Fission gas transport and its interactions with irradiation-induced defects in lanthanum doped ceria

To help understand the mechanisms of irradiation-induced defect formation and evolution in nuclear fuel, systematic experimental efforts have been carried out. Ceria (CeO ₂) was selected as a surrogate material for Uranium Dioxide (UO ₂) due to many similar properties. Lanthanum (La) was chosen as a dopant in CeO ₂ to investigate the effect of impurities. The presence of La in the CeO ₂ lattice introduces a predictable initial concentration of oxygen vacancies, making it possible to characterize hypostoichiometric effects in CeO ₂. The influence of two La concentrations, 5% and 25%, were examined. In situ Transmission Electron Microscopy (TEM) experiments were used to study the evolution of defect clusters and the influence of irradiation with two common fission products: Xe and Kr. The irradiations were performed on thin film, single crystal materials. The irradiation damage caused formation of dislocation loopsat 600 °C and defect clusters at room temperature. Dislocation networks form as the result of interactions of defect clusters. The dislocation loops were determined to be mainly of 1/9[1 1 1] interstitial type loops. Quantitative results were obtained to characterize the fluence and temperature effects of irradiation. Slow defect kinetics were found with irradiation on 25% La doped CeO ₂ at 600 °C and it is attributed to the higher concentration of oxygen vacancies due to high La dopant level.