Chernobyl Nuclear Accident

From Wikipedia:

The Chernobyl disaster was a nuclear reactor accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine (then part of the Soviet Union). It is considered to be the worst nuclear power plant disaster in history and the only level 7 event on the International Nuclear Event Scale. It resulted in a severe release of radioactivity following a massive power excursion that destroyed the reactor. Most deaths from the accident were caused by radiation poisoning.
On April 26, 1986 at 01:23 a.m. (UTC+3) reactor number four at the Chernobyl plant, near Pripyat in the Ukrainian Soviet Socialist Republic, exploded. Further explosions and the resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area. Four hundred times more fallout was released than had been by the atomic bombing of Hiroshima.[2]
The plume drifted over large parts of the western Soviet Union, Eastern Europe, Western Europe, and Northern Europe, with some nuclear rain falling as far away as Ireland. Large areas in Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people. According to official post-Soviet data,[3] about 60% of the radioactive 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 number of years while forcing the Soviet government to become less secretive.[4]
The countries of Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. It is difficult to accurately quantify the number of deaths caused by the events at Chernobyl, as over time it becomes harder to determine whether a death has been caused by exposure to radiation.

http://en.wikipedia.org/wiki/Chernobyl_disaster