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Report No.

Natural analogue studies of long term alterration of volcanic glass under the high level radioactive waste disposal conditions

Futakuchi, Katsuhito*; Sakuramoto, Yuji*; Hiroki, Minenari*

The alteration characteristics of volcanic glass and bentonite in geological medium are investigated as natural analogues of geological disposal of high-level radioactive wastes. For the study of alterlation of volcanic glass, literature survey, petrographical observation by using optical microscope, chemical analysis of pore water and groundwater, and microbiostratigraphical study were carried out. The volcanic ashes were collected from a borehole, which had been drilled in the Kanto region by the National Research Institute for Earth Science and Disaster Prevention. The volcanic glass was wholly altered in thin sections. Chemical analysis of pore water indicate the chloride-rich composition. And chemical analysis of groundwater, which are pumped up near the studied borehole, indicate the mixing product of connate marine water and fresh groundwater. Fossil evidence suggests that the studied volcanic glass is 3.65$$sim$$4.2Ma. in age, and is correlated with upper Miura Group. This study leads to the following conclusion. The volcanic glass, under the temperature condition 70$$^{circ}$$C, was wholly altered to montomorillonite and clinoptilolite. This case must be occurred in the connate marine water at last 0.5 Ma..



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