緩衝材料在熱/水力耦合作用下溫度分布與水力傳導性研究

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

王雅薇(Ya-wei Wang)

指導教授 ： 黃偉慶

國立中央大學/工學院/土木工程學系/碩士(2008年)

摘要

放射性廢棄物最終處置為確保放射性廢棄物與人類環境的隔離，採用多重障壁的深地層處置是公認最可行的辦法。緩衝材料於近場環境下長期受高放射性廢棄物衰變熱與地下水入侵的耦合作用，地下水尚未入侵前形同乾燥加熱狀態，當地下水入侵緩衝材料再飽和過程中，整個處置環境在熱-水力梯度耦合效應下，反應機制變得相當複雜。
本論文模擬處置場在近場環境下緩衝材料特性，探討因子包括黏土礦物組成成分與熱/水力耦合狀態下溫度分布與水力傳導度，並借助穿透式電子顯微鏡(TEM)觀察回脹後之微觀特徵。以國產日興土與美國懷俄明州膨潤土為研究材料，設計乾密度1.5~1.7 Mg/m3。於實驗室裡用熱探針法量測膨潤土溫度變化；以及日興土在25℃~80℃不同溫度之水力傳導係數，藉以探討緩衝材料在熱-水力效應作用下之行為。
研究結果發現：(1)日興土水力傳導性會隨著溫度上升而增加，當膨潤土乾密度增加，水力傳導係數降低。(2)X-Ray繞射分析結果顯示，日興土黏土礦物中以伊萊石的相對含量佔56％為多；其次是高嶺石相對含量約為30％；膨潤石的相對含量約14％。(3)TEM觀察顯示膠體在黏土系統內會依據不同型態排列，這些微觀組構的多變性，將可能影響著黏土組構。(4)膨潤土溫度分布靠近熱源處有明顯的溫度梯度，離熱源越遠溫度梯度越小，而與有限元素分析模擬的結果溫度分布相當接近。

關鍵字

熱-水力耦合 ； 水力傳導性 ； 緩衝材料

並列摘要

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.

並列關鍵字

hydraulic conductivity ； buffer material ； thermo/hydro coupling

參考文獻

張家銘，(2006)「以熱探針量測大地材料熱傳導係數之適用性」，碩士論文，中央大學土木工程系，中壢。

陳炳坤，(2006)「高放射性廢棄物最終處置場緩衝材料之回脹穩定性與微觀結構研究」，碩士論文，國立中央大學土木工程系，中壢。

林俊宏，(2006)「粉體在不同含水量及乾單位重下 之熱傳導係數 」，碩士論文，中央大學土木工程系，中壢。

戴豪君，(2002)「深層岩體熱力-水力-力學偶合行為之初步研究」，碩士論文，國立成功大學資源工程學系，臺南。

Bailey, S.W. (1966). The Status of clay mineral structures. Clays Clay Miner., 14, 1-24.