PNNL

Abstract

Gamma lithium aluminate (LiAlO2) is a breeder material for tritium that is one of key components in a Tritium Producing Burnable Absorber Rob (TPBAR). Dissolution and precipitation of second phases such as LiAl5O8 and voids are observed in irradiated LiAlO2. Such microstructure change causes the degradation of thermomechanical properties of LiAlO2, affects tritium retention and release kinetics, hence, the TPBAR performance. In this work, a microstructure dependent model of radiation-induced segregation (RIS) has been developed to investigate the effect of inhomogeneous thermodynamic and kinetics properties of defects on diffusion and accumulations of species in polycrystalline LiAlO2 structures. Two sublattices [Li, Al][O], and concentrations of six diffusive species, i.e., Li, Al, and O interstitials, vacancy at Li or Al lattice, vacancy at O lattice, and Li on the lattice are used to describe spatial and temporal distributions of defects and chemistry. Microstructure dependent thermodynamic and kinetic properties including the generation, reaction, and chemical potentials of defects, and grain boundary sink strength are taken into account in the model. The parametric studies demonstrated the capability of the developed RIS model for assessing the effect of thermodynamic and kinetic properties of defects on the segregation and depletion of species in polycrystalline structures and explaining the phase stability observed in irradiated LiAlO2 samples. The developed RIS model will be extended to study the precipitation of LiAl5O8 and voids by integrating the phase-field method.