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Vacancy formation and solid solubility in the U-Zr-N system
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.ORCID iD: 0000-0002-6082-8913
2010 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 406, no 3, 351-355 p.Article in journal (Refereed) Published
Abstract [en]

For the purpose of developing a nuclear fuel with enhanced thermophysical properties and better irradiation performance density functional theory calculations are used to explore UN, ZrN and (U, Zr)N. Negative deviation of ground state energy from the ideal solution model as well as energetically favourable maximal distance between substitutional metal atoms in respective nitrides indicate mutual solubility of UN and ZrN at all temperatures. Nitrogen vacancy formation energies in UN (1.81 eV) and ZrN (1.40 eV) are considerably lower than metal vacancy formation energies. A substitutional Zr atom in UN has little effect on nitrogen vacancy formation energies (similar to 1.79 eV), while U in ZrN decreases the value by similar to 0.1 eV (similar to 1.30 eV) due to elastic stress and charge density redistribution in the material. The relative distance between a substitutional metal atom and a vacancy in UN has little influence over the radially declining displacement pattern induced by the substitutional atom, while in ZrN the relaxation of atoms is governed by the position of the vacancy. The calculated vacancy formation energies indicate a lower surface energy of ZrN in comparison with UN.

Place, publisher, year, edition, pages
2010. Vol. 406, no 3, 351-355 p.
Keyword [en]
Material Property Correlations, Uranium-Nitrogen System, Advanced Nuclear-Fuels, Thermodynamic Properties, Point-Defects, Mononitride, Nitride, 1st-Principles
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-27681DOI: 10.1016/j.jnucmat.2010.09.006ISI: 000284750400009Scopus ID: 2-s2.0-78049241493OAI: oai:DiVA.org:kth-27681DiVA: diva2:380478
Funder
Swedish Research Council, 90399101
Note

QC 20101221

Available from: 2010-12-21 Created: 2010-12-20 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Experimental and theoretical studies of nitride fuels
Open this publication in new window or tab >>Experimental and theoretical studies of nitride fuels
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With respect to nitrides being considered as potential fast reactor fuels, research is conducted on the out-of-pile thermophysical properties, sintering and fabrication processes, gas migration mechanisms, self-diffusion and point defect behaviour of actinide nitrides, their surrogate materials, and the inert matrix material ZrN . The experimental research, carried out in the framework of qualifying fuel for the European Lead Cooled Training Reactor (ELECTRA), shows that sintered ZrN and (Dy,Zr)N pellet densities are influenced by the oxygen concentration in the material. The effect is confirmed in sintered (Pu,Zr)N pellets. Oxygen concentration also plays a role in the thermophysical properties of inert matrix nitride fuels, but does not have an impact on the electrical properties of these materials. With the fuel fabrication methods applied here, clean nitride powders can be synthesized. However, the subsequent fabrication phases, including milling and solid solution formation, increases the impurity levels significantly. Research of equal importance is performed on materials free of fabrication-induced impurities, whose properties are studied by employing first-principles methods. ZrN, UN and (U,Zr)N are studied, whereas the results from ZrN are expected to be applicable for actinide nitrides as a first approximation. The migration of noble gases in ZrN, on the atomic scale, confirms the experimentally observed tendency for noble gases with higher atomic number to be retained in the fuel matrix, while the majority of He is released to the fuel pin. Materials modelling implies that self-diffusion of nitrogen and metal atoms in inert matrix nitride fuels is accelerated under irradiation, since noble gas retention reduces migration barriers which govern self-diffusion. Unlike Kr and Xe, He has the capacity to be released into the fuel matrix, after having been trapped in a vacancy. The results are expected to aid in providing an explanation to the macroscopic diffusion phenomena in nitride fuels, as the diffusion behaviour of noble gases is sparsely studied. In addition, a study on the miscibility of ZrN and UN in a narrow composition range suggests solubility, based on the negative mixing energies. The results obtained from research on inert matrix nitride fuel underline several beneficial properties which are desirable in a fast reactor fuel. The relevance of these results is analyzed and contextualized in the thesis, from the perspective of current research and development in the field.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 74 p.
Series
Trita-FYS, ISSN 0280-316X ; 12013:18
Keyword
fast reactor fuel, ab-initio modelling, fuel fabrication, inert matrix nitride fuel
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-123521 (URN)978-91-7501-794-5 (ISBN)
Public defence
2013-06-14, FD5, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20130611

Available from: 2013-06-11 Created: 2013-06-10 Last updated: 2013-06-11Bibliographically approved

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Wallenius, Jan

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