Sublimation of advanced tungsten alloys under DEMO relevant accidental conditions

Abstract Tungsten (W) is deemed as the main candidate for the first wall armor material of future fusion power plants such as DEMO. Advantages of W include a high melting point, low erosion yield, low tritium retention, and a high thermal conductivity. One issue concerning W is the oxidation resistance in case of a loss-of-coolant accident with simultaneous air ingress. The major challenge in such a scenario is to suppress the sublimation which is responsible for a release of radioactivity. This work studies an alloy containing tungsten (W), 12 weight % chromium (Cr), and 0.6 weight % yttrium (Y) in DEMO-relevant conditions: a temperature in the range of 1100 K to 1473 K in humid air. The sublimation rates are measured for the first time in humid air. Tungsten oxide sublimates at a rate of 1.4 × 10 −4  mg cm −2  s −1 at 1273 K in humid air. At the same conditions the alloy suppresses sublimation by more than one order of magnitude as compared to that of pure W. This suppression is achieved due to the formation of a protective chromium oxide layer on the surface of the sample. Details about the protection mechanisms are presented and discussed. Testing is performed for up to 10 days.