Experimental Approach to Performance of Engineered Barriers under Repository Conditions

Ishiguro, Katsuhiko; Kawamura, Kazuhiro; Sonobe, Hitoshi; Nodaka, Masayuki*; Arai, Takashi; Yusa, Yasuhisa; Tsunoda, Naomi

Experimental studies have been carried out in order to evaluate durability of engineered barriers in geological disposal system. These are as follows; (1) Leaching behavior of waste borosilicate glass. Leaching experiments of simulated waste glass were carried out for more than one year in both scale of laboratory and of engineering. The leachability was suppressed under the condition of high SA/V (the surface area of glass/leachant volume). Saturation of leachant with silicon reduces leaching rates of the other elements. (2) Corrosion behavior of candidate overpack materials. Corrosion behavior of carbon steel and titanium was studied in synthetic groundwater with or without bentonite. No localized corrosion was observed in both the materials. Corrosion rate of carbon steel depends on bentonite/water ratio. Crevice corrosion resistance of titanium and its alloy was also studied. (3) Permeability of compacted bentonite as buffer material. Hydraulic conductivity of saturated compacted bentonite decreases and the swelling pressure increases with the increase of density. Influence of cracks on permeability was also studied, and significant effect was not observed. Infiltration of water into dry compacted bentonite was also studied to evaluate permeability of buffer material at the initial stage of disposal.