於用過核子燃料最終處置設施中，緩衝材料應阻止地下水或腐蝕物質直接接觸廢棄物罐，並且延緩放射性核種向生物圈遷移之速度，達到滯遲(retardation)核種遷移之效果。緩衝材料之成分與規格將直接影響其滯遲能力，本研究以MX-80膨潤土、SWy-2 鈉型蒙脫石及蒙脫石含量20%至100%之調配材料為標的，考量緩衝材料成分、壓實乾密度及溫度條件之影響，量測不同規格緩衝材料之回脹壓力、水力傳導度及不同材料對Cs+與Sr2+核種吸附能力。 MX-80膨潤土於乾密度1,300 kg/m3至1,600 kg/m3條件之回脹壓力介於964 kPa至6,767 kPa之間，隨著乾密度增加而上升；水利傳導度則隨著試體乾密度提升而降低，約介於10-15 m/s至10-12 m/s之間；環境溫度從30°C升溫至60°C及 90°C時，緩衝材料試體之水力傳導度會隨著溫度上升而增加。此外，藉由不同SWy-2 鈉型蒙脫石配比土樣之回脹及水力傳試驗結果，單位緩衝材料中之蒙脫石含量與回脹壓力呈正比，且與水力傳導度呈反比。 吸附實驗結果顯示，MX-80膨潤土及不同SWy-2 鈉型蒙脫石配比土樣對Cs+及Sr2+之吸附行為皆符合Langmuir等溫吸附曲線，各土樣對Cs+之飽和吸附量皆大於Sr2+，而飽和吸附量則與土壤之蒙脫石含量呈正比。故高蒙脫石含量之材料選擇及高設計乾密度有利於滯遲核種向外遷移之效果。 ;In the final disposal facilities for spent nuclear fuel, buffer plays a role of barrier which not only prevents canister from directly exposing to groundwater and corrosive materials but also retards the migration of radial nuclides to biosphere. The “retardation” process is derived by the composition and specification of buffer. MX-80 bentonite, SWy-2 Na-montmorillonite and blended soil (20%~100% montmorillonite) were used in this research. The objective of this paper is to survey the swelling pressure, hydraulic conductivities, and nuclide (Cs+ and Sr2+) adsorption capacities of different buffer materials and specifications under different temperature conditions. Swelling pressure and hydraulic conductivities of MX-80 bentonite with dry densities 1,300 kg/m3 ~1,500 kg/m3 were 964 kPa~6,67 kPa and 10-15 m/s ~10-12 m/s respectively; the swelling pressure increased as dry density increased while the hydraulic conductivity decreased as dry density increased. During the heating process, i.e. from 30°C to 60°C and 90°C, the hydraulic conductivity increased with increasing temperature. In addition, swelling pressure was proportional to, and hydraulic conductivity was inversely proportional to the montmorillonite content of soil. The results of the adsorption experiment using the soil with different content of montmorillonite as sorbent indicated that both adsorption behaviors of Cs+ and Sr2+ are consistent with the Langmuir isotherm model. The adsorption capacity of Cs+ was larger than Sr2+, and the maximum adsorption capacities were proportional to the montmorillonite content in the soil. It was concluded that the selection of soil with high content of montmorillonite and high dry density as buffer materials could conduce to better retardation capability of nuclide migration.
