b'finished. The diffusion couple between USnLn and Fe is in progress.The microstructures of U-Sn and U-Sn-Ln are shown in Figure 1. The microstructure is relatively simple in U-Sn, as shown in Figure 1a, with an intermetallic compound having the composition U2Sn (based on Energy Dispersive X-Ray Spectroscopy (EDS) analysis), and U with a small amount (~2 at. %) dissolved Sn. TheFigure 2. SEM backscatter intermetallic compound is not known,images of U fuels with Pd additive. a) U-Pd, with EDS and requires further investigation.maps, b) U-Pd-Ln.Upon addition of lanthanides, a large precipitate of Sn-Ln was observed, as shown in the bottom of Figure 1b. The dark region is SnLn, while the lighterIn the corresponding Zr alloys, grey region (shown with red arrows)i.e. U-10Zr-4Sn-4Ln and U-10Zr-contains less Sn, but has not been3.86Pd-4.3Ln, the additive-lanthanide identified yet. Aside from the largecompounds are dispersed throughout precipitate, the microstructure containsthe alloy. Although these compounds U2Sn and smaller precipitates of SnLn. are still not miscible in the U-Zr matrix, there may be some miscibility The microstructures of U-Pd andin the molten phase due favorable U-Pd-Ln are shown in Figure 2, alonginteractions between the additives with EDS maps of U and Pd for theand Zr. There is segregation during U-Pd alloy. Based on the EDS mapscooling, but the result is dispersion of and quantitative EDS analysis, UPd3the additive-lanthanide compounds deposited along the uranium grainthroughout the matrix.boundaries. The only other structures present in the microstructure areDiffusion couples have been run square precipitates of UO 2 . Upon addi- between the alloys and Fe (the couple tion of lanthanides, a large precipitatebetween U-Sn-Ln had to be repeated formed. The dark region on the left sideand is underway). Analysis of the data is of the image shown in Figure 2b is thein progress. A manuscript is in progress 1:1 PdLn intermetallic compound.for both the annealed structures and the diffusion couples.The large additive-lanthanide precipi-tates present in both U-Sn-Ln and U-Pd-Ln are due to the immiscibility of these phases in the U matrix. 2019|AFC ACCOMPLISHMENTS 171'