The Nuclear Regulatory Commission announced Monday that it is conducting a special inspection at the Calvert Cliffs nuclear power plant in Southern Maryland after an electrical malfunction caused the two reactors there to shut down.
The plant, which restarted both reactors over the weekend, suffered the shutdown after snow and ice during a storm Jan. 21 apparently affected a ventilation louver filter and caused a short circuit. After the electrical supply system shut down, so did several plant systems and components that rely on electricity, the nuclear regulatory agency said Monday.
Those components included motors for moving control rods and water circulating pumps for the Unit 2 reactor, the agency said. The main turbine control circuit for the Unit 1 reactor also malfunctioned after the electricity loss.
Both units shut down as a result, with "no impacts on public health and safety," the agency said.
The three-person inspection team began working at the plant Monday, the commission said.
"We want to gain a better understanding of the chain of events that caused both of the reactors to simultaneously shut down and equipment anomalies subsequent to the plant trips," said Bill Dean, the commission's administrator for the region that includes Maryland, in a statement. "This inspection is designed to shed additional light on not only why the outages happened but how the plant operators handled them."
A Constellation Energy Nuclear Group spokesman said in an email that federal reviews after shutdowns are common, adding that the company welcomed the inspection at its plant.
"Operators followed their training and performed well during the shutdowns," said Kory Raftery, the spokesman. "The site's multiple safety systems responded as designed."
But Neil Sheehan, a Nuclear Regulatory Commission spokesman, said such inspections are not common.
"In this case, the complications involving the Calvert Cliffs Unit 2 shutdown was a deciding factor in the decision to launch one at the site," he said by email.
The plant's last special inspection happened four years ago. That too was in response to both reactors shutting down after an electrical supply system was knocked out of service, Sheehan said.
Tim Judson, acting executive director at the Nuclear Information and Resource Service, a watchdog group in Takoma Park, said special inspection teams are only sent in "when something really of concern has happened."
Judson said it suggests that the agency was not happy about what it turned up in its initial assessment last week. He noted that the shutdown came at a bad time, taking out reactors capable of powering more than 1 million homes just as a sharp cold snap created intense demand for electricity.
"We'll be eager to find out exactly what happened and what the nature of NRC's response is going to be," he said.
Calvert Cliffs has had several other unplanned outages in the past year and a half, most of them involving problems with control rods. The plant's reactors first came online in 1975 and 1977.
David Lochbaum, director of the Union of Concerned Scientists' Nuclear Safety Project, said the biggest known issue in last week's shutdown is that Unit 2's water pumps — which send cooling water through the condenser to deal with heat — stopped running. A backup system kicked in.
"Any time a plant has a problem where their normal way of getting rid of heat goes away, that's almost guaranteed to invite NRC inspectors to your door to find out why that happened," he said.
It generally takes two to three months for a special inspection team to issue a report on its findings, Lochbaum said. Sometimes teams determine there were safety violations, and sometimes they don't, he said.
"You don't want to fall into the safety net too often," he added.