One of two reactors at the Calvert Cliffs nuclear power plant in southern Maryland was shut down again Tuesday, the second unplanned outage in the past two weeks.
Plant operators powered down Unit 2 manually around 5:30 a.m. after a pump that feeds water to a steam generator shut down because of high vibrations, according to Neil Sheehan, spokesman for the Nuclear Regulatory Commission. The cause of the pump's vibrations appears to be a failed mechanical coupling between the pump's motor and the pump, he said.
Sheehan and Kory Raftery, spokesman for Constellation Energy Nuclear Group, said the manual shutdown went smoothly and posed no safety risks for plant workers or the public. Raftery said the reactor was in "stable condition."
Both spokesmen said Tuesday's shutdown appears unrelated to the unplanned "scram" of the same reactor on May 8. In the earlier case, according to accounts from Constellation and the NRC, an electrical malfunction caused some valves to close that feed steam to the turbine. The turbine then shut down, prompting the reactor itself to shut down automatically to prevent the buildup of steam pressure in the cooling system.
The reactor was out of service for five days, according to Raftery, while the valves were being worked on and tested. Plant personnel also installed electrical monitors to check for further problems, he said.
Unit 2 will remain shut down until an investigation of the latest malfunction is completed, repairs are made and the system is fully tested, the Constellation spokesman said. Unit 1, the other reactor at the plant in Lusby, is operating at 100 percent power.