The historic winter storm that buried the Eastern U.S. in snow over the weekend shut the lights off for more than a million customers from Arkansas to Massachusetts as it downed power lines and hampered operations at some power plants.

According to the Department of Energy’s Office of Electricity Delivery and Energy Reliability, at one point or another over the course of the storm, power was knocked out to 1,030,618 customers. Duke Energy was the hardest-hit utility with 484,000 customers losing power. The utility reportedly has had 7,000 personnel in the field since Friday working to restore outages.

The Nuclear Regulatory Commission (NRC) reported two nuclear plant incidents in the wake of the storm. Power output at Calvert Cliffs Unit 1, in southern Maryland, was reduced to just under 15% on Saturday evening after an electrical cable associated with a main transformer was found to be disconnected. It was not immediately clear if the storm was responsible for the cable coming loose, the agency said.

Meanwhile, although the storm wasn’t as intense in upstate New York, Entergy’s James A. FitzPatrick nuclear power plant was shut down by its operators at about 10:40 p.m. on Saturday after icing impacted the facility’s flow of cooling water drawn from Lake Ontario.

“Plant personnel have checklists of specific tasks to be performed when a significant storm—no matter whether a blizzard or a hurricane—is approaching,” said NRC spokesperson Neil Sheehan on January 22. “For instance, there will be ‘walkdowns,’ or surveys, of plant grounds to ensure there are no objects or debris that could get whipped into the air by strong winds and cause damage to any structures, power lines or the switchyard.”

Another activity is to check that tanks that supply fuel to emergency diesel generators are filled. “If the flow of power from the grid to the plant is disrupted for any reason, these generators will activate and provide power to key safety systems until the normal electricity alignment can be restored,” he said. “There needs to be sufficient fuel on hand in case the generators are needed for any extended period of time.”

Additionally, plant operators must prepare for the possibility of flooding. One way to do this is to follow each site’s procedures, which can involve checking that flood-protection doors are properly secured, putting sandbags in place, stationing portable pumps, or other actions, Sheenan added.

Sonal Patel, associate editor (@POWERmagazine, @sonalcpatel)