The Kyshtym disaster

A 1957 accident at the Mayak nuclear facility in the Southern Urals that spread radioactive fallout and led to mass evacuations. It was kept secret, and the regional press guessed that the glow seen in the sky on 29 September was the northern lights.

Thomas Rabl, writing for the Environment & Society Portal of the Rachel Carson Center, says that on 29 September 1957, late in the day, people in the Chelyabinsk district saw strange bluish-violet colours overhead. Regional papers guessed at polar lights seen unusually far south. Within days the government was busy around the military zone that held the Mayak nuclear plant. Rabl says farmers had to kill their animals, bury their harvest and plough their land, and that more than 20 villages with over 11,000 inhabitants were cleared and razed.

Gazeta.ru reported in 2017 that the newspaper Chelyabinsky Rabochy ran a short item on 6 October 1957 that said nothing about an accident; Gazeta.ru's headline calls the accident a disaster passed off as the northern lights. Wikipedia says that because Mayak was secret, people in the affected area were at first kept in the dark, and that on 6 October an evacuation of around 10,000 people began, with still no reason given. Rabl's count of people moved and Wikipedia's differ.

Standring, Dowdall and Strand, in a 2009 review of doses and health near Mayak, put the release at about 740 PBq, around 90 per cent of which came down close to the site. The rest, about 74 PBq, went up in a plume thought to have reached roughly 1 km and was carried north-north-east by the wind. It left a band of contamination the authors call the EURT, about 300 km long and 30 to 50 km wide, with strontium-90 at twice the level of global fallout or more.

In 1990 a commission of the Soviet atomic energy ministry ruled that material on radiation at nuclear fuel plants and the land around them, including the Mayak area, the Techa River and its floodplain, would now be open, along with demographic, epidemiological and health data on local people and plant staff. The decision is transcribed, with the site's own commentary, by the advocacy site Ural Chernobyl: Tragedy of Tatars. None of these sources gives a firm count of deaths from the accident.