U-233: is this inaccurate?
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.