Improvements of subgroup method based on fine group slowing-down calculation for resonance self-shielding treatment

Abstract

To combine the advantages of the accuracy of ultra-fine group method and efficiency of subgroup method for resonance self-shielding treatment, the method of fine-mesh subgroup method (FSM) has been raised in this paper. FSM adopts a fine energy mesh of 289 groups for resonance energy range and the subgroup parameters are generated for each group. The Coupling procedure ensures the elimination of extra resonance interference amendment as the group structure is sufficient enough. To improve the efficiency, the micro level optimization based on “one-group” approximation is proposed to solve the subgroup fixed source equations for only 8 subgroup levels for each resonant nuclide. Finally, a group condense procedure based on neutron slowing-down equation is employed for resonance range from 289 to 16 groups, and a 47-group structure library will be used for eigenvalue calculation. Benchmarks of pin cells and lattices in reactors are applied in numerical validation and the calculating results show that FSM has a good performance with both accuracy and efficiency for complicated resonance treatment.