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气冷反应堆（AGR）。这些反应堆中的铀氧化物基燃料安全地包裹在20%Cr-25%Ni-Nb不锈钢包壳中，以承受高操作温度和相关的燃耗条件。然而，辐射和温度引起的包层微观结构变化发生在服务暴露期间，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。本博士项目旨在阐明微观结构应变对反应堆后水存储环境中材料性能和腐蚀行为的影响。研究的主要目的是了解局部微观结构应变和冷加工是否在AGR燃料棒失效中起关键作用，主要关注pH控制环境中的含水储存条件。（以及敏化，然后应变）样品将使用广泛的表征技术，包括SEM，AFM/SKPFM，EBSD，XRD和XPS。纳米，微米，和中尺度的腐蚀测量使用新的电化学表征技术将被用来探测腐蚀响应。腐蚀速率的测量，然后将相关的局部微观结构应变特性，使用原位延时成像和数字图像相关（DIC）。延伸的工作，调查干储存条件下使用类似的表征技术和方法，也将探讨通过暴露应变AGR包层的薄层电解质钴-60照射。拟议的项目借鉴了NDA支持的以前的博士研究，该研究探索了AGR燃料包壳敏化模拟物的一般腐蚀机制，确定了碳化物夹杂物的作用和相关的腐蚀机制。这里的工作重点是更现实的微观结构条件相关的AGR燃料棒，包括端盖，应变反堆积槽和焊缝。学生将有机会花几天@ NNL/卡勒姆讨论结果/文献与NNL的专家，并确定文献在NNL的数据库中，可能是感兴趣的。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，探索其原位延时钻机的应用。

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.