高放处置库高温蒸汽压损伤缓冲材料屏障性能的机理研究

The hermetic environment of high temperature exist in the buffer material for high-level radioactive nuclear waste repository, which stimulated by the heat released from copper canisters for nuclear fuel. Water is evaporated into steam of high pressure and high temperature in this specific environment. Steam prevents migration of pore-water. Lose pore-water, lose the function for water-sweeling to reduce pore radius in the bentonite. And lose pore-water, lower thermal conductivity which hinder fast-cooling in the bentonite. At the same time, it is possible that the buffer material may be shot and broken down by high temperature and high pressure steam. Therefore, the present program have thought over region-wide which more than the water vaporization temperature, and the time-space evolution of porous saturated vapor preesure firstly. Based on the ideal gas law, they are studied by experiments using the equipment of porous saturated vapor pressure from microwave heating, a thermal probe, mercury injection method and micro-CT scanning. Then, a series of experiment study on the axis-translation, the vapour equilibrium method, mercury injection and nitrogen adsorption methd are employed to measure soil-water characterisitic curve of unsaturated bentonite under different temperatures. The curves are applied to the experiments of gas permeability and mercury injection of different sections controlled by gas pressure, temperature and saturation, in order to explore the rule of damage area for pneumatic fracturing. It is significant to interpret how to use bentonite as an effective engineered buffer in high-level radioactive nuclear waste repository.

核废料金属罐的持续热能释放，使得高放处置库形成了密闭高温的特定环境。缓冲材料膨润土孔隙液态水汽化为高压、高温蒸汽，不仅阻止了孔隙液态水的迁移，导致膨润土无法实现吸水膨胀自愈的功能，也降低了膨润土导热率，致使热能不能有效释放至围岩。同时，缓冲材料还存在被高温高压蒸汽“击穿”的可能。为此，项目拟采用理想气体定律，利用微波加热孔隙饱和蒸汽压测试仪、热探针法、压汞法、X射线微显微CT，研究超过水汽化温度区域范围及相应孔隙饱和蒸汽压的时空演变规律。利用气压力-温度-饱和度控制的渗气试验，联合不同断面孔径分布演变规律，构建膨润土气裂损伤范围模型。结合在不同温度下，利用轴平移和蒸汽平衡法，以及压汞法和氮吸附法，得到的膨润土持水性能。探明孔隙蒸汽压驱动下，膨润土气裂损伤范围的动态演化。解译膨润土在处置库中的工程屏障作用，为设计更合适的缓冲材料厚度提供科学依据。

高放处置库中缓冲材料持续受到金属罐（内置高放废物固化体）释放热和围岩裂隙水作用，缓冲材料中孔隙水会在高温作用下汽化为高压蒸汽，蒸汽压如何影响缓冲材料的物理、水、力性能，是评价缓冲材料屏障性能的关键之一。本项目采用设备试制、室内试验、理论分析等手段，发明制造了考虑蒸汽作用的膨润土水、力测试仪；建立了考虑处置库多场耦合环境的膨润土土水特征方程；研究了非饱和膨润土中孔隙蒸汽迁移规律，揭示了孔隙蒸汽压力从高温区域到低温区域逐渐增大，但孔隙蒸汽压并不会改变膨润土孔隙结构，却会劣化膨润土渗透、膨胀性能；进行了不同干密度、含水率、石墨掺量的非饱和膨润土试样热传导性能测试，构建了适用于膨润土、石墨-膨润土的热传导系数模型。研究成果中模型构建均从便于进行高放处置库人工屏障系统的多场耦合分析出发，它是进行高放处置库长期安全性评估的关键。研究期间发表论文3篇，其中被EI检索1篇，另外待刊SCI期刊论文1篇，审稿中英文期刊论文4篇；授权发明专利2项；协助培养/正在培养硕士研究生5名。