Letters

Yucca Mountain Nuclear Waste Containment Standard a Hot Topic

I find it amusing in a morbid sort of way that political posturing overrides the simple fact that nuclear waste isn't going to go away. Ten thousand years or a million makes no difference. The goals are to consolidate the material; make sound policies regarding security, safety, and health; and monitor the site for a very long time.

The tack that both proponents and opponents of a nuclear waste repository at Yucca Mountain have taken is disturbing in that the focus has now been shifted from the reality to the abstract (see Physics Today, September 2004, page 29). No location on this planet is perfect in every way to house this legacy. We need to get used to that and start making real plans to deal with that material in the best way we know how. Technology will change drastically before the waste reaches radioactive equilibrium. How we handle it today will be so obsolete in 100 years—never mind 10 000—that we will wonder how we got away with it. Let's get on the stick and get this project done.

Can the US successfully license a nuclear waste repository at Yucca Mountain—or anywhere else?

After the US Court of Appeals remanded the Environmental Protection Agency's (EPA's) 10 000−year radionuclide release standard on 9 July, the issue is joined. What is the appropriate length of time that a repository needs to perform? Furthermore, how can the government prove that it will perform as advertised?

The National Academy of Sciences recommended to the EPA that the period of repository performance extend to 100 millennia and more because, based on performance modeling, peak radionuclide dosage to the environment tends to occur then. There are two good reasons, however, that the 10 000−year Figure was maintained as the regulatory limit for waste isolation. First, the EPA has experience and legal precedence using a 10 000−year containment requirement. One example is the operating permit for the Waste Isolation Pilot Project in New Mexico, which calls for a 10 000−year containment period for nuclear and hazardous wastes. Other examples are deep−well injection permits that specify no migration of hazardous wastes over 10 000 years. Second, to make courtroom arguments about compliance beyond 10 000 years challenges credulity. Most regulators simply have a hard time placing confidence in mathematical models that claim to project the performance of natural systems beyond that threshold.

Irrespective of how long a repository is required to perform, the Department of Energy's ability to prove that it does perform is still the elephant in the room. The current standard of proof for repository licensing is like that used in a criminal trial: reasonable doubt. The Nuclear Regulatory Commission calls it "reasonable assurance," which they use for licensing nuclear reactors. Is reasonable assurance appropriate for what will be a heat−perturbed geologic system—that is, a system not designed to specification? The reasonable assurance standard can make geologic disposal fail whether a 10 000−year performance period is used or 10 to 20 times that.

Geology is a postdictive science; it explains what has already happened. When one attempts to use geology to project how a perturbed natural system will behave, uncertainties in data and interpretations multiply and assumptions necessarily are substituted. Mathematical models of future performance are only as good as those assumptions. In contrast to the hubris the US Congress codified by requiring reasonable assurance for geologic disposal, the standard of proof scientists use is preponderance of evidence. Applying reasonable assurance to geologic projections is a human contrivance that gives a false sense of certainty.

On 3 September, the Appeals Court refused to reconsider vacating the 10 000−year performance standard for Yucca Mountain, so it appears that the EPA must create a new one or Congress must weigh in on the subject. If the 10 000−year period is affirmed by legislation, geologic disposal can still fail if the licensing and legal system requires a certainty that geoscience cannot demonstrate.

Let us not jeopardize the societal benefit of geologic disposal by perpetuating the illusion that science can provide a greater level of safety to regulators than it is capable of proving. Geoscience is incapable of predicting with confidence the performance of a geologic repository system over 100 millennia or more. Furthermore, geoscientific predictions cannot be demonstrated in court with any standard other than preponderance of evidence. A repository system is supposed to compensate for uncertainty in data or performance models with an in−depth defense strategy that includes multiple barriers to limit the release of radioactivity into the environment over time. If the repository program goes to licensing, regulators will need to recalibrate their expectations about what geoscience can prove. Unfortunately, it is probably too late to lower expectations. Over the years, the program countenanced an overreach for certainty, and the result is a very precarious program.

Jim Dawson asserts that "none of the parties involved [in Yucca Mountain] is advocating a radiation standard based on containment for hundreds of thousands of years or more." As one of those parties, I can say that this statement is incorrect.

The groups involved specifically advocated for an Environmental Protection Agency (EPA) standard most protective of public health and safety—that is, one based on the National Academy of Sciences recommendation of a peak dose compliance period, which Figures from the Department of Energy (DOE) indicate is several hundred thousand years. The NAS study, issued in 1995, recommended "that compliance with the standard be measured at the time of peak risk, whenever it occurs."

According to DOE's projections, the peak risk to an individual from leaking radioactivity would occur about 300 000 years after closure of the dump. But recent research by the State of Nevada indicates that the metal storage containers can corrode and fail quickly in the Yucca Mountain environment. Without the estimated benefit of long−lived containers, the peak risk could occur in as little as 2000−3000 years.

EPA should revise its standard to encompass the time of peak dose. Limiting the compliance period to less than the time of peak risk threatens public health and safety for future generations. The Yucca Mountain project should not be continued if these standards cannot be met.

July is becoming a tough month for nuclear waste. In July 2003, US District Court Judge Lynn Winmill in Idaho ruled that all of the approximately 90 million gallons of tank wastes at the Savannah River Site in South Carolina and Hanford Nuclear Reservation in Washington State are high level and must be buried in repositories. In July 2004, the US Circuit Court of Appeals for the District of Columbia ruled that a 10 000−year radiation standard for Yucca Mountain is inadequate. Congress will no doubt have to intervene to short−circuit the latter decision, or repositories in the US will never open.

Any geologic burial site will be fractured before—and especially after—tunnel boring. The very best that can be done is to supplement the rock's containment ability with engineered barriers such as thick−wall steel casks and titanium drip shields.

The least the tank wastes weigh is 360 000 tons, or nearly five times the weight that's slated to go in Yucca Mountain. The Department of Energy is committed to removing tank wastes from Savannah River and Hanford. In 1984, the department had potential crystalline repositories in North Carolina, New Hampshire, Maine, and Wisconsin on its radar screen. Rocks in those states are granitic, which means each of the sites is already fractured and will be further fractured with drilling. Anyone wanting proof of that need only consult the Oskarshamn repository, a granite site about 150 miles south of Stockholm.

At some point, we're going to have to be practical. We've enjoyed nuclear energy, and we've enjoyed our status as the world's greatest nuclear power, but everything comes with a price. We now have 410 000 tons of spent−fuel rods and tank wastes spread all over the country, and all of us would breathe easier if they were out of sight, out of mind.

Despite the astronomically long half−lives of fission products that will be contained in waste scheduled to be stored at Yucca Mountain, the politicking and debate over whether 10,000 years is a sufficiently long safety standard is absurd. It is entirely reasonable to imagine that innovative ways of treating, more securely storing, or productively utilizing nuclear waste will be developed on much shorter time scales. America needs to address energy policy, and greater use of fission will have to be an important component of that policy over at least the short and medium terms. Our elected leaders could more productively spend their time and our money on developing sensible policies toward greater national energy independence.

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