This reminds me of something I read about the Vulcan strategic bombers:

After dropping their bombs on Russia they were supposed to fly to North Africa and land on airstrips because England was expected to be gone.

I'm convinced that nuclear salt water rockets would be safe to operate in space. And a much better idea than Orion.

I mean even the "worst" of all designs, the one linked in the comment we're all replying to(SLAM - ramjet design) says this:

" Specifically, he states "The reactor radiations, while intense, do not lead to problems with personnel who happen to be under such a power plant passing overhead at flight speed even for very low altitudes." In both documents, he describes calculations that prove the safety of the reactor and its negligible release of fission products compared to the background. Along the same vein of these calculations, the missile would be moving too quickly to expose any living things to prolonged radiation needed to induce radiation sickness. This is due to the relatively low population of neutrons that would make it to the ground per kilometer, for a vehicle traveling at several hundred meters per second. Any radioactive fuel elements within the reactor itself would be contained and not stripped by the air to reach the ground"

Orion is obviously incredibly bad due to the fact it uses actual nuclear detonations for prepulsion. But it's never been a very serious project, while SLAM has been built and tested.