Operators took the plant's Unit 1 reactor offline around 8:30 a.m. to replace one of the electrical coils connected to a control rod and test all the other control rods, said Kory Raftery, a spokesman for Calvert Cliffs. The move came after monitoring of the reactor picked up "electrical noise" in that control rod, a sign that part of the connection might have gone bad, he said.
"At no time did this event have any impact on public health or safety," he said.
Raftery couldn't say when the plant might turn the reactor back on. Calvert Cliff's other reactor is running at 100 percent capacity, he said.
Calvert Cliffs has "intensely" monitored its control rods since the summer, when it had a short in another electrical coil, he said. The plant, based in Lusby, is owned by Exelon Corp. and EDF.