Federal nuclear regulators have concluded that last fall's failure of a low-pressure coolant injection valve at the Browns Ferry nuclear plant was of "high safety significance" and will result in increased Nuclear Regulatory Commission inspection and oversight of the TVA power plant.
Although TVA had argued in an early April regulatory conference that the failed valve was the result of defective manufacturing and would have opened in a few more moments to supply necessary cooling water, the NRC review today disagreed and concluded the violation was "red," or of high safety significance.
Only five red findings - the most severe ranking the agency gives to problems uncovered in its inspections - have been issued nationwide in the past decade.
The Browns Ferry plant has three nuclear reactors near Athens, Ala., and is operated by the Tennessee Valley Authority about 100 miles southwest of Chattanooga. The plant is a similar design to the Fukushima Daiichi nuclear plant in Japan that was thrown into nuclear crisis after a 9.0 earthquake and tsunami left its six reactors without cooling water.
On Oct. 23, the valve failed to open at Browns Ferry when operators shut down the Unit 1 reactor for refueling. TVA later determined that the last time the valve had definitely worked as required was on March 12, 2009.
NRC spokesman Roger Hannah said today that the public was not endangered when the valve failed because plant operators were able to use an alternative shutdown method.
"However, the system is counted on for core cooling during certain accident scenarios and the valve failure left it inoperable, which potentially could have led to core damage had an accident involving a series of unlikely events occurred," Hannah said.
TVA's nuclear spokesman Ray Golden said TVA is reviewing NRC's findings, which could include appealing the decision.
"We thought we provided a compelling argument as to why the findings should be less than red," Golden said, adding that TVA had determined in lab tests since the failure that the valve would have opened "in two to seven minutes" longer.
The problem was a manufacturing defect, Golden said.
"In any case, we are committed to safety at our plants," he said. "There were five different, redundant systems to keep the reactor cool, and at no time was the public or plant employees in danger."
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