Coupled transport-reaction modeling of the long-term interaction between iron, bentonite and Callovo-Oxfordian claystone in radioactive waste confinement systems

For the iron-bentonite interactions, the simulated results showed significant differences depending on the different hypotheses used to calculate surface areas for minerals. When different sizes of mineral particles are assumed to estimate the surface areas of primary minerals, the system explored a larger change in porosity and more intense mineralogical modifications in the zone close to the bentonite/steel overpack interface. This result is likely related to the lower diffusion of aqueous corrosion products through the bentonite barrier. The comparison between iron-bentonite and iron-COx claystone interactions confirmed a clear different behavior of reactivity. For the iron-bentonite the alteration concerns two zones in direct contact with the geological groundwater and steel overpack but for the iron-COx claystone the mineralogical modifications are predicted to occur in the whole medium. The mineralogical evolution of the COx claystone barrier is mainly impacted by the dissolution of primary minerals, especially for total transformation of interstratified illite/smectite (I-Sm) and formation of secondary minerals such as illite and berthierine-FeII. The modeling results obtained from the sensitivity test showed a significant impact of the diffusion parameter on the evolution of the COx barrier, especially the changes in pH, porosity and the mineralogical modification of the zone in contact with the steel container.