Results for the C5G7 3-D Extension benchmark using the discrete ordinates code PANDA

We present solutions of the 3-D Extension C5G7 benchmark using the discrete ordinates SN code PANDA. The problem is a 3-D heterogeneous LWR core calculation with different levels of control rod insertion. It was devised by the OECD/NEA Expert Group on 3-D Radiation Transport Benchmarks. In the present paper we describe the numerical methods used in these calculations. Considering parallelization, the first submitted results were obtained using an energy decomposition technique, since then, more accurate new results have been obtained using a 3-D spatial decomposition parallel method. For geometry and material modeling on a regular 3-D orthogonal mesh, a volume fraction method is employed for mixed material cells treatment. Numerous calculations were performed in order to study the eigenvalue and pin wise fission rates convergence as a function of spatial and angular mesh refinements. Accurate 3-D solutions of the heterogeneous reactor benchmark require a high level of spatial and angular discretization leading to huge calculations in terms of CPU time and memory requirements.