I’d love to see the physics of a nuclear reactor providing thrust. If it converts heat to steam, the amount of water necessary to convert to steam and power a missile would require so much water and so large a reactor, it wouldn’t get off the ground.
The principle behind the nuclear ramjet was relatively simple: motion of the vehicle pushed air in through the front of the vehicle (ram effect), a nuclear reactor heated the air, and then the hot air expanded at high speed out through a nozzle at the back, providing thrust.
https://en.wikipedia.org/wiki/Project_Pluto