Understanding the In-Reactor Performance of Advanced Ceramic Cladding Materials

Lead Research Organisation: University of Manchester
Department Name: Mechanical Aerospace and Civil Eng

Abstract

Accident Tolerant Fuels (ATF) are fuel designs typically intended for use in Light Water Reactors (LWRs), which comprise around 90% of the world's nuclear generating capacity. They offer significantly improved high temperature capability, due largely to the adoption of novel cladding materials, notably ceramic cladding. International fuel vendors are interested in commercialising ATF for both existing and new LWRs, but only after the gaps in technology readiness have been addressed. The aim of the research is therefore to establish the satisfactory performance of advanced ceramic cladding materials that are capable of surviving to temperatures typical of those encountered during severe accident conditions - typically around 1700 deg C. This is achieved by replacing the traditional zirconium-alloy fuel cladding with a composite ceramic cladding that is capable of surviving much higher temperatures. This would provide a very significant increase in safety compared with existing fuels, and hence provide a competitive advantage to UK fuel manufacturers. The work will focus on the performance of joined and bonded SiC-SiC composite cladding under conditions representative of those found in nuclear reactor cores.

Silicon carbide has been shown to be stable under irradiation, and has very high temperature capabilities, but it has two major difficulties.
1. The cladding must provide a gas-tight tube capable of accommodating the fuel pellets and retaining the gaseous fission products. This requires the sealing of the ends of the tube with a high-integrity joint. However, SiC cannot be welded, and previous attempts to produce mechanical and glued joints have failed.
2. Being a ceramic, SiC has very low fracture toughness, and it must be maintained in compression to provide sufficient mechanical strength. This can be achieved by winding the hollow SiC tube with SiC fibres that keep the tube in compression. However, a suitable means must be found of bonding the fibres to the underlying tube.

Recent work at Manchester has identified two promising solutions to these difficulties: the use of laser-induced ceramic brazing to produce a gas-tight seal; and the use of Selective Area Laser Deposition (SALD) to produce a deposit of SiC that can act as a bond between SiC fibres and the underlying tube. These techniques have been demonstrated at laboratory scales, but the braze and bond materials have not been demonstrated under conditions representative of in-reactor service. The principal objectives of the work are therefore to demonstrate that the brazed joints and bonded fibres are capable of surviving under in-reactor conditions.

Planned Impact

The research will create a significant body of knowledge on materials for advanced nuclear fuels, and will provide new researchers whose skills will be critical to the successful implementation of the Government's nuclear strategy. Our pathway to impact will be through two routes: Knowledge Management, and Outreach & Public Engagement.
1. Our Knowledge Management strategy considers three environments:
- the UK nuclear community of academic and industry partners;
- the international nuclear community;
- the broader non-nuclear community who may benefit from access to the research.
The priority will be to disseminate the results of the research by publication in open-access journals. We believe that knowledge retention and dissemination is best achieved using public domain systems. Whilst this covers documented knowledge, much of the learning from R&D comes from interaction with fellow researchers, and therefore engagement with fellow academic and industry researchers and practitioners will be sought throughout the project.
We will also ensure that the knowledge created is shared amongst academic researchers through regular meetings with existing groups (for example: the EPSRC NNUMAN project brings together academic and industrial researchers engaged in advanced manufacturing methods for nuclear applications, and the EPSRC-funded PACFIC programme provides a forum for academic and industry partners in the field of nuclear fuels research). Our team already includes a key industry partner that will inform and guide the direction of the research (Westinghouse), and we have strong links with other key industry partners (Rolls-Royce, EDF, and GE-Hitachi) who can also deploy the research results to obtain economic benefit for the UK and beyond, potentially in sectors beyond the nuclear industry.
2. Our Outreach and Public Engagement objectives are driven by three criteria; who (will need to be informed), why (will they want to listen) and how (will we deliver the information they need). These are considered below.
(a) Who and Why
There are four constituencies that will benefit from dissemination of the proposed research:
- Academia: the Academic Beneficiaries section of the proposal details the benefits to UK and international academics of the proposed research.
- Industry: interested in the technical knowledge and skills created by the programme, in a form which they can use to support their own commercial and technical strategies.
- Government: the research will contribute towards formulating and delivering the UK's Nuclear Energy Strategy through the new Nuclear Innovation and Research Advisory Board (NIRAB) and the Nuclear Innovation and Research Office (NIRO). Note that the proposed research is fully aligned with the preliminary recommendations of NIRAB for research to support existing and new build nuclear power stations in the UK.
- The Public: a well-informed and supportive public is vital to the future implementation of nuclear energy. The public will want to know how the research outcomes can contribute to producing safer and more economic nuclear fuel, and what associated benefits may arise in other industrial applications.
(b) How
- Regular engagement with existing communities of UK researchers in Nuclear Fuels (PACIFIC) and Nuclear Manufacturing (NNUMAN).
- Public outreach events, such as those organised by the Dalton Nuclear Institute.
- Website: the new Nuclear Fuel Centre of Excellence web site would provide an excellent showcase for disseminating key research information and outcomes.
- Press Articles describing the aim, scope and results of the ATF work.
- Small Scale Initiatives - third party public engagement opportunities, including: media interviews, public lectures, debating forums, etc.
- Training & Development - mentoring and developing our researchers to be competent in the skills and expertise that are valued inside and outside of academia.

