Reactors that have not yet been started do not contain that much radioactivity actually, nuclear detonation creates a lot of gunk during the energetic phase due

Reactors that have not yet been started do not contain that much radioactivity actually, nuclear detonation creates a lot of gunk during the energetic phase due to neutron activation and similar processes. Also you can presumably shield reactors to survive reentry or even ship the fuel in multiple such reentry proof containers. And of course longer term build these in space, given nuclear propulsion is basically in space only anyway given its characteristics.