From what I recall from my nuclear industry days, thorium had already been rejected as "uneconomical" by the nuke industry, although it was held in reserve as a fuel for the far distant future. And It's reasssuring to know that it's fission products have short half-lives and are less of a threat. What I don't understand is how the thorium reaction can make other fission products from previous uranium fission "burn up", and how those materials will not act as reaction poisons by absorbing or scattering stray neutrons.

From a safety (not arms control) point of view, it's not the heavy nuclei like Pu and U that are dangerous, it's the fission products like Ba,
I, Hf, and several others. These should not be affected at all by the neutron flux in the reactor. Is there a nuclear physicist in the house?