發生於2011年3月11日的東日本大地震造成福島第一核電廠的損害，產生了許多帶有放射性銫元素的受汙染廢棄物。由於受汙染廢棄物的體積過於龐大與危險，建造離岸廢棄物掩埋場對日本政府來說是一個適當的選擇但同時也有很多條件必須被滿足。 本研究的目的是為離岸廢棄物掩埋場的4.0公尺封存層找出適當的材料，放射性物質在封存層中的運輸方式可由平流擴散方程式呈現，為了求得方程式需要的參數: 滲透係數、擴散係數(Diffusion coefficient)與遲滯因子(Retardation factor)，針對松島灣黏土與皂土和沸石的混合材料進行壓密透水試驗，將從壓密透水試驗得到的滲出液以原子吸光分析儀測驗其濃度，取得松島灣黏土混合材料對銫元素吸附性能的部分突破曲線(Breakthrough curve)，以平流擴散方程式之曲線擬合求得試體之擴散係數與遲滯因子並以此資料繪製4.0公尺封存層的預測曲線。 實驗結果顯示，混入皂土會造成銫元素吸附性能降低，而混入沸石能提高銫元素吸附性能，至於試體厚度的增加則會使得每單位重量的試體能吸附的銫元素量輕微下降。藉由針對平流擴散方程式當中的參數做參數研究，未來的實驗將能應用此模擬方法而大幅減短實驗本身的時間長度。 在離岸廢棄物掩埋場的設計案中，封存層的厚度被設定為4.0公尺厚，而設計的內外水頭差為2.0公尺。由實驗與參數研究得到的數據進行模擬得到的結果顯示，即便將封存層厚度降為1.0公尺，由海成黏土混合材料製造的封存層仍能使滲出液的滲出時間遠大於最初的設計目標而且其放射性銫濃度遠低於日本環境省設定之標準，代表此設計方案具有可行性而且對環境來講非常安全。 ;Great East Japan Earthquake on March 11th, 2011 stroke Fukushima No.1 Nuclear Power Plant and generated a huge amount of wastes contained radioactive cesium. Since the amount of radioactive waste is too large and the radioactivity is dangerous, offshore disposal facility is a good choice for Japan Government and many points should be satisfied for it. The purpose of this study is to find out the proper material for the 4.0-meter sealing layer of offshore disposal facilities. Contaminant transportation in porous material can be described by advection-diffusion equation. To find the parameters in equation (hydraulic conductivity, diffusion coefficient and retardation factor), Matsushima Bay Clay mixed with bentonite and zeolite is tested by consolidation-permeability test. The cesium concentration of leachate from consolidation-permeability test was measured by atomic absorption spectrophotometer. In this way, the part of breakthrough curve of Matsushima Bay Clay mixture can be measured. Use curve fitting method to find out the parameters in advection-diffusion equation and make prediction of 4.0-meter sealing layer. Test result shows that bentonite makes cesium adsorption ability worse while zeolite make it better. Thickness increasing makes adsorbed cesium amount per sample mass slightly lower. By doing parameter study of advection-diffusion equation, the length of laboratory test in the future can be shorten by using simulation. In the offshore disposal facility design, sealing layer is 4.0-meter-thick and water head difference is 2.0 meter. Simulation shows that even the thickness of sealing layer decrease to 1.0-meter, sealing layer made by marine clay can still make the leakage time of radioactive cesium leachate far longer and cesium concentration quite lower than standard established by Japan Ministry of Environment, which means this design is feasible and very safe.
