Thermo/hydro coupling effects on temperature distribution and hydraulic conductivity of buffer material

• Main Authors: Ya-wei Wang, 王雅薇
• Other Authors: Wei-qing Hung
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/xg9u9w

碩士 === 國立中央大學 === 土木工程研究所 === 96 === A repository for high-level radioactive wastes would be constructed in the bedrock at the depth of several hundred meters below ground surface. The interaction of the thermal and hydration fronts will produce transient states in the barrier in which thermal flow, water movement will be coupled. A compacted bentonite block is submitted to simultaneous heating and hydration, and has been designed with the aim of simulating the heat/water flow interaction in the barrier. The transmission electronic microscope (TEM) was used in observing the microstructure of the bentonite in a swelled situation. Both Zhisin clay and Wyoming Black Hills (BH) bentonite were adopted as potential buffering materials and tested for suitability in this application. A thermal probe is installed in bentonite specimens to measure the temperature distribution and hydraulic conductivity of water saturated Ca-bentonite with dry densities of 1.5, 1.6, and 1.7 Mg/m3 , within the temperature range of 20 to 80℃. The results indicate: (1) The hydraulic conductivity of Zhisin clay increases with the rise of temperature. On the other hand, a decrease in hydraulic conductivity is observed as the dry density goes up to 1.7 Mg/m3; (2) X-Ray diffraction was conducted to identify clay minerals in Zhisin clay. The results showed that illite, as the major component, takes up 56 percent of the entire mineral proportion. The secondary clay mineral would be kaolinite and takes up about 30 percent; while smectite was found to be less then 14 percent; (3) TEM observation shows that the gel of clay system varies, and this variation in microstructure might affect the transport property of clay component; (4) The temperature gradient near the heater is found to be high, with a decrease in temperature gradient as the distance from the heater increases.