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APPENDIX E PERSONAL SUPPLEMENTARY STATEMENT OF THOMAS H. PIGFORD INTRODUCTION AND SUMMARY This supplementary statement clarifies two alternative methods of calculating racliation exposures to people in the far future. 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). ICRP also recommends that the critical group include the person at highest exposure. The objective is to ensure that if the individual at calculated maximum exposure is suitably protected, no other individual doses wit} be unacceptably high [ICRP, 1985ab]. ~ believe that this objective can be reasonably met if exposures and risks are calculated using the subsistence-farmer scenario and if the calculated risks meet the Standard's performance criterion. The subsistence-farmer is the indiviclual at calculated maximum risk. Thus, the subsistence-farmer approach is conservative and bounding. Its use represents wide national anti international consensus for safety assessment when characteristics of exposer! populations are not known. In contrast, the probabilistic critical-group calculation is based on arbitrary choices of reference populations, is not well defined, is not mathematically valid, ant! is subject to manipulation. It could leac] to much lower calculated doses and risks. There is no indication, however, that this country needs to adopt a calculational approach that is so much more permissive than current national and international practice. Its adoption wouIci undermine confidence in the adequacy of public health protection and jeopardize future success of the Yucca Mountain project. A policy decision common to exposure scenarios in Appendices C en c} D of the Report is that future humans will have cliets ant] foocI-water intake similar to that of people now living in the vicinity. In both exposure 161

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162 YUCCA MOUNTAIN STANDARDS scenarios, calculations are to be made for future people who cio not have extreme sensitivity to radiation, who have the same response to radiation as present people, and who do not have abnormal cliets. This Supplementary Statement speaks of calculating maximum and average closes ant! risks to such future humans, not to persons who may be at greater risk because of unusual diets or unusual sensitivity to radiation. COMMENTS AND EXPLANATION 1. Among the many possible exposure scenarios, the subsistence- farmer exposure scenario is the most conservative. It is bounding. All future people will be protected if the calculated subsistence-farmer dose/risk meets a prescribed safety limit. 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. Exposure calculations translate these concentrations into estimates of dose and risk to fixture people. The method of exposure calculation is the "exposure scenario"; it is sometimes called the "biosphere scenario". 2 The Committee is also concerned with the persons exposed to "the highest concentration of radiation in the environment". The environment includes air, water, and soil. The radiation in that environment consists of photons, free electrons, and alpha particles from radioactive decay of radionuclides. The "concentrations" of such radiation are rarely calculated, but could be deduced from calculated radiation fluxes. Evidently the Committee has in mind possible exposure from external radiation, such as doses to the skin from swimming in contaminated water or from being immersed in contaminated air. However, studies presented to the Committee show that such doses and risks from external radiation in the environment are minor compared to doses and risks from inhalation and ingestion of radionuclides that may be released to the (continued...)

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APPENDIX E --STAT~ENT OF THONGS H. PlGFORD 163 intake typical of that of present humans, it is also necessary to assume how much of the lifetime intake of food and water is affected by water contaminated with radioactivity, as well as how near the withdrawal well is to Me repository. These "human activity" assumptions are most difficult to deal with. Future people are deemed to be suitably protected if their calculated lifetime radiation doses and risks are less than a prescribed dose or risk limit. The calculational method should be constructed! so that if the person receiving the calculated maximum dose is suitably protected, then all future people with similar cliet and close response will also be protected [ICRP, 1985ab]. To ensure such protection we should assume conservatively that some future -individuals are subsistence farmers who use contaminated grounc! 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. It is bounding. It is patterned from the widespread practice, current and historical, of calculating close and risk to maximally exposed individuals where the exposure habits of real people cannot be specified or calculated. It is also the most stringent exposure scenario. (continued) environment from a geologic repository tNapier e' al., 1988~. 3 Large uncertainties in the calculation of radionuclide concentrations in the geosphere mean that calculated doses and risks to the subsistence farmers will also be extremely uncertain. Consequently, dose/risk estimates will be little affected whether all or only a "substantial portion" of the subsistence farmer's intake of water and food is contaminated by the extracted ground water.

