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Triggered by tripped electrical breaker

By AMANDA SCOTT

Staff writer

Both units at Calvert Cliffs Nuclear Power Plant were automatically shut down Tuesday night due to electrical problems.

About 9:25 p.m. Tuesday, units 1 and 2 were shut down due to an electrical malfunction on the non-nuclear side of the plant, according to a Constellation Energy Nuclear Group press release. All safety systems responded as designed and the plant went offline as expected, the release said.

On Wednesday, CCNPP spokesman Kory Raftery said an electrical bus that is connected to components on both units was tripped, or went offline, resulting in the automatic shutdown. Raftery said the issue is similar to a breaker in a home getting tripped and the electricity in that room not working.

In an email Wednesday morning, U.S. Nuclear Regulatory Commission spokesman Neil Sheehan said the shutdowns were triggered by a breaker for a 4-kilovolt electrical supply tripping, or going offline.

“The preliminary cause of the loss of the electrical supply is snow and ice impacting a ventilation louver filter on the building housing the supply,” Sheehan wrote, “resulting in it coming into contact with the supply and thereby tripping the breaker.”

When the electrical supply went offline, it de-energized multiple components, including circulating-water pumps and feedwater pumps, Sheehan said in the email.

In his email, Sheehan said the 4-kilovolt line is one of several lines providing off-site power to the plant.

“The station’s multiple and redundant backup power systems are designed to ensure safe shutdown of the plant during electrical disturbances and those systems responded as designed,” the CENG release states.

Sheehan said in the email that the NRC’s senior resident inspector assigned to Calvert Cliffs responded to the plant Tuesday night and independently verified that both reactors had been safely shut down and that operator responses to the event were appropriate.

“No immediate safety concerns were identified,” Sheehan said in the email. “Our two Resident Inspectors for the plant will continue to monitor the company’s efforts to troubleshoot exactly what occurred, whether any repairs are needed and plans to restart the units.”

Raftery said teams currently are investigating the causes of what happened and will be making necessary repairs and testing the systems before the units are brought online.

ascott@somdnews.com