Characterization of zeolite distribution in green pellets of UO2 by WDX-SEM

Analyses of additive elements in UO2 pellets is not easy to be performed by a chemical method. It is tried by wavelength dispersive X-Rays (WDX) which is attached on scanning electron microscope (SEM). The pellet samples were prepared by mixing UO2 powder and zeolite as an additive until the mixture was homogeneous, and it was added by zinc stearic. Compacting of the pellets was performed under pressure in a range between 1.16-3.49 ton/cm2. After the densities of the pellets were determined, the pellets were mounted with slow-resin in impregnation-vacuum under 10-4 torr using a rotary pump. Furthermore, the samples were polished until 2000 mesh in roughness and coated with gold for SEM examination. Zeolite particles were not identified by metallography technique because it could not be differentiated from uranium particles. Instead of that the scanning WDX is used. Based on sensitivity of the detector, phosphorus and silicon elements are identified to determine the zeolite distribution. UO2 pellets without zeolite did not give off intensity, meanwhile UO2 added by zeolite gave off intensity. Distribution of the elements were fairly homogeneous so that it is stated that zeolite in UO2 pellets is mixed well. The zinc elements was also examined in order to identify the zinc distribution in zinc stearic as lubricant. Based on microstructure, there were large particles in size between 50-100 microns and they were rich of zinc element. The zinc stearic particles seems to be homogeneous, in range between 400-600 particles per mm2. At pressure of 3.49 ton/cm2, zinc stearic particles become clustered. It is proved by the existing 900 particles per mm2 at a certain area. Zinc stearate starts growing at pressure compaction of 2.33 ton/cm2, that is from 40 μm to 50 μm. When pressure compaction reached 3.49 ton/cm2, zinc stearic particles grew to 60 μm at periphery and 100 μm in the middle of the pellets. This enlargement seems due to segregation. (author)