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 P 0 calculation became 0.10-0.16% larger than that by the P 5 calculation. With the transport correction, the k inf difference from the P 5 calculation became even larger than that from the P 0 calculation and the k inf value by the transport correction became 0.18-0.25% larger than that by the P 5 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 P 0 calculation, which is opposite effect to that by the P 5 calculation.

Simplified Treatments of Anisotropic Scattering in LWR Core Calculations

“…Calculation results in the pin-cell geometry and differences from the reference (P3) results are shown in Table 1. As in the previous studies, 1,2) the transport approximations (both the in-scatter and out-scatter approximations) overestimate k-infinity for all types of fuel. Especially, a positive bias is clearly observed in the high-Pu-content MOX fuels.…”

“…The maximum order of the anisotropic scattering matrix is assumed to be P3 based on the results of previous studies. 1,2) A more detailed explanation about the calculation condition will be given in section III.…”

“…However, the recent studies suggest that the consideration of higher order anisotropic scattering is important in some situations, e.g., MOX fuel-loaded or high-leakage small cores. [1][2][3][4] Therefore, recent advanced neutronics codes gradually take into account the higher order anisotropic scattering. [3][4][5]7) Especially, the utilization of the method of characteristics (MOC) allows an easy incorporation of the higher order anisotropic scattering in LWR analyses.…”

“…There are several studies that discuss the impact of transport corrected cross sections. 1,2,4,8,9,12) However, systematic investigation on the simplified treatments of the anisotropic scattering has not been carried out in an LWR configuration to the best of the authors' knowledge.…”

Convergence Improvement of Coarse Mesh Rebalance Method for Neutron Transport Calculations

“…In this section, the GCMR method is implemented to the NELAT code. 13) The NELAT code is a neutron transport code utilizing the characteristics method and mainly applied to LWR cell or assembly calculations. The NELAT code has several features, e.g.…”