Three-dimensional variational nodal method parallelization for pin resolved neutron transport calculations

Hybrid parallelization of the three-dimensional variational nodal method (VNM) for pin-resolved neutron transport calculations is presented. Sets of node-energy response and associated matrices are assigned evenly to the available set of MPI processors and OpenMP is further employed to parallelize integrations over angle in the response matrix formation. Parallelization of the solution algorithm is accomplished using non-overlapping domain decomposition with one MPI processor assigned to each subdomain. Additionally, the red and black subdomain iterations of the within-group equations are parallelized by OpenMP. Only the pre-calculated matrix sets needed in a subdomain are stored in the corresponding processor. This parallel solution strategy preserves the block Gauss-Seidel red-black iterations employed in serial calculation, with data transfer between processors only after each red and black iteration. Partitioned matrix acceleration is implemented in a similar manner.