Texture in ZIRCALOY-clad uranium

An enriched (30%235U) uranium target is being fabricated for the ANL spallation neutron source (IPNS). They have measured the orientation distribution of neutron diffraction intensities (texture) of test casting made of depleted 238U. Their results indicate the presence of large grains which may swell anisotropically with radiation damage and produce a separation of the ZIRCALOY protective cladding from the surface of the metal. Similar studies of material subjected to β-heat treating (quenching from the tetragonal β-phase into the orthorhombic α-phase, T/sub β → α/ = 6620C) shows a mild texture. The rapid formation of orthorhombic grains within the larger tetragonal ones produces an acceptable small grain size and reduced orientation. Unfortunately, diffusion bonding of the ZIRCALOY cladding requires slow-cooling from the γ-phase (T/sub γ → β/ = 7720C) and they have established that this procedure causes dramatic grain regrowth. Studies are underway to determine if the diffusion bond between the ZIRCALOY cladding and the uranium metal is weakened by the β-heat treating process. They will discuss the measurement of grain size and orientation (texture), the nature of the β → α phase transition and the problems of grain regrowth