Abstract
Recent efforts have focused on improving the performance of the 2D/1D subplane implementation in MPACT. One of the developments recently added, presented here, focuses on treating spacer grids using a subgrid approach within each subplane, avoiding the extra computation and potentially improving stability issues that can be present by explicitly modeling the spacer grid with a separate MOC plane. From the cases analyzed, it seems that the approach does a sufficient job of maintaining the accuracy of explicitly meshing the spacer grid (<10 pcm and <1% max pin power error) while offering relatively modest performance gains. Overall, the success of the approach with spacer grids opens up possibilities to apply similar approaches to other structural components, particularly those in the axial reflectors to reduce the number of MOC planes and overall computational burden.
