Weaving a way to fusion energy 24 January 2020

A 3D woven composite component, capable of withstanding extreme temperatures inside a fusion nuclear reactor, is being developed at the University of Sheffield Advanced Manufacturing Research Centre (AMRC) in collaboration with the United Kingdom Atomic Energy Authority (UKAEA) as part of the effort to accelerate the delivery of limitless zero-carbon fusion energy.

The work was commissioned by the Joining and Advanced Manufacturing (JAM) programme, which forms one of three Fusion Technology Facilities at UKAEA. The AMRC, part of the High Value Manufacturing (HVM) Catapult, worked 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 their site in Culham, Oxfordshire. Research is focussed on preparing for the international tokamak experiment at the International Thermonuclear Experimental Reactor (ITER) in Saint-Paul-lès-Durance in southern France and for the following machine that will demonstrate the generation of power from fusion

In September, the UKAEA announced that they would be building a new £22 million fusion energy research facility at the Advanced Manufacturing Park in Rotherham that 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 x 1.5m and currently weighs up to 4.6 tonnes.

“At the moment the designs being tested in ITER use steel for the breeder blankets structure, which have a network of double walled tubes of 8mm internal diameter and 1.25mm wall thickness to collect the heat. Each one is welded into place and every connection has to be inspected. That is what we were asked to replace,” said Steffan Lea, research fellow at the AMRC Composite Centre.

“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. We set out to see what materials we could use, that would enable higher temperature operation.”

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

Senior Project Manager at the AMRC’s Design and Prototyping Group, Joe Palmer, was involved in the design of the component demonstrator, and said: “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 being created by forming the composite around a disposable core.”

With a computer-aided design (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 had multiple layer weaves. The structure needed holes robust enough to include tubes and needed to maintain the preform shape without distortion.

“What we were able to produce on the loom was a 3D woven structure with pockets for the 3D-printed tubes which could be formed into a ridged component.”

Steffan continued: “What we were able to do was replace a metallic box, made of different steel components, with a malleable textile fabric which 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, these 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 forwards.”

A delegation from the AMRC took their demonstrator breeder blanket concept made from carbon fibre reinforced polymer (CFRP) to the UKAEA in Culham, where it was presented to Head of Technology, Dr Elizabeth Surrey.

Dr Surrey said: “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. 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.

“Recent advances in silicon carbide manufacturing technology may offer the possibility of using this material in a fusion reactor; it has so many advantages it has to be considered. I was impressed, but not surprised, by the progress made at the AMRC in such a short time.”

”We have successfully demonstrated the initial concept works but their designers understand what performance and functionality is required,” said Steffan.

“The next step is to continue the silicon carbide composite development and 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 are manufacturable and easily replicated. That is what we have tried to create.”

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