Preliminary investigation on the sodium fast reactor concave cores with near‐zero or negative sodium void reactivity

Abstract

A preliminary investigation on the sodium fast reactor (SFR) concave cores was conducted with the aim of obtaining near-zero or negative sodium void reactivity (SVR). The geometry of the MOX fueled 750 MWe Japanese Sodium Fast Reactor (JSFR) core is transformed into concave cores by maintaining the same power level and heavy metal fuel inventory. The inner and outer core (with axial blanket in the lower part) configuration is maintained as in the original JSFR but the height of the inner core was set lower than the outer core to improve the SVR. Also a short inner blanket (20 cm thick) is inserted into the inner core for the same purpose. Radial blanket with the same height is also adopted as in the original JSFR to maintain the breeding ratio. In this investigation, the MOX fuel composition for the fresh fuel does not contain minor actinides. JOINT-FR code system with JENDL-4.0 library is used for neutronics, burnup, kinetics parameters as well as temperature and SVR calculations in 2-D R-Z geometry multigroup diffusion approximation. Several candidates of concave cores with favorable near-zero or negative SVR have been found whose burnup performance is comparable with the original JSFR core.