It happened in Ukraine in 1986 (was part of the USSR at that time). Horrible catastrophe that changed the life of millions in Eastern and Western Europe. The Chernobyl accident is considered the 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 (the maximum classification) on the International Nuclear Event Scale, the other being the Fukushima disaster in Japan in 2011(according to Wiki)
From what I've been told by my father, who still lives in the Ukraine and who is miraculously evaded from being sent as a liquidator to deal with the consequences of the reactor explosion, the Soviet government didn't announce any information about the terrifying disaster and extremely high health risks associated with radioactive exposure. People who were sent to liquidate the disaster didn't know that they were sentenced to death. Moreover radioactive clouds spread radioactive waste and pour radioactive rains many miles away from the epicenter, thus affecting almost a half of the globe.
I've personally found this show as a well directed historical drama with a pretty accurate representation of the tragic events of that time.
