高温碱溶液中混合型缓冲材料膨胀特性研究

Swelling pressure of bentonite-sand mixture buffer materials for HLW disposal as effected by both high temperature and alkaline solutions

高放废物地下处置库中,地下水腐蚀衬砌混凝土析出的强碱性溶液,叠加核素衰变释放的辐射热,会影响缓冲材料的膨胀性能。以混合型缓冲材料(70%高庙子膨润土+30%石英砂)为试验对象,孔隙溶液选择蒸馏水和KOH溶液,溶液浓度为0.1,0.3,1.0 mol/L。设置试验温度为常温与90℃。测试不同初始干密度试样的膨胀力。试验完成后,对试样开展X射线衍射(XRD)试验,试验结果证实:高温提升了试样膨胀力发展速率与膨胀力值,最终膨胀力值最大增幅为19.3%。KOH溶液作用下缓冲材料膨胀力随时间发展出现衰退现象,是碱溶液危害膨胀性能的典型特征。最终膨胀力值对KOH浓度呈负相关,与初始干密度呈正相关。在90℃1.0 mol/L KOH溶液作用下,试样最终膨胀力值较蒸馏水,衰减程度达到52.3%以上。试样衰减主要与蒙脱石的溶解与阳离子交换有关。最严重的情况下,蒙脱石含量减小为初始的43.2%。

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.