Refractory metals as structural materials for fusion high heat flux components

Tungsten is the favoured armour material for plasma facing components for future fusion reactors, but studies examining the use of tungsten or other refractory metals in the underlying cooled structures have historically excluded them, leaving current concepts heavily dependent on copper alloys such as copper chrome zirconium. This paper first outlines the challenge of selecting an appropriate alternative material for this application, with reference to historical selection methodology and design solutions, and then re-examines the use of refractory metals in the light of current design priorities and manufacturing techniques.

The rationale for considering refractory alloys as structural materials is discussed, showing how this is the result of relatively small changes to the logic previously applied, with a greater emphasis on high temperature operation, a re-evaluation of current costs, a relaxation of absolute activation limits, and the availability of advanced manufacturing techniques such as additive manufacturing. A set of qualitative and quantitative assessment criteria are proposed, drawing on the requirements detailed in the first section; including thermal and mechanical performance, radiation damage tolerance, manufacturability, and cost and availability. Considering these criteria in parallel rather than sequence gives a less binary approach to material selection and instead provides a strengths and weaknesses based summary from which more nuanced conclusions can be drawn.

Data on relevant material properties for a range of candidate materials, including elemental refractory metals and a selection of related alloys are gathered from a range of sources and collated using a newly developed set of tools written in the python language. These tools are then used to apply the aforementioned assessment criteria and display the results. The lack of relevant data for a number of promising materials is highlighted, and although a conclusive best material cannot be identified, refractory alloys in general are proposed as worthy of further investigation.