The purpose of the Mayak Production Association facility was to produce plutonium for nuclear weapons. In its earlier years of operation, exposures to radiation were significantly higher than at other similar facilities. Mayak was one of the largest nuclear facilities in the Russian Federation, and was formerly known as Chelyabinsk-40 and later as Chelyabinsk-65. It was the site of the Kyshtym disaster (1957) when a storage tank explosion released 50-100 tons of high-level radioactive waste, contaminating a 290 square mile area in the eastern Ural mountains, causing radiation sickness and death. The event was rated 6 "serious accident" on the 7-level INES nuclear incident/accident scale. The incident received little attention, as it was kept secret for 30 years. Many laborers who worked at the plant during the 1950s and 1960s died from exposures to radiation. The accident was first reported in 1976 by Zhores Medvedev in the journal New Scientist, it was in 1992 that the Russian government officially acknowledged the accident.