Convergence studies using method of characteristics solver for the reduced-moderation water reactor model

Convergence studies and Sensitivity analyses are an important computational objective required for observing the fuel behaviour with respect to the reactor physics integration parameters. In this paper, reactor physics integration parameters have been analysed for the Reduced-Moderation Water Reactor (RMWR) using method of characteristics (MoC) deterministic code WIMS in order to observe the effect on criticality while investigating the sensitivity of these parameters. The efficient converged results of RMWR lattice can be obtained by using the higher angular approximation. Sensitivity analyses are, therefore, performed for the candidate fuels: Pu-UO₂ and Th-UO₂ for the RMWR fuel assembly. Deterministic code WIMS solves the multigroup neutron transport equations using a characteristics method that integrates the transport equation over characteristic directions. WIMS integrates the differential form of the Boltzmann transport equation along explicit tracks through the geometry which goes in a straight line; reflect off the sides of the model. This characteristics method can be utilised only to those geometries for which tracking routines can be written. Therefore, this paper investigates and discusses the effect of various integration parameters such as mesh, polar angle, azimuthal angle and tolerance on criticality value in WIMS. Two types of RMWR fuel assembly models: 1D Axial slab model and 3D lattice models are investigated for this Convergence studies in order to observe the consistency/discrepancy of the integration parameters.