HAL Id: cea-02489475
https://hal-cea.archives-ouvertes.fr/cea-02489475
Submitted on 24 Feb 2020
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Thermodynamic assessment of platinoid and molybdate phases in nuclear waste glasses
S. Gosse, S. Bordier, C. Gueneau, N. Dupin, J. Rogez, P. Benigni
To cite this version:
S. Gosse, S. Bordier, C. Gueneau, N. Dupin, J. Rogez, et al.. Thermodynamic assessment of platinoid and molybdate phases in nuclear waste glasses. CALPHAD XLIV - International Conference on Computer Coupling of Phase Diagrams and Thermochemistry, May 2015, Loano, Italy. �cea-02489475�
No data
The modeling of CaO-MoO3, Na2O-MoO3, Na2MoO4-CaMoO4 and of SiO2 -Na2O-MoO3 systems has been carried out. This study makes it possible to predict the formation of the molybdate phases in the simplified glass melt. The next step will focus on the introduction of B2O3 in the database to get closer to the real industrial glass composition.
The Pd-Se and Pd-Te systems have been modeled. An assessment of the Pd-Se-Te system will be available soon. In parallel, the Rh-Ru-O database enables to calculate the speciation of the platinoids in the glass as a fuction of oxygen potential and temperature.
Background of the study: Vitrification of the nuclear high level wastes
Results of the modeling
Conclusions and prospects
Thermodynamic assessment of platinoid and
molybdate phases in the nuclear waste glasses
Demixing phenomena of molybdate phases in a glass melt Courtesy of Sophie Schuller, CEA Marcoule
Pd-Se
Na
2O-SiO
2Na
2MoO
4-CaMoO
4Activity of Na2O in Na2O-SiO2
CALPHAD XLIV – May 31 – June 5, 2015 | Loano, Italy
S. Gossé
1, S. Bordier
1, C. Guéneau
1, N. Dupin
2, J. Rogez
3,P. Benigni
31 DEN,DANS,DPC,SCCME,LM2T CEA Centre de Saclay – 91191 Gif-sur-Yvette Cedex, France 2 Calcul Thermodynamique, 3 rue de l'avenir, 63670 Orcet, France
3 IM2NP, Faculté des Sciences et Techniques, Marseille, France
Fission products and actinides arising from the spent UOX fuel reprocessing are vitrified in borosilicate glasses. Among the fission products, platinum-group metals (Pd-Rh-Ru) exhibit very low solubility and partly precipitate as metal or oxide phases in the melt, molybdenum interacts with the glass frit to form molybdate phases known to precipitate as a complex phase called “yellow phase”. These platinoid and molybdate phases may induce modifications of the physico-chemistry of the glass melt and alter 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.
To consider the formation of molybdates, the CaO-MoO3 and the Na2 O-MoO3 pseudo-binary systems are assessed. The modeling of the Na2 O-SiO2, MoO3-SiO2 and of the ternary SiO2-Na2O-MoO3 system was carried out based on the literature and on new experiments in order to consider a simplified glass melt. Furthermore, the developed database includes the metallic and oxide complex platinoid system and some of the interactions with selenium and tellurium: Pd-Rh-Ru-Se-Te-(O).
Using this tool, the thermodynamic behavior of the platinoid and molybdate phases is calculated as a function of temperature and composition. This study throws new light on the interactions between poorly soluble fission products and the glass melt during the vitrification process of high level nuclear wastes.
Molybdate and simplified glass melt phase diagrams
Platinoids
Na
2O-MoO
3CaO-MoO
3This work will help to predict the high temperature interactions between some poorly soluble fission products (Mo, Pd, Rh, Ru) and the glass melt during the vitrification process, of nuclear wastes
Molybdate/Glass melt phase separation: the ternary system CaO-Na
2O-SiO
2-MoO
3Enthalpy increment of Na2MoO4
No data
Reassessed from Zang et al. due to a high temperature liquid miscibility gap
Mixing enthalpy of Na2O-SiO2
Ternary system Rh-Ru-O
Partial mixing enthalpy in liquid Pd-Se
The CaO-Na2O-SiO2-MoO3 system is a simplified melt representative for the industrial glass melt.
Thermodynamic calculations will make
it possible to predict the high
temperature behavior of molybdate
phases during the vitrification process of nuclear wastes
Pouring of inactive glass melt CEA Marcoule
