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(DRAFT Ver.1)DISPOSAL FACILITIES FOR INTERMEDIATE LEVEL RADIOACTVE WASTE DISPOSAL – GUIDANCE TO DEVELOP A FACILITY AND
SAFETY CASE
Drafted atTM-45865 Technical Meeting on the Disposal of Intermediate Level Waste,
Vienna, 9-13 September 2013
(Note: Reference to DS356 also needs to be added when SSG-14 is referred.)
Contents1 Background, rationale, scope.................................................................................................66
2 IAEA Definitions.....................................................................................................................66
3 IAEA and other international publications relevant to this document.....................................77
4 General aspects of ILW disposal.............................................................................................77
4.1 Legal and Organizational Infrastructure..........................................................................77
4.2 Safety Approach.............................................................................................................88
4.3 Safety Case and Safety Assessment................................................................................88
4.4 Elements in a stepwise approach to the development of an ILW disposal facility............98
5 Timescales.............................................................................................................................98
6 Waste................................................................................................................................1110
6.1 Waste Sources............................................................................................................1110
6.2 Waste characteristics..................................................................................................1110
6.2.1 Half-life and activity.............................................................................................1110
6.2.2 Waste volume.....................................................................................................1210
6.2.3 Physical and chemical properties.........................................................................1211
6.2.4 Chemotoxicity.....................................................................................................1211
6.2.5 Gas Generation....................................................................................................1211
6.2.6 Criticality.............................................................................................................1211
6.2.7 Heat Generation..................................................................................................1211
6.3 Conditioned Waste......................................................................................................1311
6.3.1 Mobilization........................................................................................................1312
6.3.2 Chemotoxicity.....................................................................................................1312
6.3.3 Gas generation....................................................................................................1412
6.3.4 Criticality.............................................................................................................1412
6.3.5 Heat Generation..................................................................................................1413
6.3.6 Chemical Compatibility........................................................................................1413
6.4 Waste Containers........................................................................................................1413
6.5 Waste Packaging.........................................................................................................1413
6.5.1 Waste Package Properties....................................................................................1413
6.5.2 Package Volume..................................................................................................1514
6.5.3 Consideration on waste packages related to Operational Period...........................1514
6.5.4 Consideration on waste packages related to Post closure......................................1514
7 Disposal Options................................................................................................................1615
7.1 General remarks.........................................................................................................1615
7.2 Near Surface...............................................................................................................1615
7.2.1 Landfill disposal..................................................................................................1615
7.2.2 Trench disposal...................................................................................................1615
7.2.3 Engineered vault.................................................................................................1615
7.3 Geological..................................................................................................................1715
7.3.1 Intermediate Depth Disposal...............................................................................1715
7.3.2 Geological Formations.........................................................................................1815
7.4 Boreholes...................................................................................................................1815
7.5 Other disposal options................................................................................................1815
7.5.1 Decay storage.....................................................................................................1815
7.5.2 In-Situ isolation...................................................................................................1816
7.5.3 Long term storage...............................................................................................1816
7.6 Aspects for Co-disposal...............................................................................................1816
7.7 Consideration on EBS..................................................................................................1816
7.8 Other factors to be considered....................................................................................1916
7.8.1 Economic & technical resources..........................................................................1916
7.8.2 Public Acceptability.............................................................................................1916
8 Site Issues..........................................................................................................................2016
8.1 Siting..........................................................................................................................2016
8.2 Site properties............................................................................................................2017
8.3 Site evolutions............................................................................................................2017
8.3.1 Precipitation/recharge.........................................................................................2017
8.3.2 Permafrost and glaciation....................................................................................2117
8.3.3 Sea level change..................................................................................................2118
8.3.4 Weathering.........................................................................................................2118
8.3.5 Uplift/Erosion and Subsidence/Sedimentation......................................................2118
8.3.6 Faulting/folding...................................................................................................2218
8.3.7 Relation with human intrusion.............................................................................2218
9 Disposal Facility.................................................................................................................2219
9.1 Requirements on the disposal facility...........................................................................2219
9.2 Design consideration...................................................................................................2219
9.3 Design consideration for long-term performance.........................................................2320
9.3.1 pH : selection of a suitable concrete take into account the alkaline plume in the design of EBS in particular with swelling bentonite. If waste is pH sensitive (high /low) this must be considered............................................................................................................2421
9.3.2 Metal (reactive with water, corrosion, hydrogen gas): waste package to limit reactivity with groundwater...............................................................................................2421
9.3.3 Nitrate (bitumen): separate nitrate waste from no-nitrate waste; take into account redox disturbance (PA).......................................................................................................2421
9.3.4 Organic (bitumen, organic waste, concrete): separate organic waste from no-organic waste during packaging and in disposal vaults and taking into account in PA.....................2421
9.3.5 Swelling (bitumen): try to characterize and take into account in design (allow volume for expansion) and in EBS......................................................................................2421
9.3.6 Fissile material: sub-critical geometry.................................................................2421
9.3.7 Mobile/gaseous radionuclide (Cl-36, C-14): take into account in PA, enhanced EBS, and/or higher retention host rock by site selection...........................................................2421
9.3.8 Great waste volume (greater than HLW): taken into account in design (larger disposal vaults, but verifying mechanical and hydrogeological impact (EDZ) on surrounding host rock)...........................................................................................................................2421
9.3.9 Interaction between various ILW: separation as necessary..................................2421
9.3.10 Interaction with other types of waste in case of co-disposal (thermal and chemical): provision for sufficient distances, respective location regard to hydrogeological system as necessary...........................................................................................................................2421
9.3.11 Large items.........................................................................................................2421
9.3.12 Waste form.........................................................................................................2421
9.3.13 Heat....................................................................................................................2421
9.3.14 Voidage...............................................................................................................2522
9.3.15 And others….......................................................................................................2522
9.4 Pre-operational period (design and planning).............................................................2522
9.5 Facility Closure...........................................................................................................2622
9.6 Post closure period.....................................................................................................2723
10 Operational issues..........................................................................................................2723
10.1 Variety of waste packages; geometry.........................................................................2823
10.2 Operational safety......................................................................................................2823
10.3 Operational time period.............................................................................................2924
11 Institutional control and Record keeping.........................................................................3024
11.1 Institutional control.....................................................................................................3024
11.2 Record keeping...........................................................................................................3125
12 Safety Case [subsection to be developed].......................................................................3225
12.1 Safety requirements (SSR 5 fully applicable).................................................................3226
12.2 Assessment bases.......................................................................................................3226
12.2.1 Waste characteristics (volume, activity, final waste form, emission type, gas release/production, heat production, chemotoxicity) – reference to chapter 6.....................3226
12.2.2 Site and disposal facility (reference to previous chapters).....................................3226
12.2.3 Assessment timeframe (reference to chapter 5)...................................................3226
12.3 Safety assessment.......................................................................................................3226
12.3.1 Scenario development (normal evolution, other evolution, human intrusion)........3226
12.3.2 Consequence analysis (radionuclide migration).....................................................3226
12.3.3 Analysis of uncertainties and sensitivity................................................................3327
12.4 Other safety arguments...............................................................................................3327
12.5 Waste acceptance criteria (reference to SSG-14)..........................................................3327
12.6 Evolution of safety case...............................................................................................3427
12.7 Documentation of safety case (transparency, traceability, comprehensiveness)............3427
13 National Examples..........................................................................................................3427
13.1 National examples.......................................................................................................3427
13.2 Analysis of common features and differing approaches..............................................3528
14 Conclusions....................................................................................................................3528
APPENDIX I: site evolution matrix.............................................................................................3730
1 Background, rationale, scopeThis document is to provide a reference for the disposal of intermediate-level waste (ILW) which is not considered either low-level that can be disposed of in a near surface facility or high-level waste that must be disposed in a deep geological formation. An IAEA safety guide currently exists for geological disposal for high-level waste (IAEA Safety Guide SSG-14) and an IAEA safety guide for near surface disposal of low-level waste is under development (draft IAEA Safety Guide DS 356). The IAEA has published other documents for these two types of wastes and relating disposal facilities. This document is intended to be used as supplemental technical document for the existing IAEA Safety Standards by examining a number of issues to determine appropriate disposal options for the ILW and for factors that may contribute to the safety case. (NOTE: improve the text above and add description on the following aspects as necessary)
Capture full range of ILW Focus on safety related issues Fill gaps between SS and existing documents Guidance, not technical description (not a collection of information, but to be used as a
guidance for developing SC and facility) Avoid need for new requirements document – interpretation of existing Show links to other documents Rationale: clear description on the issues on ILW disposal add description from DS356 also when referring SSG-14 Once DS356 is finalized, check the consistency with the latest draft
2 IAEA DefinitionsThere are a number of IAEA definitions which are relevant to ILW disposal.In the IAEA safety glossary, definitions are given in terms of radiological properties of these wastes. Intermediate-level waste is considered together with low-level waste and is defined 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
This IAEA Safety Guide GSG-1 focuses on the design of the disposal facility and waste acceptance criteria for ILW and provides the definition:
Intermediate level waste is defined as waste that contains long lived radionuclides in quantities that need a greater degree of containment and isolation from the biosphere
than is provided by near surface disposal. Disposal in a facility at a depth of between a few tens and a few hundreds of metres is indicated for ILW. Disposal at such depths has the potential to provide a long period of isolation from the accessible environment if both the natural barriers and the engineered barriers of the disposal system are selected properly. In particular, there is generally no detrimental effect of erosion at such depths in the short to medium term. Another important advantage of disposal at intermediate depths is that, in comparison to near surface disposal facilities suitable for LLW, the likelihood of inadvertent human intrusion is greatly reduced. Consequently, long term safety for disposal facilities at such intermediate depths will not depend on the application of institutional controls.
The GSG-1 definition recognises that ILW requires a higher degree of containment than LLW, and an ILW disposal facility may need a specific design. However, it is necessary to consider the many influencing properties that have an impact on the degree of containment and isolation required. The following chapters discuss important aspects that need to be taken into account in the disposal of ILW. Chapter 3 discusses the characteristics of the waste …complete sentence.
