低放射性廢棄物最終處置回填材料於近場環境下之長期穩定性研究

Long-term stability of backfill material in the near field of a low-level radwaste disposal site

王俊堯(Chun-yao 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(2011年)

摘要

本研究將以台東樟原村日興土與美國懷俄明州BH膨潤土，混合台東地區硬頁岩碎石級配料，調配成不同黏土-碎石含量之回填材料，改變回填材料含水量與調整最大碎石粒徑，進行基本材料性質、改良式夯實、自由回脹應變、定體積回脹壓力、水力傳導度等試驗，並探討其近場環境可能影響回填材料功能的各種因素，包含在混凝土工程障壁與封閉用回填材料界面處，以電滲加速試驗來了解混凝土對回填材料性質的改變，此外，低放廢棄物處置場場址鄰近濱海地區的可能性很高，處置場封閉後勢必會遭受地下水入侵之影響，調配含鹽溶液進行海水入侵到處置場之近場環境的模擬，對回填材料之工程性質與功能產生之影響。最後依據試驗結果歸納其功能特性，了解回填材料於近場環境下的長期穩定性，另一方面掌握本土回填材料之工程性質，與國際間使用之回填材料加以比較。
試驗結果顯示（1）BH 膨潤土回填材料於改變回填材料含水量與調整最大碎石粒徑下之回脹潛能皆遠高於日興土回填材料；（2）日興土與BH 膨潤土回填材料於含鹽溶液中回脹應變量均較在純水溶液中要大幅降低；（3）在電滲加速試驗後續分析中，由離子定量與回脹潛能試驗得知，二種膨潤土回填材料隨電滲時間越長，回脹量越低，且越靠近混凝土接觸面之回填材料，其鈣/鈉離子比值差距越大；( 4 ) 膨潤土回填材料隨電滲時間越長，其越靠近混凝土接觸面之回填材料pH值越低，距離越遠pH值越高；( 5 ) 二種膨潤土回填材料在電滲加速試驗後續分析TGA及XRD 中，曲線差異大部份都不明顯。

關鍵字

電滲加速試驗 ； 海水入侵 ； 回填材 ； 回脹潛能 ； 低放廢棄物

並列摘要

Zhishin clay (日興土) and Black Hill bentonite are used as raw clay materials in this study. These clays are mixed with Taitung area hard shale to produce the backfill material for low-level radioactive wastes disposal site. Engineering characteristics and barrier functions of backfill materials including compaction, free swelling, swelling pressure, and hydraulic conductivity are obtained in the laboratory for evaluation.
In order to have improved uniformity, the maximum size of the crushed gravel is reduced to 4.75 mm and 2.36 mm to produce the backfill materials. The interaction between concrete barrier and the backfill material is simulated by an accelerated migration test to investigate the effect of concrete on the expected functions of backfill material. Saline water intrusion into the near-field of disposal site is simulated to understand the engineering properties of the backfill material in such scenarios.
The results show that the reduction in maximum size of crushed gravel produces similar maximum unit weight, higher swelling potential and reduced hydraulic conductivity. Backfill material prepared using BH bentonite has higher swelling potential than that using Zhishin clay. The use of saline water as intruding solution into the backfill material results in a decrease in the swelling potential and some increase in hydraulic conductivity.
Finally, the interface between the concrete barrier and backfill material was simulated by an accelerated electro-osmosis test. The results show some decrease in swelling potential for the backfill material near the interface. Also, backfill material close to the contact of the concrete exhibits larger change in the ratio of calcium/sodium concentration, due to the release of calcium ions from the concrete barrier.

並列關鍵字

low-level radioactive waste ； backfill material ； swelling behavior

參考文獻

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