My general impression of the original nuclear powered aircraft project in the US is that it wasn't necessarily infeasible to make a flying reactor, but shielding for anyone on board would be too heavy, and ultimately there was no real mission that required it so it was cancelled.
If you suspend the reactor from a cable 1000 feet below the aircraft, it doesn't need shielding. That might be more practical for an aircraft above Venus. It could keep the air in a balloon warm.
A helicopter or balloon with an unshielded nuke reactor hanging below it, that never needs to land, seems pretty cool.
