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.
Following the accident, Ukraine continued to operate the remaining
reactors at Chernobyl for many years. The last reactor at the site was
closed down in 2000.
The accident raised concerns about the safety
of the Soviet nuclear power industry as well as nuclear power in
general, slowing its expansion for a number of years while forcing the
Soviet government to become less secretive about its procedures.
Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination
and health care costs of the Chernobyl accident. Fifty deaths, all
among the reactor staff and emergency workers, are directly attributed
to the accident. It is estimated that there may ultimately be a total
of 4,000 deaths attributable to the accident, due to increased cancer