Identification of precipitates in U-Nb-Zr alloys thermally treated at 850 °C

Simultaneously, the fabrication of U(Zr,Nb)/Zry-4 miniplates was started in 2005. As part of this last monolithic fuel development, 10 alloys with U densities between 7-10 gU/cm3 were fabricated. These alloys were homogenized in γU(Zr,Nb) phase by annealing at 850 ºC for 1 and 24 h and finished by quenching.

In this work the morphological and crystallographic characterization of this set of alloys is presented. The major phases identified were: γU (Zr, Nb) (or the transition phase γS derived from it), δUZr2 and α” (transition phase derived from the equilibrium αU phase). In addition, four types of precipitates, rich in Zr, with different morphologies were identified.

The presence of each of them was associated to the stage in which they were formed: during the casting process of the alloy, the heat treatment and / or the annealing process. This result allows us to evaluate which parameters need to be controlled to obtain a homogeneous alloy at the time of making a nuclear fuel.