Plant spokesman Ralph DeSantis said Monday that public safety was never endangered by Saturday's incident in which a dozen workers at the central Pennsylvania facility were exposed to radiation.
The unit has been shut down since Oct. 26 to refuel the reactor and replace the steam generators.
DeSantis says the radiation emanated from reactor cooling system pipes that were being cut by workers.
He says a radiation monitor at an entrance to the reactor building "temporarily went up" slightly, but a later survey detected no contamination outside.
The U.S. Nuclear Regulatory Commission says the radiation detected isn't significant.