The influence of dissolved hydrogen on the surface composition of doped uranium dioxide under aqueous corrosion conditions

Broczkowski, Michael E.; Noël, James J.; Shoesmith, David W.

doi:10.1016/j.jelechem.2006.11.021

Cited by 20 publications

(17 citation statements)

References 11 publications

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“…It has long been thought that the only two uranium oxidation states of environmental importance are U(IV) and U(VI). The likely, and perhaps reasonable, basis for the belief that the intermediate U(V) is not relevant under environmental conditions is the well documented rapid disproportionation of aqueous U(V) outside of a very narrow Eh-pH window. − However, beginning in 2004–2005, laboratory evidence started accumulating for the existence of sorbed pentavalent uranium, well outside the nominal stability of U(V)aq, during the reduction of U(VI) by ferrous minerals − and during the oxidative-dissolution of both SIMFUEL − and particulate UO 2 . , Evidence for a transitory aqueous U(V) carbonate species has also been found during microbial reduction of U(VI) . Nonetheless, sorbed U(V) persisted for weeks in the study by Ilton et al, suggesting that it could be more than just a transitory intermediate.…”

Section: Introductionmentioning

confidence: 99%

Reduction of U(VI) Incorporated in the Structure of Hematite

Ilton

Pacheco

Bargar

et al. 2012

Environ. Sci. Technol.

100

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U(VI) doped hematite was synthesized and exposed to two different organic reductants with E(0) of 0.23 and 0.70 V. A combination of HAADF-TEM and EXAFS provided evidence that uranium was incorporated in hematite in uranate, likely octahedral coordination. XPS indicated that structurally incorporated U(VI) was reduced to U(V), whereas non-incorporated U(VI) was reduced to U(IV). Specifically, the experiments indicate that U(V) was the dominant oxidation state of uranium in hematite around Eh -0.24 to -0.28 V and pH 7.7-8.6 for at least up to 5 weeks of reaction time. U(V), but not U(IV), was also detected in hematite at Eh +0.21 V (pH 7.1-7.3). The results support the hypothesis, based on previous experimental and theoretical work, that the stability field of U(V) is widened relative to U(IV) and U(VI) in uranate coordination environments where the coordination number of U is less than 8.

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Section: Introductionmentioning

confidence: 99%

Reduction of U(VI) Incorporated in the Structure of Hematite

Ilton

Pacheco

Bargar

et al. 2012

Environ. Sci. Technol.

100

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“…In experiments conducted in an N 2 purged solution, 3 wt % Pd could prevent corrosion when only radiolytically produced H 2 was present . Because at room temperature, the dissolved molecular H 2 is known to be chemically inert, these experiments confirm that the activation of H 2 by noble metals is a key mechanism in suppressing fuel oxidation. − …”

Section: Introductionmentioning

confidence: 67%

“…Dissolved H 2 has been shown to suppress fuel corrosion and radionuclide release in a number of investigations. − Broczkowski et al used electrochemical methods to show that this suppression could be attributed to the formation of reductive radicals by H 2 oxidation catalyzed on the noble metal (ε) particles present in SIMFUEL pellets, which act as galvanically coupled anodes within the fuel matrix. This catalytic effect was confirmed by Jonsson et al, who showed that during γ-irradiation, 1 bar H 2 was sufficient to inhibit UO 2 corrosion when 0.1 wt % Pd was present.…”

Section: Introductionmentioning

confidence: 99%

Roles of Radiolytic and Externally Generated H₂ in the Corrosion of Fractured Spent Nuclear Fuel

Liu

Qin

et al. 2016

Environ. Sci. Technol.

