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Report No.
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The Effect of Silica Sand Content and NaNO$$_{3}$$Concentration on Diffusions of C, Cl and I in Compacted Bentonite

Ishidera, Takamitsu ; Miyamoto, Shinya*; Sato, Haruo

For safety assessment of geological disposal of TRU waste, it is necessary to obtain the diffusivities of C-14, Cl-36 and I-129 and to estimate the effects of the dissolution of NaNO$$_{3}$$and high pH groundwater condition caused by dissolution of cementitious materials. Therefore, the effective diffusion coefficients (De) and the apparent diffusion coefficients (Da) of CO$$_{3}$$$$^{2-}$$, Cl$$^{-}$$and I$$^{-}$$in compacted bentonite were obtained as a function of silica sand content and NaNO$$_{3}$$concentration under high pH condition by Through-diffusion method. Furthermore, the diffusion mechanisms of CO$$_{3}$$$$^{2-}$$, Cl$$^{-}$$and I$$^{-}$$were discussed.The obtained De values of CO$$_{3}$$$$^{2-}$$, Cl$$^{-}$$and I$$^{-}$$were in a range of 10$$^{-13}$$to 10$$^{-10}$$m$$^{2}$$/s order and Da values in a range of 10$$^{-12}$$to 10$$^{-11}$$m$$^{2}$$/s order (CO$$_{3}$$$$^{2-}$$) and 10$$^{-10}$$m$$^{2}$$/s order (Cl$$^{-}$$and I$$^{-).}$$The De and Da values of CO$$_{3}$$$$^{2-}$$, Cl$$^{-}$$and I$$^{-}$$increased with increasing silica sand content. The changes of De and Da values appeared to be estimated by smectite partial density. The De values of CO$$_{3}$$$$^{2-}$$, Cl$$^{-}$$and I$$^{-}$$increased with increasing NaNO$$_{3}$$concentration. The increases were interpreted by the decrease of anion exclusion effect. Furthermore, it seems that the pathways of Cl$$^{-}$$and I$$^{-}$$were limited to the interstitial pore space. The CO$$_{3}$$$$^{2-}$$ions were probably retained in the Kunigel V1 as the precipitation of calcite.

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