The disaster began during a systems test on 26 April 1986 at reactornumber four of the Chernobyl plant, which is near the town of Pripyat. There was a sudden power output surge, and when an emergency shutdown was attempted, a more extreme spike in power outputoccurred, which led to a reactor vessel rupture and a series of explosions. This event exposed the graphite moderator of the reactor to air, causing it to ignite. The resulting fire sent a plumeof highly radioactive smoke fallout into the atmosphere and over an extensive geographical area, including Pripyat. The plume drifted over large parts of the western Soviet Union, EasternEurope, Western Europe, and Northern Europe. Large areas in Ukraine, Belarus, and Russia were evacuated, and over 336,000 people were resettled. According to official post-Soviet data, about60% of the fallout landed in Belarus.
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 numberof years and forcing the Soviet government to become less secretive about its procedures.[notes 1]
Russia, Ukraine, and Belarus have been burdened with the continuing and substantialdecontamination and health care costs of the Chernobyl accident. More than fifty deaths are directly attributed to the accident, all among the reactor staff and emergency workers. Estimates of thenumber of deaths potentially resulting from the accident vary enormously; the World Health Organization suggest it could reach 4,000 while a Greenpeace report puts this figure at 200,000 or more.