Federal regulators on Tuesday confirmed their preliminary finding that a fire at an idled Nebraska nuclear plant last June presented a serious safety threat.
The Nuclear Regulatory Commission said in its final determination that the small fire at the Fort Calhoun plant 19 miles north of Omaha was of "high safety significance." The finding mirrored the commission's preliminary conclusion announced March 12.
"This finding has high safety significance because it affected multiple safety systems and consequently warrants actions to prevent recurrence," said the NRC's regional administrator, Elmo Collins.
Omaha Public Power District spokesman Jeff Hanson said the utility "knew early on that this was a serious issue and we knew we were going to get a serious finding on that. That's why we did not contest it."
The faulty equipment has been replaced, he said, and similar equipment has been checked.
Such a serious finding typically means additional oversight for a nuclear plant, but Fort Calhoun already is under the NRC's strictest oversight level because of a prolonged shutdown that began last spring and several other reported problems, including the failure of a key electrical part during a test and flood planning deficiencies, both found in 2010.
The plant was shut down at the time of the fire, which started in an ill-fitting electrical breaker. The electrical system running the pumps that cool spent fuel in a pool of water was disrupted. The pumps are a key piece of safety equipment because if pumping systems were to fail for several days and were not fixed, cooling water could boil away and eventually allow radioactive releases.
The NRC said pool temperatures never exceeded safe levels and no radioactivity was released.
The fire raised major concern, the NRC said, because it could have happened any time and because workers didn't fully investigate an unusual smell in the area three days earlier, which could have led them to discover the problem and prevent the fire.
Fort Calhoun initially was shut down for refueling maintenance last spring, but major flooding along the Missouri River forced it to remain closed.
OPPD said it has repaired all flood damage and has been discussing a restart checklist with the NRC, Hanson said. But he said there's no target date for restarting the plant.