Man against a Mountain

(Scientific American, March 2003)

Rodney C. Ewing: Saying No to Yucca

·      A multidepartmental professor at the University of Michigan at Ann Arbor, spanning nuclear engineering, geology and materials science.

·      With geologist Allison Macfarlane of the Massachusetts Institute of Technology, Ewing is finishing a book, due out early next year, on Yucca Mountain's unresolved technical issues.

·      "The game is not rigged like a crooked card game, but the lack of choice at every step drives us inexorably to Yucca Mountain."

Some 75.000 feet of core samples and 18,000 geologic and water specimens have been retrieved from a desolate ridge in the Nevada Desert called Yucca Mountain. Products of a 20-year investigation by the Department of Energy, the recovered materials and their subsequent analyses have made the volcanic protrusion among the most studied features on earth. And such statistics make DOE officials confident that Yucca Mountain would be a suitable disposal site for the nation's highlevel nuclear waste, able to hold 70,000 metric tons of radioactive poison safely for 10,000 years.

 Rodney C. Ewing begs to differ. Citing the amount of research is "not the way you measure good science, any more than you judge the merits of a book by the number of words," says the 56-year-old geologist, who holds an interdisciplinary professorship at the University of Michigan at Ann Arbor. Ewing sits on the National Academy of Sciences (NAS) Board on Radioactive Waste Management and has served on the Yucca Mountain peer-review panel. One of Yucca's most knowledgeable critics, he believes that the mass of information collected, which can be measured in tons, masks even greater unknowns.

 In 1987 Congress named Yucca Mountain as the preferred site in amendments to the Nuclear Waste Policy Act of 1982, cutting off consideration of alternative sites in Texas and Washington State. Opponents of the legislation have sometimes called it the "screw Nevada" bill. The law enabled the DOE to spend $7 billion laying the foundation for a repository and building some nine kilometers of tunnels through the mountain to facilitate studies and to provide access for waste disposal.

The DOE's risk evaluation hinges on an elaborate computer calculation that tries to predict the fate of wastes buried for millennia. This "probabilistic performance assessment" has revealed no deal breakers, prompting the agency to press for continued development. The Bush administration and Congress endorsed the site in 2002. After the DOE files for a construction permit, which is not expected before December 2004, the Nuclear Regulatory Commission (NRC) will have four years to rule on the repository's future. With the NRC's sanction, the DOE can begin construction.

Ewing thinks the process has outpaced the science: "We've learned a lot about this mountain, but when you look at the substance of it, our knowledge is actually quite thin." According to Ewing, a host of problems stem from the exclusive investment in Yucca since 1987. His chief complaint is that the rules of the game have changed to fit the site. The linchpin of geologic disposal has traditionally been "defense in depth"-that is, the reliance on favorable geology plus engineered barriers, such as multilayered glass and metal packaging, to isolate wastes. At Yucca, this philosophy was quietly abandoned; site-specific standards replaced general ones, Ewing insists. "Instead of devising a regulation and finding a site that meets it," he says, "we picked a site and made a regulation for it."

years. Satisfying this standard rests on a probabilistic assessment that incorporates thousands of assumptions-an approach never before applied to such a complex system. Some parameters (such as the density of water) are well known; others (such as the likelihood of volcanic activity) vary by a factor of 100,000. No one has figured out how to combine all these uncertainties, Ewing notes.

The mathematical approach, in his opinion, keeps us from seeing how the individual components are working. For example, much stock is being placed in Alloy 22, a relatively untested metal that is supposed to confine wastes over the long haul. The corrosion rate for the alloy depends on geochemical conditions-such as the pH and carbon dioxide content of the groundwater-that are inherently difficult to predict. "We're betting on a new material about which we know little, while making optimistic assumptions about its behavior under conditions we can only guess at," Ewing states. "Uncertainties throughout the model are rolled together, which makes it hard to tell whether any of the barriers are effective." He adds that there's been no attempt to test this model on a real geological system. Further complicating the model are still unresolved concerns about the site's geology, including seismic activity and volcanism.

Ewing finds the EPA guidelines deficient as well. The designated limit of 10,000 years is too short, he says; exposures are likely to peak millennia later. That is because some of the longlived radionuclides to be buried there have half-lives of at least 24,000 years, and the geologic and engineered barriers will inevitably weaken over time. "We should do the analysis first to find out when the peak dose occurs, rather than setting the time limit in advance." He also considers the 18-kilometer distance at which the radiation is measured to be too far from the source.

When pressed, Ewing can't find much good to say about the endeavor except that some capable scientists and engineers have been employed. "But because of the way the program is designed, the work is so fragmented that people can't put it all together," he says.

 Unlike most Yucca Mountain foes, Ewing has faith in geologic waste disposal and nuclear power. For example, he approves of New Mexico's underground Waste Isolation Pilot Plant. At WIPP, burial of plutonium-contaminated debris from nuclear weapons work started in 1999, after more than 20 years of scientific and political wrangling (Ewing also served on WIPP's review panel). Compared with those for Yucca Mountain, the wastes at WIPP are not as "hot": a much smaller amount of radioactivity will ultimately be stored there, greatly reducing the possibility of thermal problems. And the geology at WIPP is much simpler, according to Ewing, raising fewer concerns about water, earthquakes and volcanic activity.

 Ewing's 12-year stint on the WIPP panel was his first prolonged involvement in the radioactive waste business. It all began as a "hobby," an offshoot of his main research on the effects of radiation on materials. While at the University of New Mexico in the 1970s (he taught there until his 1997 move to Ann Arbor), he found that none of the guest speakers from the nearby national labs could answer his questions on how radiation would damage a waste repository. The only way to find out, he concluded, was to do the experiments himself. Before he knew it, he had become an expert in the field.

 Given the advanced stage of the project, Ewing sees little opportunity for scientific input at Yucca Mountain. As a result, he is taking a broader look at the environmental impacts of the nuclear fuel cycle. But he hasn't fired his last shot at Yucca: he expects to have a book out on the subject next year.

 Ewing may induce heartburn among advocates of the Nevada facility, but he nonetheless has the respect of most of his colleagues. "He's a good scientist, someone who digs very deeply," says John F. Ahearne, chair of the NAS radioactive waste board. Although Ahearne calls him a "thoughtful critic and not at all intransigent," Ewing can be a formidable adversary because he follows a problem to the end, regardless of disciplinary boundaries. Before he's done, Yucca enthusiasts may wish he'd taken up a more traditional hobby, like stamp collecting.

Earlier Article: Scientists Voice Concerns about Yucca Mountain Repository