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s IMPLICATIONS OF OUR CONCLUSIONS Early in this study' we were asked by EPA to provide a description of how the form of the standard that we recommend differs from that of the current EPA stanciard for high-level raciioactive waste in 40 CFR 191 and, where there were significant differences, to provide an explanation of the basis for the differences. We have tried to do so in the detailed discussions of Chapters 2, 3, ant] 4. The purpose of this chapter is to provide a comparison of our recommended approach with 40 CFR 191, including both common elements ant! differences. It is our intention that this chapter provide a concise summary of what we propose should be done differently ant] what elements of the 40 CFR 191 approach we recommenc! be retained. In adclition, we discuss the approach recommended here and that of technology-based standards such as the USNRC's 10 CFR 60. Because our approach is risk-based, it is not useful to make a direct comparison with 10 CFR 60. We do discuss here some aspects of technology-based standards, including ALARA and technology requirements to minimize early releases. Finally, we note some possible administrative consequences of our recommendations. COMPARISON WITH 40 CFR 191 40 CFR 191 applies to the Waste Isolation Pilot Plant (WIPP) not to the proposed Yucca Mountain repository. Whether some other future repository would be subject to 40 CFR 191 depends on the legislative means taken to initiate it. The 40 CFR 191 standard has three major elements: containment requirements, individual dose limits, and grouncI- water protection requirements. Section X01 of the Energy Policy Act of 1992 directs EPA to issue a standard to protect the public from radionuclide releases at Yucca Mountain, and requires that the standard be stated in terms of the maximum annual dose equivalent to individual members of the public. 117
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118 YUCCA MOUNTAIN STANDARDS Considerations We believe that there are two major considerations that give rise to differences between our recommendations and 40 CFR 191. Generic vs. site-specif c standards By law, EPA is charger] with issuing generally applicable standar(ls for protection of health and the environment, and for that reason, 40 CFR 191 is a generic standard. This means that 40 CFR 191 contains provisions applicable for all conceivable terrestrial deep geologic repository sites and types. In adclition, at the time that 40 CFR 191 was drafted, the major effort towards establishing a repository was site selection, and 40 CFR 191 was developer! to give guidance regarding the feasibility of different types of sites. In contrast, our recommendations concern a standard for the proposed repository at Yucca Mountain. Consequently, we have not addressed site selection, nor have we emphasizer! potential elements of a standard that would be operationally insignificant at Yucca Mountain. For example, our fancying that a containment requirement or release limit is inappropriate is a finding specific to a Yucca Mountain repository, for another geologic setting, we might or might not have reached a different conclusion. The ctistinction between a generic stanciard and a site-specific one should be noted as our recommendations are compared with 40 CFR 191. Dose vs. risk 40 CFR ~ 91 limits individual closes from the undisturbed performance of a repository to 0. ~ 5 mSv per year (15 mrem per year). In contrast, we have recommended an approach based on individual-risk limits. Among the reasons why we have chosen risk as the regulatory basis rather than dose, two are important for this discussion. The first is that changes in our understanding of radiation health risks can be accommodates! without revision of the level of the standard. If, in the future, scientific evidence becomes available in(licating that radiation is
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IMPLICATIONS OF OUR CONCLUSIONS 119 more or less hazardous than our current scientific understanding suggests, the framework we propose wouic] incorporate that new information without a required revision to the level of the standard. The second reason that we have recommended a risk basis is that the probabilities associated with various elements of the exposure calculation can be considered. Our recommended approach is a risk limit based on the probabilistic distribution of a dose and the probability of health effects associated with that dose. Because the individual dose requirements of 40 CFR ~ 9 ~ have not been implemented, it is not possible to tell whether or how probabilities would be incorporated into estimation of dose. Because the effort at EPA with 40 CFR 191 implementation is now focused on WIPP, and because the individual dose limit is not a particularly important component of the standard for WIPP, it is not clear to us how EPA will interpret its dose limit. In any event, our proposal is clear with respect to our intention that the standard should include consideration of the probabilistic aspect of future exposures. Differences From 40 CFR 191 What follows is a brief summary of the differences between our recommendations and 40 CFR 191. Time periods Perhaps the most significant difference between our recommendations and 40 CFR 191 concerns the time period! over which the standard is applicable. In 40 CFR 191, the standard applies for a period of 10,000 years. In our proposal, we have specified that the basis for the standard should be the peak risk, whenever it occurs. Based on performance assessment calculations provided to us, it appears that for some reasonable combinations of parameters, peak risks are likely to occur after 10,000 years. Within the limits imposed by the long-term stability of the geologic environment.
