Abstract
Canister integrity and radionuclides retention is of prime importance for assessing the long term safety of nuclear waste stored in engineered geologic depositories. A comparative investigation of the interaction of uranyl ion with three different mineral surfaces has thus been undertaken in order to point out the influence of surface composition on the adsorption mechanism(s). Periodic DFT calculations using plane waves basis sets with the GGA formalism were performed on the TiO2(110), Al(OH)3(001) and Ni(111) surfaces. This study has clearly shown that three parameters play an important role in the uranyl adsorption mechanism: the solvent (H2O) distribution at the interface, the nature of the adsorption site and finally, the surface atoms’ protonation state.
Highlights
Knowledge and understanding about radionuclide retention processes are required for the safety assessment of nuclear waste repository systems
Results obtained in this study were relevant to the retention of the uranyl radionuclide on three distinctive mineral surfaces (rutile TiO2, gibbsite Al(OH)3 and Ni)
density functional theory (DFT) calculations can provide a high level of understanding that is necessary to correctly describe uranyl retention reactions
Summary
Knowledge and understanding about radionuclide retention processes are required for the safety assessment of nuclear waste repository systems. Uranium was selected as adsorbate, existing as uranyl cation UO22+ (uranium in formal oxidation state +VI) in aqueous solution and acidic pH conditions (between 3 and 4) [5] In this investigation we propose to describe uranyl interaction with three chemically and structurally different substrates: a transition metal oxide TiO2, an aluminum hydroxide Al(OH), and a transition metal (Ni), using periodic DFT (Density Functional Theory) calculations. Both rutile TiO2 and gibbsite Al(OH) were used here: i) as methodological surfaces and ii) because many experimental data on adsorption process are available. 1.5-4.5 pH range, the uranyl ion is the major species in solution, as aforementioned These two surface complexes corresponded to uranyl cations interacting with two distinct adsorption sites. Uranyl adsorption was investigated on the various hydrated surfaces with the aim of describing the created complexes, with respect to the mineral surface
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