Multi-group equivalence in subgroup method based on generalized equivalence theory

Multi-group heterogeneous reaction rates calculated by the subgroup method in resonance calculations are not reproduced, when subgroup-collapsed one-group homogeneous calculations are conducted for the same problem, giving rise to a multi-group equivalence effect. In this paper, a new non-iterative equivalence method introducing partial current discontinuity factors (PCDFs) is proposed to resolve this effect and employed into the Bamboo-Lattice code. Its validity was tested and verified through several fixed-source as well as eigenvalue problems for both single pin-cell and assembly geometries. The numerical results show that preservation of scalar flux, partial currents, neutron leakage and reaction rates is guaranteed by implementing this new method. Moreover, the computational time comparison for different equivalence methods shows that the newly proposed non-iterative equivalence method promises a significantly less computational cost compared to the traditional iterative super-homogenization (SPH) method in treating multi-group equivalence effect.