Three Mile Island accident History

The Three Mile Island accident was a partial core meltdown in Unit 2 (a pressurized water reactor manufactured byBabcock & Wilcox) of the Three Mile Island NuclearGenerating Station in Dauphin County, Pennsylvania near Harrisburg in 1979. The plant was owned and operated by General Public Utilities and the Metropolitan Edison Co. It was the most significant accident in the history of the American commercial nuclear power generating industry, resulting in the release of up to 481 PBq (13 million curies) of radioactive gases, but less than 740 GBq (20 curies) of the particularlydangerous iodine-131. The accident began at 4 a.m. on Wednesday, March 28, 1979, with failures in the non-nuclear secondary system, followed by a stuck-open pilot-operated relief valve (PORV) in the primary system, which allowed large amounts of nuclearreactor coolant to escape.