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

Lead Research Organisation: University of Bristol
Department Name: Mechanical Engineering

Abstract

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.

Planned Impact

The proposed work has an impact on three different areas: research and development including academia, civil nuclear industry, and nuclear regulator. The project is aimed at developing a predictive creep behaviour model in the presence of irradiation damage. This model will be the foundation of a new generation of high temperature engineering structural integrity codes. The codes can be used in the research and development stage of designing fusion and Generation IV fission power plants that are expected to serve for more than 60 years. The results of materials testing which we will be carrying out to verify and validate the model will be stored in a database and readily available to scientists and engineers. It provides an invaluable insight in the behaviour of materials that are expected to be used within next generation of nuclear power plants.

UK is expected to play a major role in design and fabrication of next generation of the power plants. The next generation of high temperature engineering structural integrity codes will be used by UK manufactures when they will design the reactor and its structural components. This will be putting UK at the forefront of civil nuclear industry which unfortunately we lost in the past 30 years due to diminishing highly skilled workforce. The use of codes is not limited to manufactures and operators but also by the vast civil nuclear supply chain industry such as the consultancies. The consultancy companies export UK knowledge in the field of structural integrity to other countries, China and India, particularly. Our research impacts these companies considerably once the methodology we develop is commercialised by being incorporated into the engineering code and ensures their up-to-date services remain as one of the greatest civil nuclear export of UK. It is evident that our research will impact future and to some extent present nuclear power plant operators and provide them with cost-cutting modelling techniques.

UK's regulatory system is unique as it is not prescriptive. As such, research and development carried out under RCUK plays a major role in guaranteeing the best practice is followed. Nuclear research has now been reenergised after a hiatus period in the past few decades and the experimental and modelling techniques have had an enormous development in that period. It is therefore envisaged that new research carried out using the advanced new techniques will be shedding a light on long standing questions with which the operators and regulator have been facing for many decades.

Finally, the ultimate benefit of a publicly funded research should be to the society and UK people. The proposed research will contribute to knowledge required for efficient and reliable use of nuclear energy that is essential for UK energy safety.

Publications

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Erinosho T (2018) Influence of prior cyclic plasticity on creep deformation using crystal plasticity modelling in International Journal of Solids and Structures