 BackgroundIntermediate-level waste (ILW) is, from a disposal and safety case perspective , situated between low-level waste which may generally be disposed of in a near surface facility and high-level waste that must be disposed in a deep geological formation.

Guidance on near surface disposal facilities and geological disposal facilities are found in IAEA Specific Safety Guide SSG-14 and SSG-29. While it is clear that near surface facilities may be applicable to most low-level waste and some short-lived ILW and geological disposal is required for high level waste, and spent fuel that has been declared to be waste, and some long-lived ILW, there is no specific guidance for ILW..

ILW is generated by a wide spectrum of activities, particularly: fuel production, reprocessing of spent fuel, reactor operation, nuclear research, decommissioning of nuclear facilities, and medical and industrial applications.

It includes items such as: resins, filters, sludge and evaporator concentrates from operation of nuclear facilities, components from decommissioning or maintenance which may include some irradiated large items

such as core internals, residues from materials processing such as ore treatment, control rods and neutron monitoring devices, fuel debris and ends, concrete and rubble from demolition of buildings, and sealed sources from medical and industrial applications.

Therefore, one of the features of ILW is its diversity, both in radionuclide contents and in physical and chemical form.

ILW may be roughly categorized into two main groups. One group of ILW contains a relatively high activity, but a low content of long lived radionuclides whereas the other group has a relatively high content of long lived radionuclides, but with low to moderate activity. The volume of ILW is usually more significant than HLW while the activity concentration is more significant than LLW. This justifies the treatment of ILW as a separate waste stream(s).

A particular challenge in ILW management is the legacy or historical waste, held in some countries, which may have limited characterisation. Some may have been conditioned previously but does not meet current Safety Standards and therefore requires further treatment. Legacy waste often includes sealed sources.

Sometimes ILW is described as waste that needs to be disposed of in a facility at a depth of between a few tens and a few hundreds of metres. However, it is not recommended to discuss an ILW disposal facility in terms of depth only, but rather by considering the many influencing properties of the site and engineered design that can provide the required degree of containment and isolation [add reference to WS on ILW http://www-ns.iaea.org/downloads/rw/waste-safety/korea-workshop2008/korea-findings.pdf]. Therefore, ILW can be divided into different waste streams for which different disposal options are appropriate.

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Whatever the type of waste and the depth of the disposal facility, an appropriate timescale over which the safety of the facility is considered needs to be considered. It must be consistent with the characteristics of the waste, in particular the reduction of activity with time as a function of the half-life of radionuclides, and with the natural evolution of the site.

The design considerations for a disposal facility for ILW have many similar considerations to those for other types of waste. Co-disposal of ILW with other types of waste, LLW or HLW, is considered in many countries.

Co-disposal may involve: disposal of ILW with other types of waste in the same disposal module, separate disposal modules at the same location with common infrastructure, such as access shafts or

drifts in the case of underground facilities, and separate disposal facilities for ILW and other waste at the same location.

Examples of those facilities are given in APPENDIX??

In all cases, the selected design of the disposal facility including depth and facility concept which accommodates ILW needs to be tailored to the characteristics of the waste packages, for instance the construction material used and the volume size of the cells or pits and to the characteristics of the site. All of these aspects need to act as integrated system rather than individual component.

1.2 Objectives and scopeThe objective of this document is to provide a reference for the application of the IAEA Safety Standards to the disposal of ILW.

This document examines requirements and guidance relevant to the disposal of ILW, from near-surface to geological, including the development of a safety case for such facilities. It demonstrates that the following IAEA Safety Standards provide a comprehensive basis for the implementation of ILW disposal:

IAEA Specific Safety Requirements SSR-5, Disposal of Radioactive Waste, IAEA Specific Safety Guide SSG-14, Geological Disposal Facilities for Radioactive Waste, IAEA Specific Safety Guide SSG-23, The Safety Case and the Safety Assessment for the Disposal

of Radioactive Waste, and IAEA Specific Safety Guide SSG-29, Near Surface Disposal Facilities for Radioactive Waste.

1.3 StructureChapter 2 provides definitions related to ILW and disposal options and discusses timescales.

Chapters 3, 4 and 5 are overview chapters providing information on application of Safety Standards, key characteristics of ILW that need to be taken into account, and considerations in predisposal options including packaging.

Chapters 5-10 provide detailed discussions on the application of Safety Standards; Chapter 5 discusses the approach to the selection of disposal options for ILW; Chapter 7 describes consideration for siting of the facility; Chapter 8 describes factors of ILW to be considered in the design of the facility including operational and post-closure aspects; Chapter 9 describes the safety case; Chapter 10 describes the record keeping and institutional control.

APPENDIX I give examples on the disposal of ILW provided by various Member States. APPENDIX II provides an overview of other IAEA documents relevant to ILW.

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2 Definitions and Timescales2.1 Definitions associated with ILW classification

While there are a number of IAEA definitions that are relevant to ILW disposal, there is no specific definition for ILW in the IAEA Safety Glossary. Definitions are given in terms of radiological properties of these wastes and intermediate-level waste is considered together with low-level waste as:

low and intermediate level waste (LILW). Radioactive waste with radiological characteristics between those of exempt waste and high level waste. This may be long lived waste (LILW-LL) or short lived waste (LILW-SL).

The following notes are provided: Typical characteristics of low and intermediate level waste are activity levels above clearance

levels and thermal power below about 2 kW/m3 [....]. Many States subdivide this class in other ways, for example into low level waste (LLW) and

intermediate level waste (ILW) or medium level waste (MLW), often on the basis of waste acceptance requirements for near surface repositories.

The terms short lived and long lived waste are defined as:

short lived waste. Radioactive waste that does not contain significant levels of radionuclides with a half-life greater than 30 years

long lived waste. Radioactive waste that contains significant levels of radionuclides with a half-life greater than 30 years

It is however not clearly stated what is regarded as ”significant levels” in the IAEA Safety Glossary. This needs to be determined in each Member State relating to the retention capability and the life-time of the facility as discussed in the safety case. Different national approaches have been adopted to distinguish between LLW, ILW, and HLW; therefore it is not appropriate to set a firm threshold in international standards. Instead, constraints on radioactivity need to be reflected in the waste acceptance criteria (WAC) associated with a specific site and design of a disposal facility.

The IAEA General Safety Guide GSG-1, Classification of Radioactive Waste, recognizes that ILW requires a higher degree of containment than LLW. Although GSG-1 makes a direct association between ILW and intermediate depth disposal (see Figure 1 in GSG-1 which is a conceptual illustration of the waste classification scheme), this document considers a broader depth range from near-surface to deep geological depending on the specific characteristics of both the ILW and the site.

2.2 Definitions and timescales associated with disposal optionsSSR-5 provides definitions of near-surface and geological disposal but does not list any specific requirements for ILW.

SSR-5 defines near surface disposal as disposal in a facility consisting of engineered trenches or vaults constructed on the ground surface or up to a few tens of metres below ground level.

SSR-5 suggests that near surface disposal may be designated as a disposal facility for low level radioactive waste.

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Geological disposal is defined in SSR-5 as disposal in a facility constructed in tunnels, vaults or silos in a particular geological formation (e.g. in terms of its long term stability and its hydrogeological properties) at least a few hundred metres below ground level.

SSR-5 notes that a geological disposal facility could be designed to receive high level radioactive waste (HLW), including spent fuel if it is to be treated as waste, and that with appropriate design, a geological disposal facility could receive all types of radioactive waste.

Available disposal options for ILW are referred to in Chapter 6.2.

Regardless of the type of waste, disposal facility design and the depth, the safety case has to demonstrate safety over an appropriate timescale. It must be consistent with the characteristics of the waste, in particular the reduction of activity with time as a function of the half-life of radionuclides, the natural evolution of the site and the considered depth and design of the facility.

Along with safety issues, the selection of appropriate disposal options may take into account national societal factors. Therefore, some countries have chosen deep geological disposal for all radioactive waste even when the safety criteria could be met through near surface disposal.

On the surface, natural changes occur over shorter timescales than deep underground. Significant processes leading to this evolution include erosion by wind, rain water, glacial activities, weathering and potential land uplift, large-scale landslides, subsidence and post glaciation rebound as well as climate induced processes such as glaciation, permafrost, or sea-level change. These phenomena may change the future boundary conditions of the system, for example hydrographic system and hydrogeology, as well as the system itself for example through the changing chemical, hydrological and temperature conditions. They will possibly progressively reduce the thickness and/or performance of containment barriers interposed between the waste and the environment. In an extreme situation the disposal facility and waste packages may be destroyed in the long term, leading to loss of containment, direct access to waste and dispersion of residual activity. The affected depth with time and the speed and consequence of these mechanisms are site dependent.

Geologists can extrapolate the evolution of the deep geological environment for millions of years but uncertainties increase with time. Uncertainties in the evolution of the site (that are relevant for the safety case) can be assessed through scenarios and bounding cases. However, provisions are to be made in siting geological disposal facilities to avoid excessive geodynamic disturbances that could affect the underground facilities, the host rock and the long term safety functions. SSG-14 provides that

“The site should be located in a geological and geographical setting where these geodynamic processes or events will not be likely to lead to unacceptable releases of radionuclides . (…) Geodynamic effects such as ground motion associated with earthquakes, land subsidence and uplift, volcanism and diapirism may also induce changes in crustal conditions and processes. Such types of event, which in some cases can be interrelated, may affect the overall disposal system through disturbances in the site integrity or modifications of groundwater fluxes and pathways.”

Reasonable margins are to be taken into account between the scientific capacity to predict the evolution of a site, with adequate accuracy, and the relevant timescale for the safety case. The radiological exposure of man has to be acceptable at all times. Therefore depending on site condition one may need to take into account loss of containment and potential dispersion of waste at least at the end of the considered timescale. As a consequence, the acceptable content of long lived radionuclides is a function of the applicable timescale.

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3 Application of Safety Requirements and Guides to ILW disposal

SSR-5 provides requirements for the legal and regulatory framework, safety approach, design concepts for safety, safety case and safety assessment and stepwise development that are applicable for all types of waste including ILW. It sets out the safety objective and criteria for the protection of people and the environment against radiation risks arising from disposal facilities. Applications of these requirements to near surface and geological facilities are given by SSG-29 and SSG-14 respectively. Specific information on the application of these documents to ILW is given below.

3.1 Legal and Organisational InfrastructureThe Requirements 1, 2 and 3 of SSR-5 address the national legal and organisational framework:

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.

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.

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.

