Predicting spatially dependent reaction rate for problem with nonuniform temperature distribution by subgroup method

The subgroup methods based on partial cross section fit scheme (PXSFS) and simplified partial cross section fit scheme (SPXSFS) are proposed in this paper to treat problems with non-uniform temperature distribution. These methods fit the cross sections at different temperatures as partial cross sections and share a same set of subgroup probabilities. The new methods are compared to the pre-existing methods: conventional subgroup method (CSM), the correlation model (CM), the subgroup level adjustment scheme (SLAS) and the number density adjustment scheme (NDAS). The numerical results show that the new methods can better predict the spatially dependent reaction rates than pre-existing methods. Within the new methods, the simplified scheme consumes less computation time and is more numerically stable. Additionally, the superhomogenization (SPH) correction method is studied, which is used to treat the multi-group (MG) equivalence effect. It is found that the subgroup-one-group (subgroup-1G) calculation can fully capture the MG equivalence effect.