Fusion-Ready Steel for a Sustainable Future

As the global community strives towards clean energy solutions, fusion power remains at the forefront of scientific and engineering breakthroughs. One of the most significant challenges in making fusion commercially viable is the development of materials that can withstand extreme conditions. The Materials Division at the UK Atomic Energy Authority (UKAEA), in collaboration with industry and academic partners, is addressing this challenge by pioneering new fusion-grade steels that enhance both performance and manufacturability.

The Need for Fusion-Ready Steel

Fusion power plants will require structural materials that are strong, radiation-resistant, and capable of withstanding high temperatures for extended periods. Traditional materials have failed to meet these stringent criteria. Whilst tungsten and copper alloys play specialised roles in fusion machines, steel remains the backbone of structural components.

Conventional steels contain impurities that lead to higher levels of radioactivity, complicating waste disposal and regulatory compliance. To address these concerns, UKAEA is developing Advanced Reduced Activation Ferritic Martensitic (ARAFM) steels, designed specifically for fusion applications.

Project Genesis and Goals

Recognising the need to develop fusion-ready materials, UKAEA played a pivotal role in bringing together a broad network of industry and academic partners to form the NEURONE (Neutron Irradiation of Advanced Steels) Consortium. The project commenced in April 2023 following funding from Fusion Futures through the Lithium Breeding Tritium Innovation (LIBRTI) Programme.

The NEURONE Consortium is a ~£12M collaboration between UKAEA’s Materials Division and academic and industry partners across the UK, as well as international partners, which provide access to neutron irradiation facilities.  The NEURONE Consortium is also supporting a range of PhD students and summer student placements to upskill the next generation of researchers.

The consortium’s goal is to deliver a steel variant capable of operating at temperatures up to 650°C, whilst tolerating the extreme conditions it would face in a fusion power plant. This is alongside the need to maintain a robust supply chain for future commercial fusion power plants.

Key objectives of the project include:

• Developing ARAFM steels with reduced impurities for enhanced radiation resistance.
• Conducting rigorous testing to ensure mechanical and radiation stability.
• Establishing a methodology to refine steel selection.
• Ensuring seamless collaboration between research institutions, steel producers, regulatory bodies and potential end-users.

The Scientific Approach

The research team employed a multifaceted strategy, incorporating metallurgy, physics, and engineering principles. The process involved:

• Alloy Development: Adjusting steel compositions by removing elements like nickel, niobium, and cobalt while introducing tungsten, tantalum, and vanadium for enhanced strength. Development of thermomechanical treatments to optimise microstructure and improve high-temperature performance.
• Manufacturing and Processing: Translation of smaller-scale alloy development to industrially relevant sizes. These assessments include understanding how to weld and join the material to preserve the base microstructure to a sufficient extent.
• Radiation Testing: Subjecting steel samples to bombardment by neutrons or ions to assess long-term structural integrity. These tests were followed by microstructural analysis, and micromechanical testing to establish how these materials respond to radiation damage.
• Creep Resistance and mechanical testing: Investigating the material’s ability to withstand deformation under sustained loads, including heat and mechanical forces.
• Modelling & Simulations: Assessing fundamental radiation damage effects towards predicting steel performance in reactor environments to expedite material qualification.

Key Milestones Achieved

The project’s first phase has yielded significant achievements:

• Successful production of over 50 alloy variants, advancing the search for an optimal fusion-ready steel.
• The first multi-tonne ingot of conventional RAFM steel, demonstrating the UK’s capability to scale up production for advanced variants in the future.
• Establishment of a comprehensive testing framework, including irradiation campaigns in material test reactors worldwide.
• Securing critical expertise through partnerships with leading universities and research institutions.
• Progress in computational modelling, with early research papers offering new insights into material behaviour under irradiation.
• Strengthened collaboration with key industry stakeholders, ensuring that materials developed are scalable and commercially viable.

Industry Collaboration and Production Breakthrough

A notable milestone was achieved through collaboration with the Materials Processing Institute (MPI) in Middlesbrough. Utilising a seven-tonne Electric Arc Furnace (EAF), the team successfully produced fusion-grade RAFM steel on an industrial scale. David Bowden, Group Leader for Materials Science and Engineering at UKAEA and NEURONE programme lead, highlighted the significance:

“Conventional RAFM steels are produced using vacuum arc remelting and secondary steelmaking processes, which increases the costs and limits the scalability of these alloys. Here we have demonstrated that these types of steel can be produced using ten times more affordable and scalable electric arc furnace facilities widely available to us in the UK. This is an exciting development towards the realisation of commercial fusion power and a demonstration of an economically viable approach towards obtaining the high-performance materials we will need for these devices”.

This approach has the potential to dramatically decrease production costs by up to 10 times compared to conventional RAFM counterparts, utilising existing and readily scalable infrastructure within the supply chain. Richard Birley, NEURONE project lead at MPI, emphasised:

“As the only sovereign UK steel research facility able to produce RAFM steel at this scale, this is a groundbreaking moment for fusion R&D.”

Future Prospects

Looking ahead, the next phases of the project will focus on:

• Extensive mechanical testing to confirm long-term durability.
• Creep resistance validation to ensure steels can operate at 650°C.
• Advanced neutron irradiation experiments to replicate fusion machine conditions.
• Further industrial-scale trials to refine the production process and ensure commercial viability.