A surface science study of the initial stages of hydrogen corrosion on uranium metal and the role played by grain microstructure

Controlled formation of UH3 on uranium metal surfaces was induced by a precisely limited uptake of hydrogen at 250 °C and 320 °C with 500 mbar H2 pressure. The hydride (UH3) growth sites on the sample surfaces were studied using focused ion beam (FIB) milling with high resolution secondary electron imaging. Electron backscatter diffraction (EBSD) analysis was also used to examine grain orientation of the metal in the region of the corrosion sites.Results of the analysis indicated that the location of hydride sites was predominantly found to be associated with grain boundaries at the metal surface. In addition, FIB cross-sectioning of multiple hydride sites indicates the observed morphology of very small hydride growths to be consistent with nucleation at, and not beneath, the oxide–metal interface.

► UH3 formed on uranium surfaces by a limited uptake of hydrogen at 250 °C and 320 °C
► Nucleation centres formed at the oxide–metal interface
► Hydride nucleation preferentially occurs at grain boundaries on the metal surface.
► Large crystallographic mismatch provided low energy, preferential, nucleation sites.