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GGA plus U study of uranium mononitride: A comparison of the U-ramping and occupation matrix schemes and incorporation energies of fission products
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.ORCID iD: 0000-0002-4158-0123
KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
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2016 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 478, 119-124 p.Article in journal (Refereed) Published
Abstract [en]

Uranium mononitride is studied in the DFT + U framework. Its ground state is investigated and a study of the incorporation of diverse fission products in the crystal is conducted. The U-ramping and occupation matrix control (OMC) schemes are used to eliminate metastable states. Beyond a certain amount of introduced correlation, the OMC scheme starts to find a lower total energy. The OMC scheme is chosen for the second part of this study. Furthermore, the influence of the magnetic ordering is studied using the U-ramping method, showing that antiferromagnetic order is the most stable one when the U parameter is larger than 1.75 eV. The effect on the density of states is investigated and elastic constants are provided for comparison with other methods and experiments. The incorporation energies of fission products in different defect configurations are calculated and these energies are corrected to take into account the limited size of the supercell.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 478, 119-124 p.
Keyword [en]
Antiferromagnetism, Ground state, Uranium, Antiferromagnetic orderings, Defect configurations, Density of state, GGA + U, Meta-stable state, Mononitride, Super cell, Total energy
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-192387DOI: 10.1016/j.jnucmat.2016.06.007ISI: 000381644500015Scopus ID: 2-s2.0-84974560146OAI: oai:DiVA.org:kth-192387DiVA: diva2:969038
Note

QC 20160913

Available from: 2016-09-13 Created: 2016-09-12 Last updated: 2017-02-26Bibliographically 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. 107 p.
Series
TRITA-FYS, ISSN 0280-316X ; 73
Keyword
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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