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Platinoid Group Metals Thermodynamics for Nuclear Waste Applications The Pd-Rh-Ru-Te-O System

Authors
  • Gosse, S.
  • Laurin, C.
  • Regnier, E.
  • Bonnet, C.
  • Gueneau, C.
  • Pinet, O.
Publication Date
Oct 14, 2018
Source
OpenGrey Repository
Keywords
Language
English
License
Unknown
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Abstract

The platinoid elements (Pd-Rh-Ru) exhibit very low solubility into borosilicate matrixes during vitrification process of nuclear High-Level Wastes (HLW).Due to their large affinity towards chalcogen elements O from the glass frit, Te and Se from the fission product solution, they mainly precipitate both under (Pd-Te, Pd-Rh-Ru) metallic alloys and needle-shaped or polyhedral (Rh,Ru)O2 oxide phases. Both composition and microstructures of these precipitates can affect significantly the physico-chemical properties and the electrical or thermal conductivities of the glass melt during melting in hot or cold crucible.For decades, many studies were undertaken at CEA to point out the chemical reactions in the liquid and viscous states between the glass matrix and the platinoids issuing from the calcinated waste. In parallel to these experimental studies, a Calphad database is being developed to address the thermodynamics of the metallic and oxide systems considered in these interactions.The objective of this thermodynamic database is to provide an overall thermodynamic description of the platinoid phases in nuclear waste glasses. At this point, all the binaries in the Pd-Rh-Ru-Te-O system have been modelled.This flexible tool also enables to calculate phase diagrams and thermodynamic properties to predict the relative stability between metallic and oxide phases as a function of temperature and oxygen potential mainly fixed by the glass frit.Using this thermodynamic approach, the consideration of the RedOx equilibria for some Pd-Rh-Ru-Te based phases makes it possible to explain the speciation between oxide and metallic precipitates.

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