Understanding the Effect of Strain on Microstructure Properties and Environmental Degradation of AGR Fuel Cladding

英国核能的支柱是其先进的气体冷却反应堆(AGR)。这些反应堆内的铀氧化物燃料被安全地包裹在20%Cr-25%Ni-Nb不锈钢覆层中，以承受较高的运行温度和相关的烧毁条件。然而，辐射和温度引起的包层微观结构的变化发生在使用暴露期间，这可能使材料容易受到局部腐蚀，这在反应堆后储存期间已经观察到。本PHD项目旨在阐明微结构应变对材料性能的影响以及在反应堆后水储存环境中的腐蚀行为。研究的主要目的是了解局部微结构应变和冷加工是否在AGR燃料针失效中起关键作用，主要集中在pH控制环境中的水存储条件。冷加工、应变和敏化(以及敏化然后应变)样品的微观结构将使用广泛的表征技术来表征，包括扫描电子显微镜、原子力显微镜/SKPFM、EBSD、X射线衍射和XPS。将使用新的电化学表征技术进行纳米、微观和介观尺度的腐蚀测量，以探索腐蚀响应。然后，腐蚀速率测量将使用原位时间推移成像和数字图像相关(DIC)将其与局部微结构应变特征相关联。还将通过将应变AGR覆层暴露在Co-60辐照下的薄层电解液中，探索使用类似的表征技术和方法调查干燥储存条件的工作的延伸。该项目借鉴了NDA以前支持的一项博士研究，该研究探索了AGR燃料包壳敏化模拟剂中的一般腐蚀机理，确定了碳化物夹杂物的作用和相关的腐蚀机理。这里建议的工作重点是与AGR燃料针相关的更现实的微观结构条件，包括端盖、拉紧的防堆积凹槽和焊接。学生将有机会在NNL/culham上花几天时间与NNL专家讨论结果/文献，并在NNL的数据库中找到可能感兴趣的文献。将寻求借调到核退役管理局(NDA)。(对斯旺西大学进行研究访问，探索其现场延时钻井平台的应用。

The backbone of the UK's nuclear energy is its fleet of Advanced Gas-cooled Reactors (AGR). The Uranium-oxide-based fuel within these reactors is safely encased in 20%Cr-25%Ni-Nb stainless steel cladding, to withstand the high operating temperatures and associated burn-up conditions. Radiation- and temperature-induced changes in cladding microstructure, however, occur during service exposure, which can render the material susceptible to localised corrosion, which has been observed during post-reactor storage. This PhD project aims to elucidate the effect of microstructure strain on the material performance and corrosion behaviour in post-reactor aqueous storage environment. The key objective of the research is to understand whether local microstructure strain and cold work plays a key role in AGR fuel pin failure, focusing primarily on aqueous storage conditions in pH-controlled environments.The microstructure of cold worked, strained, and sensitised (as well as sensitised and then strained) samples will be characterised using a wide range of characterisation techniques, including SEM, AFM/SKPFM, EBSD, XRD and XPS. Nano-, micro-, and meso-scale corrosion measurements using novel electrochemical characterisation techniques will be employed to probe the corrosion response. Corrosion rate measurements will then be correlated to local microstructure strain characteristics using in-situ time-lapse imaging and Digital Image Correlation (DIC). An extension of the work to investigate dry storage conditions using similar characterisation techniques and methodologies will also be explored via exposure of strained AGR cladding to thin layer electrolytes under Co-60 irradiation. The proposed project draws on a previous PhD study supported by NDA, which has explored general corrosion mechanism in sensitised simulants of AGR fuel cladding, identifying the role of carbide inclusions and associated corrosion mechanism. The proposed work here focuses on more realistic microstructure conditions relevant to AGR fuel pins, including end caps, strained anti-stacking grooves and welds.The student will have opportunity to spend several days @ NNL/Culham to discuss results/literature with NNL experts, and to Identify literature in NNL's data-base that may be of interest. A secondment into the Nuclear Decommissioning Authority (NDA) will be sought. (A Research visit to Swansea University to explore application of their in-situ time-lapse rigs.