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<p>The oxidation of UO<sub>2</sub> in Ar–O<sub>2</sub> atmospheres was studied at temperatures between 350&#xa0;°C and 600&#xa0;°C and for oxygen partial pressures (pO<sub>2</sub>) between 0.20&#xa0;atm and 0.70&#xa0;atm. The experiments were carried out on both powder samples and discs cut from sintered pellets. Oxidation kinetics were monitored by TGA and the oxides formed were characterised by XRD, SEM and specific surface area (SSA) measurements. Whatever the temperature or pO<sub>2</sub> tested, total oxidation of UO<sub>2</sub> to U<sub>3</sub>O<sub>8</sub> was systematically observed. At all temperatures studied, the conversion of UO<sub>2</sub> to U<sub>3</sub>O<sub>8</sub> seemed to involve the formation of an intermediate oxide, which could be U<sub>3</sub>O<sub>7</sub>. Experiments carried out on powders with different SSA appeared to show that the effect of solid texture predominates over the effect of temperature in the formation (or non-formation) of intermediate oxides. An increase in pO<sub>2</sub> systematically led to an increase in the UO<sub>2</sub> oxidation rate. On the other hand, an increase in the oxidation temperature seemed to cause a decrease in the density of cracks propagating through the samples, probably due to an increase in the plasticity of U<sub>3</sub>O<sub>8</sub>. The inert marker experiment also showed an inward growth of U<sub>3</sub>O<sub>8</sub> involving anionic sublattice point defects.</p>

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Effects of Temperature and O2 Partial Pressure on the Kinetics and Mechanisms of UO2 Oxidation to U3O8

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年9月3日

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  • Priscilla Berenguer-Besnard,
  • Loïc Marchetti,
  • Philippe Martin,
  • Laetitia Vieille,
  • Loïc Favergeon

摘要

The oxidation of UO2 in Ar–O2 atmospheres was studied at temperatures between 350 °C and 600 °C and for oxygen partial pressures (pO2) between 0.20 atm and 0.70 atm. The experiments were carried out on both powder samples and discs cut from sintered pellets. Oxidation kinetics were monitored by TGA and the oxides formed were characterised by XRD, SEM and specific surface area (SSA) measurements. Whatever the temperature or pO2 tested, total oxidation of UO2 to U3O8 was systematically observed. At all temperatures studied, the conversion of UO2 to U3O8 seemed to involve the formation of an intermediate oxide, which could be U3O7. Experiments carried out on powders with different SSA appeared to show that the effect of solid texture predominates over the effect of temperature in the formation (or non-formation) of intermediate oxides. An increase in pO2 systematically led to an increase in the UO2 oxidation rate. On the other hand, an increase in the oxidation temperature seemed to cause a decrease in the density of cracks propagating through the samples, probably due to an increase in the plasticity of U3O8. The inert marker experiment also showed an inward growth of U3O8 involving anionic sublattice point defects.