Direct FE² multiscale simulation of hydrogen diffusion in Zircaloy cladding

This study utilizes Direct FE² multiscale simulation techniques to propose an innovative approach for analyzing hydrogen diffusion in Zircaloy cladding. This method combines finite element simulations at two scales into a monolithic framework by utilizing downscaling rules and scaling factors. Through the investigation, it was found that voids induce non-uniform diffusion of lattice hydrogen, demonstrating a strong correlation between trapped concentration and microstructure. Additionally, the accumulation of trapped hydrogen leads to localized plastic deformation and a reduction in effective diffusivity. Furthermore, two representative volume elements were established to depict the void distribution at various stages of its evolution. It is evident that in the initial phases of void evolution, the hydrogen-induced softening effect facilitates crack propagation deep within the zirconium alloy cladding. Moreover, as void evolution progresses into the second stage, this effect intensifies the incidence of localized damage at the narrow inter-void ligaments.