Entergy (NYSE: ETR)'s Pilgrim nuclear power plant in Massachusetts lost power during the record-setting snowstorm Nemo that blanketed the northeast U.S. in inches of snow over the weekend, then lost power again days later.

The 685 MW boiling water reactor plant went into automatic shutdown at about 9:17 p.m. Friday evening after off-site power flickered then went out, leading U.S. Nuclear Regulatory Commission (NRC) spokesperson Neil Sheehan to declare an “unusual event” at the plant, the lowest, and not uncommon, safety classification.

According to the NRC, the startup transformer was declared inoperable, and diesel generators kicked on to provide backup power to the plant, allowing vital cooling systems to go into effect until offsite power returned via one of three offsite power connections at 10:55 a.m. The offsite power connection was maintained for several hours before the plant lost power again Sunday afternoon. At the time, the plant was in cold shutdown with 0 percent core thermal power.

Plant workers, according to the NRC, suspect that Sunday’s power outage was caused by falling ice striking the startup transformer. Generators resumed operation and officials have said there are no health hazards to workers or the public.

The storm knocked out power for 300,000 Massachusetts residents, and 650,000 residents across the New England region.

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