Yucca Mountain Reprieve

The Nuclear Waste Repository Is Unlikely to Explode, Berkeley Team Concludes

by Robert Sanders

Plans to build a federal repository for nuclear waste in Nevada's Yucca Mountain were dealt a serious blow last year when two scientists warned that surplus, weapons-grade plutonium stored there could conceivably explode like a nuclear bomb.

Though many dismissed the suggestion as improbable, a nine-member team of Berkeley engineers and scientists launched a systematic and more quantitative analysis.

The eight-month, $125,000 project--the first and only independent analysis of the scenario first proposed by two scientists at Los Alamos National Laboratory--indicates that while weapons-grade plutonium or highly enriched uranium could theoretically go supercritical, these scenarios are highly unlikely given the hydrology, geology and geochemistry of the Yucca Mountain site.

Furthermore, the team said, the repository and stored waste could be engineered to reduce the likelihood to virtually nil.

The group reported their findings at a symposium March 13 as part of the annual Industrial Liaison Program Conference hosted by the colleges of engineering and chemistry. They plan to submit a report to Los Alamos, which funded the study, and have submitted findings for publication in the journal Nuclear Technology.

The New York Times first publicized the warning by Los Alamos scientists Charles Bowman and Francesco Venneri on March 5 last year, stimulating doomsday headlines around the nation.

The two researchers suggested that over the lifespan of the repository groundwater would corrode steel containers and glass encasing the waste, carrying plutonium and uranium into surrounding rock. Should a critical mass accumulate, they argued, it would trigger an uncontrolled chain reaction leading to a nuclear explosion.

"The crux of the matter is, by the time you accumulate the necessary plutonium for an explosion--about 250 kilograms--most of it has decayed," said William Kastenberg, project organizer and professor and chair of nuclear engineering. "And uranium will be flushed out of the system into the groundwater without accumulating a critical mass."

"Our conclusion was that at the Yucca Mountain site there don't appear to be any geochemical or geophysical mechanisms for these supercritical scenarios to happen."

Yucca Mountain was chosen in 1987 by the Department of Energy as the sole national repository for spent nuclear fuel from commercial power plants. Opposition arose from Nevada residents, environmentalists and anti-nuclear groups.

Two years ago the government proposed also to stash excess weapons-grade plutonium at the site, plus highly enriched uranium derived from spent fuel of naval and research reactors. The opposition grew.

After Bowman and Venneri issued their warning in a Los Alamos paper, their lab colleagues conducted an internal review of the proposed scenario, which scientists at Lawrence Livermore National Laboratory also reviewed. The consensus: The scenario had serious flaws, though Los Alamos scientists could not entirely rule out an explosion.

Kastenberg proposed an independent analysis of the scenario by Berkeley faculty and was given the go-ahead by Los Alamos director Siegfried Hecker.


Copyright 1996, The Regents of the University of California.
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