放射性廢棄物最終處置場緩衝材料與混凝土障壁的交互作用

The interactions between the buffer material and concrete barrier of radioactive wastes in a repository

張皓鈞(Hao-Chun Chang)

指導教授 ： 黃偉慶

國立中央大學/工學院/土木工程學系/碩士(2011年)

摘要

本研究以台東樟原村日興土與美國懷俄明州BH膨潤土，運用壓製方式製作膨潤土緩衝材料，並且與符合ACI 349核能安全相關用途混凝土規範的ACI混凝土，以及添加鋼纖維的RPC活性粉混凝土進行電滲加速試驗，以模擬處置場近場環境混凝土與緩衝材料之間長期的交互作用，從中了解混凝土溶出失鈣效應對緩衝材料性質的影響，以評估適合放射性廢棄物處置場之緩衝材料。
試驗結果顯示，經過電滲加速試驗後的二種膨潤土緩衝材料，隨電滲時間越長，回脹量、pH值越低，且越靠近混凝土接觸面之緩衝材料，其鈣/鈉離子比值差距越大，回脹量和pH值也越低。後續的微觀分析結果顯示，二種膨潤土緩衝材料在接近混凝土接觸面的部分有受到鈣離子入侵影響的情形，並隨著電滲時間越長，影響越為顯著，其中BH膨潤土因接觸而產生的變化較明顯；二種混凝土隨電滲時間越長，氫氧化鈣、C-S-H膠體的含量越低，溶出失鈣的現象越顯著，並且在混凝土表面產生許多孔隙，其中以ACI混凝土的變化較為明顯。

關鍵字

緩衝材料 ； 溶出失鈣 ； 電滲加速試驗

並列摘要

Both concrete and clay-based materials serve as engineered barriers for isolation of high-level radioactive wastes in a repository. Being the major components in the barrier system, concrete and buffer material are expected to create an impermeable zone around the high level waste canisters, and the interactions between the two barriers need to be evaluated to insure disposal safety.
In this research, a migration technique was applied to accelerate the migration of calcium ions from the pore solution of concrete so as to investigate the alteration of compacted bentonite in contact with the concrete. The buffer material used is compacted bentonite, made using locally available Zhisin clay and Black Hills bentonite from Wyoming. And the barrier concrete mixes were proportioned according to traditional American Concrete Institute (ACI) mix design method and Reactive Powder Concrete (RPC) with steel fiber. After a target cumulative electric charge, the specimen are be removed for analysis. The physical characteristics of both bentonite buffer and concrete barrier are examined to assure that the long-term contact of these 2 barriers does not cause severe degradation.
The results show some decrease in swelling potential and the pH of the buffer material near the interface. Also, buffer material close to the contact of the concrete exhibits larger change in the ratio of calcium/sodium concentration, due to the release of calcium ions from the concrete barrier. The observed changes in BHbentonite are found to be more obvious than that in ZH bentonite.
The content of calcium hydroxide and C-S-H colloid are found to have reduced both in ACI and RPC concrete mixes after the migration test. The leaching of calcium from concrete becomes more prominent with the increase in accelerated electro-osmosis test period. Many pores are found on concrete surface. The effect of the buffer/concrete interactions on ACI concrete is more obvious than that on RPC concrete.

並列關鍵字

leaching ； accelerated electro-osmosis test ； buffer material

參考文獻

陳炳坤，（2006），「高放射性廢棄物最終處置場緩衝材之膨脹穩定性與微觀結構研究」，碩士論文，國立中央大大學土木工程研究所，中壢。

Abdullah, W.S., Alshibli, K.A., and Al-Zou''bi, M.S. (1999). “Influence of pore water chemistry on swelling behavior of compacted clays.” Applied Clay Science. Vol.15, pp.447-462.

Choi, J., Kang, C.H., and Whang, J. (2001). “Experimental assessment of non-treated bentonite as the buffer material of a radioactive waste repository.” Journal of Environmental Science and Health, Part AToxic/Hazardous Substance & Environmental Engineering, 26(5), 689-714.

Greene-Kelly, R. (1952). “Irreversible dehydration in montmorillonite.” Clay Minerals Bulletin, 221-227.

Jo, H.Y., Katsumi, T., Benson, C.H., and Edil, T.B. (2001). “Hydraulic conductivity and swelling of nonprehydrated GCLs permeated with single-species salt solutions.” Journal of Geotechnical and Geoenvironmental Engineering, 127(7), 557-567.