Evaluation of the long-term mechanical behavior in the near field considering chemical transitions of barrier materials

Sahara, Fumihiro*; Murakami, Takeshi*; Ito, Hiroyuki*; Mihara, Morihiro  ; Oi, Takao 

In order to make a reliable evaluation of the performance of TRU waste repository, development of a system that evaluates long-term transition of the hydraulic field in the near-field which takes into account the time-dependent alteration of barrier material properties is required. As part of this effort, Mechanical Analysis system considering Chemical transition of BEntonite-based and CEment-based materials (MACBECE) was developed. MACBECE firstly calculates deformations of barrier materials based on the chemical property changes and creep deformation of the host rock and consequently evaluates the hydraulic conductivity of barrier materials. By using MACBECE, the long-term deformation and the transition of hydraulic field for disposal cavities with circular cross section were evaluated, using an assumed chemical evolution as input. The analysis results indicated that the deformation of the engineered barriers depended strongly on the displacement of the tunnel wall by the creep of host rock, i.e., when the displacement of the wall was small, the deformation of the barrier materials was negligible in spite of acting swelling pressure of the buffer material. On the other hand, when the displacement is not small, the thickness of buffer material decreases, but the density increases due to compaction, therefore it is possible that the influence on the nuclide migration is not significant.