Actually in the Cold War there were some actual nuclear reactors in space:

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor#TOPAZ-I

> This could be mitigated by sending only components of the reactor and assembling it in space.

How would that help? The main problem if the launch fails is that the radioactive material will spread around (in the worst case, they are encased so exactly that doesn’t happen).

You could maybe spread out the nuclear material in multiple launches but you would just increase the risk of a small contamination in exchange for a smaller risk of a large contamination.

I don’t think the individual parts of the reactor are intrinsically safer than the reactor, it’s not like it’s going to become an atomic explosion during launch.