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The effect of Y2O3 on the dynamics of oxidative dissolution of UO2
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).ORCID iD: 0000-0003-0596-0222
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).ORCID iD: 0000-0003-0663-0751
2010 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 407, no 3, 195-199 p.Article in journal (Refereed) Published
Abstract [en]

In this work, we have studied the impact of Y2O3 on the kinetics of oxidative dissolution of UO2 and the consumption of H2O2. The second order kinetics of catalytic consumption of H2O2 on Y2O3 was investigated in aqueous Y2O3 powder suspensions by varying the solid surface area to solution volume ratio. The resulting second order rate constant is 10(-8) m s(-1), which is of the same magnitude as for the reaction between H2O2 and UO2. Powder experiments with mixtures of UO2 and Y2O3 show that Y2O3 has no effect on the oxidative dissolution of UO2, whereas the consumption of H2O2 seems to be slightly slower in the presence of Y2O3 and H-2 respectively. UO2 pellets with solid inclusions of Y2O3 show a decrease in oxidative dissolution by a factor of 3.3 and 5.3 under inert and hydrogen atmosphere, respectively. The rate of H2O2 consumption is similar for all cases and is well in line with kinetic data from powder experiments. The effects of H-2 and Y2O3 on the oxidative dissolution of UO2 under gamma irradiation are similar to those found in experiments with H2O2. No significant difference in dissolution between inert and reducing atmosphere can be observed for pure UO2.

Place, publisher, year, edition, pages
Elsevier, 2010. Vol. 407, no 3, 195-199 p.
Keyword [en]
SPENT NUCLEAR-FUEL, RADIATION-INDUCED DISSOLUTION, WASTE-DISPOSAL CONDITIONS, FISSION-PRODUCTS, URANIUM-DIOXIDE, RADIOLYSIS PRODUCTS, AQUEOUS-SOLUTION, HYDROGEN, KINETICS, SOLUBILITY
National Category
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-29530DOI: 10.1016/j.jnucmat.2010.10.014ISI: 000285859200009Scopus ID: 2-s2.0-78649484630OAI: oai:DiVA.org:kth-29530DiVA: diva2:395639
Note

QC 20110207

Available from: 2011-02-07 Created: 2011-02-07 Last updated: 2017-12-11Bibliographically approved
In thesis
1. The effect of solid state inclusions on the reactivity of UO2: A kinetic and mechanistic study
Open this publication in new window or tab >>The effect of solid state inclusions on the reactivity of UO2: A kinetic and mechanistic study
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The release of radionuclides is a key process in the safety assessment of a deep geological repository for spent nuclear fuel. A large fraction of the release is assumed to be a consequence of dissolution of the fuel matrix, UO2. In this doctoral thesis, the kinetics and the mechanisms behind oxidative U(IV) dissolution were studied. The eects of solid phase inclusions mimicking the presence of fission products, and solutes mimicking expected groundwater components were also evaluated.

Palladium, as a model substance for noble metal particle (fission products) inclusions, was shown to catalyze surface oxidation of U(IV), as well as reduction of U(VI). The second order rate constant for the surface reduction of U(VI) by H2was found to be on the order of 10-6 m s-1 (diusion controlled). Under 40 bar H2, 1 wt.% Pd was sufficient to suppress oxidative U(IV) dissolution in 2mM H2O2 aqueous solution. During g γirradiation under 1 bar H2, 0.1 wt.% Pd were sufficient to completely suppress oxidative dissolution. Under inert conditions, where H2 is only produced radiolytically, complete inhibition is observed for 3 wt.% Pd.

The presence of Y2O3 as a model substance for trivalent fission products was found to decrease U(VI) dissolution significantly under inert, as well as reducing conditions. Based on kinetic data, it was shown that pure competition kinetics cannot explain the observed decrease. From experiments using pure oxidants it was shown that Y2O3 doping of UO2 decreases the redox reactivity. In addition, from experiments where hydroxyl radical formation from the catalytic decomposition of H2O2 was monitored, it could be concluded that doping has a minor influence on this process.

On the basis of numerical simulations, the H2 concentration necessary to suppressradiolytic H2O2 production was found to increase with an increase in dose rate or HCO-3 concentration. Furthermore, the steady state concentration of H2O2 was found to be inversely proportional to the H2 pressure, and proportional to the square root of the dose rate. Fe2 diers strongly from the total reaction volume, the actual dose rate should not be converted into a homogeneous dose rate in numerical simulations.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xiv, 67 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:32
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:kth:diva-33070 (URN)978-91-7415-960-8 (ISBN)
Public defence
2011-05-27, K2, Teknikringen 28, KTH, Stockholm, 18:02 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 212287
Note
QC 20110511Available from: 2011-05-11 Created: 2011-04-27 Last updated: 2011-05-11Bibliographically approved

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