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164 YUCCA MOUNTAIN STANDARDS 2. There is international consensus to calculate doses and risks for subsistence-farmers in determining compliance with a safety limit for geologic disposal. There is no such consensus for the probabilistic critical group proposed by the Committee. There is consiclerable precedence, in the U.S. and abroad, for basing dose en c! risk predictions on a subsistence farmer, or on a critical group that includes that subsistence farmer, as defined above.4 Projects for high level waste clisposal in the UK, Sweden, Finiand,-Canada, and Switzerland follow similar practices [Barraclough et al., 1992; Charles et al., 1990; Vieno et al., 1992; Davis et al., 1993~. Switzeriand's geologic clisposal project defines the critical group as a self-sustaining agricultural community located in the areats) of the highest potential concentration. Switzerianc! assumes that no food anti water are obtained from outside sources tSwitzeriand, 1985, 1994; van Dorp, 19941. In discussing the choice of critical groups and exposure scenarios for long-term waste management, UK's National Radiological Protection Board (NRPB) [Barraclough et al., ~ 992] states: ".... it is appropriate to use hypothetical critical groups. 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". The dose/risk assumptions are the same.

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APPENDIX E - STA TEMENT OF THOMAS H. PIGFORD 165 Likewise, the U.S. 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. The GENII code [Napier et al., 1988; Leigh, et al., 1993] is used to define the biosphere scenario and to calculate doses to subsistence farmers. The U.S. Nuclear Regulatory Commission (USNRC) calculates radiation closes to future individuals who could be affected by geologic disposal fMcCartin et al., 1994; Neel, 1995:1 To calculate future human exposures, USNRC assumes a hypothetical farm family of three persons who obtain all their drinking water from a contaminateci well. Well water is used to grow a large portion of the family's vegetables, fruits and grains. All of the family's beef ant! milk is obtained from farm animals fed on vegetation irrigated by contaminates! well water Napier, et al., 1988~. The assumed farm family's well is not restricted to the location of the present populations. Well depth and withdrawal rate are not constrained by present practice in the vicinity of Yucca Mountain. These assumptions meet the criteria for the conservative subsistence farmer described above. They meet the ICRP criteria for calculating doses for geologic disposal rNeel, 1995]. There are numerous other relevant examples. The U.S. WIPP project to dispose of transuranic waste in becIdeci salt calculates radiation doses based on a biosphere scenario that is the equivalent of the conservative subsistence-farmer approach. They use the GENII code [Napier, et al., 1988; Leigh, et al., 1993:1 to calculate individual doses once concentrations in water have been estimated. The estimated doses can be converter} to risks by using the dose-risk conversion factors. Sangria National Laboratories recently user} the subsistence-farmer calculation to evaluate doses and risks from DOE-owned spent fuel emplaces} in a tuff repository [Rechard, 19953. DOE's Hanford Environmental Dose Reconstruction Project Harris, 1994ab] allows variants of the subsistence farmer approach to calculate doses when occupancy factors and locations of actual exposed people are not sufficiently known. When the location, occupancy, and foot] source of real people cannot be iclentified, as in specifying a generically safe level in drinking water or in calculating long s No one in the present population lives nearer than 20 miles from Yucca Mountain.

