在低放射性廢棄物最終處置場的服務期間長久，而混凝土和回填材料介面的交互作用時間是連續且長久，長期下來接觸介面的交互作用以及未來地下水的入侵，皆會造成回填材料內部微結構和障壁功能的改變，直接影響到原本預期的材料特性。 本研究內容主要分為兩個階段，在第一階段有兩個部分，第一部份以電滲加速試驗模擬處置場在長久未飽和狀態下，模擬混凝土襯砌及回填材料介面的交互作用，混凝土分別選用一般混凝土及低鹼混凝土，比較不同混凝土對回填材料的影響，回填材料是以 Volclay SPV 200 膨潤土取代 50 % 重量百分比的粒料；，以低鹼性混凝土作為混凝土襯砌，回填材料分別以膨潤土取代50% 及 30% 的粒料，比較碎石粒料的添加比例是否能減少混凝土對回填材料的影響。第二部份，以回脹壓力與水力傳導試驗針對處置場在飽和狀況下，了解地下水化學及pH值效應對電滲後回填材料回脹行為之影響。 研究結果顯示，在未飽和環境下混凝土襯砌與回填材料相互接觸經電滲加速試驗後，混凝土中鈣離子將會釋出，使得與其接觸的回填材料由接觸面開始，其鈣鈉比升高、pH值降低，且普通混凝土對回填材料的影響較低鹼性混凝土大。在飽和環境下，電滲後回填材料於NaCl 與 CaCl2 環境下，回脹壓力隨著陽離子濃度提升而降低，其中NaCl效應下對回脹壓力影響較大。電滲後回填材料於 pH值<13 溶液中，對回脹壓力沒有明顯影響；當回填材料於高鹼系統中，高濃度氫氧根離子入侵至膨潤土內部，造成蒙脫石溶解，導致回脹壓力永久性降低。 ;Both concrete and backfill serve as engineered barriers for isolation of low-level radioactive wastes in a repository for radioactive wastes. As the disposal site is expected to serve a very long time, the interactions between the two barriers need to be evaluated under the potential unsaturated/saturated situations. This study aims at simulating the long-term scenario of engineered barrier materials and the corresponding effects of the scenario on the expected function of barrier materials in a final disposal site for low-level radioactive wastes. In this research, a migration technique was applied to accelerate the migration of calcium ions from the pore solution of concrete so as to investigate the alteration of compacted bentonite in contact with the concrete. The backfill material was prepared by mixing 30-50% of Black Hills bentonite from Wyoming with 50-70% of Taitung area argillite to produce different ratios of sand-bentonite mixture as backfill. And the barrier concrete is a low-pH concrete having a binder comprised of 60% cement and 40% silica fume. After the migration test, backfill material was tested for swelling pressure to evaluate the effects of long-term contact. Finally, concrete barrier and backfill were both subjected to extended unsaturated situation as well as saturated situation for further evaluation. The backfill was treated with groundwater permeated through the concrete after the migration test so as to simulate the sequence of unsaturated and saturated scenarios that are expected to be experienced. Also, concrete barrier and backfill were both subjected to extended unsaturated situation as well as saturated situation for further evaluation. The backfill was treated with groundwater chemistry, pH environment after the migration test so as to simulate the sequence of unsaturated and saturated scenarios that are expected to be experienced. Results from the study show:(1) It was found from the accelerated migration test that the release of calcium from concrete in unsaturated situation results in reduction of swelling capacity of the contacting buffer. The shorter the distance to the interface, the more the increases in the ratio of calcium to sodium content in the backfill material, and the swelling pressure decreased as well. (2) in NaCl and CaCl2 solution, the swelling pressure of bentonite decreases with increasing cation concentration, and the effect of NaCl on swelling pressure is more pronounced; (3) at solutions with pH < 13, no significant reduction on swelling pressure was observed; (4) as illustrated by ICP analysis, backfill in NaOH [1.0M] solution shows decreases in montmorillonite and quartz minerals, while the Si4+ ions exhibits obvious increase.
