Potential problems connected to the radioactive spent fuel pool at the Pilgrim Nuclear Power Station in Plymouth, MA, are once again the focus of federal regulators, who are questioning how the condition of two of the panels, installed to prevent nuclear fission from occurring, can end up accurately tracked.

Panels containing neutron-absorbing boron carbide are attached to the pool racks holding the radioactive assemblies to prevent fission in reactor pools.

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The panels used at Pilgrim are a mix of three different trade names: About two-thirds are Boraflex, which has a known problem with degradation, and one-third are a mix of Boral and Metamic.

The Nuclear Regulatory Commission’s (NRC) latest concern is with the tracking of two Boral panels installed on racks in Pilgrim’s spent fuel pool in 1995. Separate sheets of Boral, referred to as coupons, are supposed to be placed in the pool at the same time as the installation, and they are used to gauge the condition of the Boral panels on the racks.

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Federal regulators question the accuracy of the information the coupons will provide.

“Please describe how the boral coupons are representative of the in-service material given the nearly five-year difference in time the material has been exposed to spent fuel pool conditions,” read the NRC letter to Entergy Corp., Pilgrim’s owner and operator.

A large portion of the five years in question predate Entergy’s ownership of Pilgrim. The company purchased the plant from Boston Edison in November 1998 and the license transfer wasn’t approved by the NRC until May 3, 1999. Based on the NRC’s current information, the test coupon for the Boral panels was installed six months after Entergy took over.

David Lochbaum, director of the Nuclear Safety Project for the Union of Concerned Scientists, said the time gap between the installation and the insertion of the test panel would be more problematic if workers at Pilgrim were doing full-core offloads during refueling, which was a practice some plants were using.

The full-core offloads, which would entail removal of 580 spent fuel assemblies at Pilgrim, transferred a high amount of heat and radiation into the spent fuel pool. Partial offloads transferred less.

Because Pilgrim only did partial offloads, “the data collection since 1999 will more easily be used” to account for the nearly five-year difference, Lochbaum said.

A spokesman for Entergy said the company is reviewing the request from the NRC.

“We are actively working to answer the questions and provide information to the NRC in the 90-day response period,” said Entergy spokesman Patrick O’Brien.

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