Basically the PoD is that either Brezhnev is granted five more years of life or he notices that his time is short and appoints a hardliner with a similar mindset, that with his support manages to gather enought votes to replace him on the aftermath.
When the Chernobyl desaster happens, a very sickly and old Brezhnev or a close headed hardliner are succesfully deceived by the local administration, thus the problem goes unproperly adressed until the chemical clouds are detected in western europe, and the government still acts in denial trying to push that it was a explosion of a water tank and not of the nuclear reactor. Eventually the radiation breaks the base of the reactor going underground and infecting the water supply of Kiev, then infecting the dnieper river and moving from it until the black sea. What happens on the aftermath?
When the Chernobyl desaster happens, a very sickly and old Brezhnev or a close headed hardliner are succesfully deceived by the local administration, thus the problem goes unproperly adressed until the chemical clouds are detected in western europe, and the government still acts in denial trying to push that it was a explosion of a water tank and not of the nuclear reactor. Eventually the radiation breaks the base of the reactor going underground and infecting the water supply of Kiev, then infecting the dnieper river and moving from it until the black sea. What happens on the aftermath?