The Revised Radiation Protection Standards for the Yucca Mountain Nuclear Waste Repository

Robert Vandenbosch and Susanne E. Vandenbosch

Introduction

In September 2008 the Environmental Protection Agency (EPA) issued its final radiation standards for the proposed geologic nuclear waste repository at Yucca Mountain. This was months after the Department of Energy had filed its license application for the repository with the Nuclear Regulatory Commission. These standards will be incorporated into NRC regulations.

Early History of the Development of the Radiation Standards

The Nuclear Waste Policy Act of 1982 established deep geological disposal as the method for disposal of nuclear waste from commercial nuclear power reactors, and in 1985 the EPA issued generic standards that would apply to all geological repositories. Part of these standards was remanded by the federal Court of Appeals for the District of Columbia in 1987. Also in 1987 Congress amended the Nuclear Waste Policy Act, designating Yucca Mountain as the only site to be characterized further for a repository instead of three sites required by the 1982 Act. Congress directed the EPA to issue radiation standards specific to Yucca Mountain in 1992, and to seek and follow the advice of the National Academy of Sciences in preparing these standards. In 1995 a committee of the National Research Council, an arm of the National Academy of Sciences, issued its recommendations in a report titled “Technical Bases for Yucca Mountain Standards”.¹ Hereafter this report will be referred to as the NAS report.

The EPA issues Radiation Standards for Yucca Mountain in 2001

In 2001, the EPA issued 40 CFR part 197, Public Health and Environmental Radiation Protection Standards for Yucca Mountain, Nevada.² The standards consist of three parts:

1. An Individual-Protection Standard of 15 mrem/yr that applies to a “reasonably maximally exposed individual” who lives in a publicly accessible area and has a diet and lifestyle representative of present residents of Amargosa Valley.
2. A Human-Intrusion Standard concerned with exposure that might occur as a result of drilling in the vicinity.
3. Groundwater Protection Standards setting separate concentration limits (15 picocuries per liter) on alpha emitters and dose limits (4 mrem/yr) from combined beta and photon emitters.

The limitation of the standards to the first 10,000 years after repository closure resulted in a Court challenge by the State of Nevada and the Natural Resources Defense Council.³ They based this challenge on the fact that the NAS report had recommended that the standards should extend to the time of expected peak dose. DOE performance assessments at the time indicated this was of the order of 300,000 years. The appeals were heard by the federal Court of Appeals for the District of Columbia in 2004. The Court ruled the EPA’s compliance period was clearly not consistent with the NAS recommendation. It said the EPA would either have to come up with a new standard or secure new legislation negating the consistency requirement with the NAS recommendation. The Court allowed the other parts of the EPA’s standards to stand, including the Groundwater Protection Standard which had been challenged by the Nuclear Energy Institute.

The EPA Responds in 2005 with Proposed Revised Standards

In August of 2005 the EPA issued its proposed amendment to the Radiation Protection Standards for Yucca Mountain which added a new protection standard of 350 mrem/yr for the period between 10,000 and 1 million years.⁴ The proposed amendment also changed the measure of how the limit was to be applied to the DOE’s performance assessment. As allowed by the Court, it let stand the Human-Intrusion Standard and Groundwater Protection Standard. It also let stand the 15 mrem/yr limit for the first 10,000 years.

The EPA opened the proposed amendment of the radiation standards to public comment for several months. More than 300 individual submittals were received before the comment period closed in late 2005.

The EPA Finalizes the Standards in 2008

Summary of the Revisions

In late September of 2008, the EPA issued its final Amendment of the Radiation Protection Standards for Yucca Mountain.⁵ The final standards reflect few but nevertheless significant changes from the Proposed revisions of 2005. Most importantly, the radiation dose for the period between 10,000 and 1 million years was changed from 350 mrem/yr to 100 mrem/yr, and the metric for the limit for this period was changed from the median to the mean. Since the mean typically exceeds the median for the distribution of expected doses in DOE performance assessments, these two changes imply a reduction of about a factor of seven in the allowed dose for the time period after 10,000 years. Since the 15 mrem/yr limit for the first 10,000 year is retained, the standard remains two-tiered.

The (il)logic of an uncertainty-based larger dose limit after 10,000 years

The EPA in its preamble emphasizes the increasing uncertainty in the reliability of dose estimates for longer times. Considerable effort is expended to demonstrate the increase in projected uncertainties with time. This is not the issue. We know of no informed individual who would argue that performance assessment uncertainties would not increase over a long period of time. Rather the issue is what the regulatory response should be to uncertainties. It would seem that to provide the same confidence in protection of the public in the presence of increased uncertainties one would have to make the standard more conservative rather than less conservative.

Perhaps an analogy might help. Consider an engineer responsible for specifying the quality rating specification of a girder for a bridge. It is found that with increasing time the uncertainty in the corrosion weakening of the girder increases. If one wants to extend the time for which one would have confidence in the integrity of the bridge, would one loosen or tighten the quality rating specification of the girder? It would seem obvious that one would tighten the specification to have the same confidence that the girder would not fail at larger times as at shorter times.

