True to forecasts, New England states bore the brunt of the winter storm dubbed Nemo. With respect to nuclear power plants in the region, only one – Pilgrim, in Massachusetts – had its operations interrupted by the powerful Nor’easter.
At 9:17 p.m. Friday, three off-site power lines that provide electricity for plant safety systems were knocked out of service. In response, the reactor, as designed, automatically shut down and the facility’s emergency diesel generators activated to provide that power.
One of the criteria for a plant to declare an “Unusual Event” – the lowest of four levels of emergency classification – is the loss of off-site power for more than 15 minutes. As such, Pilgrim made that declaration at 10 p.m. Friday. The NRC issued a press release early Saturday morning.
After one of the lines was restored, the plant was able to terminate the Unusual Event as of 10:55 a.m. Sunday. But there was a setback later in the day when the 345-kilovolt line experienced new problems. Once again, the emergency diesel generators started and will supply the power needed for safety systems until the lines are fully restored.
Since the reactor was already in “cold” shutdown condition, Pilgrim did not need to again declare an Unusual Event.
NRC inspectors, and for a good part of the weekend the NRC Region I Incident Response Center, closely monitored the storm recovery efforts at Pilgrim. That will continue as repair work is carried out and plans for placing the unit back in service are developed.