3 IAEA and other international publications relevant to this document
Documents Identified GSG-1 GSG-3.4 SSR 5 SSG-14 SSG-23 DS 356 NW-T-1.20 Technical Report series 412 TECDOC – 1572 TECDOC – 1397 TECDOC – 1325 ISAM/ASAM report ICRP-122 A number of pre-2000 publications
Check this list is comprehensiveInclude Diagrams from IAEA presentation on 9/9
4 General aspects of ILW disposalGiven that there are no significant differences between geological disposal and repositories of ILW, from the point of view of requirements, guidelines and the safety approach, the guidelines included in the SSG-14 and DS356 are applicable in the case of ILW disposal facilities.
4.1 Legal and Organizational Infrastructure
Taking into account the relatively long operational lifetime of an ILW disposal facility lifetime, the roles and responsibilities of the government, regulatory body and operator should be clearly defined and established as specified in the SSR-5. The Requirements 1, 2 and 3 of the reference SSR-5? are fundamentals for the national legal and organizational 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.
In addition, according to the long timeframes involved, an orderly transfer of responsibilities between different Organizations could be required when the decision of closure is taken. A fundamental aspect that also should be taken account is a proper record preservation, including not only the inventories of the waste but also the knowledge of development of the facility.
4.2 Safety ApproachThroughout 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 [SSR-5].
Disposal facilities for ILW will be developed and operated over a period of several years or several decades. Key decisions, such as decisions on site selection and evaluation, and on the design, construction, operation and closure of the disposal facility, are expected to be made as the project develops. In this process, decisions are made on the basis of the information available at the time.
The safety approach includes all the ways in which the safety of people and the environment is ensured throughout the lifetime of an ILW disposal facility. 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 ILW disposal programme and updated periodically.
The safety strategy is the high-level integrated approach adopted for achieving safe disposal. It should include strategies to select a site and to design, construct, operate and close a disposal facility and, in addition, should include recommendations for the preparation and maintenance of the safety case for use in decision making and, eventually, procedures for regulatory approval for the assumed duration of the period of institutional control.
4.3 Safety Case and Safety Assessment
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 [SSR-5].
The safety case (SC) and supporting safety assessment (SA), as defined in SSR-5, shall demonstrate the level of protection of people and the environment provided and shall provide assurance to the regulatory body and other interested parties that safety requirements will be met.The aspects related to timescale and depth of an ILW disposal facility should be properly considered in Safety Casethe SC and Safety AssessmentSA.
A safety case and supporting safety assessment shall be prepared and updated by the operator, as necessary, at each step in the development of a disposal facility, in operation and after closure. The safety case and supporting safety assessment shall be submitted to the regulatory body for approval. The safety case and supporting safety assessment shall be sufficiently detailed and comprehensive to provide the necessary technical input for informing the regulatory body and for informing the decisions necessary at each step.
A complete and very comprehensive document, about SC & SA, applicable to any kind of disposal of radioactive waste is SSG-23.
[NOTE: add paragraph on the relationship between timescale / WAC / and safety case]
4.4 Elements in a stepwise approach to the development of an ILW disposal facility
Disposal facilities for radioactive waste shall be developed, operated and closed in a step by step process which is an iterative process that should maximize the value of information as it evolves over the series of steps, for instance siting, design, construction, operation and closure. Relevant approval by the regulators may be needed for each of these steps, according to the Countries legislations.
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 should identify the decision that needs to be made and the information that is necessary to make the decision. The operator should also identify the appropriate interested parties and determine when and how to include them in the decision making process. Early involvement of regulatory body 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.
Recommendation 4: Add information to the draft about Safety Case and Safety Assessment based on the experience , specifically for ILW repositoires repositories ) of the facilities mentioned in Chapter 10 of the Draft document.
5 TimescalesRegardless of the type of waste, repository design and the repository depth, the safety case has to demonstrate safety during an appropriate time-scale. It must be consistent with the natural evolution of the site and the considered depth and design on the one hand, and with the characteristics of the waste, in particular the reduction of activity with time as a function of the half-life of radionuclides.
On the surface, natural evolutions occur at much faster time scales than deep underground. This includes 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 like glaciation or permafrost. 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. However, the long term geodynamic evolution has been scarcely addressed in near surface disposal.
In the IAEA Safety glossary, short-lived radionuclides are defined as radionuclides with half-lives less than 30 years The inventory of the short lived radionuclides will decrease substantially during the operational phase and the time period when institutional control can be relied on (see Chapter 6). Short lived waste is however defined in the IAEA Safety glossary as “Radioactive waste that does not contain significant levels of radionuclides with a half-life greater than 30 years”. For the waste to be consistent with the assessment time scale it is necessary to define, and implement through the Waste Acceptance Criteria, what levels of long-lived radionuclides are regarded as insignificant.
For near surface disposal facilities, limited time scales are generally considered in safety cases. IAEA Safety Guide on the Safety Assessment for Near Surface Disposal No. WS-G-1.1 provides that: “Assessments may therefore need to project the behaviour of the site and facility for time periods of the order of hundreds or even thousands of years.”
Deep geological disposal makes it possible in principle to consider very long time-scales as necessary with respect to the half-life of radionuclides in the waste. 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 time-scales that are comparable with geological changes. At great distance from the surface, such changes are particularly slow (…)”.
Geologists can extrapolate the geologic evolution of deep underground facilities in well-chosen sites for millions of years but uncertainties increase with time. It is generally recognized that a safety case for deep geological disposal is limited to about one million years. Uncertainties in the evolution of the site (that are relevant for the safety case) can be handled 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. IAEA Specific Safety Guide on Geological Disposal Facilities for Radioactive Waste No. 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.”
With regard to geodynamic evolution, shallower depth disposal facility compared with geological disposal facilities might be typically associated with an intermediate timescale between 10,000 years and 100,000 years which is a representative timescale for a glaciation cycle. At such a timescale, some radionuclides with intermediate half-lives such as C14, Ra226, and Am241 will have been substantially decreased.
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 time-scale for the safety case. The radiological exposure of man has to be acceptable at all times. Therefore one has to take into account loss of containment and potential dispersion of waste at least at the end of the considered time-scale. As a consequence, the acceptable content of long lived radionuclides is a function of the applicable time scale.
6 Waste 6.1 Waste Sources
A particular feature of ILW is its diversity. The following main sources of waste can be identified:
Operational Waste
This waste arises during the operation of any nuclear facilities, and includes resins, filters, sludges and evaporator concentrates.
Decommissioning WasteThis waste arises from decommissioning of NPP’s and other nuclear facilities such as accelerators or production facilities and includes components, concrete, rubble and metal from buildings. There may be some large items, such as pressure vessels.
Sealed SourcesThese arise from industrial and medical applications. For countries without any nuclear facilities, this is usually their only relevant ILW.
Other terms that are frequently used when describing ILW, include:
Legacy WastesThese are historic waste, often having limited or no characterisation. Some may have been conditioned previously but do not meet current safety standards and therefore require further treatment. Legacy waste often includes sealed sources.
Institutional WasteThis term is often used to describe wastes which are the responsibility of national or regional governments. The individual wastes fall into the other categories described above.
6.2 Waste characteristicsA number of IAEA documents identify waste characteristics that need to be taken into account to define disposal options and to perform relattheing safety case and related safety assessments . This section is based on the IAEA documents: Nuclear Energy Series No.NW-T-1.20: “Disposal Approaches for Long Lived Low and Intermediate Level Radioactive Waste” and to Specific Safety Guide No. SSG-14: “Geological Disposal Facilities for Radioactive Waste”.
6.2.1 Half-life and activityThe half-life of radionuclides in the waste and the evolution of waste residual activity with time are important attributes in determining the duration of the minimum containment period during which waste must be isolated from the environment. 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. The other group has a relatively high content of long lived radionuclides, but with low to moderate activityDepending on the group, the disposal option will focus more on either containment or isolation.
6.2.2 Waste volumeThe total amount of waste (volume or mass) is another important factor to be considered when choosing an appropriate disposal option. It may influence, together with radiological characteristics, the selection of both the predisposal and the disposal technologies. Typically, conditioning of a few pieces of spent sealed sources will differ from the technology applied for processing large volumes of L-ILW from, for example, NPP decommissioning. Also, the disposal option designed for accepting several cubic metres of waste is likely to be different from a facility intended for the disposal of thousands of cubic metres. The volume of waste to be disposed can be affected by the conditioning process. Requirements on the type of the package and on the conditioning/stabilization technology can result in the final volume of processed waste being several times greater than that of the raw waste. The waste volume to be disposed of will have to be assessed in the planning stage of the repository development or reconstruction. Inventories of existing (stored) and future waste arising will need to be compiled, taking into account decommissioning of existing and planned facilities.
6.2.3 Physical and chemical properties
Physical and chemical properties of ILW prior to conditioning including the properties of the radionuclide (including chemical form and physical state) and other constituents of the waste will influence both the waste conditioning route and disposal option. The possibility of changes to the properties due to chemical, or physical reactions and biological processes, for example the generation of radioactive gases (C14 or H3), should be considered.
6.2.4 Chemotoxicity
The radionuclides present in the waste only form a minor part of the total mass. The major part of the mass is made up of non-radioactive constituents that may include toxic and/or chemically hazardous substances. These constituents may be persistent so that their hazard potential remains constant with time, i.e. no decay is expected. This has important implications for the disposal of radioactive waste, whether in near surface facilities or deep geological repositories
The concentration of chemically toxic components in ILW may play a decisive role when selecting the disposal option. When disposing of large amounts of waste, even compounds with low non-radiological hazard may become problematic.
[6.2.5] Gas Generation
Gas generation is a phenomenon that may occur inside the waste itself or in a combination between waste and its containment medium.
ILW can generate gas by three main processes:
The microbial degradation of organic components of the waste (cellulose, hydrocarbons);
Metal corrosion;
Radioactive decay (radon).
Some of the gases that are generated may themselves be radioactive, e.g. 3H, 14C in carbon dioxide or methane, 222Rn.
6.2.5 CriticalityFor ILW with significant amounts of uranium or plutoniumfissile material, criticality should be taken into account.
6.2.6 Heat Generation
It is expected that ILW needs no provision, or only limited provision, for heat dissipation during its storage and disposal. The amount of heat generated is dependent upon the types and amounts of radionuclides in the waste (e.g. half-life, decay energy, activity concentration and total activity). Therefore, the significance of heat generation cannot be defined by means of a single parameter value. In the case that heat generation could be important (e.g. waste with enough amounts of radionuclides such as cobalt-60, strontium-90, caesium-127, americium-241 or silver-108m) the heat removal is the fundamental point being thermal conductivity, storage geometry and ventilation the main focuses.
