Liquid Fuels vs Solid Fuels

LFTR is one particular kind of liquid fueled reactor that converts Th232 to U233 and burns that. However, liquid fueled reactors can burn or convert and burn U233 (converted from Th232), U235, and Pu239 (converted from U238). They are very flexible. But, the big advantage is that because they use fluid fuels, the fuel stays in the reactor until is all burned/converted & burned. This leaves only shorter lived fission products regardless of which fuel is used. Solid fuels on the other hand, must remove the fuel and reprocess it after burning every 3% of the fuel or so. Reprocessing of conventional LWR fuel is very expensive, even though it is fairly easy to separate the UO2 from the clad. That gets much more difficult and expensive if we try to get rid of zirconium based fuel to eliminate the hydrogen production and something like a ceramic TRISO fuel system like in gas reactors. Ceramic fuels are much more expensive to reprocess. To say we will spend that cost every 3% burn up even in fast reactors where you get a little more burn up, is still very expensive. Solid fuels are very limited in how much burn up they can withstand before the fission product gasses damage it too much to be able to cool it and it needs replaced. That reprocessing also produces an enormous waste stream because the reprocessed fuel has to be diluted dramatically to prevent inadvertent criticality. Generally, it would also be very costly to design solid fuels to accomodate small amounts of transuranics beyond Pu, so that would probably still be waste and that is the long lived stuff that is typically of concern.