A method of producing uo2 from u3o8

Abstract

The application discloses a method for preparing UO2 from U3O8, which adopts activated carbon to reduce U3O8, shortens the intermolecular distance between the activated carbon and U3O8 by tabletting, and prevents the entrainment of gas to the powder in the reaction process; the porous structure of the activated carbon greatly increases the contact area with U3O8, improves the reduction efficiency, and the activated carbon is removed in the final product UO2, so that the purity of UO2 is ensured; the method is simple, short in period, and high in safety, and is suitable for large-scale reduction of U3O8 to prepare UO2.

Description

Technical Field

[0001] This invention belongs to the field of spent fuel reprocessing technology, specifically relating to a method for preparing UO2 from U3O8. Background Technology

[0002] Uranium dioxide is an important component of MOX fuel in fast reactors and has significant application prospects in fast breeder reactors (FBRs). The most stable oxide form of uranium is uranium trioxide (uranium octaoxide). At room temperature, uranium dioxide can spontaneously convert to uranium trioxide, causing a change in its physicochemical properties.

[0003] The common process for producing uranium dioxide is the ammonium diuranate (ADU) method: using UF6 as raw material, ammonium diuranate (ADU) is obtained through hydrolysis and precipitation, and then decomposed and reduced to uranium dioxide powder under an H2 atmosphere. However, the process for producing uranium dioxide has a long production cycle, complex procedures, and the O / U ratio of the obtained uranium dioxide powder is unstable. Summary of the Invention

[0004] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a method for preparing UO2 from U3O8 with a stable O / U ratio and a safe, simple and efficient operation process.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for preparing UO2 from U3O8, comprising the following steps:

[0006] (1) Take an appropriate amount of activated carbon and uranium oxide octoxide, mix them evenly, and compress them into tablets;

[0007] (2) The pressed activated carbon is sintered with uranium oxide at low temperature under vacuum;

[0008] (3) High-temperature vacuum heating to remove activated carbon;

[0009] (4) Cool the UO2 core block by vacuum cooling to below 50°C.

[0010] Furthermore, in step (1), the amount of activated carbon used is more than 2.9% of the mass of uranium octoxide.

[0011] Furthermore, in step (2), the temperature of low-temperature vacuum sintering is 500-1300℃, the vacuum degree is below 100Pa, and the sintering time is 0-8h.

[0012] Furthermore, in step (3), the temperature of the high-temperature vacuum heating is greater than 1300℃, the vacuum degree is less than 100Pa, and the heating time is 0 to 8 hours.

[0013] Furthermore, in step (4), the vacuum cooling temperature is 20–30°C.

[0014] The beneficial effects of adopting the technical solution of the present invention are as follows: A method for preparing UO2 from U3O8 uses activated carbon to reduce U3O8. By pressing and forming the reactants into tablets, the intermolecular distance of the reactants is shortened, preventing gas entrainment in the powder during the reaction process. Furthermore, the porous structure of the activated carbon greatly increases the contact area with U3O8, improving the reduction efficiency. Moreover, the activated carbon is removed in the final product UO2, ensuring the purity of UO2. The method of the present invention is simple, has a short cycle, and is highly safe. It is suitable for large-scale reduction of U3O8 to prepare UO2. Attached Figure Description

[0015] Figure 1 This is the XRD pattern of UO2 prepared by the method in Example 2 of this invention;

[0016] Figure 2 The XRD pattern of UO2 prepared by the method in Example 3 of this invention;

[0017] Figure 3 This is the XRD pattern of UO2 prepared by the method in Example 4 of this invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] Example 1

[0020] This invention provides a method for preparing UO2 from U3O8, comprising the following steps:

[0021] (1) Take an appropriate amount of activated carbon and mix it evenly with uranium oxide, and press it into tablets; the amount of activated carbon is more than 2.9% of the mass of uranium oxide to ensure that the activated carbon is in excess; ensure the reduction rate of uranium oxide; shorten the intermolecular distance of the reactants by pressing into tablets, making the reaction easier to occur, and preventing the gas from entraining the powder during the reaction process.

[0022] (2) The pressed activated carbon is subjected to low-temperature vacuum sintering with uranium oxide; the temperature of low-temperature vacuum sintering is 500-1300℃, the vacuum degree is below 100Pa, and the sintering time is 0-8h.

[0023] (3) High-temperature vacuum heating to remove activated carbon; the temperature of high-temperature vacuum heating is greater than 1300℃, the vacuum degree is less than 100Pa, and the heating time is 0 to 8h.

[0024] (4) The UO2 core is obtained by vacuum cooling to below 50°C. This prevents the UO2 core from being oxidized again due to contact with air during the cooling process, and maintains a stable O / U ratio.

