Technical Bases for Yucca Mountain Standards (1995) / Chapter Skim
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EXECUTIVE SUMMARY
EXECUTIVE SUMMARY
Pages 1-14
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share the responsibility for regulating the clisposal program to ensure adequate protection of the health and safety of the public. EPA promulgatecl its first stan(iar(l for deep geologic disposal of high-level radioactive waste in 1985; this standard was challengecl, litigatecI, anti ultimately reissued in 40 CFR 191 in December ~ 993.
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Based on performance assessment calculations provicled to us, it appears that peak risks might occur tens to hundreds of thousands of years or even farther into the future. Against a risk-based calculation of the adverse effect of human intrusion into the repository.
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Although we have taken a broad view of the scientific basis for the standard, we have not addressed the social, political, and economic issues that might have more effect on the repository program than the health standard. In particular, we have not recommended what levels of risk are acceptable; we have not considered whether the development of a permanent repository should proceed at this time; nor have we made a judgment about the potential for the Yucca Mountain site to comply with the standard eventually adopted.
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Moreover, risks to human health from different sources, such as nuclear power plants and toxic chemicals can be compared in reasonably understandable terms. It is essential to define specifically how to calculate risk, however, for otherwise it will not be clear what number to use to compare to the risk limit established in the standard.
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We acknowledge that determining what risk level is acceptable is not ultimately a question of science but of public policy. We note, however, that EPA has already used a dose limit equivalent to a risk level of 5x10-4 health effects in an average lifetime, or a little less than 10-s effects per year assuming an average lifetime of 70 years, as an acceptable risk limit in its recently published 40 CFR 191.
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We believe that compliance assessment is feasible for most physical and geologic aspects of repository performance on the time scale of the longterm stability of the fundamental geologic regime a time scale that is on the order of 106 years at Yucca Mountain ant} that at least some potentially important exposures might not occur until after several hundrecl thousand years. For these reasons.
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In this context, the general public includes both global populations as well as local populations that lie outside the critical group. Global populations might be affected because radionuGIide releases from a repository can in theory be diffused throughout a very large and dispersed population.
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We suggest the risk equivalent of the negligible individual incremental close recommended by the NCRP as a reasonable starting point for developing consensus. Persons in some population outside the critical group may, however, still be exposed to risks in excess of the level of the negligible incremental risk but below the level of the critical group risk.
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We further conclude that the probabilities and consequences of modifications by climate change, seismic activity, and volcanic eruptions at Yucca Mountain are sufficiently Soundable that these factors can be included in performance assessments that extend over this time frame. Exposure Scenarios Performance assessment of physical and geologic processes will produce estimates of potential concentrations of radionuclides in ground water or air at different locations and times in the future.
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We recommend against placing the burden of postulating and defending an exposure scenario on the applicant for the license. As with other aspects of defining standards and demonstrating compliance that involve scientific knowledge but must ultimately rest on policy judgments, we consiciered what to suggest to EPA as a useful starting point for rulemaking on exposure scenarios.
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We cannot predict the characteristics of future technologies for resource exploration and extraction, although continued developments in current noninvasive geophysical techniques could substantially reduce the frequency of exploratory boreholes. Although there is no scientific basis for judging whether active institutional controls can prevent an unreasonable risk of human intrusion, we think that, if the repository is built, such controls and other activities might be helpful in reducing the risk of intrusion, at least for some initial period of time after a repository is closed.
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To provide for the broadest consideration of what human intrusion scenario or scenarios might be most appropriate, we recommend that EPA make this determination in its rulemaking to adopt a standard. For simplicity, we considered a stylized intrusion scenario consisting of one borehole of a specified diameter drilled from the surface through a canister of waste to the underlying aquifer.
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after threshold regulatory requirements have been met, and calls for additional measures to be taken to achieve further reduction in the calculated health effects. While ALARA continues to be widely recommended as a philosophically clesirable goal, its applicability to geologic disposal of high-level waste is limitecl at best because the technological alternatives available for designing a geologic repository are quitelimited.
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consistent regulatory proposal and to provide for full public participation in the rulemaking process will require considerable effort by EPA. This process probably will take more than the year, currently provided in statute, for EPA to complete clevelopment of a Yucca Mountain standard in a technically competent way.
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