An estimated 100 workers wearing protective suits were contaminated by the leak Saturday afternoon, but had been decontaminated as of late Saturday night and suffered no injury, plant spokesman Ralph DeSantis told WHTM-TV, Harrisburg.

The radiation alarm sounded in the Unit 1 reactor as workers were cutting pipes to remove old steam generators and replace them with new ones, DeSantis said.

The cause of the leak was under investigation by the Nuclear Regulatory Commission and it was not known when the reactor might start up again, WPVI-TV, Philadelphia, reported Sunday.

On March 29, 1979, the Three Mile Island Unit 2 reactor suffered a partial meltdown in the worst civilian nuclear accident in U.S. history. The reactor core of Unit 2 has since been removed.