Improvements on the method of ultra-fine-group slowing-down solution coupled with method of characteristics on irregular geometries

Ultra-fine-group slowing down solution coupled with method of characteristics is a rigorous resonance calculation method which can handle complicated geometry and spectrum. However, the original approach is time-consuming due to large amount of computational cost of method of characteristics. In this research, investigations are carried out on the computational efficiency with optimized lethargy and the pre-tabulated CP table generated by MOC. Calculations of multiple types of problems are performed, and numerical results show that these techniques can obtain improved efficiency on complicated geometry and complicated neutron spectrum problems, while maintain the accuracy of resonance self-shielding. For universal problems, the optimized lethargy can save half of the calculation time comparing to the original lethargy. For the problem with local heterogeneity tested in this study, the pre-tabulated CP table generated by MOC can speed up the calculation by 30 times.