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Oxidative dissolution of doped UO2 and H2O2 reactivity towards oxide surfaces: A kinetic and mechanistic study
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. (Kärnkemi)
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Oxidative dissolution of std. UO2 and UO2 doped with Cr2O3 and Al2O3, i.e. ADOPT, induced by H2O2 and γ radiation has been the main focus in this licentiate thesis. The catalytic decomposition of H2O2 on oxides like Gd2O3, HfO2, CeO2, Fe2O3 and CuO were also investigated.

A kinetic study was performed by determining first and second order rate constants together with Arrhenius parameters for the decomposition of H2O2. The reactivity of H2O2 towards the oxides mentioned was observed to differ significantly despite their similarities. In the mechanistic study, the yields and dynamics of the formation of the intermediate hydroxyl radical from the decomposition of H2O2 was determined for the oxides and found to differ considerably. A turnover point could be found for most of oxides studied, i.e. an increase in the rate of hydroxyl radical scavenging after a specific amount of consumed H2O2.

The reactivity of the std. UO2 and ADOPT towards H2O2 was similar to what was observed for other UO2-based materials in previous studies. The oxidative dissolution in radiation experiments showed a slight but significant difference. This was attributed to a difference in exposed surface area instead of an effect of doping. The difference in oxidative dissolution yield was too small to be significant which supports the previous conclusion.

Leaching experiments using spent nuclear fuel were also performed on the two types of fuel showing the same behavior as the unirradiated pellets, i.e., a slightly lower 238U release from ADOPT. The difference was attributed to difference in exposed surface area. The release of fission products with low UO2 solubility displayed a higher release from ADOPT which was attributed to a difference in matrix solubility. Cs was released to a larger extent from std. UO2. This is attributed to the larger grain size of ADOPT, extending the diffusion distance. The release of lanthanides and actinides was slightly higher for the conventional UO2, nevertheless the difference was relatively small.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , x, 51 p.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:23
Keyword [en]
Oxidative dissolution; UO2; ADOPT; H2O2; Spent Nuclear Fuel.
National Category
Chemical Sciences
Research subject
URN: urn:nbn:se:kth:diva-145691ISBN: 978-91-7595-149-2OAI: diva2:719680
2014-06-10, K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)

QC 20140527

Available from: 2014-05-27 Created: 2014-05-26 Last updated: 2014-05-27Bibliographically approved
List of papers
1. Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides
Open this publication in new window or tab >>Catalytic decomposition of hydrogen peroxide on transition metal and lanthanide oxides
2013 (English)In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, Vol. 379, 178-184 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the reactions of H2O2 with Fe2O3, CuO, HfO2, CeO2 and Gd 2O3 in aqueous solution. The reactions rate constants at room temperature were determined. From the temperature dependence of the rate constants we extracted the Arrhenius parameters and the standard enthalpies of activation for the reactions. In addition, we studied the dynamics of formation of the intermediate species formed during decomposition of H2O 2, the HO radical. The kinetic data for H2O2 reactivity and the yields of hydroxyl radical formation differ considerably between many of the materials studied. We compared the energetic and mechanistic data obtained in this work with literature data for a set of nine oxides in total. The Arrhenius pre-exponential factors normalized to surface area for the decomposition of H2O2 vary by nine orders of magnitude for some of the oxides investigated. This indicates that the surfaces of the oxides have very different catalytic capacity towards the decomposition of H 2O2. The standard enthalpies of activation for H 2O2 decomposition vary between 30 and 73 kJ mol -1, revealing also differences in the catalytic efficiency for the different materials. The mechanistic study consists of quantifying the HO radical scavenged by tris(hydroxymethyl)aminomethane (Tris) during the course of the decomposition of H2O2 for the whole set of oxides. The yields and dynamics of scavenging of HO• differ considerably between the oxides analyzed. Surprisingly, the time-independent plots of the amount of HO scavenged as a function of the conversion of H2O 2 reveals that during the decomposition of H2O2 there are turnover points where the amount of HO scavenged by Tris suffers a sudden increase. The location of these points and the curvatures of the plots at the near-neighbours is considerably different for the different materials.

Catalysis, Hydroxyl, Oxide, Peroxide, Surface
National Category
Physical Chemistry
urn:nbn:se:kth:diva-119808 (URN)10.1016/j.molcata.2013.08.017 (DOI)000326772700024 ()2-s2.0-84884191958 (ScopusID)

QC 20131029

Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2015-08-26Bibliographically approved
2. Oxidative dissolution of ADOPT compared to standard UO2 fuel
Open this publication in new window or tab >>Oxidative dissolution of ADOPT compared to standard UO2 fuel
(English)Manuscript (preprint) (Other academic)
urn:nbn:se:kth:diva-145720 (URN)

QS 2014

Available from: 2014-05-27 Created: 2014-05-27 Last updated: 2014-05-27Bibliographically approved

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