深層地質處置場緩衝材料之沖蝕機制與沖蝕量試驗研究

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Title:	深層地質處置場緩衝材料之沖蝕機制與沖蝕量試驗研究
Authors:	徐暐東;Syu, Wei-Dong
Contributors:	土木工程學系
Keywords:	深層地質處置場;緩衝材料;膨潤土;沖蝕;Deep geological disposal;KBS-3;buffer;bentonite;erosion;MX-80
Date:	2021-08-18
Issue Date:	2021-12-07 15:06:35 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究採用MX-80膨潤土進行沖蝕試驗，試驗裝置主要以兩塊透明壓克力板模擬人工裂隙，以去離子水及不同離子濃度的溶液流過，由出水口量測液體濁度以推估沖蝕質量，再以逐日攝得之圖像，量測平均徑向膨脹距離及副礦物面積，分析不同的裂隙內寬、水化學以及水流量對於膨潤土沖蝕的影響。在本研究所設計之參數下，觀察到最嚴重的沖蝕，是使用去離子水在較大的裂隙內寬(2.0 mm)、較高的水流量(1.0 mL/min)環境中，93天時已經損失原始試體重的30.8%，而離子強度2.54 mM與4.00 mM NaCl溶液條件下，63天內量測到的沖蝕量不足原始試體重的1.0%，可見地下水中的離子強度是影響膨潤土沖蝕的關鍵。在流量1.0 mL/min裂隙內寬0.2 mm去離子水條件下的試驗，93天內量測到的沖蝕量相當於損失原始試體重的3.68%，故膨潤土沖蝕量將隨著裂隙內寬縮小而降低。而流量0.2 mL/min裂隙內寬2.0 mm去離子水條件下的試驗，104天內量測到的沖蝕量相當於損失原始試體重的8.84%，當採用較低水流量時，膨潤土之沖蝕量也有明顯的下降。藉由觀察及分析膨潤土圖像，再透過分析沖蝕試驗結束後之膨潤土試體，認為副礦物環形成最直接的原因為沖蝕是否發生，膨潤土沖蝕後若有大量蒙脫石流失，於原地停留之較粗顆粒將阻攔中型顆粒，接著較細小的顆粒也受到阻攔，這些顆粒因架橋現象(bridging)將彼此卡在適當的位置，最終形成明顯之深色副礦物環。由結果得知越大的水流量以及裂隙內寬，將導致更嚴重的沖蝕。而水化學環境的影響則是最關鍵的，在4.00 mM的NaCl溶液的試驗中，緩衝材料將穩定維持障壁功能。 ;MX-80 bentonite was used for the erosion test. The turbidity of the liquid was measured from the water outlet of the device to estimate the erosion quality. The average radial expansion distance and the area of accessory minerals were measured by the image, analyze the influence of different aperture, water chemistry and water flow on the erosion of bentonite. The most serious erosion was observed using deionized water in a large aperture (2.0 mm) and a high flow rate (1.0 mL/min) environment. 30.8% of the original weight has been lost at 93 days , And the ionic strength of 2.54 mM and 4.00 mM NaCl solution, the eroded mass measured in 63 days is less than 1.0% of the original weight. The ionic strength of groundwater is the key to the erosion of bentonite. In the test of deionized water with a flow rate 1.0 mL/min and a 0.2 mm aperture, the eroded mass measured at 93 days is equivalent to the loss of 3.68% of the original weight, so the eroded mass will decrease with the aperture. In the test of deionized water with a flow rate 0.2 mL/min and a 2.0 mm aperture, the eroded mass measured at 104 days is equivalent to the loss of 8.84% of the original weight. When a lower water flow rate is used, the eroded mass will reduce significantly. Observe and analyze the image and the bentonite sample after the erosion test. It is believed that the formation of the accessory mineral ring is whether erosion occurs. If a large amount of montmorillonite is lost after bentonite erosion, the coarser particles staying in place will block the medium-sized and fine particles, These particles will be blocked by bridging. The bridging will jam each other in place, and eventually form a accessory mineral ring. From the results, it is known that the large water flow and aperture will cause severe erosion. The impact of water chemistry is the most critical. In the test of 4.00 mM NaCl solution, buffer will maintain barrier function.
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