Am phases in the matrix of a U-Pu-Zr alloy with Np, Am, and rare-earth elements

Phases and microstructures in the matrix of an as-cast U-Pu-Zr alloy with 3 wt% Am, 2% Np, and 8% rare-earth elements were characterized by scanning and transmission electron microscopy. The matrix consists primarily of two phases, both of which contain Am: ζ-(U, Np, Pu, Am) (∼70 at.% U, 5% Np, 14% Pu, 1% Am, and 10% Zr) and δ-(U, Np, Pu, Am)Zr₂ (∼25% U, 2% Np, 10-15% Pu, 1-2% Am, and 55-60 at.% Zr). These phases are similar to those in U-Pu-Zr alloys, although the Zr content in ζ-(U, Np, Pu, Am) is higher than that in ζ-(U, Pu) and the Zr content in δ-(U, Np, Pu, Am)Zr₂ is lower than that in δ-UZr₂. Nanocrystalline actinide oxides with structures similar to UO₂ occurred in some areas, but may have formed by reactions with the atmosphere during sample handling. Planar features consisting of a central zone of ζ-(U, Np, Pu, Am) bracketed by zones of δ-(U, Np, Pu, Am)Zr₂ bound irregular polygons ranging in size from a few micrometers to a few tens of micrometers across. The rest of the matrix consists of elongated domains of ζ-(U, Np, Pu, Am) and δ-(U, Np, Pu, Am)Zr₂. Each of these domains is a few tens of nanometers across and a few hundred nanometers long. The domains display strong preferred orientations involving areas a few hundred nanometers to a few micrometers across.