Diffusion and Migration of Ions in Sedimentary Rock Matrix: Effects of Ionic Strength and Tracer Concentration on Diffus
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'LIIXVLRQDQG0LJUDWLRQRI,RQVLQ6HGLPHQWDU\5RFN0DWUL[ (IIHFWVRI,RQLF6WUHQJWKDQG 7UDFHU&RQFHQWUDWLRQRQ'LIIXVLRQRI&VLRQVLQ6DQGVWRQH Haruo SATO, Japan Nuclear Cycle Development Institute (JNC), 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki-ken 319-1194, JAPAN $%675$&7 In-diffusion experiments for Cs+ and I- in sandstone were performed as a function of ionic strength ([NaCl]=0.01, 0.51M) and tracer concentration ([CsI]=7.5E-5, 1.5E-2M) together with the measurements of the physical and chemical properties of sandstone, and apparent diffusivities + ('D) for Cs+ were obtained. The obtained 'D-values for Cs scarcely depended on [NaCl], but increased with increasing [Cs+]. This trend is consistent with that of rock capacity factors (α), indicating that distribution coefficient (.G) onto sandstone and effective diffusivity scarcely depend on [NaCl]. The concentration profiles of I were all in already breakthrough. Although this indicates that I- diffusion is faster than that of Cs+, the concentration profiles of I- may have been lower than those for blank samples,+judging synthetically from the correlations between α-values and the concentration profiles of Cs and from the concentration profiles of I in the blank samples. Finally, the effects of [Cs+] and [NaCl] on .G-values for Cs+ were discussed from the viewpoint of adsorption by ion exchange and electrostatic attraction. The .G-values were considered to be combined sorption by both reactions. ,1752'8&7,21 In safety assessment for the geological disposal of high-level radioactive waste in Japan, it is important and essential to reliably treat radionuclide migration in the geosphere, therefore a lot of studies concerning radionuclide diffusion have been conducted to date [e.g.1]. Particularly, for sedimentary rocks, since the physical and chemical data and information for diffusion are quite limited, the author has systematically made progress data acquisitions for diffusion and an understanding of diffusion mechanism for porous media. Porous media are generally treated by assuming that a continuously and homogeneously distributed pore space exists in sedimentary rocks, such as sandstone, mudstone, tuff, etc., in which no fractures develop. The processes that radionuclides and ions diffuse in the rock matrixes occur through porewater, and those radionuclides and ions take place various interactions at the surface of minerals composing the rock matrixes in the diffusion processes. For .G-values onto rocks, in the second progress report [2], retardation has been evaluated by .G-values from batch experiments, based on the judgment that the pore sizes are generally large enough compared with ionic sizes. However, actually, inconsistency is often found between .G-values from batch and diffusion experiments. If .G-values from batch experiments are used for safety assessment, this is the important problem to be solved in the data setting. In this study, as an objective to discuss the inconsistency problem of .G in the batch and intact system, non-steady sta
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