Characterization of PuGa (1at%. Ga) Oxidation under Dry Oxygen Atmosphere Exposure

Abstract

The oxidation of δ−stabilized plutonium alloy has been studied under dry oxygen exposures for temperatures varying from 100°C up to 300°C and oxygen partial pressures varying from 10^− 4 up to 500 mbar. The coupling of X-ray diffraction, Raman spectroscopy and FIB-SEM has allowed to show that the oxide scale is composed of an outer layer of PuO₂ and an inner mixed layer of α+β−Pu₂O₃ platelets propagating into a metallic zone corresponding to the stable phase of unalloyed Pu. Furthermore, the analysis of Pu oxidation kinetics has displayed first a parabolic growth governed by the diffusion of interstitial oxygen. This step consists in the thickening of the Pu₂O₃ layer with a decrease in α−Pu₂O₃ ratio in favour of β−Pu₂O₃. Then, a second step occurs consisting in a linear growth of the PuO₂−layer with the formation of thick nodules which tend to cover the whole oxide surface. Based on the results of this work, a general oxidation mechanism for δ−Pu alloy is provided.