5 Kiloton tactical nukes won’t contaminate much of anything for long.
Chernobyl released at least 1,000X that amount.
Red herring.
Anyway.
If Russia has to use nukes trying to score a few points against Ukraine. Politically it would make Russia look very weak. The world’s second army incapable of wining “mano to mano” against a few Ukrainians. It would prove to the world Russias conventional army is a failure. And that in turn would result in the beginning of the dislocation of the Russian federation. As we all know there are many Russian regions in its federation wanting to break away, becoming their own country.
They are just waiting for the Kremlin system to become sufficiently weakened.