Coarse-Mesh Angular Dependent Rebalance Acceleration of the Method of Characteristics in x-y Geometry

As the nuclear reactor core becomes more complex, heterogeneous, and geometrically irregular, the method of characteristics (MOC) is gaining popularity in neutron transport calculations. However, the long computing times require good acceleration methods. In this paper, the concept of coarse-mesh angular dependent rebalance (CMADR) acceleration is described and applied to the MOC calculation in x-y geometry. The method is based on the angular-dependent rebalance factors defined on coarse-mesh cell boundaries. A coarse-mesh cell may consist of several fine-mesh cells that can be heterogeneous and of mixed geometries with irregular or unstructured mesh shapes. The CMADR acceleration is tested on several test problems, including problems with strong material heterogeneity, and the results show that CMADR is very effective in reducing the number of iterations and the computing times of MOC calculations.