[elhigh]

Somebody came up with an idea for a hafnium fueled nucleonic reactor for powering a turbine. Its radiocontamination would have been marginal. And the shielding requirement is a lot lower too, so it's light enough to actually, you know, fly. I think I saw that in Popular Science a few years ago. <researches> Can't find it.

I also saw a concept for a huge - seriously, makes Hindenburg look like a minnow - dirigible that would use a nuclear power plant for propulsion. Since a dirigible's power requirements are so much lower (little to no energy required to generate lift, for instance) and the aircraft so large, the plant's more modest ratings and physical separation from crew and passengers also limit the exposure to radiation. I have that in a book but don't have a scanner to upload a picture, sorry.

Using hydrogen for a lifting gas would also add to the shielding. Yes, there are certain risks associated with that.