Engineering-scale test on the thermal–hydro–mechanical behaviors in the clay barrier of a HLW repository

The thermo–hydro–mechanical (T–H–M) behaviors of a clay barrier are of importance from a performance and safety viewpoint of the engineered barrier system (EBS) for a high-level waste (HLW) repository. An engineering-scale test was carried out to investigate the T–H–M behaviors in the buffer of the Korean reference disposal system (KRS). The test started on May 31, 2005 and is still in operation. The experimental data obtained allowed a preliminary and qualitative interpretation of the T–H–M behavior in bentonite blocks. The temperature was higher as it became closer to the heater, while it became lower as it was farther away from the heater. The water content had a higher value in the part close to the hydration surface than that in the heater part. The relative humidity data suggested that a hydration of the bentonite blocks might occur by different drying–wetting processes, depending on their position. The total pressure was continuously increased by the evolution of the saturation front in the bentonite blocks and thereby the swelling pressure. There was also a contribution of the thermal expansion of the bentonite blocks near the heater and the capillary force in the dry bentonite blocks which the water did not reach from the hydration surface.