Underground radioactive waste repositories: assessment of post-closure safety under extreme events

提出的研究是关于低、中水平核废料深地质处置库的长期安全评价。许多有核动力生产的国家正在考虑采用dgr。这些国家包括瑞士、法国、瑞典、美国、德国、英国和日本等。第一个进入建设阶段的项目是芬兰的Onkalo储存库，该项目于2015年11月获得监管部门的批准。在加拿大，目前正在进行选址过程，最近的工作重点是安大略省南部的泥质地层（科堡石灰石），作为DGR的可能地点。***本项目的主要目的是研究现有方法的不足，并建立一些新的方法来评估在泥质岩石中建造的DGR关闭后的安全性。这项研究将包括四个主要的研究主题，即(i)描述科堡石灰石的机械和水力特性；（ii）裂隙介质流动的水-力耦合分析；（iii）与近场评估挖掘受损区（EDZ）有关的个案研究，以及（iv）评估极端事件下DGR关闭后的安全性。***在第(i)部分中，解决的基本问题将是石灰石的强烈非均质结构与其机械/水力性能之间的相关性。织物的量化将采用基于立体学的显式张量测量，这将提供与方向相关的信息。对于水力特性，将电导率张量定义为孔隙网络几何形状的函数，并假设其与应力场相关的演化规律。在第二部分中，将对裂隙介质中流动的水-力耦合分析进行研究。将开发一种新的公式，该公式将在靠近大裂缝的参考体积内对现场算符进行平均。最后两部分，即（三）和（四），将讨论拟议办法的数字执行和核查。重点将放在评估在极端事件（如强震）和气候变化（即冰川作用和/或永久冻土）情况下DGR的长期安全性。对放射性核素通过地圈的输运时间和逃逸到环境中的可能性的评估将作为力学分析的补充。***该项目的主要成果将是加强对与核废料长期地下储存有关的物理-机械过程的了解，并制定可靠的数值程序，以评估极端事件情况下的安全边际。＊＊＊＊＊

The proposed research is concerned with a long-term safety assessment of Deep Geological Repository (DGR) for low and intermediate-level nuclear waste. DGRs are being considered in many countries with a nuclear power production. Those include Switzerland, France, Sweden, USA, Germany, UK and Japan among others. The first project to enter the construction stage is Onkalo repository in Finland, which obtained regulatory approval in November 2015. In Canada the site-selection process is currently under way and the efforts have recently focused on argillaceous formations of southern Ontario (Cobourg limestone) as a possible location for DGR. ***The primary objective of this project is to examine the gaps in the existing approaches and to establish some new methodologies for evaluating post-closure safety of DGR constructed in argillaceous rocks. The study will include four major research themes, viz. (i) description of mechanical and hydraulic properties of Cobourg limestone; (ii) coupled hydro-mechanical analysis of flow in fractured media; (iii) case studies related to near field assessment of excavation damaged zone (EDZ), and (iv) evaluation of post-closure safety of DGR under extreme events.***In part (i), the fundamental issue addressed will be a correlation between the strongly heterogeneous fabric of the limestone and its mechanical/hydraulic properties. The quantification of fabric will employ an explicit tensorial measure, based on stereology, that will provide an orientation dependent information. For hydraulic properties, the conductivity tensor will be defined as a function of geometry of the pore network and an evolution law will be postulated to correlate it with the stress field. In part (ii), the research on the coupled hydro-mechanical analysis of flow in fractured media will be conducted. A new formulation will be developed that incorporates an averaging of the field operators within the referential volume adjacent to macrocrack. The last two parts, i.e. (iii) and (iv), will deal with a numerical implementation and verification of the proposed approaches. The emphasis will be placed on assessing the long-term safety of DGR in case of extreme events, such as strong earthquakes as well as climatic changes, viz. glaciation and/or permafrost. The mechanical analysis will be supplemented by the assessment of the radionuclide transport times through the geosphere and the possibility of escape to the environment. ***The primary outcome of this project will be an enhanced understanding of the physico-mechanical processes associated with long-term underground storage of nuclear waste and development of reliable numerical procedures for assessing the safety margins in case of extreme events. *****