Unit 2 of the Calvert Cliffs nuclear plant in Maryland experienced an unscheduled outage Sept. 5, the Nuclear Regulatory Commission (NRC) reported Sept. 6.
The dual-unit Calvert Cliffs is a pressurized water reactor (PWR) facility with each unit having roughly a 900-MW capacity. The plant is currently part of the Constellation Energy Nuclear Group (CENG).
“The Calvert Cliffs Unit 2 nuclear power plant was shut down by operators last night after a single control rod dropped into the reactor core during testing,” an NRC spokesperson said Sept. 6. “The plant’s technical specifications required the shutdown if the control rod could not be realigned (successfully withdrawn) within 6 hours,” the spokesperson said.
A Calvert Cliffs plant spokesperson added that an electrical problem was discovered with the control rod upon withdrawal. It was necessary to idle the nuclear unit so maintenance people could investigate and fix the problem. Crews will be work on the situation this weekend, said the plant spokesperson, who declined to predict how long the unit might be out of service.
NRC Resident Inspectors assigned to the plant on a full-time basis were immediately notified of the condition and the eventual plans to shut down the unit. The controlled shutdown occurred without any complications and there were no impacts on the public or plant staff, according to NRC. “Plant personnel will now have to troubleshoot what caused the problem. Our inspectors will continue to follow those troubleshooting and repair activities,” said the NRC representative.
The plant is equipped with 77 control rods. They are made of materials that absorb neutrons and therefore can be used to control or halt (depending on the depth to which they’re inserted) the “fissioning” of atoms in the reactor, said the NRC representative.
Calvert Cliffs Unit 1 had experienced a single control rod drop in August 2012. Subsequent investigation determined that the drop was caused by a failure of the portion of the gripping system used to hold the rod out of the core. Nuclear power plants have specific procedures on what to do if a control rod drop occurs.
Exelon to run operations at Calvert Cliffs.
Calvert Cliffs is part of the (CENG), which is a joint venture between an affiliate of Électricité de France (EDF) and Constellation Energy, which is now part of Exelon (NYSE:EXC).
Exelon and EDF announced July 30 that they have agreed to integrate the CENG plants, located in Maryland and New York, into the Exelon nuclear fleet over a nine-month period. As part of the arrangement, Exelon received an option to purchase the plants between 2016 and 2022.
Constellation as a whole was merged into Exelon in 2012, although the former Constellation nuclear plants, including R.E. Ginna and Nine Mile Point, had remained as part of CENG.
The companies involved in the change have started filing paperwork with NRC to transfer operational control to Exelon, said the NRC spokesperson.