A VC I'm familiar with is in two modular fission reactor ventures. I was generally skeptical about a future for fission reactors, but it behooved me to learn. Among the things I learned is that there is a huge distance between making a small reactor and making a reactor of any size that can run unattended or with minimal supervision. Taking a reactor out of a nuclear powered submarine just gets you the small reactor bit. Much of what new gen fission projects do is to make reactors easy and safe to operate.

Submarines are run by a crew of trained specialists at all kinds of high stakes systems, including the reactor.