The Kyshtym disaster was a radiation contamination incident
that occurred
on 29 September 1957 at Mayak, a nuclear fuel
reprocessing plant in Russia (then a part of the Soviet Union). It measured as a Level 6 disaster
on the International Nuclear
Event Scale, making
it the third most serious
nuclear accident ever recorded (after the Chernobyl disaster, and Fukushima Daiichi
nuclear disaster, both
Level 7 on the INES scale). The event
occurred in the town of Ozyorsk, a closed city built around the Mayak
plant. Since Ozyorsk/Mayak (also known as Chelyabinsk-40 and Chelyabinsk-65)
was not marked on maps, the disaster was named after Kyshtym, the nearest known town.