ATLANTA (AP) - Federal regulators ordered an in-depth inspection Tuesday at a nuclear power plant run by the Tennessee Valley Authority in northern Alabama after deciding the failure of an emergency cooling system there could have been a serious safety problem.
The U.S. Nuclear Regulatory Commission issued a rare red finding against the Browns Ferry nuclear power plant near Athens, Ala., after investigating how a valve on a residual heat removal system became stuck shut. The NRC has issued only five red findings - the most severe ranking the agency gives to problems uncovered in its inspections - since its current oversight program started in 2001.
NRC said the utility must pay for detailed inspections of the plant's performance, its safety culture and organization. The agency said it could not immediately estimate inspection costs.
In an emergency, the failure of the valve could have meant that one of the plant's emergency cooling systems would not have worked as designed. The problem, which was identified as the plant was being refueled in October 2010, was fixed before the Unit 1 reactor was returned to service.
"The valve was repaired prior to returning the unit to service and Browns Ferry continued to operate safely," said Victor McCree, the NRC's Region II administrator. "However, significant problems involving key safety systems warrant more extensive NRC inspection and oversight."
NRC officials were critical of the utility for not identifying the problem sooner through routine inspections and testing. The valve failed sometime after March 2009 but wasn't discovered until more than a year later.
TVA officials have not decided whether they will appeal the NRC's decision.
"Obviously we're disappointed with the NRC's findings on this matter," Chief Nuclear Officer Preston Swafford said. "The safe operation of all our units is our primary concern, and we take any regulatory report of a violation very seriously."
Experts said a failure of the valve could have left one of the plant's emergency cooling systems unable to function in an emergency, for example, if the reactor suddenly lost the coolant needed to keep its nuclear fuel from melting.
The worst outcome could have resulted from a series of what McCree called unlikely events involving a plant fire. In case of a fire, operators would protectively shut down some safety equipment, potentially including one of the residual heat removal loops. If the second system did not function because of the valve failure, plant operators would be forced to rely on other cooling equipment.
"We would not want them to have to be in this situation," McCree said.
McCree said the NRC's upcoming inspections will help the organization decide whether additional regulatory actions are necessary to assure public health and safety.
TVA officials blamed the problem on a manufacturer's defect in equipment it doesn't ordinarily inspect. Utility spokesman Ray Golden said the valve failure never caused an accident or threatened public safety. The utility has inspected similar valves at the plant and has not found any problems, he said. TVA officials also said testing showed the stuck valve would have eventually opened, though NRC officials dispute this claim.
Past problems have led to increased scrutiny. The Browns Ferry Plant is known in the industry as the site where a worker using a candle to check for air leaks in 1975 started a fire that disabled safety systems. It is similar in design to the reactors that malfunctioned earlier this year at the Fukushima Dai-ichi nuclear plant in Japan after a powerful earthquake and tsunami.
The TVA voluntarily shut down its entire nuclear fleet in 1985 to address safety and performance issues. The Unit 1 reactor at Browns Ferry reopened in 2007.
TVA, the county's largest public utility, supplies power to about 9 million people in Tennessee, Alabama, Mississippi, Kentucky, Georgia, North Carolina, Tennessee and Virginia.