The Nuclear Regulatory Commission has concluded that it was correct in proposing that the Fort Calhoun Nuclear Station be dealt a so-called "red finding" for a June 2011 electrical fire in its emergency equipment.
A red finding is the most severe of four color-coded citations the commission metes out after problems at a nuclear plant.
This is the seventh red finding the commission has issued against a nuclear reactor since 2001. The nation has more than 100 reactors.
Elmo E. Collins, regional administrator for the commission, said in a statement Tuesday that the fire was of "high safety significance" because it affected multiple systems and needed to be addressed to prevent it from happening again.
The nuclear plant, about 20 miles north of Omaha, is owned and operated by the Omaha Public Power District.
Jeff Hanson, spokesman for OPPD, said the utility accepts the NRC's decision.
"This is something we take seriously," he said.
OPPD has replaced the damaged equipment and modified the system to resolve problems with the switchgear, he said.
At issue was an electrical fire in an electrical panel that guaranteed electricity to the plant's spent fuel pools.
Public safety was not immediately at risk, experts say.
The pool was without electricity for about 90 minutes, which halted active cooling. According to federal regulators and OPPD, the pool had more than 80 hours of residual cooling ability.
But there were larger safety issues raised by the fire, including the design and inadequate maintenance that led to the problem, the inability of workers to enter the electrical room during the fire because of a potentially toxic fire suppression gas and the late notice of the fire to local emergency officials.
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