Characterization of Plasma-Sprayed Zirconium Coatings on Uranium Alloy Using Neutron Diffraction

Abstract

Plasma-sprayed zirconium (Zr) metal coatings onto uranium-molybdenum (U-Mo) alloy nuclear reactor fuel foils act as a diffusion barrier between the fuel and the aluminum fuel cladding. Neutron diffraction was performed to investigate the crystallographic phase composition, crystal orientations, and lattice parameters of the plasma-sprayed Zr and the U-Mo substrate. The neutron diffraction results show that the plasma-sprayed Zr coating is crystalline, is phase pure (alpha-Zr), and has preferred crystalline orientation due to directional solidification influenced by the substrate crystalline orientation. Also, there is a slight (~ 0.01 A for a direction and ~ 0.016 A for c direction) increase in the plasma-sprayed Zr lattice parameter indicating oxygen in the lattice and some residual thermo-mechanical strain. There is little or no modification of the underlying U-Mo following plasma spraying. In particular, there is no detectable allotropic transformation of the starting gamma-U (body-centered cubic) to alpha-U (orthorhombic). The unique neutron diffraction capabilities at LANL are well suited for nuclear fuel characterization offering distinct advantages over conventional x-ray diffraction and destructive metallography.