The Calvert Cliffs nuclear power plant was shut down unexpectedly today after its emergency electrical generators were declared inoperable.
Baltimore Gas and Electric Co. declared an "unusual event," the least serious of four nuclear-plant emergency categories, at about 5:25 a.m.
The utility began shutting down the twin-reactor plant on Chesapeake Bay in Lusby. The shutdown was to be completed by 1:15 p.m.
The utility said in a statement released about noon that it declared all three of the plant's emergency diesel generators inoperable because of a possibility that "in certain, very unlikely accident conditions," Calvert Cliffs' safety systems would not get enough electricity.
The potential exists that the plant's diesel-powered generators may not be able to supply enough electricity to run emergency pumps and other safety systems if the plant loses outside power and there is a small leakage of cooling water from either of the two reactors, said Peter Wilson, the Nuclear Regulatory Commission's senior inspector at Calvert Cliffs.
The problem was identified during a routine NRC inspection of the plant, which is continuing.
Mr. Wilson said that utility officials "just don't know whether the plant would or would not respond in an accident. That's why they're shutting down."
BG&E said there is about a 1-in-10 million chance of an accident happening that might compromise the emergency electrical supply system.
Mr. Wilson said he did not know how unlikely the system's failure might be, and he did not know when the plant might be able to restart.
BG&E said Unit One was scheduled to go off line tomorrow night anyway for refueling. That outage is expected to last until June.
Unit Two will remain shut down until the utility has resolved concerns about the backup power generators. The utility said it is already conducting engineering evaluations.
Calvert Cliffs, with two 825-megawatt units, provides about 40 percent of the electricity to the utility's Central Maryland customers.
From March 1989 until last May, one or both reactors at the Calvert Cliffs plant were out of service because of various mechanical and safety problems. Unit 2, idled for refueling and equipment repairs in March 1989, began producing power again last May. Unit 1, shut down for inspection after cracks were found in Unit 2 in 1989, was returned to service in October 1990.
A 1988 NRC report concluded that BG&E placed power production over safety in its operation of Calvert Cliffs, and the utility was fined more than $650,000. Last month, the NRC removed the Calvert Cliffs nuclear power plant from its "watch list" of plants requiring extra regulatory oversight.