Breeding performance improvement of Th- 233 U fueled, Sodium-cooled fast reactor with low void reactivity

Generally, an FBR (fast breeder reactor) core with U-Pu fuel has flat geometry to enhance a neutron leakage and reduce a sodium void reactivity. Thus, the neutron economy isn’t good in the FBR core. Although the η value of U-Th fuel is smaller than U-Pu fuel in a fast spectrum, that of U-Th fuel has smaller energy dependence than Pu-U fuel. Then, if we use U-Th fuel for FBR, the sodium void reactivity will be decreased. In addition, we possibly can extend a core height to enhance the neutron economy [1]. In this paper, we assume to use a Th-UO2 fuel for an FBR core to achieve a low void reactivity. We adjust the reactor specifications to obtain the optimized aspect ratio (core height/diameter) under the design constraint conditions which are quoted from Pu-U fueled JSFR. However, the breeding ratio is aimed at 1.0 as a first step. To obtain the exact breeding ratio, the effects of cooling time and loss in reprocessing etc. should be considered. Those are not treated in the present study, and they are the future tasks.