These requirements are fully applicable to any disposal facility which accommodates ILW. SSG-14 and SSG-29 show the applicability to geological and near surface facilities respectively. In applying these requirements to ILW it is important to reflect the necessary timescales of development and operation of the disposal facility. In cases where long timeframes are involved, the possibility of a transfer of responsibilities between different organisations needs to be considered and provisions need to be made to avoid any adverse consequence on safety. In this respect, preservation of records is essential, including both characteristics and inventories of the waste taking into account the diversity of ILW, and knowledge of development of the facility.

The roles and responsibilities relevant for the different types of waste to be disposed need to be clearly defined to ensure that all aspects are clearly covered and that proper coordination is provided.

3.2 Safety ApproachSSR-5 addresses safety approach in requirements 4, 5 and 6:

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.

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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.

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.

In applying these requirements to ILW, it is important to reflect the considered ILW disposal options and the timescale necessary for the development and operation of the disposal facility.

Consistent with SSG-14 and SSG-29, the safety approach includes all the ways in which the safety of people and the environment is ensured throughout the lifetime of any disposal facility which accommodates ILW. It may be useful for the government and the regulatory body to set out the national approach in a formal safety strategy document that is produced at the start of the disposal programmes which include ILW and may be updated periodically.

In the case of co-disposal with either LLW or HLW, the specific characteristics of the waste to be co-disposed have to be taken into account.

3.3 Design Concepts for SafetySSR-5 addresses design concepts for safety in requirements 7, 8, 9, and 10:

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.

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.

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.

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.

With respect to safety functions, the choice of the design concept for the ILW disposal facility needs to take into account the diverse characteristics of waste to be emplaced. The half-lives and activities of key radionuclides in the waste determine the required duration of containment and isolation to be considered by the design including factors such as depth, geological settings, and engineered barriers. For ILW which

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contains lower amounts of relatively long-lived radionuclides, near-surface disposal may be appropriate. ILW containing greater amounts of radionuclides with intermediate or long half-life would need a greater duration of containment and isolation. It is important to note that the safety concept needs to define and understand the roles and functions of individual barriers and how they interact. They safety case needs to consider the integrated effects of the system, not the each barrier individually. For the containment function, the design needs to take into account the nature of radionuclides contained in the waste including the chemical stability of the waste and the mobility of any released radionuclides.

Surveillance and institutional controls should be consistent with the guidance in SSG-14 or SSG-29 as appropriate to the selected disposal option.

3.4 Framework for disposal of radioactive wasteSSR-5 addresses step by step development and evaluation of disposal facilities in Requirement 11:

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.

The step by step iterative process seeks to maximize the value of information as it evolves over the series of steps, for instance siting, design, construction, operation and closure.

While there may be many steps in the development, operation and closure of a disposal facility, the most important ones occur at regulatory or governmental decision points for the approval of siting of an ILW disposal facility (in some countries), the approval of construction, the approval to receive and emplace waste (operations) and the approval to close the facility (closure).

For each step in the process, the operator needs to identify the decision to be made and the information that is necessary to make the decision. The operator should also identify the appropriate interested parties Operators may define a number of steps in their own programme, however, the step by step process refers to the steps imposed by the regulatory and political decision making processes. (SSG-14) and determine when and how to include them in the decision making process. Early involvement of regulatory bodies and other relevant interested parties improves the quality of the decision making and provides clarity for the direction of the project. The step by step approach also allows opportunities for independent technical reviews, regulatory reviews, and political and public involvement in the process. The nature of the reviews and the degree of involvement will depend on national practices and on the facility in question, but engagement of the regulatory body should take place at an early stage in the developmentprocess. (SSG-29)

The step by step approach also allows opportunities for independent technical reviews, regulatory reviews, and political and public involvement in the process.

3.5 Demonstration of safety The goal of demonstrating safety should be to show that the selected concept complies with relevant Safety Standards and the national regulations. SSR-5 addresses the concept and role of the safety case and safety assessment in requirements 12, 13 and 14, as well as the steps of facility development, operation and closure in requirements 15 to 19. In addition, SSG-23 provides comprehensive guidance on safety cases and safety assessment that is applicable to any kind of disposal of radioactive waste.

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Those requirements and guidance are fully applicable to ILW disposal. The safety case needs to pay particular attention to the aspects related to the timescale over which the safety of the facility needs to be demonstrated and the depth of the ILW disposal facility. Consideration needs to be given to the specific characteristics of the waste, for example, quantity and mobility of long-lived radionuclides, potential for gas generation, presence of potential complexants (See Chapter 4 for more details). Particularly in the case of near surface disposal, WAC are more restrictive for the content of long-lived radionuclides.

In the case of co-disposal with other types of waste, the safety case needs to consider all the waste types that are disposed in the same location, especially with regards to radiological impacts to humans and the environment. Potential for interactions between different disposal modules or waste packages also needs to be considered and demonstration provided that there are no significant detrimental interactions.

3.6 Assurance of safetySSR-5 addresses WAC in requirement 20:

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.

Especially for near-surface disposal facilities, significant efforts need to be made to define acceptable radionuclide content or activity limits for ILW disposal facilities considering itsthe diversity of the waste. These requirements need to be reflected in the WAC. More generally, for any disposal options, tThe WAC for ILW disposal also needs to reflect these requirements as well as physical and chemical form of the conditioned waste including the detailed description of the non-radiological contents to assure that they meet the requirement of the safety case and the safety assessment.

Understanding of the evolution of the waste is also important in order to assess the potential for physical and chemical changes including formation of degradation products such as gases, complexing agents, and those causing chemical or physical disturbances.

The WAC needs to take into account all the aspects described in Chapter 4.Further consideration on the WAC specific to ILW disposal is addressed in Chapter 5.4.

Monitoring is addressed in Requirement 21 of SSR-5. In developing a monitoring programme for a near-surface ILW disposal facility, consideration needs to be given to the higher and longer-lived radionuclide content in ILW, compared with LLW. For geological disposal of ILW, the requirements on any monitoring programme need to take into account any longer-lived radionuclides, particularly fission products, which may be relatively mobile.

Requirement 22 of SSR-5 describes the requirements on institutional control as:

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.

This requirement is particularly important for ILW which is disposed near surface.

Requirements 23 and 24 of SSR-5 address accounting and control of nuclear material, as well as considerations on security. Generally, these considerations are not so significant for ILW when compared with HLW. However, some ILW may contain radionuclides that are subject to these requirements.

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Requirement 25 of SSR-5 addresses the management systems that are important for any types of disposal facilities.

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4 ILW characteristicsA number of characteristics of ILW, including its non-radiological properties, need to be considered when selecting treatment, conditioning and disposal options and approaches, in particular:

Radionuclide content and activity, Waste volume and geometry, Physical, chemical and biological properties, Criticality, Heat generation, Chemo toxicity, and Gas generation.

4.1 Radionuclide content and activity concentrationThe radionuclides in ILW and the evolution of activity with time are important attributes in determining the extent of containment and duration of the containment period during which the waste must be isolated from the environment.

It is important to have information on the main groups of radionuclides including:

Uranium, plutonium and minor actinides such as americiumVery long half-lives for most of them, criticality, high toxicity which are import to consider in particular in relation to assessment of Human Intrusion scenarios.

Mobile radionuclides, activation or fission products, especially those which are long-lived such as Cl-36 and I-129

These radionuclides frequently dominate dose in normal evolution scenario, which may induce specific demands on containment.

Radionuclides with half-lives of the order of several hundreds to thousands of years, such as C-14, Am-241, Ra-226

They are important to define the timescale to be considered in relation to safety. Radionuclides which have the ability to generate significant amounts of radiation and heat e.g. Co-

60.This refers to the importance for radiation and thermal protection during the operational phase and potential thermal effects after closure.

In addition to the total amount of activities, it is also important to consider its distribution. Heterogeneity of the waste, for example content of high specific activity particles or items which may be particularly important for near surface disposal with regards to assessment of human intrusion scenario.

ILW with a low content of long-lived radionuclides may be suitable for disposal near surface . That with a high content of long-lived radionuclides needs longer containment and isolation from the environment, and therefore disposal at greater depth is necessary.

4.2 Waste volume and geometry The total amount of ILW (volume or mass) and the size of individual items need to be considered when choosing an appropriate disposal option. The disposal option designed for small number of sealed sources is

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likely to be different from a facility intended for the disposal of thousands of cubic metres from the operation and decommissioning of nuclear power plants.

For the design of the disposal facility, it is important to consider the total amount of waste to be disposed of. In order to estimate the amount of waste, it is important to consider that both the waste that exists today and that which will arise in future taking into account the on-going operation and decommissioning of existing and/or planned facilities. The current “Status and Trends” project in the IAEA Waste Technology Section is an attempt to consolidate a global inventory and future forecast.

Particular consideration may need to be given to the range of sizes of ILW, in particular to the management of large components. In some cases, segregation of waste according to size might contribute to optimisation of waste stream and the capacity of the disposal facility. Some large components may be cut down to facilitate handling and improve packing efficiency. In other cases, some large components may be considered for direct disposal without packaging, provided they meet the relevant WAC.

Voidage is also a significant factor with regards to mechanical stability, biological microenvironment and accumulation of gas.

There may be opportunities to reduce the waste volume and voidage through selection of appropriate predisposal options which are discussed in Chapter 6.

4.3 Physical, chemical and biological properties

ILW contains a wide range of materials depending on its origin. The physical, chemical and biological properties of these materials influence the selection of appropriate disposal concepts:

Inorganic or organic complexants present may affect the mobility of contaminants; Organic and some other types of materials may form complexants through

degradation processes. The most well-known example is the alkaline degradation of cellulose to isosaccharinic acid (ISA) which can increase the mobility of otherwise nearly insoluble radionuclides by many orders of magnitude;

Microbes developing in the waste may influence its evolution, for example, they may enhance the mobility of radionuclides and/or contribute to gas generation.

Some organic materials such as PVC may form corrosive species (for example hydrochloric acid) as they degrade under radiation or react in aqueous solutions, which may impact the engineered barriers;

Nitrate may affect the redox conditions and therefore influence the mobility of contaminants;

Metals may react with water forming expansive corrosion products and sometimes generating heat; these processes may degrade the functions of the engineered barriers.

Some particular wastes, such as bituminous wastes may also react with water and swell. Swelling can also be induced by radiolysis of some waste;

Chlorine may accelerate corrosion; ILW may generate gas by a number of degradation mechanisms (see later section

on gas generation);and A number of materials may contain or produce particles of colloidal size, which

might impact migration of contaminants. The dominant form of the waste (gaseous, liquid or solid)

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Some material types present in the ILW may also have positive effects for the containment of contaminants: for example cements may contribute to the maintenance of a high pH environment in which corrosion of metals is lower, and to the retention of contaminants through physical and chemical processes.

