The essential components for tritium production in TPBARs are the γ-LiAlO2 pellets, which contain about 25% of the total lithium as 6Li. Despite a total Li burnup of about 12% (i.e. ~50% of total 6Li), the LiAlO2 pellets can survive very well neutron irradiation during the 18 months of in-reactor operation. In order to improve the fundamental understanding of physical phenomena occurring in TPBARs during irradiation, a series of post-irradiation examinations were conducted for the various components of the TPBAR. In the specific case of the pellets, transmission electron microscopy (TEM) and atom probe tomography (APT) identified irradiation induced microstructures at the nanoscale level. Both techniques reveal the clear the presence of nanovoids in γ-LiAlO2 pellets. While those nanovoids can affect the diffusion of tritium in pellets, first principles simulations have been conducted to evaluate the potential for tritium trapping by single and double cation and anion vacancies. It was found that tritium trapping allows recovery of a significant amount of the formation energy cost of cation vacancy, while the trapping of tritium by anion vacancies further increase the energy cost of forming a vacancy. The simulations also indicated the potential for tritium to be trapped in various forms by forming bonds such as Al—T, O—T or T2. These results raise further questions regarding the speciation and dynamics of tritium trapped in nanovoids.

Characterization and first principles modeling of tritium trapping in γ-LiAlO2 nanovoids

ACS Spring Meeting 2021

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