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Characterization of the Penetration Mechanisms of Water into Polycrystalline UO2

Published online by Cambridge University Press:  01 February 2011

Ilaria Marchetti
Affiliation:
Ilaria.marchetti@ec.europa.eu
Fabio Belloni
Affiliation:
fabio.belloni@ec.europa.eu, European Commission, JRC - Institute for Transuranium Elements (ITU), Karlsruhe, Germany
Jerome Himbert
Affiliation:
jerome.himbert@ec.europa.eu, European Commission, JRC - Institute for Transuranium Elements (ITU), Karlsruhe, Germany
Paul Carbol
Affiliation:
paul.carbol@ec.europa.eu, European Commission, JRC - Institute for Transuranium Elements (ITU), Karlsruhe, Germany
Thomas Fanghänel
Affiliation:
thomas.fanghaenel@ec.europa.eu, European Commission, JRC - Institute for Transuranium Elements (ITU), Karlsruhe, Germany
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Abstract

Following containment failure in the scenario of geological disposal of spent nuclear fuel, the penetration rate of groundwater into the UO2 matrix could cause a rapid increase of the fraction of inventory becoming available for prompt dissolution. In this respect, oxygen and water diffusion mechanisms are key issues to investigate. In this work, secondary-ion-mass-spectrometry (SIMS) depth profiling has been applied to characterize a polycrystalline UO2 pellet exposed to 18O-labelled water at room temperature. 18O depth profiling up to 25 μm beneath the pellet surface clearly indicates a combination of oxygen diffusion into the UO2 lattice and water diffusion along grain boundaries, behaving as high diffusivity paths. The lattice diffusion coefficient of oxygen, DL, and the quantity δDB – product of the grain boundary width, δ, and the grain boundary diffusion coefficient of water, DB – have been measured, resulting in DL = (2.5 ± 0.1) × 10-24 m2 s-1 and δDB = (7.5 ± 0.3) × 10-24 m3 s-1.

Type
Research Article
Copyright
Copyright © Materials Research Society 2010

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