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. An improperly stored underground tank of high-level liquid nuclear waste exploded, contaminating thousands of square kilometers of land, now known as the Eastern Ural Radioactive Trace (EURT). The matter was covered up, and few either inside or outside the Soviet Union were aware of the full scope of the disaster for nearly two decades. 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. It is the only disaster classified as Level 6 on the International Nuclear Event Scale (INES). It is the third worst nuclear disaster by population impact after the two Level 7 events: the Chernobyl disaster, which resulted in the evacuation of 335,000 people, and the Fukushima Daiichi disaster, which resulted in the evacuation of 154,000 people. At least 22 villages were exposed to radiation from the Kyshtym disaster, with a total population of around 10,000 people evacuated. Some were evacuated after a week, but it took almost two years for evacuations to occur at other sites. The disaster spread hot particles over more than 52,000 square kilometres (20,000 sq mi), where at least 270,000 people lived. Since Chelyabinsk-40 (later renamed Chelyabinsk-65 until 1994) was not marked on maps, the disaster was named after Kyshtym, the nearest known town.