Influence Of Alkaline Solution On The Hydraulic And Mechanical Behavior Of Buffer Material Of Nuclear Waste Disposal

The disposal of high-level radioactive nuclear waste has become more and more urgent.At present,most countries have been planning to build deep geological repositories.For the buffer material in the high-level radioactive waste disposal project,from the perspective of material category,we can choose pure bentonite or bentonite additive mixture with better thermal conductivity and constructability.In this paper,pure bentonite and bentonite additive mixture were used as experimental materials to study and analyze the swelling force,swelling deformation and compression deformation of samples in alkaline environment.The main research works of this paper are as follows:(1)In this experiment,Na OH solution was selected to simulate the alkaline groundwater,and a corrosion-resistant high-pressure consolidation instrument was designed and processed to complete the swelling force test of samples saturated by alkaline solutions of different concentration.The effects of initial dry density and solution concentration on the swelling characteristics were discussed.The results show that the swelling force increases with the increase of the initial dry density when the the solution's concentration are the same;when the initial dry density of the samples are the same,the stable swelling force of the 0.1 M solution saturated sample is greater than that of the deionized water saturated sample,and when the concentration of the solution is greater than 0.1 M,the stable swelling force decreases with the increase of the concentration;the swelling force evolution curve of the sample saturated by high concentration alkaline solution decrease after reaching the maximum value,and the degree of attenuation is obviously affected by the concentration of the solution,and has not clear relation with the initial dry density;according to the fitting formula of swelling force and montmorillonite void ratio in the log-log coordinate,the expression for predicting the stable swelling force of Gaomiaozi Ca-bentonite in alkaline environment is given.(2)The volume change behavior of the mixture of Gaomiaozi Na-bentonite and additives in alkaline environment were studied.Deionized water,0.1 M,0.5 M and1.0 M Na OH solution were used as the infiltration solutions.The dry density of the mixture was 1.6 g/cm~3.The swelling deformation test of bentonite-granite mixture and bentonite-sand mixture with 0?15%?30%?45%mixing ratio was carried out by using corrosion-resistant high-pressure consolidation instrument,and the saturated recompression test of bentonite-granite mixture was carried out.The results show that the stable swelling rate of the sample decreases exponentially with the increase of the concentration of the solution and decreases linearly with the increase of the additive mixing ratio.At the same mixing ratio,the swelling characteristic of bentonite-granite mixture is higher.The compression index of bentonite-grantie mixture decreases linearly with the increase of the mixing ratio,and decreases exponentially with the increase of the solution concentration.(3)The swelling force of the mixture of Gaomiaozi Na-bentonite and granite additives under the thermo-chemo coupling were studied.In this experiment,the water bath was used to provide a constant temperature for solution,and the solution was circulated in the corrosion-resistant consolidator.The test temperatures are25?and 50?.And 0.1 M,0.5 M and 1.0 M Na OH solution were used as the infiltration solutions.The swelling force test of samples were carried out,and the evolution curves of the swelling force of each sample were obtained.The effects of concentration,temperature and mixing ratio on the swelling characteristics of the mixture were analyzed.The results show that at the same temperature,the maximum swelling force and the stable swelling force decrease with the increase of the solution concentration,and at the same concentration,the maximum swelling force and the stable swelling force decrease with the increase of the ganite mixing ratio.The maximum swelling force and stable swelling force of the sample with the test temperature of 50?are lower than those of the sample with the test temperature of25?.The attenuation degree of expansion force increases with the increase of concentration and temperature.Adding granite into bentonite can reduce the attenuation effect of alkaline solution on the swelling force,and the attenuation rate of swelling force decreases with the increase of the granite mixing ratio.