Hydrogen saturation and permeation barrier performance of yttrium oxide coatings

Highlights: • Grain structure and crystallographic phase remain unchanged during the annealing in the permeation measurement. • The filling of the traps takes ∼20 h measurement time with exposure to deuterium. • The permeation reduction factor of 30 is the minimum value, after the filling of the traps was completed. • Over the measurement time of 7 days, the permeation barrier performance is degraded by a factor of 35. • For shorter measurement times than 20 h the apparent permeation reduction factor can be in the range of 1000. - Abstract: In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel inventory. Moreover, the tritium permeation barrier is necessary to avoid that the situation the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Er₂O₃ and Y₂O₃, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for Y₂O₃ due to its favorably low activation behavior compared to the other candidates. Y₂O₃ thin films are deposited on the reduced activation steel Eurofer97 by means of magnetron sputtering. To quantify the permeation reduction factor of the Y₂O₃ thin films a new gas-driven deuterium permeation measurement setup was constructed. Comparing the permeation flux through a bare substrate and a coated Eurofer97 substrate, the permeation reduction factor can be determined. The measurement results suggest that the permeation reduction factor is in the same range as for Er₂O₃. Moreover, the morphological analysis and the permeation measurements indicate that the long term stability of the permeation barrier performance depends on the deuterium saturation in the Y₂O₃ thin film.