NEWPORT, Mich. - Fermi 2 experienced unexplained turbine vibrations as its nuclear reactor was being shut down Saturday for the plant's latest refueling and maintenance outage.
DTE Energy, told the Nuclear Regulatory Commission "high vibration levels" came from a main turbine about 1:46 a.m., according to a report posted on the agency's Web site Monday.
The plant was shut down immediately by an operator who stepped in and performed a manual "scram" rather than continue with a gradual shutdown.
Manual scrams are required by safety procedures when vibrations of a certain magnitude are detected, NRC spokesman Viktoria Mitlyng said.
The cause is being investigated. The utility plans to keep Fermi 2 offline for 30 days.
The utility has augmented its work force with about 1,000 contractors to replace about a quarter of the plant's reactor core with new fuel assemblies while also performing 2,000 inspections and other activities, DTE spokesman John Austerberry said.
Nuclear plants are refueled every 18 months to two years, depending on the grade of uranium in their fuel.
The outage is the 13th in Fermi 2's history. It ended 419 days of continuous operation, the plant's second-longest.
Fermi 2 also established an internal record for electricity production in 2008, Mr. Austerberry said.
Turbines are in separate section of the plant. They are spun to generate electricity from steam produced by the reactor.
Fermi 2 experienced a fire on Christmas day of 1993 after vibrations in the plant's turbine building.
An investigation revealed that a turbine blade had broken off, ripping through a floor and igniting the blaze.
Firefighters sprayed 1.5 million gallons of water on the fire.
The water picked up radiation from the plant, but was discharged into Lake Erie according to the NRC's permitted levels.
The plant was offline for a year while damaged parts were replaced.
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