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166 YUCCA MOUNTAIN STANDARDS term performance of geologic disposal, dose/risk estimates are based on the more conservative approach involving the hypothetical maximally exposed individual. Thus, adopting the subsistence-farmer approach is the consensus among the several geologic disposal projects in other countries and in the U.S., including the USNRC plans for calculating individual closes for a high-level waste repository. It is adopted to calculate closes when actual location and habits of potentially exposer! people are not known. On the other hand, the Committee has iclentiiled no reference wherein the kind of probabilistic exposure analysis of future human activities, as proposed in Appendix C, has been adoptecl for geologic clisposal. The reference population for the Committee's probabilistic exposure can be chosen arbitrarily. The Committee's probabilistic exposure calculations are to be baser] on extrapolation of location ant! habits of an arbitrarily selectee} reference population. The Committee acknowledges (cf. Appendix C) that the selection of the reference population for probabilistic analysis would be arbitrary. The population might be present inhabitants in the vicinity, inhabitants in some adjacent area, or inhabitants of an entirely different community6, or inhabitants of a hypothetical future population. It could evidently be any population of the past, present, or future. The Committee would! only require sufficient parameters to enable a calculation to be made. 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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APPENDIXE - STATEMENT OF THOMAS H. PIGFORD 167 The subsistence-farmer calculation of dose and risk fulfills recommendations of the International Commission on lladiological Protection (ICRP), the probabilistic critical- group calculation does not. The International Commission on Racliological Protection (ICRP) endorses calculating the average dose to a homogenous~ critical group. The group shouicl include the person at highest exposure and risk. {CRP's critical-group concept has been useful in evaluating the safety of operating facilities, where habits of the present population at risk can be included in the analysis of closes ant! risks. 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! be considered! who, clue to location and time, wouic! receive the greatest dose. The habits and characteristics of the group should be based upon present knowledge using cautious. but reasonable. assumptions. For example, the critical group coup! be the group of people who might live in an area near a repository and whose water would be obtained from a nearby groundwater aquifer. Because the actual doses in the entire population will constitute a distribution for which the critical group represents the extreme, this procedure is intended to ensure that no inclivi~iual doses are unacceptably high." Emphasis added] ICRP-43 also endorses the single hypothetical individual when dealing with conditions far in the future: "In an extreme case it may be convenient to define the critical group in terms of a single hypothetical indivi(lual, for example when clearing with conditions well in the future which cannot be characterized in cietail" fICRP, 1984b]. [Emphasis added.] ICRP recommends that the group include the most exposed individual and that there be no more than a tenfold variation in exposure within the critical group.

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168 YUCCA MOUNTAIN STANDERS On the basis of the above quotes from {CRP, I concur with UK's NRPB ant! others that the subsistence farmer is the appropriate-single hypothetical individual to be considered] for close and risk calculations for the distant future. The cliet and close response of the subsistence farmer are to be based on present knowledge. as recommended by ICRP. It is cautious and reasonable that there can exist in the future a farmer whose food intake is largely that grown in contaminated water. Because the subsistence-farmer calculation is bounding, it represents the extreme of the actual doses in the entire population. Protecting the subsistence farmer will ensure that no individual doses are unacceptably high. [Emphasis shows connection to ICRP-46 and ICRP-43 recommendations.] Those wishing to identify a critical group can imagine a group that would include the subsistence farmer, subject to ICRP's homogeneity criterion that the dose or risk to individuals within the group should vary no more than tenfold.9 The full-time subsistence farmer, who receives no food and water from noncontaminated sources, is obviously the bouncing scenario. We assign a probability of unity that he can exist. Some part-time farmers will be included in the data for the Committee's probabilistic analysis, because they exist now in the Amorgosa Valley. However, because the Committee's method is expected to synthesize a continuous probabilistic ciistribution function of occupancy ant! exposure to radiation, the full-time subsistence farmer will not be found on that distribution. Speculation that the Committee's probabilistic approach will yield the full-time subsistence farmer as the individual with maximum exposure is not valid. Methods of Appendices C and D do not converge. 9 The Committee makes much of the claim that the probabilistic exposure scenario of Appendix C can predict the dose/risk variation within the calculated critical group, so that the average dose within the group can be calculated. However, the ratio of maximum to average dose/risk must lie between one and ten, if the critical group meets ICRP's homogeneity criterion. 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. Again, calculated exposures from the probabilistic scenario are of questionable validity, whereas the subsistence-farmer results are conservative and bounding.

