The U.S. Nuclear Regulatory Commission said the small amount of radiation detected at the Three Mile Island nuclear power plant is not significant.
Specialist John White told ABC News that there was no indication that radiation at the plant exceeded or even approached regulatory limits.
The commission sent investigators to the central Pennsylvania plant after a small amount of radiation was detected.
About 150 employees were sent home Saturday afternoon, but officials said there was no public health risk.
Exelon Nuclear spokeswoman Beth Archer said the radiation was quickly contained.
The unit has been shut for refueling and maintenance since Oct. 26. Workers are being tested for radiation exposure.
A partial meltdown occurred in Three Mile Island's Unit 2 reactor in 1979.