Operators shut down unit 2 at the Calvert Cliffs nuclear plant Thursday after a control rod dropped into the core during a test and could not be retrieved.
The test took place at about 1:15 p.m. The control element assembly could not be realigned within two hours, according to an event report filed with the Nuclear Regulatory Commission, and the plant's technical specifications required that the unit power down. The plant was completely offline as of Friday, according to the NRC.
A Constellation Energy Nuclear Group spokesman told the Baltimore Sun the assembly was in need of "electrical maintenance," and unit 2 will be restarted once it is repaired. Unit 1 shut down twice last year after similar malfunctions in the equipment that grips the control rods.
Both units near Annapolis, Md., are Combustion Engineering pressurized water reactors first licensed in the mid-1970s.