Federal inspectors are at Calvert Cliffs nuclear power plant this week to investigate an unexpected shutdown of both reactors last week, which a plant spokesman said apparently was triggered by melting snow leaking through the plant's roof.
The Nuclear Regulatory Commission sent a five-member "special inspection team" Monday to the 1,750-megawatt plant near Lusby in Calvert County, which is owned by Constellation Energy. It's expected to remain there all week, NRC spokeswoman Diane Screnci said.
"There was never any danger," the NRC spokeswoman said, "but we want a better understanding of why it happened and what steps they're taking to prevent a recurrence."
Both of the plant's nuclear reactors shut down automatically Thursday morning as a result of electrical malfunctions, evidently triggered by "a small roof leak" of melting snow, according to David Fitz, spokesman for Constellation Energy Nuclear Group, a subsidiary of the Baltimore-based power company.
Snow melt "trickled down onto an electrical breaker," Fitz said, which caused an "electrical fault" and loss of power to one reactor. The electrical problem on one reactor caused the other to shut down.
Their reactor coolant pumps were activated, but there was a loss of power to safety systems, according to an NRC news release. Diesel generators kept at the ready to provide backup power did start up, but one generator supplying power to Unit 2 shut down. Workers were able to tie in another power source and return power to the unit and its safety equipment, the NRC said.
Both reactors remain shut down this week, though the plant spokesman said Unit 1 was scheduled to be taken off line for refueling about now anyway. Workers are fixing the roof leak and repairing the damaged breaker relay, he said, but will also use the down time to perform other maintenance on Unit 2 before it is restarted. He declined to predict when either reactor would begin generating power again.
"We will make sure everything is electrically right before we bring everything back up," he said.