Interface current method for PHWR cluster geometry with anisotropy in the angular flux at interfaces

Abstract

A method based on combination of interface current formalism and first-flight probabilities was previously developed for solving the integral transport equation for cylindricalized lattice cells of pressurized heavy-water reactors (PHWRs), where only double- P 0 expansions (i.e. isotropic angular flux) were considered for the angular flux at various interfaces. It was found necessary to choose the correct mesh-spacing in the moderator to get good results. In order to resolve this problem, we have considered the anisotropy in the angular flux by expanding it in spherical harmonics in two half-spaces (double- P N or DP N approximation). Terms up to P 2 expansion can be considered in it. The results of present method in one-group and 27-groups, under various approximations of angular flux, have been compared with the exact collision probability ( P ij ) method for clusters by using the same mesh-spacing in the moderator for both methods. It is found that the results corresponding to DP 1 expansion of angular flux agree well with the P ij method. However, results corresponding to DP 2 expansion can be taken as standard. Even with this, the computer time taken is very much less compared to the P ij method.