A study on effects of pin cell homogenization in an actual reactor core geometry - 040

In this paper, the effects of homogenization inside a pin cell in core calculation were firstly investigated. The homogenization effects, sometimes referred as heterogeneity effect, were well studied in single or multi-assembly geometry. This is the first study of the effect in a core geometry. It is found that no remarkable effects were observed for UO₂ and MOX fuel assemblies. However significant power variation due to underestimation of reactivity of Gd fuel assembly was observed. Therefore correction of spatially homogenized cross section has to be incorporated. The feasibility to reproduce calculation results by heterogeneous calculation within the framework of pin-by-pin homogeneous calculation has been investigated. The cell-average group constants were prepared by the SPH method so that reaction rates can be preserved between precise heterogeneous model and simple homogeneous model. It was found that assembly-wise power distributions in 3-loop type PWR cores obtained by pin-by-pin homogeneous SP3 calculations agreed with those by reference heterogeneous calculations with ∼1% of R.M.S. error. (author)