Understanding the oxidation of pure tungsten in air and its impact on the lifecycle of a fusion power plant

Abstract

The oxidation of pure W and the sublimation of W oxide have been investigated to assess their impact on the lifecycle of a fusion power plant. Pure W has been oxidised at temperatures between 400 and 1050 °C and for durations ranging between 1 and 70 h. The formation of voids and cracks has been observed at temperatures above 600 °C, leading to the formation of dust or oxide spalling, which could be problematic in maintenance and waste-handling scenarios of a fusion power plant. Preferential oxidation taking place at the edge of the specimen was characterised, and its impact is discussed in relation to component design. Characterisation using electron microscopy and Raman spectroscopy revealed that the oxide scale is formed of three main layers: the inner layer is 30–50 nm thick WO${}_2$ oxide, the middle layer is a 10–20 $\mu$m thick of WO_2.72 and the outer layer is formed of WO_2.9/WO${}_3$ phases — whose thickness varies according to the total thickness of the oxide scale. The observed microstructure is discussed in relation to the parabolic-to-linear kinetics and its potential impact on tritium permeation and detritiation efficiency.