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120 Population health effects and release limits YUCCA MOUNTAIN STANDARDS A major element of 40 CFR 191 is its containment requirement, which limits releases of radionuclides to the accessible environment during the first ~ 0,000 years of operation. The stated goal of the release limit was to limit cancer deaths to the general population to 1,000 over 10,000 years. This requirement was to be implemented through a comparison of calculateci releases of radionuclides with a table of allowable release limits for each radionuclide. For reasons stated in Chapter 2, we do not think that such a requirement would provide aciciitional protection over that provided by the inctividual-risk limit for a repository at Yucca Mountain, and we do not recommend that a release limit be adopted. A related topic is our recommendation in Chapter 2 to employ the concept of a negligible incremental risk, which is the level of risk that can, for radiation protection purposes, be dismissed from consideration. Persons in some local populations outside of the critical group at Yucca Mountain might be exposer! to risk from repository releases in excess of the level of negligible incremental risk. However, as individuals, these persons wouIc] be exposed to less risk than the risk limit established by the standard for the critical group. On a collective basis, the risks to future local populations are unknowable. We conclude that there is no technical basis for establishing a collective population-risk standard that would limit risk to the nearby population of the proposed Yucca Mountain repository. Radiation releases from a Yucca Mountain repository can, in principle, be clistributed beyond! a local population to a global population. In general, the risks of radiation produced by such wide dispersion are likely to be several orders of magnitude below those to a local critical group. Human intrusion Under 40 CFR 191, an assessment must be made of the frequency and consequences of human intrusion for purposes of demonstrating compliance with the containment requirements. Human intrusion is not a consideration for compliance with the indiviclual dose limits of ground- water protection requirements. In recognition of the substantial uncertainties involved, EPA has provicled detailed guidance for analysis of
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IMPLICATIONS OF OUR CONCLUSIONS 121 human intrusion risks and is proposing a reference biosphere be used for the implementation of 40 CFR 191 at WIPP that incorporates an assumption that the future biosphere is much like the present. The EPA requirement includes releases due to drilling cuttings brought to the surface and also includes increases in other radionuclide releases that might occur, for example, through accelerated releases to grounc] water. In contrast, we conclude that it is not possible to assess the probability of human intrusion into a repository over the long term, and we do not believe that it is scientifically justifieci to incorporate alternative scenarios of human intrusion into a risk-based compliance assessment. We clo, however, conclude that it is possible to carry out calculations of the consequences for particular types of intrusion events. The key performance issue is whether repository performance would be substantially clegraded as a consequence of an inadvertent intrusion for which the intruder does not recognize that a hazardous situation has been created. This consequence assessment is to be clone separately from the calculation of compliance with the risk limit from other events and processes, and is to exclude exposures to drillers or to members of the public due to cuttings. We recommend that EPA should require that the conditional risk as a result of the assumed intrusion scenario be no greater than the risk limits adopter) for the undisturbed-repository case. Ground-water protection 40 CFR 191 inclucles a provision to protect ground water from contamination with radioactive materials that is separate from the 40 CFR 191 inclividual-dose limits. These provisions have been adcled to 40 CFR 191 to bring it into conformity with the Safe Drinking Water Act, and have the goal of protecting ground water as a resource. We make no such recommendation, and have baser! our recommendations on those requirements necessary to limit risks to indivicluals. Common Elements With 40 CFR 191 Although our recommendations differ from 40 CFR 191, there are also important similarities in approach.
