Claim: The Chernobyl disaster was a catastrophic nuclear accident.

The Chernobyl disaster , also referred to as the Chernobyl accident , was a catastrophic nuclear accident . It occurred on 26 April 1986 in the No. 4 light water graphite moderated reactor at the Chernobyl Nuclear Power Plant near Pripyat , in what was then part of the Ukrainian Soviet Socialist Republic of the Soviet Union -LRB- USSR -RRB- .   During a late night safety test which simulated a station blackout power-failure and in which safety systems were deliberately turned off , a combination of inherent reactor design flaws , together with the reactor operators arranging the core in a manner contrary to the checklist for the test , eventually resulted in uncontrolled reaction conditions that flashed water into steam generating a destructive steam explosion and a subsequent open-air graphite fire.Although most reports on the Chernobyl accident refer to a number of graphite fires , it is highly unlikely that the graphite itself burned . According to the General Atomics website < http://gt-mhr.ga.com/safety.php > : `` It is often incorrectly assumed that the combustion behavior of graphite is similar to that of charcoal and coal . Numerous tests and calculations have shown that it is virtually impossible to burn high-purity , nuclear-grade graphites . '' On Chernobyl , the same source states : `` Graphite played little or no role in the progression or consequences of the accident . The red glow observed during the Chernobyl accident was the expected color of luminescence for graphite at 700 ° C and not a large-scale graphite fire , as some have incorrectly assumed . '' Similarly , nuclear physicist Yevgeny Velikhov , < http://news.bbc.co.uk/2/hi/europe/4918742.stm > noted some 2 weeks after the accident that `` Until now the possibility of a catastrophe really did exist : A great quantity of fuel and graphite of the reactor was in an incandescent state '' That is , all the nuclear-decay heat that was generated inside the uranium fuel -LRB- heat which would normally be extracted by back-up coolant pumps , in an undamaged reactor -RRB- was instead responsible for making the fuel itself and any graphite in contact with it , to glow red-hot . This is contrary to the oft cited interpretation , which is that the graphite was red-hot chiefly because it was chemically oxidizing with the air . This fire produced considerable updrafts for about 9 days , that lofted plumes of fission products into the atmosphere , with the estimated radioactive inventory that was released during this very hot fire phase , approximately equal in magnitude to the airborne fission products released in the initial destructive explosion . Practically all of this radioactive material would then go on to fall-out/precipitate onto much of the surface of the western USSR and Europe .   The Chernobyl accident dominates the Energy accidents sub-category , of most disastrous nuclear power plant accident in history , both in terms of cost and casualties . It is one of only two nuclear energy accidents classified as a level 7 event -LRB- the maximum classification -RRB- on the International Nuclear Event Scale , the other being the Fukushima Daiichi nuclear disaster in Japan in 2011 . The struggle to safeguard against scenarios which were , at many times falsely , perceived as having the potential for greater catastrophe and the later decontamination efforts of the surroundings , ultimately involved over 500,000 workers and cost an estimated 18 billion rubles . During the accident , blast effects caused 2 deaths within the facility and later 29 firemen and employees died in the days-to-months afterward from acute radiation syndrome , with the potential for long-term cancers still being investigated .   The remains of the No. 4 reactor building were enclosed in a large sarcophagus -LRB- radiation shield -RRB- by December 1986 , at a time when what was left of the reactor was entering the cold shut-down phase ; the enclosure was built quickly as occupational safety for the crews of the other undamaged reactors at the power station , with No. 3 continuing to produce electricity into 2000 .   The accident motivated safety upgrades on all remaining Soviet-designed reactors in the RBMK -LRB- Chernobyl No. 4 -RRB- family , of which eleven continued to power electric grids as of 2013 .