The Chernobyl disaster was a nuclear reactor accident in the Chernobyl Nuclear Power Plant in the Soviet Union. It was the worst nuclear power plant accident in history.

On 26th April 1986 a nuclear reactor at the Chernobyl plant exploded. Further explosions and the resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area. Nearly thirty to forty times more fallout was released than had been by the atomic bombings of Hiroshima and Nagasaki.

Large areas in Ukraine, Belarus, and Russia were badly contaminated, resulting in the evacuation and resettlement of over 336,000 people.

The accident raised concerns about the safety of the nuclear power industry.