Waste with radionuclides such as cobalt-60, strontium-90, cesium-127, americium-241, or silver-108m generate heat during periods of time between decades and thousands of years as a function of their respective content in the waste. Heat generation can be an issue in the sizing of disposal cells as a function of their content in heat generating radionuclides and of the volume of waste to dispose of.
[6.3] Conditioned Waste Waste form properties, including non-radiological properties, are relevant to the assessment of waste disposal options and approaches. Factors to be considered include: the potential for mobilization of radionuclides, the chemotoxicity of the waste form(s) and its chemical compatibility with the disposal environment.
It is evident that tThe proper selection of a waste conditioning process may make a significant contribution to the long term safety of a disposal system. Conditioning can produce a waste form that is more chemically and physically stable than the primary waste. It can also provide an additional engineered barrier to radionuclide migration by reducing the mobility of radionuclides and other potentially harmful constituents of the waste. A basic requirement for selecting a conditioning method is that the resulting waste form (and its potential degradation products) should be compatible with the disposal environment and the other engineered and natural barriers.
Waste form properties, including non-radiological properties, are relevant to the assessment of waste disposal options and approaches. Factors to be considered include: the potential for mobilization of radionuclides, the chemotoxicity of the waste form(s) and its chemical compatibility with the disposal environment.
6.2.7[6.3.1] Mobilization
Radionuclides contained in the waste can be mobilized by water and, less often, may migrate via gaseous pathways (14C, Rn). With respect to the groundwater pathway, the tendency of a radionuclide to be dissolved and transported depends on:
Its physical and chemical forms;
The chemical characteristics of the disposal environment (e.g. high pH conditions caused by the presence of cement);
The sorption characteristics of dissolved radionuclides on the adjacent engineered barrier materials;
Non-radioactive components of the waste (e.g. presence of corrosive species and complexing ligands used in reprocessing);
The resistance of the waste form to degradation processes (e.g. biodegradation and radiation stability).
When assessing the performance of the disposed waste, chemical reactions that may result in creation of mobilizing agents should also be taken into account. As an example, some complexing ligands not originally present in the waste may be formed due to the chemical interactions between the barrier materials and the waste itself. 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. The evaluation of mobilization processes is complex and may bring unexpected findings. For example, radionuclides with a high solubility and low sorption ability, such as 36Cl and 129I, can be critical in safety assessments although they have low radiotoxicity. In contrast, highly radiotoxic plutonium isotopes are retained within the repository system due to their low solubility and high sorption characteristics and thus may contribute less to final dose of the critical group.
6.2.8[6.3.2] Chemotoxicity
The principal problem of chemotoxicity is that it does not usually decrease with time and thus the engineered barrier system may provide effective containment of these constituents of the waste for only a portion of the time during which the waste remain potentially harmful. Waste conditioning may remove chemotoxic substances or contribute to delaying or preventing their release.
6.2.9[6.3.3] Gas generation
Waste conditioning has the potential to affect gas generation. For example, aluminium is expected to corrode in a high pH environment to produce hydrogen gas. Carbon steel behaves similarly under oxygen free conditions and at much lower rate. If gas is produced in large amounts, it could lead to a build-up of pressure that may be sufficient to damage barriers. Gas will tend to migrate due to buoyancy and, where this occurs, it could cause unwanted movements of repository pore water and/or the surrounding groundwater.
If possible, waste conditioning should reduce gas generation.
[6.3.4] CriticalityBased upon the properties of the waste, conditioning of ILW should consider criticality in respect to the final disposal option. Assemblies of packages should be assessed with respect to criticality safety. Accumulation of fissile material during the post closure phase should also be assessed.
6.2.10[6.3.5] Heat GenerationBased upon the properties of the waste, conditioning of ILW should consider heat production in respect to the final disposal option. Assemblies of packages should be assessed with respect to heat production. Heat generation can be an issue in the sizing of disposal cells as a function of their content in heat generating radionuclides and of the volume of waste to dispose of.The impact of heat generation can vary by several orders of magnitude, depending on the influencing factors and the methods in place for heat removal
6.2.11[6.3.6] Chemical CompatibilityThe chemical compatibility of the waste form with other components of the engineered and natural environment should be considered.
For example, cement based materials provide an alkaline environment in which the corrosion of many metallic components is reduced, while the same environment facilitates corrosion of aluminium and magnesium. Other encapsulation materials may be preferred for these wastes.
6.3[6.4] Waste ContainersWaste containers generally contribute to waste package and repository performance by delaying the release of radionuclides, thereby allowing short-lived radionuclides to decay prior to their mobilization. The container lifetime is one component used in the safety case to demonstrate the risk criteria with respect to long-term releases of radioactivity to the environment, particularly for near surface repositories. Quality control of containers has toshould be undertaken for contributing to confidence that an adequate level of performance can be achieved.
6.4[6.5] Waste PackagingThe conditioned waste and waste container together constitute the waste package. Packaging is required to provide safe containment of the waste during handling, storage, transportation and disposal. Waste packages shall meet the waste acceptance requirements of the individual storage and/or disposal facilities. They can vary widely in their design complexity [IAEA Tecdoc 1572 with modifications]
6.4.1[6.5.1] Waste Package PropertiesMost ILW needs to be appropriately packaged for handling, storage, transportation and disposal. Packaging can improve the following characteristics:
Limiting of the gross mass (important for both handling and stacking in engineered structures).
Provide Aacceptable compressive strength and minimal void space to ensure the stability and stackability of waste packages, and the stability of the storage/disposal facility against subsidence.
Ensure Aabsence of free liquids to prevent contamination and activity release, to prevent damage to the containers during handling, and to prevent corrosion of the waste packages.
Restriction of the fissile material content to prevent nuclear criticality incidents, particularly in the event that the packages are exposed to water during storage or disposal.
Management of organic substances (e.g. decontamination solvents) that exhibit chelating or complexing behaviour.
Provide Pphysical and chemical compatibility between waste and immobilization/ encapsulation materials.
Allows Ability of the package to withstand various accident conditions, such as fire or drop/impact events.
Immobilization ofes radionuclides consistent with the requirements of waste acceptance criteria for the disposal facility.
[6.5.2] Package VolumeThe external volume and total number of waste packages will usually be the most important determinant of the repository volume. Other factors are the shape of the packages and their handling requirements. In particular, the need for remote handling of packages may cause an increase in the excavated repository volume to provide space for handling equipment such as overhead cranes. Other related aspects such as transportation may also influence the option to be selected.
(NOTE: address on voidage (e.g. section 3.6.3 on draft document))
6.4.2[6.5.3] Consideration on waste packages related to Operational Period
It is generally required for safety that the integrity of the waste package is maintained at least for the duration of the operational period. – the vault is closed and there is no longer any requirement for retrievability.
Other waste package characteristics that need to be taken into account for the operational safety of disposal facilities are:
- surface dose rate, which may require additional shielding or remote handling;
- potential surface contamination;
- resistance of waste packages to operational hazards (drop, fire, etc).
In general, provision in the waste package design (including the materials selected) regarding these factors may need to be graded to the activity level of the waste.
[6.5.4] Consideration on waste packages related to Post closure While LILW waste packages are primarily selected for transportation, handling and operational purposes, their degradation may become of concern for long-term safety considerations. As a result, the resistance of these packages to degradation is one of the principal characteristics of the waste package. The confinement of radionuclides and structural integrity of the waste package, in other words its durability, may contribute to reducing the risks to the public and the environment from disposal of ILW to acceptable levels as a function of the respective role of each component of the entire containment system.Factors affecting the waste container’s durability during disposal need to be studied in the context of the design life of the whole repository barrier system, and its host environment. Due to differences in the variety of ILW wastes, the relative importance of particular mechanisms may be important. For example, decommissioning wastes will contain much more metal than operational wastes and, therefore, corrosion and gas generation are considered to be verymore important. For metallic containers, corrosion performance is an important indicator of container integrity and lifetime. Therefore, 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. Corrosion scenarios may need to consider swelling, gas generation and loss of integrity. 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. Polymer-container materials (High Density Poly Ethylene (HDPE)), on the other hand, are not susceptible to corrosion; although creep, embrittlement, and irradiation-induced degradation can affect their durability. Along with containment, wastes packages should be designed with respect to the mechanical and chemical of the other components of the natural and engineered containment system.
[7] Disposal Options 6.5[7.1] General remarks An important factor in the management and disposal of ILW is the concentration of long lived radionuclides in the waste stream. It is an accepted practice to dispose of radioactive waste with a limited concentration of long lived radioactivity in facilities located at/or near the surface, at sites with favourable geological characteristics, remote locations, dry climate, and/or engineered barriers or other features that impede or limit the eventual release of radionuclides out of the repository environment to acceptable rates and amounts. For higher concentrations a more robust containment
system is required. Ideally, the radionuclide containment function should derive from a multi-barrier system that employs both engineered and natural barriers to achieve the required passive safety.
• Risk• Inventory
6.6[7.2] Near SurfaceAccording to SSR-5, 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 meters below ground level. Such a facility may be designated as a disposal facility for low level radioactive wasteLLW [GSG-1] or short lived ILW. Near surface solution presents the greatest vulnerability to external phenomena and therefore deserves the most attention to evaluate all geologic and non-geologic processes which can reduce the safety of repository.
6.6.1[7.2.1] Landfill disposal A Ffacility that contains no complex engineered barriers or elaborated sealing, where the requirements on the waste treatment and packaging will also be less stringent. Nevertheless, adequate waste acceptance criteria (WAC) and quality control must ensure that the radionuclide content, especially the content of long lived activity, remains at very low levels compatible with the limited containment and isolation capabilities of the design. Particular attention should 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, phenomena related to hydrogeological instability. Surveillance and monitoring are required after closure during the period of institutional control.
6.6.2[7.2.2] Trench disposal
Trench disposal is an options usually used for waste with higher radioactive content than waste asignedassigned to landfill disposal. The trench can be divided into individual compartments to increase radionuclide containment and flexibility of operation. 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 should be paid to surface phenomena that can reduce the degree of isolation and containment of the waste, as described in previous paragraph.
