Corrosion of steel canisters containing buried high-level radioactive waste is a relevant issue for the long-term integrity of repositories. The purpose of the present study was to evaluate this issue by examining two differently corroded blocks originating from a full-scale in situ test of the FEBEX bentonite site in Switzerland. The FEBEX experiment was designed initially as a feasibility test of an engineered clay barrier system and was recently dismantled after 18 years of activity. Samples were studied by ‘spatially resolved’ and ‘bulk’ experimental methods, including Scanning Electron Microscopy, Elemental Energy Dispersive Spectroscopy (SEM-EDX), μ-Raman spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and 57Fe Mossbauer spectrometry, with a focus on Fe-bearing phases. In one of the blocks, corrosion of the steel liner led to diffusion of Fe into the bentonite, resulting in the formation of large (width > 140 mm) red, orange, and blue colored halos. Goethite was identified as the main corrosion product in the red and orange zones while no excess Fe2+ (compared to the unaffected bentonite) was observed there. Excess Fe2+ was found to have diffused further into the clay (in the blue zones) but its speciation could not be unambiguously clarified. The results indicate the occurrence of newly formed octahedral Fe2+ either as Fe2+ sorbed on the clay or as structural Fe2+ inside the clay (following electron transfer from sorbed Fe2+). No other indications of clay transformation or newly formed clay phases were found. The overall pattern indicates that diffusion of Fe was initiated when oxidizing conditions were still prevailing inside the bentonite block, resulting in the accumulation of Fe3+ close to the interface (up to three times the original Fe content), and continued when reducing conditions were reached, allowing deeper diffusion of Fe2+ into the clay (inducing an increase of 10–12% of the Fe content).

中文翻译：

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瑞士 Grimsel 试验场 FEBEX 原位试验中钢-膨润土相互作用 18 年

盛放高放废物的钢罐的腐蚀是影响处置库长期完整性的一个相关问题。本研究的目的是通过检查源自瑞士 FEBEX 膨润土现场全尺寸原位测试的两种不同腐蚀块来评估这个问题。FEBEX 实验最初是作为工程粘土屏障系统的可行性测试而设计的，最近在经过 18 年的活动后被拆除。通过“空间分辨”和“体”实验方法研究样品，包括扫描电子显微镜、元素能量色散光谱 (SEM-EDX)、μ-拉曼光谱、X 射线荧光 (XRF)、X 射线衍射 (XRD)和 57Fe Mossbauer 光谱法，重点是含铁相。在其中一个街区，钢衬里的腐蚀导致 Fe 扩散到膨润土中，导致形成大的（宽度 > 140 毫米）红色、橙色和蓝色光晕。针铁矿被确定为红色和橙色区域的主要腐蚀产物，而没有观察到过量的 Fe2+（与未受影响的膨润土相比）。发现过量的 Fe2+ 进一步扩散到粘土中（在蓝色区域），但其形态不能明确澄清。结果表明新形成的八面体 Fe2+ 以吸附在粘土上的 Fe2+ 或粘土内部的结构 Fe2+ 的形式出现（随着吸附的 Fe2+ 的电子转移）。没有发现粘土转变或新形成的粘土相的其他迹象。