On Tuesday April 26th 1986 an explosion and fire at the Chernobyl nuclear power plant in Ukraine(Former USSR) released enormous quantities of radioactive contaminants into the atmosphere of western USSR and Europe.

This is considered to be the worst nuclear disaster in history, being one of only 2 events to be classified as level 7 events on the International Nuclear Event Scale. The second level 7 event being the Fukushima Daiichi nuclear disaster 20th April 2011.