[stevep98]

The smaller nuclear reactors used on submarines and aircraft carriers would be of the appropriate size, but they generate electricity using steam turbines. I don't think that would be workable in space. You'd need massive radiators to radiate away a lot of that heat to recondense the steam.

If you're generating that much heat, then you're probably better off using the nuclear reactor to directly heat the propellant.

Joe Scott has a new video up about Nuclear propulsion: https://www.youtube.com/watch?v=K5UU0GA5GAU