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Transport properties in dilute UN(X) solid solutions (X = Xe, Kr)
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.ORCID iD: 0000-0002-4158-0123
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.ORCID iD: 0000-0002-2381-3309
2016 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 17, article id 174302Article in journal (Refereed) Published
Abstract [en]

Uranium nitride (UN) is a candidate fuel for current GEN III fission reactors, for which it is investigated as an accident-tolerant fuel, as well as for future GEN IV reactors. In this study, we investigate the kinetic properties of gas fission products (Xe and Kr) in UN. Binding and migration energies are obtained using density functional theory, with an added Hubbard correlation to model f electrons, and the occupation matrix control scheme to avoid metastable states. These energies are then used as input for the self-consistent mean field method which enables to determine transport coefficients for vacancy-mediated diffusion of Xe and Kr on the U sublattice. The magnetic ordering of the UN structure is explicitly taken into account, for both energetic and transport properties. Solute diffusivities are compared with experimental measurements and the effect of various parameters on the theoretical model is carefully investigated. We find that kinetic correlations are very strong in this system, and that despite atomic migration anisotropy, macroscopic solute diffusivities show limited anisotropy. Our model indicates that the discrepancy between experimental measurements probably results from different irradiation conditions, and hence different defect concentrations.

Place, publisher, year, edition, pages
2016. Vol. 94, no 17, article id 174302
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-196974DOI: 10.1103/PhysRevB.94.174302ISI: 000386894400002Scopus ID: 2-s2.0-84994624441OAI: oai:DiVA.org:kth-196974DiVA, id: diva2:1056007
Note

QC 20161213

Available from: 2016-12-13 Created: 2016-11-28 Last updated: 2017-11-29Bibliographically approved
In thesis
1. Multiscale modeling of nitride fuels
Open this publication in new window or tab >>Multiscale modeling of nitride fuels
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nitride fuels have always been considered a good candidate for GENIV reactors, as well as space reactors, due to their high fissile density, highthermal conductivity and high melting point. In these concepts, not beingcompatible with water is not a significant problem. However, in recent years,nitride fuels started to raise an interest for application in thermal reactors,as accident tolerant or high performance fuels. However, oxide fuels havebenefited from decades of intensive research, and thousands of reactor-years.As such, a large effort has to be made on qualifying the fuel and developingtools to help assess their performances.In this thesis, the modeling side of this task is chosen. The effort istwo-fold: determining fundamental properties using atomistic models andputting together all the properties to predict the performances under irradi-ation using a fuel performance code. The first part is done combining manyframeworks. The density functional theory is the basis to compute the elec-tronic structure of the materials, to which a Hubbard correction is added tohandle the strong correlation effects. Negative side effects of the Hubbardcorrection are tackled using the so-called occupation matrix control method.This combined framework is first tested, and then used to find electronic andmechanic properties of the bulk material as well as the thermomechanicalbehavior of foreign atoms. Then, another method, the self-consistent meanfield (SCMF) one, is used to reach the dynamics properties of these foreignatoms. In the SCMF theory, the data that were obtained performing the abinitio simulations are treated to provide diffusion and kinetic flux couplingproperties.In the second step of the work, the fuel performance code TRANSURA-NUS is used to model complete fuel pins. An athermal fission gas releasemodel based on the open porosity is developed and tested on oxide fuels.A model for nitride fuels is introduced, and some correlations are bench-marked. Major issues remaining are pointed out and recommendations asto how to solve them are made.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. p. 107
Series
TRITA-FYS, ISSN 0280-316X ; 73
Keywords
Uranium Nitride Ab Initio Modelling
National Category
Other Physics Topics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-202538 (URN)978-91-7729-182-4 (ISBN)
Public defence
2016-12-16, F3, Valhallavägen 79, Stockholm, 09:30 (English)
Opponent
Supervisors
Note

QC 20170227

Available from: 2017-02-27 Created: 2017-02-26 Last updated: 2017-02-27Bibliographically approved

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