Investigating atomic-scale mechanisms of thermal ageing in steels harvested from decommissioned pressurisers from Ringhals Units 2 and 4 Reactors

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Many countries now have ambitious net zero targets. The United Kingdom was the first to commit to net-zero by 2050, requiring a significant increase in power production by both nuclear and renewables. Nuclear plants are designed to last many decades but, under extreme conditions, materials degrade potentially resulting in early plant closures. Optimising materials subject to the extreme reactor conditions, so as to minimise mechanical degradation, and maximise plant lifetime, are critical to underpinning the viability of nuclear energy for future generations. Specifically, this project will investigate the mechanisms of thermal ageing in unique materials harvested from the decommissioned pressurisers of the Swedish Ringhals Units 2 and 4 Reactors. The pressuriser is a component of the primary coolant circuit in a pressurised water reactor (PWR) which regulates pressure and temperature within the primary circuit. Hence, the structural integrity of these steel components is of critical importance for the safe long-term operation of PWRs.Using a combination of advanced microstructural characterisation techniques, in particular Atom Probe Tomography (APT), the main focus of this study will be how the atomic scale microstructure in these steels has evolved during long term thermal ageing, up to 300,000 hours in service. This change in fine-scale microstructure will be directly correlated to the observed degradation in mechanical properties. The new mechanistic insights delivered in this project will be critical to the development of thermodynamic models to understand and predict how microstructure and mechanical properties will evolve over even longer times in service and thus is of significant importance to safely extending the operating lifetimes of PWRs. The insights from this project will also help to inform the development and selection of new materials for the design of more efficient next generation future reactors. This project will be undertaken in close collaboration with our industrial partners National Nuclear Laboratory (UK) and Vattenfall (Sweden) who are one of Europe's largest producers of electricity and the owner/operator of the Ringhals power plant supplying the ex-reactor service components to be investigated in this study. The project directly addresses the EPSRC themes, Energy and Manufacturing the Future. It also directly contributes to a range of topics in the EPSRC priority area Advanced Materials, such as: Materials Engineering: Metals and Alloys and Materials for Energy Applications.