FirstEnergy Nuclear Operating Company (FENOC) confirmed that it has completed its Root Cause Analysis Report regarding the cause of the tight cracks identified in portions of the Davis-Besse Nuclear Power Station Shield Building during its fall 2011 reactor head replacement outage. The report has been submitted to the Nuclear Regulatory Commission (NRC).
FirstEnergy says the weatherproof coating could have had an impact on the concrete Shield Building, especially in controlling moisture dating back to a blizzard in January 1978 that eventually caused cracking because of freeze and thaw cycles. The root cause report concludes that the cracking occurred following the blizzard’s combination of extreme weather conditions, which included three days of driving rain preceding a drastic temperature drop to around 0-degrees Fahrenheit and intense winds throughout the storm.
At no time in the ensuing 34 years has water penetrated so deeply into the concrete, nor have seasonal temperature extremes caused any further damage, according to the report. FirstEnergy Nuclear Operating Company (FENOC), the company that operates the nuclear power operations for the utility, says it will take steps to analyze and monitor for cracks while applying a weatherproof sealant.
“With an effective exterior-protective sealant, the shield-building concrete laminar cracking will not repeat under the required combinations of extreme environmental conditions such as the shield building experienced during the severe blizzard of 1978,” the report states. “The other nuclear safety-related structures on site have a protective sealant as a barrier against moisture migration into the concrete.”
The cracking was not found for more than 33 years, Ms. Young said, because it was internal to the concrete and thus not subject to visual detection. When an opening was cut into the structure 10 years ago to replace a reactor head damaged by boric acid, she said, that hole did not touch any part of the building where cracking occurred.
The utility reporting the finding in a “root cause” report delivered to the Nuclear Regulatory Commission released today.