on the review of
PROPOSED ENVIRONMENTAL STANDARDS
MANAGEMENT AND DISPOSAL OF
SPENT NUCLEAR FUEL, HIGH-LEVEL
AND TRANSURANIC RADIOACTIVE WASTES
(40 CFR PART 191)
High-Level Radioactive Waste Disposal Subcommittee
Science Advisory Board
U.S. Environmental Protection Agency
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management Appendix E REPORT on the review of PROPOSED ENVIRONMENTAL STANDARDS FOR THE MANAGEMENT AND DISPOSAL OF SPENT NUCLEAR FUEL, HIGH-LEVEL AND TRANSURANIC RADIOACTIVE WASTES (40 CFR PART 191) by the High-Level Radioactive Waste Disposal Subcommittee Science Advisory Board U.S. Environmental Protection Agency January 1984
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management EXECUTIVE SUMMARY The High-Level Radioactive Waste Disposal Subcommittee (HLRW) of the Executive Committee of the Science Advisory Board (SAB) has completed an extensive review of the scientific and technical basis for EPA's proposed rule for the disposal of high level radioactive wastes, the highlights of which are presented in this summary. Technologies now exist for the disposal of such wastes, and standards adopted for them should strike an appropriate balance between conservatism and practicality. Overall, the Subcommittee is confident that, consistent with the intent of this standard-setting program, the job of disposing of high-level radioactive waste can be achieved with reasonable assurance for the well-being of present and future generations. The Subcommittee supports the general form of the proposed standards, including (a) the use of a societal objective as an upper bound of acceptable health (cancer and genetic) effects, (b) the focus on performance standards in terms of release limits rather than individual exposures, (c) the reference level of the initial 10,000 year time frame applicable to both the societal objective and the release limits, (d) the use of a probabilistic approach, and (e) the use of qualitative assurance requirements, as modified by the Subcommittee, but issued as Federal Radiation Protection Guidance to other Federal agencies in lieu of inclusion in the proposed rule. The Subcommittee, while accepting the general form of the proposed standards, recommends several changes in the standards and improvements in the supporting methodology. The principal recommendations are highlighted in the following summation. A more comprehensive and detailed presentation of these and other major recommendations can be found in Section IV, Major Findings and Recommendations. A. The Standard 1. The Subcommittee recommends that the release limits specified in Table 2 of the proposed standards be increased by a factor of ten, thereby causing a related ten-fold relaxation of the proposed societal objective (population risk of cancer).* The Subcommittee notes that the proposed release limits are directly related to the societal objective of not exceeding 1,000 deaths in 10,000 years, and thus, compliance with this recommendation carries with it a * Two members of the Subcommittee, Dr. Lash and Dr. Giletti, dissent from this view. They believe that the Office of Radiation Programs' more stringent standard is justified and can be met by sufficient numbers of proposed disposal sites.
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management related ten-fold increase in the societal objective. The relaxation of the release limits is, in the Subcommittee's opinion, justified for the following reasons. First, the proposed release limits in Table 2, and therefore the proposed societal objective, are considerably more stringent than those standards generally required or adopted in today's society (see for instance Table A on page 12 of this report). Second, in addition to the fact that some of the cancer deaths which might result from these releases are calculated using conservative assumptions that probably overestimate the number, some of these deaths would have resulted at least in part from the unmined ore from which the wastes were subsequently generated, and thus are substitutional rather than additional in nature. Third, the Subcommittee believes that the compounding of conservatism by EPA in the choice of probabilities and specific model parameters used throughout the analysis is not warranted. EPA should also clarify the analytical framework that forms the basis for the limits in Table 2 of the proposed standards. The Subcommittee believes that such clarification will help to establish clearly the relationship between the release limits and the societal objective, and will facilitate future amendments to the standard as knowledge increases regarding radiation health effects or radionuclide migration in the biosphere. Note: In Section IV, #7(Models) and #13(Geochemical Data), the Subcommittee has recommended that EPA make certain specific changes and corrections to their predictive models. Some of these changes will result in changes to the release limits for individual radionuclides given in Table 2 of the proposed standards, and will be separate from the ten-fold change in the release limits recommended above. The Subcommittee believes that the changes in the release limits, resulting from the changes to the predictive models, are independent of and would not lead to additional modification to the proposed societal objective beyond the ten-fold increase discussed above. B. Uncertainty and the Standard 1. We recommend that the probabilistic release criteria in the draft standard be modified to read ''analysis of repository performance shall demonstrate that there is less than a 50% chance of exceeding the Table 2 limits, modified as is appropriate. Events whose median frequency is less than one in one-thousand in 10,000 years need not be considered.'' 2. We recommend that use of a quantitative probabilistic condition on the modified Table 2 release limits be made dependent on EPA's ability to provide convincing evidence that such a condition is practical to meet and will not lead to serious impediments, legal or other-
