A detailed study of UO2 to U3O8 oxidation phases and the associated rate-limiting steps

Rousseau, G.; Desgranges, Lionel; Charlot, F.; Millot, Nadine; Niepce, J.-C.; Pijolat, Michèle; Valdivieso, Françoise; Baldinozzi, Gianguido; Berar, Jf

doi:10.1016/j.jnucmat.2006.03.015

Cited by 103 publications

(111 citation statements)

References 28 publications

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“…It implies that cracking should be taken into account in order to interpret sigmoid weight gain curves. Considering Rousseau et al 12 and Valdivieso et al 7 kinetic tests, our results also evidence that macro-and micro-cracking occur in a kinetic domain where the assumption of the rate-limiting step is verified. That is why the kinetics of the oxidation reaction will be first discussed in the framework of this assumption; the case when this assumption is not verified will be treated afterwards.…”

Section: Discussionsupporting

confidence: 80%

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On the origin of the sigmoid shape in the UO2 oxidation weight gain curves

Quémard

Desgranges

Bouineau

et al. 2009

Journal of the European Ceramic Society

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International audienceCracking and spalling are known to occur during the oxidation of UO2. However, these phenomena are not considered by the existing kinetic models of the oxidation of UO2 into U3O8. In this study the oxidation of UO2 samples of various sizes from the single crystal to nanopowders, has been followed by isothermal and isobaric thermogravimetry, environmental scanning electron microscopy and in situ X-ray diffraction at temperatures ranging from 250 to 370°C in air. It has been shown that cracking occurs once a critical layer thickness of intermediate oxide has been reached, which corresponds to the beginning of the sigmoid kinetic curve. Cracking contribution to the sigmoid kinetic curve is then discussed as a function of temperature, and on the basis of nucleation and growth processes

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Section: Discussionsupporting

confidence: 80%

“…At 250 • C, Rousseau et al 12 performed the same kinetic tests as 7 to study the oxidation of the 5 m UO 2 powder at 250 • C and evidenced 4 different kinetic domains. The first two domains, numbered I and II, correspond to U 4 O 9 and U 3 O 7 formation.…”

Section: Low Temperature: 200-330 • Cmentioning

confidence: 99%

On the origin of the sigmoid shape in the UO2 oxidation weight gain curves

Quémard

Desgranges

Bouineau

et al. 2009

Journal of the European Ceramic Society

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“…[9][10][11][12][13][14][15] The UO 2 is oxidized to U 3 O 8 via intermediate phases of U 4 O 9 and U 3 O 7 , or a mixture of these two phases. 7,9,11,[13][14][15] The formation of U 3 O 7 /U 4 O 9 on UO 2 shows diffusion-controlled kinetics and follows the discretelayer mechanism. 7,9,11) The volume contraction caused by the formation of U 4 O 9 or U 3 O 7 causes inter-or trans-granular cracks to form at the surface of the UO 2 grains.…”

Section: Resultsmentioning

confidence: 99%

Recycling Process for Sinter-Active U₃O₈Powders

Yang

Kang

Kim

et al. 2010

Journal of Nuclear Science and Technology

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The effect of the oxidation temperature of UO 2 pellets on the powder properties of oxidized U 3 O 8 powders has been investigated. The powder morphology, crystalline size, and BET surface area of recycled U 3 O 8 could be modified by controlling the oxidation temperature of the UO 2 pellets. Recycled U 3 O 8 powder with a high BET surface area and a small particle size could be obtained by lowering the oxidation temperature. It was also found that this low-temperature-oxidized sinter-active U 3 O 8 powder is effective in mitigating the density drop of the UO 2 pellets when the recycled U 3 O 8 powder is added. Moreover, the recycled powder acted as a grain-size-enlarging promoter in the UO 2 pellets.

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“…These are described as UO2 matrices enriched with oxygen atoms 20 . Solubility of oxygen in UO2+x depends on temperature 21 : above 773 K uranium oxides from UO2.26 -UO2. 33 can be converted to U3O8 22 .…”

Section: Introductionmentioning

confidence: 99%

Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study

Gasparrini

Podor

Horlait

et al. 2017

Journal of Nuclear Materials

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Abstract. In situ HT-ESEM oxidation of sintered UC fragments revealed the morphological changes occurring during the transformation between UC to UO2 and UO2 to U3O8 at 723 to 848 K and in an atmosphere of 10 to 100 Pa O2. Two main oxidation pathways were revealed. Oxidation at 723 K in atmospheres ≤ 25 Pa O2 showed the transformation from UC to UO2+x, as confirmed by post mortem HRTEM analysis. This oxidation pathway was comprised of three steps: (i) an induction period, where only surface UC particles oxidised, (ii) a sample area expansion accompanied by crack formation and propagation, (iii) a stabilisation of the total crack length inferring that crack propagation had stopped. Samples oxidised under 50 Pa O2 at 723 K and at 773 -848 K for 10 to 100 Pa O2 showed an "explosive" oxidation pathway: (i) sample area expansion occurred as soon as oxygen was inserted into the chamber and crack propagation and crack length followed an exponential law; (ii) cracks propagated as a network and the oxide layer fragmented, (iii) an "explosion" occurred causing a popcorn-like transformation, typical for oxidation from UO2 to U3O8. HRTEM characterisation revealed U3O8 preferentially grow in the [001] direction. The explosive growth, triggered by ignition of UC, proceeded as a self-propagating high-temperature synthesis reaction, with a propagation speed of 150-500 ± 50 µm/s.

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A detailed study of UO2 to U3O8 oxidation phases and the associated rate-limiting steps

Cited by 103 publications

References 28 publications

On the origin of the sigmoid shape in the UO2 oxidation weight gain curves

On the origin of the sigmoid shape in the UO2 oxidation weight gain curves

Recycling Process for Sinter-Active U₃O₈Powders

Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study

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A detailed study of UO2 to U3O8 oxidation phases and the associated rate-limiting steps

Cited by 103 publications

References 28 publications

On the origin of the sigmoid shape in the UO2 oxidation weight gain curves

On the origin of the sigmoid shape in the UO2 oxidation weight gain curves

Recycling Process for Sinter-Active U3O8Powders

Oxidation of UC: An in situ high temperature environmental scanning electron microscopy study

Contact Info

Product

Resources

About

Recycling Process for Sinter-Active U₃O₈Powders