Hydraulic-Thermal-Mechanical Properties and Radionuclide Release-Retarding Capacity of Kyungju Bentonite

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.