Uranium that has not been in a reactor is almost nonradioactive and inert. It only gets spicy after you let it go critical for a while, and fission products acc

Uranium that has not been in a reactor is almost nonradioactive and inert. It only gets spicy after you let it go critical for a while, and fission products accumulate. Any reasonable nuclear-powered craft would not start up the reactor until it's already in a nice, safe, high orbit.