April 26, 1986
Widely regarded as the worst nuclear disaster in history—and the only one to be classified a level 7 "
major accident" on the International Nuclear Event Scale—the catastrophe occurred during a systems test at reactor No. 4 at the Chernobyl plant near the town of Pripyat in the former Ukrainian Soviet Socialist Republic. A sudden power surge led the nuclear reactor to rupture, creating a series of violent explosions and eventually sending a plume of radioactive dust into the atmosphere, covering not only Pripyat, but large parts of the western Soviet Union and Europe. Four hundred times more radioactive material was released than the atomic bombing of Hiroshima, and the Soviet government initially tried to cover up the incident. It wasn't until workers at the Forsmark Nuclear Power Plant in Sweden—approximately 680 miles from Chernobyl—found radioactive particles on their clothes that the USSR admitted the disaster had taken place. Only 50 deaths—all reactor staff and emergency workers—have been directly attributed to the accident, but a
U.N. report says the incident will ultimately claim as many as 4,000 deaths.