- 學位論文
用過核子燃料最終處置緩衝材料土壤吸力行為
Soil Suction of a buffer material for spent nuclear fuel final disposal
摘要
近年來，火力發電造成空氣品質下降，其副產物PM 2.5導致環境汙染加劇，為了降低空污問題，使用核能發電是有效的方法，然而待處置的高階核廢料，若處置不當將對生態環境及人體產生嚴重危害。當前國際間對於高放射性廢棄物的處置，採深層地質最終處置法，以避免高放射性廢棄物與地下水、海水與母岩接觸，因此先填裝於廢料罐後深埋於地底後，在周圍填入具顯著隔絕效果的緩衝材料預防核種釋出，防止受熱衰變和海水或地下水侵蝕而造成影響。 因主成分為黏土礦物的BH膨潤土質地細滑且耐熱性佳，吸附水份的能力優良，所以選用為實驗緩衝材料。在試驗方法中，為模擬近場環境受高放射性廢棄物熱衰變影響及緩衝材料設置的厚度，共設計了幾種條件，其分別於溫度40、60與80 ℃，利用三種單位重 1.6、1.7及1.8 g/cm3 的試樣BH膨潤土體，各別進行反應，探討其土壤吸力行為的影響。 研究結果顯示，水汽平衡法可取得試體最終含水量、飽和度及對應之土壤吸力以繪製出土壤水份特性曲線。當試驗溫度越高時，容易吸附凝結的水分子，而導致重量增加，重量增加幅度於不飽和NaCl溶液影響最為劇烈，增幅為34~71%之間，另外試體經吸附與排除作用下，產生膨脹與收縮的現象，使得試體體積造成變化，而無法以定值表示，因此本研究以游標卡尺與近景攝影的方式進行體積之修正，其中近景攝影所量得之體積量較游標卡尺來得大，而試體產生膨裂與收縮的現象，影響試體之完整性，在游標卡尺量測下，操作簡易、量測快速且數值能隨即取得，但人為因素影響甚劇且試體剝落的部分僅能忽視不計，其體積量普遍偏低。近景攝影拍攝耗時恐影響試體內部變化，須額外利用軟體分析較為繁瑣費時，不過試體破碎或剝落的部分可另外分析納入體積量，若有脹裂之縫隙也可妥善分析，因此本研究建議若試體有明顯的破碎、剝落或裂縫之產生以近景攝影為主，當試體外型大致無異時，則以游標卡尺量測，能快速且簡易取得。最終土壤水份特性曲線因改良條件之不同而有變化。水平土柱法隨環境溫度越低，加壓水柱入滲的情形越佳而擴散係數的幅度越大，當單位重漸增，其土壤間緊密程度越扎實，水份越不易通過，另外，土壤吸力行為影響水份特性曲線之結果，對此造成不飽和水力傳導度的變化，不飽和水力傳導度受含水量、環境溫度與單位重所影響而不同，在相近的含水量下，單位重越大則不飽和水力傳導度越小。
並列摘要
In recent years, thermal power generation has caused a decline in air quality, and its by-product PM 2.5 has caused an increase in environmental pollution. In order to reduce the problem of air pollution, it is an effective method to use nuclear power generation. However, if the high-end nuclear waste to be disposed of is improperly disposed, it will resilt in serious harm in ecology and human. At present, international method for the disposal of high-level radioactive waste, the deep geological final disposal method is adopted to avoid contact between high-level radioactive waste and groundwater, seawater and parent rock. Therefore, it is buried in the waste tank and buried deep in the ground. Buffer materials with significant insulation prevent the release of nuclear species from heat decay and seawater or groundwater erosion. BH bentonite, which main component is clay mineral, exhibited excellent texture, heat resistance, and ability to adsorb moisture. Therefore, it is selected as the buffer material in this study. In the experimental method, in order to simulate the near-field environment affected by the thermal decay of high-level radioactive waste and the thickness of the cushioning material, several conditions were designed, which were respectively used at temperatures of 40, 60 and 80 °C, using three units weighing 1.6 and 1.7. And the sample BH bentonite body of 1.8 g/cm3 was reacted individually to investigate the influence of soil suction behavior. The results show that the vapour equilibrium technique will obtain the final water content, saturation and corresponding soil suction of the sample to draw the soil-water characteristic curve. When the test temperature is highe, it is easy to adsorb the condensed water molecules, resulting in an increase in weight. In the unmodified situation, the weight increase is most severely affected by the unsaturated NaCl solution, and the increase is between 34~71%. Under the action of adsorption and capillary action, the phenomenon of expansion and contraction will occur, which will cause the volume of the sample to change, but it cannot be expressed by a fixed value. Therefore, the study will use the vernier caliper and close-range photography to correct the volume, which is obtained by close-range photography. The volume is larger than that of the vernier caliper, and the soil sample produces the phenomenon of expansion and contraction, which affects the integrity of the test piece. Under the vernier caliper measurement, the operation is simple, the measurement is fast and the value can be obtained immediately, but the human factor is very influential. The part of the sample peeling can only be ignored, and its volume is generally low. Close-range photography shooting may affect the internal changes of the sample. It is cumbersome and time-consuming to use additional software analysis. However, the broken or peeled part of the sample can be additionally analyzed for the volume. If there is a crack, the gap can be properly analyzed. It is recommended that if the specimen has obvious breakage, flaking or gaps, it will be mainly for close-up photography. When the trial type is almost the same, it will be measured quickly and easily with the vernier caliper. The final soil-water characteristic curve varies depending on the conditions of improvement. The lower the horizontal soil column method with the ambient temperature, the better the infiltration of the pressurized water column and the greater the diffusion coefficient. When the unit weight increases, the soil is tighter and the water is more difficult to pass. In addition, the soil suction behavior will affect the result of the moisture characteristic curve, which will cause the change of unsaturated hydraulic conductivity.