Knowra Three Mile Island accident Three Mile Island accident The 1979 accident at Pennsylvania’s Three Mile Island nuclear station partially melted a reactor core and released small amounts of radioactive material. It caused no detectable health effects, but reshaped nuclear regulation and public opinion in the United States.
Pressurized water reactor : A nuclear reactor that transfers heat from a pressurized primary water loop to a secondary steam loop. Unit 2 used this design, whose closed primary loop contained the damaged core.
Three Mile Island Nuclear Generating Station : A nuclear power station on an island in the Susquehanna River near Middletown, Pennsylvania. The accident occurred in Unit 2 at this station on March 28, 1979.
Kemeny Commission : The presidential commission chaired by John G. Kemeny that investigated the Three Mile Island accident. Its 1979 report criticized both plant management and the nuclear regulatory system.
March 28, 1979 : The date on which the Three Mile Island Unit 2 accident began. A feedwater malfunction and relief-valve failure initiated the accident before dawn.
Loss-of-coolant accident : An accident in which coolant escapes from a reactor system faster than it can be replaced. A stuck relief valve let primary coolant escape while operators misread the resulting conditions.
Babcock & Wilcox : An American engineering company that designed nuclear steam supply systems, including the one used at Three Mile Island Unit 2. Its reactor design shaped the equipment and control-room conditions involved in the accident.
Institute of Nuclear Power Operations : A U.S. industry organization established in 1979 to promote excellence in nuclear plant operation. The accident spurred its creation to improve training, operating practices, and peer evaluation.
Three Mile Island evacuation advisory : Governor Richard Thornburgh’s March 30, 1979 advisory that pregnant women and preschool children leave the area near Three Mile Island. The advisory reflected uncertainty and confusion about possible radioactive releases.
Pilot-operated relief valve : A valve that opens when pilot pressure reaches a set point, relieving pressure in a system. Unit 2’s valve stuck open, creating an undetected coolant leak.
Nuclear Regulatory Commission : The United States federal agency responsible for regulating civilian nuclear power and nuclear materials. It had assumed responsibility for reactor safety regulation shortly before the accident.
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