A nuclear power-station near Kiev in Ukraine, the site in 1986 of the worst nuclear accident in the world to date. 31 people died trying to fight subsequent fires, and many more received radiation burns or suffered from associated diseases. The accident was the result of unauthorized experiments by the operators of one of the four reactors, in which safety systems were deliberately circumvented in order to learn more about the plant’s operation. Fallout from the explosions, containing the radioactive isotope caesium-137, affected large areas of Europe. In particular, livestock in high-rainfall areas received unacceptable doses of radiation. In the mid-1990s large areas of land in Ukraine, Belarus, and south-west Russia were still contaminated and high levels of cancer (especially leukaemia in children) were reported. The power-station was closed when its last nuclear reactor was shut down in 2000.