Study on robust energy group structure to spectral interference for PWR pin-by-pin core analysis

The energy group structure which reduces the error caused by interference effect is studied. The error in pin-power distribution becomes large at interference area of UO₂ and MOX fuel assemblies. Although the error could be reduced by increasing the number of collapsed energy groups, the target of this study is to find robust energy group structure against spectral interference without changing the number of collapsed energy groups and without introducing any additional parameters. Considering the characteristics of cross-section curve and the change of neutron flux caused by interference effect, we obtain the robust energy group structure against interference effect and evaluate the robustness of this energy group structure in cases of a multi-assembly and a single-assembly having the different interference effect. (author)