Structural and phase evolution in U3Si2 during steam corrosion

U3Si2 nuclear fuel is corroded in deuterated steam with in situ neutron diffraction. Density functional theory is coupled with rigorous thermodynamic description of the hydride including gas/solid entropy contributions. H absorbs in the 2b interstitial site of U3Si2Hx and moves to 8j for x ≥ 0.5. Hydriding forces lattice expansion and change in a/c ratio linked to site preference. Rietveld refinement tracks the corrosion reactions at 350–500 °C and preference for the 8j site. Above 375 °C, formation of UO2, U3Si5 and USi3 take place in the grain boundaries and bulk. Hydriding occurs in bulk and precedes other reactions.