Full-scale experimental study on mechanical behavior of a clay plug under HLW disposal conditions

Sasakura, Takeshi*; Masumoto, Kazuhiko*; Toida, Masaru*; Fujita, Tomoo ; Sugita, Yutaka 

High level radioactive waste is to be vitrified, and after some period of storage for cooling, put into engineered barriers such as metal canister, overpack and buffer material, and finally disposed of in the stable geology at the depth of 300 m or deeper to isolate from human environment for a long period of time in Japan. The geological repository consists of surface facilities and subsurface facilities; the later, mainly consists of tunnels for transportation and waste emplacement, will be closed using sealing technologies such as backfilling, plugging, and grouting after emplacement of the waste to prevent seepage of radionuclides for a long period of time. Effectiveness of these sealing technologies, however, has not been well demonstrated in-situ worldwide, and the technologies may be considered in the stage of research and development. Therefore, in this paper, the in-situ tunnel sealing test performed at Canada to demonstrate the effectiveness of the plug under crystalline rock environment was overviewed focusing on the plug. Then behavior of the plug, particular of mechanical behavior, during sealing tests, observation result of dismantled plug were reviewed and points to be addressed for establishing the clay plug technology were identified. Because the procedure of this tunnel sealing test and hydraulic sealing performance of the plug has already been precisely reported by Fujita et al. (2007), outline of the test is briefly summarized and mechanical behavior of the plug was focused. As a result, effectiveness of conventional construction technology of a plug was shown, the behavior of a plug during the pressurization test was clarified and important points to be addressed for establishing the clay plug technology were identified.