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 10-11m/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 MPa and they increased with increasing the dry density. The thermal conductivities were in the range of 0.80 kcal/mh .deg. C to 1.52 kcal/mh .deg. C. The unconfined compressive strength, Young's modulus and Poison's ratio showed the range of 0.55 MPa to 8.83 MPa, 59 MPa to 1275 MPa, and 0.05 to 0.20, respectively, when the dry densities of the compacted bentonite were 1.4 Mg/m3 to 1.8 Mg/m3. The diffusion coefficients in the compacted bentonite were measured under an oxidizing condition. The values were 1.7 x 10-10 m2/s to 3.4 x 10-10 m2/s for electrically neutral tritium (H-3), 8.6 x 10-14 m2/s to 1.3 x 10-12 m2/s for cations (Cs, Sr, Ni), 1.2 x 10-11 m2/s to 9.5 x 10-10 m2/s for anions (I, Tc), and 3.0 x 10-14 m2/s /s to 1.8 x 10-13 m2/s for actinides (U, Am), when tile dry densities were in the range of 1.2 Mg/m3 to 1.8 Mg/m3. The obtained results will be used in assessing the barrier properties of Kyungju bentonite as a buffer material of a repository in Korea.