Kyshtym nuclear disaster

On September 29, 1957, the cooling system failed in an underground tank holding about 70 to 80 tonnes of highly radioactive liquid waste at the Mayak plant near the closed city of Chelyabinsk-40 (now Ozyorsk) in the southern Urals. The waste dried out and heated until it exploded with the force of many tonnes of TNT, throwing off the tank's concrete lid. About 20 million curies of radioactivity were released, and a plume carried part of it northeast, contaminating a strip of land about 300 kilometers long known as the East Urals Radioactive Trace. Around 270,000 people lived in the contaminated zone; more than 20 villages were evacuated and bulldozed, many of them days or weeks later.¹²⁴

Mayak had been built in haste to produce plutonium for the Soviet atomic bomb, with waste handling an afterthought. The accident was rated level 6 on the international scale, second only to Chernobyl and Fukushima. The Soviet government kept it secret, naming it after the nearby town of Kyshtym because the plant's city did not officially exist. The Soviet scientist Zhores Medvedev described it in the West in 1976, and Moscow admitted the accident only in 1989. American intelligence had learned of it years earlier but said little in public, a choice historians still argue about.¹³