The Nuclear Regulatory Commission (NRC) on June 21 said it has completed its review of FirstEnergy Nuclear Operating Co.’s (FENOC) causal analysis of, and proposed corrective actions for, cracks in the shield building at the 908 MW Davis-Besse Nuclear Power Station in Oak Harbor, Ohio.
FENOC concluded that cracks in the shield building were caused by environmental factors that resulted from a 1978 blizzard; the lack of moisture protective coating; and certain aspects of the shield building’s design. The company submitted the root cause analysis of shield building cracks, which includes the company’s proposed corrective actions and long-term monitoring program of the shield building, on Feb. 28 in compliance with commitments the company made to the NRC.
The NRC also conducted an analysis of the company’s corrective actions to ensure shield building safety going forward, which included additional tests and laboratory analysis of the shield building; applying a protective moisture coating on the building; and plans to restore the plant’s design and licensing basis.
The NRC began looking at the issue on Oct. 10, 2011, when the NRC was informed by FENOC that its workers identified cracks in the shield building while the plant was shut down to replace the reactor vessel head. The shield building is a 2.5-foot thick reinforced concrete building that surrounds a 1.5-inch thick steel containment vessel that encloses the reactor. The two buildings are separated by a 4.5-foot space. The NRC reviewed the cracks after they were discovered and determined that they did not pose an imminent safety issue.
The NRC’s license renewal experts are evaluating the implications of this issue in the context of Davis-Besse’s request to extend its operating license.
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