On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian SSR, Soviet Union, exploded. With dozens of direct casualties, it is one of only two nuclear energy accidents rated at the maximum severity on the International Nuclear Event Scale, the other being the 2011 Fukushima nuclear accident. The response involved more than 500,000 personnel and cost an estimated 18 billion rubles. It remains the worst nuclear disaster and the most expensive disaster in history, with an estimated cost of
US$700 billion.