An investigation of damage to the concrete outer shell of the Davis-Besse nuclear power plant unearthed additional hairline cracks, FirstEnergy Corp. officials said.
The sub-surface cracks on the shield building don’t “affect the facility’s structure integrity or safety,” Akron, OH-based FirstEnergy said in a letter to investors. The company said the 913-megawatt reactor, shut since Oct. 1, will resume producing power in late November.
FirstEnergy shut the plant to install a new reactor vessel head three years earlier than previously planned. The U.S. Nuclear Regulatory Commission (NRC) in 2005 imposed a $5.45 million fine, its largest ever, for FirstEnergy’s failure to discover corrosion had eaten a hole in a prior vessel head.
Contractors found the newest cracks on the shield building, a 30-inch-thick reinforced concrete structure that protects the reactor’s containment building from wind and tornadoes. FirstEnergy previously discovered a hairline crack measuring about 30 feet on Oct. 10 after it cut a hole in the side of building to allow for installation of the new vessel head.
The commission said it was sending a concrete material expert to the plant, located 21 miles southeast of Toledo, after the Oct. 10 report of cracks.
The flaws are primarily in a decorative element that protrudes about 18 inches out from the building and plays no role in its structural integrity, said Jennifer Young, a FirstEnergy spokeswoman.
The company is still studying two other cracks found as it tested the shield building and continues “to assess their implications, if any,” she said.
Because the shield building doesn’t form the primary safety barrier to the nuclear reactor, cracking to its reinforced concrete is not a safety threat and the operator doesn’t need federal permission to resume power output from the reactor, said Viktoria Mitlyng, a NRC spokeswoman.
FirstEnergy is seeking regulatory permission to extend its operating license for Davis-Besse, which has been in service since 1977, by another 20 years. The commission should issue its decision on the application next year.