Up to 1,000 gallons of radioactive tritium-laced water spilled from a tank at the Browns Ferry Nuclear Plant on Wednesday while TVA was preparing to reactivate the plant's Unit 3 reactor.
"The level of radioactivity was still well below any regulatory limits and there was no danger to any employees or the public," said Donald Jernigan, senior vice president of nuclear operations at TVA.
"If you took the radioactive activity in this tank and you were to concentrate that from the 1,000 gallons, the total amount of radioactivity is only one-100th of the level from an exit sign at a movie theater," he said.
Nuclear Regulatory Commission spokesman Roger Hannah said the tritium release was below NRC's allowable limits, but the water does exceed allowable limits set by the U.S. Environmental Protection Agency for drinking water.
TVA officials said the contaminated water came from the closed cooling water system at the plant, spilling onto the ground from a leaking valve on top of one of the storage tanks.
Officials said the dirt around the tank, as well as the leaking valve, already have been removed and collected for shipment to a low-level radioactive waste site in Utah.
The tritium leak is the second such reportable spill in the past 28 months at Browns Ferry, TVA spokesman Ray Golden said.
Chattanoogan David Lochbaum, a member of the Union of Concerned Scientists who used to work for TVA, said the "tritiated water" is low-level radiation and TVA's quick action to find the leak and clean up should be applauded.
But he also said TVA could have prevented it if agency officials heeded industry warnings offered in 1978.
"A more proactive stance would have prevented this problem," he said. "And it could have been worse. It could have gotten off the site."
In 1978, a nuclear plant near Brattleboro, Vt., had a similar spill of 80,000 gallons of tritiated water, Dr. Lochbaum said. Shortly after that spill, many other nuclear plants began piping cooling water in spill-prone areas back into another storage tank onsite as a precaution against overflows or spills. The NRC sent notice of this preventive measure to all nuclear plants.
"Other plant owners made similar fixes. TVA chose not to," he said.
Another Chattanoogan Sandy Kurtz, a member of a local anti-nuclear group known as BEST, said the incident just increases her concerns.
"Of course, TVA will repair the leak in a hurry," she said. "However, this tritium spill due to faulty equipment only adds to radiation being released to our air and water on a daily basis during routine operations. There is no safe dose of radioactivity."
TVA reported the incident to the Nuclear Regulatory Commission on Thursday as part of 2006 voluntary industry agreement to report cases where more than 100 gallons of any potentially radioactive water is released at a nuclear plant.
TVA officials said plant personnel discovered that a small valve at the top of storage tank was leaking at a rate of about two gallons a minute early Wednesday.
NRC regulators plan to conduct a detailed inspection of the Browns Ferry water monitoring program by June, Mr. Hannah said.
TVA also will conduct increased well monitoring at the site, Mr. Jernigan said.
About one-third of America's 104 licensed nuclear reactors have had reportable tritium leaks, including all three TVA plants, Mr. Hannah said.
NRC and TVA already are monitoring plumes of leaked tritium in groundwater at all three of TVA's nuclear plants: Watts Bar, Browns Ferry and Sequoyah nuclear plants. Officials have said they track the plumes with monitoring wells.
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