Abstract Gamma lithium aluminate (LiAlO₂) is a breeder material for tritium and is one of key components in a tritium-producing burnable absorber rod (TPBAR). Dissolution and precipitation of second phases such as LiAl₅O₈ and voids are observed in irradiated LiAlO₂. Such microstructure changes cause the degradation of thermomechanical properties of LiAlO₂ and affect tritium retention and release kinetics, and hence, the TPBAR performance. In this work, a microstructure-dependent model of radiation-induced segregation (RIS) has been developed for investigating the accumulation of species and phase stability in polycrystalline LiAlO₂ structures under irradiation. Three sublattices (i.e. [Li, Al, V]^I [O, V_o]^II [Li_i, Al_i, O_i, V_i]^III), and concentrations of six diffusive species (i.e. Li; vacancy of Li or Al at [Li, Al, V]^I sublattice, O vacancy at [O, V_o]^II sublattice, and Li, Al and O interstitials at [Li_i, Al_i, O_i, V_i]^III interstitial sublattices; 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 defect mobility are taken into account in the model. The parametric studies demonstrated the capability of the developed RIS model to assess the effect of thermodynamic and kinetic properties of defects on the segregation and depletion of species in polycrystalline structures and to explain the phase stability observed in irradiated LiAlO₂ samples. The developed RIS model will be extended to study the precipitation of LiAl₅O₈ and voids and tritium retention by integrating the phase-field method.