6.6.3 Engineered vaultEngineered surface repositories of the vault type is another near surface disposal option. Here, more elaborate engineered barriers that aim to reduce the amount of water that could contact the waste are incorporated. These facilities are principally intended for the disposal of short-lived waste with the activity of long lived isotopes being limited to low concentrations.
Engineered surface repositories are equipped with surface barriers (caps), vertical barriers (cut-off vaults) and sub-horizontal barriers (floors). There are other containment technologies that may be applied, including chemical barriers that retard migration of radionuclides without impeding the water movement. 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 may be installed to allow the functioning of the barriers to be checked. Additional barriers might be constructed around the disposal unit to control the movement of water. Particular attention should be paid to surface phenomena that can reduce the degree of isolation and containment of the waste, as described in previous paragraph.
6.7[7.3] GeologicalWaste with higher contents of long lived radionuclides is usually disposed of at depth in appropriate geological formations. The nature of the wastes and the waste forms acceptable at a given site depends on factors such as waste and site characteristics. Treatment and packaging of the waste provide both physical and chemical barriers to the radionuclide migration. The selection of backfill material to fill in void spaces depends on the design requirements and must consider its compatibility with the host rock and waste characteristics.
6.7.1[7.3.1] Intermediate Depth DisposalDepending on its characteristics, intermediate level radioactive waste (ILW) can be disposed of in different types of facility GSG-[12]. Disposal could be by emplacement in a facility constructed in caverns, vaults or silos at least a few tens of meters below ground level and up to a few hundred meters below ground level. 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, in which case the overlying cover could be more than 100 m deep.
In principle, repositories in caverns provide a higher level of containment and isolation than surface repositories. Also, the likelihood of human intrusion after repository closure is much lower, since the access to a closed underground facility requires greater technical effort. A further advantage of deep disposal is that the need for institutional control after closure is much diminished — in most cases, the land can be put to a range of uses, including agriculture, immediately after closure.
Definition of ILW depth disposal Reaching safety level comparable to geologic formations Take account of possible shorter timescale and processes (geological) which can be neglected
6.7.2[7.3.2] Deep Geological DisposalDeep Geological Disposal It consists inof 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 meters below ground level. Such a facility could beis typically designed to receive high level radioactive waste (HLW) [GSG-1], including spent fuel if it is to be treated as waste. However, with appropriate design, a geological disposal facility could receive all types of radioactive waste.
6.7.3 Boreholes
Borehole disposal entails emplacement of radioactive waste in an engineered facility of relatively narrow diameter. Disposal of some wastes in boreholes drilled from the surface may be a suitable option where waste volumes are limited (e.g. sealed sources). Depth ranges from a few metres up to several hundred metres and diameters from a few tens of centimetres up to more than one metre have been implemented. The waste would normally be contained within an engineered package because of the difficulty in ensuring appropriate conditions at the location of the waste in the borehole. Boreholes can be co-located in the area of a surface repository for short lived waste, which will help reduce the cost of disposal.
6.7.4 Intermediate Depth DisposalDepending on its characteristics, intermediate level radioactive waste (ILW) can be disposed of in different types of facility GSG-[12]. Disposal could be by emplacement in a facility constructed in caverns, vaults or silos at least a few tens of meters below ground level and up to a few hundred meters below ground level. 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, in which case the overlying cover could be more than 100 m deep.
In principle, repositories in caverns provide a higher level of containment and isolation than surface repositories. Also, the likelihood of human intrusion after repository closure is much lower, since the access to a closed underground facility requires greater technical effort. A further advantage of deep disposal is that the need for institutional control after closure is much diminished — in most cases, the land can be put to a range of uses, including agriculture, immediately after closure.
Definition of ILW depth disposal Reaching safety level comparable to geologic formations Take account of possible shorter timescale and processes (geological) which can be neglected
6.7.5[7.3.3] Geological Formations See HLW (GSG- 14)
[7.4] BoreholesDisposal of some wastes in boreholes drilled from the surface may be a suitable option where waste volumes are limited. For example, sealed sources can be diposed in boreholes. Depth ranges from a few metres up to several hundred metres and diameters from a few tens of centimetres up to more than one metre have been implemented. The waste would normally be contained within an engineered package because of the difficulty in ensuring appropriate conditions at the location of the waste in the borehole. Boreholes can be co-located in the area of a surface repository for short lived waste, which will help reduce the cost of disposal.
[7.5] Other disposal options
[7.5.1] Decay storageDepending on the contents of the ILW, decay storage can provide further options before final disposal. (decay of short lived radionuclides to enable safer handling and further conditioning options, if required)
[7.5.2] In-Situ isolationA number of practices have been used in the past, mainly to deal with certain kinds of legacy waste in conditions requiring remediation measures. They are not recommended practices in situations in which the options mentioned above are available or could be easily implemented, but they can constitute an acceptable practice for remediation purposes. These practices include:
In situ immobilization in tanks; In situ deep soil mixing; In situ vitrification.
[7.5.3] Long term storageFor relatively small volumes of waste, long term storage for up to 100 years and more can be considered an option. Such a solution may contradict the principles of sustainability and intergenerational equity, and assumes the fulfilment of a number of prerequisite conditions [22]. It may, however, be the best available solution at a given time until a repository becomes available. Such an interim storage has been implemented in the Netherlands, where a final solution for radioactive waste is not available at present.
[7.6] Aspects for Co-disposalAppropriately implemented geological repositories render the highest possible degree of waste isolation, and can therefore accept waste with high contents of long lived radioactivity. But the effort for implementation is high, so that their construction might not be justified for disposal of limited amounts of long lived waste. In some cases, co-disposal of ILW with HLW may be economically attractive and feasible. Interactions between waste types have to be considered.
– HLW– LLW
6.8[7.7] Consideration on Engineered Barrier SystemThe “Engineered Barrier System” represents the man-made, engineered materials places within arepository, including the waste form, waste canisters, buffer materials, backfill, and seals. The “nearfield”includes the EBS and those parts of the host rock in contact or near the EBS, whose propertieshave been affected by the presence of the repository. The “far-field” represents the geosphere (and biosphere) beyond the near-field.There is generally good consistency in EBS designs for high-level waste and spent fuel, butless for intermediate-level waste (ILW). The greater variation in the ILW disposal systems reflects thegreater number of ILW waste streams and the wide range of disposal sites and host rocks.
The main functions of EBS components can be summarised as follows: The waste matrix is designed to provide a stable waste form that is resistant to leaching and
gives slow rates of radionuclide release for the long term. The container/overpack is designed to facilitate waste handling, emplacement and
retrievability, and to provide containment for up to 1 000 years or longer depending on the waste type.
The buffer/backfill is designed to stabilise the repository excavations and the thermohydro-mechanical-chemical conditions, and to provide low permeabilities and/or diffusivities, and/or long-term retardation. [ref OECD-nea 2003]
In the long term, progressive degradation of the engineered barrier system (EBS) cannot be ruled out and, consequently, radionuclides may be released into the geological environment where they may eventually migrate to the biosphere. The disposal system should 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. Materials used for backfilling or sealing should have properties that do not degrade unduly the safety functions of the geological barriers.
A suitable combination of waste form and engineered barrier system may reduce the reliance on retention of radionuclides in the surrounding geosphere and, therefore, allow an increase in the specific activity of long lived radionuclides that can be accepted for disposal The choice of disposal option will affect the EBS that can be applied. If there are special requirements on the EBS this will affect the disposal option selected.
6.9[7.8] Other factors to be considered
6.9.1[7.8.1] Economic & technical resourcesAny chosen waste management strategy must be economically viable; achieving a cost-effective solution is 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 countries legal framework. Because skilled personnel are needed to design, construct, operate and close a disposal facility, their availability could, in principle, influence the choice of an option.
For countries with a limited amount of LILW-LL, disposing the waste in a regional repository shared with other countries can be an alternativettractive. Since underground disposal, especially deep disposal, have high fixed costs that are independent of the volume of waste, significant economies could be achieved if a repository were shared between several countries.
6.9.2[7.8.2] Public AcceptabilityThe national radioactive waste management policy of a Member State may prescribe or proscribe some radioactive waste disposal options. In general, this will usually simplify the decision making process. National policy may also prescribe the disposal site. When this is the case, the process of developing the repository concept may be simpler than would be the case if, for example, the concept had to be capable of being implemented at a range of sites. Legislative aspects may also constrain the siting procedure and programme development. Stakeholder involvement will occur at some point, early or late in the decision making process. The nature and extent of stakeholder involvement will also vary from one case to another.
Public acceptance for all diposal options is an important factor that may influence the final decision or even exempt some options. For example, near surface disposal of ILW might be acceptable for safety and economic reasons, but public acceptance may be in favour of deep geologic disposal, or while a regional repository may be viewed as a suitable option for economic reasons, public acceptance in the receiving region will affect the outcome.
• Check Technical report series 412 for consistency
7[8] Site IssuesThe depth of a disposal facility is dependent on the geology and the characteristics of the waste. The following site properties should be considered in determining the depth of the disposal facility taking into account of both current situation and future evolution during assessment period. The depth of the disposal facility should not be determined based on a single property.
7.1[8.1] SitingSiting is a fundamentally important activity in the geological disposal of radioactive waste. In the siting process for a radioactive waste disposal facility, four stages may be recognized: (i) a conceptual and planning stage; (ii) an area survey stage, leading to the selection of one or more sites for more detailed consideration; (iii) a site investigation stage of detailed site specific studies and site characterization and (iv) a site confirmation stage.
• Criteria for geology• Public acceptance• Feasibility• Check useful content in
– DS 356– SSG-14
7.2[8.2] Site propertiesIn the early part of a siting process, a suitable disposal site is normally determined by using existing information on the site. This information needs to be improved throughout the site investigation process. The depth of the disposal facility can then be determined based on favourable site conditions. Site condition (properties) relevant to repository performance are geologic properties, hydrologic and hydrogeologic properties, geochemical properties, migration properties, thermal properties, geomechanical properties, and biosphere. In particular favourable geological contexts are ones in which the migration of the contaminants is strongly reduced thanks to the characteristics of the rock matrix (low permeability, presence of minerals capable of capturing radionuclides, etc.) and the absence of preferential paths of flow.[NOTE: could be expanded to address ”what are desirable conditions & what needs to be characterized” with regard to containment and isolation]
In considering repository depth, favourable conditions for these properties should be considered, as well as their future evolution over the assessment period.
