Radioactive Waste Repository Licensing Synopsis of a Symposium (1992) / Chapter Skim
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Appendix A: Rethinking High-Level Radioactive Waste Disposal
Appendix A: Rethinking High-Level Radioactive Waste Disposal
Pages 19-66
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Appendix A Rethinking High-Leve] Radioactive Waste Disposal
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APPENDIX A RETHINKING HIGH IEUEI nAnlD8~T111t WASTE DISPOSAI A Position Statement of the Board on Radioactive Waste Management Commission on Geosciences, Environment, and Resources National Research Council NATIONAL ACADEMY PRESS Washington, D.C.
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The material summarized in this report was the product of a July 1988 retreat sponsored by the Board on Radioactive Waste Management and was supported by the U.S. Department of Energy under Contract No.
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GLENN PAULSON, IIT Center for Hazardous Waste Management CHRIS G WHIPPLE, Clement International SUSAN D
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BERNERO, U.S. Nuclear Regulatory Commission, Washington, D.C.
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Policy and Program, 29 Scientific Consensus on Geological Isolation, 30 Treatment of Uncertainty, 31 Modeling of Geological Processes, 32 Moral and Ethical Questions, 34 An Alternative Approach, 35 The Risk of Failing to Act, 36 INTRODUCTION . ~ ~ 38 The Origins and Purpose of This Document, 38 High-Level Waste in Context, 39 Radioactive Waste Management Policy, 40 FINDINGS ~ 4 1 The Limitations of Analysis ~ ~ 41 Overview, 41 Uncertainty and Significant Risk, 41 Perceptions of Risk, 44 Moral and Value Issues.............................
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26 APPENDIX A Strategic Planning Overview, 56 ................................................................................... 56 Policy Context, 57 Alternative Management Strategies, 58 The Elements of A More Flexible System, 61 RECOMMENDATIONS ..........................
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The current program is not sufficiently flexible or exploratory to accommodate such changes. The Board on Radioactive Waste Management is particularly concerned that geological models, and indeed scientific knowledge generally, have been inappropriately applied.
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28 APPENDIX A time to assess performance and a willingness to respond to problems as they are found, remediation if things do not turn out as planned, and revision of the design and regulations if they are found to impede progress toward the health goal already defined as safe disposal. To succeed, however, this alternative approach will require significant changes in laws and regulations, as well as in program management.
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government on technical matters related to the management of radioactive waste. Today, this advice is provided by the Board on Radioactive Waste Management (BROOM or "the Board")
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It is at this point that geological isolation of radioactive waste differs in an important sense from mining. In the United States, radioactive waste management is a tightly regulated activity, surrounded by laws and regulations, criteria and standards.
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What it does mean is that a range of results are possible, and a successful management plan must accommodate residual uncertainties and still provide reasonable assurance of safety. Second, safety is in part a social judgment, not just a technical one.
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Uncertainty is treated inappropriately in the simulation models used to describe the characteristics of the waste repository. As the quantity of information about natural geological settings grows, so too does our appreciation of their variability and unpredictability.
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Similarly, when there are technical disputes over characteristics and processes that affect calculations of waste transport, sensitivity analysis with alternative models and parameters can indicate where further analysis and data are required and where enough is known to move on to other concerns. It may even turn out to be appropriate to delay permanent closure of a waste repository until adequate assurances concerning its long-term behavior can be obtained through continued in-site geological studies.
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Such an alternative approach, now being used in Canada and Sweden, promises to be far more successful in achieving a safe and practical waste disposal system. Moral and Ethical Questions Radioactive waste poses hazards that raise moral and ethical concerns.
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It would be similar to the strategies now being followed in Canada and Sweden, where the exploration and construction of an underground test laboratory and a shallow underground low-level waste repository have followed a flexible path. At each step, information and understanding developed during the prior stages are combined with experience from other underground
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The Risk of Failing to Act Given the history of radioactive waste management in the United States, a likely alternative is that the program will continue as at present. That would leave the nation's inventory of high-level waste, indefinitely, where it is now: mostly at reactor sites at or near the earth's surface.
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In judging disposal options, therefore, it is essential to bear in mind that the comparison is not so much between ideal systems and imperfect reality as it is between a geologic repository and at-surface storage. From that standpoint, both technical experts and the general public would be reassured by a conservative engineering approach toward long-term safety, combined with an institutional structure designed to permit flexibility and remediation.
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However, it notes that even if nuclear power in this country were discontinued tomorrow a highly unlikely event we would still need to dispose of nuclear waste from existing power plants and defense programs, and we would therefore still require a viable HLW disposal program. The second reason that radioactive waste management remains in trouble is the way in which the programs have been designed and carried out.
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These questions touch on far more than radioactive waste, and the rethinking they imply will be difficult to launch and to sustain. The Board believes, however, that this rethinking is essential and that radioactive waste management is a reasonable place to begin.
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In conducting these analyses, DOE has relied heavily on building computer models of the repository and surrounding geological environment, along with possible pathways of radionuclide transport. However, preparing quantitative predictions so far into the future pushes the boundaries of our understanding of geology, groundwater chemistry and movement, and their interactions with He emplaced material (radioactive waste package, backfill, sealants, and so on)
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The waste management system, which starts at the reactor and continues into the distant future of a sealed repository, includes many different parts and processes that are described through different kinds of data (with different levels of quality) , and different kinds of analysis (with different levels of accuracy)
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NRC. Specifically, with regard to the first major topic of the Science Advisory Board's findings and recommendations, "Uncertainty and the Standard," the subcommittee recommended relaxing the nuclide release limits by a factor of 10, modifying the probabilistic release criteria so that analysis of repository performance shall demonstrate that there is less than a 50% chance of exceeding the Table 2 release limits, modified as is appropriate.
