Multiscale Simulation of Second Phase Particle Evolution in Zirconium

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Zirconium alloys are widely used in nuclear fuel assemblies due to their favourable combination of properties and neutron transparency. Microstructural control is critical to obtaining zirconium alloys with the desired properties, and maintaining the desired microstructure and properties over long service lives is central to reactor performance and safety. An important feature of the microstructure is second phase precipitate particles (SPPs). These particles precipitate during processing and have a strong influence on important properties, particularly corrosion performance. It is known that control of the size and distribution of particles is vital to ensuring property targets are maintained but this is complex because the SPPs evolve under thermal and irradiation exposure, potentially negatively impacting on performance. To understand and predict these effects, a microstructural model for SPP evolution would be of great utility, but developing such a model requires capturing the complex physical mechanisms in a sufficiently simple way to enable time-efficient predictions to be made. Initial steps in this direction have already been made to establish a basic modelling framework, but to become a useful tool for quantitate prediction and reliable industrial use requires overcoming significant hurdles that must be informed by experimental insights into mechanisms. It is now timely to tackle this problem since a major UK activity (EPSRC MIDAS programme) has now launched which will explore microstructural evolution in irradiated zirconium alloys at a level of detail previously unattainable, along with development of simulation tools to predict atomic scale behaviour. This project, associated with MIDAS, will leverage the resultant data to develop a microstructure scale model for SPP evolution that includes irradiation effects, capturing the essential physical processes at higher fidelity than previously possible and validating the model against new and existing experiments to provide confidence in its application.The outcomes of this work will be a model, verified with experimental data, that can better help the nuclear power industry understand and predict the evolution of microstructure and properties of zirconium alloys used in reactors during processing and service.