1957 radiological contamination disaster in the Soviet Union. The Kyshtym disaster, 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 production site for nuclear weapons and nuclear fuel reprocessing plant located in the closed city of Chelyabinsk-40 in Chelyabinsk Oblast, Russian SFSR, Soviet Union. The disaster was the second worst nuclear incident after the Chernobyl disaster. It measured as a Level 6 disaster on the International Nuclear Event Scale, making it the third highest on the INES, behind Chernobyl and the Fukushima Daiichi nuclear disaster which are both Level 7 on the INES. At least twenty-two villages were exposed to radiation from the Kyshtym disaster, with a total population of around 10,000 people evacuated. The disaster spread hot particles over more than 52,000 square kilometres, where at least 270,000 people lived. There were no immediate reported casualties as a result of the explosion the scope and nature of the disaster was covered up both internally and abroad, and even as late as 1982, Los Alamos published a report concluding that the release was actually caused by a weapons test gone awry. Medvedev's description of the disaster in the New Scientist was initially derided by Western nuclear industry sources, but the core of his story was soon confirmed by Professor Lev Tumerman, former head of the Biophysics Laboratory at the Engelhardt Institute of Molecular Biology in Moscow.