As-cast microstructures in U-Pu-Zr alloy fuel pins with 5-8 wt.% minor actinides and 0-1.5 wt% rare-earth elements

The Idaho National Laboratory (INL) is investigating U-Pu-Zr alloys with low concentrations of minor actinides (Np and Am) and rare-earth elements (La, Ce, Pr, and Nd) as possible nuclear fuels to be used to transmute minor actinides. Alloys with compositions 60U-20Pu-3Am-2Np-15Zr, 42U-30Pu-5Am-3Np- 20Zr, 59U-20Pu-3Am-2Np-1RE-15Zr, 58.5U-20Pu-3Am-2Np-1.5RE-15Zr, 41U-30Pu-5Am-3Np-1RE-20Zr, and 40.5U-30Pu-5Am-3Np-1.5RE-20Zr (where numbers represent weight percents of each element and RE is a rare-earth alloy consisting of 6% La, 16% Pr, 25% Ce, and 53% Nd by weight) were arc-melted and vacuum cast as fuel pins approximately 4 mm in diameter. The as-cast pins were sectioned, polished, and examined by scanning electron microscopy. Each alloy contains high-Zr inclusions surrounded by a high-actinide matrix. Alloys with rare-earth elements also contain inclusions that are high in these elements. Within the matrix, concentrations of U and Zr vary inversely, while concentrations of Np and Pu appear approximately constant. Am occurs in the matrix and with some high-rare-earth inclusions, and occasionally as high-Am inclusions in samples without rare-earth elements.