Three Mile Island, site of a nuclear power plant 10 mi (16 km) south of Harrisburg, Pa. On Mar. 28, 1979, failure of the cooling system of the No. 2 nuclear reactor led to overheating and partial melting of its uranium core and production of hydrogen gas, which raised fears of an explosion and dispersal of radioactivity. Thousands living near the plant left the area before the 12-day crisis ended, during which time some radioactive water and gases were released. A federal investigation, assigning blame to human, mechanical, and design errors, recommended changes in reactor licensing and personnel training, as well as in the structure and function of the Nuclear Regulatory Commission. The accident also increased public concern over the dangers of nuclear power and slowed construction of other reactors; no new reactors were approved for construction following the accident until 2012. See also nuclear energy.