Kyshtym disaster
The Kyshtym disaster (Russian: Кыштымская авария), sometimes referred to as the Mayak disaster or Ozyorsk disaster in newer sources, was a radioactive contamination accident that occurred on 29 September 1957 at Mayak, a plutonium reprocessing production plant for nuclear weapons located in the closed city of Chelyabinsk-40 (now Ozyorsk) in Chelyabinsk Oblast, Russia in the Soviet Union. The disaster is the second worst nuclear incident by radioactivity released, after the Chernobyl disaster, and was regarded as the worst nuclear disaster in history until Chernobyl.