A two-dimensional modal method for spatial rehomogenization of nodal cross sections and discontinuity-factor correction

We propose a two-dimensional (2-D) modal approach for spatial rehomogenization of nodal cross sections in light water reactor analysis. This algorithm aims to synthesize the variation in the 2-D intranodal distributions of the few-group flux and directional net currents between the core environment and the infinite-lattice approximation. Assembly discontinuity factors are also corrected. The method is validated on a broad set of pressurized-water-reactor benchmark problems. Its accuracy is assessed on both nodal quantities and the reconstructed pin-by-pin flux and power distributions. We show that the errors in the effective multiplication factor and assembly-averaged fission power significantly decrease compared to the calculation with infinite-medium homogenization parameters. In most cases, an improvement is also found at the pin level. A thorough discussion follows, which addresses the use of the 2-D neutron current information to compute the transverse-leakage distribution for the transverse-integrated nodal equations, the potential dual application of the method for rehomogenization and dehomogenization, and the quantification of the contributions of various environmental effects (spatial, spectral, and cross energy-space) to homogenization errors.