PNNL

Abstract

Tritium must be replenished for strategic stockpile and fusion reactors. 6Li-enriched gamma-LiAlO2 pellets have been used for tritium production by thermal neutron irradiation. A fundamental study of tritium and lithium diffusion processes in irradiated gamma-LiAlO2 pellets is needed to assess and predict the material performance. This study intends to identify the trapping sites and diffusion pathways of 1H (a surrogate for 3H) and Li in polycrystalline gamma-LiAlO2 pellets irradiated with both 4He+ and 1H2+ ions. A combination of STEM-EELS, nano-SIMS and APT for chemical imaging at atomic-level and nano-scale resolutions are employed. The results provide direct evidence of preferred pathways of Li diffusion along the grain boundaries. Similar Li diffusion out of the LiAl5O8 precipitate region in irradiated gamma-LiAlO2 grains is also revealed. There are no apparent Li trapping centers identified in the gamma-LiAlO2 pellets except for LiAl5O8 precipitates. However, lithium is found to be enriched in H-containing particles, possibly lithium hydrates, on the gamma-LiAlO2 surface. The results from this study improve our understanding of lithium and tritium diffusion processes and provide data for modelling and simulation to predict material performance during neutron irradiation of gamma-LiAlO2 pellets.