Discussion on sealing performance required in disposal system; Preliminary study on hydraulic analysis of disposal panel

Sugita, Yutaka* ; Takahashi, Yoshiaki*; Uragami, Manabu*; Kitayama, Kazumi*; Fujita, Tomoo ; Yui, Mikazu

The sealing performance of a repository is very important for the safety assessment of the geological disposal system for high-level radioactive waste. NUMO and JAEA set up a technical commission to investigate sealing technology in a repository in 2004 following a cooperation agreement between these two organisations. The objectives of this commission were to present a concept of sealing performance required in the disposal system and to direct future R&D for design requirements of closure components (backfilling material, clay plug, etc.). Hydraulic analyses on tunnel intersections were carried out during the first year in 2004. This was expanded into a hydraulic analysis of a complete disposal panel with all tunnels during the second year in 2005. Since the model structure in 2005 was more complicated than the one used in 2004, the concept of equivalent permeability was adopted in and around each tunnel in the hydraulic analyses. Parameters used in the hydraulic analyses were installation positions of clay plugs, permeability of the backfilling material, permeability of disposal tunnel and directions of hydraulic gradient to estimate influences to the analytical results preliminary. Analytical results showed that flow rate in a disposal tunnel was influenced by directions of hydraulic gradient, installation of the clay plug at the both ends of each disposal tunnel and permeability of the main tunnel.