The federal Nuclear Regulatory Commission is conducting a special inspection at Diablo Canyon nuclear power plant to determine how two safety switches were misaligned, potentially impairing response in the event of a severe reactor accident.
The inspection started Monday and is expected to take several days to complete. It will be conducted by Diablo Canyon’s senior NRC resident inspector, two reactor specialists and an emergency preparedness inspector from the agency’s regional office in Arlington, Texas.
The misaligned switches were discovered Oct. 23 during a refueling shutdown. The misalignment would have prevented two cooling water valves from being opened remotely from the reactor’s control room, forcing operators to be dispatched to manually open the valves.
The valves are part of a safety system that collects water from the floor of the containment building for recirculation to cool the reactor in the event of a severe loss-of-coolant accident.
NRC and Pacific Gas and Electric officials say the misaligned valves did not endanger public safety because operators would have opened the valves manually or used another system to provide cooling water. However, manually opening the valves could have delayed response time and exposed operators to radiation.
“But we want a better understanding of why this occurred and the potential impact of this problem,” said Elmo Collins, NRC regional administrator.
The inspectors will examine the circumstances related to the problem, PG&E’s evaluation of the root cause of the problem and the effect the problem had on the availability and reliability of the plant safety systems.
The valves were evidently misaligned when the reactor underwent its previous refueling outage 18 months before.
Jane Swanson, spokeswoman for the San Luis Obispo Mothers for Peace, said she hopes the investigation will determine how the problem could have gone undetected for so long.
The inspection comes on the heels of an announcement by PG&E last week that the utility has applied to the NRC to renew the plant’s operating licenses for 20 more years.
The inspectors will report the findings of their investigation some 45 days after the inspection is complete. The report will be posted on the agency’s Web site.
Reach David Sneed at 781-7930.