LFTRs make readily-available (liquid-form) weapons-grade Uranium-233 during protactinium separation. They're the least proliferation resistant reactor known to man.
LFTR has a far larger core than a PWR. Neutron diffusion length in water is 5 cm. In LFTR graphite moderator it's 16.
Many reactors including modern SMR LWRs can cool themselves passively without backup power. Especially when floating in seawater.
Highly recommend doing PWRs for this application.
Disclaimer: I'm trying to do this with PWRs.