含盐环境中膨润土的膨胀理论及膨胀衰减机理研究

发布时间：2018-05-15 19:58

本文选题：核废料缓冲回填材料 + 膨润土　；参考：《上海交通大学》2015年博士论文

【摘要】：深层地质处置是国际上普遍接受和认可的高放射性核废料的最终处置方案。膨润土因具有高吸水膨胀性、低渗透性和强核素吸附性等优点被选作深层地质处置系统中缓冲回填材料的主料。在核废料处置库的运行过程中,围岩周围的地下水渗入缓冲回填材料中对膨润土的膨胀特性产生影响。如何准确计算和预测膨润土在地下水溶液中的膨胀特性和膨胀性衰减规律是亟待解决的关键问题。本文通过室内膨润土的膨胀试验和理化测试,结合理论分析和数值模拟,研究了膨润土在地下水溶液中的膨胀特性,提出了膨润土在盐溶液中的膨胀模型和膨胀性的计算方法,分析了膨润土膨胀性衰减机理,模拟了膨润土在核废料处置库中的膨胀特性和衰减规律,为核废料深层地质处置库的建设和安全运行提供科学依据。主要的研究内容如下:(1)采用N2吸附法测量了膨润土的表面分维。采用N2吸附法测量压实膨润土在蒸馏水和不同浓度的Na Cl溶液中浸泡后的表面分维,膨润土压实试样的表面分维与膨润土粉末试样的表面分维相当,盐溶液对膨润土的表面分维的影响很小。(2)采用固结仪测量了商用膨润土压实试样在蒸馏水和NaCl溶液中的膨胀变形和膨胀力。膨润土的膨胀特性与竖向应力、试样的干密度和盐溶液的浓度密切相关。在nacl溶液中,渗透吸力抑制了膨润土的膨胀特性,盐溶液浓度越大,膨胀越小。(3)建立了膨润土膨胀的分形模型。基于膨润土吸水膨胀过程的表面吸附作用,根据膨润土表面的分形模型,建立了膨胀吸水体积的表达式,导出膨胀变形和膨胀力的理论公式。在膨润土的渗透膨胀阶段,结合双电层理论给出分形模型中的蒙脱石膨胀系数k,完善了分形模型。在盐溶液中,基于膨润土表面的分形模型,推导出由孔隙水渗透吸力引起的有效应力,提出了盐溶液中的膨胀变形理论,并得到了盐溶液中膨胀变形数据的验证。(4)揭示了gmz01膨润土在氯盐溶液(nacl、cacl2、mgcl2)和naoh溶液中膨胀性衰减机理。膨润土与氯盐溶液混合后,阳离子交换是主要的化学反应过程,ca2+和mg2+与na基蒙脱石中的na+反应生成膨胀性较低的ca基或mg基蒙脱石,引起膨胀性衰减。与naoh混合后,高碱性溶液对蒙脱石有强烈的溶蚀作用,蒙脱石发生溶解生成非膨胀性矿物,导致膨胀性衰减。基于膨润土膨胀性衰减机理,采用膨胀变形的分形模型预测了渗透吸力、离子交换反应和蒙脱石含量引起的膨胀衰减规律。(5)基于核废料处置库中缓冲回填材料的thmc四场耦合作用,建立膨润土的多场耦合方程。采用comsolmultiphysics软件和Phreeqc软件,模拟了核废料处置库中膨润土的饱和膨胀过程和长时间多场耦合作用下的膨胀性衰减过程。分析了膨润土吸水膨胀随时间的演化规律,计算了随时间延长饱和膨润土中渗透吸力、蒙脱石含量、膨胀系数K、有效应力和膨胀力的衰减程度,给出膨润土膨胀性衰减的定量评估方法。
[Abstract]:Deep geological disposal is the ultimate disposal scheme of high radioactive nuclear waste widely accepted and accepted internationally. Bentonite is selected as the main material of buffer backfill material in deep geological disposal system because of its advantages of high water absorption, low permeability and strong nuclide absorbability. The expansion characteristics of bentonite are affected by the infiltration of water into the cushioning backfill material. How to accurately calculate and predict the swelling characteristics and the law of expansion attenuation in the solution of bentonite is the key problem to be solved. This paper studies the expansion test and physical and chemical test of bentonite in the laboratory, and studies the theoretical and numerical simulation. The expansion characteristics of bentonite in the groundwater solution, the expansion model of bentonite in salt solution and the calculation method of expansibility are put forward. The expansion attenuation mechanism of bentonite is analyzed, the expansion characteristic and attenuation law of bentonite in the nuclear waste disposal repository are simulated, which is for the construction and safe operation of the deep geological disposal repository of nuclear waste material. The main research contents are as follows: (1) the surface fractal dimension of bentonite is measured by N2 adsorption method. The surface fractal dimension of compacted bentonite in distilled water and Na Cl solution of different concentration is measured by N2 adsorption method. The surface fractal dimension of bentonite compacted sample is equivalent to the surface fractal dimension of bentonite powder sample, and the salt solution is the same The effect of the surface fractal dimension of bentonite is very small. (2) the expansion deformation and expansion force of commercial bentonite compacted samples in distilled water and NaCl solution are measured by a consolidation instrument. The expansion characteristics and vertical stress of bentonite are closely related to the dry density of the specimen and the concentration of salt solution. In the NaCl solution, the osmosis suction inhibits the expansion of bentonite. Characteristics, the greater the concentration of salt solution, the smaller the expansion. (3) a fractal model of swelling of bentonite was established. Based on the surface adsorption of bentonite, the expression of expansion water absorption volume was established according to the fractal model of bentonite surface, and the theoretical formula of expansion deformation and swelling force was derived. Based on the double layer theory, the expansion coefficient K of the montmorillonite in the fractal model is given, and the fractal model is perfected. In salt solution, based on the fractal model of the bentonite surface, the effective stress caused by the permeation suction of pore water is derived. The theory of expansion deformation in salt solution is put forward, and the data of expansion and deformation in salt solution are verified. (4) The expansion attenuation mechanism of gmz01 bentonite in chloride solution (NaCl, CaCl2, MgCl2) and NaOH solution was shown. After the mixture of bentonite and chloride solution, the cation exchange was the main chemical reaction process. The na+ reaction in ca2+ and mg2+ and Na Based Montmorillonite produced a lower expansive CA based or Mg base montmorillonite, causing expansibility attenuation. After mixing with NaOH, it was mixed with NaOH. The high alkaline solution has a strong corrosion effect on montmorillonite. Montmorillonite dissolves to produce non expansive minerals and causes expansion attenuation. Based on the expansion attenuation mechanism of bentonite, the expansion and deformation model is used to predict the expansion attenuation law caused by the permeation suction, ion exchange reaction and montmorillonite content. (5) based on the nuclear waste place The multi field coupling equation of bentonite is established by THMC four field coupling effect of buffer backfill material in the warehouse. The saturated expansion process of bentonite in the nuclear waste disposal repository and the expansion attenuation pass under long time multi field coupling are simulated by comsolmultiphysics software and Phreeqc software. The water swelling of bentonite is analyzed with time. The law of evolution is used to calculate the permeation suction, the content of montmorillonite, the expansion coefficient K, the effective stress and the attenuation of the expansion force, and the quantitative evaluation method of swelling attenuation of bentonite is given.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU443

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