Accurate understanding of diffusion of anionic radionuclides in different clays is significant to predict long‐term performance of high‐level radioactive waste (HLW) repositories. The importance of electrical double layer (EDL) on anionic tracer diffusion in different clays has been studied by both through‐diffusion experiments and pore‐scale simulations in this work. The through‐diffusion experiments measured the effective diffusion coefficient and the accessible porosity of Re (VII) in compacted montmorillonite, Na‐bentonite, and illite/smectite mixed layer (I/S) at different salinities. The results showed that the accessible porosity and the effective diffusion coefficient of Re (VII) in montmorillonite and Na‐bentonite were similar but lower than those in I/S under the same conditions. For mechanism analysis and predictions, a pore‐scale modeling was implemented to simulate the diffusion of anions in compacted clays. In the simulations, the characteristics (porosity, density, and total surface area) of microstructures of montmorillonite and I/S were used to regenerate three‐dimensional pore structures numerically by a Quartet Structure Generation Set method. The Re (VII) diffusion was then simulated by directly solving coupled Poisson‐Nernst‐Planck equations via the lattice Boltzmann method. The diminished effect of EDL was therefore calculated and compared with Donnan and multiporosity models. As EDLs overlap in compacted clays, the Donnan model overestimates the influence of EDL on Re (VII) diffusion, while the multiporosity model underestimates it. The pore‐scale modeling, which captures the structure of overlapping EDLs automatically, can simulate the diffusion of anionic radionuclides in compacted clays without any fitting parameters.

中文翻译：

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孔隙尺度模拟与实验研究压实粘土中阴离子的扩散

正确理解阴离子放射性核素在不同粘土中的扩散对于预测高放射性废物（HLW）储存库的长期性能具有重要意义。在这项工作中，通过扩散实验和孔尺度模拟，都研究了双电层（EDL）对阴离子示踪剂在不同粘土中扩散的重要性。通过扩散实验测量了在不同盐度的压实蒙脱土，钠膨润土和伊利石/蒙脱石混合层（I / S）中，Re（VII）的有效扩散系数和可达到的孔隙度。结果表明，在相同条件下，蒙脱土和钠膨润土中Re（VII）的可及孔隙度和有效扩散系数相似，但低于I / S。对于机制分析和预测，进行了孔尺度建模以模拟压实粘土中阴离子的扩散。在模拟中，利用四方结构生成集方法，将蒙脱石和I / S的微观结构的特征（孔隙度，密度和总表面积）用于数值化三维孔结构。然后通过格子Boltzmann方法直接求解耦合的Poisson-Nernst-Planck方程来模拟Re（VII）扩散。因此，计算了EDL的减弱效果，并将其与Donnan和多孔隙率模型进行了比较。由于EDL在压实粘土中重叠，因此Donnan模型高估了EDL对Re（VII）扩散的影响，而多孔隙度模型则低估了它。孔尺度建模可以自动捕获重叠的EDL的结构，