鹼環境對膨潤土之緩衝回填材料性能影響

Effect of Alkaline Environment on Bentonite Properties in Buffer and Backfill Material

李柏毅(Po-I Lee)

指導教授 ： 詹穎雯

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202003015

摘要

隨著科技的進步，現今社會對於原子能以及核能的應用與依賴日漸提高，因此使用原子能或核能伴隨產生之放射性廢棄物的處理便是如今要面對的一大課題之一。
目前針對放射性廢棄物的處置方法，各國大多利用「多重障壁」的概念建立放射性廢棄物處置場進行隔離處理，多重障壁的概念是利用低滲透性且穩定的岩盤作為天然障壁，再加上由混凝土與膨潤土組成的多道人工障壁來封存放射性廢棄物，以隔絕放射性廢棄物直到其放射性衰減至對環境無害的程度。然而要達到前述目標需要一段相當長的時間，在如此長時間的作用下，位在地下的處置場可能會由於地下水的入侵而導致混凝土發生失鈣現象，而失鈣現象所產生的鹼性孔隙液將會對以膨潤土為主要材料的緩衝回填材料有不良的影響，本研究將探討失鈣現象產生的鹼性溶液對緩衝回填材料之性能的影響進行研究與討論。
本研究以KUNIGEL-V1與MX-80之純膨潤土試體進行鹼性溶液對緩衝回填材料的膨脹性能、阻水性能與耐久性能進行試驗與分析，結果指出鹼性溶液對緩衝回填材料的影響主要可以分為陽離子的影響與蒙脫石溶解造成的影響，其中前者的影響較為立即，而後者則需要較長的時間才會對緩衝回填材料有較大的影響，但是兩者的共通點是皆會降低緩衝回填材料的膨脹性能與阻水性能表現。MX-80在整體受到鹼性溶液中陽離子的影響比較小，因此在與鹼性溶液作用時間不長的情況下MX-80有更好的膨脹性能與阻水性能表現，然而MX-80在失鈣現象產生的鹼性環境中的蒙脫石溶解速率較大，因此KUNIGEL-V1在較高初始乾密度的條件下有更好的耐久性能。
最後本研究根據試驗結果提出了可以作為工程實務設計參考的兩膨潤土的膨脹性能預測式與耐久性能迴歸式。

關鍵字

失鈣 ； 緩衝回填材料 ； 膨潤土 ； 膨脹壓力 ； 水力傳導係數 ； 鹼性 ； 預測式

並列摘要

With the improvement of science and techlology, the use of radioactive materials is becoming more common. However, the use of radioactive materials will produce radioactive waste.
Nowdays, many countries use the concept of “multiple barriers” to build radioactive waste disposal to seal the radioactive waste. The concept of multiple barriers is to use low-permeability and stable rock as natural barriers, and use concrete and bentonite as artificial barriers to seal the radioactive waste. Until the radioactivity of radioactive waste decays to harmless to human or environment. However, it takes a long time for radioactivity to decay to harmless level. During this long period, the calicium leaching of concrete may happen due to groundwater invades the disposal underground, and the alkaline pore water produced by the calcium leaching reaction has a undesirable infleunce on buffer and backfill materials made by bentonite. This study will explore the effect of alkaline solution cause by calcium leaching on the performance of bentonite in the buffer backfill materials.
In this study, the swelling performance, water blocking performance and durability of buffer and backfill material will be test by experiments in alklaline solution. Pure bentonite samples of KUNIGEL-V1 and MX-80 were used for the experiment.The result of experiments show that the influence of alkaline solution on buffer and backfull materials can be divided into the influence of cations and the influence caused by the dissolution of montmorillonite. The influence of cations has an immediate effect, while the influence caused by the dissolution of montmorillonite takes a longer time to have a greater impact on buffer and backfill materials. However, the common point of the two is that they will adversely affect the swelling performance and water blocking performance of the buffer and backfill materials. MX-80 is relatively less affected by the cations in the alkaline solution, so MX-80 has better swelling performance and water blocking performance when the reacted time is not too long. On the contrary, the montmorillonite dissolution rate of MX-80 is higher than KUNIGEL-V1 when the alkaline solution is caused by calicium leachingof concrete. Therefore, KUNIGEL-V1 has better durability in backfill material with higher initial dry density.

並列關鍵字

calcium leaching ； buffer and backfill materials ； bentonite ； swelling pressure ； hydraulic conductivity ； alkaline ； prediction

參考文獻

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[3] International Atomic Energy Agency (IAEA), “Classification of radioactive waste: general safety guide, IAEA Safety Standards Series No GSG-1”, 2009.

[4] SKB, “International perspective on repositories for low level waste”, SKB R-11-16, Svensk Kärnbränslehantering AB, 2011.

[5] 行政院原子能委員會網站，低放射性廢棄物最終處置，2019。