Chernobyl

The accident at Chernobyl occurred on April 25th, 1986 in Ukraine. Lack of experience by the people working at the nuclear reactor and the shut down down process being carried out incorrectly led to an unstable condition. Several people died from the immediate explosion, and the clean up following the accident due to extreme radiation doses

http://www.world-nuclear.org/info/chernobyl/inf07.html