“These new cracks were so microscopic, they could not been seen before with our old equipment,” FirstEnergy spokeswoman Jennifer Young said.
An improved highdefinition camera at the end of a flexible tube allowed workers to find seven previously unseen cracks, according to the Nuclear Regulatory Commission.
The shield building’s concrete walls are 2.5-feet thick, and they’re reinforced with steel rebar. The building contains a 1.5-inch-thick carbon steel vessel, which contains the reactor. The shield building is designed to protect the reactor in the event of tornados, storms or other disasters. In effect, it is a last line of defense to protect the public from a catastrophe.
The problems with cracks in the shield building were first discovered in October 2011, when FirstEnergy workers cut into the building’s walls to replace a reactor head. That work was being done because workers had previously found cracks near the old nuclear reactor head, which forced the company to move up a planned replacement by three years.
Initially, the company found a single crack running alongside a piece of steel rebar in the shield building’s walls. Upon further inspection, they found a series of hairline cracks. FirstEnergy determined the cracks were caused by weather conditions from the Blizzard of 1978 — blowing wind drove moisture into the concrete, which froze in rapidly falling temperatures.
The Nuclear Regulatory Commission eventually green-lighted the plant to reopen, as long as Davis-Besse agreed to weatherproof the building. The facility restarted operations in December 2011.
Three of the seven cracks workers recently found in the shield building’s walls may have existed in 2011, but workers didn’t find them at the time because their equipment wasn’t sensitive enough, Young said.
The new cracks have not compromised the structural integrity of the building, Young said. FirstEnergy employees determined the cracks were in the outer layer of the concrete walls, so they had no bearing on the integrity of the structure.
The Nuclear Regulatory Commission has an inspector at the site as well, said Viktoria Mitlyng, the agency’s spokeswoman.
“He is independently looking at what is being found,” Mitlyng said.
If at any point it appears the shield building is unsafe, the company must halt operations at the facility, Mitlyng said.
The regulatory commission has not determined if these newly discovered cracks are newly formed, but if they are, it could throw the Blizzard of ’78 cause out the window.
“When I first began to investigate this, it was clear there were questions regarding the integrity of the concrete surrounding the nuclear reactor,” former U.S. Rep. Dennis Kucinich said. “There is clearly a deterioration of the concrete.”
This would be a critical problem in a region often punished by harsh weather and winter storms, he said.