In 1986, the Chernobyl disaster occurred in Ukraine, then part of the Soviet Union. A safety test at the Chernobyl Nuclear Power Plant's Reactor 4 went horribly wrong. The explosion released huge amounts of radioactive particles. Nearby Pripyat, home to the plant workers, was severely contaminated. Soviet authorities initially tried to cover up the disaster. 

The explosion spread radiation beyond the USSR, forcing evacuations. Over 100,000 people were displaced, and many suffered health effects. The disaster led to long-term environmental damage. It highlighted flaws in nuclear safety and government secrecy. Chernobyl remains a symbol of nuclear risks and the collapse of the Soviet Union.