Countermeasures against piping and erosion of bentonite buffer; Piping inhibition due to pre-hydration

Shirase, Mitsuyasu*; Ishii, Tomoko*; Kobayashi, Ichizo*; Jo, Mayumi*; Ono, Makoto*; Nakayama, Masashi

no journal, , 

A candidate emplacement concept of the engineered barrier system (EBS) for geological disposal in Japan is vertical emplacement option, which has a certain gap is between the wall of the disposal hole and the buffer material. This gap is considered to be filled with the swollen buffer material (self-sealing function) when the underground water is infiltrated to the buffer material. However, some underground water flow conditions such as a pipe-shaped water channel induce erosion of the buffer material, which causes lowering of the function of the EBS. Therefore, RWMC (Radioactive Waste Management Funding and Research Center) studies engineering countermeasures against piping and erosion. RWMC used an intentional water supply system to test the pre-hydration of bentonite buffers.

Using natural systems data to test models of transformation of montmorillonite

Savage, D.*; Wilson, J.*; Benbow, S.*; Sasamoto, Hiroshi; Oda, Chie; Walker, C.*; Kawama, Daisuke*; Tachi, Yukio

no journal, , 

Safety functions for the clay buffer in a repository for HLW are fulfilled if the presence of montmorillonite is maintained in the long-term. Its transformation to non-swelling minerals (e.g. illite) is addressed in most safety assessments by using semi-empirical kinetic models. However, this approach contrasts with all other near-field geochemical modelling activities that employ complex reaction-transport simulations. Here we investigate the consistency of these two approaches by modelling the montmorillonite to illite transformation in the marine sediment profile penetrated by the Ocean Drilling Program (ODP) Site 1174. Illitisation of smectite at Site 1174 using the semi-empirical approach has been modeled by previous studies, and shown to provide a reasonable match to the gradual change of illite content with depth. In comparison, the initial results of reaction-transport simulations showed rapid (conservative) conversion of montmorillonite to illite. The cause of this rapid conversion appears to be the transformation of amorphous silica to quartz over a similar timescale. Subsequent simulations have focused on alternative mechanisms for mineral growth that may explain the discrepancies between the semi-empirical and reaction-transport approaches.

The Impact of cement on argillaceous rocks in radioactive waste disposal systems; An Overview of research needs, and ongoing work being undertaken in Japan

Wilson, J.*; Bateman, K.*; Kawama, Daisuke*; Tachi, Yukio

no journal, ,