The Fort Calhoun plant north of Omaha was shut down at the time of the fire, which started in an ill-fitting electrical breaker, and temperatures never exceeded safe levels, the Nuclear Regulatory Commission said in a preliminary report obtained by The Associated Press before its official release. But the commission said the fire is considered a major concern because it could have happened any time and because workers didn't fully investigate an unusual smell in the area three days earlier that could have led them to discover the problem and prevent the fire.
A serious threat finding typically could mean 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.
Fort Calhoun initially was shut down for refueling maintenance last spring, but major flooding along the Missouri River forced it to remain closed. The Omaha Public Power District is working to repair any flood damage and double-check all the plant's systems before restarting.
Utility spokesman Jeff Hanson said OPPD doesn't plan to contest the severity of the NRC's finding on the fire.
The fire started in an electrical breaker that had been replaced about 18 months earlier. NRC spokeswoman Lara Uselding said the new breaker had to be modified to fit the existing switches, and the breaker didn't line up properly. That allowed grease to accumulate on the components, which allowed enough heat to build up to start the fire.
During the fire, smoke and soot spread into Fort Calhoun's backup electrical system and knocked that out as well. Uselding said the utility is working to redesign the system to prevent a fire from being able to knock out both power systems again.
The NRC said in December that Omaha Public Power District officials also were too slow to notify state emergency response officials about the fire when it happened.
Hanson said the faulty breaker already has been replaced, and was successfully tested last week. He said the utility is making progress toward restarting Fort Calhoun, but won't rush the process.
"We're hoping for a spring restart," Hanson said.
The NRC will have to sign off on all repairs before any restart.
The utility submitted a detailed improvement plan to the NRC that regulators approved last fall. Utility officials have said they need to improve the way Fort Calhoun's staff identifies and fixes any concerns at the plant.
