Pseudo-resonant-nuclide subgroup method capable to precisely treat spatial self-shielding effect

Considering that the conventional Bondarenko-Iteration Method (BIM) would introduce much error in treating resonance interference effect, the Resonance-Interference-Factor Method (RIFM) and the Heterogeneous-Pseudo-Resonant-Isotope Method (HPRIM) was developed by researchers. Though these two methods can give relatively precise pin-averaged self-shielded cross sections by considering resonance interference effect, they cannot give exact spatial dependent self-shielded cross sections for coarsely modeling spatial self-shielding effect. In order to overcome this problem, the Pseudo-Resonant-Nuclide Subgroup Method (PRNSM) is proposed in this paper. The PRNSM takes into account the resonance interference effect by making resonance cross section table of the pseudo resonant nuclide on-line. The subgroup parameters of the pseudo resonant nuclide and the partial resonant nuclide are obtained by fitting method. The spatial dependent self-shielded cross sections are obtained by condensing the subgroup cross sections of the partial resonant nuclide with the subgroup flux which is obtained by solving subgroup fixed source problem of the pseudo resonant nuclide. The numerous numerical results show that the PRNSM can give both precise pin-averaged self-shielded cross sections and precise spatial dependent self-shielded cross sections for UO₂ problems with different enrichments. (authors)