The physical and chemical properties of ILW may be modified by treatment and /or conditioning and may evolve during storage operations and with time after emplacement in the disposal facility. Liquid ILW is generally processed to a solid form using techniques such as immobilization in cements. Other ILW may be treated using processes such as incineration. Therefore it is important to consider the whole life cycle of the waste, including predisposal and disposal options, when deciding the management route for the waste and verify that the waste can meet the requirements of the WAC for the anticipated disposal facility (see Chapter 5.4).

4.4 CriticalityFor ILW with significant amounts of fissile material, criticality needs to be taken into account when considering its disposal. The distribution of fissile material within a single package and across the facility needs to be assessed with respect to criticality safety particularly in the event that the waste is exposed to water during or after disposal. The possible accumulation of fissile material within a package or elsewhere in the disposal system during the post closure phase also needs to be considered. It also needs to be considered the potential presence of neutron reflectors such as beryllium or other moderating materials such as graphite that may have an impact on criticality.

4.5 Heat generationThe classification of waste as ILW requires that it needs no or only limited provision, for heat dissipation during its storage and disposal. The amount of heat generation depends on the types and amounts of radionuclides in the waste (e.g. half-life, decay energy, activity concentration and total activity). If the ILW contains significant amount of radionuclides such as Co-60, Sr-90, Cs-137, Am-241 or Ag-108m, the heat generated may need to be considered in the design and operation of the disposal facility, e.g. by ventilation during the operational period, arrangement of heat-generating packages or disposal cells, or by limiting the inventory of heat-generating material in a package.

Graphite has the potential to combust, due to the stored Wigner energy it may contain.

4.6 ChemotoxicityIn addition to the radiological hazard, ILW may also contain chemically toxic components, such as heavy metals and small organic complexing agents. Contaminated asbestos may also be present in legacy facilities. These constituents may be persistent since their hazard potential remains constant with time, i.e. no decay is expected. In addition to radiological requirements, when disposing of ILW it is necessary to demonstrate compliance with relevant requirements, relating to chemical toxicity for example, with respect to the maximum permitted concentrations of particular chemically toxic materials in ground water or in drinking water. It should be noted that some elements such as uranium present both a radiological and a chemotoxic hazard.

IAEA-TECDOC-1325 describes the issues associated with the management of chemically toxic materials in LILW (add reference). It should be noted that waste conditioning may remove contribute to remove chemotoxic substances or contribute to delaying or preventing their release to the environment.

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4.7 Gas generationILW can generate gas by three main processes:

Metal corrosion,

Chemical or microbial degradation of organic components of the waste (cellulose, hydrocarbons), and

Radioactive decay (radon).

Gas generation may also occur as a result of radiolysis, especially if the ILW contains significant amounts of gamma emitters. Radiolysis-induced gas may need to be considered for operational safety, but in general, this effect would be expected to be minor after closure when compared with the processes above.

If gas is produced in large amounts, it could lead to a build-up of pressure that may be sufficient to damage the waste form or the surrounding barriers. Gas will tend to migrate by buoyancy and, where this occurs, it could disturb the surrounding environment. Some of the gases may themselves be radioactive, e.g. H-3, C-14 in carbon dioxide or methane, Rn-222.

Waste conditioning has the potential to affect gas generation. For example, cement-based material provides an alkaline environment, in which the corrosion rate of many metallic materials is low and the associated gas generation rate is also low. However, aluminium and magnesium in a cemented waste corrode readily in the high pH environment which can lead to the production of hydrogen gas. Therefore, other immobilization approaches may be preferred for these wastes.

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5 Preparing ILW for DisposalAlong with waste characterisation, the proper selection of predisposal options including treatment, conditioning, and storage may make a significant contribution to both operational and long term safety of a disposal system. All of these processes may be particularly beneficial for ILW due to its diversity and volume. However, it is noted that once the waste has been conditioned, the volume for disposal may be significantly greater than that of raw waste.

For the specific cases of decommissioning waste, there may be an opportunity to delay the waste arising, for example, by delaying the dismantling of nuclear facilities. This practice sometimes refer to deferred dismantling [reference to GSR Part 6].

5.1 Waste characterization

5.2 TreatmentTreatment of ILW may be beneficial for safety and/or economy by changing the characteristics of the waste. Treatment may result in volume reduction, removal of some radionuclides, and change in physical form and chemical composition. For example, ILW may be incinerated to remove organic and combustible materials and convert radionuclides into stable oxide forms. Large items may be cut into smaller pieces to optimize packaging and disposal operations. Treatment may also contribute along with conditioning to control free liquids in the waste.

If the hazard of the waste is reduced by treatment, it may also be possible to reduce the requirement on the containment system provided by both engineered and natural barriers. However, in evaluating treatment options, the consequences of chemical or physical reactions during waste treatment need to be considered, for example, radioactive gases (e.g. H-3 and C-14) may be released.

5.3 Conditioning Conditioning of ILW is important to produce a waste package suitable for handling, transport, storage and/or disposal, and typically includes immobilization of the waste and packaging in metal or reinforced concrete containers. Immobilization of ILW can increase its physical integrity and reduce potential for the dissemination of contaminants. It contributes to minimize free liquids in the waste package to prevent contamination and activity release in the case of any damage to the containers during handling and operation, and to prevent corrosion. Immobilisation also contributes to control residual void space. Voidage may affect the stability of the waste package during both operational and post-closure phases against subsidence. Voidage can facilitate the development of micro-environments within the waste package which may also be detrimental to long-term containment. On the other hand, voidage in a waste package can also be beneficial, e.g. to provide expansion space for degradation products, swelling. Consideration may need to be given to the homogeneity of waste package with respect to containment and to the position of centre of gravity in order to ensure that waste packages are stable during lifting and stacking (e.g. to avoid floatation of waste when grouting).

In selecting an immobilization material, its chemical and physical compatibility with the waste and the surrounding engineered and natural materials need to be considered. Cement is widely used as a fixing material and offers a number of potential benefits, including neutralising acids present in or generated by the waste and providing a chemical environment in which the corrosion rate of many metals is reduced.

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However, other materials such as glass, ceramics, and polymers may be preferred for specific types of ILW. Bitumen has also been used for certain waste.

Packaging waste in containers contributes to control of the gross weight of the waste package and facilitates standardization of package dimensions and lifting mechanisms for handling, transportation and emplacement. This is particularly useful for ILW due to its diversity. Containers need to be designed to provide sufficient containment of contaminants during normal operations and in the event of an incident such as fire or impact. In addition, containers may also be designed to provide shielding. For some wastes types, for example those containing bitumen, the container may contribute to limit the increase of temperature of the waste in the case of a fire in the facility. ILW containers are usually made from metal or reinforced concrete. Mild or stainless steels are commonly used, although copper is occasionally considered for ILW. The choice will depend on both the characteristics of the waste and the containment capacity of the host rock and other engineered barriers.

In selecting the container and immobilization material, consideration also needs to be given to any potential contaminants present within them (e.g., heavy metals) particularly if the contaminants are or may become mobile. This is particularly relevant for near-surface disposal.

It is generally required for safety that the integrity of the waste package is maintained at least for the duration of the operational period. During this period, the waste packages need to withstand any incidents during handling and operation, such as fire or drop/impact events. The stability of the facility with respect to subsidence needs to be considered as part of the assessment of the post-closure safety. This assessment will also need to consider voidage that may exist or form within or between the waste for example, as a result of organic degradation

Disposal concepts for ILW typically involve the stacking of containers to optimise the disposal capacity. Therefore, the waste package needs to have acceptable structural integrity and compressive strength to ensure the can be safely stacked.

Furthermore, in some disposal concepts, particularly for near surface disposal, the container has a role as a barrier after closure delaying the release of radionuclides and therefore allowing short-lived radionuclides to decay before there is any migration to the environment. In these cases, container lifetime is one component used in the post-closure safety case. For near surface especially, the waste package may also provide structural support for the cap and cover system (to prevent subsidence). This structural support is less important for deep facilities which rely on cap rock for support.

For metallic containers, corrosion performance is an important indicator of container integrity and lifetime. It is essential to establish underlying corrosion scenarios, considering swelling, gas generation and loss of integrity, that contribute to container failure for the various types of material. Carbonation rate degradation due to chemical and mechanical attack and corrosion of reinforcing metals need to be considered in order to estimate the lifetime of concrete containers. On the other hand, polymer-container materials (for example High Density Poly Ethylene (HDPE)) are not susceptible to corrosion; although creep, embrittlement, and irradiation-induced degradation can affect their durability.

The safety functions of the waste package are provided by the combination of the form of the treated waste, its immobilization and the container. There may be trade-off between the properties of the immobilized waste and the requirements on the container. Moreover, if the containment performance of the waste package is increased by conditioning options, it may enable the requirements on other engineered and natural barriers to be less demanding. If the other engineered and natural barriers are strong, it may reduce the requirements for conditioning.

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5.4 StorageStorage prior to disposal can offer benefits for the design and operation of disposal facilities for some types of ILW. For example, thermal outputs at disposal can be reduced, especially from wastes with a high content of Co-60. Storage may allow the quantities of radiolysis-induced gases and short-lived radionuclides such as H-3 to be reduced prior to disposal. More generally, storage of ILW is essential where waste is being generated and conditioned before an appropriate disposal facility is available.

Storage period of ILW to be disposed in geological disposal facilities may be anticipated to be longer than that for near surface facilities as the timescales for the development of geological disposal facilities tends to be longer, often for several decades. Therefore, the waste package needs to be designed to take account of the anticipated storage timescales prior to disposal, the storage environment and handling requirement. IAEA Safety Guides WS-G-6.1 further provides guidance on storage of radioactive waste, which is also applicable to ILW.

Storage of ILW may require remote handling due to radiation fields. Optimization may be required between use of self-shielded packages and shielded storage facilities. This optimisation may also be relevant when selecting transportation packages. In the case of decay storage for high dose rate, but short-lived waste, a shielded storage facility may be better than self-shielded waste packages since the amount of shielding required (and hence waste package size and mass) at time of disposal will be significantly less at time of disposal than time of first storage.

[5.5] Waste acceptance criteria for disposal, Identification and compliance with waste acceptance criteria for disposal

Waste packages have to meet the WAC of the individual storage and disposal facilities, which can vary widely in their design complexity. Further information on WAC can be found in IAEA TECDOC 1572.

Quality control of waste packages is important to enhance the confidence that an adequate level of performance can be achieved.

A key step in preparing ILW for disposal is the preparation of comprehensive documentation describing the origin and characteristics of the waste as well as the history of its treatment and conditioning. In order to ensure traceability, each individual waste package needs to be uniquely identified at every step up to its final emplacement at the disposal facility. As the waste management may take place over several years or even decades, appropriate measures to ensure maintenance of records over the required time frame is essential including any arrangement related to the transfer of ownership or responsibility regarding waste management.

