JP3071516B2 - Method for producing powdery uranium-containing compound - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a uranium-containing compound. More specifically, the present invention relates to a method for producing a urania gadolinia oxide such as U ₃ O ₈ to (U, Gd) ₃ O ₈ , and in particular, pellets of UO ₂ , (U, Gd) O ₂ , or ( U, Pu) O
_The present invention relates to a method for converting dioxide such as No. ₂ into powdery 8.3 oxide by a dry method.

The powdery 8.3 oxide converted in this way is useful as a material for controlling the density of dioxide pellets such as UO ₂ , (U, Gd) O ₂ or (U, Pu) O _2. is there.

[0003]

A conventional techniques and to be Solved by the Invention Conventionally, in order to obtain a U ₃ O ₈ is eighty-three oxide granular or pellet-like UO ₂ is, UO _2, for example 500 to 700 ° C. in air Is mainly used. The reaction in this case is such that the free energy of formation of U ₃ O ₈ is about −
850 Kcal / mol, the free energy of formation of UO ₂ is about -260 Kcal / mol, and U ₃ O is relatively easily formed.
It can be seen that it is oxidized to ₈ .

However, in the conventional method, when the raw material is shaped pellets, it is necessary to pulverize all of the raw materials into powder in order to effectively perform the oxidation reaction. It is complicated and it is difficult to make all of the pulverized material into powder having a size of, for example, 100 mesh or less. For example, when classifying powder, the sieving operation is complicated and time-consuming. Conventionally, it takes about 12 hours to recover 90% or more of powder of 100 mesh or less. Assuming that the actual working time of a worker is about 2 hours a day,
Classification is extremely disadvantageous in the production process.

The present invention has been made in view of the above-mentioned prior art, and does not substantially require a pulverizing step or a classifying step, and is capable of producing a powdery 83 oxide which has a simplified production step. It is intended to provide a way.

[0006]

According to the present invention, there is provided a method for producing a powdery uranium-containing compound, comprising the steps of preparing a powdery urania-containing compound from urania-gadolinia oxide (U, Gd) O _2.
A method for obtaining gadolinia oxide (U, Gd) ₃ O ₈ , comprising: urania gadolinia oxide (U, Gd) O
₂ is heat-treated in a carbon dioxide-containing gas to form urania gadolinia oxide (U, G
d) Oxidation and pulverization of O ₂ are carried out to obtain powdery urania gadolinia oxide (U, Gd) ₃ O ₈ .

[0007] In the method of the present invention, the raw material to be heat treated is urania gadolinia oxide (dioxide) (U,
Gd) O ₂ , in which UO ₂ or (U, G
d) An excipient of an oxide represented by O ₂ (for example, a pellet or a lump) is included.

[0008] In the present invention, the shaped dioxide as described above is subjected to a heat treatment in its original shape or in a state of being ground or classified to some extent. This heat treatment is performed in a carbon dioxide-containing gas. As the carbon dioxide-containing gas in this case, a mixture of air and carbon dioxide can be preferably used. In this case, the pressure of carbon dioxide is preferably about 1 to 2 atm. The pressure of the entire carbon dioxide-containing gas is suitably from 1 to 3 kg / cm ² .

The heat treatment temperature is 400 to 7
The range of 00 ° C is suitable, and more preferably 500 to
600 ° C.

By the above heat treatment, UO ₂ or (U, G
d) O ₂ is oxidized to U ₃ O ₈ or (U, Gd) ₃ O
₈ is produced, but by performing this in an atmosphere of carbon dioxide-containing gas as described above, powdering is remarkably promoted. The reason for this is not necessarily clear, but it is thought to be due to the catalytic performance of the uranium compound surface and the accompanying action of activated oxygen derived from CO ₂ gas.

Generally, a UO ₂ or (U, Gd) O ₂ sintered body is extremely stable under ordinary conditions and does not easily oxidize. For example, it is gradually oxidized in an air atmosphere at a temperature of 500 to 700 ° C., and finally becomes U ₃ O ₈ or (U, Gd) ₃ O _8. In the heat treatment in the inside, it is difficult to satisfactorily pulverize the pellet-shaped sintered body, and a granular substance or a lump remains.

In the method of the present invention, the catalytic performance of the uranium compound is utilized to promote the decomposition of CO ₂ gas and increase the partial pressure of oxygen in the atmosphere. In general, the catalytic performance of transition metals and the like is explained by the contribution of d-electrons in atoms, but it is considered that f-electrons contribute to actinides such as uranium. That is, as uranium is understood in electron configuration ^5f 3 ^{6d7s 2,} is usually tetravalent, especially (U, Gd) to maintain the charge balance between the Gd (3 valence) in _{O 2,} U is It also exists as pentavalent, and the following reaction occurs.

U ⁴⁺ = U ⁵ ++ ^e− And, in this case, the carbon in CO ₂ is negative and CO ₂
It is thought that the oxygen released easily is different from oxygen in the air and is active so-called nascent oxygen, and such a mechanism contributes to efficient oxidation and pulverization. It is thought that it is.

According to the method of the present invention, good oxidation and pulverization are achieved, the time for sieving the oxide powder when recovering the obtained 183 oxide as a powder is reduced, and the yield of the recovered powder is reduced. Can be significantly improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Urania gadolinia oxide (U, Gd) O
₂ in air (1 atm), air and carbon dioxide (1 atm), and air and carbon dioxide (2 atm)
When the heat treatment was performed in an atmosphere consisting of, these atmosphere gases were passed through a heat treatment furnace at a pressure of ² kg / cm ² . The heating temperature was 500 ° C.

The recovery of the thus obtained powder of urania gadolinia oxide (U, Gd) ₃ O ₈ was measured.

The recovery rate in this case means (weight of powder after sieving) / (input weight to sieve).

FIG. 1 shows the change over time in the recovery rate of the obtained powder under each condition. In the figure, A is in the air (1 atm), B is air and carbon dioxide (1 atm).
In case m), C is the case of air and carbon dioxide (2 atm).

According to the method of the present invention using CO ₂ gas, the sieving time at which the ratio of those passing through a sieve (100 mesh or less) is 90% or more is 300 to 350.
Minutes, which makes it possible to reduce the time to about 1/2 compared to about 600 minutes in the conventional method. In addition, the frequency at which the stainless steel net used for sieving was broken by uranium granules during use was also reduced from conventional twice / month to substantially zero / month.

[Brief description of the drawings]

FIG. 1 is a graph showing a change over time in a powder recovery rate.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-259596 (JP, A) JP-A-2-95298 (JP, A) JP-A-63-214693 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G21C 3/62 G21C 21/02

Claims (3)

(57) [Claims] 1. Urania gadolinia oxide (U, Gd)
Powdery urania-gadolinia oxide from the shaping product of O ₂ (U, _Gd) 3 A method for obtaining _{O 8,} urania-gadolinia oxide (U, Gd) dioxide shaping product of _{O 2} By performing heat treatment in a carbon-containing gas, both oxidization and powderization of urania gadolinia oxide (U, Gd) O ₂ are performed to obtain powdery urania gadolinia oxide (U, Gd) ₃ O ₈ . A method for producing a powdery uranium-containing compound, comprising: 2. The method of claim 1, wherein said carbon dioxide-containing gas comprises a mixture of air and carbon dioxide. 3. The pressure of the carbon dioxide-containing gas is from 1 to 3.
The method of claim 1, wherein the method is kg / cm ² .