Select Committee on Science and Technology Third Report


CHAPTER 4: TECHNICAL ANALYSIS

GEOLOGICAL DISPOSAL OF HLW AND ILW

4.19 The evidence given to us shows that there is a strong international scientific and technical consensus that there is enough confidence in geological disposal of HLW and ILW to make it worthwhile to work towards it (see Chapter 3 and, for example, p 136, QQ 957-959). Only a small minority in the geological community, and in other disciplines, feel that there is so little confidence in geological disposal that it should be abandoned, or that it should cease to be the focus of most R&D (see, for example, Friends of the Earth, pp 322-328).

4.20 Various courses of action can be defined which involve proceeding with geological disposal, using surface storage until one or more deep repositories are available. At one end of the scale is the strategy followed over the last decade in the United Kingdom, in which the surface storage period was planned to be as short as possible, and it was envisaged that the repository would be finally sealed when all the wastes had been emplaced[28]. In the middle of the spectrum of courses of action is a strategy with a surface storage period prior to emplacement in a repository, and a long time in which a repository is kept open with wastes in a retrievable form (see, for example, p122, QQ1706-1714, QQ545-547). At the far end of the spectrum of courses of action is indefinite storage of long-lived wastes on the surface, combined with an R&D programme on longer-term management methods including, perhaps, geological disposal (see, for example, Friends of the Earth, P318).

Status of knowledge

4.21 The main scientific determinant of the way to proceed with geological disposal is the ability to predict the performance of a deep repository over the hundreds of thousands of years it will take for the radioactive constituents of the wastes to decay to very low levels. By "performance" we mean the capability of all the parts of a repository to prevent releases of radionuclides and/or to slow down their rates of movement into the surface environment. Assessments of repository performance are necessarily probabilistic because it will never be possible to predict exactly what will happen over such long times. Rather the aim is to identify possibilities and to quantify, or at least describe, uncertainties. Performance assessment is a mixture of quantitative analyses, using mathematical models (for example, of radionuclide migration with groundwater), semi-quantitative analyses ("scoping calculations") and qualitative reasoning[29]. Similarly, the criteria by which the adequacy of predicted repository performance will be judged are both quantitative and qualitative[30].

4.22 .  The research carried out to date world-wide has increased considerably the ability to assess repository performance over very long times.[31] Initial "guesstimates" about the rates at which waste packages will corrode and the rates at which radionuclides will be leached out of wastes into groundwater have been replaced by firmer estimates, based on better understanding of the physical and chemical processes involved. Very simple generic models of rates and patterns of groundwater movement and radionuclide migration have been superseded by models founded on site specific hydrogeological and geochemical conditions. Some processes which were omitted entirely from early performance assessments can now be included (for example, the generation of gases such as hydrogen when metallic wastes and waste canisters corrode under anaerobic conditions in a repository).

4.23 .  Nevertheless, there are still significant gaps in knowledge. One of the most important for a deep repository in the United Kingdom concerns the effects of future changes in climate on rates and patterns of groundwater flow. It is possible, using probabilistic techniques and palaeoclimatic data, to generate a series of possibilities for how climate may change in the future and to provide probability estimates for these sequences of climatic conditions. Thus probabilistic predictions can be made of rates and magnitudes of changes in sea level, and of the timing and extent of future glaciations. Means to predict the effects of climate changes, particularly glaciations, on rates and patterns of groundwater flow are, however, at present incomplete. Techniques such as palaeohydrogeology, in which attempts are made to reconstruct past groundwater conditions as an indicator of future ones, are in their infancy.[32]

4.24 Similarly, advances in scientific knowledge are needed before the effects of seismic events on groundwater flows can be predicted with any confidence. For fractured rocks, in particular, there are problems in characterising the rock in enough detail to be able to model groundwater flow through it, without disturbing it so much that repository performance is affected (Q 925). While rates of generation of bulk gases can be quantified if groundwater conditions are known, much less has been done on the effects of gases on water flow patterns and on the transition period when a sealed repository is resaturating. Quantitative prediction of the rate of evolution of chemical conditions within and around a repository is not yet possible[33]. For example, for a repository with a cementitious backfill, it is not known how long it will take to establish the conditions in which the solubilities of most radionuclides will be very low, nor how the movement of the minerals in the backfill will affect radionuclide migration. A further major type of uncertainty is the extrapolation of the results of short term laboratory experiments to thousands of years, and longer. This applies to canister corrosion, waste leaching and the sorption of radionuclides on geological media. These gaps in knowledge are not a reason for postponing action: they are a reason for increased effort.

