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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.

The first wall armor of a DEMOnstration fusion power plant (DEMO) is planned to be built from tungsten. However, in case of loss-of-coolant accident with air ingress, the temperature of the first wall may exceed 1000 °C due to nuclear decay heat. At such temperatures, tungsten forms volatile radioactive oxides, which may be mobilized into the environment at a rate of 10–600 kg per hour. Advanced “smart” tungsten alloys adjust their properties to the environment: during the plasma operation, preferential sputtering will form almost pure tungsten surface facing the plasma. In case of an accident, the remaining alloying elements form a protective layer, preventing tungsten mobilization. The new smart alloys contain tungsten (W), chromium (Cr) and yttrium (Y). The first bulk smart alloys produced using field-assisted sintering technique, revealed excellent oxidation resistance for a timescale of 10–20 hours. W-Cr-Y systems underwent combined plasma and oxidation test. During plasma exposure, smart alloys demonstrated nearly the same mass loss as the reference pure tungsten samples. Subsequent oxidation confirmed superior oxidation resistance of new alloys compared to the former W-Cr-Ti systems. Experiments attaining oxidation times and plasma fluence required for DEMO, are started. First results show necessity in further improvement of W-Cr-Y alloys.