核素渗漏对地下水污染的数值仿真研究

研究放射性核素在地下水环境中传输的动力学行为是评价核废料处置库安全性能的一个关键性问题。以双重介质理论为基础，充分考虑了地下水变密度对核素浓度分布的影响，建立了孔隙-裂隙介质中核素随地下水迁移的耦合数值模型，其中相对密度项使地下水流控制方程具有非线性性，为此将Galerkin有限元法和Picard迭代法相结合对耦合模型进行了离散，并模拟了核素泄漏对地下水污染的动态过程。数值仿真的结果表明：污染面积随时间推移不断扩大，且纵向扩散显著：数值仿真结果没有出现弥散现象，验证了数值算法的可靠性；核素浓度的分布对水密度变化表现较为敏感，且不同核素（^226Ra、^210Pb和^90Sr）由于各自放射性衰变特征的巨大盖异，受到水密度影响的程度也有很大差别．因此，在对裂隙介质核素迁移的数值仿真分析过程中，不能忽略地下水密度的变化对其造成的影响。

Study on Numerical Simulation of Nuclides Leakage for Groundwater Pollution

Study on dynamical behavior of nuclides transportation in subsurface flow is a critical part of a performance assessment for an underground repository for radioactive waste. Based on dual media theory, the effect on concentration contribution of nuclides is considered due to variable density groundwater flow, and a coupling numerical model has been developed for describing the transportation of radionuclides in matrix-fracture media. The groundwater flow equation is nonlinear because of the relative density. A Gelarkin finite-element method and a Picard iteration scheme are used to approximate the coupling model, and the process of nuclides leakage is presented. Numerical simulation results show that the contaminated plume is continually extended as time increases, and the vertical diffusion is more obvious. Numerical oscillation does not appear which verifies the reliability of the algorithm. The concentration distribution of nuclides is subtle to variation of fluid density, and fluid density can have various effect on different nuclides (226Ra,210Pb and 90Sr), because radioactive decay of nuclides are different from each other. Therefore, the variation of groundwater density can not be neglected in the process of numerical simulation of nuclides in fractured porous media.