Clays in radioactive waste disposal

Abstract

International audienceClays and argillites are considered in some countries as possible host rocks for nuclear waste disposal at great depth. The use of compacted swelling clays as engineered barriers is also considered within the framework of the multi-barrier concept. In relation to these concepts, various research programs have been conducted to assess the thermo-hydro-mechanical properties of radioactive waste disposal at great depth. After introducing the concepts of waste isolation developed in Belgium, France and Switzerland, the paper describes the retention and transfer properties of engineered barriers made up of compacted swelling clays in relation to microstructure features. Some features of the thermo-mechanical behaviors of three possible geological barriers, namely Boom clay (Belgium), Callovo-Oxfordian clay (France) and Opalinus clay (Switzerland), are then described, including the retention and transfer properties, volume change behavior, shear strength and thermal aspects

Consequences of the Thermal Transient on the Evolution of the Damaged Zone Around a Repository for Heat-Emitting High-Level Radioactive Waste in a Clay Formation: a Performance Assessment Perspective

“…An important thermally-induced effect in low permeability media such as clays and claystones is the pore water pressurization that occurs upon heating (Delage et al 2010;Mohajerani et al 2012). Such strong THM couplings were clearly demonstrated from both in situ experiments and laboratory tests performed in the TIMODAZ project.…”

“…However, an increase of intrinsic permeability from -19 m² to 2×10 -16 m² was observed in one drained shearing test on the Boom Clay performed at Laboratoire 3SR in Grenoble (Delage 2010). According to Viggiani and Bésuelle (2012), this can be explained by the reopening of pre-existing cracks under a low mean stress (p'=0.3 MPa).…”

“…An important consequence of the existence of pre-existing damage in clay samples before testing is that the calibrated parameters from lab tests may deviate from their in situ counterparts and should therefore be used with great caution in case they are applied to full size repositories (Delage 2010).…”

The Modified Eulerian-Lagrangian Formulation for Cauchy Boundary Condition Under Dispersion Dominated Flow Regimes: A Novel Numerical Approach and its Implication on Radioactive Nuclide Migration or Solute Transport in the Subsurface Environment

“…The main component used for EBS is very low permeable Bentonite clay to limit any advection transfer (Delage et al, 2010;Bianchi et al, 2014). In this real situation, if the radionuclide transport occurs or engineering barrier layer fails, initially it transports through low hydraulic conductivity medium of bentonite clay (diffusion dominated) and it enters to the GBS later onwards gradually it enters to the geological medium (advection dominated) (Bianchi et al, 2014).…”

“…The hydraulic conductivity and dispersion coefficient of each medium varies drastically from one layer to another. The seepage velocity and dispersion coefficient for EBS, geological barrier and geological medium are adopted from previous studies which have shown in Table 2 (Delage et al, 2010;Yi et al, 2012). The peclet Number (Pe) of EBS and geological media were calculated using equation, Pe = by applying adopted hydrological parameters.…”