MIDAS - Mechanistic understanding of Irradiation Damage in fuel Assemblies

Lead Research Organisation: University of Manchester
Department Name: Materials

Abstract

In order to meet the UK's carbon reduction targets, and achieve an energy mix that produces less CO2, we must continue to investigate ways in which to make nuclear power cleaner, cheaper and safer. At the same time, as new reactors such as Hinkley Point C are built, the UK needs to develop the work force who will operate, regulate and solve technical problems in civil nuclear power, in order to capitalise on our investment in nuclear energy. Important in this respect is that the UK currently operates mainly old advanced gas-cooled reactors, fundamentally different from the next fleet of UK nuclear power stations, which will be light-water reactors. Key to this change, in terms of this research project, is that Zirconium is a preferred fuel cladding material in LWRs.

A major part of a nuclear reactor is the fuel assembly - the structure that encapsulates the highly radioactive nuclear fuel. Understanding the performance of the materials used to make these assemblies is critical for safe, efficient operation, and they must be able to maintain their structure during normal operation, handling and storage, as well as survive in the unlikely event of an accident, when they become crucial in preventing the escape of radioactive materials. Because of the need to operate nuclear reactors as safely as possible, fuel is often removed well before it is spent, as we currently do not know enough about fuel assembly materials, so must adopt a highly cautious, safety-first approach. This does mean, however, that it is more costly to run a reactor, as assemblies must be replaced well before all the fuel is consumed, and this also means the assembly then - prematurely - becomes additional nuclear waste, which must be safely handed and stored, at further high cost.

By gaining greater understanding of how assembly materials perform when irradiated, we will be able to make more accurate safety cases, which will mean that fuel assemblies can be used for longer periods without additional risk. Such knowledge will enable the UK to operate the next generation of reactors far more efficiently, significantly reducing the cost of nuclear power. This is particularly important now, given that the UK is going to have light-water, instead of advanced gas-cooled, reactors, and with it the fuel assembly and its material will change very fundamentally.
This research effort will also significantly benefit other countries using nuclear energy, which will establish the UK as a centre of expertise in the area. This will further attract inward investment in research and development in the UK, creating future wealth and employment alongside cleaner energy.

A second key theme of the project will be to explore the use of zirconium alloys in critical components for future fusion reactors. The UK has a leading position in defining the materials that will be chosen for the ITER and DEMO international fusion projects, and this theme will contribute to maintaining the UK's reputation as a centre of excellence in fusion research.

Planned Impact

Who might benefit? UK and international nuclear energy companies and supply chains. The community developing future fusion machines.
How might they benefit? MIDAS will generate far deeper understanding of key nuclear fuel assembly degradation mechanisms during normal operation, fuel storage and accident scenarios. Improved understanding will feed into more physically informed performance codes, improving safety cases, reducing nuclear energy costs, and reducing produced and stored nuclear waste. Specific impacts should include new cladding compositions with higher burnup levels (manufacture and operation), zero fuel failure in normal operation, and safer storage through improved assembly handling and better definition of storage parameters. MIDAS will bring better understanding of accident performance, reducing uncertainty in structural integrity predictions and developing guidance on modified fuel cladding for greater accident tolerance, as well as improving normal operation. One day of reactor downtime costs an operator ~£1M, so by safely operating fuel assemblies for longer savings run into £10Bns during a reactor lifetime, including waste management costs. Even small improvements in performance, or limited relaxation of safety-driven rod out-loading scheduling, will result in very large economic benefits to UK and international civil power industries.
The new work proposed on Zr alloys for future fusion breeder blanket designs will expand options available to the fusion community, where materials selection for performance-critical assemblies is proving extremely difficult - relying on alloys like EUROFER that have never been manufactured at the necessary scale. Pre-existing, nuclear-qualified Zr-alloys could play a major part in solving these issues.

Who: UK nuclear workforce.
How: MIDAS will contribute to the challenge of developing the next generation of nuclear researchers, growing the UK skills-base and retaining UK talent, by training PDRAs and ~30 PhDtudents. We will generate a new workforce trained in nuclear research strategies, planning campaigns on active materials, and working with industry and national lab partners. Many alumni will progress to industry, providing direct knowledge transfer of specialist techniques and modelling tools developed in MIDAS. Some will join regulators (with a shortage of staff experienced in radiation damage), or become next generation young academics, building nuclear research groups.

Who: UK Government - clean energy strategy.
How: MIDAS will contribute to UK strategy for a CO2-free energy mix, influencing policy and investment via its focus on safety-critical material systems used in new fleet LWRs, e.g. Hinkley Point C. MIDAS will help UK Govt achieve its Nov 2017 White Paper aim to "continue to work closely with the nuclear [industry] to further drive down the costs of clean power, while building UK supply chains".

Who: UK nuclear research community.
How: MIDAS will be demonstrate the potential of high-impact advanced post-irradiation examination, establishing the UK as the go-to place for this in future irradiation campaigns, generating inward investment. The UK has already been selected as the best place for work on this unique sample set (£10M worth), and MIDAS will further position the UK as a centre of excellence in active nuclear materials research.

Who: National Nuclear User Facility; Henry Royce Institute.
How: MIDAS is the only UK research team with access to any significant volume of active material. The team will make extended use of National Nuclear User Facilities (NNL, Dalton Cumbrian Facility, the new Materials Research Facility at Culham), and Henry Royce Institute facilities. This will demonstrate to Govt the benefit of considerable investment to-date in these facilities, contributing to their output/impact, and future-proofing UK capability development by raising the nation's profile in nuclear research, attracting further investment.

Publications

10 25 50