The Method of Characteristics (MOC) has seen wide interest in full-core reactor physics analysis due to its computational efficiency and ability to easily treat complex geometries. Recently, the OpenMOC reactor physics code was extended to include 3D MOC capability. In this study, we present verification for the 3D MOC solver in OpenMOC and sensitivity of 3D MOC to the axial geometry discretization and axial track laydown. Results for the Takeda Model 1 benchmark show excellent agreement with the reference eigenvalues. A sensitivity study was conducted on a UO [subscript 2] quarter-assembly extracted from the C5G7 3D unrodded benchmark geometry in order to show the effect of the axial MOC parameters on the solution eigenvalue for a heterogeneous problem. The sensitivity results demonstrated that the solution accuracy was highly dependent on the axial source region discretization, but insensitive to axial spacing between tracks below ~0.2 cm. Using the equal angle quadrature set, at least 10 and 18 polar angles were required to converge the problem to with 100 and 10 pcm, respectively. These results both verify the 3D MOC solver in OpenMOC and provide inUnited States. Office of the Assistant Secretary for Nuclear Energy (Nuclear Energy Uni- versity Programs Fellowship)Center for Exascale Simulation of Advanced Reactors (Contract No. DE-AC02-06CH11357
