Three Mile Island

Three Mile Island: Three Mile Island accident was a incomplete core condense 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 knowledgeable a failure in the secondary, non nuclear section of the plant.

The main feed water pumps stopped running, caused by either a mechanical or electrical failure, which prohibited the steam generators from removing heat. First the turbine, then the reactor automatically shut down. without delay, the weight in the primary system (the nuclear portion of the plant) began to raised. In order to prevent that pressure from becoming too much, the pilot-operated release control device (a valve located at the top of the pressurizer) opened. The valve should have closed when the strain decreased by a certain quantity, but it did not. Signals available to the operative failed to show that the valve was still open. As a result, cooling water poured out of the stuck-open valve and caused the core of the reactor to overheat.