Polynomial axial expansion in the Method of Characteristics for neutron transport in 3D extruded geometries

Abstract

Recently a solver based on the Method Of Characteristics (MOC) for 3D extruded geometries has been developed in the APOLLO3® project [1]. In this method the domain is divided in regions and the Step Characteristics (SC) approximation is used in each of them to represent the solution of the transport problem. Since the biggest degree of heterogeneities is found along the radial direction, the idea proposed in this paper is to keep the SC approximation to compute the solution over the radial plane and to implement a polynomial expansion of the flux along the vertical direction. In fact the results of the previous works [1] show that the flux gradient along the z axis are likely to be represented by a classical polynomial basis. In this paper we weigh up the benefits of using a less refined mesh.