The 873 MW Unit 1 at the Calvert Cliffs nuclear power plant in Maryland automatically shut down on May 1.
Plant operator Exelon said the shut down happened due to an RPS actuation during electrical breaker testing. A notice with the U.S. Nuclear Regulatory Commission (NRC) said there was no known steam generator tube leakage and the control rods fully inserted. There was no known cause of the malfunction.
Unit 2 remains at full power.
Calvert Cliffs is located in Lusby, Maryland, 40 miles from Annapolis. Unit 1, a pressurized water reactor, was first issued its operating license in 1974.
The nuclear power plant is owned and operated by CENG, a joint venture between Exelon and Ã‰lectricitÃ© de France.