Evaluation of time dependent neutron transport algorithms using 2D modular ray tracing MOC

Abstract

Three algorithms for solving the multigroup time dependent neutron transport in two dimensions utilizing the method of characteristics (MOC) are developed in this study. These algorithms are distinguished base on the average angular flux calculation along the characteristic line (track) and the applied approximation to the angular flux time derivative. Since the calculation of the scalar flux in the characteristics method requires the average angular flux along the track, two approaches for implementation of track averaged angular flux are presented. In the first approach, the effect of the angular flux in the previous time step as an extra term added to the source is considered. Second, the average angular flux is applied similar to the common method used in the steady state form. Moreover, two states for the angular flux time derivative in implementing the transient neutron transport solution are considered. First, the angular dependency of the angular flux in time derivative is preserved. Second, isotropic scalar flux approximation is applied to the time derivative.Considering the vital role of ray tracing and improving the non-physical disturbances effect caused by ray tracing methods, the latest modular ray tracing (MRT) method is utilized for the transient calculation. For verification, the well-known TWIGL benchmark is modeled and the results are compared with MPACT and DeCART codes. Additionally, the heterogeneous benchmark problems MOXK_2G and MOXK_7G are simulated and the results are compared with DeCART and VARIANT_K codes.