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On the redox reactivity of doped UO2 pellets - Influence of dopants on the H2O2 decomposition mechanism
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-0086-5536
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0663-0751
2012 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 430, no 1-3, 6-11 p.Article in journal (Refereed) Published
Abstract [en]

The reactivity of doped UO2 such as SIMFUEL, Y2O3 doped UO2 and Y2O3/Pd doped UO2 towards H2O2 has been shown to be fairly similar to that of pure UO2. However, the oxidative dissolution yield, i.e. the ratio between the amount of dissolved uranium and the amount of consumed H2O2 is significantly lower for doped UO2. The rationale for the observed differences in dissolution yield is a difference in the ratio between the rates of the two possible reactions between H2O2 and the doped UO2. In this work we have studied the effect of doping on the two possible reactions, electron-transfer and catalytic decomposition. The catalytic decomposition was studied by monitoring the hydroxyl radical production (the primary product) as a function of time. The redox reactivity of the doped pellets was studied by using MnO4- and IrCl62- as model oxidants, only capable of electron-transfer reactions with the pellets. In addition, the activation energies for oxidation of UO2 and SIMFUEL by MnO4- were determined experimentally. The experiments show that the rate of catalytic decomposition of H2O2 varies by 30% between the most and least reactive material. This is a negligible difference compared to the difference in oxidative dissolution yield. The redox reactivity study shows that doping UO2 influences the redox reactivity of the pellet. This is further illustrated by the observed activation energy difference for oxidation of UO2 and SIMFUEL by MnO4-. The redox reactivity study also shows that the sensitivity to dopants increases with decreasing reduction potential of the oxidant. These findings imply that the relative impact of radiolytic oxidants in oxidative dissolution of spent nuclear fuel must be reassessed taking the actual fuel composition into account.

Place, publisher, year, edition, pages
2012. Vol. 430, no 1-3, 6-11 p.
Keyword [en]
Radiation-Induced Dissolution, Waste-Disposal Conditions, Spent Nuclear-Fuel, Uranium-Dioxide, Oxidative Dissolution, Fission-Products, Aqueous-Solution, Corrosion, Radicals, Kinetics
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-109203DOI: 10.1016/j.jnucmat.2012.06.016ISI: 000310940700002ScopusID: 2-s2.0-84864026579OAI: diva2:580431
EU, FP7, Seventh Framework Programme, FP7-212287

QC 20121221

Available from: 2012-12-21 Created: 2012-12-21 Last updated: 2013-03-22Bibliographically approved
In thesis
1. Reactions of aqueous radiolysis products with oxide surfaces: An experimental and DFT study
Open this publication in new window or tab >>Reactions of aqueous radiolysis products with oxide surfaces: An experimental and DFT study
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reactions between aqueous radiolysis products and oxide surfaces are important in nuclear technology in many ways. In solid-liquid systems, they affect (and at the same time are dependent on) both the solution chemistry and the stability of materials under the influence of ionizing radiation. The stability of surface oxides is a factor that determines the longevity of the materials where such oxides are formed. Additionally, the aqueous radiolysis products are responsible for corrosion and erosion of the materials.

  In this study, the reactions between radiolysis products of water – mainly H2O2 and HO radicals – with metal, lanthanide and actinide oxides are investigated. For this, experimental and computational chemistry methods are employed. For the experimental study of these systems it was necessary to implement new methodologies especially for the study of the reactive species – the HO radicals. Similarly, the computational study also required the development of models and benchmarking of methods. The experiments combined with the computational chemistry studies produced valuable kinetic, energetic and mechanistic data.

  It is demonstrated here that the HO radicals are a primary product of the decomposition of H2O2. For all the materials, the catalytic decomposition of H2O2 consists first of molecular adsorption onto the surfaces of the oxides. This step is followed by the cleavage of the O-O bond in H2O2 to form HO radicals. The HO radicals are able to react further with the hydroxylated surfaces of the oxides to form water and a surface bound HO center. The dynamics of formation of HO vary widely for the different materials studied. These differences are also observed in the activation energies and kinetics for decomposition of H2O2. It is found further that the removal of HO from the system where H2O2 undergoes decomposition, by means of a scavenger, leads to the spontaneous formation of H2.

  The combined theoretical-experimental methodology led to mechanistic understanding of the reactivity of the oxide materials towards H2O2 and HO radicals. This reactivity can be expressed in terms of fundamental properties of the cations present in the oxides. Correlations were found between several properties of the metal cations present in the oxides and adsorption energies of H2O, adsorption energies of HO radicals and energy barriers for H2O2 decomposition. This knowledge can aid in improving materials and processes important for nuclear technological systems, catalysis, and energy storage, and also help to better understand geochemical processes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 121 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2013:12
hydrogen peroxide, hydrogen production, metal, oxides, lanthanide, catalysis, density functional theory, surface, reactions, chemistry
National Category
Physical Chemistry Materials Chemistry Theoretical Chemistry
Research subject
SRA - Energy; SRA - Production
urn:nbn:se:kth:diva-119780 (URN)978-91-7501-683-2 (ISBN)
Public defence
2013-04-12, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
StandUpXPRES - Initiative for excellence in production research

QC 20130322

Available from: 2013-03-22 Created: 2013-03-21 Last updated: 2013-03-22Bibliographically approved

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