Right now there's no real answer for disposal of carbide (VHTR/PBR) or fluoride (MSR) fuels. Geological disposal and reprocessing are credible for today oxide fuels, but not for these. A fuel damage incident happened at the Oak Ridge MSR about 30 years after it was shut down -- radiolysis caused the production of F gas, which in turn caused the production of UF6, which migrated out of the drain tanks into carbon traps. There were no serious consequences, but enough U233 was involved that there could have been a criticality accident.
There is a grassroots thorium movement behind the MSR these days -- they're a bunch of smart, wonderful, and idealistic people but they're running against a headwind. The U.S. government is not interested in radical innovation in the nuclear space because it may open up new paths to proliferation. I think the most credible MSR concept is Moir and Teller's idea of having clusters of reactors built in huge underground bunkers. Small, modular reactors are exciting, but I find it hard to believe that online reprocessing would be practical for something small that isn't being watched over by a team of specialists.
Prehaps I'm a dinosaur but I till think FBRs on the plutonium cycle may have a market in the long term. It would take a long time for this to replace the LWR because of the slow rate Pu gets generated, but the amounts of Pu available in spent fuel would be sufficient to open up new markets for small modular reactors that are highly proliferation resistant. (A sodium fire probably kills you if you try to open it up, and then there's so much Pu240 you'll never make a bomb of it)
There is a grassroots thorium movement behind the MSR these days -- they're a bunch of smart, wonderful, and idealistic people but they're running against a headwind. The U.S. government is not interested in radical innovation in the nuclear space because it may open up new paths to proliferation. I think the most credible MSR concept is Moir and Teller's idea of having clusters of reactors built in huge underground bunkers. Small, modular reactors are exciting, but I find it hard to believe that online reprocessing would be practical for something small that isn't being watched over by a team of specialists.
Prehaps I'm a dinosaur but I till think FBRs on the plutonium cycle may have a market in the long term. It would take a long time for this to replace the LWR because of the slow rate Pu gets generated, but the amounts of Pu available in spent fuel would be sufficient to open up new markets for small modular reactors that are highly proliferation resistant. (A sodium fire probably kills you if you try to open it up, and then there's so much Pu240 you'll never make a bomb of it)