Parallelization of Characteristics Solvers for 3D Neutron Transport

In this paper, recent advances in parallel software development for solving neutron transport problems are presented. Following neutron paths along their characteristics, these solvers use ray tracing techniques to collect the local angular flux components. Due to the excessive number of tracks in the demanding context of 3D large-scale calculations, reliable acceleration techniques are shown in order to obtain fast iterative solvers. The load balancing strategies include a global round-robin distribution of tracks, an approach where we forecast the calculation load implied by each track length and a macro-band decomposition where tracks crossing the same regions are grouped together. The performance of the PVM implementations for these various track distributions are analyzed for realistic applications.