【作者】 李寻；

【导师】 张土乔；

【作者基本信息】 浙江大学 ， 市政工程， 2009， 博士

【摘要】 与其它溶质运移问题相比,高放废物深地质处置中的溶质运移问题具有迁移途径、迁移规律复杂、迁移过程长等特点。因此,本文根据高放废物地质处置的“多屏障系统”设计及其安全评价要求,围绕地下水重返处置库时,与工程屏障中回填材料的相互作用,以及地质屏障中的核素迁移问题进行了初步的探讨与研究。主要的工作和创新成果如下:首先,基于地下水情景是其安全评价基本情景的考虑,在考虑T-H-M-C耦合作用的情况下,利用EOS1与EOS2分别模拟了盐水和淡水入侵近场时,地下水与回填材料的相互作用。模拟结果表明,在给定的模拟条件下,盐水入侵时氯化钠的沉淀富集并不严重,整个模拟过程中没有出现盐的沉淀;而在淡水入侵时,方解石的沉淀会引起膨润土孔隙度的变化,但是这种变化对其它阳离子的迁移影响并不大,且通过模拟发现,在整个过程中Ca²⁺对系统的影响比其它阳离子更大.这些模拟对今后继续研究地下水与回填材料之间的相互作用有一定的参考价值,也为进一步研究近场T-H-M-C耦合作用进行了有益的尝试。其次,基于双重介质理论,针对远场裂隙介质中的溶质运移问题,从单裂隙介质中溶质运移问题入手,初步探讨了溶质在单裂隙中运移的概念模型和数学模型,利用拉普拉斯变换推导了在裂隙入口处具有指数衰变注入源条件下的解析解。在此基础上,分别计算了Th-229、Cs-135及Se-79三种核素在低渗透花岗岩裂隙域与基质域中的相对浓度分布,并对它们在裂隙域中的迁移距离与基质域中的扩散深度进行了比较。结果表明:在其它条件相同的情况下,迟滞系数与这三种核素的迁移距离、扩散深度成负相关关系。此外,就水力坡度、隙宽对这三种核素在单裂隙介质中的迁移进行了分析,结果表明:核素的迁移距离及相对浓度都随水力坡度或隙宽的增大而增大;且对同一种核素而言,水力坡度越小时其变化对相对浓度的变化影响越大。而在隙宽较小时(5.89×10^-5m),通过对Se-79、Cs-135两种核素相对浓度的比较发现半衰期的大小对核素在裂隙介质中的迁移也有影响。针对裂隙系统的复杂性,利用一维多途径溶质运移模型描述裂隙系统,对前述三种核素进行了模拟研究,模拟结果表明Th-229迁移是最慢的,而Se-79迁移是最快的;且这些核素在裂隙域中的相对浓度约在3×10⁷年内基本达到稳定。并将其计算结果与单裂隙介质中所得结果进行对比,结果说明裂隙介质特征的准确描述对溶质运移数值模拟至关重要。最后,以西北某地的花岗岩为迁移介质,利用一维多途径溶质迁移模型,选取国内在花岗岩中研究较多的核素Cs-134、Co-57、Tc-99,模拟了这几种核素在其中的迁移.模拟结果表明:在其他条件都相同的情况下,Cs-134的迁移是最快的,而Tc-99迁移是最慢的。更多还原

【Abstract】 Comparing with other solute transport,solute transport in geological disposal system of HLW is characterized as complex way and law of transport,long distance,and so on. Therefore,based on the "multi-barrier system" design of HLW and analysis of safety assessment,the interaction between groundwater and the buffer in engineering barrier,and nuclide transport in geological barrier are primary researched when the groundwater comes back to the repository.The main works and conclusions are as follows:Firstly,on the basis of considering groundwater scenario as basic scenario of safety assessment and T-H-M-C processes,the interactions between saline water and buffer and the interactions between the fresh groundwater and buffer are simulated with EOS1 and EOS2 respectively.The simulated results of saline water show that salt accumulation in buffer material is not so significant,if properties of buffer material and saline water are nearly similar with those which are given in this paper;and the latter results show that precipitate of calcite will change the porosity of bentonite,but the effect on the other cation resulting from this change is not evident,moreover the impact on simulated system caused by Ca²⁺ is more obvious than the other cations.These simulated results are the corresponding reference for study on the interaction of groundwater and the buffer materials and the basis of further research of coupled T-H-M-C processes in near-field.Secondly,in order to resolve solute transport in the fractured media of far field, conceptual and mathematical models of solute transport in single fracture are built according to the double media theory,and analytic solutions with injection of exponential disintegration are deduced by Laplace transform.Relative concentrations of Th-229,Cs-135 and Se-79 in fracture and matrix are calculated respectively based on the analytic Solution,and their transport distance in fracture and diffusion depth in matrix are researched in detail.The results show that the retardation coefficient is negatively related with transport distance and diffusion depth of these nuclides.Moreover,many parameters,such as aperture,hydraulic gradient,will influence on these nuclide transport in fractured media,these influences are analyzed,and the results indicate that transport distance and relative concentration of these nuclides will increase with increase of aperture or hydraulic gradient.For the same nuclides,the change of hydraulic gradient has more influence on relative concentration when the hydraulic gradient is getting smaller.While the aperture is small(5.89×10^-5 m),the half life of the nuclides will affect relative concentration in fractured media by comparison the relative concentration of Se-79 and Cs-135.Because of the complex of fractured media,the fractured media is described by one dimensional multi-way solute model,and the transport of above-mentioned nuclides in fractured media is simulated with this model,the results show that the transport of Th-229 is the lowest while the Se-79 is the farthest,and the relative concentration of these nuclides in fracture will getting stable about 3×10⁷ years.In addition,these results are compared with the results which are calculated in single fracture,the comparison indicates that the correct description of fractured media is the sticking point of successfully numerical simulation.Finally,the nuclides which are researched widely in domestic by experiments,such as Cs-134,Co-57 and Tc-99,are chosen,and their transport in granite is simulated with one dimensional multi-way model.The results show that the transport of Cs-134 is the farthest and Tc-99 is the lowest under the same condition,which is the tentative gist of safety assessment of HLW geological disposal.更多还原