A site in southern Nevada under consideration as a permanent geologic repository for high-level radioactive waste may be more unstable than previously thought, according to the findings of a team of geologists and geophysicists who studied the area for seven years.
Earth's crust around the site near Yucca Mountain about 100 miles northwest of Las Vegas is "stretching" at least 10 times faster now than in the past, according to the report, which was published in the March 27 issue of Science magazine.
If so, this stretching could result in earthquakes that could expose buried radioactive waste to the environment, according to the article, "Anomalous Strain Accumulation in the Yucca Mountain Area."
The study was led by Brian Wernicke of the California Institute of Technology and James Davis of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. The study, conducted from 1991 to 1997, was funded by the Nuclear Regulatory Commission and the National Science Foundation.
The Department of Energy has since 1987 been studying the suitability of the site as a permanent repository for storage of both government and commercial waste. An important condition in the determination of its suitability is whether volcanic events might release radioactive material into the environment over the lifetime of the repository, which is being planned to last from 10,000 to 100,000 years.
"Our study showed that over the past seven years Yucca Mountain has been pulling apart at the rate of one or two millimeters per year," Wernicke told BNA. "This is 10 to 100 times higher than the geologic average rate."
Period of Strain
This faster rate appears to indicate that Yucca Mountain is in a period of accelerated strain, which could result in more volcanic activity, he said. "I was very surprised by the results of the study," Wernicke said. The monitoring at Yucca Mountain was part of a survey covering a much larger area, he said.
"Something strange is going on here," Wernicke said. "Our study is in some sense preliminary. But it shows that Nevada, DOE, and NRC should support a redoubled need for geodatic monitoring in the area. There's a clear need to fully characterize the geologic data in a lot more detail."
Wernicke said monitoring needed to be more widespread than the five sites looked at by the study. With more study, scientists would have a much better understanding of the site in a few years, he said.
Eric Olds, a spokesman for DOE at Yucca Mountain, told BNA the department plans to meet with the U.S. Geological Survey to review the results of the study with information DOE has been collecting since 1987. USGS has indicated the review will take about six weeks, Olds said.
DOE, USGS to Review
DOE's volcanic hazard assessment, released in 1996, showed the probability of a volcanic occurrence at Yucca Mountain was about 1 in 70 million per year over the next 10,000 years.
Depending on the outcome of the review with USGS, the findings of the new study could be reflected in DOE's "viability assessment" due in September, Olds said. "Or, if necessary, we'll plan additional studies," he said.
Construction has yet to begin on the Yucca Mountain repository, and DOE has said the earliest it could open is 2010.
In recent months, Congress has been debating whether to build an interim storage facility at the Nevada Test site, which is near Yucca Mountain, while site characterization activities continue for the permanent repository.
The House and Senate passed bills in 1997 that would establish such an interim facility (211 DEN A-7, 10/31/97; 27 DEN A-8, 4/16/97) A conference to resolve differences in the bills could take place within weeks, according to congressional aides.
Sen. Richard Bryan (D-Nev), a long-time opponent of building a repository at Yucca Mountain, said in a statement the study could be "the straw that breaks the nuclear camel's back."
'Nuclear Camel's Back.'
According to Bryan, the ability of scientists to adequately predict future geological events at Yucca Mountain and their consequences is a major factor in determining its suitability to store nuclear waste. "The suggestion that scientists likely will not be able to provide adequate predictions is of grave concern to me," he said.
"The biggest question for me is whether the Department of Energy will pay attention to this latest report or sweep it under the run along with the rest of the scientific reports and analyses which could lead to the conclusion that Yucca Mountain doesn't fit the bill," Bryan said.
Other "red flags" have been the discovery of fault lines at Yucca Mountain and studies showing problems with ground water flow, according to a spokeswoman for Bryan.
Nevada's other senator also welcomed the results of the study.
"These findings will help bury the notion that Yucca Mountain is the right place to bury nuclear waste," Sen. Harry Reid (D-Nev), long an opponent of a repository at Yucca Mountain, said in a statement. "We've been saying for years that science would demonstrate that Yucca Mountain is not suitable as a permanent repository."
Reid called on DOE to "move beyond doing what they know how to do and do what needs to be done -- use the best science and the best scientists to study Yucca Mountain's suitability."
By Patricia Ware
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