- More than half of the nation's nuclear power plants have
been told to correct a design flaw that federal researchers believe increases
the risk of an accident.
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- The concern is that water bursting under extremely high
pressure from a ruptured pipe inside the building that houses the reactor
could churn up enough debris to clog sump pumps designed to return the
water to the reactor's cooling system.
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- If that happened, the risk that control room operators
would not be able to keep the reactor cool increases by a factor of 10,
according to a study conducted at the Los Alamos National Laboratory. Nuclear
reactors, like car engines, can be severely damaged if allowed to overheat.
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- Researchers are concerned that the design flaw could
lead to accidents like the one that destroyed the Unit 2 reactor at Three
Mile Island in 1979.
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- According to the Union of Concerned Scientists, a watchdog
group, the Los Alamos study reports that debris blockage would raise the
probability of an accident at TMI from one in 67,000 years to one in 432
to 536 years.
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- During the 1979 accident at the Londonderry Twp. plant,
operators failed to realize that a release valve jammed open, allowing
water and steam to leak out of the cooling system. The error resulted in
a partial meltdown of the reactor fuel and the release of radiation into
the air.
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- In a bulletin issued in June to the owners of 69 of the
nation's 104 nuclear plants, including TMI and Beaver Valley in Shippingport,
Beaver County, the U.S. Nuclear Regulatory Commission called on plant owners
to assess their plants' vulnerability and take corrective measures.
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- The changes could range from installing larger filtering
screens around the pumps to training operators how to manipulate water
flows to dislodge clogs, said Scott Burnell, a spokesman for the agency.
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- Officials at Exelon Nuclear, part owner of TMI, said
they have determined that the plant is not at high risk.
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- The problem affects the largest class of nuclear reactors
in use in the country -- pressurized water reactors, or PWRs. The other
class, boiling water reactors, identified and fixed the problem in the
1990s. The NRC only recently concluded that PWRs were also vulnerable to
the problem.
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- But fixing the PWRs will not be as easy because their
designs are more varied, said John Butler, senior project manager of risk
regulations for The Nuclear Energy Institute, an industry group.
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- "You can't easily identify a single solution that
will fix it for everyone," Butler said. "It's not even easy to
identify whether or not it's a problem for an individual plant."
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- The cost of the upgrading the plants could run from several
hundred thousand dollars into the millions, Butler said.
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- Plant operators must shut down their plants to make the
changes. Commercial nuclear plants shut down for maintenance and refueling
every two years. Some may not be able to complete the work during one outage.
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- TMI is scheduled to shut down for refueling in October.
At that time, workers will inspect the building for dirt, dust and small
debris, said Ralph DeSantis, a spokesman for the energy company.
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- TMI is not a high-risk plant because its piping, valves
and other hardware are separated from the sump pumps by a concrete wall
3 to 4 feet thick.
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- Water reaches the sump pump through a series of drains,
DeSantis said. "We do inspections after outages to make sure there
is no foreign material where it shouldn't be," he said.
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- The Union of Concerned Scientists has been prodding the
NRC to move faster to correct the design flaws. UCS director David Lochbaum
was critical of the agency's decision to give plant operators until 2007
to make changes.
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- In a recent statement, he accused the agency of "virtually
ignoring" the issue and choosing instead to focus its attention on
the financial performance of the nuclear industry.
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- "According to the NRC's data, there's about a 34
percent chance that one of the ... [reactors] will experience core damage
between now and the time that the agency intends to fix the containment
sump issue," he wrote.
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- Lochbaum also took issue with an NRC recommendation that
plants shut down backup pump systems that would delay the start of the
main sump system.
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- "Many of the proposed interim measures can actually
increase risk quite substantially," Lochbaum wrote in a letter to
NRC Chairman Nils J. Diaz.
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- The Nuclear Energy Institute shared Lochbaum's concerns.
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- Butler said the group warned its members to take a broad
view of the situation to ensure that the change "would not have a
detrimental effect on other events."
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- The NRC's Burnell said the agency never advocated taking
actions that would adversely affect the safety of the plants.
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- "We fully expect the licensees will do detailed
analysis of what actions they expect to take [and] that in doing one thing
they don't make another thing worse," he said.
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- GARRY LENTON: 255-8264 or glenton@patriot-news.com
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