7.3[8.3] Site evolutionsWhen considering future evolution of the site, major change could be caused by climate change and geologic processes. Climate change will affect precipitation/recharge, permafrost, glaciation, sea level change, weathering and erosion. As to geologic processes, uplift/subsidence, unfavourable features such as active faults and active volcanoes should be generally avoided during siting. However, it’ important to take into account indirect effects from active faults, active volcanoes or others tectonic processesHowever, we might need to take into account of indirect effect from active faults or active volcanoes outside the excluded area. Indirect effects include heat from volcanoes, hydrothermal flow from volcanoes, from deep crust, and pyroclastic flow and differential uplift/subsidence.
Among aforementioned issues, precipitation/recharge, permafrost glacier, sea level change, weathering erosion/landslide, fault/fold are the most important for determining repository location and depth.For what concern near surface solution, climate change can also affect extreme meteorological events, eventually increasing intensity and frequency of events, reducing repository safety. This aspect has to be considered in safety case.
Indirect volcano phenomena, such as heat, hydrothermal and pyroclastic flow, are less important because their influence is not so significant and not related with depth.
[8.3.1] Precipitation/rechargeIn humid condition, due to greater precipitation, ground water table level can increase and greater recharge is expected, consequently fresh water could enter deeper part of the geosphere modifying geochemical conditions of the site and favouring migration processes of radionuclides. On the other hand, in arid condition, water table level will be decreased and reduced recharge is expected. When the water table is low, oxidized condition could develop in deeper part, consequently migration properties could change. Therefore, groundwater level change in long-term should be considered, when selecting repository depth.
Precipitation/recharge could strongly affect the biosphere and these should be appropriately treated in safety case.
7.3.1[8.3.2] Permafrost and glaciationMaterials used during the construction of the disposal facility may be impacted by permafrost and/or glaciglaciationser if the temperature becomes lower than freezing point. Permafrost and glaciations glacier could also reduce the hydraulic conductivity; glacier could force to inject oxic glacial (melt) water into deep underground. When determining the depth of the disposal facility, these need to be considered. Options may include a permafrost free environment as a function of the half-lives and toxicity of the radionuclides in the waste. However these processes need to be considered in the safety case. In the case of a permafrost permafrost-free depth and glacier glacial load , the changing boundary conditions caused by the permafrost and glacier glaciations need to be considered.Effects of Ppermafrost (and glaciations) could very strongly affecton the biosphere and these should be appropriately treated in safety case.
7.3.2[8.3.3] Sea level changeIn the case of sea level reductionchange (during glaciation), hydraulic gradient could increase and consequently water table level can decrease and redox condition and chemical composition including salinity of groundwater, as well as surface hydrology could be affected. These could further alter the migration properties. Options may include choosing greater depth. to avoid as a function of the half-lives and toxicity of the radionuclides in the waste. But, dDrawbacks of selecting greater depth could be more saline condition which would ma affect bentonite swelling properties. However, if the safety case shows safety, greater depth does not need to be considered.On the other hands the global warming could decrease the hydraulic gradient and water table level can increase and chemical composition of groundwater could change. Global warming is less important than glacier for safety of disposal facility.Sea level change could strongly affects the biosphere if the site is located in coastal area and these should be appropriately treated in safety case.
7.3.3[8.3.4] Weathering At some locations, weathering is an important consideration in the long term properties of rock hosting
disposal facility, since weathering could develop up to 100m from the surface and consequently alter geology itself, hydrologic/hydrogeologic properties, redox conditions, migration and mechanical properties. Options may include choosing greater depth to avoid weathering as a function of the half-lives and toxicity of the radionuclides in the waste, as well as a weathering progress rate.
7.3.4[8.3.5] Uplift/Erosion and Subsidence/SedimentationAt some locations, uplift/erosion is an important and crucial consideration in the long term properties of a disposal facility. Erosion could reduce the geosphere/host rock thickness and alter the hydrologic/hydrogeologic properties, redox condition and geochemical conditions. On the other hand, subsidence/sedimentation could increase repository depth in longer time, and generally work in favourable way, unless rock stress reaches too high to degrade repository properties. In the uplift/erosion area, repository depth should be chosen taking into account of as a function of the half-lives and toxicity of the radionuclides in the waste, as well as an erosion rate. In some area, such as a mountainous area, not only consecutive erosion but also possibility large-scale landslide needs to be evaluated.
7.3.5[8.3.6] Faulting/foldingEven after avoiding active faults and/or folding during siting, effect of active faults/folds can remain such as a block movement in kilometres to several tens of km scale. These can be treated as uplift/subsidence.
7.3.6[8.3.7] Relation with human intrusionThe type of human intrusion scenarios will be determined by the depth and the location of the disposal facility, as well as site evolution such as glaciation, sea level change, and uplift/erosion.
8[9] Disposal Facility 8.1[9.1] Requirements on the disposal facility[NOTE: add description from DS356 also]
Specific Safety Requirements No. SSR-5 specify 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 designs of disposal facilities for radioactive waste may differ widely, depending on the types of waste to be disposed of and the host geological formation and/or surface environment. In general, optimal use has to be made of the safety features offered by the host environment. This has to be done by designing a disposal facility that does not cause unacceptable long term disturbance of the site, is itself protected by the site and performs safety functions that complement the natural barriers. The layout has to be designed so that waste is emplaced in the most suitable locations.”
Specific Safety Guide No. SSG-14 relating to Geological Disposal Facilities for Radioactive Waste provides design guidelines which can be applied to disposal facilities for ILW. Draft Safety Guide DS 356 relating to Near Surface Disposal Facilities for Radioactive Waste can also be used in a complementary way. It stipulates in particular that: “The initial design of the facility should be used to validate the suitability of a candidate site for the disposal facility. The design of the facility, the physical characteristics of the site, and the characteristics of the waste or inventory are mutually interdependent and need to be managed in such a way that a set of independent and complementary safety functions can be proposed in order to achieve the desired performance of the disposal system. The initial design of the facility should be used to demonstrate that the site, in combination with the design of the facility and the characteristics of the waste, will provide adequate containment and isolation of radionuclides for the necessary period of time.”
Taking into account these existing or draft guidelines, there is no need for specific guidance for ILW. As a function of the ILW characteristics one can use either SSG-14 or DS-356.
8.2[9.2] Design considerationThe layout of the facility, the design of the individual vaults and the volume and characteristics of the waste determines the footprint of the repository. A generic design is adopted to make best use of the space available at the selected site.
The potential impact on the degradation of the waste form and package and on the dissolution and retention of radionuclides must be considered when selecting materials used to construct the disposal cells and pits. The differences of the 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 , in many cases due to co-location and large waste volumes considered and in some cases due to co-location. A long containment period provided by durable waste packages may not be needed utilised for lower activity long-lived waste. The engineered and natural materials in the near-field also need to be selected taking into account potential chemical disturbances induced by the waste (e.g. nitrate resistant cement).
Gas generated by the wasteILW needs to be managed during the operational phase to protect workers. The facility also needs to be designed to account for gas generation during closure and beyond.
Engineered structures need to resist hydrostatic pressures and in-situ stresses at the chosen depth. This may affect the sizing of the disposal cells/pits, the distance between them, the dimensions of the rock support and other engineered structures. The above considerations apply to underground works or on pits with an engineered cover.
The safety case and supporting safety assessment for a particular design will provide the required demonstration of its suitability.
[9.3] Design consideration for long-term performanceThe design considerations for an ILW disposal facility are typically no different than for other types of disposal facilities, i.e. Geological Disposal Facilities for Radioactive Waste (IAEA Safety Guide SSG-14). The objective of any disposal facility should be to provide containment or isolation on the necessary timescale.
The multi-barrier concept and repository depth should form the foundation of the design considerations. The design considerations need to take into consideration the waste type and form, site properties and their evolution, repository depth. Design considerations also needs to address disposal facility access-ways, shaft layout, cage and hoisting system, facility layout and development sequence, ventilation system, room and tunnel configurations, waste package handling system, waste rock management and finally shaft seal system.
Issues of importance for design is program dependant, a relatively complete list may be obtained by a systematic analysis of the relevant FEP:s based on the characteristics of the waste and the engineered and natural barrier system.
An example of factors that may be relevant as design consideration are: #Write a paragraph for each topic#.
8.2.1[9.3.1] pH : selection of a suitable concrete take into account the alkaline plume in the design of EBS in particular with swelling bentonite. If waste is pH sensitive (high /low) this must be considered.
8.2.2[9.3.2] Metal (reactive with water, corrosion, hydrogen gas): waste package to limit reactivity with groundwater.
8.2.3[9.3.3] Nitrate (bitumen): separate nitrate waste from no-nitrate waste; take into account redox disturbance (PA)
8.2.4[9.3.4] Organic (bitumen, organic waste, concrete): separate organic waste from no-organic waste during packaging and in disposal vaults and taking into account in PA
8.2.5[9.3.5] Swelling (bitumen): try to characterize and take into account in design (allow volume for expansion) and in EBS
8.2.6[9.3.6] Fissile material: sub-critical geometry
8.2.7[9.3.7] Mobile/gaseous radionuclide (Cl-36, C-14): take into account in PA, enhanced EBS, and/or higher retention host rock by site selection
8.2.8[9.3.8] Great waste volume (greater than HLW): taken into account in design (larger disposal vaults, but verifying mechanical and hydrogeological impact (EDZ) on surrounding host rock)
8.2.9[9.3.9] Interaction between various ILW: separation as necessary
8.2.10[9.3.10] Interaction with other types of waste in case of co-disposal (thermal and chemical): provision for sufficient distances, respective location regard to hydrogeological system as necessary.
8.2.11[9.3.11] Large itemsMoreover, dDecommissioning of installations may produce a number of large LLW/ILW components (i.e. steam generators, control rods, pumps, and motors, etc..), fFor these items, the (metalic) waste form in itself may be necessary to limit radionuclide releases.
