FirstEnergy says an extreme winter storm caused the cracks discovered at the Davis-Besse Nuclear Power Plant last year.
In a report submitted to the Nuclear Regulatory Commission, the company says the absence of a weatherproof coating on the shielf building allowed moisture from the Blizzard of 1978 to penetrate the concrete. The moisture froze and expanded, creating subsurface cracks.
FirstEnergy insists the structural integrity of the shield building remains intact and is still able to perform its safety functions. The company says they plan to apply a weatherproof coating to protect the exterior walls and perform additional inspections.