Neutronic analysis of VVER-1000 MOX fuel assembly with burnable absorber Gadolinia and Erbia

Abstract

This paper represents the neutronic characteristics and feasibility of using Gadolinia and Erbia in integral burnable absorber (IBA) rods for the proposed MOX fuel assembly of VVER-1000 reactor by Nuclear Energy Agency (NEA). For comparison the 4.0% Gd2O3 IBA is considered as a reference. The assembly was burned to 40 GWd/t, and by neutronic calculation, the optimum percentage of Gd2O3 and Er2O3 was determined using SRAC-2006 code and JEFF-3.1 data library. The burnup dependent reactivity of a MOX assembly containing 12 UO2-Gd2O3-Er2O3 (U-Gd-Er) IBA rods with 0.9% Gd2O3, and 5.0% Er2O3 was found almost identical to the reference assembly with 4.0% Gd2O3 in IBA rods. However, the assembly with U-Gd-Er IBA rods has a flatter pin-wise power distribution and lower power peaking factor (PPF). Long-lived fission products, poisons, and minor actinides are also investigated for choosing Gd2O3 and Er2O3 as IBA over only Gd2O3 for the VVER-1000 MOX fuel assembly.