膨潤土在乾溼循環下之緩衝回填材料性能

現代世界雖然積極朝綠色能源發展，但在許多國家，核能依舊是非常重要的發電方式。而核能發電以及其他途徑所產生的放射性廢棄物，需要妥善處理，否則將對環境及人類造成傷害。目前世界各國對於放射性廢棄物的處理方式，大都是以地下處置場為主，並使用多層的材料，妥善的將放射性廢棄物包裹在處置場內，稱為「多重障壁」。膨潤土作為一種能夠吸附輻射物質，且膨脹性能與阻水性能佳的材料，常被取用於多重障壁，用來阻止地下水的入滲，從而防止核種滲漏。在台灣兩處候選場址，除了有海水入侵的可能性外，由於地下水的水位面會隨時間改變，膨潤土將長時間受到乾溼循環的影響，隨著地下水位面改變的過程中可能造成乾燥收縮與裂縫，以及陽離子交換使土壤產生膨脹行為上的變化。本研究將研究乾溼循環對於緩衝回填材料的影響，並進行討論。本研究使用日本進口的 KUNIGEL-V1 與美國進口的 MX-80 純膨潤土試體，在固定的乾密度、不同的濕潤溶液與不同相對濕度條件下進行乾溼循環試驗，從材料的膨脹率、含水量以及液性限度進行試驗以及分析。綜合比較後發現以去離子水乾溼循環對於膨潤土的膨脹性能影響不大，甚至有增加的趨勢，以人工海水進行實驗的組別則出現不同幅度的膨脹率折減，推測主要是因為土壤鹽化以及陽離子交換而造成。同時從液性限度也能看到類似的趨勢。由於乾燥裂縫加速陽離子的交換，有乾溼循環的試體之膨脹率與液限度相較無乾溼循環的試體低，因此在設計最終處置場的緩衝回填材料時，乾溼循環為需要納入考慮的重要因素之一。

關鍵字

放射性廢棄物；緩衝回填材料；海水；乾溼循環

並列摘要

Although the modern world is actively developing renewable energy, nuclear energy is still a very important way of power generation in many countries. However, the radioactive wastes generated from nuclear power plant and other ways need to be properly disposed, otherwise they will cause harm to the environment and human beings. Most countries in the world deal with radioactive waste mainly in underground final disposal repository, and use multi-layer materials to wrap radioactive waste properly , which is called "multiple barriers". Bentonite is a kind of material that can absorb radiation and has good swelling properties and low-permeability. It’s often used in multiple barriers to prevent the infiltration of groundwater and the leakage of radionuclides. At the two candidate disposal repository sites in Taiwan, seawater intrusion may occur, furthermore, bentonite in multiple barriers will be affected by the dry wet cycle due to the change of groundwater level over time. Drying shrinkage and cracks may be caused during the change of groundwater level, and cation exchange may cause changes in clay swelling behavior. This study will explore the influence of dry wet cycle on buffer and backfill materials. In this study, KUNIGEL-V1 imported from Japan and MX-80 pure bentonite imported from the United States were used for dry wet cycle test under the conditions of fixed dry density, different wetting solutions and different humidity. The swelling strain, water content and liquid limit of the material were tested and analyzed. After comprehensive comparison, it is found that the dry wet cycle of deionized water has little effect on the swelling performance of bentonite, but the specimens tested with artificial seawater has a reduction in the swelling strain of different ranges, it’s speculated that bentonite is mainly caused by soil salinization and cation exchange. At the same time, a similar trend can be seen from the liquid limit. As the drying cracks accelerate the cation exchange, the swelling strain and liquid limit of the specimens with drying and wetting cycles are lower than those without it. Therefore, drying and wetting cycles are one of the important factors to be considered in the design of buffer backfill materials for the final disposal repository.

並列關鍵字

radioactive waste ； buffer and backfill material ； seawater ； dry-wet cycle

參考文獻

[1] Ahonen, L., “Quality Assurance of the Bentonite Material”, Posiva Oy, May 2008.

Google Scholar

[2] Bensallam, S., Bahi, L., Ejjaaouani, H., Shakhirev, V., “Shrinkage Curve: Experim-ental Study and Modelling” , Applied Clay Science, Vol. 25, No.3, 2012.

Google Scholar

[3] Bouazza, A., Stephan Jefferis, Thaveesak Vangpaisal, “Investigation of the effects and degree of calcium exchange on the Atterberg limits and swelling of geosynthetic clay liners when subjected to wet–dry cycles” Geotextiles and Geomembranes, Volume 25, Issue 3, June 2007, Pages 170-185.

Google Scholar

[4] Bradbury, M.H., Bart Baeyens, “Porewater chemistry in compacted re-saturated MX-80 bentonite”, 2003.

Google Scholar

[5] Camillis, M.D., Gemmina Di Emidio, Adam Bezuijen, Daniel Verastegui Flores, Jeroen Van Stappen, Veerle Cnudde, “Effect of wet-dry cycles on polymer treated bentonite in seawater:swelling ability, hydraulic conductivity and crack analysis” ,Applied Clay Science Volume 142, 15 June 2017.

Google Scholar

主題瀏覽