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Modélisation thermodynamique de l'interaction entre le verre et les phases molybdates.

Résumé : Fission products and actinides arising from the spent UOX fuel reprocessing are vitrified in borosilicate glass matrices. Among the fission products, platinum-group metals (Pd-Rh-Ru) exhibit very low solubility and partly precipitate as metal or oxide phases in the glass melt. Molybdenum can form molybdate phases which are known to precipitate in the glass as a complex molybdate phase called yellow phase. These molybdate phases may induce modifications of the physico-chemistry of the glass melt and have an impact on the final glass confinement properties.To understand the relative stability of these phases depending on both temperature and oxygen potential of the melt, a thermodynamic database is being developed using the Calphad method.This database includes the metallic and oxide complex platinoid system and the interactions with tellurium Pd-Rh-Ru-Te-(O). To consider the formation of molybdates, the CaO-MoO$_3$ and of Na$_2$O-MoO$_3$ pseudo binary systems are taken into account. The modeling of Na$_2$O-SiO$_2$ and of the ternary SiO$_2$-Na$_2$O-MoO$_3$ system was carried out based on the literature and on new experiments performed at the CEA.Using this tool, the thermodynamic state of the molybdate phases is calculated as a function of temperature and composition and the ruthenium redox behavior is predicted as a function of temperature and oxygen pressure in the melt. This study throws new light on the interactions between molybdenum and platinum-group metals with the glass melt during the vitrification process of high level nuclear waste.
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  • HAL Id : cea-02509088, version 1

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S. Bordier, S. Gossé, J. Rogez, S. Schuller, J.-L. Flèche. Modélisation thermodynamique de l'interaction entre le verre et les phases molybdates.. 2ème réunion sur la Thermodynamique des Matériaux Haute Température organisée par le GdR ThermatHT, Jan 2015, Annecy, France. ⟨cea-02509088⟩

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