Influence of Cement Leachate on Bentonite Impermeability(Waste Management and Clay Barriers and Civil Engineering,Proceedings of the 13^<th> International Clay Conference)

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Cementitious materials and bentonite are planned to be used as engineered barriers for disposal of radioactive wastes from nuclear fuel reprocessing. After a repository has been closed, groundwater may permeate cementitious barriers, and hyperalkaline water containing Na, K and Ca ions may leach out. When the water comes into contact with bentonite, physicochemical changes resulting in degradation of barrier performance might occur. Furthermore, ion concentration of cement leachate may increase due to dissolution of nitrate in the waste. To investigate the hydraulic characteristics of bentonite under a disposal environment, hydraulic conductivity tests were performed using simulated cement leachate. It was shown that interlayer cations were exchanged with cations in the permeant solutions and the hydraulic conductivity of bentonite increased as the solution's cation concentration increased, and the hydraulic conductivity of the soak-treated bentonite increased as free swell decreased. This study demonstrated that bentonite changed physicochemically by penetrating the simulated cement leachate, and both cation concentration of permeant solution and the dominant interlayer cation of smectite had a great impact on the hydraulic characteristics of bentonite.
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