Calorimetric Study of Phase Stability and Phase Transformation in U-xZr (x = 2, 5, 10 wt pct) Alloys

FCRD Advanced Reactor (Transmutation) Fuels Handbook

“…Although these phases do not appear in phase diagrams, their presence can complicate experimental studies of equilibrium phenomena. Whether these phases form in a given sample depends on its cooling rate as well as its composition [77,78,[81][82][83].…”

“…Transformation mechanisms are poorly understood, although it is generally agreed that the transformation from γ 2 to δ-UZr 2 is an -transformation analogous to that in Ti, Zr, and Hf, and involves ordering of Zr atoms in the  2 crystal structure to form the metastable ω structure followed by collapse of the  2 lattice planes to form δ-UZr 2 [55,56,78]. Unless the sample is cooled very slowly (~0.1 K/min), the room-temperature assemblage is likely to be a combination of (α-U), α', and δ-UZr 2 [77].…”

“…A recent study by Rai et al indicates that details of the transformations involved in the disappearance of δ-UZr 2 during heating may depend on the starting phases in the sample [77]. If the sample starts with an equilibrium assemblage of α-U and δ-(UZr 2 ), the δ-UZr 2 will form γ-(U,Zr) directly.…”

“…However, the solidus temperature measured by Rai et al for the alloy with 22.5 at% Zr seems anomalously high, possibly because of reported difficulties in obtaining an accurate baseline[77]. The solidus temperatures measured by Kaity et al[84]are consistent with the solidus measurements of Balakrishnan et al; however, the single liquidus measurement by Kaity et al is significantly below the measurements of Balakrishnan et alBalakrishnan et al suggested that this difference was due to a hightemperature reaction between liquid U and the alumina crucibles used by Kaity et al[50].The entire liquidus of the Sheldon and Peterson phase diagram is consistent with the new data, as is the solidus for compositions with less than ~30 at% Zr (Figure2).…”

Preliminary Study on the Fabrication of Particulate Fuel through Pressureless Sintering Process

“…Centrifugal atomization involves melting, atomizing, and collecting. U and Zr raw materials were heated to a temperature approximately 200 K higher than the melting point, 1650 K, of the alloy [18], and the molten metal was fed through a small nozzle onto a rotating disk. The alloy-melt droplets, which formed from the melt by centrifugal force, were spread from the disk toward the atomizing chamber wall.…”