高庙子膨润土在高水平放射性废物深地质处置中成熟化行为分析及其长效性能研究

KBS-3 and very deep borehole (VDH) concepts are two major types of long-term geological disposal methods for high-level radioactive waste (HLW) isolating from the biosphere. The KBS-3V concept for isolating the HLW at the depth of 400-500 m, is the officially proposed option in Sweden and has been the subject of considerable research in the past few decades, while the VDH concept is about the HLW isolated under a depth of 2km in the 4 km deep bore hole with 800 mm diameter. The HLW boreholes have a spacing of individual holes of 200m for avoiding thermal overlap. The greatest merit of the VDH concept is that the almost stagnant groundwater in the deep boreholes prevents the transport of the possible release of radionuclides into the rock or up to the ground level. One of the major challenges for borehole sealing is to anticipate the maturation behavior of clay seals in the borehole. The ultimate homogeneity of clay seals is expected to stabilize the borehole and prevent possible leakage of radioactivity. In this project, the investigating of maturation of buffer-backfill clay in the HLW deep borehole will be performed. A numerical model will be proposed to simulate the maturation process, both the expeditious water transport and clay migration in the initial stage as well as the slow subsequent homogenization. By performing numerical simulations for various clay types as well as different combinations of dimensions and initial densities of mud and dense clay the maturation process and the end result can be theoretically studied thereby to be the reference for selecting a suitable design for buffer-backfill clay in HLW repository.

KBS-3和VDH是高水平放射性废物长期地质处置的两种主要方法。KBS-3的设计概念是将高放废物储置于地下400-600米深度；VDH处置是将高放废物储置于距地表约2千米以下的区域，深度可达4-5千米。VDH处置方法最大的优点是：在深孔深处地下水几乎停滞不动，有效地阻止了可能泄漏的放射性物质进入岩石甚至上升到地平面。VDH处置概念中深孔缓冲-回填-密封技术面临的主要挑战之一是预测膨润土的成熟化行为。缓冲/回填体系的长期低渗性，以及成熟最终均质化是维护深孔密封稳定和阻止核素泄露的重要因素。本课题拟采用实验与理论建模相结合的方法，对VDH处置库中高庙子膨润土的成熟化行为及其长效性能进行研究。探索水在高庙子膨润土中的运动和膨润土体系的均质化发展，以期建立成熟化数学模型。模拟计算结果对预测高压实膨润土在长期处置过程中渗透密封性能的变化规律有重要意义，为高放废物处置缓冲回填材料的设计提供参考参数。

在高水平放射性废物深钻孔地质处置库中，作为缓冲/回填材料的膨润土会经历地下水环境的长期作用。本项目以我国高放废物处置库首选缓冲/回填材料高庙子（GMZ）膨润土为研究对象，利用自行研制的径向水运移渗流实验装置，开展了水在GMZ膨润土缓冲/回填体系中的运移实验研究，揭示膨润土成熟均质化行为机理和规律；结合化学和细微观测试技术，明确Ca2+在体系中伴随溶液运移行为扩散的演化特征，探讨溶液运移与膨润土试样初始物理性能的相互关系和对膨润土长期性能的影响；建立水运移作用下膨润土成熟化理论模型，深入阐明膨润土缓冲/回填体系水化均质化发展和体系长效性能的演化；初步对处置库尺度膨润土体系的长期水运移特性进行了数值模拟；相关结论可为高放废物处置库膨润土材料的选择设计和工程屏障系统的密封安全性评价提供参考。