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management wise, to the licensing of high-level-waste geologic repositories. If such evidence cannot be provided, we recommend that EPA adopt qualitative criteria, such as those suggested by the NRC. The Subcommittee believes that the modified probabilistic criteria will make the proposed standards more practical to apply without undue, time-consuming disagreements. Further risk studies need to be performed and subjected to systematic, critical evaluation in order to establish a more acceptable probabilistic basis for the standard. C. The Time Frame-10,000 years and Beyond 1. We recommend that EPA retain the 10,000 year time period as the basis for determining the adequacy of repository performance. We believe that use of formal numerical criteria limited to this approximate time period is a scientifically acceptable regulatory approach. 2. We recommend that the process of selection of sites for disposal systems also take into account potential releases of radioactivity somewhat beyond 10,000 years. Particular attention should be focused on potential releases of long-lived alpha-emitting radionuclides and their decay products. Although the selection of a time frame is in large part arbitrary, we endorse EPA's choice of 10,000 years. Modeling and risk assessments for the time periods involved in radioactive waste disposal require extension of such developing techniques well beyond usual extrapolations; however, the extension for 10,000 years can be made with reasonable confidence. Also, the period of 10,000 years is likely to be free of major geologic changes, such as volcanism or renewed glaciation, and with proper site selection the risk from such changes can be made negligible. Potential radionuclide releases will not stop with 10,000 years, however, but may continue in amounts equal to or exceeding those estimated for the initial period. The degree of confidence with which impacts can be modeled much further in the future is much less certain. We do not recommend detailed modeling calculations regarding post-10,000 year releases, but estimates should be made, and should be considered as factors in disposal site selection. D. Population vs. Individual Risk 1. We recommend that EPA retain the use of a population risk criterion as the measure of performance for the proposed standards.
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management We find that an approach employing individual dose limits, i.e., considering some "maximally exposed individual" or alternatively some "average exposed individual" would, in practice, make the standard difficult to meet with high assurance for very long times, and that use of a population risk approach is more practical. In our view, however, it is important that for the first several hundred years residents of the region surrounding a repository have very great assurance that they will suffer no, or negligible, ill effects from the repository. For longer periods, we believe that EPA should rely on the existence of continuing requirements similar to its current drinking water standards to protect groups of individuals. E. Coordination of Policies and Standards 1. We recommend that EPA initiate action within the Federal Government for the establishment of an interagency council to coordinate the development of high-level radioactive waste disposal policy, standards, and regulatory practices and to serve as a forum for exchange of scientific and technological information. Several Federal agencies are involved in the process of establishing radiation protection policies, standards and operational requirements governing the disposal of high-level radioactive wastes, including EPA, NRC, DOE and DOD, together with states, appropriate entities of Congress and the judiciary. Overlapping and independent authorities and responsibilities exist under present laws. Conflicting terminology and standards exist, e.g., the definitions of high-level and other radioactive wastes. Coordination of Federal policies and practices is essential to the U.S. high-level radioactive waste disposal program. Success of the program will depend on extensive interaction and agreement among the appropriate Federal agencies. While the lead in coordination could be appropriate for the NRC or DOE, the Subcommittee feels that the obligation for achieving mutual interaction more appropriately belongs to the EPA under its authority to issue environmental standards and Federal Radiation Protection Guidance. F. Research Needs-A Matter of Priority 1. We recommend that EPA support, or encourage other agencies to support, continuing research in technical areas where major uncertainties still exist, particularly in the biological effects of radiation, the geochemical transport of radionuclides, and the characterization of rock-mass deformation.
