Simulation of diffusive uranium transport and sorption processes in the Opalinus Clay

Hennig, Theresa; Stockmann, Madlen; Kühn, Michael

doi:10.1016/j.apgeochem.2020.104777

Cited by 17 publications

(68 citation statements)

References 49 publications

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“…Furthermore, the effect of anion exclusion on the migration lengths was estimated by an adapted porewater diffusion coefficient, what reduced uranium migration by 30%. The work presented here thus aims to extend the findings of Hennig et al [11] by means of the MC approach.…”

Section: Introductionmentioning

confidence: 82%

“…The Opalinus Clay is subdivided into shaly, sandy and carbonate-rich facies [10], which differ in their mineralogical composition. As a result of the water rock interaction, the geochemical conditions in the porewaters of the facies vary and impact on sorption and transport of radionuclides [11].…”

Section: Introductionmentioning

confidence: 99%

“…In the geochemical system of the Opalinus Clay, uranium is mainly present as anionic as well as neutral, ternary uranyl complex bound to calcium and carbonate. In a previous study, the migration of uranium in the Opalinus Clay was assessed in one-dimensional diffusion simulations using Fick's laws as a function of different partial pressures of carbon dioxide (pCO 2 ) covering the range of measured values for the formation and depending on the mineralogical heterogeneity in the facies [11]. The various facies govern the geochemistry of the system, especially via the pCO 2 and thus by the carbonate and calcium concentrations as well as the resulting pH through which the anionic, ternary uranyl complex CaUO 2 (CO 3 ) 2− 3 is the predominant species in the system [11].…”

Section: Introductionmentioning

confidence: 99%

“…In a previous study, the migration of uranium in the Opalinus Clay was assessed in one-dimensional diffusion simulations using Fick's laws as a function of different partial pressures of carbon dioxide (pCO 2 ) covering the range of measured values for the formation and depending on the mineralogical heterogeneity in the facies [11]. The various facies govern the geochemistry of the system, especially via the pCO 2 and thus by the carbonate and calcium concentrations as well as the resulting pH through which the anionic, ternary uranyl complex CaUO 2 (CO 3 ) 2− 3 is the predominant species in the system [11]. Based on their results, Hennig et al [11] prioritized the governing parameters for the sorption of uranium in the Opalinus Clay as follows: pCO 2 , Ca 2+ concentration, pH, pe and clay mineral quantity.…”

Section: Introductionmentioning

confidence: 99%

“…The various facies govern the geochemistry of the system, especially via the pCO 2 and thus by the carbonate and calcium concentrations as well as the resulting pH through which the anionic, ternary uranyl complex CaUO 2 (CO 3 ) 2− 3 is the predominant species in the system [11]. Based on their results, Hennig et al [11] prioritized the governing parameters for the sorption of uranium in the Opalinus Clay as follows: pCO 2 , Ca 2+ concentration, pH, pe and clay mineral quantity. Furthermore, the effect of anion exclusion on the migration lengths was estimated by an adapted porewater diffusion coefficient, what reduced uranium migration by 30%.…”

Section: Introductionmentioning

confidence: 99%

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Surrogate Model for Multi-Component Diffusion of Uranium through Opalinus Clay on the Host Rock Scale

Hennig

Kühn

2021

Applied Sciences

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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.

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Section: Introductionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%