Abstract Uranium dioxide with low fluoride content and excellent milling characteristics suitable for making ceramic grade UO2 pellets is produced by initially hydrolyzing uranium hexafluoride in a fluidized bed of UO2F2 particles at a temperature in the range between 500*F. and 900*F. and preferably between 650*F. and 750*F. to produce initially substantially nonhygroscopic freeflowing uranyl fluoride powder having an average particle size of +60 mesh. The uranyl fluoride thus obtained is subjected to at least two separate pyrohydrolysis treatments in fluidized beds with gaseous mixtures of hydrogen and steam to produce uranium dioxide. In the initial pyrolysis treatment, the ratio of hydrogen and steam is adjusted to provide a mixture with a relatively low defluorination potential and the flow rate of the mixture is also regulated to suppress the rate of defluorination. The resident time of the particle in the fluidized bed for the first pyrolysis treatment is sufficiently long so that about 98 percent of the fluoride in the feed is removed. The incompletely defluorinated particles are then further treated in a second fluidized bed with a hydrogen and steam gaseous mixture having a higher ratio of H2/H2O which will provide a higher defluorination potential and the gas rate is also preferably increased to reduce the partially defluorinated feed to uranium dioxide with a fluoride content less than about 100 ppm and preferably below 40 ppm.
A process according to claim 1 wherein the hydrolysis of uranium hexafluoride in the first reaction zone is carried out in the presence of an inert gaseous diluent.
Claim 2
Dependent Claim
11 words
A process according to claim 2 wherein the diluent is nitrogen.
Claim 3
Dependent Claim
23 words
A process according to claim 1 wherein the temperature in the first reaction zone is maintained in the range between 650*F. and 750*F.
Claim 4
Dependent Claim
24 words
A process according to claim 1 wherein the gaseous uranium hexafluoride is premixed with not more than about 50 percent by volume of N2.
Claim 5
Dependent Claim
61 words
A process according to claim 1 wherein the particle size of uranyl fluoride in the first reaction zone is stabilized to within the range of 80 percent to 98 percent by weight of +60 mesh by recycling less than 15% by weight of the total fluidized bed of UO2F2 seed having particle size in the range between -60 and +100 mesh.
Claim 6
Dependent Claim
24 words
A process according to claim 1 wherein the defluorination of uranyl fluoride in the second reaction zone is carried out in a fluidized bed.
Claim 7
Dependent Claim
24 words
A process according to claim 1 wherein the defluorination of the uranyl fluoride is carried out successively in at least two separate fluidized beds.
Claim 8
Dependent Claim
36 words
A process according to claim 1 wherein the defluorination in the second reaction zone uses a 0.30 hydrogen and steam mixture and the subsequent defluorination treatment is carried out using a 0.40 hydrogen and steam mixture.
Claim 9
Dependent Claim
25 words
A process according to claim 1 wherein at least a portion of the excess uranyl fluoride is recovered as a secondary product of the process.