TY  - JOUR
A1  - Hennig, Theresa
A1  - Kühn, Michael
T1  - Surrogate model for multi-component diffusion of Uranium through Opalinus Clay on the host rock scale
JF  - Applied Sciences : open access journal
N2  - Multi-component (MC) diffusion simulations enable a process based and more precise approach to calculate transport and sorption compared to the commonly used single-component (SC) models following Fick's law. The MC approach takes into account the interaction of chemical species in the porewater with the diffuse double layer (DDL) adhering clay mineral surfaces. We studied the shaly, sandy and carbonate-rich facies of the Opalinus Clay. High clay contents dominate diffusion and sorption of uranium. The MC simulations show shorter diffusion lengths than the SC models due to anion exclusion from the DDL. This hampers diffusion of the predominant species CaUO2(CO3)32-. On the one side, species concentrations and ionic strengths of the porewater and on the other side surface charge of the clay minerals control the composition and behaviour of the DDL. For some instances, it amplifies the diffusion of uranium. We developed a workflow to transfer computationally intensive MC simulations to SC models via calibrated effective diffusion and distribution coefficients. Simulations for one million years depict maximum uranium diffusion lengths between 10 m and 35 m. With respect to the minimum requirement of a thickness of 100 m, the Opalinus Clay seems to be a suitable host rock for nuclear waste repositories.
KW  - facies
KW  - uranium speciation
KW  - sorption
KW  - reactive transport
KW  - heterogeneity
KW  - PHREEQC
KW  - Mont Terri
KW  - repository far-field
Y1  - 2021
U6  - https://doi.org/10.3390/app11020786
SN  - 2076-3417
VL  - 11
IS  - 2
PB  - MDPI
CY  - Basel
ER  -