Most of the nuclear fission stuff that is simple enough that you might hope to analyze with back-of-the-envelope QM has so much energy that it tends to act like a classical particle of negligibly short wavelength (but not enough energy to bring QM back into the picture by QED creating new particles upon collision). And while there is probably various quantum mechanical stuff deeply involved in a power reactor in one way or another --- e.g., electrical conductivity tends to involve band theory, and water is often used as a working fluid and at a fundamental level its thermal properties depend on stuff like hydrogen bonds --- I doubt it was helpful for a naval nuclear reactors guy to try to analyze things at that level in the middle of the last century.