Chernobyl accident, was a catastrophic nuclear accident. It occurred on 25–26 April 1986 in the No. 4 light water graphite moderated reactor at the Chernobyl Nuclear Power Plant near the now-abandoned town of Pripyat, in northern Ukrainian Soviet Socialist Republic, Soviet Union, approximately 104 km north of Kiev.
During the accident, steam-blast effects caused two deaths within the facility: one immediately after the explosion, and the other compounded by a lethal dose of radiation. Over the coming days and weeks, 134 servicemen were hospitalized with acute radiation sickness (ARS), of which 28 firemen and employees died in the days-to-months afterward.
The Chernobyl accident is considered the most disastrous nuclear power plant accident in history, both in terms of cost and casualties.