Smart first wall materials for intrinsic safety of a fusion power plant

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.