The nuclear reactor after the disaster. Reactor 4 (center). Turbine building
(lower left). Reactor 3 (center right).On April 26, 1986, reactor number four at the
Chernobyl plant, near Pripyať in the Ukrainian Soviet Socialist Republic, had a
meltdown. The resulting fire sent a plume of radioactive fallout into the
atmosphere and over an extensive geographical area, including the nearby
town of Pripyat. The plume drifted over large parts of the western Soviet Union,
Eastern Europe, Western Europe, and Northern Europe. Large areas in Ukraine,
Belarus, and Russia had to be evacuated, with over 336,000 people resettled.
According to official post-Soviet data,[2] about 60% of the fallout landed in
Three Mile Island

The accident began at 4:00 a.m. on Wednesday, March 28, 1979,
with failures in the non-nuclear secondary system, followed by a
stuck-open pilot-operated relief valve (PORV) in the primary
system, which allowed large amounts of reactor coolant to