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APPENDIX E - STATEMENT OF THOMAS H. PIGFORD 169 The probabilistic approach can yield a maximum value of the close/risk calculated by that method. However, that maximum is not the maximum to which future people can be exposed. It is not bounding. Although the probabilistic approach may suffice for those who desire a self-consistent calculational exercise as a matter of policy, it cannot fulfill the desired goal that "if the indiviclual at calculated maximum risk is suitably protected, all other inclividuals will also be protected." The Committee justifies its probabilistic scenario on {CRP's use of the words "basecl upon present knowleclge". By attempting to extrapolate data on the present nearby population to predict probabilities of location, number, and exposure of future people, the Committee overextends its use of present knowledge. The Committee's probabilistic approach is neither "cautious" nor "reasonable". It can lead incorrectly to low values of calculated doses and risks to a group selected as "the critical group". The mmittee's probabilistic procedure cannot ensure that no individual closes ^~ ~~ ~ rid ~ are unacceptabiv high. It does not fulfill the recommendations of 1c quoted above. (see Comments 6 and 71. According to the Committee, probabilities of habits and behavior of future humans can be clerived from data on any arbitrarily chosen reference population, whether past, future, hypothetical, or present. The Committee adopts the present population only to illustrate the probabilistic method. However, past, immature, or hypothetical reference populations could not provide the kind of "present-knowledge" human data that the Committee claims must be used to satisfy ICRP's recommendation. 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. Even if correctly formulated, the Committee's probabilistic approach can tell us nothing about whether a subsistence farmer family can and will exist during any of the thousands of generations when people can be at significant risk. Common sense tells us that it is not reasonable to assume that the probability that a subsistence-farmer will not exist cluring one of the many thousands of future generations is necessarily low. The subsistence farmer is the bounding scenario for calculating doses and risks

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170 YUCCA MOUNTAIN STANDARDS to the types of people who, by policy, are to be protected. Therefore, protecting a critical group that includes the subsistence farmer Is necessarily the only cautious and reasonable approach that will fulfill ICRP's goal of ensuring that no indivi(lual doses are unacceptably high. Clearly, the Committee's less stringent probabilistic approach cannot ensure that no individual doses are unacceptabiv high. The Committee wishes to avoic! calculating dose/risk to a single individual or to a family of subsistence farmers as adopted by NRPB and USNRC (see Comment 2~. The Committee does not explain why. As quoted above, ICRP-46 accepts a "representative indiviclual" for calculation, and {CAP-43 endorses the single hypothetical individual when clearing with conditions far in the future: The Committee's argument against the subsistence farmer appears in the following statement in Chapter 2 of the Committee's report: ''... we believe that a reasonable en c! practicable objective is to protect the vast majority of members of the public while also ensuring that the decision on the acceptability of a repository is not prejudiced by the risks imposed on a very small number of individuals with unusual habits or sensitivities. The situation to be . avoidecI, therefore, is an extreme case definer! by unreasonable assumptions regarding the factors affecting dose and risk, while meeting the objectives of protecting the vast majority of the public." [From Chapter 2, emphasis added] 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. The Committee infers, in the above quote, that it is the subsistence farmer (or maximally exposed individual) who is to be ruled out because of "unusual habits or sensitivities." The Electric Power Research Institute (EPRI) reaches a similar conclusion and so states. The Committee and EPRI have apparently adopted words by UK's NRPB: "The purpose of the critical group concept ....is to ensure that the vast majority of members of the public do not receive unacceptable exposures, whilst at the same time ensuring that

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APPENDIX E STATEMENTOF THOMAS H. PIGFO~ 171 decisions as to the acceptability or otherwise of a practice are not prejudiced by a very small number of individuals with unusual habits." [Barraclough, et al., ~ 992] Both the Committee and EPR] have taken the NRPB words out of context and have misinterpreted NRPB. As is apparent from the full quotes of NRPB (see Comment 2), the individuals with "unusual habits" whom NRPB refers to are those with unusual sensitivities to radiation and with unusual diets.~ It is a mistake to assume that the NRPB statement about "a very small number of individuals" refers to the subsistence farmer, because NRPB endorses the use of the subsistence farmer. 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. There is consensus that the subsistence-farmer approach is consistent with the critical-group concept. The USNRC adopts a critical group that consists of a subsistence- farmer family of three people [McCartin, et al., 19941. According to Neel t1995] this is the "reference-man" concept developed by ICRP. Nee} also states that a similar approach has been taken by a working group within BlOMOVS, the international Biospheric Model Validation Study, for making long term assessments of dose. BlOMOVS is a cooperative effort by selected members of the international nuclear community to cievelop and test models designed to quantify the transfer and big-accumulation of raclionuclides in the environment. A Some precedence for excluding such individuals arises from UK's recent Sizewell Inquiry, which concerned a proposal to construct a new operating facility that could affect existing populations. A study of present population revealed that several individuals subsisted almost entirely on clams obtained in the vicinity. Because of the unusual diet, UK did not include those individuals in its analysis of the critical group.

