科研之友
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摘要
The deep geological disposal has been considered as safe and effective way to dispose high-level radioactive nuclear waste internationally. When nuclear waste is sealed in the repository, it will continue to decay and release a large amount of decay heat, and therefore, the bentonite used as a buffer/backfill layer in the repository will remain in a high temperature state for a long time. After experiencing continuous high temperature, whether the hydro-mechanical behaviour of bentonite will change significantly needs to be resolved. In this paper, the swelling, shrinkage and water retention behaviour of compacted MX80 bentonite experiencing different heating times at temperature of 200 degrees C were investigated by the swelling pressure, shrinkage and vapour equilibrium technique, together with the thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The test results show that with increasing the heating time, the swelling and shrinkage indexes (swelling pressure, free swelling rate, shrinkage limit, and shrinkage coefficient) dropped sharply in the first 15-30 days, after that the indexes changed very little. In addition, the total reduction rates in the swelling pressure, free swelling rate, shrinkage limit, and axial shrinkage coefficient of MX80 bentonite experiencing 0 to 120 days heating are 35.4, 45.1, 49.8 and 25.5%, respectively. After experiencing high temperature of 200 degrees C, the main mineral montmorillonite in the MX80 bentonite was partially transformed into a low-swelling mineral paragonite from the XRD test results. From the TGA test results, the adsorbed water content decreased first and then remained unchanged with increasing the heating time, and the total reduction rates of free water, strong and weak bound waters were 82.5, 68.8 and 96.5%, respectively. From the SEM test results, the high temperature caused the layered structure to shrink and become tighter.
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单位上海大学; 桂林理工大学
