Crews should soon pour concrete to patch an access portal cut into the outer shield building at Davis-Besse nuclear plant to replace the plant’s reactor head, a FirstEnergy spokesman said.
But the plant cannot resume operation until a probe of hairline cracks found in the shield building’s concrete after they cut that hole in October is complete, said a Nuclear Regulatory Commission (NRC) spokesman.
“Until we have confidence that the cracks in the Shield Building don’t have any safety implications, the plant won’t go back online,” said Viktoria Mytling, spokesman at the NRC’s regional office in Chicago.
She said a minor electrical fire that FirstEnergy Nuclear Operating Co. reported early Wednesday morning at the plant “is not a safety concern,” but the federal agency expects FirstEnergy to investigate why a valve leak blamed for the fire occurred and will review the utility’s findings.
NRC inspectors at the plant were “monitoring the situation as it happened,” the spokesman said.
An alert released at Davis-Besse at 2:22 a.m. because of the fire, which affected an electrical panel in the plant’s auxiliary building. The fire burned itself out within about 15 minutes, FirstEnergy spokesman Jennifer Young said. The alert ended at 4:43 a.m.
Water leaking from a valve on a pipe supplying water to offices in the building leaked onto the electrical panel, which supported a sump pump in the building, Young said. The water caused an electric arc that started the fire, she said.
The plant shut down Oct. 1 for the reactor head replacement and thus was not operating when the fire occurred.
The reactor remains contained and protected by separate 1 1/2-inch steel and 2-foot concrete structures through which they cut a large hole to provide external access for replacing the reactor head.
After they cut the concrete, workers discovered an “indication” of a 30-foot hairline crack, and subsequent tests revealed similar “indications” throughout the structure. FirstEnergy later said most such cracks were in decorative “architectural” concrete attached to the building’s exterior to give it texture, but also disclosed it was investigating several “indications” of cracks of a different nature in the concrete.
The reactor head replacement wrapped up and they welded the steel removed to create the access hole back into place and pressure tested, Young said. The shield building hole should be ready to go by the end of this week, she said.
Mytling said such patching would not affect the NRC investigation, and no timetable is in place for restarting the plant.