• Tunnel and Underground Space
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• v.21 no.4
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• pp.264-273
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• 2011

Bentonite buffer is one of the major components of an engineered barrier for an HLW (High-Level Waste) repository. The bentonite buffer is significantly exposed to the decay heat from radioactive wastes, the inflow of groundwater from the surrounding rock of the repository, and the high swelling pressure of densely-compacted bentonite that comes in contact with the groundwater. Therefore, it is essential to understand the THM (Thermal-Hydro-Mechanical) behavior of the bentonite buffer and to acquire the input data of its related constitutive models for the performance and safety assessment of an HLW repository. This paper analyzed the THM properties which have been obtained by conducting laboratory tests with a candidate buffer material for a Korean HLW repository. Moreover the formulation recipe of the reference bentonite buffer was defined on the basis of functional criteria, thus suggesting the THM properties which correspond to the formulation recipe of the reference bentonite buffer.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.13 no.4
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• pp.283-293
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• 2015

The buffer is a key component of the engineered barrier system in a high-level radioactive waste (HLW) repository. The present study reviewed the requirements and functional criteria of the buffer reported in literature, and also based on the results, proposed an approach to establish a buffer concept which is applicable to an HLW repository in Korea. The hydraulic conductivity, radionuclide-retarding capacity (equilibrium distribution coefficient and diffusion coefficient), swelling pressure, thermal conductivity, mechanical properties, organic carbon content, and illitization rate were considered as major technical parameters for the functional criteria of the buffer. Domestic bentonite (Ca-bentonite) and, as an alternative, MX-80 (Na-bentonite) were proposed for the buffer of an HLW repository in Korea. The technical specifications for those proposed bentonites were set to parameter values that conservatively satisfy Korea's functional criteria for the Ca-bentonite and Swedish criteria for the Na-bentonite. The thickness of the buffer was determined by evaluating the means of shear behavior, radionuclide release, and heat conduction, which resulted in the proper buffer thickness of 0.25 to 0.5 m. However, the final thickness of the buffer should be determined by considering coupled thermal-hydraulic-mechanical evaluation and economics and engineering aspects as well.