Zirconium alloys for high burn-up fuel in current and advanced light water-cooled reactors

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In order to improve the efficiency of modern nuclear reactors, reduce operating costs and minimise nuclear waste the fuel manufacturers together with plant operators and nuclear waste agencies are trying to develop fuel assemblies, which can operate for substantially longer times than what is currently achieved. Since Uranium-enrichment technology has progressed significantly in the last two decades it is now the fuel cladding material that limits the level of energy produced from a fuel assembly (termed burn-up by the nuclear industry). Increasing the so-called burn-up of fuel assemblies will improve the fuel economy/fuel usage of civil nuclear reactors, extend refuelling cycles (i.e. reduce the number of shutdowns for refuelling the reactor), and hence reduce the operating costs and nuclear waste. In modern nuclear reactors fuel cladding is based on zirconium alloys due to their good performance in the environment of water-cooled reactors and their transparency to neutrons. The time the cladding material can operate in such an environment (and therefore the level of energy that can be produced from a fuel assembly) is proportional to the corrosion properties. Longer lasting cladding material would require zirconium alloys with a more protective oxide layer, which would avoid any accelerated corrosion, breakaway of the oxide layer and protect against hydrogen pick-up. To date, any development in this area has been purely empirical and has not resulted in the required step change, which would allow operating the fuel assemblies to the desired burn-up. The scientific basis of this application is to address these issues by studying the influence and inter-relationships of all relevant microstructural features, local stresses, electronic defects in the oxide, in both commercial and model alloys when corrosion tested in an autoclave environment. This requires the project team to use the latest generation of analytical techniques in a coherent, interdisciplinary program. In addition our industrial partners provide access to additional specialist facilities such as autoclaves or melting facilities to produce model alloys. The key theme is to develop a mechanistic understanding of the corrosion process to enable the development of physically-based models, which will enable the design and full exploitation of alloys optimized to delay breakaway oxidation and oxidation growth. The research will be undertaken by a multi-university team, encouraging PhD students and post-doctoral research associates to form a core group of researchers who work together to exploit world-class facilities from different institutions.