【作者】 王玉平；

【导师】 易发成；

【作者基本信息】 西南科技大学 ， 环境科学与工程， 2022， 博士

【摘要】 随着核能利用需求的不断增长,高水平放射性废物（HLW）深地质处置问题越来越受到岩土工程界的关注。HLW的科学处置已是技术和工程界所面临的挑战性问题。缓冲材料中温度（thermal）-渗流-（hydraulic）-应力（mechanical）-化学迁移（chemical）（简称THMC）多场耦合动态响应特征,是研究HLW地质处置库性能评估与优化设计的重要基础。本文重点研究了高压实膨润土-砂混合物（CBM）缓冲材料,在多场耦合作用下的动态响应特征和核素在缓冲层中的迁移变化。利用课题组多场耦合缓冲材料长期阻滞性能Mock-up实验系统,进行多场耦合作用下CBM在不同条件下的数值模拟研究。本论文根据以下思路开展工作:（1）通过试验得出膨润土-砂混合物的最佳配比;（2）探索THMC耦合试验台架的搭建和试验方法,查明缓冲材料的THMC耦合响应特征。（3）采用有限元数值方法,探究缓冲材料的THMC耦合作用。主要开展的研究工作包括:1.研究了高庙子（GMZ）钠基膨润土的基本物理力学性能。在多因素条件下（不同干密度、不同掺砂率、不同温度）,建立了CBM三向膨胀力模型,讨论了CBM三向膨胀力的变化规律。研究发现,膨胀力在试验前期迅速发展,达到膨胀力峰值的85%。CBM的各向异性随干密度的增大而增大。CBM的三向膨胀力随掺砂率、温度增加而减小。2.利用HotDiskTPS 2500S热常数分析仪测定了GMZ膨润土-砂混合型缓冲材料在多因素条件下（不同干密度、不同含水率、不同掺砂率）的导热性能,并运用微观模型等效结构图和SPSS软件,对混合物导热性能的影响因素进行了机理探讨和分析。研究结果表明,石英砂可以提高GMZ膨润土的导热性能,当掺砂率在20%-30%,干密度1.6g/cm³-1.8g/cm³时,GMZ膨润土-砂混合型缓冲材料能满足IAEA对HLW处置库缓冲材料导热性能的要求,考虑到缓冲材料膨胀渗透特性,建议HLW处置库混合型缓冲材料的干密度为1.7g/cm³,掺砂率为20%。3.利用课题组的“多功能膨胀-渗透测试系统”,探讨不同干密度（1.7,1.8,1.9g/cm³）的CBM在不同水介质（去离子水、模拟北山地下水、NaCl-Na₂SO₄和NaOH溶液）入侵过程中的动态膨胀-渗透响应特征。借助XRD和TEM手段分析化学孔隙溶液对试样矿物学和微观结构的影响。结果表明,NaOH对试样膨胀力和渗透率的影响大于NaCl-Na₂SO₄。4.建立多场耦合缓冲材料Mock-up试验台架的搭建和试验方法,监测缓冲材料在复杂环境下的温度、孔隙水压、饱和度、膨胀力等响应特征。以Mock-up台架为几何原型,建立非饱和THM多场耦合数值模型,利用COMSOL Multiphysics软件的PDE模块分析了处置库缓冲层的温度、饱和度、膨胀力、水平位移等变化过程。5.以Mock-up台架为几何模型算例,建立了核素在饱和缓冲材料中迁移的THMC全耦合分析模型,利用COMSOL软件模拟了核素在缓冲层中的空间分布。研究了渗透系数、表观扩散系数、孔隙度、阻滞因子和导热系数对核素迁移的敏感程度。更多还原

【Abstract】 With the increasing demand for nuclear energy utilization,the deep geological disposal of high-level radioactive waste（HLW）has attracted more and more attention in geotechnical engineering.The scientific disposal of HLW has become a challenging problem in the field of technology and engineering.The research of multi field coupling dynamic response characteristics of thermo-hydro-mechanical-chemical migration（THMC）in buffer materials,is significant base to the function estimate and devise of HLW repository.This paper focuses on the dynamic response characteristics of high-compacted bentonite-sand mixture（CBM）buffer material under multi field coupling and the migration of nuclides in the buffer layer.Using a self-designed multi field coupling laboratory test device,the numerical simulation of CBM is carried out under different conditions of multi field coupling.This paper carries out the following ideas:first,the best ratio of bentonite-sand mixture is obtained through experiments;secondly,explore the installation and test methods of THMC coupling test bench,and understand the THMC coupling response characteristics of buffer materials;finally,the finite element numerical method is used to explore the THMC coupling effect of buffer materials.The main works are as follows:1.The basic physic-chemical properties of Gaomiaozi（GMZ）Na-bentonite were studied.The three-dimensional swelling pressure tests on the CBM are carried out under different dry density,sand content and temperature.The three-dimensional expansion force model of CBM is established,and the variation law is discussed.The result indicated that the swelling pressure reached 85%of the maximum pressure in the early stage,and the anisotropy of CBM increases with the increase of dry density.The three-dimensionalswelling pressure decreases withthe increase of sandcontent and temperature.2.In this study,the thermal conductivity of GMZ bentonite-sand mixed under multi-factor conditions was measured by thermal constant analyzer.Using the equivalent structure diagram of micro model and SPSS software,these factors of thermal conductivity of mixed are discussed.The result indicated that increasing the sand content can improve the thermal conductivity of GMZ bentonite-sand mixed.When the sand content is 20%-30%and the dry density is 1.6g/cm³-1.8g/cm³,the thermal conductivity of buffer material meets the requirements of the IAEA.Considering the expansion and permeability characteristics of buffer materials,it is suggested that the dry density of buffer material is 1.7g/cm³ and the sand content is 20%.3.The self-developed“Multifunctional swelling permeability test system”was used.The dynamic response characteristics of CBM with different dry densities（1.7,1.8,1.9 g/cm³）and different water media（deionized water,simulated Beishan groundwater,NaCl-Na₂SO₄ and NaOH solution）were investigated.The effects of chemical pore solution on the mineralogy andmicrostructure of the samples were analyzed by X-ray diffraction（XRD）and transmission electron microscope（TEM）.The results show that the influence of NaOH on the expansion force and permeability of the sample is greater than that of NaCl-Na₂SO₄..4.The methods of construction and test for the Mock-up test bench of buffer materials under multi-field coupling conditions was established.By monitoring the temperature,pore water pressure,saturation and swelling pressure of buffer materials under complex environment,the response characteristics of buffer materials under multi-field coupling conditions were revealed.Taking the Mock-up bench as the geometric prototype,the unsaturated THM multi field coupling numerical model is established.The PDE module of COMSOL is used for secondary development,and the change processes of the buffer layer of the HLW repository,such as temperature,saturation,expansion force and horizontal displacement,are analyzed.5.Taking the Mock-up bench as geometric model,a transport model with THMC full coupling of nuclide migration in saturated buffer material was proposed.The spatial distribution of nuclides in the buffer layer is simulated by COMSOL software.The sensitivity of permeability coefficient,apparent diffusion coefficient,porosity,retardation coefficient and thermal conductivity of buffer materials to nuclide migration was studied.更多还原