The Nuclear Regulatory Commission has begun a special inspection at the Calvert Cliffs nuclear power plant to review issues during the unplanned shutdown of both reactors on April 7. The plant, which is operated by Exelon, is located in Lusby, Md.
Calvert Cliffs, like all nuclear power plants, transmits power to the grid but also receives power back for operational purposes. A grid disturbance due the failure of a transmission line in Southern Maryland on April 7th caused both Calvert Cliffs reactors to automatically shut down as designed.
Following the grid disturbance, one of Unit 2’s emergency diesel generators (which provide power to safety systems when off-site power is lost) started, but tripped after 11 seconds. This same diesel generator failed to start in 2010 after a loss of off-site power. In addition, one of three saltwater pumps on Unit 2 failed to automatically restart when power switched to the emergency diesel generators. Per procedure, operators manually started the pump, which provides cooling water to certain plant equipment.
“While there was no impact on public health and safety, the issues with the emergency diesel generator and the saltwater pump warrant a closer look,” said Dan Dorman, NRC Region I Administrator.
The three-member team that arrived on-site today is tasked with developing a sequence of events; reviewing and assessing equipment response to the event; reviewing operator performance; and assessing the effectiveness of Exelon’s response to this event.
An inspection report documenting the team’s findings will be issued within 45 days of the end of the inspection.