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A 2-D model for the corrosion of spent nuclear fuel inside a failed nuclear waste container has been modified to determine the influence of various redox processes occurring within fractures in the fuel. The corrosion process is driven by reaction of the fuel with the dominant α radiolysis product, HO. A number of reactions are shown to moderate or suppress the corrosion rate, including HO decomposition and a number of reactions involving dissolved H produced either by α radiolysis or by the corrosion of the steel container vessel. Both sources of H lead to the suppression of fuel corrosion, with their relative importance being determined by the radiation dose rate, the steel corrosion rate, and the dimensions of the fractures in the fuel. The combination of H from these two sources can effectively prevent corrosion when only micromolar quantities of H are present.

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“…Numerous studies using electrochemical methods combined with surface characterization techniques such as XPS have demonstrated that, upon oxidation of UO 2 in aqueous solution, the surface will first be oxidized to a U IV 1–2 x U V 2 x O 2+ x layer followed by further oxidation to U(VI). Depending on the uranyl-complexing ability of the anions in solution, U(VI) will either deposit on the UO 2+ x surface or dissolve. − XPS results in these studies show that when HCO 3 – is present, the oxidized surface was effectively U(V) with negligible amounts of U(VI). The latter being soluble is uranyl carbonate complexes.…”

Section: Resultsmentioning

confidence: 99%

Exploring the Change in Redox Reactivity of UO₂ Induced by Exposure to Oxidants in HCO₃^– Solution

Liu

Jönsson

2023

Inorg. Chem.

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Understanding the possible change in UO2 surface reactivity after exposure to oxidants is of key importance when assessing the impact of spent nuclear fuel dissolution on the safety of a repository for spent nuclear fuel. In this work, we have experimentally studied the change in UO2 reactivity after consecutive exposures to O2 or γ-radiation in aqueous solutions containing 10 mM HCO3 –. The experiments show that the reactivity of UO2 toward O2 decreases significantly with time in a single exposure. In consecutive exposures, the reactivity also decreases from exposure to exposure. In γ-radiation exposures, the system reaches a steady state and the rate of uranium dissolution becomes governed by the radiolytic production of oxidants. Changes in surface reactivity can therefore not be observed in the irradiated system. The potential surface modification responsible for the change in UO2 reactivity was studied by XPS and UPS after consecutive exposures to either O2, H2O2, or γ-radiation in 10 mM HCO3 – solution. The results show that the surfaces were significantly oxidized to a stoichiometric ratio of O/U of UO2.3 under all the three exposure conditions. XPS results also show that the surfaces were dominated by U(V) with no observed U(VI). The experiments also show that U(V) is slowly removed from the surface when exposed to anoxic aqueous solutions containing 10 mM HCO3 –. The UPS results show that the outer ultrathin layer of the surfaces most probably contains a significant amount of U(VI). U(VI) may form upon exposure to air during the rinsing process with water prior to XPS and UPS measurements.

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The influence of dissolved hydrogen on the surface composition of doped uranium dioxide under aqueous corrosion conditions

Cited by 20 publications

References 11 publications

Reduction of U(VI) Incorporated in the Structure of Hematite

Reduction of U(VI) Incorporated in the Structure of Hematite

Roles of Radiolytic and Externally Generated H₂ in the Corrosion of Fractured Spent Nuclear Fuel

Exploring the Change in Redox Reactivity of UO₂ Induced by Exposure to Oxidants in HCO₃^– Solution

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The influence of dissolved hydrogen on the surface composition of doped uranium dioxide under aqueous corrosion conditions

Cited by 20 publications

References 11 publications

Reduction of U(VI) Incorporated in the Structure of Hematite

Reduction of U(VI) Incorporated in the Structure of Hematite

Roles of Radiolytic and Externally Generated H2 in the Corrosion of Fractured Spent Nuclear Fuel

Exploring the Change in Redox Reactivity of UO2 Induced by Exposure to Oxidants in HCO3– Solution

Contact Info

Product

Resources

About

Roles of Radiolytic and Externally Generated H₂ in the Corrosion of Fractured Spent Nuclear Fuel

Exploring the Change in Redox Reactivity of UO₂ Induced by Exposure to Oxidants in HCO₃^– Solution