PRODUCTION OF URANIUM DIOXIDE B Y FLAME DENITRATION W.
H . HEDLEY,'
R. J.
ROEHRS,* AND W . T. TRASK, JR.
1 'raniurn Dir3ision: .\lailinci;rodt Cheniical T4'ool.ks: Saint Charles, .\fa.
A continuous process has been developed for the direct conversion of uranyl nitrate solution to uranium dioxide. The solution i s sprayed directly into a reducing hydrocarbon-air flame in which dehydration, denitration, and reduction take place. The reactor temperature, normally at least 1800" F. at the exit end, i s controlled by the uranyl nitrate flow and by excess hydrocarbon introduced around the spray nozzle. Powder build-up on the wall and residence time i s controlled by a Venturi-shaped reaction chamber. Conversions to 82% UOz have been achieved at production rates of 242 pounds of uranium per hour on a pilot scale, while percentages as high as 9670 have been produced in the laboratory. The product i s a finely divided, low-density powder which i s equally adaptable to oxide fuel element fabrication or additional chemical processing. Additional work i s needed to optimize the processing variables in order to provide conversion to UOSin excess of the 97% (assuming the remainder i s Us08)necessary for the production of highgrade uranium metal.
u
dioxide is an important compound in the current United States atomic energy program. It is an intermediate in producing the uranium hexafluoride used in the gaseous diffusion process for uranium-235, and in the production of uranium metal. In addition, it is the raw material from which uranium oxide fuel elements are constructed for poLver reactors. There are several current techniques for producing uranium dioxide. One of these is a two-step sequence in which purified uranyl nitrate solution [ L T 0 2 ( S 0 3 )xH,O] 2. is dehydrated and denitrated in gas-fired, batch calciners ( 2 ) . The resulting uranium trioxide is then reduced to the dioxide by hydrogen in a fluid-bed reactor system ( 4 )or a screw-reactor system ( 3 ) . Fluid-bed uranium dioxide and screiv-reactor uranium dioxide both require additional treatment in the form of rigorous grinding before they are suitable for current oxide fuel element fabrication processes. A second common method of uranium dioxide production involves the conversion of precipitated ammonium diuranate [(SHJ2UZOi] to the dioxide (5). Such material requires no grinding prior to fuel element fabrication. Flame denitration likeivise produces a dioxide which can be used direct1:- for fabrication of high-density oxide fuel elements. The flame denitration process is based o n the conversion of uranyl nitrate solution to uranium dioxide by spraying the solution into a reducing flame. An over-all equation for the reduction may be ivritten: RAXIVM
+
5 L 7 0 2 ( N 0 3 ) 2 2 C 3 H 8 + 5 LO2
unit \
