Three Mile Island | Three Mile Island accident
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 in 1979. The plant was owned and operated by General Public Utilities and the Metropolitan Edison Co. The Three Mile Island accident began about 4:00 a.m. on March 28, 1979, when the plant experienced a failure in the secondary, non nuclear section of the plant. The main feedwater pumps stopped running, caused by either a mechanical or electrical failure, which prevented the steam generators from removing heat. First the turbine, then the reactor automatically shut down. Immediately, the pressure in the primary system (the nuclear portion of the plant) began to increase. In order to prevent that pressure from becoming excessive, the pilot-operated relief valve (a valve located at the top of the pressurizer) opened. The valve should have closed when the pres...