8.2.12[9.3.12] Waste formThe waste form provides certain radionuclide containment. The physical-chemical properties of the waste form, including the nature of the contaminant, and its compatibility with other engineered barriers and specific environmental conditions, will determine the rate of radionuclide release. Once the container degrades, giving rise to access of water to the waste, releases of radionuclides are determined primarily by the properties of the waste form.
8.2.13[9.3.13] HeatTaking into account the volume of ILW (section 3.1) the number of waste packages per disposal cell or pit and its volume has to be optimized with regard to the footprint of the disposal facility whereas the optimisation of the design of an HLW disposal facility is generally driven by heat generation.
However some ILW may generate heat which should not be neglected in the facility design. Then provision needs to be made in the design and spacing of the disposal cells to dissipate heat to comply with temperature limits assigned to:
- engineered and natural materials with respect to their safety functions and- operational conditions (protection of people and operating systems).
8.2.14[9.3.14] VoidageResidual voidage in conditioned waste and/ or in the packaged waste should be addressed in respect to the desired properties of the engineered system. Voidage may result in the establishment of a local chemical environment which facilitates corrosion or microbial activity. Large voids may cause structural instability which, in turn, may lead to collapse of the engineered system.
8.2.15[9.3.15] And others…
At the time scale of the repository, degradation of the waste and the waste package should be taken into account, for instance:
Corrosion Gas generation Degradation of organics and formation of complexing agents Chemical reaction with particular compounds (i.e. heat production) Mechanical stability of the waste and packaging Swelling of waste
Also degradation of the EBS must be taken into account, for instance
- Bentonite alteration- Concrete degradation- Fracturing- Mechanical load due to alteration of the waste- Load due to gas generation and gas breakthrough- Geological loading- Rebar corrosion and associated fracturing of concrete- Fluid intake- Embrittlement of polymers
Bases for design should be built on assessment of long-term performance.
[9.4] Pre-operational period (design and planning)The pre-operational period includes the definition of concepts, site investigation and confirmation, safety assessment, site selection, design studies and development of the aspects of the safety case for safety during operation and safety after closure that are required in order to set the conditions of authorization, to obtain the authorization and to proceed with the construction of the disposal facility and the initial operational activities. The monitoring and testing programmes necessary to inform operational management decisions are put in place in this period.
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.
Site characterization is an activity undertaken in order to understand the natural features, events and processes at a site (at the present time, in the past and potentially in the future) and to describe adequately their spatial and temporal extent and variability. Site characterization contributes to a comprehensive description of the site, which may include information concerning anthropogenic characteristics.
In the siting process for a radioactive waste disposal facility, four stages may be recognized: (i) the conceptual and planning stage, (ii) the área 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. Detailed site characterization is required for site confirmation for construction of the disposal facility and may continue through the phases of construction and operation.
Site characterization should comprise both surface based investigations and underground investigations. The latter may be undertaken as a precursor to commencing construction of the disposal facility, whereby characterization and in situ experiments could be carried out in an underground laboratory or rock characterization facility at the potential disposal site.
Site characterization should be undertaken in an iterative manner with safety assessment, as it provides input to, and is, in turn, guided by, the development of the safety case.
• Verify Waste streams• Check useful content in
– DS 356– SSG-14– Technical report 412 (p11)
•
8.3[9.5] Facility ClosureA disposal facility shall be closed in a way that provides for those safety functions that have been shown by the safety case to be important after closure. Plans for closure, including the transition from active management of the facility, shall be well defined and practicable, so that closure can be carried out safely at an appropriate time [SSR-5].Closure has to be considered in the initial design of the facility, and plans for closure and seal or cap designs have to be updated as the design of the facility is developed.
The disposal facility has to be closed in accordance with the conditions set for closure by the regulatory body in the facility’s authorization, with particular consideration given to any changes in responsibility that may occur at this stage.
Backfilling and the placement of seals or caps may be delayed for a period after the completion of waste emplacement, for example, to allow for monitoring to assess aspects relating to safety after closure or for reasons relating to public acceptability.
Availability of the necessary technical and financial resources to achieve closure has to be assured.
• Conditions at closure• Technical• Time considerations• Check other documents
8.4[9.6] Post closure periodNational safety regulations for a repository should reflect the basic principles and safety requirements issued by the IAEA [IAEA Safety Standards Series SSG-14, SSR-5, BSS]. These regulations should describe the required level of safety for a facility. This will usually be expressed as a probabilistic risk of death or, in the case of exposure to radiation, it may be expressed in terms of dose. The regulators in many countries either specify a radiological risk of death of less than 10 –6 per year, or an individual dose of less than 0.1–0.3 mSv per /ayear to an individual from the most exposed group. However, because predictionsestimates of either risk or dose in the long term have considerable uncertainties, these predictionsestimates should be supported by ‘multiple lines of argument’, which demonstrate the robustness of the disposal approach with respect to safety.
Post-closure safety is usually a major factor in deciding on the repository option that should be selected, and a frequently used approach is to develop a normal scenario that describes the way the repository is expected to evolve over time. This might include, for instance, gradual degradation of the engineered barriers and changes in climate. Complementing this is a series of non-normal or less-likely scenarios that include events or processes that have a lower probability of occurring.
Compliance with the national requirement must be demonstrated by a long term performance assessment for the repository and the waste inventory for which a license is being sought. A normal scenario should include consideration of all features, events and processes (FEPs) that are likely to occur over the timescale of interest. These include extreme meteorological events and expected climate states such as might be expected to result from anthropogenic warming and future glaciations.
Post-closure safety assessments must also be used to assess less likely scenarios that assess the possibility that the repository evolution may not follow the normal scenario. If the safety requirement is expressed in terms of risk, the total risk, including any possible combinations of FEPs, must be shown to be less than the regulatory constraint. Some of the potential events that should be considered are discussed below, inadvertent human intrusion being usually the most important of these: inadvertent human intrusion; aircraft crash; seismic event; tsunami; extreme climatic conditions and other natural effects [NES NW-T-1.20].
• Active and Passive periods of control
9[10] Operational issues
Disposal facilities receiving waste from nuclear fuel cycle facilities will generally be licensed nuclear facilities and have to operate under the terms of a facility license. Disposal facilities for small quantities of waste may not be regarded as nuclear facilities in some Member Sstates but have to be subject to an appropriate regulatory process and have to be licensed accordingly.
In radiation safety terms, the disposal facility is considered to be a source of radiation that is under regulatory control in a planned exposure situation. In the operational period, any radioactive release can be verified, exposures can be controlled and actions can be taken if necessary.
The operational period of a repository is the period during which the repository, after construction, is operated and finally closed. During this stage, radiation exposures to workers and to the general public could hapenoccur. In the context of radioactive waste disposal, protection and safety must 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.
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 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.
[10.1] Variety of waste packages; geometry One main difference between a disposal facility for HLW and one for ILW is the larger variety of waste types that need to be managed in an ILW disposal facility. This larger variety of waste types may also exist in the characterization of LLW in a near-surface disposal facility, This large variety of waste types result in a potentially large variety of waste packages in terms of dimensions and shapes of the packages, for instanceetc. In addition, there may also be a desire to dispose of larger components which is not the case for HLW-only disposal facility. When designing handling equipment and other parts of the disposal system, this has to be taken into account.
Furthermore in an ILW disposal facility both operational and decommissioning waste may need to be considered. There is a higher potential to standardise operational waste than there is for decommissioning waste. The waste for an ILW disposal facility may, for instance, consist of large components (i.e. pumps, steam generators, pipes) that, in order to minimise dose to workers, need to be disposed of intact.
The disposal of large components, for example those resulting from decommissioning operations, may create operational issues, both logistically and radiologically. Some ILW including large components 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. The other issue that needs to be considered is the radiological issue during the operational phase. These large components may need additional shielding and workers may have to operate close to the component. Large components may also put other requirements on the disposal system, such as the installation of a ramp as opposed to a shaft.
The large variety and the composition of the ILW needs to consider various issues that are not associated with HLW such as chemical interactions between different waste types as well as between the waste and the engineering system.
9.1[10.2] Operational safety Operational safety assessment may include events and processes like:
Internal eventso Fire hazardso Component failureo Operational mistakeso Loss of powero Contamination on waste packages and equipmento Drainage watero Ventilation exhaust air
Processeso Underground worko Waste transporto Waste emplacemento Radon generation
o Radiation External events
o Metrological changeso Earth quakeso Sea level changes and floodingo Antagonistic events and airplane crash
For an underground ILW facility the same regulations are applicable as for deep geological disposal facilities. Depending on the amount of fissile material in the waste, criticality may be an issue even for ILW.
9.2[10.3] Operational time periodThe amount of waste being produced may depend on a variety of factors. Therefore, it is often difficult to define the duration of the operational time period well in advance. This may cause the need for extending the originally planned operational time period. 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. Handling principlesWaste handling may be governed by national worker safety, transport and radiation protection regulations or others. Waste handling and transport equipment of the disposal facility has to take into account all the different types of waste planned to be disposed of. Waste packages with higher surface doses may need remote handling and/or shielding. This may be even more complicated for large components.
Retrievability & Reversibility
Retrievability denotes the possibility of reversing the action of waste emplacement. It is thus a special case of reversibility. Retrieval is the action of recovery of the waste or waste packages. Retrievability, the potential for retrieval, may need to be considered at various stages after emplacement, including after final sealing and closure. In discussing retrievability and retrieval, it is important to specify what is to be retrieved, since this affects the implementation and technical feasibility. Retrievability could, for example, refer to: retrieval of individual waste packages which are identified as faulty or damaged, even as emplacement of other packages continues; retrieval of some or all of the waste packages at some time after emplacement; or retrieval of the waste materials if the packages are no longer intact. Retrievability may be facilitated by the repository design and operational strategies, for example, by leaving underground access ways open and emplacement/retrieval systems in place until a late stage. [Reversibility and Retrievability in Geologic Disposal of Radioactive Waste. Reflections at the International Level – NEA, 2001]
Reversibility denotes the possibility of reversing one or a series of steps in repository planning or development at any stage of the programme. This implies the review and, if necessary, re-evaluation of earlier decisions, as well as the means (technical, financial, etc.) to reverse a step. Reversibility denotes the fact that fallback positions are incorporated in the disposal policy and in the actual technical programme. Reversibility may be facilitated, for example, by adopting small steps and frequent reviews in the programme, as well as by incorporating engineering measures.
