Achieving tritium self-sufficiency is essential for the practical deployment of deuterium–tritium fusion energy. Tritium permeation through breeding blanket structural materials may lead to fuel losses, contamination of auxiliary systems and increased radiological risks. Tritium permeation barrier (TPB) coatings are therefore being developed to suppress hydrogen isotope transport. This review examines hydrogen isotope transport mechanisms, including diffusion-limited and surface-reaction-limited processes, and the theoretical basis of the permeation reduction factor (PRF). Recent advances in metallic, oxide ceramic, non-oxide ceramic, composite and emerging TPB coatings are systematically reviewed in terms of their barrier mechanisms, fabrication techniques, performance and service compatibility. Particular attention is given to the effects of high temperatures, thermal cycling and liquid lithium–lead corrosion. Previous studies indicate that dense oxide-based coatings can substantially reduce hydrogen isotope permeation under laboratory conditions, whereas their effectiveness under practical service conditions is strongly influenced by coating defects, interfacial degradation and corrosion. Moreover, barrier performance measured in gaseous environments cannot necessarily be extrapolated to liquid-metal blanket conditions. The relationships between fabrication processes, coating microstructure and permeation resistance are further discussed, together with current limitations in performance evaluation. Finally, future research priorities are identified, including standardized testing under representative blanket conditions, long-term coating reliability and scalable fabrication technologies to facilitate the engineering application of TPB coatings in fusion reactors..
 

fusion reactor blanket,tritium permeation barrier coating,hydrogen isotope permeation,permeation reduction factor