Both Calvert Cliffs nuclear units in Maryland tripped offline on April 7, according to a report that operator Exelon filed with the Nuclear Regulatory Commission (NRC).
Both units were still listed at zero generation early April 8, according to NRC data. In a news release, Exelon confirmed that the shutdown was the result of “localized grid disturbance that caused power outages in the Washington, D.C./Maryland area.”
The resulting power interruption temporarily spooked the Washington, D.C., area, causing a brief blackout at several federal buildings. Even the White House had to briefly shift to backup power.
"A loss of Main Generator Load which caused a Reactor Trip on Unit's 1 & 2. A switchyard voltage transient from a highline occurred which caused an undervoltage condition on both units' safety related 4KV buses,” according to the NRC report.
Calvert Cliffs is designed to shut down automatically during significant electrical disturbances. The plant shut down safely and without incident. Both reactors will remain in “hot shut-down,” which means the reactor remains ready to resume power production, until the offsite grid disturbance can be addressed, Exelon said.
Calvert Cliffs is located on the western shore of the Chesapeake Bay in Calvert County and is Maryland’s only nuclear energy facility. The station is home to two pressurized water reactors (PWRs) capable of generating 1,768 MW combined. Units 1 and 2 began commercial operation in 1975 and 1977, respectively.
In the fall of 2014, NRC a 40-year license renewal for both units.
This past spring the NRC operating license for Calvert Cliffs and several other Northeast nuclear units were transferred from Constellation Energy Nuclear Group (CENG) to Exelon.
Exelon and Électricité de France (EDF) said in a joint announcement in the summer of 2013 that they had agreed for the Constellation Energy Nuclear Group (CENG) nuclear units, located in Maryland and New York, to be blended into the Exelon Nuclear fleet.
Exelon currently owns 50.01 percent of CENG, which is jointly owned with a U.S. affiliate of the French EDF Group.