A small amount of radiation was detected in a reactor building at the Three Mile Island nuclear power plant in central Pennsylvania on Sunday. Officials say there is no public health risk. About 150 employees were sent home after the radiation was detected. Exelon Nuclear spokeswoman Beth Archer said investigators were searching for the cause. She said the radiation was quickly contained. Radiological surveys showed the contamination was confined to surfaces inside the building. The unit has been shut down for refueling and maintenance since Oct. 26. The company hopes to resume maintenance work Sunday. Officials were testing workers for possible unusual radiation exposure. A partial meltdown occurred in Three Mile Island's Unit 2 reactor in March 1979.