Comparative Study of Turbo and Spray Drying Techniques in the Production of Nuclear Grade Uranium Dioxide

Abstract

Natural Uranium Di-Oxide (UO₂) powder for the manufacturing of fuel for Pressurised Heavy Water Reactors (PHWR) is produced through the Ammonium Di-Uranate (ADU) route. The characteristics of the virgin UO₂ powder influence the sintered density of UO₂ pellets, which in tum is decided by the physical state of the starting material ADU. The physical characteristics such as the morphology, particle size, particle size distribution of ADU depend a lot on the precipitation and drying conditions. Different modes of drying are utilised on industrial scale to obtain sinterable grade UO₂ powder. Nuclear Fuel Complex, Hyderabad has successfully developed both the spray and turbo drying techniques for the production of dry ADU for further thermal treatment.

Turbo drier is basically a bulk drier where the mechanism of drying is 'cross and through circulation'. The spray drier is a micro drier in which the slurry is atomised in a hot gas stream inside a chamber where drying takes place within a few seconds, because of high specific surface area. Design and operational parameters for the spray drier were optimised based upon the comparative study of product quality. Scanning Electron Microscope(SEM) images of ADU and UO₂ produced by turbo and spray dried routes were analysed.

This paper deals in detail with the comparative studies carried out on both drying techniques, along with their behavior on further processing steps such as calcination, reduction, stabilization and sinterability of UO₂ powder.