Hydrogen saturation and permeation barrier performance of yttrium oxide coatings

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.