Cluster dynamics modeling of hydrogen saturation retention in tungsten with a universal trapping-site sink strength

Abstract: Hydrogen isotope (HI) retention poses a key issue for tungsten (W)-based plasma-facing materials (PFMs) in fusion devices, where microstructures such as dislocations (DLs) and grain boundaries (GBs) play a dominant role. Existing theoretical sink strength models for microstructures like DLs and GBs fail to account for the observed saturation of HI retention. In this study, we propose a novel universal trapping-site model that dynamically represents sink strengths as time-dependent site concentrations, which is incorporated into an improved cluster dynamics model for high-fluence HI irradiation. Our simulations quantitatively reproduce the saturated low-energy deuterium (D) retention and depth profiles in W, in good agreement with experiments. A critical saturation fluence of approximately 1023 m-2 is identified, below which unsaturated D retention is governed by both GBs and ion-induced defects, whereas above this threshold GBs dominate D retention by trapping free D and approaching their theoretical saturation limit. The trapping-site sink strength model enables quantification of H trapping by diverse microstructures via unified effective site concentrations, providing mechanistic insights into microstructural effects and facilitating direct evaluation of HI retention in PFMs under different irradiation conditions.