Frankly I don't see why people speak of Russia using nukes against the Ukraine. Afaik Putin only mentioned nukes in regards to "other powers" (aka the US, mostly) interfering. Which isn't a first in Russia-US relations (both sides had alluded to "being forced" to use nukes, if the other attacked - at different eras, of course).
No nuclear power (at least of the serious ones) will use nukes against a non-nuclear power. It only happened once, with vastly inferior atomic weapons, against Japan, in the end of a massive world war.
By the way, those atomic bombs didn't play a role in Japan capitulating. Russia declared war on them, and that played a massive role (they guessed that if they didn't immediately sign peace with the US, part of Japan would become soviet).