High- and low-Am RE inclusion phases in a U-Np-Pu-Am-Zr alloy

Structural, microstructural, and microchemical data were collected from rare-earth inclusions in an as-cast U-Pu-Zr alloy with ∼3 at.% Am, 2% Np, and 9% rare-earth elements (La, Ce, Pr, and Nd). Two RE phases with different concentrations of Am were identified. The composition of high-Am RE inclusions is ∼2-5 at.% La, 15-20% Ce, 5-10% Pr, 25-45% Nd, 1% Np, 5-10% Pu, and 10-20% Am. Some areas also have O, although this does not appear to be an essential part of the high-Am RE phase. The inclusions have a face-centered cubic structure with a lattice parameter a ∼ 0.54 nm. The composition of the only low-Am RE inclusion studied in detail is ∼35-40 at.% O, 40-45% Nd, 1-2% Zr, 4-5% La, 9-10% Ce, and 6-7% Pr. This inclusion is an oxide with a crystal structure similar to the room-temperature structure of Nd₂O₃. Microstructural features suggest that oxidation occurred during casting, and that early crystallization of high-temperature oxides led to formation of two distinct RE phases.