Garnetti, David J. (2009-12). Uranium Powder Production Via Hydride Formation and Alpha Phase Sintering of Uranium and Uranium-zirconium Alloys for Advanced Nuclear Fuel Applications. Master's Thesis.
The research in this thesis covers the design and implementation of a depleted
uranium (DU) powder production system and the initial results of a DU-Zr-Mg alloy alpha
phase sintering experiment where the Mg is a surrogate for Pu and Am. The powder
production system utilized the uranium hydrogen interaction in order to break down larger
pieces of uranium into fine powder. After several iterations, a successful reusable system
was built. The nominal size of the powder product was on the order of 1 to 3 mm.
The resulting uranium powder was pressed into pellets of various compositions (DU,
DU-10Zr, DU-Mg, DU-10Zr-Mg) and heated to approximately 650?C, just below the alphabeta
phase transition of uranium. The dimensions of the pellets were measured before and
after heating and in situ dimension changes were measured using a linear variable
differential transducer (LVDT).
Post experiment measurement of the pellets proved to be an unreliable indicator of
sintering do the cracking of the pellets during cool down. The cracking caused increases in
the diameter and height of the samples. The cracks occurred in greater frequency along the
edges of the pellets. All of the pellets, except the DU-10Zr-Mg pellet, were slightly conical
in shape. This is believed to be an artifact of the powder pressing procedure. A greater density occurs on one end of the pellet during pressing and thus leads to gradient in the
sinter rate of the pellet. The LVDT measurements proved to be extremely sensitive to
outside vibration, making a subset of the data inappropriate for analysis.
The pellets were also analyzed using electron microscopy. All pellets showed signs
of sintering and an increase in density. The pellets will the greatest densification and lowest
porosity were the DU-Mg and DU-10Zr-Mg. The DU-Mg pellet had a porosity of 14 +or-
2.%. The DU-10Zr-Mg porosity could not be conclusively determined due to lack of clearly
visible pores in the image, however there were very few pores indicating a high degree of
sintering. In the DU-10Zr-Mg alloy, large grains of DU were surrounded by Zr. This
phenomena was not present in the DU-10Zr pellet where the Zr and DU stayed segregated.
There was no indication of alloying between the Zr and DU in pellets.