From what I understand, TRISO is more about reactor safety than proliferation. A proliferating entity could easily ground up the particles and chemically leech

From what I understand, TRISO is more about reactor safety than proliferation. A proliferating entity could easily ground up the particles and chemically leech the useful fissile material, they need to do enrichment anyway which is orders of magnitude more difficult. A good anti-proliferation design are traveling wave U238 fast breeders. They are filled with depleted uranium and breed plutonium 239, but, due to the long residence time in the reactor, the isotopic vector is heavily polluted with things like Pu240 which spontaneous fissions reducing the yield, Pu238 which generates massive heat etc. This reactor grade plutonium is completely worthless as a bomb material and would require reprocessing that is even more difficult then enrichment of natural Uranium. Alas, none of the TWR proposals (CANDLE, Terrapower etc.) ever made it into production.