US 4,053,559 AGranted

Production of uranium dioxide

AssigneeWestinghouse Electric Corp.

InventorsJames E. Hart, David L. Shuck, Ward L. Lyon

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Abstract

A continuous, four stage fluidized bed process for converting uranium hexafluoride (UF.sub.6) to ceramic-grade uranium dioxide (UO.sub.2) powder suitable for use in the manufacture of fuel pellets for nuclear reactors is disclosed. The process comprises the steps of first reacting UF.sub.6 with steam in a first fluidized bed, preferably at about 550.degree. C, to form solid intermediate reaction products UO.sub.2 F.sub.2, U.sub.3 O.sub.8 and an off-gas including hydrogen fluoride (HF). The solid intermediate reaction products are conveyed to a second fluidized bed reactor at which the mol fraction of HF is controlled at low levels in order to prevent the formation of uranium tetrafluoride (UF.sub.4). The first intermediate reaction products are reacted in the second fluidized bed with steam and hydrogen at a temperature of about 630.degree. C. The second intermediate reaction product including uranium dioxide (UO.sub.2) is conveyed to a third fluidized bed reactor and reacted with additional steam and hydrogen at a temperature of about 650.degree. C producing a reaction product consisting essentially of uranium dioxide having an oxygen-uranium ratio of about 2 and a low residual fluoride content. This product is then conveyed to a fourth fluidized bed wherein a mixture of air and preheated nitrogen is introduced in order to further reduce the fluoride content of the UO.sub.2 and increase the oxygen-uranium ratio to about 2.25.

Claims8

Dependent claims

A continuous process for converting uranium hexafluoride (UF.sub.6) to ceramic-grade uranium oxide product having a low residual fluoride content, comprising the steps of:

a. establishing and maintaining in contact with a first fluidized bed a mixture consisting essentially of uranium hexafluoride (UF.sub.6) and steam (H.sub.2 O) the proportion of from about in 2 to 8 mols of steam per mol of uranium;
b. concurrently heating the first fluidized bed to a temperature within the range from about 475.degree. C. to about 600.degree. C. to produce a first intermediate reaction product including solid particles of uranyl fluoride (UO.sub.2 F.sub.2) and the oxide U.sub.3 O.sub.8 and an off-gas including hydrogen fluoride (HF);
c. conveying the first solid intermediate reaction product to a second fluidized bed reactor;
d. controlling the mole fraction of hydrogen fluoride in the second reactor to minimize the formation of uranium tetrafluoride UF.sub.4 ;
e. maintaining the second fluidized bed comprising a mixture of the first solid intermediate reaction product and additional steam and hydrogen in the proportions of from about 4 to 12 mols of steam and from about 1 to 6 mols of hydrogen per mol of uranium;
f. concurrently heating the second fluidized bed to a temperature within the range from about 575.degree. C. to about 675.degree. C. to produce a second intermediate reaction product including uranium dioxide (UO.sub.2);
g. conveying the second intermediate reaction product to a third fluidized bed;
h. maintaining the third fluidized bed comprising a mixture of the second intermediate reaction product and additional steam and hydrogen in the proportions of from about 2 to 11 mols of steam and from about 0.5 to 6 mols of hydrogen per mol of uranium;
i. concurrently heating the third fluidized bed to a temperature within the range from about 575.degree. C. to about 675.degree. C. to produce a third intermediate reaction product consisting essentially of uranium dioxide (UO.sub.2) having an oxygen-uranium ratio of about 2 and a low residual fluoride content;
j. conveying the third intermediate reaction product to a fourth fluidized bed;
and
k. maintaining the fourth fluidized bed comprising the third intermediate reaction product and a mixture of air and nitrogen to further reduce the fluoride content and increase the oxygen-uranium ratio to about 2.2 to about 2.3 to produce ceramic-grade uranium oxide product suitable for use in the manufacture of fuel pellets for nuclear reactors.

9 more elements

A continuous process for converting uranium hexafluoride (UF.sub.6) to ceramic-grade uranium dioxide (UO.sub.2) having low residual fluoride content, comprising the steps of:

a. establishing and maintaining in contact with a first fluidized bed a mixture cnsisting essentially of uranium hexafluoride, steam (H.sub.2 O) and hydrogen (H.sub.2) in the proportions of from about 2 to 8 mols of steam and from about 1 to 8 mols of hydrogen per mol of uranium;
b. concurrently heating the first fluidized bed to a temperature within the range from about 475.degree. C. to about 600.degree. C. to produce a first intermediate reaction product including solid uranyl fluoride (UO.sub.2 F.sub.2) and an off-gas including hydrogen fluoride (HF);
c. diverting the off-gas from the first reactor including the hydrogen fluoride to a gas scrubber system and conveying the solid intermediate reaction product including the uranyl fluoride to a second fluidized bed reactor using steam as a transport medium;
d. maintaining the second fluidized bed comprising a mixture of the uranyl fluoride and additional steam and hydrogen in the proportions of from about 4 to 12 mols of steam and from about 1 to 6 mols of hydrogen per mol of uranium;
e. concurrently heating the second fluidized bed to a temperature within the range from about 575.degree. C. to about 675.degree. C. to produce a second intermediate reaction product including uranium dioxide (UO.sub.2);
f. conveying the second intermediate reaction product to a third fluidized bed;
g. maintaining the third fluidized bed comprising a mixture of the second intermediate reaction product and additional steam and hydrogen in the proportions of from about 2 to 11 mols of steam and from 0.5 to 6 mols of hydrogen per mol of uranium;
h. concurrently heating the third fluidized bed to a temperature within the range from about 575.degree. C. to about 675.degree. C. to produce a third intermediate reaction product consisting essentially of uranium dioxide (UO.sub.2) having an oxygen-uranium ratio of about 2 in a low residual fluoride content;
i. conveying the third intermediate reaction product to a fourth fluidized bed;
and
j. maintaining the fourth fluidized bed comprising the third intermediate reaction product and a mixture of air and nitrogen to further reduce the fluoride content and increase the oxygen-uranium ratio to about 2.25 to produce ceramic-grade uranium dioxide suitable for use in the manufacture of fuel pellets for nuclear reactors.

8 more elements

Dependencies are inferred from the claim text.