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OAK HARBOR, Ohio — FirstEnergy Corp. and Nuclear Regulatory Commission engineers Thursday were studying a hairline crack in the concrete shield building outside the reactor containment structure at the Davis-Besse nuclear plant to determine if it constitutes a major problem for the plant.
The crack, about 30 feet long, was revealed when a FirstEnergy contractor cut a large hole in the shield building to create an entry point for installing a new reactor head as part of a scheduled maintenance shutdown that began Oct. 1.
Jennifer Young, a FirstEnergy spokesman, said late yesterday that engineers had yet to determine if the "barely visible" crack was caused by the hole-cutting operation or if it is evidence of a broader problem with the shield building's 2?½-foot, steel-reinforced concrete.
Consequently, its effect on completion of the reactor-lid installation and future plant operations is unknown, she said.
"The experts are still doing their review," she said. "We don't have an expert opinion on that yet."
The shield building surrounds the reactor containment structure, made of 1?½-inch thick steel. It is intended to protect the containment structure from external damaging forces. It was built in the early 1970s.
The crack parallels a reinforcing steel (rebar) rod in the concrete and runs along a plane parallel to the shield building's surface, so if it existed before the hole was cut, it would not have been visible, Ms. Young said.
She said she did not know whether the crack was big enough to have been detected by ultrasonic means during plant inspections.
Viktoria Mytling, an NRC spokesman, said her agency already had inspectors at the power plant to oversee the reactor-head installation when the cracked concrete was discovered.
Because it did not involve the containment structure itself, the crack "is not a reportable event," Ms. Mytling said, but once FirstEnergy has completed its assessment of the problem, the NRC will independently review that finding.
"We don't have an immediate safety concern because the plant is shut down," she said, adding that the crack "doesn't look, at this point, really deep or bad" and may simply be a product of the hydro-blasting technique used to create the access hole for the new reactor head.
Citing "competitive reasons," FirstEnergy declined, before the planned shutdown began, to say how long the plant would be out of service for the reactor-head replacement and other maintenance.
Ms. Mytling said the crack "may not have any impact" on when power generation resumes at Davis-Besse, but the NRC will not take such scheduling into consideration as it assesses the matter.
"We are there to be sure that whatever they [FirstEnergy] do is done safely," she said.