Implementation of coarse mesh finite difference acceleration scheme for irregular geometry

An unstructured CMFD acceleration scheme (uCMFD) has been developed for the 3D irregular geometry problems formed by 2D unstructured finite element meshes with axial extrusions. In this scheme, the coarse mesh structure is determined in polygonal shapes by partitioning the 2D fine meshes based on a user-specified structured stencil grid. Using the resulting coarse meshes, the CMFD calculation is performed to accelerate the convergence of fission source iterations. The uCMFD scheme was successfully implemented in PROTEUSMOC by extending the existing CMFD acceleration scheme and tested using the C5G7 benchmark problem and the modified EMPIRE micro reactor problem. The test results showed that the uCMFD acceleration scheme reduced the total computational time by a factor of 5 - 15 for both problems. (authors)