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Jae-Owan Lee,Won-Jin Cho,Pil-Soo Hahn 한국방사성폐기물학회 2004 방사성폐기물학회지 Vol.2 No.2
고준위방사성폐기물 처분장의 완충재 후보물질 선정을 위해 경주 벤토나이트를 대상으로 수리특성, 팽윤특성, 열적특성, 역학특성 및 핵종유출 저지특성을 조사하였다. 실험결과, 압축 벤토나이트의 수리전도도는 m/s 이하로 매우 낮았으며 건조밀도가 증가할수록 감소하였다. 팽윤압은 0.66 ㎫∼14.4 ㎫ 사이의 값을 보였으며 건조밀도에 따라 증가하였다. 건조밀도가 1.4 Ms/㎥ ∼ 1.8 Mg/㎥1.4 일때, 열전도도, 열축압축강도 (unconfined compressive strength), 탄성계수 (Young's modulus of elasticity), Poisson 비는 각각 0.80 ㎉/m ∼1.52 ㎉/m , 0.55 ㎫ ∼ 8.83 ㎫, 59 ㎫ ∼ 1275 ㎫, 0.05 ∼ 0.20의 값을 나타내었다. 압축벤토나이트에 대한 핵증 확산계수는 산화 환경에서 측정되었으며, 주어진 실험조건에서 삼중수소 (H-3)는 1.7 /s ∼ 3.4 /s. 양이온 핵종 (Cs, Sr , Ni)은 8.6 /s ∼ 1.3 /s, 음이온 핵종 (I, Tc)은 1.2 /s ∼ 9.5 /s, 악티나이드 핵종은 3.0 /s ∼ 1.8 /s 사이의 값을 나타내었다. 이때 확산계수는 모든 핵종에 대해 압축벤토나이트의 건조밀도가 증가할수록 감소하는 경향을 보였다. Studies were conducted to select the candidate buffer material for a high-level waste (HLW) repository in Korea. This paper presents the hydraulic properties, the swelling properties, the thermal properties, and the mechanical properties as well as the radionuclide release-retarding capacity of Kyungju bentonite as part of those studies. Experimental results showed that the hydraulic conductivities of the compacted bentonite were very low and less than m/s. The values decreased with increasing the dry density of the compacted bentonite. The swelling pressures were in the range of 0.66 MPa to 14.4 ㎫ and they increased with increasing the dry density. The thermal conductivities were in the range of 0.80 ㎉/m to 1.52 ㎉/m . The unconfined compressive strength, Young's modulus and Poison's ratio showed the range of 0.55 ㎫ to 8.83 ㎫, 59 ㎫ to 1275 ㎫, and 0.05 to 0.20, respectively, when the dry densities of the compacted bentonite were 1.4 Ms/㎥ to 1.8 Mg/㎥. The diffusion coefficients in the compacted bentonite were measured under an oxidizing condition. The values were $1.7{\times}10^{-10}/s to 3.4{\times}10^{-10}/s for electrically neutral tritium (H-3), 8.6{\times}10^{-14}/s to 1.3{\times}10^{-12}/s for cations (Cs, Sr, Ni), 1.2{\times}10^{-11}/s to 9.5{\times}10^{-11}/s for anions (I, Tc), and 3.0{\times}10^{-14} /s to 1.8{\times}10^{-13}/s $for actinides (U, Am), when tile dry densities were in the range of 1.2 Mg/㎥ to 1.8 Mg/㎥. The obtained results will be used in assessing the barrier properties of Kyungju bentonite as a buffer material of a repository in Korea.n Korea.
Dual-structure of Expansive Clays and its Response to Hydro-mechanical Loadings: A Review
Jae Owan Lee,Yohan Cha,Changsoo Lee,Jin-Seop Kim 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1
Expansive clays (for examples, bentonites) are favored as buffer and backfill materials because of their low hydraulic conductivity, high swelling potential, and good mechanical properties, and are installed in highly compacted blocks in repositories. Compacted expansive clays have a dual-structure system: macrostructural system which is a complex of clay aggregates with the inter-aggregate pores (macropores) which can be filled by either liquids or gases; microstructural system with the intraaggregate pores between or within clay particles (micropores) which is usually considered to be saturated by liquid. Understanding the dual-strucure system of expansive clays is essential for characterizing and modeling multiphysics (stress-strain, swelling pressure, etc.) in buffers and backfills. Existing multiphysics studies of expansive clays, as in non-expansive soils, were mostly conducted with a single structure approach based on the behavior of macropores, and there have been limitations in the comprehensive interpretation and modeling of experimental results. However, with the recent development of measurement techniques, a lot of available information on the pore structure of compacted expansive clays has been reported, and with the results, a dual-structure approach considering both microstructural and macrostructural systems has been increasingly applied to improve the modeling of multiphysics of expansive clays. This study reviewed the dual-structure system of compacted expansive clays, analyzed previous studies on its evolution according to hydromechanical loading (loading-unloading and wetting-drying paths), and based on these, intended to provide technical knowledge and information needed for multiphysics research of expansive clays-based buffer and backfill for the KRS repository.