OAK HARBOR, Ohio - Federal regulators said Wednesday they have no problem with Davis-Besse's repaired nuclear reactor head being put back into service for the next 15 months.
But that's conditioned upon FirstEnergy Corp. following through on a commitment it made with the NRC recently to shut down the plant and start replacing the massive lid with a new one by Oct. 1, 2011, the agency said.
The NRC's summary of those talks was made public yesterday in a government document known as a confirmatory action letter. In it, the NRC's Midwest regional administrator, Mark A. Satorius, spelled out in writing what his agency expects from FirstEnergy if the utility follows through with its plans to put Davis-Besse back into service with its existing head in July.
Todd Schneider, FirstEnergy spokesman, said the utility "accepts the terms and conditions" outlined in the letter and continues to focus on a July restart.
The letter, addressed to Barry Allen, Davis-Besse site vice president for FirstEnergy Nuclear Operating Co., the utility's nuclear subsidiary, said there exists "reasonable assurance" that any cracks that may develop in the weakened head's control-rod drive mechanism nozzles over the next 15 months will not be circular-shaped ones, known as circumferential cracks.
Those are among the most dangerous a nuclear plant could encounter because of their ability to pop off like champagne corks, allowing radioactive steam to form.
That's what nearly happened with Davis-Besse's original head, which FirstEnergy had allowed to deteriorate to historic proportions. The extent of damage revealed on April 6, 2002, was never before seen in U.S. nuclear history.
The plant was allowed to resume operation after a two-year shutdown. The damaged lid was replaced with one that had been in storage for 25 years at a mothballed plant in Midland, Mich.
Both the original head and its replacement, though, were made of an inferior metal known as Alloy 600. Once thought to be impermeable, it has shown a propensity to crack under prolonged heat and stress. It exists at most of the nation's 104 nuclear plants but has been a particular problem at Davis-Besse because that plant has been operating for years at higher temperatures than others, according to research by the NRC, FirstEnergy, and a FirstEnergy consultant, the California-based Electric Power Research Institute.
Twenty-four of the existing head's 69 nozzles were found to have flaws on them following the plant's Feb. 28 outage.
"The examination results from the current outage indicate that only two nozzles had developed circumferentially oriented cracks, with a relatively small extent," the NRC's letter said. "These cracks would not have challenged the head's structural integrity. The cracks in the remaining identified nozzles were characterized as axial [along the length of the nozzle] in nature, which can cause leakage, but will not directly challenge the structural integrity of the [reactor pressure vessel] head."
FirstEnergy engineers told the NRC June 3 they felt the existing head was strong enough to last at least 21 months, to Davis-Besse's next slated refueling in the spring of 2012. The NRC disagreed.
Regulators wanted to be more conservative, in part because "we've already gone through this" in 2002, Viktoria Mitlyng, NRC spokesman, said.
"The question for the NRC was how long the head could remain in service before developing cracks and leaks," she said. "At the end of the day, it's probably more efficient just to replace the head."
The NRC said in its letter that it believes FirstEnergy did a thorough job in examining all 69 nozzles once the latest problems were identified, and in making appropriate repairs.41.50821 -83.14501 Federal regulators said Wednesday they have no problem with Davis-Besse's repaired nuclear reactor head being put back into service for the next 15 months.