PNNL

Abstract

Sequential irradiations of polycrystalline gamma-LiAlO2 pellets were performed at 573 K with He+ and D2+ ions to overlap the deuterium (D) profile with the He+ ion damage peak. The D depth profiles were measured using time-of-flight secondary mass spectrometry before and after thermal annealing steps. A linear concentration gradient approximation is adopted to estimate the diffusion coefficient. The combined isothermal and isochronal data are used to determine the activation energy for D migration. At and above 1E17 He++D+/cm2, a double-peak structure in the D profile was observed. The D diffusion coefficient in the irradiated gamma-LiAlO2 pellets is on the order of 1E-12 cm2/s at 773 K for the first 2 min annealing and the average values after 5 min tend to decrease to 1E-13 or 1E-14 cm2/s, depending on the ion fluence. The activation energy for D migration was determined to be 1.0 - 0.3 eV at 2E16 He++D+/cm2 and 0.6 - 0.3 eV at 1E17 He++D+/cm2. The results from this study may help better understand and predict tritium diffusion behavior during neutron irradiation of gamma-LiAlO2 pellets.