If they ride up to aspirant stairs with the EU, soon there would be a country again rising of the ashes.

EU is no elixir, though.

That's a fair point in general. Exploding all nuclear reactors in Ukraine isn't going to do that though.

And, of course, Russia could do much blowing up with conventional weapons, too.

Just one nuclear reactor can be used to create continent wide Red forest. Chornobyl disaster was just an incident without evil intent. Small fraction of nuclear fuel was released into atmosphere. With evil intent, much larger percent of nuclear fuel can be turned into thin dust and released into atmosphere. Larger reactors contain much more nuclear fuel. With evil intent, much more radioactive elements, such as radioactive iodine or radioactive noble gases, can be breed in reactor before blow up. With evil intent, safety systems can be disabled to produce maximal amount of dangerous elements. Depending on time given for preparation and technique used, it can be from 1 Fukushima to 10k Chornobyls. If NATO will give initiative to Russians, they can blow up reactor in good weather, so RF will not be affected, but EU will gone.

Maybe. I am sure you can do more damage, if you optimize for that, than an accident would do.

However: for a nuclear power like Russia, blowing up nuclear reactors only makes sense if they can make it look like an accident.

Otherwise: just use your nukes.