Oxygen Potentials and Lattice Parameter of Irradiated BWR Fuels.

Abstract

Abstract The oxygen potentials and lattice parameter of oxide fuels (UO2 and UO2-2 w/0Gd2O3) irradiated in commercial BWRs have been measured by using a solid electrolyte galvanic cell technique and X-ray diffractometry. The fuel burn-up was 13–30 GWd/t for the former measurements and 6–35 GWd/t for the latter. The oxygen potentials at 750°C for irradiated UO2 ranged from −420 kJ/mol at the fuel rim to −480 kJ/mol at the fuel center. The corresponding values for irradiated U02-2 w/0Gd2O3 ranged from −460 to −540 kJ/mol. The lattice parameter near the fuel rim in the irradiated UO2 increased with burn-up, and was distinctly larger than that at the fuel center. This lattice dilatation was mainly due to the accumulation of radiation defects, not to a decrease in O/M ratio, and was almost recovered after the annealing at 1,600°C for 5 h. KEYWORDS: oxygen potentiallattice parametersmixed oxide fuelsuranium dioxidegadolinium oxideBWR type reactorsirradiationlattice defectsradiation effectsfission productsthermodynamic propertiesO/M rationonstoichiometry