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176 YUCCA MOUNTAIN STANDARDS Arbitrary assumptions could result in low probabilities of exposure or to a conclusion that a less stringent calculation of doses and risks is warranted. For example, one such assumption is that the future population could be large in number but confined to present population boundaries, effectively imposing a 20-mile exclusion distance. Another such assumption is that, if not confined to present boundaries, future populations would use wells no deeper than used by the present population 20 or more miles away, so future people nearer the repository would have to import foot! and water producer! farther from Yucca Mountain. Such assumptions would certainly result in low probabilities ant! lower calculated doses and risks. The assumptions are arbitrary and not clefensible. One might argue that the benefits of the arid climate and present low population near Yucca Mountain will be lost if closes ant} risks are calculates] for individuals exposed to radioactivity extracted from wells. However, there are advantages and disadvantages. The arid climate ant! lack of flowing surface water may invite people to use water extracted from wells. At other sites flowing surface water may dilute the contaminated ground water before it is user} by humans pNRC, 1983~. 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. There is no evidence that would! justify adopting a calculational method for Yucca Mountain compliance that is less stringent than the subsistence-farmer method adopted in other countries. The recent individual dose/risk calculations for the proposed Yucca Mountain repository are preliminary. They involve many conservative and unrealistic assumptions about engineering features. The hydrogeological, environmental, and engineering-clesign features of Yucca Mountain do not suggest that a less stringent calculational approach is necessary. Indeed, there are many features that can favor long-term performance.~4 i4 A repository in unsaturated tuff at Yucca Mountain may have much greater dilution of many radionuclides than repositories in those other countries that calculate doses from using ground water contaminated by waste buried in saturated rock. For radionuclides whose release Tom waste solids is limited by (continued...)

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APPENDIX E - STATEMENTOF THOlL4SH. PIGFORD 177 If a less stringent approach were justified, it would be far better to adopt a less restrictive value of the close/risk limit than to adopt a probabilistic exposure calculation that will be so difficult to clefenci. The probabilistic exposure approach is neither cautious nor reasonable. It cannot ensure that no future individual will receive an unacceptable dose or risk. Calculational techniques described in Appendix C are not mathematically valid. They can be manipulated to produce even lower calculated doses/risks. The Committee proposes to establish full distributions, with respect to space and time, of numbers of future populations and of their water ant! food sources in the area surrounding Yucca Mountain. The surrounding area is to be clivideti into subareas. Each subarea can be arbitrarily large and can contain as many people as one chooses. Baser} on the assumed and extrapolated probabilities of location and living habits of future people, ant] using calculates! concentrations of contaminants in ground! water, closes anti risks to individuals in each subarea are to be calculated.~5 The arithmetic average of all individual doses/risks in a (...continuecl) solubility, the release rate from the solid waste will be far less for the unsaturated repository, because of the low infiltration rate of ground water in the unsaturated zone. Contaminants in this infiltration flow will be highly diluted when they reach the underlying aquifer. 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. There is no basis for proposing a less-stringent calculation of doses and risks for Yucca Mountain. s The Committee's probabilistic method will yield calculated individual doses and risks that will depend on the population density and number of people in a subarea. The Committee has not explained how the growth in population is to be predicted; how the probabilistic distributions of number of people with respect to location and time, together with probabilistic distributions of parameters of occupancy, food source, etc., can result in a map of potential farm (continuecI...)

