August 10, 1999

New Questions Plague Nuclear Waste Storage Plan
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    By JON CHRISTENSEN

    AMARGOSA VALLEY, Nev. -- For more than 20 years, scientists have been trying to figure out if Yucca Mountain, a barren desert ridge in southern Nevada, is a suitable burial ground for the nation's deadliest radioactive waste.

    After years of analysis, debate and political maneuvering, they now say the answer may lie inside tiny crystals glittering in finger-wide crevices and football-sized cavities that pockmark the walls of the mountain's dusty tunnels. It is here, if the Department of Energy gets its way, that canisters would be sealed forever.
    Though the site is in a desert, water flow is the crucial factor.

    Some scientists believe the crystals were formed by hot water welling up from under the mountain in the last half-million years. That would mean hot underground water has invaded the mountain and might again in the time when radioactive waste would still be extremely dangerous. The results would be catastrophic. Hot water would rapidly corrode the canisters and dissolve the water. Radioactive steam would vent from the mountain and contaminated water would spread underground.

    Other scientists believe the crystals were formed when the volcanic ash that makes up Yucca Mountain was laid down millions of years ago, and that the crystals continued to grow as rainwater carried minerals like calcium carbonate and opal through fractures in the rocks. In this view, hot water would be unlikely to invade the mountain again. Rainwater might still percolate through it, but the water could be shunted around the waste for as long as necessary.

    It is no coincidence that the first group, which says the calcite crystals prove that Yucca Mountain is a poor place to store atomic waste, works for the state of Nevada, which opposes the project. The scientists who say that the crystals pose no problem for a waste repository work for the Energy Department.

    Scientists have been searching for a place to bury the waste since 1954, when the Atomic Energy Act allowed commercial nuclear reactors to generate electricity and assigned responsibility for the spent nuclear fuel to the Federal Government. Over the years, as radioactive waste accumulated n holding tanks at nuclear power plants around the country, the search for a site became a political hot potato and a difficult scientific question.

    In 1982, the Nuclear Waste Policy Act required that two sites be selected, one in the East and one in the West. But five years later, Congress told the Energy Department to study only Yucca Mountain.

    From above, Yucca Mountain looks like a wave breaking over Amargosa Valley, about 100 miles northwest of Las Vegas, Nev. In cross section, the mountain looks like a slightly tilted layer cake, with some layers of compacted ash that are as soft as sandstone, and other layers of welded ash as hard as granite. The layers were formed by massive volcanic eruptions 12 million to 15 million years ago.

    About 4 to 10 inches of rain falls on Yucca Mountain each year, barely enough to support a thin cover of grass and the creosote bush, but it is the water that will make or break the proposed repository.

    Opponents of the Yucca Mountain waste site have seized on the crystals as evidence that could disqualify the site. A geologist from the University of Nevada at Las Vegas has been asked to determine the age of the crystals and to analyze microscopic bubbles of air and water that were trapped inside some of them. This should help to determine whether they formed in hot or cool water, that is, whether they are evidence of a relatively recent invasion of hot water.



    The New York Times
    But other questions about the mountain's suitability as a storage site for radioactive waste will not be as easy to answer; some may never be resolved, although advocates hope to obtain enough information to satisfy Federal regulators.

    In February, a scientific peer review panel convened by the Energy Department produced what it called a "highly critical" report on the department's own assessment of Yucca Mountain, especially its computer model of what would happen to the waste once it was stored. The review panel said the model had so many uncertainties -- like the corrosion rates of the waste containers, the area's vulnerability to earthquakes and how climate changes would affect rainfall -- that its reliability was limited.

    In fact, the review panel concluded, predicting how radioactive waste would behave once it is stored in the mountain "may be beyond the analytical capabilities of any scientific and engineering team."

    Still, advocates of using Yucca Mountain for the storage project are confident they can persuade the Energy Secretary, the President, Congress and the Nuclear Regulatory Commission to approve the site. Their optimism was bolstered last week by a draft environmental impact statement by the Energy Department that suggested disposal at Yucca Mountain would be safer, in the long run, than leaving waste at the 77 sites around the country where it is now stored.

    As a result, the Energy Department is moving ahead on repository designs to submit to the Energy Secretary in 2001 and licensing hearings before the Nuclear Regulatory Commission beginning in 2002. Construction of the repository would begin around 2005 and it would begin accepting waste in 2010. The cost is expected to be about $43 billion over the next century. It would be financed by a tax on nuclear power.

    The Federal Government has already spent $3 billion, making this desolate ridge one of the most intensely studied spots on Earth. "We think we can handle the uncertainty," said Dr. Michael D. Voegele, the senior engineer in charge of licensing and regulation for the project. "This is technically an awesome site. The picture fits together very well at Yucca Mountain."

    But in the last year major changes have been made in the proposed design of the repository. Just last year project scientists favored a so-called hot design in which waste canisters in closely spaced tunnels would heat the entire repository area above boiling temperature and drive water away from the waste for thousands of years.