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Others are based on explicit or implicit assumptions that cannot be plausibly proved or disproved for example, the consequences of climatic changes that could increase rainfall and groundwater flows at a repository site. The data and methodologies for modeling of repository isolation performance are still under development.
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The perception of integrity and competence in risk managers depends not only on their personal attributes but also on the character of the policies they implement and the institutions they represent. The current decision process is structured in a way that does not promote trust in those who are implementing the waste management program.
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As a rule, the values determined from models should only be used for comparative purposes. Confidence in the disposal techniques must come from a combination of remoteness, engineering design, mathematical modeling, performance assessment, natural analogues, and the possibility of remedial action in the event of unforeseen events.
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During its 1988 study session, the Board examined recent work on ethical questions in radioactive waste management conducted by scholars from a variety of disciplines. These ethical concerns fall into two principal areas: (1)
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When the questions are no longer scientific, scientists alone cannot be expected to answer them. Sheldon Reaven suggests that the Nuclear Waste Policy Act (NWPA)
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The evidential uncertainties in assessing repository safety may point to a more flexible and evolutionary approach (see below) ; but this conflicts with the concerns to keep to a fixed schedule, so as to limit costs, discharge obligations to future generations, and meet contractual commitments to utilities holding spent fuel.
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Such an approach may lead to policies that have a greater chance of surviving over time because they are more widely perceived as fair. Modeling and Its Validity Overview Models based on geological principles play a central role in the design and licensing of a waste repository.
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Models are not well suited to describe the risk and uncertainties to lay audiences, however. Natural analogues, if they can be found, are far more useful for this purpose (see below)
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The Board believes that this is scientifically unsound. This conclusion is based on review of the modeling approach used by DOE and the regulatory agencies in order to implement the NWPA.
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Many computer simulation models of geological environments are based on deterministic models that have been used successfully in branches of mechanics such as aerospace engineering, where the basic phenomena are much better defined. Such models are of limited value for the ill-defined, data-limited, long-term situations such as the repository isolation problem.
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Groundwater flow is also generally accepted as the primary mechanism by which radionuclides could move from the repository to the biosphere, so it has been emphasized in modeling studies of repository isolation. Several experts, however, have commented on the difficulty of applying classical hydrology models to the problem of radioactive waste isolation.
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As further information is developed about the candidate site, it is also used in the performance assessment. Many of the uncertainties associated with a candidate repository site will be technically interesting but irrelevant to overall repository performance.
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Because models cannot be conclusive with regard to the safety of a repository site, it is important to think carefully about natural analogues. These are natural "test cases," geological settings in which naturally occurring radioactive materials have been subjected to environmental forces for millions of years.
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That misapplication prompts this Board to outline an alternative management strategy. The next section describes an alternative management approach that employs natural analogues and professional judgment in a program design that uses science appropriately in the search for a safe disposal system.
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At the Waste Isolation Pilot Plant (WIPP) in New Mexico, the discovery of pockets of pressurized brine in formations below the repository level led to public outcries and a continual National Research Council review of the suitability of the site.
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A well-documented alternative to this approach is being followed, to various degrees, by countries such as Canada and Sweden. The exploration and construction of a geological test facility and a low-level waste repository, respectively, follow a flexible path, allowing each step in the characterization
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This approach continually integrates new data into the expert judgments of geologists and engineers. It makes heavy use of natural analogues, such as undisturbed natural deposits of radioactive elements and groundwater systems, in order to illuminate the behavior of the geologic environment.
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The combination of a conservative engineering approach and designed-in maximum flexibility, to allow unanticipated problems to be corrected, should reassure both technical experts and concerned nonexperts. The barrier is not logical but institutional, and the prescriptive approach in the U.S.
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The Elements of a More Flexible System In a program governed by this alternative approach, change would not be seen as an admission of error; the system would be receptive and responsive to a continuing stream of information from site characterization. The main actors would reduce their reliance on detailed preplanning during initial site characterization, making it possible to debug the preliminary design during rather than before characterization.
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This is no reason to arbitrarily abandon the release limits it is the more detailed requirements that may need to be reconsidered, since they ultimately affect the release limits and the imputed dose. However, one should not take EPA's release standards or the USNRC's detailed licensing requirements as immutable constraints.
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The following activities should be included: publicly negotiated prelicensing agreements with the USNRC on how to deal with the high levels of uncertainty arising from numerical predictions of repository performance;
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7. Although geologic disposal has been the national policy for many years, and the Board believes it to be feasible, contingency planning for other sites and options (for example Subseabed Disposal of spent fuel and high-level radioactive waste)
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; "The Relation of Equity Issues to Risk Perceptions and Socioeconomic Impacts of a High Level Waste Repository," Waste Management '89, proceedings of the Waste Management '89 Conference (University of Arizona, 1989~; "The Policy Conflicts in the Siting of Nuclear Waste Repositories," Annual Review of Energy, Vol.
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15. Department of Energy, Office of Civilian Radioactive Waste Management, Site Characterization Plan: Yucca Mountain Site, Nevada Research and Development Area, Nevada, DOE/RW-0199 (U.S.
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