Abstract
從緩衝材料觀點研究放射核種在膨潤土中的吸附與擴散行為 林哲毅國立清華大學原子科學系 中文摘要本論文在研究鍶、銫、碘及部分錒系元素在黏土礦物中的吸附與擴散機制，此黏土礦物是被計畫作為放射廢料處置場的候選緩衝材料。理想的緩衝材料需具有防止地下水入侵與遲滯核種外釋的雙重功能。 在此係以日興土及比例添加 MX-80之懷俄明膨潤土作為候選緩衝材料進行研究。放射性核種的吸附常數係由批次實驗求得。鍶、銫在壓密黏土管柱中的擴散係數係由非穩態法求得，填充密度由1.5至2.0g cm-1。 由實驗結果知道﹕核種在黏土礦物中的吸附特性符合週期表元素性質。而鍶銫的擴散則以孔隙水擴散和表面擴散兩個機制加以解釋，孔隙水擴散機制可由黏土含水量決定，而表面擴散則是由礦物相表面電雙層所吸附核種的擴散所造成的。黏土壓密成低密度時孔隙水擴散和表面擴散一起主導著整個核種擴散﹔黏土壓密成高密度時孔隙水擴散機制主導核種的擴散。影響黏土礦物中核種吸附與擴散機制的因素有核種的電荷、離子半徑、氧化還原電位、溶解度，以及溫度、黏土礦物特性和土壤水成分。 關鍵字﹕吸附，擴散，放射核種，膨潤土Study on Sorption and Diffusion Behaviors ofRadionuclides in Bentonite from the BufferMaterial StandpointJe-Yie Lin Department of Nuclear Science, National TsingHua University Abstract Thisstudy deals with the diffusion and sorption mechanisms of137Cs, 90Sr,129I and a few actinides in clay, which can beconsidered as a condidatebuffer material in radwaste disposal.Both reducing or even preventing thegroundwater intrusion andalso possessing excellent sorption capabilities ofnuclides arethe two important criteria for an ideal buffer material. Inthe study, Jishin soil and adding with Wyoming bentonite (MX-80 ) werechosen as candidate buffer materials. The sorptionfactor of radionuclidewas determined by batch experiment. Thediffusivities of Sr2+ and Cs+ wereperformed by non-steady statemethod in the clay diffusion column, with acompacted dry bulkdensity from 1.5 to 2 g cm-3. According to the experimentresults, it is found that sorption of nuclide in clay mineralsaccords with elements character of periodic table ；diffusion of Sr2+ and Cs+ can be explained in the bothmechanisms--pore water diffusion and surface diffusion. In thelow compact density range, both the pore water diffusion andsurface diffusion encompassing the diffusion of thesorbednuclide within the electrical double layer next to the mineralsurfacecontrol together diffusion mechanism. Whereas thepore water diffusionmechanism which depends on clay moistureis the dominate mechanism when claysample was compacted inhigh density range. Factors that influence sorption anddiffusion mechansim of radionuclide in clay are also discussedin detail--such as charge, ionic radius, solubility andredox poteneial of nuclide,temperature, clay mineral character,and soil water content. Key words: sorption, diffusion,radionuclide, bentonite