The Chernobyl disaster was a well-known nuclear accident of catastrophic proportions that occurred on 26 April 1986, at the Chernobyl Nuclear Power Plant in Ukraine (then in the Ukrainian Soviet Socialist Republic, part of the Soviet Union). It is considered the worst nuclear power plant accident in history and is the only level 7 event on the International Nuclear Event Scale.
The disaster occurred on 26 April 1986, 1:23 A.M., at reactor number four at the Chernobyl plant, near the town of Pripyat, during an unauthorized systems test. A sudden power output surge took place, and when an attempt was made at an emergency shutdown, a more extreme spike in power output occurred which led to the rupture of a reactor vessel as well as a series of explosions. This event exposed the graphite moderator components of the reactor to air and they ignited; the resulting fire sent a plume of radioactive fallout into the atmosphere and over an extensive area, including Pripyat. The plume drifted over large parts of the western Soviet Union, and much of Europe. As of December 2000, 350,400 people had been evacuated and resettled from the most severely contaminated areas of Belarus, Russia, and Ukraine. According to official post-Soviet data, up to 70% of the fallout landed in Belarus.
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