Not really ukraine already has sufficient nuclear material expertise and equipment to build a plutonium based nuke. The power plants are mostly irrelevant except for dirty bomb type destruction. Its the nuclear waste reprocessing that is almost identical to the processes of refining a critical mass of plutonium. Stick that in a tube with 2 regular bombs and boom u got a nuke. Refining the plutonium is the hard part and ukraine has got that covered. Once u got the plutonium u can probably build a nuke in cave with a box of scraps.