Geomechanics and Engineering

Techno-Press (테크노프레스)
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Physio-mechanical and X-ray CT characterization of bentonite as sealing material in geological radioactive waste disposal

  • Melvin B. Diaz (Department of Energy and Resources Engineering, Korea Maritime and Ocean University) ;
  • Sang Seob Kim (Department of Energy and Resources Engineering, Korea Maritime and Ocean University) ;
  • Gyung Won Lee (Department of Energy and Resources Engineering, Korea Maritime and Ocean University) ;
  • Kwang Yeom Kim (Department of Energy and Resources Engineering, Korea Maritime and Ocean University) ;
  • Changsoo Lee (Radioactive Waste Disposal Research Division, Korea Atomic Energy Research Institute) ;
  • Jin-Seop Kim (Radioactive Waste Disposal Research Division, Korea Atomic Energy Research Institute) ;
  • Minseop Kim (Radioactive Waste Disposal Research Division, Korea Atomic Energy Research Institute)
  • Received : 2022.10.13
  • Accepted : 2023.07.19
  • Published : 2023.08.25
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Abstract

The design and development of underground nuclear waste repositories should cover the performance evaluation of the different components such as the construction materials because the long term stability will depend on their response to the surrounding conditions. In South Korea, Gyeonju bentonite has been proposed as a candidate to be used as buffer and backfilling material, especially in the form of blocks to speed up the construction process. In this study, various cylindrical samples were prepared with different dry density and water content, and their physical and mechanical properties were analyzed and correlated with X-ray CT observations. The main objective was to characterize the samples and establish correlations for non-destructive estimation of physical and mechanical properties through the utilization of X-ray CT images. The results showed that the Uniaxial Compression Strength and the P-wave velocity have an increasing relationship with the dry density. Also, a higher water content increased the values of the measure parameters, especially for the P-wave velocity. The X-ray CT analysis indicated a clear relation between the mean CT value and the dry density, Uniaxial Compression Strength, and P-wave velocity. The effect of the higher water content was also captured by the mean CT value. Also, the relationship between the mean CT value and the dry density was used to plot CT dry densities using CT images only. Moreover, the histograms also provided information about the samples heterogeneity through the histograms' full width at half maximum values. Finally, the particle size and heterogeneity were also analyzed using the Madogram function. This function identified small particles in uniform samples and large particles in some samples as a result of poor mixing during preparation. Also, the μmax value correlated with the heterogeneity, and higher values represented samples with larger ranges of CT values or particle densities. These image-based tools have been shown to be useful on the non-destructive characterization of bentonite samples, and the establishment of correlations to obtain physical and mechanical parameters solely from CT images.

Keywords

Acknowledgement

This work was supported by the Institute for Korea Spent Nuclear Fuel (iKSNF) and National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science and ICT, MSIT)(No. 2021M2E1A1085197 & No. 2021R1A2C2011634).

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