Three Mile Island Unit-2 nuclear power plant ( 40° 9'18.22"N, 76°43'24.82"W), located on the Susquehanna River in central Pennsylvania, was the site of one of the worst nuclear reactor accidents in U.S. history on March 28, 1979. The accident started at 4 am when the water pumps that supplied the steam generators of the plant stopped abruptly. The subsequent lack of steam was detected by the plant's safety system which then automatically shut off the steam turbine powering the generator.
As a result, pressure began building up in the nuclear reactor of the plant, causing the core of the reactor to substantially heat up until at least half of it had melted in the beginning stages of the accident. The plant was experiencing problems because of a lack of coolant, that, if adequately supplied, would have controlled the overheating.
Fortunately, the majority of the radiation released from the accident was contained within the plant. The radiation that did manage to escape only caused negligible harm to human health and the environment.
The three primary causes of the Three Mile Island nuclear accident included mistakes made by employees, faulty plant design, and the breakdown of key elements in the proper operation of the plant. This accident altered public perception of the nuclear industry and the Nuclear Regulatory Commission (NRC). The public began to lose trust in nuclear power.
This public shift would ultimately change the way the NRC did business. After the accident at Three Mile Island, the NRC substantially restructured their management practices of U.S. nuclear power plants, created stricter rules, and extended their control. Although these changes eased the public's fears somewhat, they were not enough to secure the future success of the U.S. nuclear industry. The last order for a new nuclear power plant in the U.S. had been made nearly six years earlier in 1973. As a result of the accident at Three Mile Island, this trend continued and no new plants have been built in the U.S. in over three decades.