Thermodynamic Modelling of the Pd-Ru-Te-O for Nuclear High-Level Waste Immobilization
Résumé
Pd and Ru are the main platinoid fission products formed during burnup of nuclear fuels. During fuel reprocessing, these element partly dissolve in nitric acid and they exhibit very low solubility into borosilicate glasses during the vitrification process. Due to their affinity towards tellurium from the fission product solution, palladium mainly precipitates under (Pd-Te) intermetallics [1] and ruthenium is likely to form hcp solid solutions [2]. The composition and microstructures of these phases are also sensitive to oxygen potential [3]; oxydation of ruthenium can lead to needle-shaped or polyhedral (Rh,Ru)O2 oxide phases [4]. These precipitates can affect significantly the physico-chemical properties of the glass melt during melting in hot or cold crucible.
For decades, many studies were undertaken at CEA [5] to point out the high temperature interactions of the platinum group metals (PGM) issuing from the calcinated waste. In parallel to these studies, a Calphad database is being developed to address the thermodynamics of such systems to provide an assessment of the PGMs in nuclear waste.
This study presents the assessed binary systems. Some calculations are also performed to highlight how this flexible tool makes is used to predict the stability between metallic and oxide phases as a function of temperature and oxygen potential mainly driven by the glass.
[1] S. Gossé, C. Guéneau, Intermetallics 19 (2011) 621-629
[2] S. Gossé, N. Dupin, C. Guéneau, J.-C. Crivello, J.-M. Joubert, J. Nuclear Mater 474 (2016) 163-173
[3] S. Gossé, S. Bordier, C. Guéneau, E. Brackx, R. Domenger, J. Rogez, J. Nuclear Mater 500 (2018) 252-264
[4] R. Pflieger, L. Lefebvre, M. Malki, M. Allix, A. Grandjean, J. Nuclear Mater 389 (2009)
J. Nuclear Mater, Vol. 389, N°3
[5] O. Pinet, S. Mure, Journal of Non-Crystalline Solids, 355 (2009) 221-227