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

• Main Authors: Lee, Chuan-Pin, 李傳斌
• Other Authors: Hsu, Chun-Nan
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/64782623626648087925

博士 === 國立清華大學 === 生醫工程與環境科學系 === 97 === 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.