Improved size uniformity of sol-gel spheres by imposing a vibration on the sol in dispersion nozzles

Abstract

A major part of the Th-- /sup 233/U fuel cycle program at ORNL has been concerned with the development of sol-gel processes to prepare ThO/sub 2/ and ThO/ sub 2/--/sup 233/UO/sub 2/ spheres. The formation of sol drops having a uniform and controlled diameter is important to any sol-gel process for preparing oxide kernels for High Temperature Gas-Cooled Reactor fuels. A recently developed technique that incorporates use of a sol disperser with vibration has met the dispersion requirements for ORNL sol-gel processes better than any of the previous techniques employing dispersers alone. With this new technique, the breakup of sol streams from orifices or capillaries is made more uniform and regular by imposing a vibration, at the natural frequency of drop formation, on the sol at the entrance to the orifices or capillaries. This techn-que has been applied to two-fluid nozzles to form 1,000 to 88,000 sol drops per minute. Batches consisting of 1 to 13 kg of fired ThO/sub 2/ spheres 370 to 500 mu in diameter had average diameters within 1% of the predicted values and standard deviations of 2.5 to 5.0 mu . Yields after both size and shape separation were greater than 95% and were usually greater than 98% in a 30- mu range. The same technique was applied to shear nozzles at rates up to 192,000 drops per minute. Nozzles of this type use multiple orifices and are more dependable for larger capacities than multiple two-fluid nozzles. (auth)