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178 YUCCA MOUNTAIN STANDARDS subarea is to be calculated. The subarea that is calculated to have the highest average dose/risk, together with aciditional subareas in which the average subarea risk is greater than or equal to one tenth of the risk in the subarea with maximum average risk, is said to clefine a critical subgroup. The average subgroup risk is said to be calculated as the arithmetic mean of the average risks of the selected subareas. The process is repeated for many different samplings of parameters that affect the probabilistic distributions, to produce new values of the critical-subgroup risks. The critical-group risk is said to be the arithmetic average of all calculates! critical-subgroup risks. (see Appendix C) However, the Committee's interpretation of {CRP would require calculating closes/risks for individuals over a large area, properly utilizing the many probability distribution functions of the geosphere and biosphere to calculate probabilistic distributions and expected values of consequences, selecting the inclivicluals whose risks are within the top ten percent, and calculating the average risk of that critical group. This method is mathematically inconsistent with the Committee's proposed subarea/subgroup method. It would be fortuitous if the two methods were to produce the same result. The subarea method! will tend to calculate lower doses and risks. The Committee's subarea method will not necessarily yielc} a critical group that inclucles the inclividual at maximum exposure ant} risk. That individual may be locater! in a subarea wherein are many indivicluals at much lower exposure. The subarea size and boundaries are arbitrary. There could result so low an arithmetic average dose for that entire subarea that it would not be selected for calculating the critical group. The (...continued) 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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APPENDAGE - STATEMENT OF THOMAS H. PIGFO~ 179 resulting "critical group" would not meet the ICRP criterion that the individual of greatest exposure should be included. Further, to achieve a lower calculated average dose in a subarea, one would need only to move the outer boundaries of the subarea farther from Yucca Mountain, to add more people exposed to lower closes. Appliecl to all subareas, arithmetic average doses would decrease, as would the average dose for the calculated "critical group." The repository would appear to be safer! The calculated critical-group doses and risks wouIc! be much lower than those for a critical group that includes a subsistence farmer. Or, to lower the calculates! risk, a different reference population could be selected. The calculates! lower closes ant! risks would be obtained with an illusion of safety, but with a serious loss of credibility. X. Calculated uncertainties in terms of confidence levels should be used to test compliance. Large uncertainties are inherent in predictions of the transport of radionuclides to the environment far into the future. Even larger uncertainties wouIc} be introduced by the probabilistic approach based on current-population data. The Committee does not discuss how information on uncertainties is to be conveyer! and used in compliance determinations. The performance measure of risk recommended by the Committee is the expected value of the probabilistic distribution of consequences. The Committee recommends that the expected value be compared directly to the risk limit to determine compliance. However, uncertainty should be considered in determining compliance. The expected value (or mean value) conveys nothing about uncertainty. Basing compliance on the expected-value comparison is not sufficient. A technique commonly used to convey uncertainty is to express the "confidence range" of the result. UK's NRPB illustrates presentation of the results in terms of the 95 percent confidence level. This states a range of values of dose or risk, such that 9S percent of the possible values of the distribution are calculated to fall within that range. NRPB then compares that range with a close or risk limit [Barraclough et al., 1992] . Effectively, the upper value of the range becomes the close or risk value for determining compliance. Methods of calculating confidence levels are well documentecl.

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180 YUCCA MOUNTAIN STANDARDS Presenting 90 or 95 percent confidence levels is done extensively for the geologic disposal projects in Sweden ant! Finland. It is a technique commonly used in the U.S., particularly when the results are important to public understanding and acceptance [e.g., Farris et al., 1994abl. 9. The Yucca Mountain project needs a soundly based standard for performance assessment and compliance. The U.S. program needs to share the benefits of an international approach towards developing standards and technology for geologic disposal. A standard and regulatory guidance to ensure public health ant! safety in the long-term for geologic disposal must include both a regulatory limit as well as guidance on assumptions of habits of future individuals and population groups to be adopted in calculating those individual closes ant} risks. ~ agree with and support the Committee's recommendation that the measure of performance best suited to assure public health and safety for the long term is the dose and risk to future individuals. That measure was adopted by the National Research Council's Waste Isolation Systems Committee (WISP) [NRC, 1983], after review and analysis of the release limits then proposer! by EPA, and was subsequently incorporates] in EPA's standard, 40 CFR 191. The WISP Pane! concluded that individual dose is a traditional and sound measure in assessing public-health protection. It was also noted that most, or possibly all, other countries undertaking geologic disposal use individual dose (or individual risk) as a performance measure. 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. ~6 I agree that individual risk is better than dose as a measure of performance, because it allows for possible fixture changes in the dose/risk conversion factor. As has already been explained in the Panel's report, calculated values of radiation dose would include probabilistic analysis of uncertainty and probabilities, if calculable, of being exposed to the radiation.

