Kyshtym disaster

The Kyshtym disaster 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 in the Soviet Union. It measured as a Level 6 disaster on the International Nuclear Event Scale (INES), making it the third most serious nuclear accident ever recorded, behind the Fukushima Daiichi nuclear disaster and the Chernobyl disaster (both Level 7 on the INES). The event occurred in the town of Ozyorsk, Chelyabinsk Oblast, a closed city built around the Mayak plant. Since Ozyorsk/Mayak (named Chelyabinsk-40, then Chelyabinsk-65, until 1994) was not marked on maps, the disaster was named after Kyshtym, the nearest known town.

After World War II, the Soviet Union lagged behind the US in development of nuclear weapons, so it started a rapid research and development program to produce a sufficient amount of weapons-grade uranium and plutonium. The Mayak plant was built in haste between 1945 and 1948. Gaps in Soviet physicists' knowledge about nuclear physics at the time made it difficult to judge the safety of many decisions. Environmental concerns were not taken seriously during the early development stage. Initially Mayak was dumping high-level radioactive waste into a nearby river, which flowed to the river Ob, flowing further down to the Arctic Ocean. All six reactors were on Lake Kyzyltash and used an open cycle cooling system, discharging contaminated water directly back into the lake. When Lake Kyzyltash quickly became contaminated, Lake Karachay was used for open-air storage, keeping the contamination a slight distance from the reactors but soon making Lake Karachay the "most polluted spot on Earth".

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