Kyshtym disaster

The Mayak combine is responsible for the appearance of a radioactive cloud over Europe in 2017.

An excerpt from the article 42 facts about Kyshtym disaster

A large area of the European Union was contaminated with the radioactive isotope ruthenium-106. Luckily, small amounts of the isotope did not adversely affect the health of European residents. The Russians have denied reports by scientists and analysts, claiming that the contamination occurred due to the failure of an orbiting satellite.