Cracks found in the containment building wall of the 913 MWe Davis-Besse nuclear power plant in Ohio was caused by lack of an exterior weatherproof coating on the shield building, according to a report from plant owner FirstEnergy Nuclear Operating Co. (FENOC).
FENOC said in its Root Cause Analysis Report that moisture associated with the blizzard of January 1978 migrated into the concrete, froze and expanded, causing the tight, subsurface cracks in the containment building. The cracks were found during a reactor head replacement outage in the fall of 2011.
The report said the cracking occurred following the blizzard’s combination of extreme weather conditions, which included three days of driving rain before a drastic temperature drop and intense winds.
The report also concluded that the structural integrity of the shield building remains intact, and the building is able to perform itssafety function. FENOC will apply a weatherproof coating to protect the exterior walls, perform additional inspections to verify the cracks have not spread and develop a long-term building monitoring plan.
In the course of the root cause investigation, an exhaustive list of potential cracking causes was examined, including possible design, construction, environmental and operational issues.
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