Abstract

We evaluate the long-term near-field behavior of a geological repository for high level radioactive waste disposal, using the centrifugal near-field model test under the coupled thermal-hydraulic-mechanical condition. The model consisted of a sedimentary rock mass, bentonite buffer, and heatable model overpack, and was enclosed within a pressure vessel. Tests were conducted with a centrifugal force field of 30 G under isotropic stress-constrain conditions with confining pressures of 6 to 10 MPa and injection of pore water. The temperature conditions of the overpack are constantly 25 °C and 95 °C (normal temperature- and heating-test, respectively). As the result, the measured values were obviously different depending on confining pressure, and were not converged in test-time. The long-term behavior in the near-field may be changed by the geomechanical interaction between the deformation stress of the bedrock/disposal hole and the swelling behavior of the bentonite buffer. In addition, X-ray CT scanning of the model after the centrifugal tests shows that the density of bentonite dose note reaches the supposed saturated value in the heating-test. It is a possible that water vapor is relatively generated in the bentonite around the overpack with high temperature compared with the bedrock. As a result, it is inferred that pore water is pushed away from the bentonite to the bedrock, and the zone of a low density in the bentonite is formed.

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