Repository Timing

4.25 In the technical evidence presented to us the predominant scientific view is that enough is known to begin a deep repository site selection process in the United Kingdom (for example, p29, p136, p224, p245). It will be necessary to begin by establishing clear site selection criteria (geological and other), then to perform desk studies to identify sites for preliminary field investigations. The next steps are to decide which sites merit more detailed investigations and to carry these out (pp 254-255). Based on scientific and technical considerations, we estimate that these steps are likely to take at least a decade. The need to build public confidence (see Chapter 5) could prolong this.

4.26 To plan interim surface storage arrangements and repository related research it is essential to take a view on how rapidly to proceed with repository construction and operation once the repository site (or sites, see para 4.4) has been selected. Concerns about the ability to monitor and retrieve the wastes are a major consideration here. We believe that it is essential not to proceed from one stage to the next until there is a sound technical basis for doing so, and ideally the programme would contain no, or very few, points of no return.

4.27 A repository can be built and operated so that there is monitoring during the operational period (eg of the integrity of waste packages) and so that it is relatively easy to retrieve wastes if necessary (eg Q1417). The repository operational period can, in effect, be made one of underground storage. It will also be possible to retrieve wastes after a repository is backfilled and sealed, although retrieval would then be more difficult and might pose significant risks to the workers involved (eg Q1418). In developing a repository design it is necessary to decide how much ability to monitor and retrieve should be built in, for both the operational period and after closure, without compromising long term safety (Q 1011)[34] [35].

4.28 In our opinion, the best course of action would be to begin repository construction without undue delay after site selection, and to place wastes in the repository in such a way that they can be monitored and retrieved, only backfilling and sealing the repository when sufficient knowledge has been judged to be gained. We do not believe that the length of the period for which the repository is to remain open needs to be, or should be, prescribed precisely now, but it is necessary to have some idea of how long it might be. The minimum would be several decades, to allow sufficient time for research and observation of waste packages underground. To proceed more rapidly to repository closure would not give the flexibility to adjust development programmes in the light of research findings, and would be unlikely to satisfy desires for monitorability and retrievability.

4.29 We believe that it is important that repository operation starts within the next fifty years, before a major programme of store replacements or refurbishments, perhaps with repackaging of intermediate level wastes, is required[36]. We are therefore not in favour of delaying the start of the United Kingdom site selection process until further research has been carried out. Expert opinion is that such research might take a decade or two (Q 938). Adding this to the one or two decades for site investigation and selection, and a few years for construction and commissioning, means that a repository would only just be ready to receive wastes fifty years from now. There would be no leeway in such a programme, and a danger that the latter stages would be carried out with undue haste. We believe that research is best carried out in parallel with site selection, and subsequently when wastes are emplaced in a monitored and retrievable way.

4.30 The above course of action might be described as a combination of surface storage, underground storage and geological disposal, or a phased approach to geological disposal. It is the course we favour.

INDEFINITE STORAGE

4.31 We use the term indefinite storage to mean storage on or just below the ground surface while R&D is carried out on longer-term options. Such a strategy implies that something else will be done with wastes eventually, but that it is not known now what this will be or when it will occur. This differs from permanent storage, which carries no implication of different actions in the long term, and which is not a tenable strategy (see, for example, Cm 2919 and evidence from Friends of the Earth, p318).

4.32 Surface storage of conditioned, packaged wastes in modern facilities for several decades is feasible and safe (p 156, p 160). Beyond periods of this length it will be necessary to refurbish stores extensively and perhaps replace them. Repackaging of wastes may also become necessary [37].

4.33 Storage for several centuries raises much greater problems. The major one is the likelihood of societal breakdown. World-wide, there are many examples of civilisations which have appeared and disappeared within a century. If this occurred to our civilisation, stores, wastes and packages would degrade, and R&D on longer-term management options would cease. Eventually there would be rapid and substantial leakage of radionuclides into soils and groundwater, and perhaps into the atmosphere. Even a lesser change in society would be serious if it led to stores falling into disrepair, and wastes and packages degrading to such a degree that it would be risky to retrieve packages and very difficult to convert wastes to a stable form again. The maintenance of facilities does not always receive the economic priority that it deserves.

4.34 Over several centuries there could be climatic changes (particularly sea level rises) which would make it necessary to move wastes to new stores in other locations. This would entail risks, particularly to workers. Another concern is that over centuries the foundations and reinforcement in stores could weaken, making them more vulnerable to earthquake damage. Again this would necessitate building new stores and moving wastes to them.

4.35 A further problem with indefinite storage is the R&D programme to accompany it. We have not been able to find in the evidence presented to us, or in the literature, any definite suggestions as to what R&D might be carried out to look for new long-term management options. Many methods have been thought about, and some have been the subject of much research, but has been found to be more promising than geological disposal for the ILW and HLW which exists now and which will arise from the current civil and defence nuclear programmes (see Chapter 2). In view of these difficulties we do not favour indefinite storage as a policy.

