Treatment of corner crossing ray-traces in CMFD acceleration of MOC

Treatment of corner crossing ray traces in the coarse-mesh finite-difference (CMFD) acceleration of a method of characteristics (MOC) transport calculation is discussed. The contribution of the corner crossing ray trace at a CMFD mesh is independently tallied as partial current at the corner of the CMFD mesh to reduce computational burden during transport sweeps in MOC. The tallied partial current at the corner is distributed to the partial currents at the sides of CMFD meshes. Some details of implementations in rectangular and triangular CMFD meshes are explained. The present method is implemented to the GENESIS neutron transport code, and its validity is confirmed through the 3×3 square cells and the hexagonal cell geometries. The calculation results indicate that the present method resolves the issue of corner crossing ray trace in the CMFD acceleration of MOC.本文探讨了特征线法（method of characteristics，MOC）输运计算的粗网有限差分（coarse-mesh finite-difference，CMFD）加速框架下的跨角射线追踪处理方法。为降低MOC输运扫描过程中的计算负担，将CMFD网格处跨角射线追踪的贡献作为该网格角点处的部分流进行独立统计，并将角点处统计得到的部分流分配至CMFD网格各边的部分流中。本文阐述了矩形与三角形CMFD网格的部分实现细节。本方法已集成至GENESIS中子输运程序，并通过3×3正方形栅元与六边形栅元几何构型验证了其有效性。计算结果表明，本方法解决了MOC的CMFD加速中跨角射线追踪的相关问题。