A watchdog group has faulted the handling of a "near miss" incident at Calvert Cliffs nuclear power plant last year, in which wind-driven snow triggered a series of malfunctions that shut both reactors down. It was the second weather-related outage in four years at the facility in Lusby.
The Union of Concerned Scientists, in its annual review of nuclear plant safety nationwide, criticized both Exelon Corp.'s management of Calvert Cliffs and the Nuclear Regulatory Commission's response to the incident.
"Twice within the past five years, precipitation leaked into the Calvert Cliffs nuclear plant and shorted out electrical power supplies," the report says, "causing one reactor to automatically shut down and components to malfunction that should have protected the second reactor from automatically shutting down."
The report added that "other plant owners have successfully prevented even one intrusion event while Calvert Cliffs has been unable to prevent repeated events."
The Calvert Cliffs shutdown was one of nine incidents at nuclear plants nationwide last year that prompted the NRC to dispatch a special inspection team in response. The union says it considers those "near misses" because the problems at each facility increased by 10-fold the risk of seriously damaging radioactive reactor cores, the group said.
The report acknowledges that the number of "near misses" has declined since 2011, as has their relative seriousness. But even so, said David Lochbaum, the report's author, "it would be a mistake for the NRC to declare victory and stop playing close attention."
The NRC sent a special inspection team to Calvert Cliffs last year after a Jan. 21 shutdown attributed to moisture causing a loss of power to one unit and then other malfunctions that shut down the other reactor. Melting snow leaking through the roof in 2010 also triggered an unplanned shutdown. Yet NRC inspectors found no violations last year.
NRC spokesman Neil Sheehan said the causes of the two shutdowns actually were substantially different, even though both were weather-related. Federal inspectors determined that fixes made after the 2010 incident could not have prevented last year's problem, Sheehan said, "so a performance deficiency was not identified."
Exelon spokeswoman Lacey Dean said that since last year's shutdown, plant operators have taken steps to redesign the electrical switches to keep out snow and stepped up inspections during the winter.