Understanding the In-Reactor Performance of Advanced Ceramic Cladding Materials

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.

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.