- The Energy Department has discovered levels of fluoride
in water and rock at the proposed Yucca Mountain repository that could
cause early corrosion of containers and titanium shields designed to
protect
buried nuclear waste.
-
- DOE scientists said they need to find the source of the
fluoride, because corrosion in pits and nicks on the metal surfaces could
cause the burial containers to fail in much less time than the 10,000-year
life of the repository.
-
- Nevada officials, who oppose burying nuclear waste at
Yucca Mountain, and regulators are keeping a close watch on the DOE's
progress, because the fluoride is an issue that could delay a license
to allow repository construction. A repository would open by 2010 at the
earliest.
-
- State officials argue that the mountain cannot keep
radiation
from escaping into the environment. If containers or drip shields fail,
dangerous radioactivity will pollute the water and possibly the air, they
argue.
-
- The DOE has argued that the mountain combined with
containers
and shields will contain any radiation for the required 10,000
years.
-
- In four water samples collected from Yucca Mountain after
April 2001, fluoride content ranged from 5 parts per million to 66 parts
per million. In earlier samples, the level was 1 part per million
consistently.
-
- When fluoride is heated to temperatures as low as 280
degrees Fahrenheit and dissolved in water, it becomes corrosive, the
scientists
say. One repository design is expected to allow the repository to heat
to temperatures above boiling, or 212 degrees Fahrenheit.
-
- "This could have the potential to enhance corrosion
on the drip shields and waste packages," according to a DOE technical
paper written in November.
-
- The DOE reported two possible sources for the fluoride.
They believe the fluoride leached either from Viton, a material used to
pack boreholes in the mountain, or from Teflon-lined tubes that collect
samples of air and water in the boreholes.
-
- Another possible source "that cannot be ruled
out,"
is fluoride occurring in the mountain's rocks, the DOE report said.
-
- Nevada researchers worry that, whether it's brought
in or naturally occurring, the fluoride can concentrate in the nooks and
crannies on the surfaces of waste packages and cause early erosion, Susan
Lynch, a state scientist, said.
-
- The state has conducted one study at Catholic
University
in which a strip of titanium sitting in water from Yucca Mountain at
213 degrees Fahrenheit cracked in less than five months, Lynch said. The
water had fluoride in it.
-
- "Fluoride is definitely a problem," Lynch said.
The heat from buried wastes can intensify fluoride's reaction to the metal
drip shields or the containers, she said.
-
- The U.S. Geological Survey is trying to date the fluoride
in an effort to determine whether it is natural or from materials
introduced
during 20 years of experiments, project manager Zel Peterman said.
-
- The Nuclear Regulatory Commission, which would license
the construction and operation of a repository at Yucca Mountain, is
watching
the issue closely, Brett Leslie of the NRC said.
-
- If the DOE introduced fluoride into the rock during its
experiments, it is a major technical issue to solve before the NRC could
license a repository, Leslie said. The DOE has to account for how chemicals
placed in Yucca's rock and water would affect buried wastes, he
said.
-
- "It is not a significant threat according to them
(DOE scientists)," said William Reamer, NRC's deputy director of the
Division of Waste Management, "but we haven't reviewed it
yet."
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