Robust relaxation-free multiphysics simulation via power-iteration-level-coupled CMFD acceleration in MPACT

This paper describes a new multiphysics iteration scheme for coarse mesh finite difference (CMFD) accelerated transport problems where the multiphysics feedback is coupled with the low-order diffusion equation at the power iteration level. The power-iteration-level- coupled CMFD (X-CMFD) is demonstrated to improve the stability of the CMFD-accelerated transport schemes involving feedback. The X-CMFD method is described and optimized for implementation in the neutron transport code MPACT based on the existing CMFD solvers. The numerical results show that the performance of the X-CMFD method is consistent regardless of the presence or type of feedback. (authors)