    But when some scientists voiced uncertainty about what would happen to water that might collect above the repository, the design was scrapped in favor of tunnels spaced farther apart -- 81 meters rather than 20 meters -- so the boiling regions around each tunnel would not overlap and water could drain between them. The change also simplified the construction of computer models: Scientists can now model each tunnel independently.

    "Those design changes take a lot of the larger uncertainties off the table," said Dr. Chris Whipple, the chairman of the critical peer review panel.

    Water has always been the major uncertainty at Yucca Mountain. Different estimates on the amount of water that could seep through the mountain has led to calculations for radiation release "that vary by several orders of magnitude," a report released in June by the Nuclear Regulatory Commission shows.

    A five-mile tunnel drilled into Yucca Mountain to test its suitability was dry and dusty. But water is locked in tiny pores and is flowing through fractures in the rock. Scientists are conducting the first full-scale test of heated mock radioactive waste casks to see how the heat affects water in the rock. Hot water poured from a bore hole when scientists took samples in July.

    Scientists have been examining Yucca Mountain for two decades, but they continue to be surprised by the water. Originally, the volcanic ash where the waste would be buried, 800 feet below the surface and 1,000 feet above the water table, was thought to be so tightly compressed that water would not flow through.

    But as they dug into the mountain, scientists found that the compressed ash was riddled by 15 to 30 fractures per meter, fractures through which water could flow. They thought the water would move slowly through the fractures because there is so little rainfall in the desert. But last year scientists found Chlorine 36, a chemical isotope left by atmospheric atomic bomb testing in the 1950's, had trickled down fractures to the repository level. That meant rainwater had percolated halfway through the mountain in just 50 years.

    And at the nearby Nevada Test Site, scientists found that plutonium from underground bomb tests had hitched a ride on microscopic specks of clay suspended in ground water and had traveled 1.3 kilometers in 30 years, much faster than they had expected.

    All of these variables go into the model that predicts whether the repository can contain radioactive waste long enough so it does not pose a health risk for people when radioactive particles eventually do leak from corroded canisters into the groundwater. Project scientists predict that most of the 10,039 radioactive waste containers in Yucca Mountain would survive for about 10,000 years.

    The scientists assume that at least one canister would fail within 1,000 years because of manufacturing defects, and that all of the canisters would corrode after 10,000 years. During the first 10,000 years the most potent radioactive emitters, cesium and strontium, would have decayed. Plutonium, neptunium, iodine and technetium decay much more slowly and are not strong emitters. The major harm to humans would come from ingesting the particles.

    During the hundreds of thousands of years the radioactive waste inside Yucca Mountain would remain dangerous, scientists expect that climate changes would leave this desert somewhat more lush and green, with trees covering the now bare flanks of Yucca Mountain and lakes forming in the arid valleys below. Then, more water would move through the mountain, washing radioactive waste into the groundwater, thus diluting it.

    "In some sense it's science fiction to project out 300,000 years," said Abraham E. Van Luik, policy adviser for performance assessment. "It gets more and more difficult to defend your assumptions as you move into the future. But our modeling is over-conservative. Absolutely nobody is going to get hurt by this repository for hundreds of thousands of years."

    If there are farmers then in the Amargosa Valley, about 20 miles away, as there are now, they would be the first to drink contaminated water and use it on their crops. At 10,000 years, project scientists predict, people in the valley would be exposed to an additional 0.007 millirems of radioactivity a year, well below the 25 millirem maximum limit suggested by the Nuclear Regulatory Commission in proposed regulations for the repository. It would take 310,000 years to reach the 25 millirem dose, the scientists say, as more contaminated water leaked.

    The peak dose of 85 millirems a year would come in 620,000 years, the scientists predict. Most people are exposed to background radiation of about 300 millirems a year, half of that from natural sources like the sun, and the other half from sources like medical procedures and radon that collects in buildings.

    These predictions are not necessarily reassuring in Nevada. "Yucca Mountain does not provide geologic isolation," said Steven A. Frishman, a geologist and technical adviser to the Nevada Nuclear Waste Project Office. "Yucca Mountain is not capable of keeping it where you put it. It's not a question of will it be contained, but how fast will it leak out."

    If the Energy Department goes ahead and recommends Yucca Mountain in 2001 and the President approves, Gov. Kenny Guinn of Nevada has vowed to formally object. In that case, Congress could override the state with a majority vote in both the House and the Senate.

    Some scientists believe that even though Yucca Mountain has been debated for 20 years, the process is moving too fast for a decision that would have consequences for many millenniums.

    "We shouldn't be rushing the process," said Dr. Allison Macfarlane, a science fellow at Harvard University's Kennedy School of Government who is studying Yucca Mountain. "We should make sure we get it right. This is a really complex project, maybe more complex than the Manhattan Project. You're trying to predict geologic processes over geologic time lines. That's really difficult."

    The Energy Department concedes that the project may not be operating by 2010, as it now plans. "There is certainly science left to do and being done," said Dr. Ernest Moniz, the Under Secretary of Energy who oversees scientific research at Yucca Mountain.

    But he added: "One way or another we've got to advance toward geological disposal. We're pushing it hard. The science case is building up nicely. If we have to delay in the end we'll delay. But I see no reason not to push forward."

    Copyright 1999 The New York Times Company