高放废物地质处置库围岩的长期屏障性能研究

With the development of nuclear power, geological repository of high-level radioactive wastes becomes a hot topic over the world. Based on our previous investigations, we find that the surrounding rocks not only need to meet the stabilization but also the long term barrier in order to safely, effectively and permanently dispose high-level radioactive wastes. The mechanism of microcrack initiation, propagation and its influences on multi-phase low permeability are first investigated. Concrete-granite reaction tests are performed to analysis the effect of reaction degradation on porosity, mechanical and microstructure properties. The mechanism of diffusion, absorption/desorption in pre-fabricated crack is analyzed, and the evolutions of crack growth, aperture, intrinsic permeability, diffusion coefficient, retardation coefficient under hydro-mechanical-chemical coupling effects are also analyzed. Based on the experimental results, a mechanical-chemical-transport coupling model is proposed for cracked granite according to the coupling mechanism of permeability, diffusion, chemical reaction and stress. An algorithm of mechanical-chemical-transport coupling process in surrounding rocks is developed by XFEM method for the evaluation of long-term barrier properties of surrounding rocks in geological repository of high-level radioactive wastes. The results of this project are highly important for the realization of good barrier properties and low-risk of nuclide leakage in geological repository of high-level radioactive wastes.

随着核电工程的快速发展，高放废物地质处置成为我国和世界各国的研究热点。项目组前期研究发现要保证安全、有效、永久性处置高放废物，必须保证处置库围岩结构稳定性；但是，围岩结构稳定并不能保证核素不发生泄露，还必须保证围岩具有良好的长期屏障性能。设计一系列针对性试验，从微裂纹入手，研究围岩破坏过程中微裂纹萌生、扩展机理及其对低渗多相渗流的影响机理；然后，研究混凝土溶液─花岗岩溶蚀作用，分析其对围岩力学、孔隙率和细观结构的影响机理；进而，采用预制裂隙，研究核素在预制裂隙中扩散、吸附/解吸等作用，并深入分析在应力─化学─渗流长期耦合作用下裂隙扩展、隙宽、固有渗透率、扩散系数、表面阻滞系数等长期演化规律及其机理；最后，分析渗流、扩散、溶蚀、应力等因素之间耦合作用机理，建立准确评估高放废物处置库长期屏障性能的理论模型和分析方法，为我国高放废物地质处置库选址、设计和核素泄漏风险分析提供重要的科学依据。

随着核电工程的快速发展，高放废物地质处置成为我国和世界各国的研究热点。项目组前期研究发现要保证安全、有效、永久性处置高放废物，必须保证处置库围岩结构稳定性；但是，围岩结构稳定并不能保证核素不发生泄露，还必须保证围岩具有良好的长期屏障性能。本项目针对处置库围岩可能出现的屏障性能劣化和核素迁移的风险增加，开展了一系列针对性研究，完成了不同应力路径下的气体渗透试验，分析不同应力路径下花岗岩微裂隙萌生和扩展规律；采用预制裂隙，研究了核素在预制裂隙中扩散、吸附/解吸等作用；完成了混凝土过饱和溶液─花岗岩溶蚀作用试验，分析了溶蚀后的花岗岩试样表面进行细观物性和细观压痕试验，比较溶蚀过程中花岗岩试样表面的矿物成份、细观结构和细观力学参数的变化；完成了单裂隙花岗岩短长期应力─化学─渗流耦合试验，并深入分析不同应力水平、裂隙倾角、隙宽下裂隙扩展、变形、渗透率等的演化规律；在试验的基础上，分析渗流、扩散、溶蚀、应力等因素之间耦合作用机理，建立花岗岩裂隙应力─化学─迁移耦合模型；提出花岗岩裂隙应力─化学─迁移耦合数值分析方法。本项目的研究成果为我国高放废物处置库选址、设计和稳定性分析提供重要的科学依据和技术支持。