I’d imagine it’s not doable because of how quickly they’d develop insane amounts of heat.

Wasn’t Trump literally trying to bring it back last time?

https://whyy.org/articles/trump-wants-to-make-asbestos-great-again/

Diesel subs are also different kinds of beasts. They’re terrible for international conflict, but for short range operations, they’re silent. You can turn off a diesel engine, but not a nuclear reactor.