Design of a gadolinia bearing mixed-oxide fuel assembly for pressurized water reactors Original Research Article

A study on neutronics design of a gadolinia (Gd2O3) bearing mixed-oxide (MOX) fuel assembly (MOX-UO2 (Gd2O3) assembly) was performed for the purpose of suppressing the use of fresh lumped burnable poison rods (BPRs). The MOX-UO2 (Gd2O3) assembly investigated consists of MOX and UO2 (Gd2O3) fuel rods, which have already been verified through both fabrication and irradiation experiences. In all, 16 UO2 (10 wt% Gd2O3) fuel rods are located at every corner and the peripheral region of the MOX-UO2 (Gd2O3) assembly in order to reduce the power peaking of MOX fuel rods due to the thermal neutron inflow, and to reduce the reactivity penalty at the end of cycle (EOC). Since fresh BPRs are not expected to be inserted and UO2 (Gd2O3) fuel rods are located at every corner of the assembly, the number of splits in plutonium (Pu) content can be only two, which is less than three splits required for a standard MOX assembly. Core characteristics of an equilibrium core loaded with MOX-UO2 (Gd2O3) assemblies are evaluated and it is verified that adoption of the MOX-UO2 (Gd2O3) assembly is effective to avoid the use of fresh BPRs with securing both the core safety and cycle length. The simplication of the splits in Pu content is also supposed to be beneficial, since it has the possibility of reduce MOX fuel fabrication costs.