Assessing the influence of microstructure on uranium hydride size distributions via small angle neutron scattering

The effect of microstructure on the internal hydriding behavior of both cast (1 mm grain size) and rolled (25 mu m grain size) uranium containing hydrogen concentrations between 0 and 1.8 wppm were evaluated via small angle neutron scattering (SANS). Increasing hydrogen content up to 1.8 wppm in the cast uranium only weakly affected the average uranium hydride (UH3) precipitate size, calculated from the SANS data. Conversely, the UH3 phase fraction was found to strongly depend on the hydrogen content in the same cast samples. A substantially reduced UH3 particle size distribution was observed in the rolled uranium relative to cast uranium containing the same nominal hydrogen content. It is hypothesized that the suppression of UH3 formation in the rolled uranium is driven by increased hydrogen trapping at grain boundaries, and theoretical calculations that account for trap density, potency, and hydrogen diffusion kinetics support this hypothesis.