DESIGN OF A GADOLINIUM BEARING MIXED-OXIDE FUEL ASSEMBLY FOR PRESSURIZED-WATER REACTORS

A study on neutronics design of a gadolinia (Gd2O3) bearing mixed-oxid e (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 U O2 (Gd2O3) fuel rods, which have already been verified through both fa brication and irradiation experiences. In all, 16 UO2 (10 wt% Gd2O3) f uel 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 f uel rods due to the thermal neutron inflow, and to reduce the reactivi ty penalty at the end of cycle (EOC). Since fresh BPRs are not expecte d 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 b e only two, which is less than three splits required for a standard MO X assembly. Core characteristics of an equilibrium core loaded with MO X-UO2 (Gd2O3) assemblies are evaluated and it is verified that adoptio n of the MOX-UO2 (Gd2O3) assembly is effective to avoid the use of fre sh BPRs with securing both the core safety and cycle length. The simpl ification of the splits in Pu content is also supposed to be beneficia l, since it has the possibility of reduce MOX fuel fabrication costs. (C) 1997 Elsevier Science S.A.