Parallel Session A-6: Geological disposal of radioactive waste - Chair: Laura Asensio

Sodium ion has profound effects on the properties of bentonite, such as hydraulic conductivity and swelling behaviours. In this study, wetting time, specimen dry densities and initial water contents were varied to find their effects on sodium ion infiltration.It is found that under the 0.1mol/L NaCl solution case, there is almost no sodium ion infiltration in compacted bentonite. In the cases of 0.5mol/L and 1mol/L NaCl solutions, the leached sodium cation from specimens increases with the increase of concentration of supplied NaCl solution under the same wetting time.

In this study, a multi-disciplinary approach has been adopted to investigate the shrinkage effects in Opalinus clay. The highlights of this work can be summarized as follows: 1. Unique configuration of a customized desiccator cell designed for studying anisotropic strength characteristics of Opalinus clay under various humidities. 2. Development and implementation of coupled Richard's Mechanics formulation in the framework of the Finite Discrete Element Model (FDEM). 3. Capturing desiccation fracturing mechanisms in Cyclic Deformation (CD-A) field experiment in sandy facies of Opalinus Clay in Mont Terri Underground Rock Laboratory.

• The coupled THM response of a generic HLW disposal facility under high temperature has been analysed focusing on thermal pressurization and thermal fracturing. The simulations use an advanced elastoplastic constitutive model with damage to represent the mechanical behaviour of the host rock. • Numerical simulations have been carried out for generic disposal configurations. The host rock is assumed to be the Callovo-Oxfordian claystone. • Near field damage is caused by both the excavation of galleries and the effect of thermal pressurization. The development of shear bands is limited during the initial excavation and waiting stages, but they increase

- This study introduces lab scale tests simulating piping erosion in compacted bentonite buffer under rapid groundwater inflow in a disposal repository. Compacted bentonite were exposed to continuous water injection under varying conditions of flow rate, chemical composition, and flow direction of injected water. - The erosional piping phenomena of bentonite buffer including the formation of piping channels, critical inflow water pressure, and self healing behavior are are analyzed. In addition, X ray CT scanning was utilized to analyze the post piping behavior (dessication crack). - The results will utilized to development of design guidance and construction of safe HLW repository.