Abstract: Computing methods of assembly-parameters were studied for annular UO₂ fuel and annular MOX fuel. A mixed core pattern containing 193 annular UO₂ and MOX fuel assemblies was designed to possess an 18-month refueling cycle. Key physical parameters of the core were analyzed, and the burnup calculation was performed for each cycle. The results show that while the core’s electric power reaches 1 000 MWt, a long refueling cycle can be obtained by loading about 30% MOX assemblies. The core can be transferred from an initial loading pattern to an equilibrium pattern, and key physical parameters of each cycle meet all design requirements. Therefore, the designed core and fuel management program are safe and feasible.