Engineered geologic disposal will be implemented in a step-wise manner, with well-defined stages interspersed with decision points that allow opportunities for technical, regulatory, policy, and, in some cases, public review. Steps that can be recognised in most programmes include: concept development, site selection, repository construction, performance confirmation (or demonstration phase), waste emplacement, backfilling and sealing of the repository. In addition, many sub-steps may be defined that are specific toindividual programmes.
Retrievability of ILW is usually less of an issue compared to HLW disposal. However, in some cases it has been decided to retrieve single waste containers or the whole waste out of a disposal facility. In this case retrieval is easier if it was taken into account during facility design and for operational features. For example, when grouting is done during waste emplacement it will be more difficult to retrieve waste compared with grouting at the end of the operational time period.
Transport to disposal facility
Transportation of radioactive waste is regulated, in mostly of the Members States, by Safety Requirements N0 TS-R-1 “Regulations for the Safe Transport of Radioactive Material”.
Transport of waste following standardised specifications should not be an issue during the operational time period of the facility. Usually, transport to the disposal facility is governed by a separate license. For the transport of large components or waste with properties outside standardised specifications special considerations may be necessary.
Conditioning of wasteConditioning of waste can be made at the disposal site or inat another installation to facilitate the transport of the waste. It will depend of the radioactive waste management at national level.
Waste acceptance requirements and criteria for a given disposal facility have to ensure the safe handling of waste packages and unpackaged waste in conditions of normal operation and anticipated operational occurrences. They also have to ensure the fulfillment of the safety functions for the waste form and waste packaging with regard to safety in the long term.at the disposal facility may be needed depending on national programmes. It might for instance be disadvantageous to transport heavy grouted waste packages to the disposal facility or it might be advantageous to condition waste at a centralised location. When planning conditioning of waste one also has to take into account the possible large variety of ILW should be taken into account.
10[11] Institutional control and Record keeping10.1[11.1] Institutional control[NOTE: add description from DS356 also]
Specific Safety Requirements No. SSR-5 provide that
“after its closure, the safety of the disposal facility is provided for by means of passive features inherent in the characteristics of the site and the facility and the characteristics of the waste packages, together with certain institutional controls, particularly for near surface facilities. Such institutional controls are put in place to prevent intrusion into facilities and to confirm that the disposal system is performing as expected by means of monitoring and surveillance.”
IAEA Specific Safety Requirements No. SSR-5 points out differences between near surface and geological disposal with regard to the institutional control:
- “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. (…) Near surface disposal facilities are generally designed on the assumption that institutional control has to remain in force for a period of time. (…) The waste acceptance criteria will limit any consequences of human intrusion to within the specified criteria, even if control over the site is lost.”
- “For geological disposal of radioactive waste, isolation is provided primarily by the host geological formation as a consequence of the depth of disposal. (…) Geological disposal facilities have not to be dependent on long term institutional control after closure as a
safety measure. Nevertheless, institutional controls may contribute to safety by preventing or reducing the likelihood of human actions that could inadvertently interfere with the waste or degrade the safety features of the geological disposal system.”
According to ICRP 122:
“During the post-operational phase, the presence of man is no longer required to directly manage the facility. This is the longest phase, and it can be divided into two relevant time periods.
_ The period of indirect oversight. After closure, safety is assured totally through the intrinsic, built-in safety provisions of the design of the disposal facility. Nevertheless, it is expected that monitoring of the baseline environmental conditions will continue for a period of time as well as regulatory or societal oversight. Archives of technical data and configuration of waste packages and the disposal facility are kept, and the use of warning signs or markers to remind coming generations of its existence may be considered. The relevant international safeguards and controls continue to apply. Inadvertent human intrusion in the disposal facility can be ruled out.
The period of no oversight. It is not possible to foresee the point at which indirect oversight might terminate; nevertheless, it must still be considered in the design and planning stage as there is no guarantee that the memory of the site will persist into the distant future, and therefore that the oversight will be maintained indefinitely. Eventually, loss of memory and consequently loss of oversight may take place, either progressively or following major unpredictable events such as war or loss of records. Therefore, inadvertent human intrusion in the disposal facility cannot be ruled out during this time period. The intrinsic hazard of the waste decreases with time, but it may continue to pose a significant hazard for a considerable time. Nevertheless, the loss of oversight does not result in a change in the intrinsic protective capability of the disposal facility.”
The maximum duration of the institutional control period should be less than the duration of the societal capability to control the land use with time. This is generally considered as restricted to a few hundred years. In France for instance, a 500 years limit is considered in their national safety guides. The time period Whether iiInstitutional control canould solely be relied on depends on half-life and activity level of the disposed waste. Specific Safety Requirements No. SSR-5 indicates that for short lived waste disposed of in near surface disposal facilities, “the period [of the institutional control] will have to be several tens to hundreds of years following closure.” IAEA safety standards do not impose any minimum duration for the institutional control of geological disposal after closure.
Since the safety case cannot rely on institutional periods longer than several hundred years , human intrusion scenarios must be considered after the institutional control period. For shallower depths, civil works such as tunnel boring are to be considered. For greater depths, drilling might be the reason for human intrusion. Potential mining or the construction of other underground storage facilities may also be considered. It is generally considered that the deeper the disposal facility, the likelihood of human intrusion decreases. Human intrusion scenarios in the safety case can limit the acceptable activity in the disposal facility after the institutional control period and justifies the duration of the institutional control.
Avoidance of human intrusion may not just be depth dependant. For remote sites, the need to take active measures to avoid human intrusion may be different for sites located near people provided a limited timescale for the safety case is appropriate.
10.2[11.2] Record keeping
The lifetime expected for ILW disposal is very long and eventually, loss of memory and consequently loss of oversight may take place, either progressively or following major unpredictable events such as war or loss of records. This would be a very undesirable situation that could be saved if a good programme of record keeping is established.
In meeting the requirements, it is necessary that the operator retain all information relevant to the safety case and the supporting safety assessments of the disposal facility, 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 organization assumes responsibility for the facility, at which time the records should be transferred to the organization that assumes that responsibility.
The management systems for records should be structured to accommodate the information associated with waste acceptance, including the data indicated in the previous paragraph, and records on waste generation and processing.
Institutional controls may include the construction of durable markers, the posting of facility records in national and international archives accessible to future populations and the transfer of responsibility for the facility to a successor organization. A suitable mechanism may need to be developed for the transfer of responsibility from one generation to the next.
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
• Describe good practice– Longevity– comprehensive
• OECD – NEA project
11[12] Safety Case [subsection to be developed]• Other safety arguments
• Reference Relevant Documents (SSG-23)
11.1[12.1] Safety requirements (SSR 5 fully applicable)
11.2[12.2] Assessment bases
11.2.1[12.2.1] Waste characteristics (volume, activity, final waste form, emission type, gas release/production, heat production, chemotoxicity) – reference to chapter 6
11.2.2[12.2.2] Site and disposal facility (reference to previous chapters)
11.2.3[12.2.3] Assessment timeframe (reference to chapter 5)
11.3[12.3] Safety assessment
11.3.1[12.3.1] Scenario development (normal evolution, other evolution, human intrusion)
Surface processes
Gas migration
Interaction between waste, EBS/rock and co-disposal
11.3.2[12.3.2] Consequence analysis (radionuclide migration)The main purpose of a disposal facility is to isolate the waste from the biosphere. When considering a disposal facility, the capability to isolate the waste must be considered and this capability should not be related to the depth itself but to depth related properties.
Depth related properties should be considered in order to impede or minimize radionuclide migration. Over time containment of the radionuclides cannot be assured, therefore isolation from the biosphere needs to be considered. The biosphere is defined in the glossary as:
Biosphere That part of the environment normally inhabited by living organisms. In practice, the biosphere is not usually defined with great precision, but is
generally taken to include the atmosphere and the Earth’s surface, including the soil and surface water bodies, seas and oceans and their sediments. There is no generally accepted definition of the depth below the surface at which soil or sediment ceases to be part of the biosphere, but this might typically be taken to be the depth affected by basic human actions, in particular farming.
In waste the safety casein particular, the biosphere is normally distinguished from the geosphere.
Measures for the protection of the biosphere may include means other than depth itself, such as: impermeability to water, dissolution, leach rate and solubility; retention of radionuclides; and retardation of radionuclide migration. Some of these properties are related to the geosphere and may be depth related and may be used to impede and minimise the transport of radionuclides to the biosphere. Over time the migration of longer lived radionuclides in a disposal facility may be inevitable. The use of geological conditions at certain depths will assist in impeding the migration of the radionuclides but the bulk of the geosphere may be sufficient to provide isolation.
The required performance concerning radionuclide migration can be graded to the activity level of the waste with respect to the long-term protection of man and environment.
11.3.3[12.3.3] Analysis of uncertainties and sensitivity
11.4[12.4] Other safety arguments
11.5[12.5] Waste acceptance criteria (reference to SSG-14)[might be moved to a new chapter][NOTE: - Provide more detail- Challenge between standardization and innovation or diversity- Site specific issues- Challenging wastes
Small volume with specific hazardsLarge itemsLegacy
- Recognize its an important link to safety case]As with any other disposal facility, the establishment of waste acceptance criteria is essential to ensure the continued validity of the safety case. In the case of an ILW disposal facility, it is important to recognize that due the large variety and complexity of the ILW waste, the waste acceptance criteria will need to be reviewed and adjusted if required. Any changes of the waste acceptance criteria will need to keep in mind the boundaries of the safety case.
Paragraph 6.38 in SSG-14 identifies some issues to consider in the waste acceptance criteria that are also applicable to ILW waste.
(a) The permissible range of chemical and physical properties of the waste andthe waste form;(b) The permissible dimensions, weight and other manufacturing specificationsof each waste package;(c) Allowable levels of radioactivity in each package;(d) Allowable amounts of fissile material in each package;(e) Allowable surface dose rate and surface contamination;(f) Requirements for accompanying documentation;
(g) Allowable decay heat generation for each package.
11.6[12.6] Evolution of safety case
11.7[12.7] Documentation of safety case (transparency, traceability, comprehensiveness)
12[13] National Examples• Ask countries for input – short summaries • Cover all aspects from definition to solution • Analysis of common features and differing approaches
12.1[13.1] National examples[Needs to be improved and completed by Member States]Canada:
Intermediate level waste disposal facility at 683m. The reason for choosing this depth is a suitable host formation at that depth, not the depth itself. In the facility also LLW will be disposed.
