The Notice of Unusual Event was lifted just before 1:30 p.m. and workers were permitted to return to the building.
Al leak involving a mixture of ammonia and water led to an evacuation and declaration of an "unusual event" at TVA's Watts Bar Nuclear Plant Friday morning.
The leak happened just before 9 a.m. in the turbine building, according to Travis Brickey, a spokesman for the Tennessee Valley Authority.
Because some of the workers had to evacuate the area, TVA was required to file an NOUE, which is the least serious classification on the Nuclear Regulatory Commission scale, according to Brickey.
The ammonia is used to control and maintain the pH levels in the secondary water system in the turbine building. The leak never affected the Unit 1 reactor, which continues to operate at 100 percent.
Brickey said there were no injuries, and there was never a threat to public safety.
The area has been vented, and the cleanup is underway.
The "all-clear" is expected by early afternoon, at which time the NOUE will be lifted.
Brickey said state officials have been notified, and TVA is investigating the cause of the leak.