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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。
DECOVALEX (development of coupled models and their validation to experiments) is dedicated to the study of the coupling of multiple physical fields in the surrounding rock of high-level radioactive waste disposal and the feasibility assessment of engineering barriers. For the first time, the Chinese team participated in the DECOVALEX program. The subproject Task_D and the results of the phased study are introduced, including two kinds of disposal methods: FEBEX in Switzerland and Yucca Mountain in the United States. A set of non-isothermal flow and deformation control equations for the thermo-hydraulic (THM) coupling process in a complex unsaturated porous media are established, involving solid, liquid and gas phases and four components (solid framework, water, dry air and steam). It is characterized by four types of relatively independent and overlapping models: (1) a model of water expansion stress deformation considering effective stress, thermal expansion stress and bentonite; (2) a flow model considering the exchange of water and steam during evaporative condensation; (3) steam molecular diffusion and convection models that include the relative motion of steam / dry air; and (4) heat exchange models of three-phase local non-isothermal processes. On this basis, according to the Task_D setting requirements simplified to a more practical equation, and the development of the corresponding program to 1 × 106 a THM coupling behavior prediction simulation, the results in February 2005 Task_D seminar and DECOVALEX working conference Compared with the results of independent research conducted by many countries, the degree of agreement is very high, which brings confidence in the establishment of the model and the development of the program.