meltdown

The melting of the core of a nuclear reactor, due to overheating.

To prevent such accidents all reactors have equipment intended to flood the core with water in an emergency. The reactor is housed in a strong containment vessel, designed to prevent radiation escaping into the atmosphere. The result of a meltdown would be an area radioactively contaminated for 25,000 years or more.

At Three Mile Island, Pennsylvania, USA, in March 1979, a partial meltdown occurred caused by a combination of equipment failure and operator error, and some radiation was released into the air. In April 1986, a reactor at Chernobyl, near Kiev, Ukraine, exploded, causing a partial meltdown of the core. Radioactive fallout was detected as far away as Canada and Japan. Dozens of people died in the immediate aftermath of the disaster, and thousands more will probably die prematurely of radiation-induced cancers in the longer term, according to an IAEA estimate.