Abstract: Radionuclides will transport to the biosphere after the overpack destroyed in the high-level radioactive waste(HLW) disposal repository. The hydraulic conductivity of buffer/backfill material plays an important role in evaluating the properties of the engineering barrier of HLW disposal repository. The permeability characteristics of Gaomiaozi bentonite-sand mixtures are studied by using the flexible wall permeameter and taking 2.0×10-5 mol/L Eu(III) solution as influent. The hydraulic conductivities are measured at K=(2.07-5.23)×10-10 cm/s. Test results show that there is no significant change in hydraulic conductivity of bentonite-sand mixtures, swelling with water, with the sand ratio ranging from 0% to 50%. Therefore, the requirement of low permeability for buffer/backfill material should be met by these mixtures. The effective clay dry density (ECDD) is used in this paper; and a good exponential relationship between volume swelling strain and ECDD and a linear-attenuation relationship between the logarithm value of hydraulic conductivity and ECDD of bentonite-sand mixtures are obtained. Compared with the distilled water, the hydraulic conductivities of bentonite-sand mixtures are smaller when influent is the 2.0×10-5 mol/L Eu(III) solution, which may result from the effect of influent viscosity.

Key words: high-level radioactive waste (HLW), Eu(III) solution, bentonite-sand mixtures, hydraulic conductivity, effective clay dry density (ECDD)