This month marks the 30th anniversary of Chernobyl disaster. It is the worst nuclear power plant accident in history. On 26 April 1986, reactor four suffered a catastrophic power increase, leading to explosions in its core. In the first days after the explosion more than 115 thousand people were evacuated within a 30 kilometers radius. The explosion and fire threw hot particles of the nuclear fuel forming a radioactive cloud on the night of the explosion that covered Ukraine, some parts of Russia and Belarus. The cloud traveled across Europe as well.