Sourcing extraterrestrial Nuclear fuel

> If anyone knows of an extraterrestrial process for
> concentration that I don't know of, please speak up.

I think (but must admit my understanding of the science involved here is
risible) that all radioactive material was originally formed in the core of
particularly large stars, and then dispersed when the star goes
super-nova... (big stars are like that... ;)
Those radioactive elements can later be captured by other clouds and become
part of new stars and new planets. Because of that, heavy elements like
uranium should also exist, at least as trace, in all celestial bodies.
My knowledge of geology is also extremely superficial, but I was under the
impression that uranium is naturally occurring in the Earth crust, in much
larger quantities than on meteorites but still at a very low concentration,
and that most igneous rock contains higher concentrations, but still much
less than uranium ores, is all this dependant on the existence of water
then?
I hope Thor can explain better the issue to uneducated people like me in
simple words... :)

What about radioactive gases? Any chance to find radon in space? Would it
possible to use radon a nuclear fuel anyway?

In any case, it would seem that if there are ET nuclear fuels they are
hardly easy and economical to use. Given we have loads of that stuff here at
home, I'd guess we will be shipping the stuff up for a long time... after
all an Atlas payload of plutonium can probably power a hundred cyclers for a
century... :)

Cheers,

Claudio