An innovative, multi-scale, real-time approach to the understanding of deformation and fracture in irradiated nuclear reactor core graphites

石墨是目前英国反应堆中使用的最具吸引力的材料之一，也是新一代高温反应堆（Gen IV）的候选材料，设计运行时间为60至100年。石墨在辐照下具有复杂的微观结构和行为;它是先进气冷反应堆（AGR）中不可更换的反应堆堆芯组件，因此寿命有限。这些材料吸引了广泛的学术和工业审查，以协助核裂变反应堆的安全运行。目前，英国有16座反应堆，约占其发电量的20%，除一座外，所有反应堆都计划在2023年退役。然而，已计划将AGR装置的寿命平均延长7年。距离这些AGR最早的“寿命终止”情景还有8年，这为石墨工作方案确定了前景。AGR的寿命延长具有战略意义，不仅对EDF能源及其商业利益，而且对英国在新一代反应堆能够上线之前满足电力需求的能力也具有重要意义。进一步了解AGR慢化剂组件中的石墨结构将继续确保其安全性。关键的挑战仍然存在，必须在提高对核石墨的基本机械理解方面加以解决。虽然在这些领域的研究是困难的和具有挑战性的，目前的项目建议建立在PI的专业知识在这个主题领域，结合使用新兴的新技术，攻击这个关键问题。核石墨的多尺度表征为了在适当的长度尺度上对辐照核反应堆堆芯石墨的显著变形、断裂机制和一般机械性能进行基于微观结构的描述，并对损伤演化进行量化，布里斯托大学的PI开发了一种研究局部损伤的新方法。这种方法，并结合计算机模拟的结果，具有建立一个坚实的基础基础，为结构完整性分析和寿命预测的核石墨.核石墨在温度下的基于微观结构的变形和断裂为了提供三维的、原位的、在温度（超过1000度）下的、基于微观结构的变形和断裂，第四代反应堆）使用计算机同步加速器X射线显微断层扫描表征石墨的变形和断裂。没有对核石墨进行过这种试验。这一目标将考虑到英国AGR反应堆中产生的微观结构梯度，因此，对寿命延长决策产生直接影响。这项工作的一部分将与美国伯克利加州大学的Robert里奇教授一起进行。核石墨在应力作用下基于微观结构的热蠕变为了提供对石墨在使用寿命期间尺寸变化的机械理解，即评估在从环境温度到反应堆温度（超过1000摄氏度）的负载下，原始石墨和辐照石墨对蠕变的热贡献。第四代反应堆）。英国国家物理实验室的Bryan Roebuck教授将提供实现这些研究的设备。从上述三个方面优化项目产出和投入将有助于产生经修订的寿命评估方法。在完成上述三个关键领域的项目后，对石墨及其所代表的材料类别的机械理解将直接使相关学术界受益。在项目结束时以研讨会的形式传播结果将为工业界提供投入，从而对英国现有反应堆的持续安全运行决策和全球未来反应堆的验证产生直接影响。

Graphite is one of the most fascinating materials used in the current UK reactors and is a candidate for the new generation of high temperature reactors (Gen IV) designed to operate for 60 to 100 years. Graphite has complex microstructure and behaviour under irradiation; it is a non-replaceable reactor core component in Advanced Gas-cooled Reactors (AGRs) and, hence, is life-limiting. This material has attracted extensive academic and industrial scrutiny to assist in underwriting the safe operation of nuclear fission reactors. Currently, the UK has 16 reactors generating about 20% of its electricity and all but one of these is scheduled to retire by 2023. However, life extension averaging 7 years for AGR units has been planned. There is 8 years before the earliest "end-of-life" scenarios for these AGRs is reached and this has set the horizon for this work programme on graphites. Lifetime extension of the AGRs is of strategic importance, not only for EDF Energy and its commercial interests but also for the UK's ability to meet electricity demand before the new generation of reactors are able to come online. Further understanding of the graphite structure in the moderator components of AGRs continues to ensure their safety. Key challenges remain, and have to be addressed in terms of improving the fundamental mechanistic understanding of nuclear graphite. Although research in these areas is difficult and challenging, the present project proposal builds on the PI's expertise in this topic area, combined with the use of emerging novel techniques, to attack this critical problem.1. Multi-scale characterisation of nuclear graphiteTo generate microstructure-based descriptions at appropriate length-scales - with quantification of damage evolution - of the salient deformation, fracture mechanisms and general mechanical properties of irradiated nuclear reactor core graphites, a novel approach to investigate local damage has been developed by the PI at the University of Bristol. This approach, and combining the outcomes with computer modelling, has the advantage of establishing a solid fundamental base for structural integrity analysis and lifetime prediction of nuclear graphite.2. Microstructure-based deformation and fracture of nuclear graphite at temperatureTo provide three-dimensional, in situ, at-temperature (over 1000 deg. C for Gen IV reactors) characterisation of the deformation and fracture of graphites using computed synchrotron X-ray micro-tomography. No such tests have been undertaken on nuclear graphite. This objective will take into account the microstructural gradient created in AGR reactors in the UK and, hence, provide direct impact on life extension decision making. Part of this work will be undertaken with Prof. Robert Ritchie at the University of California, Berkeley, U.S.3. Microstructure-based thermal creep in nuclear graphite under stressTo provide mechanistic understanding of the dimensional change of graphite over service life, i.e. to evaluate the thermal contribution to creep of virgin and irradiation graphite under load from ambient to reactor temperature (over 1000 deg. C for Gen IV reactors). Prof. Bryan Roebuck, of the National Physical Laboratory in the UK, will provide access to equipment that allows the realisation of these investigations.4. Optimisation of project outputInputs from the above three aspects will assist in generating a revised life evaluation methodology. On completion of the project with the above three key areas addressed, mechanistic understanding of the graphite, and the class of materials it represents, will directly benefit the related academic community. Dissemination of the results at the end of the project in the form of workshops will feed the input to industry and, thus, allow direct impact on the decision making for the continued safe operation of current reactors in the UK and validation for future reactors globally.