I doubt the Ukrainians have the resources to develop their own from scratch, but could be wrong.
Ukraine has four nuclear power plants; three of them are west of the Dnieper River.
I’d be a lot more worried about the Russian “loose nukes” than whatever the Ukraine might be able to do. Before its collapse in 1991, the Soviet Union had more than 27,000 nuclear weapons and enough weapons-grade plutonium and uranium to triple that number. Between rampant corruption, theft, and sabotague/bribed employees the likelihood of some being on the black market is non-zero. But I guess if Bin Laden couldn’t afford the price, Kiev can’t either.