- Traces of plutonium from a test blast
in the Nevada desert migrated nearly a mile through groundwater, according
to a study that prompted the government to recalculate slightly the risks
that would be posed by an underground nuclear waste storage site.
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- Scientists said the amount of radioactivity
that can move this way is too small to endanger the public, and the U.S.
Energy Department, in reassessing the risks of the government's proposed
waste site beneath Nevada's Yucca Mountain, agreed.
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- Until recently, it was commonly believed
that significant amounts of plutonium would not move through groundwater
because the element dissolves at a very low rate and attaches strongly
to any rocks it touches.
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- But in a study published Wednesday in
the journal Nature, researchers confirmed suspicions that plutonium can
hitch a ride on colloids, or particles of debris suspended in water.
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- Scientists from Lawrence Livermore National
Laboratory in California and Los Alamos National Laboratory in New Mexico
looked at a 30-year-old nuclear blast that reached below the water table
on the Nevada Test Site, where the United States has conducted 828 underground
nuclear tests between 1956 and 1992. The site is 70 miles northwest of
Las Vegas.
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- The scientists found minute amounts of
plutonium measurable only by the most sensitive equipment in test wells
nearly a mile away from the blast, and concluded that the plutonium had
flowed downstream on colloids.
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- ``We have shown there is a new potential
pathway that has been suggested before, but never definitely shown. The
question is what the maximum amount is that you could move. We don't know
that,'' said Annie Kersting, a Lawrence Livermore scientist.
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- The Energy Department wants to build
a nuclear waste repository at Yucca Mountain, about 90 miles northeast
of Las Vegas. The government has already spent $2.2 billion in 15 years
of research in hopes of entombing 80,000 tons of used reactor fuel that
will remain deadly 300,000 years.
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- The department took the latest findings
into account and concluded that the seepage wouldn't happen for 10,000
to 100,000 years, and even then, the escaped radiation would be less than
the background amount.
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- ``They are not rates that would bust
any kind of standards. We see no impact,'' said Abe Van Luik, senior technical
advisor for performance assessment for the Energy Department.
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- Bruce Honeyman, a professor at the Colorado
School of Mines, said the very nature of colloids their extremely small
size and low concentrations assure that they would never move large amounts
of radiation.
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- ``The radioactivity is so low that it
probably is not of significance for adverse human health effects,'' he
said. ``Conceptually, you can think of colloids being like a conveyor belt.
The belt is really not turning very quickly.''
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- The Energy Department's conclusions did
not satisfy Bob Loux, executive director of the Nevada Agency for Nuclear
Projects in the Nevada governor's office. He said he believes containers
holding the waste will fail much more quickly than the government estimates
and allow unknown quantities of contaminants to escape within 500 years.
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