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Gosse S.,CEA Saclay Nuclear Research Center | Dupin N.,Calcul Thermodynamique | Gueneau C.,CEA Saclay Nuclear Research Center | Crivello J.-C.,CNRS East Paris Institute of Chemistry and Materials Science | Joubert J.-M.,CNRS East Paris Institute of Chemistry and Materials Science
Journal of Nuclear Materials | Year: 2016

Palladium, rhodium and ruthenium are abundant fission products that form in oxide fuels in nuclear reactors. Under operating conditions, these Platinum-Group Metal (PGM) fission products accumulate in high concentration at the rim of the oxide fuel and mainly precipitate into metallic solid solutions. Their thermochemistry is of significant interest to predict the high temperature chemical interactions between the fuel and the cladding or the possible precipitation of PGM phases in high level nuclear waste glasses. To predict the thermodynamic properties of these PGM fission products, a thermodynamic modeling is being developed on the ternary Pd-Rh-Ru system using the Calphad method. Because experimental thermodynamic data are scarce, Special Quasirandom Structures coupled with Density Functional Theory methods were used to calculate mixing enthalpy data in the solid solutions. The resulting thermodynamic description based on only binary interaction parameters is in good agreement with the few data on the ternary system. © 2016 Elsevier B.V. All rights reserved. Source

Stein F.,Max Planck Institute Fur Eisenforschung | He C.,Guangxi University | Dupin N.,Calcul Thermodynamique
Intermetallics | Year: 2013

The central part of the Al-Co phase diagram is dominated by the high-melting B2 CoAl phase. Although this phase is well-known since long and has been intensively investigated in the literature, neither its melting behaviour nor its homogeneity range is well established. Therefore, a series of Al-Co alloys in the composition range 30-60 at.% Co were produced and analysed by differential thermal analysis, scanning electron microscopy, and electron-probe microanalysis. The composition dependence of the melting temperatures was determined and from the analysis of heat-treated, two-phase CoAl + Al 5Co2 samples, the Al-rich phase boundary of the CoAl phase and the Co-rich boundary of the Al5Co2 phase were established. The melting temperatures of CoAl were found to be significantly higher than previously reported in the literature; for the stoichiometric compound a value of 1673 C was obtained. On the basis of these new results and further relevant literature data, the complete Al-Co phase diagram was finally thermodynamically re-assessed applying the CALPHAD technique. The optimized thermodynamic parameters not only give a good description of the new experimental data, but also fit very well to most of the literature data. © 2013 Elsevier Ltd. All rights reserved. Source

Breidi A.,CNRS East Paris Institute of Chemistry and Materials Science | Andasmas M.,CNRS East Paris Institute of Chemistry and Materials Science | Crivello J.-C.,CNRS East Paris Institute of Chemistry and Materials Science | Dupin N.,Calcul Thermodynamique | Joubert J.-M.,CNRS East Paris Institute of Chemistry and Materials Science
Journal of Physics Condensed Matter | Year: 2014

In order to clarify controversial reports on the Fe-Re phase diagram, a new experimental investigation has been carried out. Three intermetallic phases have been evidenced, including the new report of the P phase found for the first time in a binary system. The phase relations involving the σ phase were established. In parallel, a first-principles study has been performed which provided the heat of formation of every ordered configuration for four intermetallic phases (D8b, A12, A13 and P). The mixing energy of solid solutions (fcc, bcc, hcp) was calculated using the special quasi-random structure method. Calculations were performed with the help of the density functional theory, with and without spin polarization. From these results, in the frame of the Compound Energy Formalism using the Bragg-Williams approximation, the Fe-Re phase diagram has been computed without the use of adjustable parameters. Different thermodynamic parameters obtained experimentally and theoretically, as the site occupancies, are compared. The computed phase diagram presents several differences with the experimental one. To understand these differences, the influence of several parameters on the phase stability, such as the magnetic contribution has been evaluated. © 2014 IOP Publishing Ltd. Source

Berche A.,CEA Saclay Nuclear Research Center | Dupin N.,Calcul Thermodynamique | Gueneau C.,CEA Saclay Nuclear Research Center | Rado C.,CEA Marcoule Nuclear Site | And 2 more authors.
Journal of Nuclear Materials | Year: 2011

Within the framework of a complex Calphad thermodynamic database for the 4th generation nuclear fuels, called Fuelbase, the description of different binary systems involving U are obtained. For most of the systems considered, only limited experimental work is available, often without any thermodynamic data. Assumptions as simple as possible were made in order to derive descriptions showing a reasonable agreement with experimental data and which allow to extrapolate in complex systems. © 2011 Elsevier B.V. All rights reserved. Source

Kormann F.,Max Planck Institute Fur Eisenforschung | Breidi A.A.H.,Ruhr University Bochum | Dudarev S.L.,Culham Center for Fusion Energy | Dupin N.,Calcul Thermodynamique | And 5 more authors.
Physica Status Solidi (B) Basic Research | Year: 2014

This paper provides a comprehensive overview of state-of-the-art computational techniques to thermodynamically model magnetic and chemical order-disorder transitions. Recent advances as well as limitations of various approaches to these so-called lambda transitions are examined in detail, focussing on calphad models and first-principles methods based on density functional theory (DFT). On the one hand empirical implementations -based on the Inden-Hillert-Jarl formalism -are investigated, including a detailed interpretation of the relevant parameters, physical limiting cases and potential extensions. In addition, Bragg-Williams-based approaches as well as cluster-variation methods of chemical order-disorder transitions are discussed. On the other hand, it is shown how magnetic contributions can be introduced based on various microscopic model Hamiltonians (Hubbard model, Heisenberg model and beyond) in combination with DFT-computed parameters. As a result of the investigation we were able to indicate similarities between the treatment of chemical and magnetic degrees of freedom as well as the treatment within the calphad and DFT approaches. Potential synergy effects resulting from this overlap have been derived and alternative approaches have been suggested, in order to improve future thermodynamic modelling of lambda transitions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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