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Surface Reactions of H2O2, H-2, and O-2 in Aqueous Systems Containing ZrO2
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0552-6282
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0596-0222
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-2673-075X
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0663-0751
2016 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 3, 1609-1614 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

In radiolysis of water, three molecular products are formed (H2O2, O-2, and H-2). It has previously been shown that aqueous hydrogen peroxide is catalytically decomposed on many oxide surfaces and that the decomposition proceeds via the formation of surface-bound hydroxyl radicals. In this work, we have investigated the behavior of aqueous H-2 and O-2 in contact with ZrO2. Experiments were carried out in an autoclave with high H2 pressure and low O-2 pressure (40 and 0.2 bar, respectively). In the experiments the concentration of H-abstracting radicals was monitored as a function of time using tris(hydroxymethyl)aminomethane (Tris) as scavenger and the subsequent formation of formaldehyde to probe radical formation. The plausible formation of H2O2 was also monitored in the experiments. In addition, density functional theory (employing the hybrid PBE0 functional) was used to search for reaction pathways. The results from the,experiments show that hydrogen-abstracting radicals: are formed in the aqueous H2O2-system in contact with solid ZrO2. Formation of H2O2 is also detected, and the time dependent production of hydrogen-abstracting radicals follows the time-dependent H2O2 concentration, strongly:indicating that the radicals are produced upon catalytic decomposition of H2O2. The DFT study implies that H2O2 formation proceeds via a pathway where HO2 is a key intermediate. It is interesting to note that all the stable molecular products from aqueous radiolysis are precursors of quite intriguing radical reactions at water/oxide interfaces.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016. Vol. 120, no 3, 1609-1614 p.
National Category
Engineering and Technology Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-182780DOI: 10.1021/acs.jpcc.5b10491ISI: 000369116100026Scopus ID: 2-s2.0-84956691050OAI: oai:DiVA.org:kth-182780DiVA: diva2:906037
Note

QC 20160223

Available from: 2016-02-23 Created: 2016-02-23 Last updated: 2017-04-21Bibliographically approved
In thesis
1. Experimental studies of radiation-induced dissolution of UO2: The effect of intrinsic solid phase properties and external factors
Open this publication in new window or tab >>Experimental studies of radiation-induced dissolution of UO2: The effect of intrinsic solid phase properties and external factors
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dissolution of the UO2 matrix is one of the potential routes for radionuclide release in a future deep geological repository for spent nuclear fuel. This doctoral thesis focuses on interfacial reactions of relevance in radiation-induced dissolution of UO2 and is divided in two parts:

In the first part, we sought to explore the effects of solid phase composition:

The impact of surface stoichiometry on the reactivity of UO2 towards aqueous radiolytic oxidants was studied. H2O2 reacts substantially faster with stoichiometric UO2 than with hyperstoichiometric UO2. In addition, the release of uranium from stoichiometric UO2 is lower than from hyperstoichiometric UO2. The behavior of stoichiometric powder changes with exposure to H2O2, approaching the behavior of hyperstoichiometric UO2 with the number of consecutive H2O2 additions.

The impact of Gd-doping on the oxidative dissolution of UO2 in an aqueous system was investigated. A significant decrease in uranium dissolution and higher stability towards H2O2 for (U,Gd)O2 pellets compared to standard UO2 was found.

In the second part, we sought to look at the effect of external factors:

The surface reactivity of H2 and O2 was studied to understand the overall oxide surface reactivity of aqueous molecular radiolysis products. The results showed that hydrogen-abstracting radicals and H2O2 are formed in these systems. Identical experiments performed in aqueous systems containing UO2 powder showed that the simultaneous presence of H2 and O2 enhances the oxidative dissolution of UO2 compared to a system not containing H2.

The effect of groundwater components such as bentonite and sulfide on the oxidative dissolution of UO2 was also explored. The presence of bentonite and sulfide in water could either delay or prevent in part the release of uranium to the environment. The Pd catalyzed H2 effect is more powerful than the sulfide effect. The poisoning of Pd catalyst is not observed under the conditions studied.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 77 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:23
Keyword
Oxidation, dissolution, uranium dioxide, gadolinium, bentonite, sulfide, hydrogen, gamma radiation, radiolysis, hydrogen peroxide, hydroxyl radical, repository
National Category
Physical Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-205605 (URN)978-91-7729-343-9 (ISBN)
Public defence
2017-05-12, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20170421

Available from: 2017-04-21 Created: 2017-04-20 Last updated: 2017-04-21Bibliographically approved

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