To this day I'm terrified by this concept - so much that I would frankly rather have nukes detonated behind a ship for propulsion. :P But yeah, if it could be made to work, it has some serious benefits!
On a related note, lets also look at the nuclear salt-water rocket - arguably the king of crazy (yet theoretically viable) on the nuclear rocket field right now:
What is so terrifying about that? It could be the middle way between fission as we know it, and fusion as we can't do reliably/practically(as of now). Just need some superconducting magnets to tame and stop the fusing uranium hexaflouride from touching the fused silica walls :-)
The exhaust is clean, because the system is closed.
Also it reminds me of some descriptions of so called 'Vimanas' which occur in old Indian scriptures, and nerdy people from today tried to reconstruct/reverse engineer/remimagine what's described in there.
And this fits, perfectly so.
Edit: I think of this as even more terrifying thant that saltwater thing:
Indeed, this is also very clever and actually sounds quite doable (still I wonder about how much radiation it will give off when running - probably quite a bit! :D) when compared to some of the other concepts.
Actually, I kinda think it demonstrates we really are not done with nuclear engines & even better, more crazy and higher performance propulsion methods will show up. And also, we really need to finally start building some of them them! :)
Like, even some simple NERVA or NEP would be at least a start. :)
On a related note, lets also look at the nuclear salt-water rocket - arguably the king of crazy (yet theoretically viable) on the nuclear rocket field right now:
https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket