If Russia really wanted to create nuclear fallout problems, they have weapons that do so far more targeted and effectively.

But they can't "easily" blame such Weapon usage on the EU (saying they accidentally caused it) or "Ukraine" terrorists.

I assume its to make sure no one in the Ukraine makes a dirty bomb, not the other way around. Revenge is a powerful motivator and Chernobyl has the raw materials to make for a horrific revenge.

It'd be easier to cover up by claiming it was an accident or they were fired on by the Ukranians. You don't really have the same leeway when you drop a nuke.

True - but Russia has nuclear weapons which are more precise and would send the strongest possible message. This is also important because destroying a country might land you a victory, but if it's destroyed, that is a shallow victory. A well-placed nuke is scary and controlled.

Russia would never nuke Ukraine because of the reaction from the West. Using existing radioactive materials wouldn't provoke the same reaction.

I'm not saying Russia will do anything here, but the two are very different from a geopolitical standpoint.