Saving Icarus: Designing high temperature steels for fusion applications

Context The discovery of high-temperature superconducting magnets has allowed the design for fusion devices to shrink considerably. Whilst this will result in large economic benefits, operating components in such a proximity to the reactor core only pushes them closer to the point of failure: containing a Sun in a box is no mean feat. “Saving Icarus” aims to increase the operating temperature of reduced-activation fusion steel using additive manufacture (AM) to design and engineer a microstructure that is stable at elevated temperatures. The connection enabled by this project This collaborative project brings together experts on AM and alloy design at the University of Cambridge (UoC) with the Materials and Fusion Technology divisions at the UKAEA. The alloy design will revolve around a spatially engineered microstructure concept, which is pioneered by the group at UoC and is enabled by AM. The goal of the project is twofold. First it will demonstrate the viability of using AM technology to improve performance and lower the cost of fusion applications. Second, it will showcase the benefits brought about by materials with spatially varying microstructure, which may have implications for different engineering problems. The challenge addressed Current reduced-activation ferritic-martensitic (RAFM) steel alloys proposed for use in plasma-facing components in the reactor core—such as breeder blankets—cannot operate at temperatures exceeding 550°C. Beyond this baseline, creep, thermal cycling, and radiation damage accumulation will cause failure and limit the lifetime of the reactor significantly. The UKAEA has identified a class of high-strength RAFM steels with finely dispersed nano-precipitates as a possible material solution to raise the operating temperature to 650°C. However, these materials are difficult to manufacture and assemble into large components. As a result, making breeder blankets out of these materials is costly and would require multiple weld joins, which irremediably compromise the alloy’s unique microstructure and introduce possible failure points. Aims and objectives This project will address the above challenges by enabling net-shape manufacturing of these advanced steels with spatially controlled microstructure using AM technology. The part design consolidation offered by AM will allow reducing the number of joints required to make large scale parts, lowering the production cost and ensuring safer operations. Moreover, site-specific ‘tuning’ of the alloy microstructure will be used to make parts with graded precipitate density; high in the hot, plasma-facing regions and absent in colder ones, which may be safely welded to other subcomponents. The objectives of this project are thus two: 1) demonstrating the printability of these high strength alloys with tuneable density of precipitates and 2) producing a demonstrator breeder blanket subcomponent with optimized microstructural gradient. Potential applications and benefits The adoption of advanced, near-net shape manufacturing technologies is a crucial step to realising commercially-viable power generating nuclear fusion reactor designs. As such, this manufacturing development will be of interest to a range of public and private organisations which are currently engaged in these designs. This represents an exciting opportunity for the UK to lead the energy revolution. As an indication of scale, the Fusion Industry Association reported that in 2023 the fusion sector global invested $1.4B, of which private sector operators raised $271M. Translation projects, such as Saving Icarus, are ideally positioned to feed into and leverage off this growing industrial opportunity.