Tennessee Valley Authority officials met nuclear regulators on Monday to explain the failure last year of a key valve used to operate a reactor cooling system at a nuclear plant in Alabama.
Word of the malfunction, which occurred last October at the Browns Ferry plant in northern Alabama, comes amid public demand for reassurance over the safety of U.S. nuclear reactors after an earthquake and tsunami last month caused a crisis at Japan's Fukushima nuclear plant.
Browns Ferry and the crippled Fukushima plant both have Mark 1 boiling water reactors made by General Electric.
TVA officials said they discovered the fault when they tried to cool uranium at the Alabama plant's No. 1 reactor during a refueling outage only to find that a valve in the secondary containment system did not work.
"There was never any danger to the public. We shut the plant down," said TVA manager of nuclear communications Ray Golden.
"The risk would be that you would have to find an alternate path to cool the uranium fuel and we were able to do that," he said, adding that plant operators used back-up pumps to cool the reactor.
TVA argued at a meeting it requested with the Nuclear Regulatory Commission in Atlanta on Monday that the valve had a manufacturing defect, Golden said.
Browns Ferry has three reactors and the valve was in place when reactor one went online in 1974. It is part of a residual heat removal system that takes away heat still in the fuel once the reactor has been shut down, he said.
"Any time you have safety systems that are potentially inoperable it decreases the safety system and increases the risk," said NRC spokesman Roger Hannah, adding that a key question was how long the valve had been inoperable.
Regulators have already conducted an inspection and issued an apparent violation for the incident. They will decide on further action in the next few weeks, Hannah said.
TVA officials say a repeat of the Fukushima disaster could not happen because of the Alabama plant's superior safety and back-up power systems.