膨潤土於人工海水環境下之緩衝回填材料性能比較

Abstract

現今世界上許多國家皆享受著核能發電與原子能應用帶來的效益，但隨著科技的進步與便利，處理隨之產生的放射性廢棄物與輻射汙染便成為了重要的課題。 目前各國對於放射性廢棄物處置皆採取「多重障壁」概念， 利用堅固的天然地形，搭配人造工程障壁組成的多層防護措施來隔絕放射性廢棄物與外界環境，讓其輻射強度在長時間下能減弱至無害的範圍內。然而考慮到放射性廢棄物最終處置場之設計可能位於靠海或海島地區，例如台灣的金門縣烏坵鄉，因此有可能發生海水入侵的狀況，本研究將探討工程障壁中之緩衝回填材料在海水情況下之性能變化。 本研究在不考慮粒料添加之情況，選用日本進口之KUNIGEL-V1膨潤土與美國進口之MX-80膨潤土作為緩衝回填材料，藉由土壤基本性質試驗、單向度膨脹率試驗、束制膨脹壓力試驗、水力傳導度試驗來探討兩種膨潤土在不同單位重下，純水與海水環境之各項性能。結果發現，海水環境下，鈉系膨潤土之膨脹率表現會大幅折減，然而膨脹壓力之折減較不嚴重。綜合比較後，MX-80有較好之膨脹性能與阻水性能，但兩種膨潤土在國外規範中皆是表現良好的緩衝回填材料。除此之外，透過試驗結果建立兩種膨潤土之性能預測式，期望能建立資料庫並提供後續工程界設計參考之依據。

Nowadays, many countries in the world enjoy the benefits brought by nuclear power generation and atomic energy applications. However, with the advancement and convenience of technology, it is an important issue to deal with the resulting radioactive waste and radiation pollution. At present, countries adopt the concept of “multiple barriers” for the disposal of radioactive waste. They use strong natural terrain and multi-layered protective measures composed of artificial engineering barriers to isolate radioactive waste from the external environment, so that its radiation intensity can be reduced to a harmless range. However, considering that the design of the final disposal site for radioactive waste may be located in coastal or island areas, such as Wuqiu, Taiwan, therefore, seawater intrusion may occur. This study will explore the performance changes in buffer and backfill material used in the engineering barrier in seawater conditions. In this study, KUNIGEL-V1 bentonite imported from Japan and MX-80 bentonite imported from the United States were used as buffer and backfill materials without considering the addition of aggregate. Tests for material characteristics, swelling rate, swelling pressure and hydraulic conductivity were conducted to investigate the properties of two bentonites under different unit weights, pure water and seawater. It was found that the swelling rate of sodium bentonite was greatly reduced in seawater environment, but the reduction of expansion pressure was less serious. After comprehensive comparison, MX-80 has better expansion performance and water blocking performance, but both bentonites are good buffer and backfill materials in foreign specifications. In addition, through the test results to establish two kinds of bentonite performance prediction formula, it is expected to establish a database and provide a basis for subsequent engineering design reference.