High temperature chromium volatilization from Cr2O3 powder and Cr2O3-doped UO2 pellets in reducing atmospheres

Autor: Jean-Claude Palussière, Marie Andrieu, Véronique Peres, Christine Delafoy, Loïc Favergeon, Julien Balland, Michèle Pijolat
Přispěvatelé: Laboratoire des Procédés en Milieux Granulaires (LPMG-EMSE), École des Mines de Saint-Étienne (Mines Saint-Étienne MSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-Centre National de la Recherche Scientifique (CNRS), Centre Sciences des Processus Industriels et Naturels (SPIN-ENSMSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT), Procédés et REactivité des Systèmes Solide-gaz, Instrumentation et Capteurs (PRESSIC-ENSMSE), Institut Mines-Télécom [Paris] (IMT)-Institut Mines-Télécom [Paris] (IMT)-SPIN, AREVA NP, AREVA NP - Centre Technique (FRANCE), Areva NP, Areva NP FBFC
Rok vydání: 2012
Předmět:
Zdroj: Journal of Nuclear Materials
Journal of Nuclear Materials, Elsevier, 2012, 423 (1-2), pp.93-101. ⟨10.1016/j.jnucmat.2012.01.001⟩
ISSN: 0022-3115
Popis: Chromium volatilization from Cr 2 O 3 powder and Cr 2 O 3 -doped UO 2 pellets during sintering in reducing atmospheres has been studied by thermogravimetry (TG) coupled with differential thermal analysis (DTA) up to 1700 °C. The sintering of Cr 2 O 3 -doped UO 2 pellets was also followed by dilatometry. Oxygen partial pressures in the range 10 −20 –10 −11 atm (10 −15 –10 −6 Pa) have been fixed in all the experiments thanks to mixtures of hydrogen and carbon dioxide. A linear heating rate of 20 °C min −1 was applied to all the experiments. The dopant amount was in the range 0.18–0.9 mol% Cr in UO 2 . For all the oxygen potentials, the mass loss of Cr 2 O 3 powder was found to start at temperatures as high as 1470 °C due to Cr 2 O 3 dissociation, the lower the oxygen potential, the lower the starting temperature and the higher the volatilized amount. For intermediate oxygen potentials, an exothermic DTA peak observed during cooling, from 1700 °C to room temperature, attested for the crystallization of a liquid phase which was attributed to CrO (l) according to thermodynamic predictions. Then, the dilatometry and TG studies allowed following the behavior of Cr 2 O 3 -doped UO 2 pellets. The mass loss at temperatures higher than 1470 °C was attributed to chromium volatilization for all the doped samples. During the sintering of doped UO 2 pellets, the liquid phase CrO (l) seemed to appear at a lower oxygen potential than in Cr 2 O 3 powder, which probably contributed to enhance the densification rate. For the highest dopant amount, 0.9 mol% Cr, the volatilization process was found to be rather similar to that of Cr 2 O 3 powder, due to the part of chromia not solubilized in the UO 2 crystal. Moreover, as the initial pellets were not dense, as long as the pellet porosity remained open, the chromia particles were able to dissociate as in the Cr 2 O 3 powder. Thus the volatilization of chromium from doped UO 2 pellets under sintering in reducing atmospheres must be understood as the result of several phenomena whose contribution depends on temperature, oxygen potential and heating rate: before the porosity closure, both dissociation of chromia into Cr(g) and oxygen from excess Cr 2 O 3 particles, and Cr volatilization from doped UO 2 particles; then chromium volatilization from the doped UO 2 ceramic during further densification process.
Databáze: OpenAIRE
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