Investigation of coarse mesh acceleration methods for the S_N nodal method in unstructured geometries

The S_N nodal method with unstructured nodes is an effective approach for modeling the complicated geometries in solving the neutron transport equation. However, it hits an efficiency bottleneck when triangular nodes are adopted in the modeling. Against this backdrop, this study investigated acceleration methods for the S_N nodal method based on unstructured coarse meshes to address the efficiency problem. To achieve this, the study first proposed a coarse mesh generation algorithm from arbitrary triangular meshes. Then, various CMFD schemes, including pCMFD, odCMFD, and gCMFD, were developed. The proposed method can process regular triangular meshes in structured geometries of hexagonal and rectangle assemblies, as well as arbitrary triangular meshes generated in unstructured geometries using the Delaunay triangulation method. A set of eigenvalue problems with various mesh counts and geometry types was selected to verify the accuracy and evaluate the performance of different acceleration schemes. Results indicated that an acceleration ratio of up to 2–3 can be achieved for different conditions.