RESEARCH REQUIREMENTS

4.36 With a phased approach to geological disposal of the type outlined above, research would be carried out in three steps:

·  before the deep repository site selection programme starts and while it is in progress;

·  after the site (or sites) has been selected, during repository construction and waste emplacement;

·  while wastes are underground in monitored and retrievable form, before the repository is sealed.

4.37 In each phase there would be a need for multi-disciplinary research, covering, in particular, geology, hydrogeology, geochemistry, and the materials science relevant to the behaviour of wastes and their packages under disposal conditions. Processes in the surface environment (the "biosphere") also merit attention, primarily from the point of view of how they affect conditions at depth (for example, how changes in sea level and rainfall could affect groundwater flow).

4.38 The first phase of research would be largely generic and would be partly aimed at assisting site selection and repository design. It will be important to address the wastes which were not included in the Nirex deep repository programme (vitrified high level waste, spent fuel, depleted uranium, surplus plutonium etc). For some of these wastes much can be gained from research carried out in other countries. Development of means to build into a repository the ability to monitor and retrieve the wastes should be included, because there has been little work on this in the United Kingdom to date. Although the ability to monitor and retrieve wastes while the repository is open is the first priority, it would be valuable to consider what could be done for the post-closure period.

4.39 The second phase of research would be mainly site specific. It would include experimental work at the repository site (or sites), in addition to site characterisation activities. The third phase of research would be a continuation of the second, but with the addition of observations of waste packages and groundwater conditions in the repository.

4.40 As well as disposal related research, it would be necessary to carry out some work on surface storage. Amongst the aims of this R&D would be to provide better estimates of the length of time for which such storage could be maintained without carrying out major operations, and to develop the technology for repackaging wastes. This would be needed if there were unforeseen delays in the repository development programme.

4.41 It has been suggested that future United Kingdom R&D on geological disposal should include establishing an underground laboratory at a site which will never be used for a repository. While such a laboratory would have been valuable in the past, there would be little merit in having one in the future if a search for deep repository sites were to be started soon. United Kingdom researchers have made good use of underground laboratories in other countries for generic studies. They could continue to do so until our site selection process was complete and then move on to site specific research.

4.42 We have had various suggestions put to us as to topics on which research is particularly required (see, for example, The Royal Society P365, and RWMAC, September 1998[38]). It would not be appropriate to comment on details of these topics now. When there is agreement on the national strategy, a comprehensive research programme should be set out, linked to milestones in a repository development programme (assuming that geological disposal is to be pursued). The DETR project on a research strategy for HLW and spent fuel disposal provides an indication of how such a research programme could be developed, and will contain information which is valuable in establishing a research programme for disposal of all long-lived wastes[39].

DEVELOPMENT OF REPOSITORY SAFETY STANDARDS

4.43 The current United Kingdom standards for the long term safety of a deep repository are those given in the 1997 Environment Agency / SEPA / DoE Northern Ireland document entitled "Disposal Facilities on Land for Low and Intermediate Level Wastes: Guidance on Requirements for Authorisation", which is known for short as the GRA. This document takes into account NRPB advice on radiological protection objectives for waste disposal[40]. For repository operation, including the whole time for which a repository is open, the HSE would apply standards based on their "Safety Assessment Principles for Nuclear Plant" (SAPS)[41], as well as the Ionising Radiation Regulations (currently being revised in the light of the 1996 European Directive on basic safety standards for radiation exposure of workers and the public).

4.44 As is evident from its full title, the GRA would not apply to a repository for HLW, nor for one for co-disposal of HLW and ILW. For this reason alone new safety standards would be needed if an integrated strategy for all long-lived wastes is put in place. More importantly, the GRA will need to be revised and expanded as a repository development programme progresses, so that it specifies in more detail the principles to be applied in repository design and the safety-related criteria to be met.

4.45 The current GRA contains only one numerical standard for long term safety: the target that the risk that an individual human being will suffer a serious health effect (fatal or genetic) from any releases of radioactive material from a sealed repository should be less than one in a million (10-6) per year. It is clear that one numerical standard will not be enough. There is confusion about what the risk target means, and concern that it does not address aspects such as cumulative releases of radionuclides to the surface environment, the extent of environmental contamination and deleterious effects on organisms other than humans. It is also possible that the figure of 10-6 will need to be revised in the light of technological and medical developments, and changes in societal expectations.

4.46 It would also be anticipated that an expanded GRA would contain many more qualitative requirements. The majority of standards in the SAPs are qualitative "engineering principles", which reflect accumulated knowledge of what is good practice in the design of nuclear plants. The GRA should be developed in a similar way and might become as extensive as the SAPs.

