Improved two-level p-CMFD acceleration in neutron transport calculation

This work verifies the cause of slow convergence for optically thick coarse mesh cell sizes when coarse mesh based acceleration is applied to the neutron transport criticality calculation. To overcome the limitation, the present paper introduces two two-level iterative schemes to speedup coarse mesh based acceleration. In the schemes, a fine mesh based acceleration with the fixed source is augmented in a coarse mesh based acceleration with the fission source. These techniques are applied to the partial current-based coarse mesh finite difference (p-CMFD) method, that is a more stable acceleration method than other coarse mesh based acceleration methods. Simple analyses of numerical problems show that the techniques enhance the convergence speed of p-CMFD, especially for optically thick coarse mesh cells. (authors)