| Safe disposal of high level radioactive HLW is an important issue related to the development of nuclear industry and protecting of the environment. Deep geological disposal is the widely accepted concept for HLW which is considered the most reliable and technically feasibility in the world. The concepted model of HLW deep geological disposal is based on a multi-barrier system. In order to ensure the long-term safety of the repository and establishment of the performance evaluation basis, the scientific simulation test must be carried out under repository condition for the bentonite.This thesis is based on the research status of HLW geological disposal in China. It takes Gaomiaozi sodium bentonite as the research object. Ion concentration, chemical composition and the cation exchange characteristics were test regularly with continuous monitoring of pH electrical conductivity and temperature. Effect of groundwater on mechanical properties and gas permeability of bentonite were studied. Main conclusions are as follows:(1) Under the interaction between bentonite and groundwater, the cation exchange capacity tends to be stable after fluctuation. Exchangeable sodium,magnesium and calcium ion show the characteristics of stable except for obvious changes within first month. Exchangeable potassium ion increases first and then decreases. A few illite were observed under an optical microscope when potassium ion was maximum. It shows the obvious negative correlation between p H value and conductivity with stirring action. The pH value decreases and conductivity increases rapidly without stirring.(2) After interaction with groundwater, the mechanical properties of bentonite remain consistent. The unconfined compressive strength of compacted bentonite index increases with the increase of the dry density. The strain of lower part increases obviously than the upper part. The change of the volumetric strain of lower part is more obvious. The elastic modulus of the lower part is the smallest but the poisson’s ratio is the largest. Failure is the most likely to happen in the lower part under different loading rate. The typical tensile shear failure with the main shear plane of incomplete X conjugate and a cone fracture surface at the lower part was observed. The fracture strength and stains of the sample increases with the increase of confining pressure. When the dry density is 1.4 g/cm3 or 1.6 g/cm3, brittle failure transitiones gradually to plastic failure. Failure form of sample for 1.8 g/cm3 is plastic failure. And it shows that the greater the confining pressure is, the more obvious the strain hardening process is.(3) To study gas permeability of compacted bentonite, experiments were carried out on different dry density of compacted bentonite under different loading pressure and confining pressure. It has certain nonlinear relationship between gas permeability and dry density. The gas permeability remarkably decreases with the dry density increases, by 10-15m2 gradually reduces to 10-17m2. Gas permeability and loading confining pressure have the certain relations. It gradually reduces to constant with increase of loading confining pressure and slightly reduces with the increase of loading pressure. It has no significant effect on gas permeability with groundwater. |
