Assessment of the burnup characteristics of UO2 and MOX fuel in the mixed solid and annular rod configuration

Abstract

Modeling and burnup analysis of Uranium dioxide (UO2) and Mixed Oxide (MOX) fuel in square assemblies comprising both solid and annular rods was carried out. The lattice pitch of the models was optimized first in terms of infinite multiplication factor (k∞) using OpenMC. The burnup analysis was performed at the optimized pitch by lattice physics code Dragon for 1620 EFPD. The burnup dependent fission rate density was studied, and the thermal fission rate was found higher for the models as compared to reference designs. The values of k∞ and reactivity were determined and higher values were found for the models at low fuel burnup period. However, models showed a higher criticality period than the reference design consisting of only the annular rod. The fuel and moderator temperature sensitivity of reactivity was investigated for different fuel burnup periods. The burnup-dependent atomic concentrations of fissionable materials, minor actinides, and neutron poisons were also studied. The production of neutron poison, namely Xe-135 and Sm-149 and minor actinides viz. Np-237, Am-241, Cm-242 and Cm-244 were found lower in models as compared to the reference designs.