Publications

10 25 50
 
Description A ceramic braze material suitable for establishing a robust joint between SiC components has been identified. Autoclave testing has been undertaken to demonstrate that the joint survives over 200 hours at temperatures and pressures representative of a PWR primary circuit. Some limited ion beam irradiation testing has also been undertaken at the University of Manchester's Dalton Cumbria Facility, again with the joint successfully surviving proton irradiation. Further ion beam irradiation testing is planned, together with extended autoclave testing. We also plan to optimise the braze composition, and to investigate the sensitivity of the joints to the manufacturing parameters, in order to identify conditions that can be best integrated within an industrial manufacturing strategy. This planned research work is currently underway within the Nuclear Fuel part of the UK Government's Nuclear Innovation Programme (NIP), in the frame of a collaboration between the University of Manchester and the National Nuclear Laboratory. The NIP is working towards higher TRL implementation of ceramic cladding technology, but we perceive an important need to better understand the more fundamental underpinning science, and we therefore anticipate a further proposal to EPSRC to complement the NIP.
Exploitation Route Our industry partners have indicated that our results are likely to be useful in developing specific designs for nuclear fuel that employ SiC as an accident-tolerant cladding, and also in identifying the process parameters that offer the most suitable means of integration with commercial-scale manufacturing. Our results are also likely to be useful to other UK and international researchers working in this field.
Sectors Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology

 
Description Results from the research have been used to inform UK Government nuclear research policy via the Nuclear Innovation and Research Advisory Board (NIRAB), which published research recommendations in 2016 (including the further development of Accident Tolerant Fuel employing ceramic cladding materials). Subsequently, the recommendations of NIRAB have formed the basis for a new UK national research programme in nuclear technology that specifically includes research into the manufacture of SiC-SiC composite claddings and joining technologies for application to Accident-Tolerant Fuel designs. The results have also been used to inform industry investments and research directions, specifically for our main industry partner Rolls-Royce, but also for our collaborator Westinghouse, which is pursuing SiC-SiC cladding technology to improve the safety of future nuclear fuels.
First Year Of Impact 2016
Sector Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology
Impact Types Economic,Policy & public services

 
Description Participation in NIRAB by Prof. Abram, Prof. Lees, and Prof. Grimes
Geographic Reach National 
Policy Influence Type Membership of a guidance committee
Impact The research that is being recommended by NIRAB will be important in improving the safety and economic performance of current and future UK nuclear power facilities, as well as UK environmental impacts and UK education and training.
 
Description Collaboration with Rolls-Royce on silicon carbide 
Organisation Rolls Royce Group Plc
Department Rolls-Royce Civil Nuclear
Country United Kingdom 
Sector Private 
PI Contribution The University partners have conducted research into the joining and bonding of silicon carbide, and into the performance of silicon carbide samples in conditions representative of water-cooled reactor primary circuits (except for the presence of radiation).
Collaborator Contribution Rolls-Royce have contributed consultancy expertise and materials samples, as well as hosting a research student from the University of Surrey (Peter Cheung).
Impact Publications (separately listed), and proprietary Rolls-Royce evaluations. Disciplines involved include: mechanical engineering, nuclear engineering, materials science, physics, and chemistry.
Start Year 2015