Intergenerational Equity

The principle of intergenerational equity has been endorsed by several broadly-based organizations, including the International Atomic Energy Agency and the Organisation for Economic Co-operation and Development’s Nuclear Energy Agency. This principle requires that the risks to future generations be no greater than the risks that would be accepted today.⁶ A straightforward interpretation of this principle would require that the radiation standard not allow future generations to be exposed to more radiation than the present generation. Thus the two-tiered Standard in the EPA’s rule with an appreciably larger dose limit at later times (100 mrem/yr) than at early times (15 mrem/yr) is not consistent with this principle. The EPA in its preamble to its rule recognizes this problem. It falls back on a statement in the NAS report that “whether to adopt this or some other expression of the principle of intergenerational equity is a matter for social judgment”.⁷ The EPA tries to argue that intergenerational equity does not require that the same compliance standard must apply at all times. It says that such a requirement ignores the complexities involved in establishing protection standards for periods as long as 1 million years, and that the basis for judgment at different times is not the same. The EPA’s final defense of its position is that the less restrictive standard for longer times is still “protective of public health and safety, and will offer comparable, if not identical, protections to the affected generations”. If this is true, one wonders why they didn’t use the same “protective” standard of 100 mrem/yr for both time periods.

Are the Standards Protective of Human Health?

Finally we address the most important question regarding the Final Yucca Mountain Radiation Standards- are the numerical values of the dose limits reasonably protective of the public? This discussion will focus on the 100 mrem/yr standard, because if this standard is acceptable surely the more stringent 15 mrem/yr standard will be also. First, it may be helpful to translate the effective dose rate limit into the expected detrimental health effects of such a dose. Assuming a linear relation between dose and the probability of developing a fatal cancer of approximately 5 x 10-7 per mrem⁸, a one-year exposure to a dose of 100 mrem would result in a probability of developing a fatal cancer of 5 x 10-5 for each individual.

1. The NAS report did not make a specific recommendation regarding the dose or risk level that should be established by the protection standard. The report states that what risk is acceptable is a question of public policy rather than of science. The report does give some examples of risk limits established by other U.S. nuclear regulations and by authorities outside of the U.S. These are generally in the range 10-5 to 10-6 per year. The NAS report suggests that this range could be used as a reasonable starting point in the EPA’s rulemaking.⁹ Thus we see that the 100 mrem (risk= 5 x 10-5) standard is an order of magnitude larger than, most other standards.

The EPA says the present standard is based on a recommendation of the International Commission of Radiation Protection (ICRP). This commission has issued recommendations for the dose to be used to select constraints in various situations, including both occupational exposure and general public exposure. An apparently relevant situation covered by the Commission recommendations is for the practices where there is no direct benefit for the exposed individual but where there may be a societal benefit. For this situation the Commission recommends a maximum effective dose of 100 mrem/yr¹⁰, and this is the value incorporated in the EPA’s rule for the period between 10,000 and 1 million years. The EPA does not mention however a more ICRP specific recommendation¹¹ of a dose constraint of 30 mrem/yr for members of the general public for exposure resulting from nuclear waste management. This lower value for waste disposal is based on the idea of apportionment of the total allowable 100 mrem/yr limit for all anthropogenic sources of radiation, excluding medical exposures.¹² The EPA does discuss the apportionment issue, arguing that it is reasonable to allocate the entire 100 mrem/yr to the repository. It bases this on the lack of other significant anthropogenic sources in the area, and assumes that current conditions will apply in the future. The apportionment issue is mentioned in a Nevada suit against the EPA filed with the Court of Appeals within weeks of the issuance of the final standards.¹³

Remembering the NAS’s assertion that setting a risk limit is a matter of public policy, what can we use as guide in setting a standard? It would seem that a standard set as a matter of public policy should be informed by risks that the public routinely takes without governmental regulation. Of particular relevance are risks related to radiation. The average natural background citizens are exposed to varies greatly (primarily due to differences in radon) in different parts of the country. These differences can exceed the 100 mrem/yr limit for exposure to individuals living the closest to Yucca Mountain. There is also appreciable radiation exposure to individuals who fly frequently. One cross country flight results in an exposure of 2.5 mrem, so that airline personnel making 50 cross country round trips per year receive two and one half times as much extra radiation as would a maximally exposed resident near Yucca Mountain. The government makes no attempt to regulate public residence in areas of higher radiation background, or to limit radiation exposure associated with frequent flying. Thus it may be reasonable to allow a radiation exposure that is still less than that society and government accepts in other circumstances.

In conclusion, we suggest that an exposure limit of 100 mrem/yr may be of an acceptable magnitude, although a limit of 30 mrem/yr might be easier to justify on the basis of international practice and advice. We reject the EPA’s argument that a less stringent limit at longer times is consistent with intergenerational equity, and argue that the proper response to larger uncertainties in repository performance for longer times would be for more stringent rather than less stringent dose limits for longer times.

Can the Yucca Mountain Repository meet the EPA Standards?

The Department of Energy filed a license application to construct the Yucca Mountain repository in June, 2008, prior to the EPA’s release of its final standards. In preparation for the license application, the DOE has published a report¹⁴ detailing performance assessments for the proposed repository. These assessments indicate that individuals residing close to Yucca Mountain would receive a maximum of about 0.25 mrem/yr during the first 10,000 years, and a maximum of about 2 mrem/yr during the 10,000 to 1 million year period. The Nuclear Regulatory Commission will be examining the data, models, and assumptions used in these assessments in their consideration of whether to grant a construction license.

Footnotes

---

This contribution has not been peer refereed. It represents solely the view(s) of the author(s) and not necessarily the views of APS.