The sintering behavior of uranium and uranium-zirconium alloys in the alpha phase were characterized in this research. Metal uranium powder was produced from pieces of depleted uranium metal acquired from the Y-12 plant via hydriding/dehydriding process. The size distribution and morphology of the uranium powder produced by this method were determined by digital optical microscopy. Once the characteristics of the source uranium powder were known, uranium and uranium-zirconium pellets were pressed using a dual-action punch and die. The majority of these pellets were sintered isothermally, first in the alpha phase near 650°C, then in the gamma phase near 800°C. In addition, a few pellets were sintered using more exotic temperature profiles. Pellet shrinkage was continuously measured in situ during sintering. The isothermal shrinkage rates and sintering temperatures for each pellet were fit to a simple model for the initial phase of sintering of spherical powders. The material specific constants required by this model, including the activation energy of the process, were determined for both uranium and uranium-zirconium. Following sintering, pellets were sectioned, mounted, and polished for imaging by electron microscopy. Based on these results, the porosity and microstructure of the sintered pellets were analyzed. The porosity of the uranium-zirconium pellets was consistently lower than that of the pure uranium pellets. In addition, some formation of an alloyed phase of uranium and zirconium was observed. The research presented within this thesis is a continuation of a previous project; however, this research has produced many new results not previously seen. In addition, a number of issues left unresolved by the previous project have been addressed and solved. Most notably, the low original output of the hydride/dehydride powder production system has been increased by an order of magnitude, the actual characteristics of the powder have been measured and determined, shrinkage data was successfully converted into a sintering model, an alloyed phase of uranium and zirconium was produced, and pellet cracking due to delamination has been eliminated.

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.

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The proceedings of the Ninth International Symposium on [title], held in Kobe, Japan, November 1990, address current trends in the development, performance, and fabrication of zirconium alloys for nuclear power reactors. the bulk of the most recent work on zirconium alloy behavior has concerned corr