Solution of the C5G7MOX benchmark three-dimensional extension problems by the DeCART direct whole core calculation code

The three-dimensional (3-D) extension problems of the C5G7MOX benchmark are solved by the DeCART direct whole core calculation code which realizes the planar method of characteristics (MOC) solution based coarse mesh finite difference (CMFD) formulation. Extensive sensitivity studies are performed to ensure convergence of the solution by varying the number of angles, ray spacing, and axial node sizes. The analysis indicates that accurate solutions, of which the eigenvalue errors and the RMS errors in the axially integrated pin power are in the range of 60 pcm and 0.4%, respectively, can be obtained within minutes on the LINUX personal computer clusters. However, it is also observed that there could be nontrivial errors originating from the diffusion approximation employed in the axial solution if the axial mesh size becomes too small. Nonetheless, it can be concluded that the direct whole core calculation delivering excellent solution accuracy is quite affordable with the 3-D calculation methods employed in DeCART.