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APPENDIXE-STATEMENTOFTHOM~4SH. PIGFORD 181 The EPA release-limit standard has now been set aside for Yucca Mountain after considerable effort has been expended in designing for compliance with that standard. Adopting a performance measure based on indiviclual dose and risk is an important step towards cleveloping a standard that has a clear basis for protection of public health. The international consensus favoring individual dose/risk is likely to ensure unclerstanding and support of its adequacy for protecting public health. Both the technical community and the general public can be reasonably expected to see the virtues in individual dose/risk as a performance measure. However, acceptance ofthe use of inclividual dose/risk for ensuring safety cannot be expected if methods of calculating doses and methods of assessing compliance are not visibly sound, suitably conservative and understandable. 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. Aclopting the probabilistic exposure calculation would again put the U.S. repository program on a course divergent from that in other countries. One must expect continued questioning, by the scientific community, by the public, and by geologic programs in other countries, of why the U.S. finds it necessary to adopt such a unconservative approach to regulating geologic clisposal. The U.S. program needs to share the benefits of an international approach towards developing standards and technology for geologic disposal, including how to calculate individual doses and risks for compliance determination. The U.S. geologic disposal program needs a standard, including regulatory guidance, that can be clearly implemented and that can be expected to survive challenges. Serious challenges are likely to arise many years hence when an application is finally submitted to the regulatory agency for licensing determination. By that time an enormous investment of public and electric-utility funds will have been expended in the i7 See Comment 4.

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182 YUCCA MOUNTAIN STANDARDS development of repository technology and in the performance analysis to assure compliance with the new performance standard. Of the total funds expended, most will have been to develop technological and geosphere information, to produce designs of engineering barriers that can assure safety, to produce calculations of individual risk for determining compliance, and for administration and services. The cost of constructing the repository is expected to be small in comparison. Therefore, it is essential that the new regulatory standard and guidance be on firm ground so that this enormous effort, measured in money and time, is not wasted. Adopting an individual dose/risk standard is a step in that direction. Adopting the probabilistic exposure calculation, however, would leave the U.S. program vulnerable to future challenge on grounds of reasonable assurance of safety. I advocate an approach that ensures that all individuals are suitably protected, that is based on sound science and logic, and that does not compromise scientific validity and credibility under the aegis of policy. 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. REFERENCES FOR APPENDIX E Andrews, R. W., T. F. Dale, and J. A. McNeish, "Total System Performance Assessment -- An Evaluation of the Potential Yucca Mountain Repository," Yucca Mountain Site Characterization Project, iNTERA, Inc., Las Vegas, Nevada, 1994. Barraclough, I. M., S. F. Mobbs, and J. R. Cooper, "Radiological Protection Objectives for the Land-Based Disposal of Solid Radioactive Wastes," Documents of the National Radiation Protection Board (NRPB), 3, No. 3, 1992.

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APPENDIX E - STATEMENTOFTHOMASH. PIGFORD 183 Charles, D., and G. M. Smith, "Project 90 Conversion of Releases From the Geosphere to Estimates of Individual Doses to Man," Swedish Nuclear Regulatory Commission, SK] Technical Report 91: 14, 1991. Davis, P. A., R. Zach, M. E. Stephens, B. D. Amiro, G. A. Bird, I. A. K. Reid, M. T. Sheppard, S. C. Sheppard, M. Stephenson, "The Disposal of Canacia's Nuclear Fuel Waste: The Biosphere Moclel, BIOTRAC, for Postclosure Assessment," AECL-10720, 1992. Electric Power Research Institute (EPRI), "A Proposed Public Health and Safety Standard for Yucca Mountain: Presentation ant} Supporting Analysis" Report EPIC TR- ~ 040 ~ 2, April 1994. Farris, W. T., B. A. Napier, T. A. {kenberry, ]. C. Simpson, D. B. Shipler, "Atmospheric Pathway Report, 1944- ~ 992," Hanford Environmental Dose Reconstruction Project, Pacific Northwest Laboratories, PNWD-2228 HEDR, 1994a. Farris,W.T.,B.A.Napier,T.A.Ikenberry,].C. Simpson,D.B. Shipler, "Columbia River Pathway Dosimetry Report," 1944- 1992," Hanford Environmental Dose Reconstruction Project, Pacific Northwest Laboratories, PNWD-2227 HEDR, 1994b. International Commission on Radiological Protection (ICRP), "Racliation Protection Principles for the Disposal of Solid Raclioactive Waste," Report {CAP-46, Annals of the ICRP, 1985a. International Commission on Radiological Protection (ICRP), "Principles of Monitoring for the Radiation Protection of the Population," Report ICRP-43, Annals of the ICRP, 1985b. International Commission on Radiological Protection (ICRP), "1990 Recommendations of the International Commission on Radiological Protection," Report ICRP-60, Annals of the {CRP, Pergamon, 1991.

