It boggles me that any country in the 21st century would attempt to build such a horrifyingly irresponsible machine, geopolitics be damned.

This thing is basically a dirty bomb on an unstoppable cruise missile. Any reactor powerful enough to drive a thing like that is going to make a big radioactive mess wherever it lands. There's no safe way to test it, either - you can use a dummy warhead, but you can't use a dummy reactor.

Also, clearly such a thing must be air-cooled, which means the moment you have a launch failure, you have a meltdown on your hands (dollars to doughnuts something like that happened here). Just developing such a thing is going to cause a huge raft of nuclear incidents.