What about a Radio-Thermal Generator like on the Voyager probes? Not as powerful, Not as radioactive but power for a century of use?
If only we could build a plane that could stay airborne that long.
But I have to say using a nuclear reactor for a passager aircraft is just a waste of a good reactor use it for a reuseable launch platform for space plane launches like in 2001 (the novel not the movie).
__________________
 
|