The Three Mile Island power station is near Harrisburg , Pennsylvania . The accident began on Wednesday , March 28 , 1979 , and resulted in a partial core meltdown in Unit 2 of the nuclear power plant . The Three Mile Island accident was a partial core meltdown in Unit 2 ( a pressurized water reactor manufactured by Babcock & Wilcox ) of the Three Mile Island Nuclear Generating Station in Dauphin County , Pennsylvania near Harrisburg , United States in 1979 .