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Application of the CALPHAD method to the thermodynamic modeling of a miscibility gap in the U-Nd-O phase diagram

Published online by Cambridge University Press:  27 January 2014

Giannina Dottavio ,
Yves Pontillon ,
Lionel Desgranges ,
Christine Gueneau  and
J-C. Dumas
Giannina Dottavio
Affiliation:
CEA, DEN, DEC, SA3C, LAMIR, F-13108 Saint Paul lez Durance, France.
Yves Pontillon
Affiliation:
CEA, DEN, DEC, SA3C, LAMIR, F-13108 Saint Paul lez Durance, France.
Lionel Desgranges
Affiliation:
CEA, DEN, DEC, SESC, LLCC, F-13108 Saint Paul lez Durance, France.
Christine Gueneau
Affiliation:
CEA, DEN, DPC, SCCME, LM2T, F-91191 Gif-sur-Yvette, France.
J-C. Dumas
Affiliation:
CEA, DEN, DEC, SESC, LLCC, F-13108 Saint Paul lez Durance, France.
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Abstract

During neutron irradiation in nuclear power plants, uranium dioxide (UO2), the most used nuclear fuel, changes gradually its chemical composition because of the incorporation of new chemical elements which are created by fissions and named Fission Products (FP). As a consequence, the fluorine-type crystalline structure and its lattice parameters may also be modified. In order to better understand this behavior, neodymium-doped UO2 ceramics have been prepared with the aim to simulate the crystallographic matrix of irradiated fuels, since Nd is one of the most abundant FP. In a previous work, high temperature X-ray diffraction was performed on a sample (U0.72Nd0.28)O2, annealed under reducing conditions. The diffractograms evidenced, for the first time, the existence of a miscibility gap in the U-Nd-O system.

In this paper, we present the first results of a thermodynamic modeling of the ternary system U-Nd-O based on the CAlculation of PHAse Diagrams (CALPHAD) method, in order to obtain a complete description of this miscibility gap. The very first results of this modeling seem to confirm the presence of a region presenting two FCC (fluorite) phases (instead of a single solid solution, which is expected from literature). At room temperature, the gap appears from a Nd content as small as about 0.02 at. % and an O/M ratio slightly lower than 2.

Keywords

nuclear materialscrystallographic structurephase transformation
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1645: Symposium EE/ZZ – Advanced Materials in Extreme Environments , 2014 , mrsf13-1645-ee04-04
Copyright
Copyright © Materials Research Society 2014 

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