High Temperature Zirconium Alloys for Nuclear Fusion and Generation IV Fission Reactors

This research will develop new zirconium-based materials needed for future nuclear fusion and generation IV fission reactors, which allow carbon-free energy generation with nil or reduced long-lived nuclear-waste. The work will be carried out in partnership with Culham Centre for Fusion Energy (CCFE) and Rolls-Royce, with collaborations across Manchester, Oxford, Imperial College, Bangor, DECHEMA Frankfurt and ANSTO Sydney.

Nuclear power is a key part of the energy mix in our transition away from fossil fuels and their large-scale emission of carbon dioxide. However, nuclear is held back by concerns over long-lived radioactive waste, safety and cost. Future advanced nuclear reactor concepts address these concerns. Nuclear fusion produces no such long-lived radioactive waste and is inherently safe with a runaway reaction impossible. Next Generation IV fission reactors have increased efficiency and capacity for significantly reduced fuel usage and cost whilst being intrinsically safe. For both fusion and fission, in addition to plasma physics and reactor engineering challenges, there is a need for advanced materials that are beyond current capabilities.

The advanced materials developed in this programme will be designed for stability at the high operating temperatures required for fusion and next-generation fission reactors. Zirconium alloys developed 1950-70 excel in current fission reactors, owing to their low neutron cross section and corrosion resistance, with adequate strength at moderate temperatures (~330 degrees C). However, fusion and Gen IV fission operate at much higher temperatures (500-800 degrees C) associated with their advanced coolants: liquid metal, helium gas or molten salt. The current Zr alloys lack high temperature strength, necessitating this project's development of new high temperature Zr alloys.

Alloy design approaches that were developed for high temperature Ti alloys, through the 80's and 90's, will be extended to Zr, exploiting their common crystal structure. Strength will be gained (1) by structural refinement and (2) by reinforcement with high strength intermetallic compounds. Attention will be made to see whether Si, Al and Cr additions employed to generate such mechanical property improvements also promote environmental resilience against oxidation, corrosion or irradiation damage. A second alloy design strategy will employ the topical high entropy alloy (HEA) approach, which is a recent and rapidly growing field of materials science. Work will be undertaken to characterise zirconium-based HEAs, building from our recent proof of concept study on the ZrTiVNb HEA system (https://doi.org/10.1016/j.actamat.2019.01.006), to ZrTiVTa and ZrTiV(Nb/Ta)X (X = Cr, Si, Al) HEA systems. These have the potential to further increase high temperature mechanical properties and environmental resistance.

This project will help to keep the UK at the cutting edge of fusion and Gen IV fission research, as well as establishing the UK's presence in the rapidly developing HEA field, where it is currently underrepresented.

On knowledge, two-way transfer will be ensured with both industry and academic partners. For the Industrial partners, CCFE and Rolls-Royce, new capability will be developed that also benefits current materials. In return, they will aid in design, expertise, and onward scale-up. With the academic partners, there will be two-way transfer of ideas, staff, students and skills, extending collaborations with Manchester, Oxford, Imperial College, Bangor, DECHEMA Frankfurt, MPIE Düsseldorf, and ANSTO Sydney. The research will be promoted at international conferences, e.g. The Minerals, Metals & Materials Society (TMS) USA, specialised workshops, including, UK Nuclear Academics Meetings, EPSRC Grant meetings (e.g. MAPP, MIDAS), and invited seminars. Further, the work will be contributed to a new pilot EU Joint Programme on Nuclear Materials (JPNM) on High entropy alloys (HEAs), which has 24 EU participants, with A Knowles the sole UK representative. Such pilots have often led to onward EU funding. HEAs are a rapidly growing new branch of materials science, however, of over 1000 papers last year only ~30 were from UK authors, which is mirrored in international funding (e.g. USA >£1.87 mil, Germany >£2.19 mil, Japan >£8 mil). This highlights the strategic need for the UK to develop its HEA research, as targeted by this proposal.

On people, there is a skills shortage at all levels across nuclear and materials science/engineering. This programme will develop new knowledge whilst training a new generation of scientists and engineers. The postdoctoral researcher and linked PhD will learn expertise in alloy development, advanced characterisation, and mechanical testing, which are essential physical metallurgy skills and along with nuclear fusion/fission knowledge are in great demand. The group members will be closely linked to the industrial partners (CCFE and Rolls Royce) to ensure their development and employability.

Economically, the UK's Grand Challenge of Clean Growth targets carbon-free energy generation, with nuclear energy a key part of the mix. Long-term this vision includes fusion, and nearer-term with generation IV fission, for reduced/nil long-lived waste. Such innovations seek to address concerns over long-lived waste, safety and cost, which are holding back increases in nuclear energy. On fusion the UK is at the cutting edge and we must continue to invest and innovate to maintain this position internationally. Whilst the UK is a nuclear leader, in the 1990's it stepped back from gen IV fission. This has now changed with the UK's Advanced Modular Reactor (AMR) programme and the UK having in 2018 re-joined the Gen IV International Forum (GIF). In these initiatives and for fusion and Gen IV reactors, materials innovations are needed that realise improved operating temperatures and develop skills capability. This is the target of this research, by demonstrating new Zr alloys with high temperature strength, environmental resistance and low neutron cross section.

Societally, outreach targets four groups:
1) Ages 12-16, encouraging STEM uptake, at local secondary school visits, via UoB and CCFE, and at science festivals, e.g. New Scientist Live.
2) Ages 16-18, encouraging science and engineering degrees, utilising the widening participation programme at UoB on underrepresented groups, and engaged audiences at Pint of Science, Café Scientific and university open days.
3) Public of all ages, will be engaged to promote Science & Engineering and nuclear energy. At festivals, events and talks as mentioned, and the BlueDot festival with CCFE, working with the Henry Royce Institute engagement officer based at UoB, and to seek media engagement via the UoB and CCFE press offices and Science Media Centre.
4) Public policy, will be influenced via the annual UK Nuclear Academics Meetings, National Engineering Policy Centre, BEIS and Parliamentary secondments, UK AMR programme and UK GIF representation.