高放射性廢棄物為國際間重要的環保議題，先進核能國家一致認為以多重障壁概念設計的深地層處置場，是目前解決高放射性廢棄物最可行的方法。而高放射性廢棄物因具有長半衰期核種(鈾、鈽)，因此其深地層處置設施的安全評估長達萬年以上，地下水入侵成為重要的評估項目之一。當處置場坑室受到地下水入侵，其內部緩衝材料的含水量隨之改變。緩衝材料在吸水後產生膨脹，進而壓縮緩衝材料內部孔隙，使得孔隙比產生改變。 本研究主要在於研析緩衝材料水力性質，以建立未來研究THMC耦合效應之基礎。研究內容採用有限元素法，針對處置場受地下水入侵後之含水量分佈，利用有效應力理論及緩衝材料持水曲線，進行數值分析模擬。受限於模擬所需之材料性質及相關模擬參數，難以完全從傳統的實驗室試驗中得到，所以必須對試驗步驟與邊界條件做適當的調整，以進行試驗，來取得所需之參數。首先利用本身所建立之模型，套用國外數據，將所得之結果與國外模擬結果相比較，以判斷所建模型之適用性。目前國內對日興土相關參數尚未完整建立，故再進一步透過參數分析及日興土攝取水試驗推估出日興土材料參數，以供未來設置地下處置場之設計參考。 Most countries make choice of deep geologic disposal as the best method to achieve the isolation and retardation of nuclide migration by multiple barriers. In an underground disposal site, the radioactive wastes are encapsulated in containers surrounded by a buffer material and the excavation backfilled with a mixture of clay and sand. Bentonites serve as buffer material in an engineered barrier system for isolation of high-level radioactive wastes. This research investigates the hydraulic behavior of the buffer material, in order to provide a basis for evaluating the thermal-hydro-mechanical (THM) coupling effects in a underground repository. Water uptake tests were conducted on bentonite specimens prepared at different densities to simulate groundwater intrusion to the buffer material. With these tests the degree of saturation (and void ratio) can be plotted as a function of the distance from the water inlet. The finite element program ABAQUS was used to perform numerical simulation of the hydraulic behavior of the buffer material. By comparing the experimental results and the numerical simulation, a model for describing the hydraulic behavior of buffer material was developed. In addition, material parameters suitable for Zhisin clay, a potential buffer material for Taiwan, are recommended based on the analysis.
