NEW YORK, Sept 25 (Reuters) - The U.S. Nuclear Regulatory Commission is conducting a special inspection at American Electric Power Co Inc's AEP.N 1,029-megawatt Unit 1 at the Cook nuclear power station in Michigan, the nuclear regulator said in a report Wednesday.
The NRC will review circumstances around a turbine generator fire on Sept. 20 and degradation of the fire suppression system.
A malfunction in the turbine generator resulted in a fire and caused the operators to manually shut the reactor. The turbine generator transforms steam into electricity.
AEP said it would return the unit to service after inspecting the turbines, which will likely take about one to three weeks.
In a release on Sept. 23, AEP said initial indications were the fire occurred when turbine vibrations led to a leak of generator hydrogen that ignited.
Hydrogen is used to keep the generator cool during operation and the seals that contain the hydrogen were likely damaged by the vibrations, it said.
Damage to the turbines and generator from the fire was minimal, but vibrations did damage the low pressure turbines, bearing supports and some steam piping.
AEP believed the cause of the vibrations was an imbalance from the loss of turbine rotor blades.
The NRC said all nuclear safety systems functioned as expected and were not affected by the fire, which occurred in a building separate from the nuclear reactor.
The utility declared an unusual event, the lowest of NRC’s four emergency classifications, when the fire could not be extinguished within 15 minutes. The fire was extinguished 25 minutes after it started.
There were no injuries and no hazard to the public.
After the fire was extinguished, operators received a signal indicating a problem with the fire suppression system due to a rupture in the pipe that is a source of water for the plant’s fire protection systems, the NRC said. Alternate sources of water were available for fire suppression in case they were needed.
The NRC said it could not determine the length of the special inspection, noting the average duration of a special inspection is seven days. The NRC will issue an inspection report about 45 days after the inspection is complete.
The 2,106 MW Cook station is located in Bridgman in Berrien County, about 80 miles east of Chicago. There are two units at the station, the 1,029 MW Unit 1 and 1,077 MW Unit 2, which entered service in 1975 and 1978, respectively.
Unit 2 continued to operate at full power.
One MW powers about 800 homes in Michigan.
In 2005, the NRC renewed the plant’s original 40-year operating licenses for both units for another 20 years to 2034 and 2037.
AEP, of Columbus, Ohio, owns and operates more than 38,000 MW of generating capacity, markets energy commodities, and transmits and distributes electricity to more than 5 million customers in 11 states. (Reporting by Scott DiSavino; Editing by Walter Bagley)
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