Experimental study of aging-induced cementation effect on permeability property of bentonites
Experimental study of aging-induced cementation effect on permeability property of bentonites
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DOI：
10.1088/1755-1315/1124/1/012118
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发表时间：
2023-01
期刊：
影响因子：
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通讯作者：
D. Ito;H. Wang;H. Komine
中科院分区：
文献类型：
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作者：
D. Ito;H. Wang;H. Komine
在高放射性废物的地质处置中，日本计划将锂蒙脱石用作放射性废物周围的缓冲材料。膨润土基缓冲材料需要低的水渗透性以延迟地下水与废物之间的接触。由于废物中放射性核素的半衰期极长，设计了包括缓冲材料在内的若干屏障，以维持地质处置设施数万年的可用性。然而，在高水压、高温和各种地下水化学的处置环境中，会发生胶结作用，从而使缓冲区中的膨润土的性质发生变化。由于难以通过实验模拟长期的蚀变过程，很少有研究能够了解胶结作用对膨润土性质的影响。从天然类似物的观点看，缓冲层的胶结作用可视为膨润土成矿过程的一部分。为此，本研究分别对日本、美国和中国三种不同地质时代的钠型膨润土矿石进行渗透性试验，考察胶结作用对膨润土渗透性的影响。为了进行比较，制备了未扰动和复溶的样本。结果表明，各矿石原状和重塑试样的导水率相差小于一个数量级，且这种差异与矿石的地质年龄无关。从这些结果来看，胶结作用对膨润土缓冲层水力特性的影响似乎不大。也可能是胶结作用抑制蒙脱石膨胀、堵塞水流通道的结果。
In geological disposal for high-level radioactive waste, bentonites are planned to be used as the buffer material surrounding radioactive waste in Japan. Bentonite-based buffer material requires low water permeation for delaying contact between groundwater and the waste. Because of the extremely long half-lives of radionuclides of the waste, several barriers including the buffer material are designed to maintain workability of the geological disposal facility for tens of thousands of years. However, in the disposal circumstances with high water pressure, high temperature and various groundwater chemistries, occurrence of cementation and consequently property changes of the bentonite in the buffer are concerned. Few studies are available to understand the effect of cementation on bentonite properties because of the difficulties of simulating long-term alteration process experimentally. From the viewpoint of natural analogues, cementation process of the buffer may be regarded as part of formation process of bentonite ore. Thus, in this study, permeability tests were conducted on three kinds of Na-type bentonite ores with different geological ages from respectively, Japan, USA, and China to see the influence of cementation on permeability of bentonites. For comparison, undisturbed and reconstituted specimens were prepared. The results show that difference of hydraulic conductivities of the undisturbed and reconstituted specimens for each ore is less than one order, and this difference seems not to correlate with the geological age of the ores. From these results, the influence of cementation on the hydraulic properties of bentonite buffer seems small. It may also be a counteracted result by cementation effects in terms of restriction of the swelling of montmorillonite and blockage of water flow paths.