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Inhibition of radiation induced dissolution of UO2 by sulfide-A comparison with the hydrogen effect
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: 0000-0003-0552-6282
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: 0000-0003-0663-0751
2013 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 434, no 1-3, 38-42 p.Article in journal (Refereed) Published
Abstract [en]

In this work we have studied the influence of H2S on radiation induced dissolution of spent nuclear fuel using simple model systems. The reaction between H2O2 and H2S/HS- has been studied experimentally as well as the effect of H2S/HS - on γ-radiation induced dissolution of a UO2 pellet. The experiments clearly show that the reaction of H2O 2 and H2S/HS- is fairly rapid and that H 2O2 and H2S/HS- stoichiometry is favorable for inhibition. Radiolysis experiments show that H2S/ HS- can effectively protect UO2 from oxidative dissolution. The effect depends on sulfide concentration in combination with dose rate. Autoclave experiments were also conducted to study the role of H 2S/HS- in the reduction of U(VI) in the presence and absence of H2 and Pd particles in anoxic aqueous solution. The aqueous solutions were pressurized with H2 or N2 and two different concentrations of H2S/HS- were used in the presence and absence of Pd. No catalytic effect of Pd on the U(VI) reduction by H2S/HS- could be found in N2 atmosphere. U(VI) reduction was found to be proportional to H2S/HS- concentration in H2 and N2 atmosphere. It is clearly shown the Pd catalyzed H2 effect is more powerful than the effect of H2S/HS-. H2S/HS- poisoning of the Pd catalyst is not observed under the present conditions.

Place, publisher, year, edition, pages
2013. Vol. 434, no 1-3, 38-42 p.
Keyword [en]
Anoxic aqueous solutions, Autoclave experiments, Catalytic effects, Dose rate, Hydrogen effect, Model system, Oxidative dissolution, Pd catalyst, Pd particle, Radiation-induced, Spent nuclear fuels, Sulfide concentration, Experiments, Hydrogen, Radiation chemistry, Radioactive wastes, Solutions, Stoichiometry, Dissolution
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:kth:diva-118121DOI: 10.1016/j.jnucmat.2012.10.050ISI: 000315752000006Scopus ID: 2-s2.0-84871742513OAI: oai:DiVA.org:kth-118121DiVA: diva2:604880
Note

QC 20130212

Available from: 2013-02-12 Created: 2013-02-12 Last updated: 2017-04-21Bibliographically approved
In thesis
1. Radiation Induced Processes at Solid-Liquid Interfaces
Open this publication in new window or tab >>Radiation Induced Processes at Solid-Liquid Interfaces
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the thesis, the reactions between water radiolysis products—H2O2, HO• and O2—with metals and metal oxides utilized in nuclear industry are studied. The reactions include not only surface reactions, e.g. redox reactions and catalytic decomposition of H2O2, but also solution reactions (Haber-Weiss reactions). To study the interfacial reactions, it is crucial to monitor the dissolution of the solid material, reactivity of H2O2 and formation of the intermediate hydroxyl radicals.Hydroxyl radicals are captured by probe (Tris or methanol) to generate CH2O which can be quantified by the modified Hantzsch method. The results from γ-irradiation experiments on homogeneous system show that the conversion yield of CH2O from hydroxyl radicals is affected by O2 and pH. A mechanism of CH2O production from Tris is proposed.Besides, the consumption rate of H2O2 in the H2O2/ZrO2/Tris system is found to be influenced by Tris. A mechanism for the catalytic decomposition of H2O2 upon ZrO2 surface is proposed which includes independent surface adsorption sites for H2O2 and Tris. Moreover, it is demonstrated that the deviation of detected CH2O concentration by the modified Hantzsch method from actual concentration increases with increasing [H2O2]0/[CH2O]0.The inhibition of sulfide on the radiation induced dissolution of UO2 is confirmed and is dependent on sulfide concentration. And the inhibition of sulfide is independent to that of H2/Pd.It is found that the reactivity of H2O2 and dynamics of CH2O formation are different for the studied materials in the H2O2/MxOy/Probe system. The kinetic parameters, such as rate constant, activation energy, frequency factors are determined.Both surface and solution reactions are observed in the aqueous W(s)/H2O2/Tris system. It is also demonstrated that Haber-Weiss reactions which produce HO• continuously are dominating. Furthermore, it is found that hydroxyl radicals are formed simultaneously during the dissolution of W in aerobic aqueous system.The knowledge conveyed by the thesis is relevant to nuclear technological applications, as well as the applications related in photocatalysis, biochemistry, corrosion science, catalysis and optics/electronics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 74 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:39
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-172421 (URN)978-91-7595-656-5 (ISBN)
Public defence
2015-09-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150826

Available from: 2015-08-26 Created: 2015-08-21 Last updated: 2015-08-26Bibliographically approved
2. 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)
Opponent
Supervisors
Note

QC 20170421

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

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