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management The Subcommittee strongly endorses support of research aimed at diminishing or clarifying as many of these uncertainties as can be attacked with some hope of resolution. The research, although expensive, could bring about a substantial reduction in the overall cost of the disposal system. G. Responses to Original Subcommittee Charge At the time of the Subcommittee's formation, it was directed, by the Executive Committee of the Science Advisory Board, to address six (6) principal issues. Although a brief response to each charge is presented here, the charges are broad in scope and the Subcommittee's review of them generated a number of more explicit and specific issues which are addressed in detail in the body of this report. 1. The scientific and technical rationale behind the choice of a 10,000 year time period as the basis for assessment of disposal facility performance. This issues has been addressed in C above. 2. The technical basis for the selection of the proposed performance requirements, including risk-assessment methodology, uncertainties in the data and in the analytical methods, and the estimation of premature deaths. These aspects of the analysis form the basis for the proposed standards and were areas most carefully and critically evaluated by the Subcommittee. Although the Subcommittee makes a number of recommendations regarding risk assessment, pathway and health modeling and the need for improved documentation, we believe that Office of Radiation Programs, EPA, has handled these subjects well and furthermore, has been positively responsive to the recommendations of the Subcommittee. We think, however, that EPA has made overly conservative choices and decisions throughout the development of the technical bases supporting the standards, leading to overestimation of the long-term effect of disposal, and hence that the proposed standards are too restrictive and compliance may be difficult to verify. 3. The scientific appropriateness of concentrating on disposal in geologic media. This part of the charge needed no consideration by the Subcommittee,
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management since disposal in geologic media is mandated for at least the first two sites by the Nuclear Waste Policy Act of 1982 (PL 97-425), enacted after the charge was prepared. No member of the Subcommittee, however, disagrees with this initial approach. 4. The validity of the conclusion that, under the proposed rule, the risks to future generations will be no greater than the risks from equivalent amounts of naturally occurring uranium ore bodies . In reviewing this conclusion, we found, and EPA acknowledged, that the comparison is uncertain because of the extreme variability of uranium ore bodies. The Subcommittee thinks that the conclusion is valid in a very general way, if suitably qualified, but feels that it is unwise and not scientifically defensible to use the unmined ore as the only reference for comparison. We recommend that the comparison be extended to include the radioactivity of natural waters and the ambient radiation in the natural environment. 5. The adequacy of the economic analysis. The Subcommittee considers there are significant shortcomings in the economic analyses supporting the proposed standards. Since the management, storage, and disposal of high-level waste is a multi-billion dollar venture, we believe that the shortcomings are important and should be remedied. It is noteworthy that, even though the savings associated with individual choices may seem relatively insignificant, the absolute costs are so large that even small percentage savings are worthwhile. The high absolute costs appear to be relatively independent of the proposed standard, and simply reflect the decision to use deep mined geologic disposal sites with multiple barriers. Thus, appreciable savings are not likely to be realized in terms of basic cost by relaxation of the standards. However, the cost of demonstrating compliance may be very high, and cost reductions that may be achieved by sophisticated compliance demonstrations could be substantial. We recognize the need for cost/benefit analyses, using the best available data, but we note that a precise economic analysis will not be possible or meaningful until it is performed upon an actual repository at a specific site. 6. The ability of the analytical methods/models used in the analysis to predict potential releases from the disposal facility and their resultant effects on human health. Included would be an evaluation of the model's ability to deal with uncertainty and the confidence, in a statis-
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Radioactive Waste Repository Licensing: Synopsis of a Symposium sponsored by the Board on Radioactive Waste Management tical sense, that the model predictions are adequate to support selection of projected performance requirements. In general, EPA's analytical methodology and modeling used throughout the development of the generic repository's performance, including releases and subsequent cancer deaths, are deemed to be conservative. The Subcommittee makes several suggestions for specific improvements and updating. We emphasize that modeling, including the evaluation of uncertainty and confidence therein, is an emerging and developing technique. Adding to the uncertainties implicit in a technique that is still under development are the multitude of poorly known factors associated with the extrapolation in time to 10,000 years and beyond, and the problem of securing public acceptance of the standard. We believe, nevertheless, that the EPA's effort, modified as recommended by this report, will fulfill the intent of the Nuclear Waste Policy Act of 1982.