A man crashed a car through the gates at the Three Mile Island nuclear plant on Sunday, spending four hours inside before being arrested, police said.
Pierce Nye, 31, was found hiding under a piece of machinery inside the turbine building, which houses electrical generating equipment, said state police and plant officials.
Police spokesman Charles Tocci said Nye told authorities that he acted alone, had no explosives and did not tamper with anything.
Nye refused to say why he entered the plant, officials said. Details of his activities while he was inside the plant were not released.
A York County Emergency Management Agency official said Nye was released Jan. 17 from the psychiatric ward of Ephrata Community Hospital. The hospital would not confirm that he had been a patient.
No radiation was released and the plant continued to operate at full power, plant spokesman Ralph DeSantis said.
Nye drove a station wagon past an open chain-link fence, then drove a three-quarter-mile stretch and crashed through a second chain-link fence, officials said. DeSantis said the first gate was open because of a shift change.
Nye then drove the car into the partially opened, roll-up truck delivery door of the plant's turbine building, officials said.
Nye was arraigned on charges of causing or risking a catastrophe, criminal mischief, criminal trespass and reckless endangerment. He was jailed in lieu of $250,000 bail.
Three Mile Island was the site of the nation's worst commercial nuclear accident in 1979.