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Contractors preparing the Davis-Besse nuclear reactor for a new lid have encountered a new problem, a tiny crack in the outer shell, that could keep the power plant idled longer than expected.

Plant owner FirstEnergy Corp. shut down the Oak Harbor plant near Toledo almost two weeks ago in order to install a new, upgraded reactor lid, equipped with components more resistant to the heat and stress cracking that have plagued Davis-Besse over the last 10 years.

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Replacing the lid should take two months and work remains on schedule.

This newly found crack that a spokesman called a “barely visible indication” of a crack, running 30 feet vertically in the reinforced concrete of the outer shell of the reactor’s containment building is causing some issues.

Schneider Bold

That huge structure, which the industry calls a “shield building,” is 2 1/2 feet thick, made of “nuclear grade” concrete and packed with reinforcing steel bars.

The building’s job is to protect the reactor from anything striking it from outside – anything from tornado debris to a terrorist in an aircraft. That’s why cracks in the concrete could be a problem.

The building surrounds a 1 1/2-inch-thick steel containment building, designed to contain any high-pressure radioactive emissions in the event of a nuclear accident and is the true “pressure barrier” by federal regulators and the industry.

To replace the reactor lid, the company hired expert contractors Bechtel and Sargent & Lundy to cut a 33-foot by 22-foot hole in the concrete shield building and the steel containment building inside of it.

After finishing the hole in the concrete building, engineers spotted the internal crack, visible on one edge of the new hole, FirstEnergy spokesman Todd Schneider said.

The company brought in additional consulting engineering experts in an effort to figure out the significance of the crack, whether the cutting created it or whether it was inside the concrete before the project began.

And the Nuclear Regulatory Commission (NRC) sent its own concrete expert to assist the NRC inspectors already at the plant.

The significance of the crack is not clear at this point, NRC spokeswoman Viktoria Mytling said.

“We will review what the company and its engineers find, and we are doing our own independent assessment,” she said. “We will have to resolve this issue before they re-start the reactor.”

The steel building remains intact, Schneider said. “Right now we are conducting an investigation of the [crack] issue with several experts from nationally known engineering firms,” he said. “We may not need to take any further action. Or we will develop a plan to address the issue.”

Schneider added so far the issue has not disrupted the work schedule for the lid replacement. Crews inside the containment vessel were continuing to off-load fuel from the reactor and preparing to remove the old lid, he said.

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