Everything within a 30-kilometer radius will be completely destroyed, including the three remaining reactors at Chernobyl.
The entirety of the radioactive material in all of the cores will be ejected at force and dispersed by a massive shock wave, which will extend approximately 200 kilometers and likely be fatal to the entire population of Kiev as well as a portion of Minsk.
The release of radiation will be severe and will impact all of Soviet Ukraine, Latvia, Lithuania, Byelorussia, as well as Poland, Czechoslovakia, Hungary, Romania, and most of East Germany.
For much of the area, a nearly permanent disruption of the food and water supply, a steep increase in the rates of cancer and birth defects.
For Byelorussia and the Ukraine, "impact" means completely uninhabitable for a minimum of 100 years.