Tungsten smart alloys for the first wall armour of fusion power plants

In order to operate future fusion power plants reliably and safely, tungsten (W) is considered as a prime candidate as first wall armour material. However, in accidental conditions with a loss of coolant and air ingress, the nuclear decay heat will cause the radioactive W to oxidise and volatilise, imposing a severe hazard for the environment. Smart alloys aim at preserving the properties of W during plasma operation and suppressing the release of radioactive material in case of an accident. This goal is approached by alloying with chromium (Cr) and yttrium (Y). Bulk samples for full testing were consolidated by field assisted sintering technology. A relative density of 99 % is achieved. The accident is resembled by oxidation at 1273 K in air: the Cr diffuses to the surface forming a protective Cr₂O₃ layer and stopping WO₃ formation - after 44 h the layer has a thickness of 1.3 μm. This process is supported by the Y. After oxidation times of more than two days W-containing oxides form and a sublimation rate of 10^-6 mg cm^-2 s^-1 is measured. After three weeks the oxide layer has a thickness of 0.1 mm.