Mechanistic calculation of the effective silver diffusion coefficient in polycrystalline silicon carbide: Application to silver release in AGR-1 TRISO particles

•A mesoscale effective Ag diffusion coefficient in SiC is derived from atomistic calculations of bulk and GB diffusivity.•The effective Ag diffusion coefficient in SiC accounts for temperature and microstructure effects.•Microstructures with grains that are smaller in the direction perpendicular to diffusion promote faster Ag diffusion in SiC.•The multiscale effective Ag diffusivity is within an order of magnitude of the empirical diffusion coefficient currently used in Bison.•Accounting for the microstructure effects on Ag diffusion increases the prediction accuracy of Ag release from AGR-1 TRISO fuel.