Structural and phase evolution in U${}_3$Si${}_2$ during steam corrosion

Abstract

U${}_3$Si${}_2$ 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 2$b$ interstitial site of U${}_3$Si${}_2$H${}_x$ and moves to 8$j$ for $x\ge 0.5$. 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 UO${}_2$, U${}_3$Si${}_5$ and USi${}_3$ take place in the grain boundaries and bulk. Hydriding occurs in bulk and precedes other reactions.