Spent Nuclear Fuel oxidation under dry storage controlled conditions for studying its radial oxidation behavior

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In this work we have studied, for the first time, the oxidation of highly-irradiated Spent Nuclear Fuel (SNF) at in-situ conditions, with a controlled temperature and atmosphere, and measuring in the same experiment the oxidation in both the pellet center and the rim. The oxidation of the SNF matrix is of paramount importance from the nuclear fuel safe storage point of view, mainly because the potential threat that the formation of the oxidized phase U3O8 entails. In this work a measurement protocol for following in-situ the oxidation of SNF at controlled conditions (350 °C, constant air flow), based on the use of Raman spectroscopy as the measuring technique, is presented. The installation of the set-up inside a hot cell has been successfully applied. The radial surface oxidation of the irradiated fuel sample (63 MWd/kgU) is followed. In the center, U3O8 is obtained after 62 h. In the pellet periphery, the first spectrum of U3O8 is not observed until almost 92 h, although even after that not-oxidized spectra are still acquired. These results prove that the higher local burn-up and increase of fission products could enhance the oxidation resistance of the fuel in these conditions. This is the first time that this effect is proved in a temperature-controlled oxidation, single experiment.