It is considered to use underground rock mass for the repositories of radioactive wastes. Additionally, it is considered to use High Strength and Ultra Low Permeability Concrete (HSULPC) to confine transuranic (TRU)wastes including 14Cfor the geological disposal of radioactive wastes.Therefore, it is important to create a technology to maintain or improve the confining ability of solids such as rocks and HSULPC. In order to maintain or improve the confining ability of solids, it is important to seal poresand cracks.Usually it takes extremely long term such as geological time scale to seal poresand cracksin rock. If the sealingof poresand cracksin rock can be accelerated by precipitation of some mineralsand completed with a short term, it is effective for the engineering project such as radioactive waste disposal. In this study, we investigated the precipitation of minerals on the surface of rocks to consider whether sealing of poresand cracksin rock can be accelerated or not. As rock samples, we used 4kinds of rocks including igneous rocks and sandstones. At first, we prepared cylindrical specimens, and then kept them in distilled water with powders of HSULPC. Then, we observed thesurface of rock specimens with a microscope, and measuredthe weight of rock specimens. It was shown that precipitation occurredon the surface of rock specimens. It was also shown that precipitation did not occur on rock specimens kept in water without HSULPC. The weight of all specimens kept with HSULPC increased. The amount of increase was larger for the rock with higher porosity. It is concluded thatthe precipitation of minerals occur on the rock surface when the rock was kept in water with HSULPC powders. From the results obtained in this study, it is suggested that sealingof poresand cracksin rock can be accelerated.

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