If I remember correctly, the main problem with nuclear powered airplanes is the amount of radiation the crew would be exposed to - but logically, I'm thinking that has more to do with the form-factor of aircraft itself not having the capacity for proper shielding. I'm only guessing at this because nuclear powered submarines exist, so that must mean it can reasonably be pulled off given enough size. That being said, assuming you wanted to build an enormous relatively stationary object (a building) that's supposed to remain airborn indefinitely, then nuclear power would be the way to go. This brings up another question though........I wonder if dependable turbines and propellers can be built for this kind of task? How long can they continuously run without risk of failure at some point? This would definitely require huge amounts of redundancy. Maybe a Zeppelin type design would work?
