Nuclear and Radiation Accidents: (3) 1986 Chernobyl Disaster: Main articles: Chernobyl disaster and Chernobyl disaster effects. Map showing Caesium-137 contamination in Belarus, Russia, and Ukraine as of 1996. The Chernobyl disaster was a nuclear accident that occurred on 26 April 1986 at the Chernobyl Nuclear Power Plant in Ukraine. An explosion and fire released large quantities of radioactive contamination into the atmosphere, which spread over much of Western USSR and Europe. It is considered the worst nuclear power plant accident in history, and is one of only two classified as a level 7 event on the International Nuclear Event Scale (the other being the Fukushima Daiichi nuclear disaster). The battle to contain the contamination and avert a greater catastrophe ultimately involved over 500,000 workers and cost an estimated 18 billion rubles, crippling the Soviet economy. The accident raised concerns about the safety of the nuclear power industry, slowing its expansion for a number of years. UNSCEAR has conducted 20 years of detailed scientific and epidemiological research on the effects of the Chernobyl accident. Apart from the 57 direct deaths in the accident itself, UNSCEAR predicted in 2005 that up to 4,000 additional cancer deaths related to the accident would appear "among the 600 000 persons receiving more significant exposures (liquidators working in 1986-87, evacuees, and residents of the most contaminated areas)". Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl disaster. Eleven of Russia's reactors are of the RBMK 1000 type, similar to the one at Chernobyl Nuclear Power Plant. Some of these RBMK reactors were originally to be shut down but have instead been given life extensions and uprated in output by about 5%. Critics say that these reactors are of an "inherently unsafe design", which cannot be improved through upgrades and modernization, and some reactor parts are impossible to replace. Russian environmental groups say that the lifetime extensions "violate Russian law, because the projects have not undergone environmental assessments"