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122 Dose apportionment YUCCA MOUNTAIN STANDARDS In the recently revised 40 CFR 191, EPA has enciorsec} the dose limit anti dose-apportionment recommendations of the ICRP. We support this approach. Reference biosphere In view of the almost unlimited possible future states of society ant! of the significance of these states to future risk and dose, both EPA and we have recommended that a particular set of assumptions be used about the biosphere (including, for example, how anti from where people get their foot! and water) for compliance calculations. Both EPA and we recommence the use of assumptions that reflect current technologies and living patterns. Exclusion zone The original standarcI, 40 CFR 191, container! a provision for an exclusion zone in the immediate vicinity of the repository. The purpose was to provide a boundary for calculating releases. The zone was presumably to be protected! from human activity. In light of our conclusion in Chapter 4 that it is not reasonable to assume that institutional controls can be maintained for more than a few centuries, we also conclude that there is no scientific basis for assuming that human activity can be prevented from occurring in an exclusion zone or that defining such a zone will provicle protection to future generations from exposures in the vicinity of the repository. If, as we recommend, human intrusion is treated separately from the performance of an undisturbed repository, it is reasonable in our view to define a region in which human activities are to be regarded as intrusion and to exclude that region from calculation of the undisturbed repository performance. Beyond the repository footprint, however, there seems to be no practical purpose for deEning a larger exclusion zone for the form of the standard! we recommend. Without either a release limit or a time limit for the
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IMPLICATIONS OF OUR CONCLUSIONS 123 standarc! for undisturbed performance, an arbitrary boundary serves no purpose. Use of mean values We recommend that the mean values of calculations be the basis for comparison with our recommended standards. LIMITS OF THE SCIENTIFIC BASIS Our assignment has been to assess the scientific bases for a standard to protect the public health from radiation exposures that might result from radionuclicle releases associated with a high-level waste repository at Yucca Mountain. In so cloing, we have conclucled that for some decisions there presently exists a limited scientific basis required to set and administer such a standard. We have explicitly noted these issues in the preceding chapters, and have indicated that they must be decided on a policy, rather than a scientific, basis. This interplay of scientific ant] policy issues in the standard! has two major implications. First, where we have iclentified policy issues, we have recommencled that sounc! public policy would have these issues addresses! in rulemaking by the appropriate federal agency, EPA or USNRC. The process of addressing these issues by rulemaking or an equivalent procedure must provide a full opportunity for public participation, especially by the citizens of the affected jurisdictions, an(l allow the agency the flexibility to take a broad range of public opinion into account in its final public policy judgments. We regard these characteristics as essential for the policy judgments that are required in formulating the standard. In contrast, the licensing process is not suited to this policy-making role, but rather is the arena in which compliance with the standard can be tested. Several times we have identified possible positions that could be used by the responsible agency in formulating a proposed rule, which is often the initial step in the process. Other starting positions are possible, and of course the final rule might differ markedly from the one proposed. We have tried only to illustrate by reference to other authorities or by
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124 YUCCA MOUNTAIN STANDARDS example that there seems to be a reasonable policy position from which to begin. The second implication of the limitations that we have identified is that since they represent current gaps in scientific knowledge, it might be possible that some of these gaps and uncertainties might be reduced by additional research. It seems reasonable, therefore, to ask what gaps could be closed by taking time to obtain more scientific and technical knowledge on such matters as the nature of the waste, its potential use, the health effects of radionuclides, the value of waste products for later generations, and the security of retrievable storage containers. New information in these and other areas could improve the basis for setting the standards if, for example, this information reduced the uncertainty about the effects of very low doses of radiation. Whether the benefit of new information would be worth the additional time and resources required to obtain it is a matter of judgment. This judgment would be strengthened by a careful appraisal of the probable costs and risks of continuing the present temporary waste disposal practices and use of storage facilities as compared with those attaching to the proposed repository. No such comprehensive appraisal is now available. Conducting such an appraisal, however, should not be seen as a reason to slow down ongoing research and development programs, including geologic site characterization or the process of establishing a standard to protect public health. TECHNOLOGY-BASED STANDARDS Technology-based standards play an important role in regulations designed to protect the public health from the risks associated with nuclear facilities. The purpose of these standards is typically to help ensure protection by employing the best available technology, considering cost and other factors. Three issues involving technological approaches have been raised in our study, and we comment on them below.