Note for WG activities: To include table 4.1 of draft IAEA report of ….. WAC to be ILW specific as much as possible.

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6 Disposal Options6.1 Principal safety functionsContainment and isolation are the principal safety functions of any disposal facility. The choice of disposal option, concept and design of the disposal facility needs to ensure that these requirements are met during operation and after closure of the facility.

Containment can be defined in (IAEA Safety Glossary as methods or structures that perform a confinement function, namely preventing or controlling the release of radioactive substances and their dispersion in the environment. Although related to confinement, containment is normally used to refer to methods or structures that perform a confinement function, namely preventing or controlling the release of radioactive substances and their dispersion in the environment.

Isolation is defined in SSR-5 and SSG-14 as retaining the waste and keeping its associated hazard away from the biosphere in a disposal environment that provides substantial physical separation from the biosphere, making human access to the waste difficult without special technical capabilities, and restricts the mobility of most of the long lived radionuclides.

The disposal system needs to provide a combination of natural and engineered characteristics to support efficient containment and isolation of the waste by maintaining package integrity, limiting the solubility of radionuclides and the waste form, minimizing where possible groundwater inflow and/or providing a long travel time for radionuclide transport from the disposal facility to the biosphere. In the long term, progressive degradation of the engineered barrier system cannot be ruled out and, consequently, radionuclides may be released and eventually migrate to the biosphere. Materials used for backfilling, sealing and capping need to have properties that do not degrade unduly the safety functions of the barriers.

As discussed in Chapter 2, timescales for isolation and containment of ILW are a function of the half-lives, activities and types of the radionuclides contained in the waste to be disposed of. Containment performance of the disposal facility needs to account for the properties of the contained radionuclides in relation to their mobility potential.

6.2 Available Disposal OptionsAn important factor in the management and disposal of ILW is the concentration of long lived radionuclides in the waste stream. Radioactive waste with a limited concentration of long lived radioactivity may be suitable for near-surface disposal.

If the waste requires isolation and containment for a period of the order of hundreds of thousands of years, it will require geological disposal at a sufficient depth with regards to the local geodynamic evolution. Wastes with an assessment timescale considered for safety which is within a glaciation cycle (up to around 100,000 years), may be suitable for disposal at a shallower depth. The depth of the disposal facility in this case needs to be justified considering the site condition and geodynamic evolution taking into account the assessment timeframe necessary for safety. Over these timescales, some radionuclides with half-lives of the order of several hundreds to thousands of years, such as C-14, Am-241 and radium bearing waste containing low amounts of uranium, will have been substantially decreased. For wastes with higher amounts of uranium, the ingrowth of Ra-226 needs to be considered.

Containment derives from a multi-barrier system that employs both engineered and natural barriers to achieve the required safety. The role of the barriers, engineered and natural, in providing containment will depend on the disposal option, the properties of the natural surface and underground environment and the radiological inventory, particularly with respect to half-lives and the mobilities of the radionuclides.

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An overview of the various disposal options is given below. Additional information is available in IAEA publication, NW-T-1.20 Disposal Approaches for Long Lived Low and Intermediate Level Radioactive Waste.

It is noted that not all of near-surface disposal options described in the following sections may be appropriate for ILW disposal. The choice of appropriate disposal options will depend on the assessment timescale, requirements for containment and isolation, and safety assessment.

6.2.1 Near surface optionsAs stated in SSR-5 and SSG-29, a near surface disposal is a facility consisting of engineered trenches or vaults constructed on the ground surface or up to a few tens of metres below ground level. These near surface disposal options are the most vulnerable to external phenomena which constrains the types of wastes that can be disposed of.

IAEA Technical Reports Series No. 412, Scientific and Technical Basis for the Near Surface Disposal of Low and Intermediate Level Waste describes that near surface disposal options include two main types of disposal system: (a) shallow facilities consisting of disposal units located either above (mounds, etc.) or below (trenches, vaults, pits, etc.) the original ground surface; and (b) facilities where the waste is emplaced at greater depths in rock cavities or boreholes. In the first case, the thickness of the cover over the waste is typically a few metres, whereas in the second case, the layer of rock above the waste can be some tens of metres thick. These depths can be contrasted with the case of geological disposal of long lived radioactive wastes, where the wastes are emplaced at depths of hundreds of metres.

Advantages of near surface facilities are that they may be quicker or more economical to site, construct and operate.

6.2.1.1. Landfill disposalA landfill disposal facility often contains no complex engineered barriers or elaborate sealing. Therefore, adequate WAC and quality control are needed to ensure that the radionuclide content, especially the content of long lived activity, remains at levels compatible with the limited containment and isolation capabilities of the design. Particular attention needs to be paid to surface phenomena that can reduce the degree of isolation and containment of the waste, with particular reference to the extreme meteorological events, flooding, and erosion and , phenomena related to hydrogeological instability. Surveillance and monitoring are required during the period of institutional control.

This disposal concept is not generally considered as a disposal option for long-lived ILW.

6.2.1.2. Trench disposalTrench disposal is an option usually used for waste with higher radioactive content than waste associated with landfill disposal. The trench can be divided into individual compartments to increase radionuclide containment and flexibility of operation and may be lined if required for mechanical stability or to enhance containment. After filling, a waterproofing top cover is installed. Surveillance and monitoring are required after closure during the period of institutional control. The WAC also will limit the type, concentration and quantity of radionuclides allowed in waste packages, reflecting the limited retention capability of this type of site. Particular attention is required to surface phenomena that can reduce the degree of isolation and containment.

6.2.1.3. Engineered vaultAn engineered surface disposal facility of the vault type provides more robust engineered barriers that aim to provide greater measure of containment and isolation compared with landfill or trench disposal. These

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facilities are principally intended for the disposal of short-lived waste with the activity of long lived isotopes being limited to low concentrations.

Engineered vault facilities may be equipped with surface barriers (caps), vertical barriers (cut-off walls) and sub-horizontal barriers (floors). These features may contribute to reduce the amount of water which contacts the waste and to retard migration of radionuclides. They also provide protection against intrusion of human or animals. After the waste is disposed of, the void spaces in vaults are usually filled with grout or some other backfill material. The engineered barrier system may include drainage collectors to channel out infiltrating water. Underground galleries or other detection systems such as drainage with monitoring or leak detection may be installed to allow the functioning of the barriers to be checked. Additional barriers might be constructed around the disposal vault to control the movement of water. Particular attention is required to surface phenomena that can reduce the degree of isolation and containment.

6.2.1.4. Near surface underground disposal facilitiesNear surface underground disposal facilities can be developed either in natural or excavated cavities in various geological formations. The construction and operation of such facilities require access tunnels, ramps or shafts. In general, isolation capability of the facility tends to increase with depth.Isolation capability of the facility increases with depth. Contribution of the host formation to containment depends upon its geological and hydrogeological properties. The engineered barriers also contribute to containment.

There is generally an increase in isolation and containment function provided by the natural barrier between near-surface and geological disposal.Other issues such as complexity in construction, operation and closure

There is a gradual smooth transition with no clear boundary between near surface underground disposal facilities and geological disposal facilities with respect to containment and isolation as well as other issues such as construction, operation and closure. Definitions for depth ranges of both near surface and geological disposal facilities vary from country to country depending on national contexts. Consistently with SSR-5, it is not appropriate to set a firm threshold at the international level. Instead, the definition needs to be established on the basis of the local geological and geodynamic properties.

6.2.2 Geological disposalILW with higher contents of long-lived radionuclides is usually disposed of at depth in appropriate geological formations. In general, geological disposal facilities provide a higher level of isolation for longer periods of time than near-surface disposal facilities.

Human intrusion scenarios are a function of facility depth, as is the performance of isolation at any given time. Depending upon the depth of the facility and geological setting, intrusion by near surface human processes can be avoided.

A further characteristic of geological disposal is that the need for institutional control is much diminished - in most cases, the land can be put to a range of uses, including agriculture, after closure.

Containment provided by the host formation can be optimized by an appropriate location of the underground facility within the host formation which includes depth taking into account geodynamic evolution. Containment also relies on other factors such as the waste form and other engineered barriers for which depth induced stresses must be taken into account.

ICRP Publication 122 on the Radiological Protection in Geological Disposal of Long-Lived Solid Radioactive Waste indicates that “the goal of a geological disposal facility is to achieve the isolation and containment of the waste and to protect humans and the environment for timescales that are comparable with geological changes. At great distance from the surface, such changes are particularly slow (…)”.25 | P a g e

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Depending on its characteristics, geological disposal of ILW can be carried out in various designs of underground facilities. Disposal could be by emplacement in a facility constructed in caverns, vaults or silos. It could include purpose built facilities and facilities developed in or from existing mines. It could also include facilities developed by drift mining into mountainsides or hillsides. However, disposal in pre-existing excavations may be contemplated, but would need to meet the same requirements for safety (see SSG-14 para.1.9).

6.2.3 Other disposal options

6.2.3.1. BoreholesDisposal of ILW in boreholes drilled from the surface may be a suitable option where waste volumes and diameter of waste packages are limited (e.g. disused sealed sources). The required depth of the borehole will depend on the characteristics of the waste and local geological and environmental conditions. Sealing of the boreholes after wastes have been emplaced is particularly important for the purposes of containment and isolation. Further information on borehole disposal is given in IAEA Specific Safety Guide SSG-1, Borehole Disposal Facilities for Radioactive Waste.

6.2.3.2. In-situ immobilization

A number of practices for in-situ immobilization of radioactive waste, including entombment of nuclear facilities, are available. They are not recommended practices in situations in which the options mentioned above are available or could be reasonably implemented, but they can constitute an acceptable practice for remediation purposes. This practice is out of the scope of this document, and therefore it is not discussed further.

6.3 Factors for the selection of a disposal optionThe selection of an appropriate disposal option for ILW must firstly be based on safety considerations. It may also depend upon aspects that are related to waste inventory, economic considerations and social acceptability reflecting the national context.

6.3.1 Safety related factorsAppropriate disposal options will depend upon a number of safety related factors. Recognition of safety related factors will enable the identification of appropriate options. Important factors include:

Radiological characteristics of the waste (half-lives and activities) Chemotoxic characteristics of the waste The amount of mobile or potentially mobile radionuclides in the wastes The physical and chemical form of the waste, including the distribution of radioactivity The characteristics of the site and its surroundings (geological setting, hydrogeology and

environmental factors) The timescale and degree of containment provided by the disposal option, including its evolution The degree of isolation provided by the disposal option (depth in particular)

Identification of appropriate disposal options may result from an analysis of all individual factors and an assessment of the compatibility of each factor with the others. Safety-related factors will determine that, while ILW with lesser amounts of long-lived radionuclides are may be more appropriate for near surface facilities, those with greater amounts of long-lived radionuclides are more appropriate for geological disposal.A suitable combination of waste form and engineered barrier system may allow an increase in the specific activity of long lived radionuclides that can be accepted for disposal at a given site.

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Segregation of ILW streams with different characteristics may enable each disposal option to be tailored more effectively. For example, a portion of ILW may be suitable for near-surface disposal. Segregation of ILW streams may also allow more effective use of facilities.. The principle of iterations addressed in Requirement 11 in SSR-5 (see Section 3.4) may also be applied to define appropriate segregation.

6.3.2 Waste volume related factorsWhere there are several appropriate disposal options for ILW with regard to safety, the waste volume may influence the selection of disposal option, of one or several dedicated ILW disposal facilities, or co-location of some ILW with LLW or HLW disposal facilities. Factors to be considered here are waste inventory and potential interactions between co-located wastes. Section ??? provides additional information on the potential interactions..

6.3.3 Economic and technical resourcesCost considerations in the development of an ILW management strategy are an important aspect in managing national liabilities and resources, but must not preclude achieving an acceptable level of safety which complies with national policy and lies within the country’s legal framework. Because skilled personnel are needed to design, construct, operate and close a disposal facility, their availability their availability needs to be considered early on in the development phase and thereafter.

Disposal facilities generally have high fixed costs that are largely independent of the volume of waste. Therefore, significant economies may be achieved if a disposal facility is shared for different types of waste (for example co-location of ILW with LLW or HLW) or existing facilities are expanded instead of iplementing a new facility. If it is decided to co-locate facilities, it should be confirmed that the safety of any co-located facilities are not compromised. IAEA TECDOC 1552 provides further guidance on this aspect. (add reference to TECDOC-1552).

6.3.4 National policy and social aspectsThe national radioactive waste management policy of a Member State may prescribe or proscribe radioactive waste disposal options for ILW. For example, near surface disposal of ILW might be acceptable for safety and economic reasons, but national policy may require deep geologic disposal. Legislative aspects may also constrain the siting procedure and programme development for ILW disposal. IAEA INSAG-20 and NG-T-1.4 provide additional information on this topic (add reference).

It is important that stakeholder involvement is taken into account in the decision making process. Public acceptance is an important factor that may influence decisions.

The choice of disposal options and design of the facility need also to take account of any national requirements with respect to reversibility or retrievability. Note that the drivers for retrievability for ILW may be different than those for spent fuel, particulary with respect to its potential future value as a resource. In all cases, it has to be ensured that reversibility and retrievability do not jeopardize the safety of the facility. Further information can be found in NEA 7085, OECD 2012, Reversibility of Decisions and Retrievability of Radioactive Waste – Considerations for National Geological Disposal Programmes). IAEA NW-T-1.19 and NG-T-1.4 provide additional information on this topic (add reference).

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7 SitingSiting is a fundamentally important activity in the development of any disposal facilitiy, either near surface or geological. In site selection, one or more preferred candidate site(s) are identified on the basis of environmental and geological setting and with account taken of other factors. In addition to safety, sociopolitical factors may also be an important consideration in any site selection process (e.g. social acceptance, transport infrastructure, existing land use).

Site selection for ILW disposal needs to take into account specific requirements related to these wastes in terms of isolation and containment and related timescales required for isolation and containment as well as compatibility with volume, chemical and physical properties of the waste. This concerns both current natural properites of the site and their expected evolution over time. The consideration of the consistency of the site properties with the requirements for safe disposal of the ILW may take into account potential trade-offs between engineered and natural barriers.

The main natural factors to be considered are common to both near-surface and geological disposal facilities. However, depending upon the disposal options being considered, there may be differences in the weighting of the factors being considered. For example, the stability of the surface enviornment would generally have a greater impact on the safety of a near surface disposal facility than a geological disposal facility, which would be focused more upon the geological stability of the underground environment.

Siting of any disposal faciity is usually carried out as a stepwise process, with the level of detail in the understanding increasing as the process proceeds. This process is described in SSG-14 and SSG-29 as follows:

”In the siting process for a radioactive waste disposal facility, four stages may be recognized: (i) the conceptual and planning stage, (ii) the area survey stage, (iii) the site investigation stage, and (iv) the stage of detailed site characterization leading to site confirmation for construction of the disposal facility.”

The level of understanding which needs to be achieved in site characterisation is set out in Requirement 15 of SSR-5:

“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 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.”

7.1 Site natural propertiesNatural properties of the site relevant to an ILW disposal facility that have an impact on containment are listed in SSG-29 and SSG-14 for near-surface and geological disposal facilities respectively. They include:

geology, hydrology and hydrogeology, geochemistry, tectonics and seismicity, geomechanical, thermal, and

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surface and meteorological processes (mainly for near-surface disposal).

To guarantee sufficient isolation the natural properties of the site must be favourable. Considerations will include the necessary depth of the facility to achieve containment and separation from the biosphere and the absence of significant, favourable characteristics for containment need to occur at a depth which can provide the required separation from the biosphere and the absence of significant natural resources for materials, energy or other potential uses of the space (e.g. for underground storage).

The likelihood ofAvoidance of human intrusion may not just be depth dependent. For sites remote from human populations, the need to take active measures to avoid human intrusion may be different from sites located near populated areas, provided a limited timescale for the safety case is appropriate due to the short lived nature of the waste.

The size of the site must be sufficient to accommodate the volume of the waste to be emplaced. For co-location of ILW with either LLW or HLW, the site must be sufficient to accommodate the adequate spacing of the different types of waste, to ensure that there would be no significant adverse reaction between them.

Geological disposal provides a higher level of isolation for ILW. than near surface disposal. Favourable geological contexts are ones in which the migration of contaminants are strongly reduced due to the characteristics of the rock matrix (low permeability, presence of minerals capable of attenuating radionuclide mobility, etc.) and the absence of preferential paths of flow. Some ILW contains a significant amount of long-lived and potentially mobile radionuclides, such as Cl-36 or chemical contaminants such as nitrates or lead. For these wastes, the geometry of the host rock and presence of features which will delay and/or mitigate the migration of mobile radionuclides and other contaminants (for example volume of intact rock, frequency of conducting fractures, thickness of sedimentary layers as host rock or in overburden) are particularly important. Similar features would also be help to compensate for the presence of complexants and organic materials in the ILW.

Where colloids may be present in the ILW, the mobility of these particles in pores or natural fractures and their ability to transport radionuclides needs to be investigated.

Sorption in the host rock can be a favourable attribute for the retention of some radionuclides in ILW, such as aqueous C-14, radium and actinides. The presence of minerals such as iron oxide and clay phases are therefore important.

Redox conditions may also be important for containment of some radionuclides, particularly the actinides. For near-surface disposal, the impact of saturation/desaturation cycles along with climatic variation may need to be taken into account.

The redox buffering capacity of the host rock may compensate for the presence of oxidising agents, such as nitrates in the waste.

Geomechanical properties are important for construction and may dictate, for example, the maximum size of vaults, their separation and the migration properties and extent of the damaged zone. The EDZ is a particularly important consideration for ILW with a high content of mobile radionuclides and/or producing particles of colloidals size. The potential swelling of some waste and the expansion of corrosion products may also require consideration with respect to the mechanical properties of the host rock.

A particular feature of some ILW is its potential to generate gas. The permeability of the host rock with respect to gas and its ability to withstand gas pressure are therefore significant considerations in these cases.

Whilst less significant than for HLW, heat generation may still need to be considered for some ILW. The thermal conductivity of the host rock and its response to an increase in temperature, for example THM interactions in porous materials, may require consideration.

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Although both near surface and geological disposal options have similar factors that must be considered with regards to site natural properties, depending upon the disposal options being considered, there may be differences in the weighting of these factors considered. For example, a near-surface disposal facility would consider that the properties of the surface environment would have a greater impact on safety than for a geological disposal facility, which would be focused more upon the geological characteristics of the underground environment.

Specific site properties are required to be assessed in the safety case and safety assessment.

7.2 Site evolutionIn selecting a site for ILW, it is important to consider not just the current status of the site but also its expected evolution over the time period for which isolation and containment of the waste will be required.

The future evolution of the site will be influenced by existing environmental processes, future climate change and geologicgeological processes. Future climate change may affect precipitation/recharge, permafrost, glaciation, sea level change, weathering and erosion. As to geologicgeological processes, significant uplift/subsidence, unfavourable features such as active faults and active volcanoes should be avoided. MoreoverHowever, indirect effects from active faults, active volcanoes or other tectonic processes that may be occurring within the region should be considered.

For a near surface disposal facility in particular, an understanding of existing environmental processes such as erosion by rain, or weathering or water bodies are most important factors affecting the evolution of the site over the relevant timescale of the next few hundreds to thousands of years. For geological disposal, the relevant timescales are much longer and therefore future climate and geological processes become significant.

7.2.1 Precipitation and rechargeOne potential impact of climate change is alteration of the magnitude and/or distribution of precipitation. In cases of significant precipitation or where groundwater is recharged via other mechanisms, the height of the water table can increase. This may influence the hydraulic gradient and therefore the groundwater movement, especially for near-surface disposal.

In situations where the water table level is low or decreasing, oxidizing or unsaturated conditions could develop deeper into the underground environment, changing the redox conditions and therefore the mobility of radionuclides.

Therefore, groundwater levels and their potential for change within the time period relevant for safety of the ILW disposal needs to be considered when selecting the appropriate disposal option and designing the facility, particularly for near-surface disposal of ILW with significant amounts of redox sensitive radionuclides.

7.2.2 Permafrost and glaciationMaterials used during the construction of the disposal facility may be impacted by permafrost and/or glaciation. If permafrost or glaciation occurs, there would be a reduction in hydraulic conductivity of the area being impacted. Additionally, glaciation could have the effect of forcing the injection of oxic glacial (melt) water deep underground affecting geochemical conditions.

The development of ice sheets may also significantly alter the stresses on the natural environment and engineered barriers and/or erode or otherwise reshape the superficial geology to a significant depth.

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When determining the depth of the disposal facility, these factors will need to be considered. The depth of the disposal facility may need to be increased in order to achieve a permafrost free environment and/or reduce the likelihood of or consequences of other changes during the time period relevant for the safety of the ILW disposal. Surface facilities should be avoided if the required timeframe for isolation and containment extends beyond the expected date of the next glaciation.

7.2.3 Sea level changeSea level change could alter the migration of radionuclides including the discharge environment where they may return to the surface. This merits particular consideration in the case of long-lived ILW as the time periods to be addressed for safety are very long.

In the case of sea level reduction, the hydraulic gradient could increase resulting in a decreased water table impacting the existing redox environment, chemical composition of groundwater (including salinity), as well as surface hydrology.

Sea level rise, from global warming for example, could decrease the hydraulic gradient, increasing the water table resulting in associated changes to the chemical composition of groundwater.

7.2.4 WeatheringWeathering of rock may alter the geology, hydrological/hydrogeological properties, existing redox conditions, migration potential of the radionuclides and mechanical properties up to 100m from the surface. It is particularly important when considering near-surface disposal of ILW where the time period to be considered is relatively long.

7.2.5 Uplift/erosion, faulting/folding and subsidence/sedimentationAt some locations, uplift/erosion and the movement of faults/folds are important considerations in the long term safety of a disposal facility. Uplift followed by erosion could reduce the geosphere/host rock thickness and alter the hydrological/hydrogeological properties, affecting existing redox and geochemical conditions.

On the other hand, subsidence/sedimentation could increase the disposal facility depth and generally work favourably to safety, unless rock stress increases to a level that is detrimental to the disposal facility.

In mountainous areas, the possibility of a large-scale landslide and any associated impacts may need to be evaluated.

Glaciation is an important cause of uplift and erosion (see Section 7.2.2).

7.2.6 Other tectonic related processesDepending on geology and tectonic setting, following processes may need to be considered;In salt formation, salt diapir may act similar way as uplift and consequently decrease repository depth coupled with erosion.

In unconsolidated rock region, if mud diapir directly hit the repository, it may cause degradation of engineered barrier system and/or may even bring wastes to surface. In tectonically active country, active faults and active volcanos should be avoided in the siting process, however even after avoiding these features, indirect effects such as head change and liquefaction due to seismicity, and hydrochemical change due to volcanic activity in adjacent area may need to be evaluated.

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7.2.7 Impact of geodynamic evolution on the consideration of human intrusion

The likelihood of human intrusion may be impacted by site evolution processes including glaciation, sea level change, and uplift/erosion. This issue needs to be considered over the timescale relevant for the radiological content of the ILW, especially for near-surface disposal. More detailed discussion on human intrusion is undergoing as HIDRA project (human intrusion in the context of disposal of radioactive waste) [refer to HIDRA webpage].

AsAs of 2014, currently, the IAEA has organized an international project focusing on human intrusion for various types of waste disposal facilities, which is called HIDRA Project (human intrusion in the context of disposal of radioactive waste). The HIDRA project is focused on various issues such as the difference and commonality of human intrusion scenarios for geological and near-surface disposal facilities and approaches that have been used for such assessments in different countries.”

[7.2.6] Natural and social environmentIn addition to geological considerations, there are a number of other factors which need to be taken into account in the siting of any disposal facility, including ILW. The relevant factors apply to both near surface and geological disposal and include:

existing and future land use; proximity to population, especially urban centres transport of waste, including ease of access to existing or new transportation networks; protection of environmentally-significant sites

SSG-14 and SSG-29 provide detailed guidance on these considerations.

For ILW containing or generating gaseous radionuclides, control of environmental impacts of possible releases of radioactive gases during the operational phase may need to be considered.

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8 Disposal Facility Design for ILW8.1 Design processDesign development in radioactive waste disposal is an iterative process involving regular testing of the proposed solution for compliance with the requirements and feasibility of implementation with respect to both technical and economic aspects. The principal requirements on the disposal facility relate to safety. Therefore, the iterations are driven by the safety case.

Feedback from the design cycle is used to refine the requirements and optimise the solutions. In the early stages of the development, the focus is more on clarifying and increasing details of the requirements. As the design process becomes more mature, increased emphasis is placed on detailing and optimising solutions.

8.1.1 Requirements on the disposal facility Developing disposal designs firstly requires a compilation of a comprehensive list of the functions and requirements that are applicable to each stage of the facility lifecycle: construction, operation, closure and post-closure. The external requirements to be considered in the design of a disposal facility arise from the following sources:

international and national standards, regulations, and guidance, waste inventory and characteristics, constraints from the selected site, and stakeholder expectations, especially those of a potential host community.

The requirements are progressively refined through the iterative process of design and safety case development.

The overarching requirements for the design of a disposal facility are given in SSR-5, Requirement 16 which states that:

“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. ”

The detail, whilst recognising that there is a wide range of design solutions, specifies requirements on the engineered barrier system, which needs to:

make optimal use of the safety features offered by the host environment; be designed so that it does not cause unacceptable long term disturbance of the site; be protected by the site; perform safety functions that complement the natural barriers; and have a layout designed so that waste is emplaced in the most suitable locations.

SSG-14 and SSG-29 contain guidance for geological and near-surface facilities respectively, but list a number of common requirements:

The design needs to take into account at an early stage of the types and quantity of waste that will be disposed at the site

In the course of the design of the facility, information about the waste needs to be used to support the identification of a concept and the actual design

The design needs to provide safety during both the operational and post-closure periods

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The design needs to take account of any requirements foro Monitoringo Accounting and control of nuclear materials, if necessaryo Concurrent underground activities (such as excavation and nuclear operations)o Any local requirement for retrievability and reversibility

The designs need to be developed in sufficient detail and accuracy to enable the effect of design requirements to be appropriately evaluated in assessments of operational and post-closure safety. In accordance with the stepwise approach to implementation, as the facility design evolves and becomes progressively more detailed over the phases of facility development, safety assessments need to be updated to evaluate the effects of design changes on compliance with regulatory criteria. Implementation of this requirement places importance on effective record-keeping (see Chapter 10).

The design for safety in the post-closure period needs to meet the precepts of robustness, simplicity, technical feasibility and passivity whilst that in the operational period will include both active and passive systems.

The licencing of a disposal facility will require an initial inventory of the waste which is planned to be disposed there, in terms of waste volume, waste types and physical and chemical content, including radiological properties. It is good practice to design the ILW facility in a manner which is sufficiently adaptable to incorporate a level of evolution in the disposal inventory, for example to respond to extensions in lifetime of operating nuclear power plants. The amount of waste being produced and the date of delivery to the facility will depend on a variety of factors, particularly for decommissioning waste. Therefore, it is often difficult to define the duration of the operational time period early in the planning phase. When extending the operational time period, the allowable extension must be assessed taking into account the planned life time of the waste handling, maintenance and support devices.

8.1.2 Design solution developmentThe selected disposal concept forms the foundation of the design considerations for an ILW facility. Concept selection is therefore an early step of the iterative process of design development. The concept is selected to provide the safety functions required for the specific waste type and form, site properties and their evolution and repository depth. In more advanced stages, the design becomes progressively more detailed consistently with the refined requirements derived from earlier iterations.

In addition to disposal volumes, design considerations need to address access ways, operating systems, services and support facilities. Those parts of the facilities located on the surface need to be properly interfaced with the surrounding environment.

8.1.3 Verification of complianceThe safety case and supporting safety assessment for a particular design will provide the demonstration of its compliance with safety-related requirements. The safety case and assessment (see Chapter 8.3) need to be supported by demonstration tests under appropriate conditions, as appropriate. For ILW, demonstration of an understanding of any interaction between the engineered system and the surrounding environment is particularly important.

Best practice suggests a stepwise implementation process, with the safety case being developed in increasing detail as knowledge of the engineered and natural systems matures and intermediate findings from the safety case development are used to refine and optimise the design in an iterative approach.

It will be important to demonstrate safety for the full range of ILW to be disposed in the various disposal options being considered.

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8.2 Safety considerations for ILW disposal facility design

8.2.1 Construction phaseSafety considerations during construction of an ILW facility are those related to non-nuclear industrial activities. Construction regulations apply and mining regulations may also apply to the construction of underground facilities depending on the national context.

8.2.2 Operational phaseThe main functions during the operational phase of the facility are to receive and emplace the waste, which requires constructing disposal capacities facilities and supporting and maintaining the resulting open structures or underground caverns as necessary until closure. A further function to be provided during operation is to backfill and cap or seal the excavations to the standard required to comply with post-closure requirements. Monitoring of performance is important to demonstrate that the facility is operating and evolving with time as planned. Retrievability may also need to be considered if this is required by national legislation or to meet stakeholder expectations.

All of these operational functions need to be performed in a way which ensures conventional and radiological safety and environmental protection consistently with Requirement 18 in SSR-5:

Operation of a disposal facility: 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.

The design needs to include systems to comply with the relevant operational safety functions. Typical safety functions for ILW during this phase are to:

limit the exposure of workers and the public to radiation, contain radioactive materials in a robust manner, dissipate gas produced from radiolysis and corrosion, provide for criticality safety, and dissipate heat, if any.

During operation of an ILW disposal facility, protection and safety has to be optimized so that the magnitude of individual doses, the number of people exposed and the likelihood of incurring exposures are kept as low as reasonably achievable, economic and social factors being taken into account. This applies to both workers and the public. In addition to nuclear safety, protection against non-radiological hazards must also be accommodated in the design.

Systems have to also be included to avoid, detect, and mitigate operational hazards such as fire, impact accidents from e.g. drops, explosion and external aggressive events such as seismicity or flooding. Particular consideration needs to be given to any hazards induced by potential interaction between different types of activities performed at the same time, such as disposal vault construction and waste emplacement.

For surface facilities in particular, planning for and management of extreme weather events during operation is important. Compared with similar LLW facilities, more consideration is required as the potential consequences of a failure in the engineered system may be more significant.

For a disposal facility, as for any other operational nuclear facility or facility where radioactive material is handled, used, stored or processed, an operational radiation protection programme, commensurate with the radiological hazards, is required to be put in place to ensure that doses to workers during normal operations are controlled and that the requirements for the limitation of radiation doses are met. In addition, emergency 35 | P a g e

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plans are required to be put in place for dealing with accidents and other incidents, and for ensuring that any consequent radiation doses are controlled to the extent possible, with due regard for the relevant emergency action levels.

Compared with HLW, gas production during operation from radiolysis or other causemeans may be a significant issue, where disposal of ILW is underground. Ventilation systems need to be able to dissipate gas effectively to eliminate the possibility of explosion due to a local build-up of hydrogen gas. Approaches to ensure the ongoing safety of the facility in the event of ventilation failure and during the closure process as ventilation is removed also need to be developed.

Depending on the specific waste types, management of criticality during operation may be important. ILW with a higher content of fissile material may be more suitable for underground disposal. Balancing the competing demands of maximising the cavern size for ILW and managing for criticality safety needs to be considered.

Whilst heat is not generally an issue for ILW, there may be cases where active management of the heat needs to be factored into the design for protection of workers and equipment during operation , in addition to the consideration on heat conduction into the host rock. Where the design incorporates a cement-based backfill, management of the heat generated during cement hydration also needs to be considered.

8.2.3 Post-closure phaseIn the post-closure phase, isolation and containment are provided through passive means. Multiple safety functions are required to provide robustness in safety. The requirements on the various components in order to achieve their contributions to post-closure safety depend heavily on the selected disposal option and on the properties of the chosen site. Therefore, the safety functions of containment and, as necessary, isolation, need to be broken down so that the contributions of the various components of the disposal system can be designed appropriately.

It is recommended that the features and processes are identified which may contribute to containment in the various parts of engineered and natural barrier systems, specifically:

factors which delay or reduce access of water to waste, such as container integrity and lifetime, factors which reduce the release of radionuclides into water, e.g. chemical conditions provided by

materials in the engineered barrier system, and factors which delay and limit migration of radionuclides, e.g. low advection and high sorption

provided by the engineered and natural barriers.

The weighting of the various factors and related requirements on the design will depend on the specific properties of the ILW to be considered:

materials that the ILW comprise of (e.g. metal, concrete, bitumen, glass etc.) and expected changes to them over timeframes relevant for safety (e.g. corrosion, dissolution, hydrolysis etc.),

major radionuclides contained within the ILW (e.g. mobile fission/activation products or actinides etc.),

chemical form of contaminants (e.g. oxide, organic complex etc.), and the physical form in the ILW (e.g. labile contamination, within immobilization matrix, in activated

metal etc.).

Consideration of these matters will enable waste-specific requirements for the post-closure safety to be derived. In turn, it enables the disposal option and engineering solution to be optimised.

Due to the potentially wide range and composition of ILW there is a need to consider various constraints such as chemical interactions between different waste types as well as between the waste and other engineered materials.

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Gas, heat and criticality management may continue to be important after closure. Under the anaerobic conditions which will develop after closure, a build-up of gas may damage the engineered barriers and/or alter the transport of radionuclides. Whilst not generally significant, thermal effects may be important for some specific ILW types and may also impact the engineered barriers and the host rock. Management options may include waste emplacement strategies which distribute the thermal loads across the disposal volumes and provisions for sufficient heat conduction within the engineered barriers. For ILW with a relatively high concentration of fissile material, the possibility of an accumulation of this material following degradation of the engineered structures needs to be considered in the design with respect to the criticality safety.

If a co-located facility is proposed, the design of the disposal facility and in particular the potentials of separation of waste types needs to ensure that interactions do not have significant adverse effects on safety.

8.3 Design considerations for ILW

8.3.1 General considerationsThe external volume and total number of waste packages is usually the most important determinant of the size of a disposal facility for ILW. Other factors are the shape of the packages and their handling requirements. In particular, for some types of ILW, the need for remote handling of packages may cause an increase in the excavated size of the disposal facility to provide space for handling equipment such as overhead cranes. Other related aspects such as transportation to the disposal facility may also influence the design For example, incorporation of shielding material into the waste package may increase the size and weight of waste packages on one hand. On the other hand, it can reduce the demands for remote operation or additional shielding.

As the volume of ILW for disposal is often significant, designs are often based on disposal pits or vaults, rather than individual deposition holes. The vaults are generally designed as large as possible to make effective use of the space but with consideration of criticality and dissipation of any heat generated by the ILW for underground disposal facilities. The excavated size may be limited by the in-situ stresses of the host rock at the disposal depth and also by the objective to limit mechanical disturbances to the host formation, which may increase the permeability of the rock in the excavation damaged zone (EDZ). The characteristics of the EDZ need to meet the requirements related to containment, e.g., the extent should be limited compared with the thickness of the host formation.

Because concepts based on large vaults are often selected for ILW, consideration may also need to be given to the extent of residual voidage in the disposal system at closure and the way in which it will evolve or increase further. Voidage may result in the establishment of a local chemical environment which may facilitate corrosion or microbial activity with potential impact on safety. A large volume of voids may cause structural instability which, in turn, may lead to collapse of the engineered system and potentially the host rock, depending on the characteristics of the facility design.

A particular feature of an ILW facility is the potential for gas generation. The facility needs to be designed to account for gas generation during operation, closure and beyond. During the operational period, the gas may be controlled by ventilation. After closure of the facility, it may be possible to manage gas by increasing the robustness of the engineered barrier system to contain gas, by providing space for gas accumulation, or by making provision for release considering the permeability to gas of the engineered barriers.

The potential for the degradation of the waste package and the dissolution and retention of radionuclides needs to be considered when selecting materials used to construct the disposal cells and pits. The difference in waste properties and volumes, between ILW and HLW may lead to the use of significantly different design and hence the materials used. On the other hand, materials used when designing for LLW and ILW are often similar due to the large waste volumes considered and in some cases due to co-location. A long containment period provided by durable waste packages may not be practicable for large volumes of long-

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lived waste. The engineered materials need to be selected taking into account potential chemical disturbances induced by the waste (e.g. nitrate resistant cement may be preferred for use with nitrate-bearing wastes).

Cement-based materials are often used for structural stability and/or to provide an alkaline environment in which the corrosion of many metallic elements is reduced. This is particularly relevant for ILW containing activated metal. It can also be favourable for the containment of actinides.. However, fluids present in a cement-based environment can react with other engineered components, especially those made of swelling clay, and with the surrounding geological environment. Any potential detriments from these interactions must be compensated for in the design. In some cases ‘low pH’ cements may be preferred.

When selecting materials for the engineered system for ILW, special consideration needs to be given to the evolution of the engineered barrier system. The waste containers maintain integrity during operations but, after closure, will gradually degrade and allow water to contact the waste. Corrosion products may interact with the barrier materials and impact on their containment performance. Bentonite swelling capacity may be reduced and cracks induced in cementitious materials. In cement-based systems, the cement may contribute to containment by buffering the groundwater to an alkaline pH. The cement gradually dissolves in this process and degrades. Therefore it is particularly important to reflect the requirements for long-term performance in the design basis.

Structural stability of the excavated volumes needs to be ensured during construction, waste emplacement, and during any period of planned monitoring or easy1 retrieval up to the time of backfilling or sealing. This requirement may be more demanding for underground near surface or geological ILW facilities than for those for HLW as the excavated caverns may need to be larger.

8.3.2 LayoutThe available area or geological volume may be a constraint on the facility design. The number and size of individual cells required for the waste volume, together with access routes and any requirements for any additional areas required for the performance or protection of the facility, determine the footprint of the facility and need to be adapted to the specific conditions at the selected site. Provision also needs to be included for any waste preparation and transfer facilities.

It may be useful to segregate different ILW streams which may interact, for example to separate organic containing wastes from radionuclides sensitive to complexing agents, such as plutonium. Similarly nitrate containing waste could be separated from those wastes which may be particularly sensitive to the presence of oxidants. The relevant separation distances will need to be defined during the design process, taking into consideration the waste characteristics and migration properties of the host environments. Any requirement for sealing materials in access tunnels to reinforce the separation would need to be decided at the design stage.

Where ILW is being co-disposed with other waste streams, the separation of the different wastes must be appropriate to ensure that there are no significant detrimental interactions, particularly thermal or chemical interactions. The layout may also be optimised with regard to the hydrogeological system as necessary.

8.3.3 Access ways Access to a near surface underground or geological disposal facility may be by horizontal tunnels, inclined ramps and/or vertical shafts. Selection of the location and design of the specific access way may be influenced by the characteristics of the site, including relief and depth and the presence of aquifers. Provisions in the location and design need to be made with respect to long-term safety. The cross section of the access ways need to take into account the maximum dimensions of waste packages that are planned to be accommodated during the operation of the facility and any associated shielding and handling equipment. The cross section of the access ways also needs to take into account any services provided, such as piping, ventilation ducting, wiring, etc, as well as passing bays for vehicles, space for pedestrians where needed, etc. The requirements for access ways to an ILW facility may be particularly demanding due to the potential need 1 Level 2 on the NEA retrievability scale38 | P a g e

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to handle large items. As a function of the specific rock properties of the host rock and any overlying strata, reinforcement may need to be incorporated in the design as required for the protection of workers during construction and for rock support during the operational phase.

8.3.4 Operating systemsWaste inspection, handling and transfer equipment at the disposal facility need to take into account all the different types of waste packages planned to be disposed of. Waste packages with higher surface dose rates may need remote handling and/or shielding, which must be designed to take account of waste package dimensions. Conventional health and safety needs to be considered in addition to transport and radiation protection regulations.

There may also be a need to consider some predisposal management activities, in particular conditioning, where this is carried out at the disposal site.

One main difference between HLW and ILW is the larger variety of waste types that need to be managed in ILW disposal. This larger variety of waste types is also commonly found in LLW disposal. This variety of waste types results in a potentially large variety of waste packages in terms of dimensions and shapes and also in terms of dose rates. Some packages may be suitable for direct handling, whilst others must be managed remotely or with additional shielding. When designing handling equipment and other parts of the disposal system, this has to be taken into account.

In addition, there may also be a desire to dispose of large components (e.g. pumps, steam generators, pipes) intact to minimise dose to decommissioning workers or for reasons of cost and time efficiency. Sometimes these components may not be packaged.

The disposal of large components or waste packages may create operational issues, both radiologically and logistically. These large components may need additional shielding as workers may have to operate close to the component. The handling of large components may also place other requirements on the disposal system, such as the installation of a ramp as opposed to a shaft.

Waste packages may need to be delivered at the disposal facility at a time when it is suitable for the waste producers. Therefore temporary accommodation of the waste may need to be considered at the disposal site prior to emplacement, if compatible with the national strategy.

Electrical and mechanical installations need to be of a standard suitable for radiation-controlled environments. Systems need to be included to limit and control hazardous substances such as explosive or flammable materials. Selection of designs which contain inherent prevention of hazards such as fire can be preferable especially for ILW that are sensitive to temperature (e.g. concerning bituminous waste).

Detection systems of a suitable sophistication to give early warnings of hazards need to be employed. Should a hazard occur, appropriate mitigation systems need to be provided. Particular challenges for ILW when compared to HLW may include fire, gas generation, airborne radioactivity and the potential .consequences of accidents which result in loss of containment.

The key function of the ventilation system is to provide a safe environment for the operation of the facility. Particular demands may include dust or particulates from construction, exhaust gases and heat from equipment which may be larger for ILW than other waste and management of any gas generated by the waste. The design of the ventilation system potentially needs to consider filtration systems for the management of particulates, which could also be generated during normal operating and accident conditions. Consideration needs to be given to potential drying and shrinkage of cement based components and the host environment due to ventilation.

The long operating lifetime of many ILW facilities means that maintenance and refurbishment of the operating system will be required and provision for this needs to be included in the design solution.

