Axial Function Based on an Asymmetric 4-Point Finite Difference Method for 3D MOC/DD Neutron Transport Calculations

Abstract

The Three-Dimensional Method of Characteristics/Diamond-Difference (3D MOC/DD) method serves as an advanced numerical technique in reactor physics, addressing the limitations inherent in traditional two-step approaches and full three-dimensional methods when performing high-fidelity reactor core analysis. This thesis proposes a novel axial function to replace the conventional axial function derived from the basic central 2-point finite difference method applied in the 3D MOC/DD approach. The new axial function is derived from an asymmetric 4-point finite difference method that utilizes the information from both the previous and current meshes. The verification of the new axial function is performed using STREAM (Steady-state and Transient REactor Analysis code with Method of Characteristics), a neutron transport analysis code. The direct 3D transport calculation capability of STREAM is implemented based on the 3D MOC/DD method. The contents of this thesis are as follows: (1) Derivation of a new axial function for the 3D MOC/DD method using an asymmetric 4-point finite difference method, (2) Detailed implementation of the axial function in STREAM, and (3) Verification and performance analysis through various 3D benchmark problems.