For the record an RTG was recovered from the seabed after a launch failure intact - and then relaunched! https://rps.nasa.gov/about-rps/safety-and-reliability/

I'm sure the same can be done for nuclear reactor fuel. Even better actually, as reactor fuel is basically just a very expensive and pure heavy metal & only slightly radioactive. Only once the reactor is first started all sorts of unstable radiation releasing elements are formed in the fuel.

So if you only start the reactor once it is in space & pack the fuel securely for launch, all should be good to go! :-)