Chernobyl Nuclear Disaster; World's Worst Civil Nuclear Power Accident

On April 26, 1986, a reactor at the Chernobyl Nuclear Power Plant in Ukraine, then part of the Soviet Union, exploded during a safety test. The explosion and subsequent fire released massive amounts of radioactive particles into the atmosphere, which spread over much of the western USSR and Europe. The disaster caused immediate deaths, long-term health issues for thousands, and the permanent evacuation of an exclusion zone. It remains the most disastrous nuclear power plant accident in history in terms of cost and casualties.