NEWPORT, Mich. — Hours before DTE Energy's Fermi 2 nuclear plant resumed operation Friday morning, about 100,000 gallons of radioactive cooling water overflowed a holding tank and stood about an inch high in portions of the plant's turbine building and its radioactive waste building, according to the U.S. Nuclear Regulatory Commission.
The mishap, discovered Wednesday afternoon, contaminated shoes and outer clothing of about a half-dozen workers.
“Low-level contamination was limited to some of the workers' shoes and outer clothing during the event. The inspectors are reviewing the licensee's follow-up surveys,” an NRC online report said.
Up to 100 gallons flowed through a bathroom drain into a Monroe County sewer line, causing some of the sewage near the plant to have trace amounts of radiation, DTE Energy spokesman Guy Cerullo said.
“We've determined a very small amount reached the Monroe County sewage system,” he said.
Sewage plants process millions of gallons of water each day.
Though the sewage-laden plume was well below NRC levels for releases and so small that DTE needed laboratory tools to confirm its existence, NRC spokesman Viktoria Mitlyng said nuclear plants — as a matter of federal policy — must strive to contain all radioactive particles to its site.
DTE, through labwork, detected a release of .0007 millirem a few yards offsite. The concentration dropped to nondetectable levels long before reaching populated areas, Mr. Cerullo said.
“As it goes toward town, it gets diluted,” Ms. Mitlyng said.
Both Mr. Cerullo and Ms. Mitlyng said there was no danger to plant employees or the public. They also said there was no problem with safety systems.
The average American who lives at sea level is exposed to 300 millirems of radiation a year; in higher-altitude cities, such as Denver, the average is about 400 millirems a year. NASA astronauts get as many as 25,000 millirems a year, according to the Massachusetts Institute of Technology.
The overflow filled a ventilation line, spilling into portions of the plant's turbine building and radwaste building.
The problem was attributed to a valve that got stuck open when it should have closed.
The valves in question are in a part of the plant where silt and particles are washed off a large condenser system. The tank that overflowed is only supposed to be holding runoff water from the cleaning operation, Ms. Mitlyng said. “It's not even a reportable event,” she said.
Fermi 2 is in northern Monroe County, about 30 miles north of Toledo and along the western Lake Erie shoreline.
It had been down for refueling and maintenance since Oct. 24. Nuclear plants are refueled every 18 to 24 months.
The reactor is ascending in power and should synchronize to the regional electrical grid sometime this weekend. Nuclear reactors are typically operating at 20 or 25 percent capacity when that happens.
DTE predicted the plant would be operating at full capacity within a few days but would not be more specific.
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