[0025] Preferably, in step (1), the pressure range for tableting is 56 to 226 MPa; under this pressure range, the formed activated carbon and uranium oxide blocks are not loose and are not easily broken.

[0026] Preferably, in step (2), the vacuum temperature is 900℃, the vacuum degree is 0.1Pa, and the sintering time is 4h.

[0027] Preferably, in step (3), the high-temperature sintering temperature is 1500℃, the vacuum degree is 0.1Pa, and the sintering time is 4h.

[0028] Preferably, in step (4), the vacuum temperature is reduced to 20°C to 30°C.

[0029] Example 2

[0030] The method for preparing UO2 using U3O8 according to Embodiment 1 of the present invention includes the following steps:

[0031] (1) Weigh out activated carbon with a mass ratio of 0.12:1 and mix it evenly with uranium oxide octoxide. Press it in a steel mold (8mm) for 3 minutes under a pressure of 113MPa.

[0032] (2) Place the sample in a vacuum furnace and sinter it under vacuum at 900℃-0.1Pa for 4 hours;

[0033] (3) Cool down to room temperature under vacuum of 0.1 Pa and take out the sample.

[0034] The sample was weighed, and the mass of the sample after the reaction was 1.053g, with a mass loss of 0.067g. The sample was completely burned in air at 600℃, and the mass of the powder obtained was 0.99g.

[0035] See attached document Figure 1 This indicates that the sample prepared by the method of this embodiment contains excess activated carbon doping.

[0036] The rest is the same as in Example 1.

[0037] Example 3

[0038] The method for preparing UO2 using U3O8 according to Embodiment 1 of the present invention includes the following steps:

[0039] (1) Weigh out activated carbon with a mass ratio of 0.12:1 and mix it evenly with uranium oxide octoxide. Press it uniaxially in an 8mm steel mold for 3 minutes under a pressure of 113MPa.

[0040] (2) Place the sample in a vacuum furnace and sinter it under vacuum at 900℃-0.1Pa for 4 hours;

[0041] (3) Vacuum sintering at 1500℃-0.1Pa for 4 hours;

[0042] (4) Cool down to room temperature under vacuum of 0.1 Pa and remove the sample.

[0043] See attached document Figure 2 The method in this embodiment of the invention completely converts U3O8 into UO2. The sample is weighed, and the sample mass loss is 0.159g, indicating that the excess activated carbon has been basically removed.

[0044] The rest is the same as in Example 1.

[0045] Example 4

[0046] The method for preparing UO2 using U3O8 according to Embodiment 1 of the present invention includes the following steps:

[0047] (1) Weigh out activated carbon with a mass ratio of 0.12:1 and mix it evenly with uranium oxide octoxide. Press it uniaxially in an 8mm steel mold for 3 minutes under a pressure of 113MPa.

[0048] (2) The sample was placed in a vacuum furnace and sintered under vacuum at 900℃ and 0.1Pa for 4 hours;

[0049] (3) Continue vacuum sintering at 1500℃ and 0.1Pa for 4 hours;

[0050] (4) Cool down to 300°C under vacuum conditions of 0.1 Pa and open the furnace lid.

[0051] During the opening process, the columnar sample inside the furnace burned rapidly and turned into powder within 1 minute. After collection, it was weighed and the mass was 0.98g.

[0052] See attached document Figure 3 This indicates that the reduced U3O8 was re-oxidized during the opening process; the 0.02g mass loss is due to operational errors during the powder transfer process.

[0053] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for preparing UO2 from U3O8, characterized in that, Includes the following steps: (1) Take an appropriate amount of activated carbon and uranium oxide, mix them evenly, and press them into tablets. The amount of activated carbon used is more than 2.9% of the mass of uranium oxide. (2) The pressed activated carbon is sintered with uranium oxide at a low temperature in a vacuum. The temperature of the low temperature vacuum sintering is 500-1300℃, the vacuum degree is below 100Pa, and the sintering time is 4-8h. (3) High temperature vacuum heating to remove activated carbon, the temperature of high temperature vacuum heating is greater than 1300℃, the vacuum degree is less than 100Pa, and the heating time is 4~8h; (4) Cool the UO2 core block by vacuum cooling to below 50°C.

2. The method for preparing UO2 from U3O8 according to claim 1, characterized in that, In step (2), the low-temperature vacuum sintering temperature is 900℃, the vacuum degree is 0.1Pa, and the sintering time is 4h.

3. The method for preparing UO2 from U3O8 according to claim 1, characterized in that, In step (3), the high-temperature vacuum heating temperature is 1500℃, the vacuum degree is 0.1Pa, and the sintering time is 4h.

4. The method for preparing UO2 from U3O8 according to claim 1, characterized in that, In step (4), the vacuum temperature is reduced to 20℃~30℃.

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