A Linear Prolongation Approach to Stabilizing CMFD

In this paper, we propose a new prolongation method to replace the conventional flat flux ratio–based scaling approach of coarse-mesh finite difference (CMFD) for updating the flux. The new prolongation method employs a linear interpolation of the scalar flux differences at the coarse-mesh cell edges between the neutron transport and CMFD calculations. This linear prolongation scheme, called lpCMFD, can greatly improve the stability of CMFD, particularly for problems with large optical thickness. A detailed convergence study of lpCMFD based on Fourier analysis and numerical testing shows that lpCMFD is unconditionally stable and effective for a wide range of optical thicknesses.