An electrical fire last June posed a high safety risk at the Fort Calhoun Nuclear Station, the Nuclear Regulatory Commission has ruled in a preliminary finding released Monday.
A spokesman for the Omaha Public Power District said the utility had been expecting the so-called “red” finding by NRC regulators and has already taken some of the recommended corrective actions.
At the time of the fire the plant was idled because of flooding along the nearby Missouri River. Though the fire caused a loss of electrical power to cooling pumps, the fuel remained cool.
“The public was not in danger,” said spokesman Jeff Hanson. “The plant was safely shut down at the time of the fire.”
The fire was quickly extinguished, he said, and the alert was lifted about three hours after the fire began.
However, NRC officials — who inspected the plant in September and December — identified several concerns with how the fire started, how it was detected and how it was put out.
Among other things, the inspectors noted, workers had noticed an “acrid” odor in an electrical switchgear room three days before the fire started. The odor smelled more like chlorine than electrical overheating, so workers dismissed it as being somehow related to the flooding, said Lara Uselding, an NRC spokeswoman based in Texas.
The fire was determined to have started in a replacement electrical breaker that had been modified in its 2009 installation to fit inside existing electrical switchgear. The parts weren’t properly fitted, causing electrical resistance that built up heat and sparked a fire.
The breaker in question was one of 12 that had been modified — thus, all could be prone to higher electrical resistance and fire risk.
Soot and smoke breached a fire wall shielding a backup electrical system, tripping a circuit breaker and shutting down that system as well.
In addition, the fire-suppression system that extinguished the fire would have made it difficult for workers to enter the switchgear room to make repairs.
“In the event of the incident, other measures could have been used to safely shut down the plant, but it wouldn’t have been the desired normal measures,” Uselding said.
The Fort Calhoun plant already is under the NRC’s highest oversight level because of last year’s flooding, as well as the fire and other problems detected earlier. The problems must be resolved before the nuclear power plant can be restarted.
Hanson said OPPD hopes to resume operations at the plant this spring. He said the utility has made repairs to the breakers, including lowering resistance on the electrical connections and tightening connections. He said plant procedures also are being revised. The repaired electrical equipment became operational March 4 for the first time since the June fire.
Hanson said OPPD does not plan to contest the NRC’s findings.
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