Oxygen diffusion coefficient and characterization of leachant in UO2 corrosion studied by new methods

Abstract

UO2 corrosion is a key issue in the study of the safe storage of spent nuclear fuel (SNF). In this work, corrosion experiments were performed on UO2 samples exposed to 18O labelled water during 290 days at room conditions, thereafter a complete analysis of the solid and leachant (labelled water) allow us obtaining new data and exploring new methods.

Thus, a new application of the Nuclear Reaction Analysis (NRA), as a simple and low-cost approach, has been developed to estimate the oxidized layer thickness and the diffusion coefficient of oxygen through the oxidized layer. These results were verified by comparison with the ones obtained by traditional Secondary Ion Mass Spectrometry (SIMS).

The diffusion coefficient obtained is two orders of magnitude larger than the scarce published ones at room temperature, highlighting the great effect of the composition of the oxidized layer due to the UO2 corrosion on this parameter. In addition, the water used in the corrosion experiments (leachant) has been analyzed by Raman spectroscopy, being the main purpose for the in situ analysis.

The data obtained in this study bring out the great ability (higher than expected) of the oxygen to break through the oxidized layer which could endanger the SNF pellet integrity.

Besides, this work shows new methods for analyzing corrosion experiments which can be used to obtain new data for completing the database.