An alert imposed after smoke was spotted at the Quad Cities Generating Station in western Illinois was lifted after eight hours.
Exelon Generation officials say the smoke was spotted Wednesday after a pipe released water onto an electrical system.
Spokesman William Stoermer says Quad Cities Unit 2 had been removed from service Monday so workers could replace a valve. The unit was in being restarted when smoke was detected around 1:40 p.m. The alert was lifted around 9:30 p.m.
Exelon officials say the unit is stable and another unit at the facility remains at full power.
The U.S. Nuclear Regulatory Commission says there were no abnormal releases of radioactive material and no one was injured.
The plant is about 20 miles northeast of Moline.