Abstract Bentonite buffer is a part of the engineered barrier systems (EBS) for sub-surface disposal. The EBS is required to meet two quality standards at completion of construction. One is very low permeability of less than 5×10 −13 m s −1 and the other is very low diffusibility of less than 1×10 −12 m 2 s −1 . The bentonite buffer is required for the first quality standard of low permeability and must be constructed with high density in order to make the buffer a low-permeability layer. To confirm that the bentonite buffer is actually constructed with high density, we have carried out a full-scale mock-up test for part of the Demonstration Test of Underground Cavern-Type Disposal Facilities commissioned by the Japanese government in fiscal year 2005. This paper covers the test results from the construction of the bentonite buffer.

Abstract The main part of this chapter describes a geological journey westwards from central to SW Japan and is specically aimed at the overseas visitor new to Japanese held geology. This is followed by a brief overview of the Japanese geopark system and museums with geological exhibits. There are currently over 30 geoparks in Japan, providing one of the most dense networks in the world of sites of special geological interest.

Abstract It is planned to use bentonites as buffer materials in various types of geological repositories designed to host radioactive waste. For the bentonite materials, the hydrological and hydrogeochemical conditions are two of the main environmental factors affecting their evolution, assessed for a period of up to 1 Ma. Since it has been observed in laboratory tests that smectite, in particular montmorillonite, forms colloids and disperses in very dilute conditions, a scenario for chemical erosion has been discussed at length, especially in relation to geological repositories located in future glaciated terrains and locations otherwise potentially hosting dilute groundwaters. General understanding, based on laboratory experiments, is that bentonite erosion does not occur when the total charge equivalent of cations in groundwater is higher than 4 mM. However, based on current knowledge, it seems that chemical erosion is not observed in repository-relevant natural systems where groundwater conditions are below the given limit. Further investigation is therefore suggested to provide a better scientific understanding of the mechanisms involved in stabilizing smectites in these natural systems.