Minimization of U-232 content in advanced high-conversion multirecycling thorium reactors by blanket fragmentation

Abstract

The handling of recovered Th-232 is perhaps the most important problem in thorium breeder reactors due to the presence of the undesirable nuclide U-232 and its daughter Th-228. In advanced multirecycling reactors with high conversion ratios, the amount of this nuclide might reach 5000 ppm after several rounds of recycling, an amount that is almost 50-fold higher than that in conventional PWRs resulting in very high remote reprocessing costs. A reduction of U-232 via a reduction of the fast neutrons available for the (n,2n) reaction by increasing the moderator is not a feasible option in advanced reactors because of the loss in conversion. In this paper the possibility to minimize U-232 by blanket fragmentation while maintaining both the fuel-to-volume moderator volume ratio and amount of material is analyzed. The result show that reductions of up to 10% are feasible with an associated -reduction of the reprocessing cost.