Room‐temperature diffusion coefficients for oxygen and water in UO2 matrices: a SIMS study. (24th May 2012)

• Record Type: Journal Article
• Authors: Marchetti, I.; Carbol, P.; Himbert, J.; Belloni, F.; Fanghänel, T.
• Is Part Of: Surface and interface analysis. Volume 45:Number 1(2013:Jan.)
• Page Start: 360
• Page End: 363
• Publication Date: 2012-05-24
• Subjects: Surfaces (Physics) -- Periodicals; Surface chemistry -- Periodicals; Thin films -- Periodicals; 541.33
• DOI: 10.1002/sia.5028
• Languages: English
• ISSNs: 0142-2421

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>To understand the mechanism of fuel oxidation, in the event of exposure of spent nuclear fuel to groundwater in a final repository, the key parameters are the diffusion coefficients for oxygen and water in UO₂. In the temperature range relevant for geological disposal (20–100 °C), we conducted static corrosion experiments, for 3–6 months, with ¹⁸O‐labelled water on different UO₂ matrices (single‐crystal, polycrystalline UO₂, SIMFUEL) so that we could evaluate the penetration of the ¹⁸O‐tracer by means of secondary ion mass spectrometry depth profiling, measuring the ¹⁸O/¹⁶O ratio. Fick's second law was applied to fit the diffusion profiles in the single crystal and to determine the chemical diffusion coefficient of oxygen, which was found to be in good agreement with the Arrhenius plot extrapolation from high‐temperature literature data. Profiles of polycrystalline UO₂ could be fitted with the Levine–MacCallum model, showing that grain boundaries behave like high‐diffusivity paths. The presence of secondary phases precipitated along the grain boundaries, as in the case of SIMFUEL, showed a hindering effect for this grain‐boundary diffusion, reducing the measured penetration depth. Copyright © 2012 John Wiley &amp; Sons, Ltd.</p> </abstract>