The Nuclear Regulatory Commission has determined that an inspection finding at the Fort Calhoun Station involving an electrical breaker fire is of “red” or high safety significance.
The plant, operated by the Omaha Public Power District, is located 19 miles north of Omaha, Neb.
“This finding has high safety significance because it affected multiple safety systems and consequently warrants actions to prevent recurrence,” said NRC Region IV Administrator Elmo E. Collins.
The finding stems from an NRC special inspection regarding an electrical fire that led to the declaration of an Alert at Fort Calhoun on June 7, 2011. The fire started in a replacement electrical breaker where poor alignment between components and inadequate maintenance increased the electrical resistance on some parts, causing them to heat up and fail.
Soot and smoke from the resulting fire then knocked out power to a redundant electrical system used for distributing power to vital equipment needed for the safe shutdown of the plant. The plant was shut down at the time because of flooding along the Missouri River.
The fire resulted in the loss of spent fuel pool cooling for approximately 90 minutes and could have resulted in the loss of a safety function or multiple failures in systems used to mitigate a severe accident, had one occurred. In the event of a serious accident, operators would have had to take compensatory measures to safely shut the plant down.
OPPD has taken appropriate corrective action to prevent recurrence.
The NRC staff has characterized the finding as “red.” NRC evaluates performance at plants with a color-coded process which classifies regulatory findings as either green, white, yellow or red, in order of increasing significance.
Fort Calhoun is receiving a special category of increased NRC oversight for plants that have been shut down for extended periods and have significant performance issues. The plant cannot restart without NRC approval.