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More deteriorating panels found at Pilgrim nuclear plant



By Christine Legere

A spent fuel pool at the San Onofre Nuclear Generating Station near San Clemente, Calif., is similar to the pool at Pilgrim Nuclear Power Station in Plymouth. Boraflex panels are attached to spent fuel racks holding bundles of radioactive fuel and prevent fission. A new examination has shown 885 of those panels at Pilgrim will be susceptible to deterioration by September 2017. AP file

PLYMOUTH - Nearly 900 neutron-absorbing panels used to prevent a nuclear reaction from occurring in Pilgrim Nuclear Power Station's spent fuel pool could be deteriorating by this time next year, increasing the chances of a fire and radioactive release.

A new evaluation of the Boraflex panels in Pilgrim's pool found that 885 will be susceptible to deterioration by September 2017.

Spent fuel pools at nuclear power plants store highly radioactive fuel assemblies removed from reactors when they are no longer usable. The assemblies are kept under at least 20 feet of water to prevent any radiation from leaking into the atmosphere.

Boraflex panels were installed in the 1980s when fuel pools at nuclear plants were accommodating more spent fuel than they were originally designed to hold.

The panels contain neutron-absorbing boron carbide and are attached to racks holding bundles of radioactive fuel. They 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 pool to boil and evaporate. If exposed, the rods could ignite and result in a radiation release.

Pilgrim, owned and operated by Entergy Corp., currently has over 2,800 spent fuel assemblies in a pool originally designed for 880. About 170 freshly used assemblies will be added to the pool this spring when the reactor is refueled.

Neil Sheehan, spokesman for the Nuclear Regulatory Commission, said degradation of the panels has been a known problem for decades and one experienced by a number of nuclear plants. Deterioration is caused by the combined effects of radiation from the spent fuel and long-term exposure to water.

"Our resident inspectors assigned to Pilgrim and our spent fuel storage experts are continuing to closely follow Entergy's actions to address the problem," wrote Sheehan in an email.

Sheehan pointed out a problem involving the spent fuel pool "would be slow to develop and would allow ample time for response actions."

Sheehan added that maintaining the neutron-absorbing material in spent fuel pools is important. All it takes is four fuel assemblies to start a nuclear chain reaction, he wrote.

Entergy spokesman Patrick O'Brien said Pilgrim is licensed by the NRC to have 3,859 assemblies in the spent fuel pool. Pilgrim currently has 2,822 assemblies in the pool, 1,000 below its licensed limit.

"Entergy is taking action to make changes to the configuration of the spent fuel assemblies within the spent fuel pool to maintain safety and keep the Boraflex panels within NRC requirements. This move will not affect the plant's ability to refuel in the spring of 2017," O'Brien said.

A single panel showing deterioration was found in Pilgrim's pool last spring. Further testing was done, along with modeling based on data from Pilgrim and Grand Gulf Nuclear Station, where pools are equipped with Boraflex panels manufactured and installed in 1986 by the same company. Based on the information, it was estimated that 500 panels might be experiencing deterioration.

Entergy hired an outside expert to test the panels. The expert used a small radioactive source to determine whether a panel was properly absorbing the neutrons.

That further study resulted in a conclusion that 885 panels will be susceptible to unacceptable levels of deterioration by next September. Pilgrim has 4,963 Boraflex panels in its spent fuel pool, which means nearly 18 percent are susceptible to deterioration.


David Lochbaum, director of the Nuclear Safety Program for the Union of Concerned Scientists, said post-9/11 regulation changes require checkerboard arrangements of the fuel assemblies in the pools. The hottest assemblies - those recently removed from the reactor - must be spread out.

"It may make it harder to keep the freshly used rods far enough apart," Lochbaum said. "It depends on the location of the 800 panels."

- Follow Christine Legere on Twitter: @ChrisLegereCCT.

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