France: SL-ILW co-disposed with SL-LLW in a near-surface facility. LL-ILW planned at 500m, the reason for choosing this depth is a suitable host formation at
that depth, not the depth itself. However, regulations require a depth of more than 200m for this kind of waste. In this facility, CIGEO, HLW will also be disposed.
LL-LLW, disposal concept not yet decided. Siting and conceptual design is still ongoing. Depth will at least be around 15m or more due to geological properties (hydrogeological and chemical) at the site.
Germany:Waste classified based on heat generation
Heat generating waste, will probably be co-disposed with spent nuclear fuel and HLW. Non-heat generating waste will be disposed of in the Konrad repository at a depth between
800m and 1200m, the chosen depth is due to geology at the site. LLW and SL-ILW has been disposed of at the Morsleben repository at a depth of about 500m
in a former salt mine.Sweden:
SL-ILW is co-disposed with LLW in the SFR facility. The depth of the facility is between 70 and 120 m. The depth of the facility was selected based on the geological properties (hydrogeological) at the site.
LL-ILW, design of the facility is ongoing. USA
LL-ILW from defence disposed of in the WIPP disposal facility at a depth ~655 m. The reason for choosing the depth is geological conditions at the site.
Italy: Legislative Decree n. 31/2010 establishes realization of a near surface repository for the LLW,
SL-ILW disposal and the LL-ILW, HLW long term interim storage. It provides criteria for siting and approval procedures, with compensation rules for the local municipality.
The Decree assigns to Sogin (Italian WMO) the responsibility to propose candidate sites to host the repository, based upon criteria established by the IAEA, by the national Nuclear Safety Authority and considering results of Strategic Environmental Evaluation.
Siting and conceptual design of the repository is ongoing. Radioactive waste are temporary stored in the original nuclear plant or facility, until repository will not be available.
12.2[13.2] Analysis of common features and differing approaches
13[14] Conclusions(needs to be updated by using following description (output from consultancy in April))
Intermediate-level waste (ILW) is, from a disposal and safety case perspective, situated between low-level waste which can be disposed of in a near surface facility and high-level waste that must be disposed in a deep geological formation. 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. This justifies the treatment of ILW as separate waste stream(s).
For some ILW with significant amounts of uranium or plutonium, criticality and safeguards can be an issue. Also heat generation can be an issue for the sizing of disposal cells for some ILW. Concerning chemotoxicity the situation of some ILW waste can be similar to LLW waste whereas it is not an issue with HLW waste. With regard to mechanical and chemical disturbances induced by the waste packages, the properties of ILW are generally closer to low level waste characteristics than to HLW characteristics. Regarding dose rates, potential surface contamination and resistance of the waste packages to operational hazards, such as fire and drop scenarios, provision in the design regarding these factors are to be graded to the activity level of the waste.
It is not recommended to discuss an ILW disposal facility only in terms of depth but rather by considering many influencing properties that can provide an acceptable degree of containment and isolation. The depth of the disposal facility should be primarily determined based on a set of site specific properties, such as site geology, permafrost and glaciation, erosion, redox, as well as waste properties and facility design.
Whatever the type of waste and the repository depth, the safety case has to define an appropriate time-scale. It must be consistent with the natural evolution of the site and the considered depth on the one hand, and with the characteristics of the waste, in particular the reduction of activity with time as a function of the half-life of radionuclides. An assessment timescale over 1 million years may require disposal in a deep geological formation. An assessment timescale between 10,000 and 100,000 years may result in disposal at a swallower depth. The acceptable content of long lived radionuclides is a function of the applicable time scale.
The safety case cannot rely on institutional 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.
The design considerations for an ILW disposal facility are typically no different than for other types of disposal facilities; however, the final design will be specific to the characteristics of the waste, for instance the construction material used and the volume size of the cells or pits.
The large variety and the composition of the ILW waste needs to consider various issues that is not associated with a HLW waste such as gas generation and compatibility between different waste types as well as between the waste and the engineering system. These issues are however more related to LLW waste.
Paragraph 6.38 in SSG-14 identifies some issues to consider in the waste acceptance criteria that are also applicable to ILW waste.
<recommendations>1. It is recommended to revisit the definition of the ILW (GSG-1) to potentially provide more
flexibility. Consideration on long-lived LLW and short-lived ILW could be included without imposing the types of disposal facilities in the sense of near surface or geological.
2. Historically, the depth has been associated with the class of wastes, e.g. LLW is associated with near-surface disposal. This has resulted in confusion with respect to disposal facilities for ILW. The depth of the disposal facility should be adapted to the characteristics of the waste such as the half-life as well as site-specific geological and technological features.
3. Consideration should be given to one or more separate waste streams for ILW as a function of half-life.
4. Some ILW can be characterized by intermediate half-life nuclides (radium 226, carbon 14 or americium 241) which are compatible with an intermediate timescale that can be used in the safety case. This timescale lies between short-lived LLW and HLW.
5. ILW has a higher diversity than HLW and different mechanisms, in particular interactions between the waste and its environment, are to be considered in the design and safety case.
6. ILW waste streams needs development of specific disposal options which can be co-located or not with other types of waste.
7. While developing disposal options for ILW, the existing IAEA safety guides relating to LLW and HLW can be used as appropriate.
8. This report can constitute a first draft in the development of a TECDOC of which the purpose is to assist in the use of existing guides for the development of ILW specific disposal facilities.
9. On this basis, existing guides could be updated to make them more efficient for ILW for instance to take into consideration all potential characteristics of ILW and to adapt the wording.
APPENDIX I: site evolution matrix
(NEED TO ADD DESCRIPTION)
Extract depth related issues to 1) for selecting repository depth2) for identifying issues when site properties change due to climate change and geological processes
Future site evolutionProperties
Depth dependency
Climate change Tectonic
Precipitation/Recharge Permafrost Glacier Sea level
change1Weathering(max 100m)
Erosion/landslide
Uplift/Subsidence
Fault/fold
Volcano phenomena Mud-volcano3
(max 10km dia.700m high)
Heat Hydrothermal Pyroclastic flow
Relevant time scale<70,000 yrs
70,000 yrsEvery 100k yrs 4
70,000 yrsEvery 100k yrs 4
70,000 yrsEvery 100k yrs 4
>20,000 yrs1,000,000yrs(0.1mm/y)5
>several 100k yrs
>several 100k yrs
Any time Any time Any time Any time
Design considerationsRepository depthEnhanced EBS
Repository depthEnhanced EBS
Repository depthEnhanced EBS
Repository depthEnhanced EBS
Repository depthEnhanced EBS
Repository depth/location
Repository depth/location
G Geology Depends on geology
N N N N S SThickness can change
N N N N N N
H
Hydrology S S S S1 SS
Could change
topography
W S N NS
Volcanic rock tends to high K
N
HydrogeologyPossible increase in groundwater flow
Hydraulic conductivity
Generally decreases with depth (depends on geology)
N S2S (?)
Depends on ice
thickness
N S2 S2
Thickness can change
N N N N N N
GradientGenerally decreases with depth
MS
Permofrost act as a “cap
rock”S M-S N S M
M-SFolding
could alter topograph
y
N W N N
C
HydrochemistryPossible growth of oxic conditions and chemical composition change, including salinity
RedoxGenerally more reducing with depth
S2
In arid climate,
water table can be
lowred and provide oxic
cond.
NM (?)Oxic
gracial water
injected
S1
Water table can be
lowered
S2
Water table is low.
S2 N/W N N S N N
Chemical composition
S2 W (?)
SOxic
glacial water
injected
S1
Fresh water can seep in
deeperS1 S2 N/W N/W N S W-M? S
SalinityGenerally increase with depth
M M (?)S
Oxic glacial
S1
Lower salinity
N M M M N N N S
Notes1 – It depends on repository depth and location (coastal/inland).2 – It depends on repository depth (less than 100 m)3 – It occurs in young (tertiary) sediments, typical of Japan and Indonesia.4 – Because of the global warming timeframe can be lowered5 – Erosion rate can increase because of glacier and landslide(mass movement)
LegendN: No influenceW: Weak influenceM: Moderate influenceS: Strong influencehigh:Issues relating to repository depth
water injected
during retreat
MI
Migration propertiesPossible reduction of distribution coefficient (kd) – Faster migration
Depends on geochemistry
S2 N (?) S S1S2 S2
N/W N/W N S N S
M Mechanical
Rock stenght/stress Possible decrease/increase of rock stress
Higher stress as depth
N N SIncreased
stressN S
S2
(Rock stress will change)
N
W-MFolding could
increase horizontal
stress
N N N N
T Thermal
TemperaturePossible increase in temperature
increase N S S N N N N N S S S2 N
B Biosphere S S S S N M N N N N S N
HI Human intrusion N N S S N S N N N N N N
(Left)Berca Mud Volcanoes near Berca in Buzău County, Romania
(Right)Hydrate-bearing sediments, which often are associated with mud volcano activity.Source: USGS, 1996
Waste type/volume: high pH (concrete): selection of low pH concrete or limitation of volume of waste which can be affected by high pH; take into account the alkaline plume in the design of EBS in particular with swelling bentonite Metal (reactive with water, corrosion, hydrogen gas): waste package to limit reactivity. Nitrate (bitumen): take into account redox disturbance (PA); separate nitrate waste from no-nitrate waste Organic (bitumen, organic waste, concrete): separate organic waste from no-organic waste during packaging and in disposal cells and taking into account in PA Swelling (bitumen): try to characterize and take into account in design (volume for expansion) and in EBS Fissile material: sub-critical geometry Mobile/gaseous radionuclide (Cl-36, C-14): take into account in PA, EBS, site selection Great waste volume (greater than HLW): taken into account in design (larger disposal vaults, but verifying mechanical impact on surrounding host rock) Interaction between various ILW: separation as necessary Interaction with other types of waste in case of co-disposal (thermal and chemical): provision for sufficient distances, respective location regard to hydrogeological system as necessary.
Waste degradation: Corrosion Gas generation Degradation of organics Chemical reaction with particular compounds (i.e. heat production)
