On 26 April 1986, the unthinkable happened near the Ukrainian town of Pripyat: two massive steam explosions ruptured No. 4 Reactor at the Chernobyl Nuclear Power Plant, immediately killing 30 people and setting off the worst nuclear accident in history.
The explosions were followed by an open-air reactor core fire that released huge amounts of radioactive contamination into the atmosphere for the next nine days, spreading across the Soviet Union, parts of Europe, and especially neighbouring Belarus, where around 70% of the waste landed.
The following clean-up operation involved more than half a million personnel at a cost of $68 billion, and a further 4,000 people were estimated to have died from disaster-related illnesses in the following 20 years.