1MW Molten-Salt Test Reactor by Copenhagen Atomic for €88k [video]
To the best of my understanding, one of the main reason that MSRs have not gone to market is that the salts are so corrosive that containment over the long term is not currently possible.  Note the questions about materials, alloys, and flow sensors in the video.<p>ORNL had fully functional reactors in the 60's, but those reactors were only safe to operate for a few years, and they were at lower temperatures than what we are targeting today.  Liquid fluoride thorium salts at 700+ C will readily dissolve chromium, which makes working with stainless very difficult.  Other common alloying agents are susceptible to radiation (Co & Ni transmute when irradiated) which further shortens the lifespan.  There is also the issue of tritium, which can permeate stainless steels, cause embrittlement, and escape into the environment.<p>ORNL developed Hastelloy N to help address these issues, and there is an effort to certify other structural steels to for use in reactors (316H, 800H, inco 617).  None of the studies that I have seen indicate that any of these metals will survive for more that 5 years or so.