Corrosion of uranium in liquid water under contained conditions with a headspace argon overpressure. The ternary U + H2O(l) + Ar(g) system

The corrosion reaction of unirradiated uranium with deuterated liquid water under an argon (Ar) overpressure was investigated. Two samples were examined at two temperatures (55 °C and 70 °C) under an argon atmosphere and contained conditions. The rate of corrosion was derived by monitoring the pressure changes in the cell as a function of time (ascribed to D2 generation from U-corrosion). Post-corrosion examination was conducted using FIB and XRD. Measurements of water pH were made immediately after the experiments were stopped. From the analyses, it was concluded uranium-deuteride (UD3) was formed in the reaction products as part of the U‑D2O(l) -Ar(g) reaction. This result confirms the formation of uranium hydride/deuteride as part of the uranium-liquid water reaction in an enclosed environment, where deuteride forms through the reaction of U with oxidation-generated D2. From reaction rate behaviour combined with post-reaction surface/interface analysis, it is suggested that after a gas ‘threshold’ pressure limit is reached (~0.5 bar) UD3 formation is facilitated, leading to volume expansion and generation of stress in the overlying oxide. Breakage of this oxide would lead to direct exposure of UD3 and U to aqueous oxidation, leading to reaction rate enhancement. •UD3 was identified to form in the reaction products as part of the U D2O(l)-Ar reaction.•UD3 formation confirms that hydride is produced from U and oxidation generated D2.•After a ‘threshold’ pressure (∼0.5 L) is reached, UD3 formation is facilitated.•Ar cover gas usage in enclosed systems could lead to pressure build-up and further UH3 formation.