Retained fuel removal from plasma-facing materials: effects of baking methods and hydrogen isotope exchange

Tungsten (W) is a prominent plasma-facing material for deuterium-tritium (D-T) fusion reactors, yet T fuel retention in W poses critical challenges to safety and operational viability. This study systematically compares three baking methods—vacuum baking, H2 gas atmosphere baking, and hydrogen (H) plasma baking—for removing D retained in W at 513 K, simulating realistic conditions for T removal in reactors. Experimental results demonstrate that D removal efficiencies reach 75% for vacuum baking after 16 h, 83% for H2 atmosphere baking after 16 h, and 99% for H plasma baking after 1 h. The superior performance of H2 atmosphere and H plasma baking is primarily driven by hydrogen isotope (HI) exchange, with efficiency strongly dependent on the concentration of H introduced into W. Higher H concentrations promote more complete exchange, leading to significantly reduced D retention. A multi-isotope Fill Level model was developed to simulate the end-to-end H plasma exchange process. The simulation reproduces the experimentally observed D removal kinetics and the emergence of HD desorption, with the D retention in good agreement with measurements. The pronounced disparity between H2 atmosphere baking and H plasma baking is fundamentally governed by the quantity of H entering W: H plasma promotes significantly greater H ingress, thereby enhancing HI exchange and resulting in a drastic reduction in D retention. This work provides both experimental validation and modelling support for HI exchange as an efficient T removal strategy.