The commercial production of high-purity low-activation steels for fusion reactor application

The usual steelmaking processes, raw materials and analytical techniques employed in the steel industry do not meet the stringent demands of low activation steels in which the concentrations of critical residual elements must be kept to very low levels. Elemental concentration limits satisfying the ‘hands-on’ dose rate criterion (25 μSv h −1 at 100 y) are taken as reference values. A way forward is indicated, based on the precedents set by the nickel-based superalloy industry for manufacture of aerospace components. As many as 44 elements are typically specified in superalloys, some at the sub-ppm level, compared with a typical maximum 16-element analysis for state-of-the-art high-temperature steels such as FV448. The special alloy producers are believed to be capable of manufacturing steels to the purity standards required of low-activation materials, given the necessary high purity raw materials and the employment of techniques such as vacuum melting and vacuum arc refining, with precautions to avoid impurity pickup during processing.