Research on acceleration of ultra-fine-group calculation based on method of characteristic

Ultra-fine-group slowing down equation solved by method of characteristic (UFG-MOC method) is capable of performing the rigorous self-shielding calculation of complicated geometry and complicated neutron spectrum problems. Compared with the conventional ultra-fine-group code with pin-cell geometry and collision probability pre-tabulation, the UFG-MOC method is more flexible in the geometry processing, but it is inefficient since tens of thousands of fixed-source calculations are performed. In this study, some strategies are discussed to decrease the number of fixed-source calculation and the corresponding acceleration scheme is proposed. Numerical results show that the acceleration scheme can effectively reduce the computational time without the impact of accuracy compared with the original UFG-MOC method. (author)