Russia divested itself of Ukraine not long after the Chernobyl disaster. It gave the Russians a degree of separation from that mess. Now that that has been entombed, they want the Ukraine back (along with its resources, which include uranium, among other things). With the 'green' agenda likely to shift to nuclear power, those known resources could important to Russia, if they can take them. Besides, if you spill some, it takes the right gear to even know it is there.