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In situ neutron powder diffraction experiments are applied to physical, kinetic, and microstructural characterization of uranium mononitride as a promising light water reactor fuel material. The temperature-variable coefficient of thermal expansion and isotropic Debye Waller factors are obtained by sequential Rietveld refinement over 499–1873 K. Oxidation of a UN pellet (95.2% density) under flow of 11 mg/min D 2 O is observed to initiate above 623 K and the rate increases by a factor of approximately 10 from 673 to 773 K, with activation energy 50.6 ± 1.3 kJ/mol; uranium oxide is the only solid corrosion product. [ABSTRACT FROM AUTHOR]

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 ≥ 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 8 j 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. [Display omitted] • In situ neutron diffraction measures U 3 Si 2 corrosion in deuterated steam. • Rigorous thermodynamic description of hydride using key entropy contributions. • H absorption at 2 b interstitial site of U 3 Si 2 H x , moves to 8 j site for x ≥ 0.5. • From 350 °C, U 3 Si 2 H x fragmented by 1–2% anisotropic lattice expansion. • From 375 °C, UO 2 , U 3 Si 5 and USi 3 form in bulk and in grain boundaries. [ABSTRACT FROM AUTHOR]

Two polymorphs of lithium magnesium tellurate Li 4–2 x Mg 1+ x TeO 6 have been prepared by solid-state reactions and their crystal structures characterised by powder X-ray and neutron diffraction. For x ​≈ ​0, a monoclinic C 2/ m phase is obtained, structurally similar to other O3 type honeycomb layered tellurate and antimonate compounds. The basic structure consists of [Mg 2 TeO 6 3− honeycomb layers alternating with Li layers, with some anti-site disorder of Li and Mg between layers, analogous to the structure of Li 4 ZnTeO 6. For 0 ​< ​ x ​< ​~0.5 (specifically, x ​= ​0.33) an orthorhombic Fddd phase is obtained, with a rock-salt superstructure containing disordered Li/Mg cation sites surrounding ordered TeO 6 octahedra, analogous to the structure of Li 3 Co 2 TaO 6. Figure caption : XRD pattern and illustration of the crystal structure of the O3-type monoclinic phase obtained for x ​≈ ​0 of the Li 4–2 x Mg 1+ x TeO 6 phase space. Image 1 • Layered oxides; Honeycomb; Neutron diffraction; polymorphs. [ABSTRACT FROM AUTHOR]