MAINTAiN - Multi-scAle INTegrity assessment for Advanced high-temperature Nuclear systems

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This project aims to provide a predictive model for creep deformation of in-core nuclear components in the presence of irradiation damage. Creep deformation is time-dependent permanent deformation of materials under load nominally at temperatures higher than half the material melting point. Creep deformation plays a crucial role in the structural integrity of engineering components that work at high temperature such as those in aerospace propulsion and energy generation. It is one of the main life limiting factors of nuclear power plants that work at high temperature. This includes fusion reactors, Gen IV fission nuclear reactors, and UK's unique Advanced Gas-cooled Reactors. The context of this project is nuclear. UK's energy mix currently is and planned to continue to benefit from substantive contributions from nuclear. In addition, UK is the only country in the world that has in-depth and knowledge of designing, building, and operating high temperature nuclear power plants with many of its structural components working in the creep regime. The immediate new build reactors at Hinckley Point, Wylfa, and Moorside do not work at temperatures that induce creep. However, fusion reactors and Gen IV fission nuclear reactors are envisaged to be working at much higher temperatures to increase their thermal efficiency and as such they are susceptible to creep deformation and damage. Therefore, there is a high risk that UK loses its current unrivalled authority on high temperature structural integrity by the time the next generation of nuclear power plants are built, currently planned for 2050. One of the objectives of this proposal is to maintain UK lead in high temperature structural integrity of nuclear industry by developing new knowledge and new skilled scientists in the field.The current creep engineering structural integrity codes are based on empirical equations extracted from tests in certain standard conditions. They ignore the material microstructure, which evolves during a 60 years' service of a power plants. An important limiting factor that is currently ignored in the engineering codes and will be highly influential in the mechanical response of components for next generation power plants is irradiation damage. One of our objectives is therefore to include the effects of irradiation damage on the macro-scale mechanical response of materials by including the changes it makes on the material microstructure in their constitutive laws. To this end our main objective is to develop a predictive, multi-scale, microstructurally informed creep deformation model. The model spans from the fundamental physical equations that govern the dislocation mobility at high temperature (dislocations are imperfection in material crystal structure and their movements under load account for most the material permanent deformation) to the behaviour of engineering components with complex geometries and varied loading history and conditions made from homogenised material. The model will help engineers to predict the behaviour of critical components in a nuclear reactor and make informed decision on their fitness for service which is a crucial safety decision.Once our creep model is validated and verified by experiments across three mico, meso, and macro length scales, it will provide the foundation for a new generation of engineering structural integrity codes that are based on a mechanistic understanding the material and its microstructure and therefore is predictive, more accurate and not confined to the test conditions it is based on. This will be an invaluable asset for the UK to play a major role in designing, building, and operating future nuclear power plants.