The purpose of this study is to investigate the effects of operation parameters on BWR fuel reactivity and nuclide inventory. The three high-priority parameters that are suggested by NRC/ORNL , that is, axial burnup profile, axial moderator density profile, and control blade insertion during operation, were examined in order to evaluate their impact on BWR burnup credit. All of the calculations were performed using SCALE6.1 based on the ENDF/B-VII nuclear data library and involved 238 energy groups.
The results indicate that the axial burnup profile is the most critical factor in reactivity when the burnup value is greater than 10 GWd/MTU. The insertion of control blades during operation is also more important for the reactivity of spent fuel as compared to the influence of the axial moderator density profile. At a burnup of 60 GWd/MTU, these three operation parameters (i.e., axial burnup profile, axial moderator density profile, and control blade insertion during operation) in turn lead to multiplication factor differences of 18850, 7600, and 1980 pcm, respectively, for set2 nuclides. The influence between different parameters was also investigated in this study. The results reveal that multiple operation parameters affect the reactivity reduction tendency. In addition to the three parameters investigated in this study, other important factors related to burnup credit analysis are also currently under investigation.