On 26 April 1986, reactor 4 of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian SSR, Soviet Union, exploded. With dozens of direct casualties and thousands of health complications stemming from the disaster, it is one of only two nuclear 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.