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8.3.5 Backfilling, capping and sealingThis comprises the backfill, seals and caps to be constructed during and after waste emplacement in order to provide the required isolation and containment after the facility is closed. The requirements for this activity are driven by the post-closure safety functions and will depend on the characteristics of the ILW being disposed and on the disposal option and concept.

The re-use of excavated materials may be considered if they fulfil the safety function. In that case, some protection of this material may need to be provided during storage in order to facilitate its reuse.

Particular attention may need to be given to the expected performance of the backfill around non-standard waste packages particularly for large items.

Consideration also needs to be given on the sealing of any exploration boreholes in the vicinity of the facility.

Requirements for these activities for ILW are generally more demanding than for other waste types as the hazard is higher than for LLW and the dimension are typically larger than for HLW facilities.

8.3.6 Monitoring and retrievabilityRequirements for monitoring and retrievability are influenced by national legislation and stakeholder expectations. Monitoring and retrievability may be required to contribute to confidence building and to decision-making during stepwise development of a facility.

ILW packages are typically less robust than HLW packages and contain more activity than LLW. Therefore, monitoring of container evolution and integrity may be particularly relevant.

Some ILW packages may generate gas, which may be radioactive or non-radioactive. There may be a need to monitor gases during the operational period.

There may also be a need to undertake other engineering and system monitoring (e.g. temperature, strains rock movement, water ingress).

8.3.7 Management of concurrent construction and operation

On the surface, the construction zone can be separated by fences from the operational area to limit unnecessary traffic between the two zones and to ensure separation of personnel, equipment and materials. In a geological or underground near surface facility, separate access tunnels and ventilation systems with limited and controlled connection between them are sometimes used and access to them may also need to be separated at the surface.

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9 Safety Case DevelopmentSSG-23 is fully applicable to the development of the safety case and safety assessment for ILW. Therefore, this chapter only focuses on the aspects that are specific to the ILW.

9.1 Iterative Approach of the Safety Case SSG-23 states in paragraph 4.20 that;

“The safety case will be developed as the project progresses and will be used as a basis for decision making, for both regulatory decisions and other decisions relating to, for example, the design, supporting research work or site characterization activities. The context for each revision of the safety case should be set out clearly and should be updated as necessary and appropriate for subsequent revisions of the safety case.”

Paragraph 4.21 of SSG-23 states

“The purpose of each revision of the safety case will depend on a number of factors, such as the stage of development of the disposal facility, and whether the safety case is to be submitted to the regulatory body as part of a formal licensing procedure or to obtain directions from the regulatory body. For each revision of the safety case, the operator should provide a clear description of its purpose, which, depending on the stage of development of the facility”

Among the issues addressed in this paragraph, the following needs particular consideration for specificity of ILW disposal:

- Testing of initial ideas for safety concepts;- Optimization of the facility design;- Identification of safety related issues to be addressed by research and development

programmes;- Definition or revision of limits, controls and conditions such as WAC;- Assessment of the maximum inventory that can be disposed of (the ‘radiological capacity’ of

the facility).

A specificity of ILW disposal is thatThe testing of safety concepts is particularly important for ILW disposal, to underpin the selection of an appropriate disposal options, as such a wide range such wide ranges areis available (see Chapter 5). Optimization of the facility design is also particularly important, at the facility scale, to optimise the number, dimensions, and spacing of vaults and, at the vault scale, to ensure efficient stacking of the variety of waste packages and to minimize voidage.

Due to the diversity of the materials present in ILW and the wide range of treatment and imobilization options, there are various specific issues that may need R&D to underpin safety. This may includes:

Identification of complexing agents present in the waste or arising from degradation of materials and their effects on the mobility of contaminants contained in the waste;

Characterisation of chemical and physical forms of contaminants within the waste and understanding of the release mechanisms;

Understanding of release of chemically disturbing species and their effect on the engineered barriers and on the mobility of contaminants, such as corrosive species or oxidising agents;

Gas generation and migration; Swelling potential of some ILW (e.g. bituminous waste and reactive metal) and physical interactions

with surrounding materials;

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Potential exothermic reactions within some ILW induced by internal or external energy (e.g. bituminous and graphite waste);

Colloid production and its migration; Evolution of pH with time in cementitious material; Evolution of materials and geometries within the vault for ILW with relatively high concentration of

fissile nuclides; and Interactions between ILW specific engineered barrier(s) and the host rock.

It may be necessary to limit or control the quantities of some contaminants and the maximum inventory, particularly for near surface disposal. These limits need to be derived from the safety case. Any requirements of this type need to be captured in the WAC.

9.2 Demonstration of safetyThe adoption of a graded approach in determining the scope, extent and level of detail of the safety case and supporting assessment as described in Paragraph 4.25 of SSG-23 is particularly applicable to ILW disposal:

”A graded approach is required to be taken in determining the scope, extent and level of detail of the safety case and supporting assessment. The graded approach adopted should be explained and justified, and should be such that the scope, extent and level of detail of the safety case and supporting assessment are commensurate with the level of risks posed by a facility or activity and the stage of facility development, e.g. generic disposal concepts being considered prior to site selection might be considered in less detail than for a specific site and disposal facility.

For ILW, the level of risk is a function of its content in long-lived and/or mobile radionuclides as well as the activity level. These factors will also influence the timescales over which safety needs to be assessed.

In the case of co-disposal of ILW with other waste types, the scope, extent and level of detail of the safety case and supporting assessment must reflect the potential of the most hazardous waste type and of the potential interactions between the two waste types.

9.3 Aspects of safety assessment

Aas descibed in SSG-23, key elements of the safety assessment are the following:

Radiological impact assessment for the period after closure, Site and engineering aspects, Passive safety , Multiple safety functions, Robustness, Scientific and engineering principles, Quality of the site characterization, Operational safety aspects, Non-radiological environmental impact, and Management system.

With regards to those key elements, the large variety of ILW is important. The safety assessment needs to take into account various processes which were described in previous sections that may affect some types of ILW and needs to be tailored to specific characteristiccharacteristics of the individual vaults.

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It should be noted that in the case of codisposal of other waste types with ILW, the safety case and safety assessment must take into account any possible interactions between the wastes types.

Safety cannot rely on institutional control periods longer than a few hundred years. Human intrusion scenarios must be considered in the safety case after the end of the institutional control period. The type of intrusion scenario is depth dependent. This leads to the identification of limits for the acceptable residual activity within the waste after the institutional control period. The institutional control has an influence only on the initial amount of short lived radionuclides in the waste. The acceptable content in long lived radionuclides is a function of the type of intrusion scenarios to be considered and therefore a function of repository depth..

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10 Institutional Control and Record Keeping10.1 Institutional controlSSR-5 Requirement 22 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.”

In applying this concept in ILW disposal, the requirements for control are a function of the depth of the disposal facility, not of the type of the waste disposed. This is stated in paragraph 3.43 of SSR-5 as follows:

For near surface facilities, isolation has to be provided by the location and the design of the disposal facility and by operational and institutional controls. For geological disposal of radioactive waste, isolation is provided primarily by the host geological formation as a consequence of the depth of disposal.

There are a number of different national requirements on this issue.

10.2 Record keepingAsAs for all other types of waste, the operator needs to retain all information relevant to the safety case and the supporting safety assessments of the ILW disposal facility, the emplaced wastes, the facility design and the records that demonstrate compliance with regulatory requirements. Such information and records have to be retained by the operator unless or until such time as another organizationorganisation assumes responsibility for the facility, at which time the records should be transferred to the organizationorganisation that assumes that responsibility. Records should also include information associated with waste generation, processing and waste acceptance.

Consideration should be given to the physical and electronic forms of the records to ensure that information remains available and is archived appropriately for the benefit of future generations. The use of warning signs or markers to warn of the presence of the disposal facility may also be considered. An important consideration is that the location of where the records are archived may be lost to future generations, so care must be takenthat care in determining the location of the archives must be taken. The use of warning signs or markers to warn of the presence of the disposal facility may also be considered. Record keeping may include the posting of facility records in national and international archives accessible to future generations and the transfer of responsibility for the facility to a successor organizationorganisation. A suitable mechanism may need to be developed for the transfer of responsibility from one generation to the next.

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REFERENCE

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APPENDIX I: National Examples• Analysis of common features and differing approaches may be added to Chapter 9 (to be

discussed at the plenary)

<NATIONAL EXAMPLES TO BE PREPARED BY PARTICIPANTS>

<Proposed new structure for national example>1. National Waste Classification and Policy

- Describe national waste classification focusing on the results, no description on the process (give reference of the process or other relevant materials

- Be consistent with the description in the main text

2. Approach to managing the ILW- Provide overview of Existing or Planned Disposal facilities (options) for ILW, link to Chapter 3

of this annex- Try to use terms consistent with the main text for disposal options- Can be described with a schematic figure- Also describe specific project schedule & current status (about 4-5 lines)

3. Details of Existing or Planned Disposal Facilities (maximum 1 page/site including figures)3.1 Site A

3.1.1 Disposal option and timescales (about 4-5 lines)- use the term consistent with the main text, not the wording in the national context

- Explain national example in relation to Chapter 3.2 Timescales 3.1.2 Waste characteristics and volume (about 4-5 lines)3.1.3 Siting and safety function of natural barriers3.1.4 Disposal facility design including EBS design3.1.5 Facility specific considerations (e.g. institutional control, retrievability and reversibility)

3.2 Site B3.2.1 Disposal option and timescales3.2.2 Waste characteristics and volume3.2.3 Siting and safety function of natural barriers3.2.4 Disposal facility design including EBS design3.2.5 Facility specific considerations

3.3 Site C Reference-Reference to waste classification-Rference to safety case & supporting documents

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APPENDIX II: IAEA publications relevant to this document

The IAEA has published a number of Safety Standards and other technical documents relevant to ILW disposal. The following are suggested for background information and additional technical details.

1. IAEA Safety Standard series IAEA General Safety Requirements, GSR Part4, Safety Assessment for Facilities and

Activities IAEA General Safety Guide GSG-1, Classification of Radioactive Waste IAEA General Safety Guide GSG-3, The Safety Case and Safety Assessment for the

Predisposal Management of Radioactive Waste

2. Other technical series documents NW-T-1.20, Disposal Approaches for Long Lived Low and Intermediate Level Radioactive

Waste Technical Report series TR-412, Scientific and Technical Basic for the Near Surface Disposal

of Low and Intermediate Level TECDOC – 1572, Disposal Aspects of Low and Intermediate Level Decommissioning Waste TECDOC – 1397, Long Term Behaviour of Low and \intermediate Level Waste Packages

Under Repository Conditions TECDOC – 1325, Management of Low and Intermediate Level Radioactive Waste with

Regard to Their Chemical Toxicity ISAM/ASAM report

There are also a number of publications published before 2000, which have not been included in the list.

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