DECOVALEX_IV TASK_D项目的热–水–力耦合过程的数值模拟(英文)

NUMERICAL MODELLING AND SIMULATION OF COUPLED THM PROCESSES IN TASK_D OF DECOVALEX_IV

核废料地下处置系统研究的国际合作项目 DECOVALEX(development of coupled models and their validation against experiments) 致力于高放射性核废料地质处置系统围岩中多个物理场的耦合过程研究和工程屏障的可行性评估。中国研究小组第一次参加 DECOVALEX 计划。介绍了其子课题 Task_D 的情况和阶段性研究结果,包括 2种处置方式——瑞士 FEBEX 和美国 Yucca Mountain 类型的 1×104 a 以上的预测模拟及其比较分析。建立一套复杂的非饱和多孔介质中热液力(THM)耦合过程的非等温流动和形变控制方程,涉及到固、液、气三相和四种组分(固体骨架,水,干空气和水蒸汽)。其表现为相对独立同时又相互交叠的 4 类模型:(1) 考虑有效应力、热膨胀应力和膨润土的水膨胀应力变形模型;(2) 考虑水与蒸汽在蒸发凝结时物质交换的流动模型;(3) 包含蒸汽/干空气相对运动的蒸汽分子扩散和对流模型;(4) 三相局部非等温过程的热交换模型。在此基础上根据 Task_D 的设定要求简化为较为实用的方程,并发展了相应的程序对 1×106 a THM 耦合行为进行了预测模拟,其结果在 2005 年 2 月Task_D 讨论会和 DECOVALEX 工作会议与多个国家相互独立的研究结果进行对比,吻合程度很高,这给模型的建立和程序发展都带来了信心。

The purposes of the DECOVALEX project（development of coupled models and their validation against experiments） are focused on the various coupled thermo-hydro-mechanical（THM） and geochemical processes occurring in the near field of a high activity radioactive waste disposal facility, of a demonstration for the feasibility of the construction of engineered barriers, and of how they affect the role of performance assessment for radioactive waste disposal, Task_D of the DECOVALEX_IV project includes predictive analysis of the long-term coupled processes（up to 1× 10^4 years） in two generic repositories FEBEX type and Yucca Mountain Project type for comparison. To better understand the coupling THM processes and their influences on the system behaviours, this paper presents a rigorous treatment of the theory of non-isothermal flow and deformation in unsaturated porous media. The governing equations based on the conservation equations of mass and energy and the equations of equilibrium, Darcy＇s law, Fourier＇s law are derived by using a systematic macroscopic approach. Each of the three phases（solid, liquid and gas） is viewed as an independent continuum endowed with its own kinematics. Four constituents（solid, water, vapour and dry air） are identified. Four separate but overlapping models are developed as follows： （1） deformation model for solid considering the fluid effective stress, thermal stress, and bentonite saturation swelling pressure; （2） flow model for water and gas considering the mass exchange between water and vapour in evaporation or condensation processes; （3） vapour molecular diffusion and advection model considering the relative movement of vapour to dry air in presumed homogenous pore gas phase, and （4） heat transfer model considering the non-equilibrium local thermal processes that three phases are not at a same temperature. Based on above equations, practical models are developed according to the given Task_D BMT（bench mark test） request, and the codes are programmed to simulate coupled THM processes in 1×10^6 years with Task_D BMT set-up, Simulation results are shown and verified in Task D force meeting and the third workshop of DECOVALEX_IV in Kunming（2005）, China. There is a good agreement with results of participant teams from other countries.