Stability of Clay Barriers Under Chemical Perturbations

5-year chemico-physical evolution of concrete–claystone interfaces, Mont Terri rock laboratory (Switzerland)

“…An increase in porosity in the cement paste close to the interface, and clogging in the claystone adjacent to it are commonly predicted by reactive transport modelling (De Windt et al 2008;Marty et al 2009;Kosakowski and Berner 2013;Bradbury et al 2014). Changes in porosity and its distribution-and therefore also permeability-near such interfaces are an important process governing the long-term physicochemical evolution of the engineered barrier and its geological near-field (Kosakowski and Berner 2013, Bildstein and Claret 2015). Clayrich rocks that are currently under consideration at an advanced stage of repository planning include Opalinus Clay in Switzerland (Nagra 2002), Callovo-Oxfordian ''argillite'' in France (ANDRA 2005), and Boom Clay in Belgium (SCKÁCEN 2012).…”

RTM for Waste Repositories

“…Today, numerical models are ubiquitous tools that can be used either for long-term predictive evaluation of solute transport or design optimization of nuclear waste geologic repositories (Tsang et al 1994;Johnson et al 2017). They are also used to make predictive multi-physical assessments within a timeframe and space scale larger than experiments can cover (Bredehoeft 2003;Bildstein and Claret 2015). These numerical simulations require integrating, in a consistent framework, an increasing amount of scientific knowledge (Geckeis and Rabung 2008) acquired for each of the individual components of such repositories.…”

“…There are also numerous chemical effects as foreign materials like borosilicate glasses (Poinssot et al 2010;Gin et al 2015), metallic canisters (King and Shoesmith 2010), and concrete (Alonso et al 2010) that are introduced into the repository will induce chemical gradients across the repository components (Nagra 2002;Andra 2005Andra , 2009. Because of these chemical gradients, perturbations such as pH and redox changes may alter the performance of the barriers over time (Bildstein and Claret 2015). Last but not least, radiological effects also exist in association with the radiological inventory of waste independently from the technological solution, retreatment or direct disposal of irradiated fuels (Odorowski et al 2017) or after reprocessing (Gong et al 1999;Berner et al 2013).…”

“…Under these conditions, the prevailing reducing conditions will be perturbed and redox-sensitive minerals (e.g., Fe-bearing minerals) will react. The expected chemical changes have been recently reviewed (Bildstein and Claret 2015) and the main weathering effects to be expected are recalled here. In claystone, oxidation mainly affects pyrite, which is ubiquitously found in the mineral assemblage.…”

“…While the measured pH in concrete is in the range 10.4 to 13.6 depending on time and formulation (Lothenbach and Wieland 2006;Luke and Lachowski 2008;García Calvo et al 2010;Lothenbach 2010;Bach et al 2012;Lothenbach et al 2012Lothenbach et al , 2014, the pH of pore water in clay materials is generally in the range of 7 to 9 Baeyens 2003, 2009;Wersin 2003;Bildstein and Claret 2015;Lerouge et al 2018). Therefore, even for low-pH concrete material, the pH difference at the interface may be as much as two pH units.…”