Abstract

Deep, underground repositories are needed to isolate radioactive waste from the biosphere. Because bentonite is an integral component of many multibarrier repository systems, information on the hydraulic behavior of bentonite is crucial for modeling the long-term viability of such systems. In this paper the hydraulic behavior of bentonite samples was analyzed as a function of aggregate size, and samples were subjected to hydrothermal treatments involving contact with NaCl, KCl, and deionized water. Neutron and X-ray imaging were used to quantify water sorption into packed bentonite samples and bentonite swelling into the water column. The distance between the original clay-water interface and the wetting front was determined as a function of time. Average water uptake exhibited a square-root-of-time dependence in freshly prepared samples, but more variable rates were observed for samples previously in contact with water. The radiography was supported by small-angle neutron scattering analysis and ultra-small-angle neutron scattering analysis of aggregate size distributions and by inelastic neutron scattering to understand the physicochemical environment of the sorbed water. Results showed that hydrothermal treatment with KCl had the greatest effect of increased water transport in the bentonite, possibly as a result of the interaction of K⁺ with smectite layers in the clay.

摘要

需要深层地下储存库将放射性废物与生物圈隔离。由于膨润土是许多多屏障储存系统的组成部分，因此有关膨润土水力行为的信息对于模拟此类系统的长期生存能力至关重要。在本文中，膨润土样品的水力行为作为集料尺寸的函数进行了分析，样品经过了与 NaCl、KCl 和去离子水接触的水热处理。使用中子和 X 射线成像来量化填充膨润土样品中的吸水性和膨润土膨胀到水柱中的情况。原始粘土-水界面和润湿前沿之间的距离被确定为时间的函数。在新鲜制备的样品中，平均吸水量表现出时间的平方根依赖性，但对于先前与水接触的样品，观察到更多的可变速率。射线照相术得到了聚集体尺寸分布的小角中子散射分析和超小角中子散射分析以及非弹性中子散射的支持，以了解吸附水的物理化学环境。结果表明，用 KCl 进行水热处理对增加膨润土中的水传输的影响最大，这可能是 K 相互作用的结果⁺粘土中有蒙脱石层。