Chernobyl disaster Chernobyl disaster The Chernobyl disaster, also referred to as the 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 north of Kiev. The event occurred during a late-night safety test which simulated a station blackout power-failure, in the course of which safety systems were intentionally turned off. A combination of inherent reactor design flaws and the reactor operators arranging the core in a manner contrary to
Effects of the Chernobyl disaster were involved in the cleanup of the 30 km evacuation zone around the reactor, but many of them entered the zone two years after the disaster. Estimates of the number of "liquidators" vary; the World Health Organization, for example, puts the figure at about 600,000; Russia lists as liquidators some people who did not work in contaminated areas. In the first year after the disaster, the number of cleanup workers in the zone was estimated to be 2,000. These workers received an estimated average dose of 165 millisieverts (16.5 REM). A sevenfold increase in DNA mutations has been identified in