Oxidation and dissolution rates of UO2(s) in carbonate-rich solutions under external alpha irradiation and initially reducing conditions
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Tomo Suzuki
This paper describes the effects of aqueous carbonate concentrations on the UO2 oxidation and dissolution rates under an alpha beam irradiation in a cyclotron. As solid samples, UO2 colloids were synthesized by nano-particle precipitation. The specific surface area obtained is 85.3 m2/g. All aqueous solutions were buffered in the pH range 8<pH<9.
The observation of particles under TEM and X-ray diffraction showed well-crystallized UO2. Molecular radiolysis products such as H2O2 and carbonate degradation products where analysed. Solution analysis of dissolved uranium and of radiolytically generated H2O2 allowed to deduce dissolution rates of UO2 as well as H2O2 consumption rates (deduced from the H2O2 concentrations in presence of UO2 colloids and those in irradiated blank solutions). In absence of carbonate, the dissolution rates of UO2 are much lower than the H2O2 consumption rates. The difference is explained by the oxidation of uranium(IV) at the UO2/solution interface (e.g. formation of U3O7). In contrast, in the presence of carbonate (up to 4×10-2 mol/L), the dissolution rates of UO2 are similar to H2O2 consumption rates. In this case the oxidized uranium is complexed with carbonate ions resulting in highly soluble species as indicated by the geochemical model PHREEQC calculations [UO2(CO3)34 -]. The high carbonate concentration did not affect the H2O2 formation/consumption rates. Radiolytic decomposition of carbonate ions and formation of organic radiolytic degradation products were negligible.
The results indicate that under the present experimental conditions, UO2 oxidation by H2O2 and UO2 dissolution are connected as a sequential reaction: for a given H2O2 concentration, UO2 oxidation occurs at a constant rate. At low carbonate concentration, the dissolution of oxidized UO2 is slower than the oxidation rate (hence oxidation is not rate limiting), while at high carbonate concentrations all oxidized UO2 becomes immediately dissolved and UO2 oxidation becomes rate limiting for UO2 dissolution. This mechanism is in agreement with that proposed in the Matrix Alteration Model (MAM).
© Oldenbourg Wissenschaftsverlag
Artikel in diesem Heft
- Preface Migration 2005
- Solubility measurement of zirconium(IV) hydrous oxide
- Solubility of ThO2·xH2O(am) and the formation of ternary Th(IV) hydroxide-carbonate complexes in NaHCO3-Na2CO3 solutions containing 0−4 M NaCl
- Ion interaction (SIT) coefficients for the Th4+ ion and trace activity coefficients in NaClO4, NaNO3 and NaCl solution determined by solvent extraction with TBP
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- The fate of the epsilon phase (Mo-Ru-Pd-Tc-Rh) in the UO2 of the Oklo natural fission reactors
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Artikel in diesem Heft
- Preface Migration 2005
- Solubility measurement of zirconium(IV) hydrous oxide
- Solubility of ThO2·xH2O(am) and the formation of ternary Th(IV) hydroxide-carbonate complexes in NaHCO3-Na2CO3 solutions containing 0−4 M NaCl
- Ion interaction (SIT) coefficients for the Th4+ ion and trace activity coefficients in NaClO4, NaNO3 and NaCl solution determined by solvent extraction with TBP
- Leaching of neptunium from garnet- and murataite-based ceramics
- Coprecipitation of thorium and lanthanum with UO2+x(s) as host phase
- Rare Earth element (REE) incorporation in natural calcite: Upper limits for actinide uptake in a secondary phase
- Protonation of D-gluconate and its complexation with Np(V) in acidic to nearly neutral solutions
- Complexing properties of α-isosaccharinate: thorium
- Determination of the thermodynamic quantities of complexation between Eu(III) and carboxylic acids by microcalorimetry
- Potentiometric investigations on the interaction of humic acid with Cu(II) and Eu(III) ions
- Investigation of complexation of thorium by humic acid using chemically immobilized humic acid on silica gel
- Correlation between X-ray chemical shift and partial charge in Tc(IV) complexes: Determination of Tc partial charge in TcnOy(4n-2y)+
- Oxidation and dissolution rates of UO2(s) in carbonate-rich solutions under external alpha irradiation and initially reducing conditions
- On the stability of Pu(III) at different pH under non-inert conditions
- Reduction behavior of uranium in the presence of citric acid
- Leaching of zirconolite ceramics under H+ and He2+ irradiation
- Reduction of plutonium(VI) in brine under subsurface conditions
- Theoretical first step towards an understanding of the uranyl ion sorption on the rutile TiO2(110) face: A DFT periodic and cluster study
- Cm(III) sorption onto γ-Al2O3: New insight into sorption mechanisms by time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure
- Modelling sorption data for the actinides Am(III), Np(V) and Pa(V) on montmorillonite
- Sorption of Cs, Ni, Pb, Eu(III), Am(III), Cm, Ac(III), Tc(IV), Th, Zr, and U(IV) on MX 80 bentonite: An experimental approach to assess model uncertainty
- The uptake of radium by calcium silicate hydrates and hardened cement paste
- Np(V)O2+ sorption on hydroxyapatite-effect of calcium and phosphate anions
- Uranium(VI) interaction with pyrite (FeS2): Chemical and spectroscopic studies
- Interaction of U(VI) with pyrite, galena and their mixtures: a theoretical and multitechnique approach
- Technetium sorption by stibnite from natural water
- Mechanisms of cesium sorption onto magnetite
- Sorption of cesium on granite under aerobic and anaerobic conditions
- Comparative study of cesium sorption on crushed and intact sedimentary rock
- The INE-Beamline for actinide research at ANKA
- Evaluation of the reversibility of iodide uptake by argillaceous rocks by the radial diffusion method
- Thermal diffusion of chlorine in uranium dioxide
- Effects of ionic strength on the coordination of Eu(III) and Cm(III) to a Gram-negative bacterium, Paracoccus denitrificans
- Interaction mechanisms of bacterial strains isolated from extreme habitats with uranium
- Biotransformation of plutonium complexed with citric acid
- Iodination of humic acid samples from different origins
- The fate of the epsilon phase (Mo-Ru-Pd-Tc-Rh) in the UO2 of the Oklo natural fission reactors
- Rhenium migration at the Maqarin natural analogue site (Jordan)
- Classic adsorption isotherms incorporated in modern surface complexation models: Implications for sorption of actinides
- Use of thermodynamic sorption models to derive radionuclide Kd values for performance assessment: selected results and recommendations of the NEA sorption project
- Modeling spent nuclear fuel alteration and radionuclide migration in disposal conditions
