A report made public by nuclear regulators last week detailed an annunciator panel failure at Brown's Ferry unit 3 in January.
According to a filing with the Nuclear Regulatory Commission, plant personnel noticed flames and smoke coming from the panel at 7:08 p.m., Jan. 26. Operators notified the plant's fire brigade and opened a breaker, quickly extinguishing the fire that was confirmed out ten minutes later. According to TVA, the damaged equipment did not result in a loss of assessment capability.
Subsequent inspection, TVA reported, showed a resistor in the panel likely ignited from prolonged exposure to overcurrent caused by the breakdown of an aged electrolytic capacitor. Similar equipment had failed in 2008 and 2009, and in response to the fire the plant recently replaced control room annunciator power supplies more than four years old at both units.
Because of its short duration and the systems affected, TVA reported that it was not required to declare an unusual event or an alert, making the voluntary licensee event report filed in March and made public in the NRC's records system July 9 the first public report of the fire.
The NRC may look into the incident further. In an interview with The Huntsville Times, an NRC spokesman said the agency's on-site inspector was told there was not a fire when he responded to the control room. The agency first learned the situation represented an actual fire in TVA's report, the spokesman said, and while there has not been a regulatory finding issued, the NRC is reviewing the incident.