The idea is that you get unlimited range and an (almost) unlimited loiter time. If this would ever work, they could be cruising 24x7 and then sent in for surprise attacks. Didn’t work for us when we tested years ago. Too dirty with the radiation. Nuclear engines are just flying dirty bombs waiting for an accident.
They would also shine like huge beacons and be vulnerable to simultaneous takedowns by anti missile fire. If the Pentagon deems Russia reaching success with these things the Pentagon will be working hard on countermeasures which will be successfully developed before the Russkies have their devices up. These are not the doomsday weapons the Russians would like us to believe.