SEABROOK — A reactor at the Seabrook Station nuclear power plant was shut down Friday night after a computer problem caused a valve to unexpectedly close, a spokesman for the Nuclear Regulatory Commission said Tuesday.

The reactor tripped around 9:25 p.m. when the valve used to regulate the flow of water into one of the plant’s steam generators closed due to a faulty computer card, said Neil Sheehan, a public affairs officer for the NRC.

Nuclear power plants are equipped with computerized systems designed to detect any anomalies involving safety systems and components, Sheehan said. If it detects any problems, Sheehan said it can automatically shut down, or trip, the reactor by inserting all of the control rods into the reactor in rapid fashion.

Sheehan said a resident inspector from the NRC assigned to Seabrook traveled to the plant Friday night to independently verify the shutdown was being safely and effectively carried out and did not identify any concerns.

Sheehan said the plant’s safety systems automatically detected the problem and shut down the reactor in response.

“The problem did not pose any safety risk to workers or the public. Plant safety systems responded as designed and the reactor was safely shut down,” he said.

The reactor remains offline.

Sheehan said the plant was preparing to enter a refueling and maintenance outage at the time of the trip Friday night, so it decided to enter that outage earlier than planned.

“These outages take place once every 18 months to two years at nuclear power plants and involve replacing a third of the fuel in the reactor and various maintenance projects. The plant will be down for a period of time while this work is taking place,” Sheehan said.

jschreiber@newstote.com