In spite of the discovery of small cracks in the shield building at the Davis-Besse Nuclear Power Station, FirstEnergy expects to have the plant return to service around the end of November.
Ronald Seeholzer, Vice President Investor Relations, says in a letter to investors dated Oct. 31 that a team of structural concrete experts and Davis-Besse engineers have determined the cracking doesn’t affect the facility’s structural integrity or safety.
The plant was shut down Oct. 1 as scheduled to install a new reactor vessel head and maintenance and the new reactor head was successfully transported to the containment vessel late last month, according to the letter.
What is described as a “sub-surface hairline crack” was found in the shield building when workers were cutting into the side of the building to remove the old reactor head.
The shield building is made of 2 ½-foot-thick reinforced concrete and is designed to protect the steel containment vessel from external hazards. There is a space of about 4 ½ feet between the shield building and the containment vessel.
While investigators were examining the crack, other cracks were found through concrete sampling and electronic testing in other parts of the building called architectural elements, which the company says “do not have structural significance.” The elements protrude up to 18 inches from the main portion of the building.
Other hairline cracks in other areas of the building, while similar to those found in the elements, are being investigated as a separate issue.
“Our overall investigation and analysis continues,” the Seeholzer letter says.
Viktoria Mitlyng, a spokesperson for region 3 of the Nuclear Regulatory Commission, said the commission sent a concrete material expert to the plant and two resident inspectors and specialists from the region 3 office were already on site monitoring the reactor head replacement.
“They are now also conducting an independent assessment of this new issue and are reviewing the utility’s effort to understand the issue and any potential safety significance,” she says in an NRC blog. “If there are any challenges identified with the design function of the shield building the NRC will expect the utility to resolve them before restarting.”