Officials are trying to determine how workers cutting a pipe stirred up radioactive dust at the Three Mile Island nuclear power plant.
Plant spokesman Ralph DeSantis said Monday that the public was not endangered Saturday, when a dozen workers were exposed to radiation.
The central Pennsylvania plant has two reactors. One suffered a partial meltdown in 1979 and is mothballed. The other is still in use, but has been shut down since last month so steam generators could be replaced.
DeSantis says the radioactive dust emanated from reactor cooling system pipes the workers were cutting. He says a radiation monitor "temporarily went up" slightly, but a later survey detected no contamination outside.
The U.S. Nuclear Regulatory Commission says the radiation isn't significant.