(Harrisburg, PA) -- A leak of low-level radiation at Pennyslvania's Three Mile Island nuclear power plant has sent inspectors from the Nuclear Regulatory Agency to the scene.

The leak occurred Saturday afternoon in the Unit 1 reactor containment building, which was open at the time to move in new equipment. Investigators are trying to determine the cause of the leak, which exposed about 20 workers to radiation.

Officials said the highest exposure to one worker equaled about three chest X-rays. Plant officials and the NRC said there was no danger to the public.

Three Mile Island shut down last month for refueling, steam generator replacement and other routine maintenance.

Three Mile Island was the site of the nation's worst civilian nuclear accident in March 1979 when nuclear fuel in Unit 2 overheated and partially melted due to a cooling water leak. Although some radiation was released during the accident, no one died.

The partially melted nuclear fuel was finally cleaned up and removed in 2001. The owners of the plant have no plans to repair or restart Unit 2.

Unit 1, where the low-level radiation leak occurred Saturday, resumed operation in 1985.

The current owners, Exelon Energy, have applied for a 20-year extension of the Unit 1 license to operate the plant through 2034.

(Copyright 2009 by VERTEXNews/Newsroom Solutions)