Small nuclear reactors in space make a tremendous amount of sense technically. Almost the perfect power source. I understand that political and environmental opposition have mostly focused around the dangers of getting the nuclear fuel into space in the first place.
I believe people object by saying that rockets going into orbit explode in a non-trivial percentage of launch attempts.
So the objection goes that getting nuclear fuel into space would almost inevitably involve (eventually, anyway) an accident that would scatter nuclear fuel.
I’m unclear that such an accident would actually pose significant risk to anyone on Earth. But I haven’t looked into the matter very deeply.