本研究針對高放射性廢棄物最終處置場之緩衝材料，探討其近場環境可能影響緩衝材料功能的各種因素，包含緩衝材料受含鹽溶液以及與混凝土反應使pH值改變對回脹潛能造成的影響、廢棄物包件底部的緩衝材料長期處於高荷載狀態下產生的沈陷效應及地下水入侵後造成的體積改變、緩衝材料受廢棄物包件衰變熱作用下產生之乾縮 行為對材料緩衝性質之影響等。 本研究試驗材料為台東樟原的日興土以及美國Wyoming州的BH膨潤土，試驗結果顯示（1）BH膨潤土於各種狀態下之回脹潛能皆遠高於日興土；（2）BH膨潤土於含鹽溶液中回脹應變量隨著溶液濃度及離子價數增加而降低；（3）BH膨潤土回脹應變量隨著酸性或鹼性增加而降低；（4）日興土於高壓荷載狀態下產生沈陷行為，BH膨潤土於高壓荷載狀態下產生解壓回脹效應，壓縮後之兩種黏土材料於含鹽溶液中產生微量回脹行為，回脹應變量隨著溶液濃度及離子價數增加而降低，日興土壓縮後回脹應變量除了在極端pH值溶液中回脹量略微提升，其餘回脹量皆隨著酸性或鹼性的增加而降低；（5）兩種緩衝材料於初始含水量下之乾縮行為並不受不同乾燥環境溫度的影響，且不會產生乾縮裂縫；（6）日興土與BH膨潤土提高含水量至臨界值後可能會因乾燥而產生裂縫。 Abstract Compacted bentonites are attracting greater attention as buffer material for deep geological repository of high-level radioactive waste. Properties of buffer material would be affected by near-field environment. The objective of this research is to find out the volumetric stability of buffer material under near field conditions. The following scenarios are experimentally simulated, including groundwater intrusion, loadings from waste package, and the decay heat from waste package. The buffer materials used in this study are Zhisin clay produced in eastern Taiwan and Black Hill (BH) bentonite from Wyoming. Experimental results show that: (1) the swelling potential of BH bentonite is higher than that of Zhisin clay; (2) the swelling strain of buffer material decreases in the presence of electrolyte in the pore fluid, and the swelling strains in NaCl solution are higher than that in CaCl2 solution; (3) compaction settlement of Zhisin clay increases with increasing compaction pressure; (4) swelling strain upon immersion in solution after compaction varies with groundwater chemistry; (5) volumetric shrinkage of bentonite in its initial water content was not influenced by drying temperature and desiccation cracking was not observed; (6) the shrinkage upon drying could result in cracks for bentonite prepared at high water contents.
