OAK HARBOR, Ohio — Three degrees might not sound like much. But according to FirstEnergy Corp., a three-degree reduction in Davis-Besse's operating temperature will provide enough safety over the next two years to ensure there is no additional cracking of the steel nozzles that penetrate the reactor's interim head.
Now it's up to the Nuclear Regulatory Commission to decide whether it agrees with the utility's analysis of what caused 24 of the massive steel device's 69 nozzles to either develop flaws or full-blown cracks.
One had been leaking reactor acid on top of the lid when the flaws were found in mid-March, though — unlike eight years ago — the problem was caught long before any noticeable amount of steel had melted, according to Vito Kaminskas, Davis-Besse's director of plant engineering.
The company's root-cause report was unveiled to the public at a meeting in the Camp Perry clubhouse that was attended by more than 200 people.
The NRC made no comment, saying it was withholding statements about FirstEnergy's findings until a special inspection team empaneled by the agency issues its own report. That is likely later this month, said Anne Boland, director of reactor safety for the NRC's Midwest regional office near Chicago, which oversees Davis-Besse and 23 other reactors.
In an interview prior to the meeting, Mr. Kaminskas told The Blade the latest problem was diagnosed as “primary stress corrosion cracking,” an industry term for metal fatigue when certain conditions exist.
Those include susceptible material, heat, and tensile stress.
FirstEnergy knew Davis-Besse had susceptible material. That plant and others have many components — including reactor-head nozzles — made of Alloy 600, a metal that has come under scrutiny nationwide because it is not nearly as robust and corrosion-resistant as what scientists in the 1960s thought. Alloy 600 is now being replaced by the more durable Alloy 690, a much stronger alloy.
And the utility knew Davis-Besse generates heat — a lot of it.
Davis-Besse has been known as the nation's hottest-operating nuclear plant since at least June of 2002, when experts from the California-based Electric Power Research Institute told members of the NRC's Advisory Committee on Reactor Safeguards that it had been operating for some time at an average temperature of 605 degrees, 20 degrees hotter than the industry average.
Of the nation's 104 nuclear plants, Davis-Besse is one of seven with a Babcock & Wilcox design — all of which, according to that presentation eight years ago, had been operating above the industry norm because of their design.
What wasn't known was just how rapidly components made of Alloy 600 can break down under such heat, Mr. Kaminskas said.
The latest head came from a mothballed nuclear plant in Midland, Mich., where it had sat for 25 years without being used because that power station was never completed. When it was installed on top of the Davis-Besse reactor in 2004, the thought was that it would not begin to show symptoms of deterioration for 15 or 20 years.
But under such extreme heat, it aged more quickly.
Scott Plymale, Davis-Besse's manager of plant engineering, told the NRC Thursday night the utility had underestimated how much hotter the reactor head got with heat rising.
Although the reactor had been operating at an average 606.4 degrees since the 2008 refueling, the company believes the reactor head was as hot as 616 degrees. The core, where the nuclear fuel exists, is usually cooler than the steel head.
By reconfiguring the core, FirstEnergy believes it can get the reactor head's temperature down to 613 degrees and still operate Davis-Besse at full power. The company believes that, in addition to the welding and other repairs it has made, will keep cracks from forming until the next refueling outage in 2012, Mr. Kaminskas said.
The head will then undergo a similar battery of ultrasonic, electrical, and dye testing to see if any new cracks have developed.
If not, it should last until a new head made of the more durable Alloy 690 is ready to be delivered and installed in 2014, he said.
The plant's latest outage began Feb. 28.
The NRC has lauded FirstEnergy for turning around its operation of Davis-Besse, and for being both more proactive in diagnosing problems and forthcoming with information.
While the NRC considers the latest problem relatively minor compared to what happened eight years ago, officials within the agency said they have not forgotten Davis-Besse's historic two-year shutdown that started in 2002.
It culminated in a record $33.5 million in fines for lying to the government and convictions of two former employees on criminal charges.
Those fines and probes centered around the near-rupture of Davis-Besse's original reactor head, a device that had become so degraded by acid that it came within a fraction of an inch of bursting and allowing radioactive steam to form in containment of a U.S. nuclear vessel for the first time since the half-core meltdown of Three Mile Island Unit 2 in 1979.
All three Ottawa County commissioners, Ottawa County Administrator Jere Witt, and Ottawa County Sheriff Bob Bratton attended Thursday night's meeting.
Mr. Witt, who admittedly grew cynical of FirstEnergy as the cover-up surrounding the near-rupture of Davis-Besse's old nuclear head was played out eight years ago, said he continues to be pleased by what he's seen from FirstEnergy recently.