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IMPLICATIONS OF OUR CONCLUSIONS The ALARM Principle 125 The "as low as reasonably achievable" (ALARA) principle has been a basic feature of racliation protection for nearly 30 years. It is intended to be applied after threshold regulatory limits have been met, and calls for additional measures to be taken to achieve further reduction in the calculated health effects resulting from radiation exposure of workers or of a population so that final exposures are "as low as reasonably achievable taking account of economic and social factors." ALARA requires a balancing of costs ant! benefits. While ALARA continues to be widely recommended as a philosophically desirable goal, its applicability to geologic disposal of high-level wastes is limited at best because the technological alternatives available for designing a geologic repository are quite limited (IAEA, 1989~. Further, the difficulties of demonstrating technical or legal compliance with any such requirement for the post-closure phase could well prove insuperable even if it were restricted] to engineering ant! design issues. We conclude that there is no scientific basis for incorporating the ALARA principle into the EPA stanciarct or USNRC regulations for the repository. However, it is nothing other than sound] engineering practice to consider whether reductions in radiation close or risk can be achiever! through engineering measures that can be implemented in a cost-effective manner. 10 CFR 60 If EPA issues a standard based on individual risk, USNRC is required to revise its current regulations embodies] in 10 CFR 60 to be consistent with such a stanciard. One purpose of the existing USNRC regulations is to help ensure multiple barriers within the repository system. The concept of multiple barriers, implemented through subsystem requirements, has its origin in the Nuclear Waste Policy Act of 1982. Recognizing this origin, we nonetheless conclude that because it is the performance of the total system in light of the risk-based standard that is crucial, imposing subsystem performance requirements might result in a suboptimal repository design. Care shouIc] be taken to ensure that any
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126 YUCCA MOUNTAIN STANDARDS subsystem requirements for Yucca Mountain do not foreclose design options that ensure the best long-term repository performance. For example, in 10 CFR GO, there is a subsystem requirement that ''the geologic repository shall be located so that the preemplacement ground water travel time along the fastest path of likely radionuclicle travel from the disturbed zone to the accessible environment shall be at least 1,000 years. . ." This regulation was written with the presumption that the repository would be located in a saturated zone. At Yucca Mountain, the repository is being considered! for location in the unsaturated zone where there is a direct pathway to the atmosphere. This subsystem requirement has focuses] attention on the grounc! water and away from the gaseous pathway. As an explicit example of suboptimization, it could be that in a specific geologic setting the requirement to keep grounci water travel times to the accessible environment above 1,000 years, as required by 10 CFR 60, might have next to no effect on future indiviclual risks. However, such · . . ~ ~ .. · . . · . . .. .. · ~ a requirement COU10 force the repository design team to alter the specific location ofthe emplaces] waste to a location that, although it could meet the travel-time requirement, would be less optimal. That is, it could imply greater future incliviclual risks clue to other factors such as, for example, a less optimal gaseous pathway or a different geochemical setting that wouIcI leac} to higher raclionuclide solubilities or lower retardation. Minimum Early Release Several persons suggested to our committee the use of a technology-basec] standard that would specify a strict release limit from an engineered barrier system during the early life of the repository. A representative proposal of this type would permit the release of less than 1 part in 100,000 per year of the radionuclides present at 1,000 years after repository closure. It was suggested that this proposal would be consistent with the essentially complete containment concept of 10 CFR 60, and would result in essentially no public health impact for an initial period of time of 300 to 1,000 years, cluring which the integrity of the engineered barrier system conic} be assurer! with a high level of confidence. We find that such a limitation on early releases from the repository would have no effect on the results of compliance analysis over the long
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IMPLICATIONS OF OUR CONCLUSIONS 127 term. Nevertheless, some members of the committee believe that such a limitation might provide adclec! assurance of safety in the near term. Whether to provide such assurance by using a limitation on early releases is a policy decision that EPA might wish to consider. ADMINISTRATIVE CONSEQUENCES FOR EPA, USNRC, AND DOE Our recommenciations, if adopted, will imply the development of regulatory and analytical approaches for Yucca Mountain that are different from those employed in the past and from some approaches currently user] elsewhere by EPA. We further note that several parameters important in risk-based assessment require determination by rulemaking. Both the change in approach and the time required to develop a thorough and consistent regulatory proposal anti to provide for full public participation in the rulemaking process, particularly in devising the biosphere models, identifying the critical groups, and clefining intrusion scenarios, will require considerable effort by EPA. Incleed, this process probably will take more than the year, that is currently provided for in the statute, for EPA to complete development of a Yucca Mountain standard in a technically competent way. Although it is important to obtain a timely result, we also believe it is important that EPA take sufficient time to produce a thorough, competent, and consistent standard. A similar duty is imposed on USNRC to assure that its regulation implementing the EPA standard] is not compromiser! by time constraints. Although a new standard ant] its implementing regulations might not be available within the two years envisioned in the Energy Policy Act of 1992, that floes not mean that DOE's Yucca Mountain Site Characterization Project cannot proceed usefully in the interim. The site- characterization ant} iterative-performance assessment efforts can continue in the absence of a promulgated standar~i. DOE has, in fact, been making progress consistent with our recommendations with its series of total-system performance assessments (TSPAs) anti we hope that progress will continue. For example, the TSPA-1993 reports from the Sandia National Laboratory (Wilson et al., 1994) and Intera, Inc. (Anctrews et al., 1994) examined the performance measure of radiation close to a maximally
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128 YUCCA MO~TAINSTANDA=S exposed individual, in addition to consideration of normalizeci cumulative releases as dei inert by EPA in 40 CFR 191.13. The TSPA has also reporter} on repository performance for a period of one million years as well as for the ~ 0,000-year period. Both the dose calculation anti extension of the time perioc} move in the direction of our recommendations. On the other hanci, progress for some aspects of DOE's program might depencl on the nature of EPA's promulgates! standard. For example, the potential risks to a critical group living near Yucca Mountain cannot reaclily be assesses! until the rules for identifying the critical group are defined.
Representative terms from entire chapter: