[in Japanese]

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[in Japanese]

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In order to select an available inlet source material for a migration test of radionuclides in a sedimentary layer, 8 different materials; carbonated cement, coastal sand, chromosorb, sandstone, cation-exchange resin, zeolite, silica gel and Toyoura standard sand, were tested in terms of adsorption ability and leaching rate with time for ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs. The adsorption terms of adsorption ability and leaching rate with time for 60Co, 85Sr and 137Cs. The adsorption abilities obtained as distribution coefficients (Kds) were tested by batch-type experiments, and the leaching rates were examined using column-type experiments.
Among the materials, silica gel had the smallest Kd of approximately 60ml/g for the three radionuclides, and its Kd values did not fluctuate with time. Cement, sandstone and silica gel had a constant leaching rate for ⁶⁰Co, ⁸⁵Sr and ¹³⁷Cs, ranging from 50 to 300ml inflow of groundwater. Approximately 70% of the three radionuclides were leached out from silica gel by 500ml inflow of groundwater. These results suggest that the silica gel is a suitable inlet source material for constantly supplying a solution with various radioactivities into a geologic layer.

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Performance assessment of each barrier consisting of geologic disposal system for high-level radioactive wastes is carried out quantitatively, and key radionuclides and parameters are pointed out.
Chemical compositions and solubilities of radionuclides under repository conditions are determined by PHREEQE code starting from compositions of granitic groundwater observed in Japan. Glass dissolution analysis based on mass transfer theory and precipitation analysis have been done in order to determine the inner boundary condition for radionuclide diffusion through a bentonite-filled buffer region, where multi-member decay chain and isotopic sharing of solubility at the inner boundary are considered. Natural barrier is treated as homogeneous porous rock, or porous rock with infinite planar fractures. Performance of each barrier is evaluated in terms of non-dimensionalized hazard defined as the ratio of annual radioactivity release from each barrier to the annual limit on intake.
At the outer edge of the engineered barriers, ²³⁹Pu is the key nuclide to the performance, whereas at the exit of the natural barrier, weakly-sorbing fission product nuclides such as ¹³⁵Cs, ¹²⁹I and ⁹⁹Tc dominate the hazard.

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