Entergy has notified the Nuclear Regulatory Commission that 885 spent fuel panels at the Pilgrim Nuclear Power Plant in Massachusetts are susceptible to degradation that could challenge their effectiveness by September 2017.
The panels act as neutron absorbers. A decline in their effective use increases the possibility of fissioning reactions in spent fuel pools, which can lead to water boiling, fuel assembly exposure outside the water, and potential fires. NRC spokesman Neil Sheehan noted Tuesday that such an event would be slow to develop, however, and Entergy would be warned through water-level alarms, enabling it to address the issue long before a criticality event.
Entergy detailed the situation in a license event report supplement on Nov. 18, which was made public Tuesday. The company had originally estimated that 534 Boreflex panels were threatened, but increased the number to 885 in the latest supplement. Pilgrim contains some 3,000 spent fuel assemblies in its spent fuel pool.
The supplement describes evaluations Entergy has completed to “conservatively” identify spent fuel configurations within spent fuel storage racks equipped with Boraflex panels to ensure subcriticality conditions are maintained in the pools, according to Sheehan. Plant operators hire third-party vendors to test Boraflex degradation.
The 44-year-old facility, which is scheduled to close in 2019 for economic reasons, has experienced a long list of operational issues, including various unplanned shutdowns, dating to 2013. The plant was downgraded in 2015 to Column 4 of the NRC’s Action Matrix, the lowest safety rating a plant can have while remaining in operation, following a series of unplanned shutdowns and issues with safety relief valves. The NRC is conducting the third and final increased oversight inspection tied to the downgrade, in which the agency will decide what corrective actions are needed in order for the plant to transition back to a normal level of oversight.
