The work has been commissioned by the Joining and Advanced Manufacturing (JAM) programme, which forms one of three fusion technology facilities at UKAEA. AMRC, part of the High Value Manufacturing(HVM) Catapult, has been working with technical lead for non-metallics, Dr Lyndsey Mooring, to explore how composite materials could produce components that are stiffer, lighter and easier to manufacture that those currently in use, but which retain the necessary capabilities.

The UKAEA is involved in developing the next generation of magnetic confinement reactor, called a ‘tokamak’ at its site in Culham, Oxfordshire. Research is focussed on preparing for the global tokamak experiment at the International Thermonuclear Experimental Reactor (ITER) in Saint-Paul-lès-Durance in France, and for the subsequent machine that will demonstrate the generation of power from fusion.

In September 2019, the UKAEA announced it would be building a new £22 million fusion energy research facility at the Advanced Manufacturing Park in Rotherham, which includes a test facility that reproduces the thermohydraulic and electromagnetic conditions in a fusion reactor. The centre will work with industrial partners to commercialise nuclear fusion as a major source of low-carbon electricity.

Fusion occurs when two types of hydrogen atoms, tritium and deuterium, collide at enormously high speeds to create helium and release a high energy neutron. Once released, the neutron interacts with a much cooler breeder blanket to absorb the energy. The breeder blanket must capture the energy of the neutrons to generate power, but also prevent the neutrons escaping and ‘breed’ more tritium through reactions with lithium contained in the blanket. Each blanket module typically measures 1 by 1.5 m, and weighs up to 4.6 tonnes.

“At the moment, the designs being tested in ITER use steel for the structure of the breeder blankets, which have a network of double-walled tubes measuring 8 mm internal diameter and 1.25 mm wall thickness to collect the heat,” explains Steffan Lea, research fellow at the AMRC Composite Centre. “Each one is welded into place, and every connection has to be inspected. That is what we were asked to replace. Currently, their steel modules are limited to approximately 500˚C, so UKAEA asked us if there was anything we could do to get it up to 600˚C.”

Engineers at the AMRC proposed making use of high-performance ceramic composite materials and forming a unitised 3D woven structure with additively manufactured components. The cooling tubes in the breeder blanket would be integrated into the material, and the 3D printed parts used to define features such as connectors and manifolds.

Senior project manager within the AMRC’s Design and Prototyping Group, Joe Palmer, was involved in the development of the component demonstrator, and says: “We wanted to maximise the available surface area for heat transfer while being as lightweight as possible, but ensure it occupied a similar volume to the existing breeder blanket designs. To achieve a lightweight, temperature-resistant structure, a silicon-carbide composite material was chosen for the breeder blanket, with the internal flow channels created by forming the composite around a disposable core.”

With a CAD model produced, Chris McHugh, dry-fibre development manager at the AMRC Composite Centre, then created a weave design for the composite.

“The design I created had multiple weave zones and multiple layer weaves,” he says. “This structure required holes robust enough to include tubes, and needed to maintain the preform shape without distortion. What we produced on the loom was a 3D woven structure with pockets for the 3D-printed tubes that could be formed into a ridged component.”

Lea adds: “We were able to replace a metallic box, made of different steel components, with a malleable textile fabric that had cooling pipes running the length of it. Using advanced manufacturing technologies available at the AMRC we have integrated the functionality of cooling, simplified the design and removed the welding operation, so lessening the burden of qualification. When maintenance happens in the nuclear fusion reactors, the components are lifted in remotely using a robot, so using these materials, which are far lighter – and can also be stiffer – would bring great benefits in terms of how the reactors are built going forward.”

A delegation from the AMRC took the demonstrator breeder blanket concept made from CFRP to the UKAEA in Culham, where it was presented to head of technology, Dr Elizabeth Surrey.

She says: “Designing a fusion reactor is possibly the most challenging engineering project ever undertaken. We need to explore disruptive manufacturing technologies to satisfy the operational requirements of high temperature, low weight and high-strength structures using materials that offer low nuclear activation.

“For fusion to become a commercial, clean energy source the structures need to be modular and easily manufactured, and provide operational lifetimes of decades,” adds Surrey. “Standard manufacturing routes struggle to deliver across all of these requirements. That is why we turned to the expertise of the AMRC, to investigate the possible application of silicon carbide to this problem.”

Says Lea: “The next step is to build a demonstrator that can be tested inside a reactor test facility, in order to understand how it performs and reacts to the environment. If nuclear fusion is going to be realised, you need a simple design for breeder blankets that can be manufactured and easily replicated. That is what we have tried to create.”

Mooring adds: “This successful project has been an excellent first step in demonstrating alternative structural materials and manufacturing routes for scalable fusion reactor components. It opens the design space and offers problem-solving solutions that can assist in realising a future fusion power plant.”