Calculation of multi-group migration areas in deterministic transport simulations

Recent work on the Cumulative Migration Method (CMM) has demonstrated that it is possible to define multi-group transport cross sections directly from Monte Carlo spectral calculations by utilizing edits of the energy-dependent neutron migration areas. However, it is difficult to demonstrate that downstream deterministic transport calculations actually preserve Monte Carlo migration areas. This paper addresses this issue by: 1) demonstrating the relationship of migration area with the concept of mean squared displacement, 2) deriving, and validating vs. Monte Carlo, an analytic expression for computing one-group migration areas for a homogeneous medium with energy-independent cross sections, 3) deriving, and validating vs. Monte Carlo, an analytic expression for computing multi-group migration areas for a homogenized medium with energy-dependent cross sections, and 4) rigorously proving that energy condensation of multi-group transport cross section must be inverse flux weighted in order to preserve Monte Carlo neutron migration areas. Published by Elsevier Ltd.