Technical Bases for Yucca Mountain Standards (1995) / Chapter Skim
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APPENDIX E - PERSONAL SUPPLEMENTARY STATEMENT OF THOMAS H. PIGFORD
APPENDIX E - PERSONAL SUPPLEMENTARY STATEMENT OF THOMAS H. PIGFORD
Pages 161-186
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From page 161... ...
They are the exposure scenarios involving the "probabilistic critical group" describeci in Appendix C and the "subsistence-farmer critical group" Ascribed in Appenciix D Both exposure scenarios involve critical groups, as recommended by the International Commission on Radiation Protection (ICRP)
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From page 162... ...
Future humans can be exposed to radiation by drinking well water containing radionuclides and consuming food grown from that contaminated well water. 2 In addition to assuming diets and food-water Calculated concentrations of radionuclides in ground water are a function of location and time.
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From page 163... ...
water for Winking and for growing their food over their entire lifetime.3 To ensure that no future person receives a greater lifetime dose, we assume that the water used by the subsistence farmer is extracted from the location of maximum concentration in ground water. The subsistence farmer calculation is the most conservative for the type of people assumed for dose/risk calculations.
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From page 164... ...
For the purposes of solid waste disposal assessments, these are assumed to exist, at any given time in the future, at the place where the relevant environmental concentrations are highest, and to have habits such that their exposure is representative of the highest exposures which might reasonably be expected." and, for long-term estimates of racliation dose and risk, Barraclough et al., state: " the 'reference community' replaces the critical group, and is locater} so as to be representative of individuals exposer! to the greatest risk, at the point of highest relevant environmental concentrations The reference community should normally comprise 'typical' subsistence farmers, i.e., perhaps a few families who produce a range of food to feed themselves." 4 Many ofthese projects adopt the term "maximally exposed individual" instead of the "subsistence farmer".
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From page 165... ...
Yucca Mountain project estimates radiation doses to future indivicluals on the basis of conservative subsistence farmers whose entire foot} ant! water are contaminated with radionuclides from the proposed repository [Anclrews et al., 1994; Wilson et al., 19941.
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From page 166... ...
The Committee illustrates the probabilistic method by adopting an arbitrary reference population consisting of those people living 20 or more miles away from Yucca Mountain.7 6 It has been suggested by proponents of the Appendix C approach that the population of Las Vegas could be a suitable reference population instead of the population in the region surrounding Yucca Mountain. 7 No people now live nearer than 20 miles from Yucca Mountain because the nearer land is publicly owned.
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From page 167... ...
However, because the habits and population at risk in the far future are not known, ICRP recommends (see "Radiation Protection Principles for the Disposal of Solid Radioactive Waste", ICRP-46 [ICRP, 1985al) : "When an actual group cannot be defineci, a hypothetical group or representative incliviclual should!
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From page 168... ...
An assumed linear variation results in a ratio of two, as assumed in the subsistence-farmer approach. I have already noted that the large uncertainties in calculating geosphere performance, together with the additional uncertainties inherent in the Committee's proposed probabilistic exposure calculations, do not justify such attempts to refine the ratio beyond that assumed above.
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From page 169... ...
Therefore, the Committee's definition of reference population does not satisfy the Committee's interpretation of {CRP guidance concerning use of "present knowledge" for establishing a critical group. The Committee does not claim that its probabilistic exposure scenario can predict the habits of future generations; it only presents what is said to be a self-consistent calculation of individual risks based on assumer} extrapolation from an arbitrary reference population.
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From page 170... ...
The objectives are laudable, but the Committee and others [EPRI, ~994] infer that it is necessary to calculate doses and risks to groups of future people rather than to an indiviclual such as a subsistence farmer, contradicting {CRP tICRP 1984,19853.
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From page 171... ...
Because the Committee's probabilistic approach cannot predict the actual habits of future people, and because it will predict lower doses ant! risks than would be calculated for a subsistence farmer, there will be no way of knowing whether the Committee's objective to protect the vast majority of members of the public will be fulfilled.
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From page 172... ...
(see Comment 2) Representatives of geologic disposal projects in other countries indicate that their subsistence farmer calculations are consistent with {CRP recommendations.
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From page 173... ...
In the written record of this study there is abundant information, contribute(l by knowledgeable scientists, concerning the stringency of calculating doses and risks to subsistence farmers as well as information on possible benefits of the Committee's proposed probabilistic approach. That information bears on several questions relevant to this study.
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From page 174... ...
Some calculated doses to subsistence farmers were high. The studies made no attempt to estimate the number of subsistence farmers who might receive these doses.
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From page 175... ...
for subsistence farmers. (see Comment 71.
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From page 176... ...
However, at least two projects in other countries are calculating doses/risks to subsistence farmers who are assumed to use contaminated ground water clirectly, similar to what would occur at Yucca Mountain. These projects expect that they can meet performance goals similar to those suggested in this study.
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From page 177... ...
Water flow past waste packages in saturated rock will be far greater, as will the release rate of such radionuclides to ground water. It would be premature to conclude that Yucca Mountain would be at a disadvantage relative to other repositories.
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From page 178... ...
density or water use; how many such maps will have to be generated and how they are to be used in conjunction with the many equivalent maps of sampled plume concentration; how population changes from the many expected cycles of climate change are to be calculated; how the expected values of consequence to individuals at various times and locations are to be obtained without simultaneously sampling distribution functions of geosphere performance and biosphere performance; and how the probability distribution functions are to be generated if any of the other arbitrary reference populations suggested by the Committee are adopted.
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From page 179... ...
The calculated critical-group doses and risks wouIc! be much lower than those for a critical group that includes a subsistence farmer.
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From page 180... ...
Adopting the same performance measure as other countries wouIcI provide a framework for interchanging and sharing information with other countries on the developing technology for geologic disposal. The technical approach to design and performance analysis, for the purpose of ensuring long-term safety, depends greatly on the performance criterion that is adopted.
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From page 181... ...
Selecting an exposure scenario to be used in calculating long-term doses is a crucial step that can greatly affect the magnitude of calculated inclividual doses and risks. If calculated risks to the bounding subsistence farmer are found be within compliance limits, then no future inclividual doses would be unacceptably high.~7 In contrast, the probabilistic exposure calculation is too vaguely defined, subject to too many arbitrary and unconservative policy decisions and subject to too many questions of valiclity to meet any reasonable test of acceptability, once the shortcomings of that approach have been sufficiently understood.
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From page 182... ...
Adopting the unconservative probabilistic exposure scenario will undermine public confidence. The scientific community and the public will find it difficult to understand why the Committee endorses the probabilistic exposure scenario that is demonstrably less stringent in protecting public health than the subsistence-farmer approach, the approach that has been adopted for geologic disposal projects in other countries and in the U.S.
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From page 183... ...
Shipler, "Columbia River Pathway Dosimetry Report," 19441992," Hanford Environmental Dose Reconstruction Project, Pacific Northwest Laboratories, PNWD-2227 HEDR, 1994b. International Commission on Radiological Protection (ICRP)
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From page 184... ...
Walton, "Models for Source Term, Flow, Transport and Dose Assessment in NRC's Iterative Performance Assessment, Phase 2," Proc. International Conference on High Level Radioactive Waste Management, Las Vegas, NV, 1994.
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From page 185... ...
Switzerland National Cooperative for the Storage of Radioactive Waste, "Kristallin - I: Safety Assessment Report," Technical Report 9322E, February 1994. UK Department of the Environment, "Review of Radioactive Waste Management Policy: Preliminary Conclusions," August, ~ 994.
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