高放废物深地质处置地下水数值模拟应用综述

Review of groundwater numerical simulation for deep geological disposal of high-level radioactive waste

开展地下水数值模拟研究是高放废物处置场地安全评价的重要组成部分,然而深地质处置介质类型的复杂性、基岩深部资料的相对匮乏性导致模拟结果存在不确定性,如何刻画深部地下水动力场并评估可能引起的风险已成为高放废物处置安全评价中重点关注的问题。在大量文献调研的基础上,综述了世界典型国家高放废物深地质处置场地的地下水数值模拟与不确定性分析应用,并归纳总结该领域研究经验,得到以下认识:(1)深地质处置场深部构造、裂隙的发育与展布决定了地下水循环条件,探究适用于基岩裂隙地区新的水文地质试验方法是提高地下水数值模型仿真性的基础;(2)不同尺度模型融合是解决深地质处置地下水模拟的有效技术方法,区域尺度多采用等效连续介质法,场地尺度使用等效连续多孔介质和离散裂隙网络耦合模型,处置库尺度使用离散裂隙网络方法,其次需重点关注未来大时间尺度下放射性核素在地质体中的迁移转化规律,模拟预测场址区域地下水环境长期循环演变对核素迁移的潜在影响;(3)考虑到不同的处置层主岩岩性以及在多介质中发生的THMC(温度场—渗流场—应力场—化学场)过程,目前国内外常用的地下水模拟软件有:Porflow、Modflow、GMS及MT3DMS等用于模拟孔隙或等效连续介质,Connectflow、Feflow及FracMan等用于模拟地下水和核素在结晶岩、花岗岩等裂隙中的迁移,TOUGH系列软件主要应用于双重介质的水流、溶质及热运移模拟;(4)指导开展有针对性的模型和参数的不确定性分析工作,减少投入工作量,提高模型精度,并可针对处置库长期演变、废物罐失效、极端降雨等多情景预测模拟,为处置库安全评价及设计提供基础数据支撑;(5)针对我国深地质处置地下水数值模拟研究现状,下一步应加强区域地质、水文地质、裂隙测量以及现场试验等相关的调查及监测工作,多介质耦合、多场耦合模拟及不确定性分析研究将会是未来的研究重点。

Groundwater numerical simulation is an important part of the safety assessment for high-level radioactive waste(HLW)disposal sites.The complexity of deep geological disposal media and the relative lack of deep bedrock data lead to uncertainties in the simulation results.How to characterize the deep groundwater dynamic field and evaluate the possible risks has become a key issue in the safety assessment of HLW disposal.Based on a lot of literature investigation,this paper reviews the application cases of groundwater numerical simulation and uncertainty analysis of HLW deep geological disposal sites in typical countries,and summarizes the research experience in this field.The results show that(1)the structure and fracture development and distribution of deep geologic repositories determine the groundwater circulation conditions,and exploration of the new hydrogeological test method suitable for fractured bedrock areas is the basis of improving the accuracy of groundwater numerical simulation.(2)The integration of different scale models is an effective technical method to solve the groundwater simulation for deep geological disposal.The equivalent continuum method is mostly used at a regional scale,the coupling model of equivalent continuous porous medium and discrete fracture network is used at a site scale,and the discrete fracture network method is used at a repository scale.Furthermore,it is necessary to pay more attention to the migration and transformation of radionuclides in geological formations,to simulate and predict the potential impact of the long-term groundwater environment evolution on radionuclide migration in the site area.(3)Considering different host rocks in the disposal layers and the thermal-hydrogeological-mechanicalchemical process occurring in multiple media,the commonly used software for groundwater numerical simulation in HLW deep geological disposal includes Porflow,Modflow,GMS and MT3 DMS,which are used to deduct pores or fractures into equivalent continuum,and groundwater flow and nuclides migration in fractures of crystalline rock and granite can be generalized by using Connectflow,Feflow and Fracman,whereas TOUGH series is mainly used to simulate flow,solute and heat transport in dual media.(4)Targeted uncertainty analysis of the models and parameters should be carried out to reasonably reduce workload and improve the model accuracy.Moreover,the prediction simulation of repository long-term evolution,waste canister failure,extreme rainfall and other scenarios can provide basic data support for the safety assessment and design of the repository.(5)In view of the current researches on groundwater numerical simulation of HLW deep geological disposal in China,it is necessary to strengthen the investigation and monitoring of geology,hydrogeology,fissure measurement and field test in the next step,and the multi-medium coupling model,multi-field coupling simulation and uncertainty analysis will be the focus of future researches.