Like.... LFTR
Basically, the normal operation of the reactor doesn't allow the production of weapons-useful nuclear isotopes.
You'll probably also need a smaller footprint reactor
Like.... LFTR
And you'll want something that can be turned on, shut off, and has natural anti-meltdown abilities in case hurricanes or other disasters threaten the ractor
Like ... LFTR
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.
https://www.quora.com/Why-do-so-many-people-claim-thorium-br...
I'm no expert on U enrichment, but if there's even just a little U-232 that mixes in with the U-233 then the gamma rays get pretty hard to handle? I guess the breeding process might produce a lot of pure U-233, but again to the point of the quora response... not a lot of U-233 was used in "real" weapons.
I've never heard of MSRs being "large". The ORNL one fit in a closet, but that wasn't a breeder from thorium AFAIK. The penetration doesn't matter much if you have a blanket of Thorium to intercept neutrons.