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标题：Possibilities and Limitations in Using Smectite Clay for Isolating High-Level Radioactive Waste (HLW)
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作者：Roland Pusch ; Richard Weston ; Jörn Kasbohm 等
期刊名称：Journal of Earth Sciences and Geotechnical Engineering
印刷版ISSN：1792-9040
出版年度：2020
卷号：10
期号：5
页码：87-130
语种：English
出版社：Scienpress Ltd
摘要：Global interim storage of HLW has reached a level that requires large extension ofthe storage capacity, which puts pressure on regulatory authorities and nationalparliaments for finding and applying ways of safe disposal of such waste. Animportant option is to use very dense natural expandable clay for isolating spentnuclear fuel in boreholes where it will be exposed to high temperature for hundredsto a few thousand years. The clay must be placeable and homogeneous and be ableto sustain significant shear strain and temperatures up to 150oC without leaking orlosing its ductile behaviour and self-healing potential. In this document the longterm function of such seals, which have the form of dense smectite blocks and softsmectite mud surrounding the containers/canisters will be described with respect tothe impact of degrading physical/chemical mechanisms. Focus is on clay barriersfor isolating spent nuclear fuel in up to 3-4 km deep boreholes but aspects are alsoprovided on disposal in mined repositories at a few hundred m depth below theground surface.In either case the dense clay surrounding the waste containers will expand andenclose them, and consolidate the surrounding mud, which successively becomesdenser, while the dense clay seal softens until its swelling pressure and the pressureof the mud is the same.The clay seals in deep boreholes used for disposal of spent nuclear fuel consist of acentral core of dense expandable clay in perforated tubes (“supercontainers”)submerged in clay mud according to a concept termed VDH. In the lower parts of3-4 km deep boreholes these tubes, made of copper, Navy Bronze, titanium or steel,host canisters lined with highly compacted expandable clay. In the upper parts ofthe holes the same type of supercontainers with no waste but with dense smectiteclay blocks make up a primary barrier to possibly released radionuclides. A secondbarrier is the heaviness of the strongly saline groundwater at depth, which preventssuch water to reach high up to the biosphere. The role of the mud is to save thesupercontainers from touching the borehole walls when being placed, and to sealvoids in the borehole walls with clay. The dense clay and soft clay mud will interactphysically and ultimately become a homogeneous silicified clay body. Creep strainin the rock causes the deposition holes to con, which increases the radial pressureon the clay seals and thereby eliminates flow and diffusive migration of possiblycontaminated porewater from the deployment part to move to the ground surface.
关键词：Smectite; High Level Radiation Waste (HLW); VDH Concept; Clay.