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184 YUCCA MOUNTAIN STANDARDS Leigh, C. D. et al., "User's Guide for GENII-S: A Code for Statistical and Deterministic Simulation of Radiation Doses to Humans from Radionuclides in the Environment," Sandia National Laboratories, SAND-9 1-0561, 1993. McCartin, T., R. Codell, R. Neel, W. Ford, R. Wescott, J. Bradbury, B. Sagar, I. 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. Napier, B. A., R. A. Peloquin, D. Is. Streng, J.V. and I.V. Ramschell, "GENII: The Hanford Environmental Radiation Dosimetry Software System," Richland, Washington, Pacific Northwest Laboratory, PNL-6584, 1988. Neel, R. B., "Dose Assessment Module", in NRC Iterative Performance Assessment Phase 2: Development of Capabilities for Review of A Performance Assessment for a High-Level Waste Repository," R. G. Wescott, M. P. Lee, T. J. McCartin, N. A. Eisenberg, and R. B. Baca' eds., U. S. Nuclear Regulatory Commission, NUREG- ~ 464, 1995. PigforcI, T. H., I. O. Blomeke, T. L. Brekke, G. A. Cowan, W. E. Falconer, N. J. Grant, I. R. Johnson, J. M. Matuszek, R. R. Parizek, R. L. Pigford, D. E. White, "A study of the Isolation System for Geologic Disposal of Radioactive Wastes,", National Academy Press, Washington, D.C., 1983. Planning Information Corporation, Nye County, Nevada, "Socioeconomic Conditions ant! Trends," 1993. Rechard, Rob P., Ed., "Performance Assessment of the Disposal in Unsaturated Tuff of Spent Nuclear Fuel and High-Level Waste Owned by U.S. Department of Energy, Vol. I: Methodology and Results," Sanclia National Laboratories, SAND94-2563/2, March 1995.

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APPENDAGE - STATEMENT OF THO - S H. PIGFO~ 185 Switzerland National Cooperative for the Storage of Radioactive Waste, "Nuclear Waste Management in Switzerland: Feasibility Studies and Safety Analyses," Project Report NGB 85-09, June 1985. Switzerland National Cooperative for the Storage of Radioactive Waste, "Kristallin - I: Safety Assessment Report," Technical Report 93- 22E, February 1994. UK Department of the Environment, "Review of Radioactive Waste Management Policy: Preliminary Conclusions," August, ~ 994. van Dorp, F., NAGRA Project Manager for Biosphere Models, Switzerland, Private Communication, 1994. Vieno, T., A. Hautojarvi, L. Koskinen, and H. Nordman, "TVO-92 Safety Analysis of Spent Fuel Disposal," Report Y1T-92-33E, Technical Research Centre of Finland, Nuclear Engineering Laboratory, Helsinki, 1992. Wilems, R. E., Presentation to the National Academy of Sciences Committee on Technical Bases for Yucca Mountain Standards, 1993. Wilson,M.~.,].H.Gautahier,R.W.Barnard,G.E.Barr,H.A. Dockery, E. Dunn, R. R. Eaton, D. C. Guerin, N. Lu, M. I. Martinez, R. Nilson, C. A. Rautm an, T. H. Robey, B. Ross, E. E. Ryder, A. R. Schenker, S. A. Shannon, L. H. Skinner, W. G. Halsey, I. D. Gansemer, L. C. Lewis, A. D. Lamont, I. R. Triay, A. Meijer, D. E. Morris, "Total System Performance Assessment for Yucca Mountain," Sandia Laboratories, SAND93-2675, 1994.

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