Swelling pressure of bentonite-sand mixture buffer materials for HLW disposal as effected by both high temperature and alkaline solutions
In the HLW repository,the strong alkaline solution precipitated by the corrosion of the lining concrete by the groundwater and the radiant heat released by the decay of the nuclide will affect the swelling performance of the buffer backfill material.The mixture of 70％bentonite and 30％quartz sand is used as the test object.Distilled water and KOH solution are selected for the pore solution,and the concentration of the solution is 0.1,0.3,1.0 mol/L.Set the test temperature to normal temperature and 90 ℃.Test the swelling pressure of samples with different initial dry densities.After the test was completed,X-ray diffraction(XRD)test was carried out on the sample.The test results confirmed that the high temperature increased the swelling pressure development rate and the swelling pressure value of the sample,and the final swelling pressure value increased by 19.3％.Under the action of KOH solution,the swelling pressure of the buffer backfill material decays over time,which is a typical feature of the alkali solution's damage to the swelling performance.The final swelling pressure value is positively correlated with the KOH concentration and negatively correlated with the initial dry density.Under the action of 90 ℃ 1.0 mol/L KOH solution,the final swelling pressure value of the sample is higher than that of distilled water,and the attenuation degree reaches more than 52.3％.The attenuation of the sample is mainly related to the dissolution of montmorillonite and cation exchange.In the most severe case,the montmorillonite content is reduced to 43.2％of the initial.
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