CONCLUSIONS OF TECHNICAL ANALYSIS AND RECOMMENDATIONS

4.47 It is essential that the United Kingdom has a comprehensive and integrated strategy for the management of all long-lived wastes. The strategy should set out the long-term management methods for all existing wastes, for all those wastes which are certain to arise from the current civil and defence nuclear programmes, and for all those materials that are at present held in store and which are likely to be declared wastes (see also para 4.50). The United Kingdom inventory of radioactive wastes should be expanded to include all such materials, so that it becomes a better tool for use in strategy development. The strategy should take full account of plans for decommissioning reactors, so that there are no inconsistencies in timing of waste arisings and the provision of storage and disposal facilities. In developing the strategy the long-term management of nuclear powered submarines and their fuel should be considered fully and MoD policy should be brought into line with, and incorporated in, the national strategy.

4.48 There is a spectrum of possible courses of action which the United Kingdom could follow for the management of its long-lived wastes which has been identified in the course of this enquiry, from "early disposal" in a deep repository to indefinite surface storage. In an early disposal strategy a repository would be constructed as soon as a suitable site could be found and the repository would be finally sealed There is a spectrum of possible courses of action which the United Kingdom could follow for the management as soon as all wastes had been emplaced in it. We are not in favour of such a strategy because it has too many large irreversible steps, with too little flexibility and opportunity to build technical confidence. Nor are we in favour of indefinite storage of wastes on the surface: this relies too heavily on human intervention and societal stability over many centuries.

4.49 Our strong preference is for a phased approach to geological disposal, in which wastes are stored on the surface whilst a site is found and a repository is constructed, and then emplaced in a repository in such a way that they can be monitored and retrieved. The repository would be kept open while data are accumulated from the monitoring and from additional research. When there is sufficient confidence to do so the repository would be backfilled and sealed. Monitoring would then continue and it would still be possible (but difficult) to retrieve wastes.

4.50 To proceed with repository site selection and design, it is essential to know what wastes will be placed in it. Thus decisions are needed soon on whether materials which are not yet declared to be waste are to be so declared. It is possible that more than one repository will be required to take all long-lived wastes and this has to be recognised before a site selection process begins.

4.51 One or more United Kingdom deep repositories should be operational within 50 years, so that no major programme of store replacement or refurbishment, or repackaging of intermediate level wastes, has to be undertaken.

4.52 When there is agreement on the national strategy a comprehensive research programme should be set out, linked to milestones in repository development. The first phase of research would be largely generic, to assist repository site selection and design. The second phase of research would be mainly site specific. The third phase would include observations of waste packages and groundwater conditions in the repository. The current United Kingdom standards for the long-term safety of deep repositories should be revised and expanded as the repository research and development programme progresses.

4.53 Small users of radioactive materials who produce limited quantities of LLW that will decay quite rapidly to LLW should commission a study of the options for management of this waste. The options considered should include the provision of a national decay store (to allow the waste to decay to LLW prior to disposal), and direct disposal to Drigg. They should then make a formal proposal to regulators and Government for their preferred option.

4.54 Plans should be made for the establishment of a new LLW disposal facility, to open before Drigg closes. The Government should also consider alternatives to landfill disposal of less active LLW and produce a national policy that is accepted by local authorities, landfill operators, the nuclear industry and organisations outside the nuclear industry that currently dispose of LLW to landfills.


28   Review of Radioactive Waste Management Policy, Final Conclusions, Command Paper (Cm) 2919, 1995. Back

29   The Royal Society, Disposal of Radioactive Wastes in Deep Repositories, 1994. Back

30   The Environment Agency, SEPA, Department of the Environment for Northern Ireland, Disposal Facilities on Land for Low and Intermediate Level Radioactive Wastes: Guidance on Requirements for Authorisation, 1997. Back

31   The Royal Society, ibid.Back

32   The Royal Society, ibid.Back

33   The Royal Society, ibidBack

34   QuantiSci, High-Level Waste and Spent Fuel Disposal Research Strategy: Project Status at the Half-Way Point, report DETR/RAS/98.006, May 1998.  Back

35   RWMAC, The Radioactive Waste Management Committee's Advice on The Interim Report of the High Level Waste and Spent Fuel Disposal Research Project, November 1998. Back

36   Health and Safety Executive Nuclear Safety Directorate, Intermediate Level Radioactive Waste Storage in the UK: A Review by HM Nuclear Installations Inspectorate, November 1998. Back

37   Health and Safety Executive Nuclear Safety Directorate, ibid. Back

38   RWMAC, The Radioactive Waste Management Advisory Committee's Advice on the Scope and Content of the Core Scientific Research Programme on Intermediate Level Radioactive Waste Disposal. Back

39   RWMAC, The Radioactive Waste Management Committee's Advice on The Interim Report of the High Level Waste and Spent Fuel Disposal Research Project, November 1998. Back

40   Doc. NRPB 3, No.3, 1-3, 1992 Back

41   HSE, Safety Assessment Principles for Nuclear Plants, 1992. Back


 
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