Engineering Geology ( IF 7.4 ) Pub Date : 2022-07-29 , DOI: 10.1016/j.enggeo.2022.106800 Huaxiang Yan, Andrey Jivkov, Majid Sedighi
Compacted bentonite is considered as an engineered barrier in geological disposal of nuclear waste in fractured rocks. One concern with this concept is that the expansion of bentonite into fractures as the system saturates may lead to its erosion by flowing water. The loss of bentonite through erosion over long times may compromise the barrier. Commercial bentonite contains less soluble accessory minerals and experimental observations have shown that these are co-transported with clay minerals during expansion and form a mineral film at the eroding boundary. Quantifying the effects of the mineral film on the erosion rate is important for the assessment of the long-term sealing capacity of bentonite barriers. The paper presents a model for the extrusion of bentonite into fractures that considers key processes governing the co-transport of less soluble accessory minerals and explains why and where the mineral film forms and how it affects the erosion rate.
The model is tested against two sets of published experimental data. It is demonstrated that the model predicts the phenomena observed in experiments: the build-up of a mineral film near the extrusion boundary; and the progressive growth of the mineral film thickness. Importantly, the model allows for investigating the effects of key environmental and material parameters – water chemistry, filtration coefficient, and mineral fraction – on the expansion and erosion. The results of such investigations are presented. It is shown that higher water ion concentration, larger filtration coefficient, and larger fraction of accessory minerals retard the swelling and extrusion of bentonite, thus reducing the overall erodibility. It is further shown that the presence of less soluble accessory minerals may reduce the loss of bentonite by a factor of 2 compared to a pure bentonite.
中文翻译:
压实膨润土膨胀过程中难溶性辅助矿物的共运及其对侵蚀的影响
压实膨润土被认为是地质处置破碎岩石中核废料的工程屏障。对这一概念的一个担忧是,当系统饱和时膨润土膨胀成裂缝可能导致其被流动的水侵蚀。膨润土因长时间侵蚀而损失可能会损害屏障。商业膨润土含有较少的可溶性辅助矿物,实验观察表明,这些矿物在膨胀过程中与粘土矿物共同运输,并在侵蚀边界处形成矿物膜。量化矿物膜对侵蚀速率的影响对于评估膨润土屏障的长期密封能力很重要。
该模型针对两组已发布的实验数据进行了测试。结果表明,该模型预测了实验中观察到的现象:在挤压边界附近形成矿物膜;以及矿物膜厚度的逐步增长。重要的是,该模型允许研究关键环境和材料参数(水化学、过滤系数和矿物分数)对膨胀和侵蚀的影响。介绍了此类调查的结果。结果表明,较高的水离子浓度、较大的过滤系数和较大比例的副矿物会阻碍膨润土的膨胀和挤出,从而降低整体的可蚀性。