合成地下水與海水中硒銫在粉碎花崗岩及泥岩的收附與擴散行為

Sorption and Diffusion of Selenium and Cesium on Crushed Granite and Mudrock in Synthetic Groundwater and Seawater

李傳斌(Chuan-Pin Lee)

指導教授 ： 許俊男

國立清華大學/原子科學院/生醫工程與環境科學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00030

摘要

本論文針對硒和銫在台灣本土的潛在母岩，於好氧及厭氧條件下的吸附及擴散行為，作一個比較深入的研究和探討，包括花崗岩與泥岩。由於在高放射性廢棄物處置場的設計中，以深地層概念及多重障壁圍阻的處置方式是目前一致公認為最可行的方法，因此本實驗除了針對屬於天然障壁的台灣花崗岩與泥岩，進行好氧與厭氧批次動力收附吸附實驗之外，另外還進行好氧與厭氧條件下的管柱擴散實驗，以探討未來高放射性廢棄物處置場，在地下水或海水入侵時，使放射性核種釋出後在地質圈的傳輸行為研究。
由實驗結果可看出，花崗岩與泥岩對於硒和銫的吸附能力有所差異。不管是在好氧或厭氧條件下，泥岩對個別硒和銫的收附能力均優於花崗岩，主要是在泥岩中含有豐富的黏土礦物與鐵氧化物。此外，在混合硒和銫的動態收附研究中，明顯發現泥岩或花崗岩對銫的收附平衡反應較快，與單一銫的結果相同。然而，在混合硒和銫的結果卻發現，不管是在好氧或厭氧條件下，硒的收附平衡反應變慢，且在厭氧條件下，即使經歷90天仍無法觀察到收附平衡的情形。
由好氧及厭氧的管柱實驗可知，由於在厭氧條件下受溫度的影響，擴散係數比在好氧條件下稍高。另外，在地下水中管柱內因產生碳酸鈣沈澱，因而降低各核種（氚水、硒和銫）的擴散係數。而由批次實驗中的結果可發現，泥岩對硒和銫的收附能力高於花崗岩。由管柱實驗的結果也可看到，泥岩對硒和銫的遲滯因數也比花崗岩大。
最後，比較批次與管柱實驗結果。在厭氧條件下，由地下水中花崗岩的擴散實驗，卻得到與批次實驗相反的結果，由此而更可確定除了固體介質對核種的收附行為有影響之外，也必包含了其他的影響因素，如緊縮度與曲撓度等。因此，希望能以本研究成果，作為台灣本地的處置場場址評估工作上的一項參考，並且奠定今後針對天然障壁作進一步研究的基礎。

關鍵字

高放射性廢棄物 ； 深地層處置 ； 硒 ； 銫 ； 花崗岩 ； 泥岩 ； 收附 ； 擴散

並列摘要

Sorption and diffusion behaviours of selenium (Se) and cesium (Cs) on Taiwan host rock including granite and mudrock under aerobic and anaerobic conditions were
performed in this study. The attention of this study was paid on sorption and diffusion experiments under both conditions as the multi-barrier concept in deep geological
disposal has been considered to be the most feasible way to construct a high-level radioactive waste (HLW) repository, where whole rocks and crushed rocks were taken as natural barriers. The reducing groundwater (GW) or seawater (SW) prepared in glove box were used in batch kinetic tests and column diffusion experiments under both conditions to reflect the extreme situation of highly reducing groundwater or seawater underground 300 m or more that might intrude into HLW repositories and release toxic radioactivity to the environment.
There is an obvious difference between granite and mudrock in sorption behaviors of Se and Cs under both conditions. Sorption of individual Se and Cs in mudrock is higher than that in granite due to high mineral contents of clay and iron oxides. Moreover, fast equilibrium reaction in sorption of Cs by coexisting Se and Cs tests was similar to individual Cs tests according to experimental results. However, equilibrium reactions in sorption of Se by coexisting Se and Cs under both conditions turned into slower and slower and it didn’t reach even in 90 days under anaerobic conditions.
The diffusion results showed that higher apparent diffusion coefficients (Da) under anaerobic conditions were observed due to higher temperature in glove box. However, Da of HTO, Cs and Se in GW decreased because of CaCO3 precipitation in column. A higher retardation factor (Rf) value of mudrock in column diffusion experiments is in agreement with the results of batch sorption tests.
According to experimental results of column and batch tests, it showed a difference in anaerobic results of granite in GW. In addition to sorption effects, diffusion of Se and Cs depends on the microporous structure of tested media, such as constrictivity and tortuosity. The results from this study provide a reference for performance assessment of HLW repository and for further studies of natural barriers.

並列關鍵字

high-level radioactive waste ； deep geologic disposal ； selenium ； cesium ； granite ； mudrock ； reducing groundwater and seawater ； glove box ； sorption ； diffusion

參考文獻

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