July 30--PLYMOUTH -- Nearly 600 panels used to prevent a nuclear reaction from occurring in the Pilgrim Nuclear Power Station's spent fuel pool might be susceptible to the same kind of deterioration found recently in one panel during routine testing.
The Boraflex panels at issue, which contain neutron-absorbing boron carbide, are attached to the racks holding bundles of radioactive spent fuel.
The panels were installed in the 1980s when fuel pools at nuclear plants were accommodating more spent fuel than they were originally designed to hold.
Pilgrim has about 3,300 spent fuel assemblies in a pool initially designed for 880.
The Boraflex panels prevent fission, which would cause the spent rods to heat up the same way they do in a nuclear reactor. The heat would cause the water in the fuel pool to boil and evaporate. If exposed, the rods could start a fire and release radiation.
Entergy's recent analysis of the Boraflex panels was done following a discovery of a degraded panel in Pilgrim's pool in May.
Based on that discovery, Entergy was required to file a report with federal regulators, explaining the cause of the problem and plans for fixing it. Company experts created a model using data collected over 28 years from Pilgrim and Grand Gulf Nuclear Station, which both had Boraflex panels designed, manufactured and installed around 1986 by the same company.
"Based on the model, about 589 panels at Pilgrim are susceptible to degradation levels greater than those allowed," said Nuclear Regulatory Commission spokesman Neil Sheehan. "There are 4,963 Boraflex panels in the Pilgrim spent fuel pool. Roughly 10 percent of the pool's Boraflex panels are considered potentially susceptible to degradation."
In its report, Entergy attributed the cause of the degradation of the panel to damage done by gamma radiation and "long term exposure to the fuel pool environment."
David Lochbaum, director of the Nuclear Safety Project for the Union of Concerned Scientists, explained that a panel's location in the spent fuel pool is a factor in its susceptibility to degradation. Panels positioned where the newer and hotter spent fuel is located are most at risk. That is also where there is a heavier water flow, which can cause a washout of the Boraflex.
The NRC has required a "checkerboard" arrangement of spent fuel, with hot fuel surrounded by older and colder fuel, to address terrorist threats as part of its 9/11 upgrades, Lochbaum said.
"It was done for terrorist reasons, but it provides additional margin for criticality," he said.
Entergy has relied on a rolling testing schedule of the Boraflex panels along with a computer model that predicts degradation rates. The company will use its new analysis for determining locations of possible panel degradation and devising "acceptable fuel storage configurations" as corrective actions, according to its report.
"The top priority is the company's submission of its criticality analysis," Sheehan wrote. That analysis is still being completed by Entergy.
Patrick O'Brien, spokesman for Entergy Corp., provided a statement from the company: "The Boraflex panel degradation is a known issue in the industry, which is why we conduct regular testing and have adopted measures such as fuel reconfiguration to ensure the safety of plant equipment, employees and the public."
The statement went on to say the measures in place "ensure safety is maintained and the spent fuel remains sub-critical."
Mary Lampert, director of the Pilgrim Watch citizens group, said the solution to the problem is clear: "Pilgrim's spent fuel pool is too densely packed, risking criticality," Lampert wrote in an email. "If criticality in the pool did occur, goodbye New England. The real solution is needed and obvious -- NRC require Entergy to thin the pool."
Sheehan, however, recently said an incident in the fuel pool is different from an incident in the nuclear reactor. "It could takes days for radioactivity to escape," he said. "You would be able to replace the water (in the fuel pool). Post 9/11, we have portable pumps."
-- Follow Christine Legere on Twitter: @ChrisLegereCCT.
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