Modelling iron-bentonite interactions

Stability of Clay Barriers Under Chemical Perturbations

“…Reconciling the results from experiments using grinded or powdered materials with those using compacted clay mineral or plug core and steel coupons cannot be resolved solely by considering simple hypotheses for reactive surface areas: pore structure effects, heterogeneities and access to water must be taken into account (Peters, 2009;Landrot et al, 2012;Noiriel et al, 2012;Tian et al, 2014). Predicting the long-term behavior of this type of systems is also still hindered by the uncertainty in the data for the kinetics of the processes involved, especially mineral precipitation (i.e., nucleation and growth; Fritz and Noguéra, 2009;Savage et al, 2010b;Kampman et al, 2014). The key may lie in understanding the differences between the kinetic rate/reactive surface area determined in batch experiments, in integrated/in situ experiments, and in the field (e.g., Maher et al, 2006).…”

Thermodynamic and fully-coupled reactive transport models of a steel–bentonite interface

“…Reactive transport modelling suggests that true chlorite minerals could form over relatively longer timescales (timescales of tens of thousands of years or longer) via Ostwald processes (e.g. Savage et al, 2010a). However, the data required for constraining models that include Ostwald processes are lacking, and therefore such models currently have a limited predictive capacity.…”

“…A number of modelling studies have been undertaken on iron-bentonite interactions, ranging from simple thermodynamic approximations (Wilson et al, 2006a) through to more elaborate reactive transport modelling of engineered radioactive waste repository systems (Bildstein et al,7 2006; Montes-H et al, 2005;Savage et al, 2010a). Many of these more recent models include complex reaction kinetics (Bildstein et al, 2006;Montes-H et al, 2005;Savage et al, 2010a).…”

“…Many of these more recent models include complex reaction kinetics (Bildstein et al, 2006;Montes-H et al, 2005;Savage et al, 2010a).…”

“…In addition to this uncertainty, many of the previouslypublished reactive transport models of iron-bentonite or iron-claystone interfaces use a finite volume approach in which steel reacts with a volume of water that is not part of the bentonite porosity, but is present either as a gap (present prior to bentonite resaturation after repository closure) or as a fictive steel porosity (steel having no inherent porosity) to allow for growth of steel corrosion products that can then interact with the bentonite (e.g. Bildstein et al, 2006;Marty et al, 2010;Savage et al, 2010a). In such models, there is a potential for artificial dilution effects to lead to the development of water compositions in the gap that are different to those that would be likely in the bentonite pore space immediately adjacent to the steel surface 8 once it is in contact with the bentonite.…”