Neutron Anisotropic Scattering Effect in Heterogeneous Cell Calculations of Light Water Reactors

Abstract

A study on the anisotropic scattering effects in heterogeneous square cells of light water reactors has been performed using the characteristics method. It was found that the effects of the anisotropic scattering were relatively large for the MOX fuel cell because of the large neutron current from the moderator to the fuel region and the k inf value by the P0 calculation became 0.10–0.16% larger than that by the P5 calculation. With the transport correction, the k inf difference from the P5 calculation became even larger than that from the P0 calculation and the k inf value by the transport correction became 0.18–0.25% larger than that by the P5 calculation for the MOX fuel cell. The transport corrected self-scattering cross sections of the moderator region become smaller than the non-transport corrected ones and the angular flux distribution becomes more anisotropic with the transport correction. Therefore, more neutrons toward the moderator region between the fuel pellets can slow down to the lower energy region with the transport correction. As a result, the k inf value by the transport correction becomes larger than that by the P0 calculation, which is opposite effect to that by the P5 calculation.