JPH0657607B2 - Method for producing uranium dioxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field) The present invention is one of the methods for producing UO ₂ powder suitable for reactor fuel production by converting uranium hexafluoride.
Regarding improvement of U method.

(Prior Art and Problems Thereof) There are a wet method and a dry method for converting uranium hexafluoride into uranium dioxide powder for nuclear reactor fuel. Wet method is UF ₆
It is a method to obtain uranium dioxide powder by hydrolyzing gas by gas-liquid reaction to give a uranyl ion-containing liquid, adding chemical substances to it to form a precipitate, and then performing separate, drying, roasting, and reduction steps. However, the wet method has drawbacks such as a large number of steps and a complicated amount of waste liquid generation as described above,
The resulting uranium dioxide powder has advantages such as excellent characteristics and a small amount of residual F.

In the wet method, the ADU (ammonium heavy uranate) method is most often used. In this method, an aqueous ammonia solution is added to the above uranyl ion-containing liquid to obtain a precipitate of ammonium diuranate, and then uranium dioxide powder is obtained through the steps of over-drying, roasting, and reducing. It can be represented by a reaction formula.

In this reaction, ammonia water is the target product, ADU
In addition to the precipitation reaction of (1), since it also reacts with HF by-produced in the formula (1), ammonia water in excess of the originally intended amount is required. It also leads to the generation of NH ₄ F, which migrates into the liquid in the subsequent overstep.

(Object of the Invention) The object of the present invention is to reduce the amount of ammonia water used in the conventional ADU method, to reduce the amount of NH ₄ F generated, and to contain the uranyl ion obtained by hydrolysis of UF ₆ gas. It is an object of the present invention to provide a method for producing uranium dioxide, which makes it possible to make the related apparatus compact by increasing the uranium concentration in the solution as compared with the case of the ADU method.

(Object of the Invention) That is, according to the present invention, in the method for converting UF ₆ gas to uranium dioxide, (a) UO ₂ gas is produced by a gas phase reaction between UF ₆ gas and steam.
First step for separating F ₂ particles and HF gas, (b) Second step for dissolving UO ₂ F ₂ particles from the first step in water, (c) Aqueous ammonia solution for UO ₂ F ₂ aqueous solution in the second step Third, adding ammonium to precipitate ammonium diuranate
Step 4, (d) Separate the precipitation of ammonium biuranate from the third step and dry it, and step (e) Roast and reduce the dried ammonium heavy uranate of the fourth step to convert it into UO ₂ powder. And a fifth step for converting uranium hexafluoride to produce uranium dioxide powder.

Next, the present invention will be described with reference to the drawings. The accompanying drawing is a system diagram of an apparatus used in an embodiment of the invention.

In the figure, in the first step, the UF ₆ gas is vaporized by the vaporizer 1
Is vaporized and is spray-introduced into the device 2 from a nozzle in the first fluidized bed reactor 2. At the same time, water vapor as reaction gas and fluidizing gas is introduced into the bottom of the device 2 via the conduit 9. The UF ₆ gas sprayed from the nozzle reacts with this water vapor to produce UO ₂ F ₂ particles. The operating temperature of the first fluidized bed reactor 2 is 400 ° C. or lower, preferably 220 to 300 ° C. from the viewpoint of controlling the particle size of the fluidized bed.

The HF gas by-produced in the first fluidized bed reactor 2 is HF.
It is recovered as an HF aqueous solution by the condenser 2a and received by the HF receiver 2b.

Next, in a second step, the produced UO ₂ F ₂ particles overflow from the fluidized bed and are discharged from the device 2 and introduced into the dissolution device 3, where they are dissolved by the water introduced from the conduit 10. . In the third step, the UO ₂ F ₂ aqueous solution is sent to the reaction device 4, and in the reaction device 4, the ammonia aqueous solution is introduced from the conduit 11 and reacted with the UO ₂ F ₂ aqueous solution to be converted into ammonium diuranate. In the fourth step, the ammonium heavy uranate precipitate and the aqueous ammonia solution are passed through a passer 5, separated into a precipitate and a liquid, and the separated precipitate is dried. In the fifth step, the ammonium diuranate dried in the fourth step is sent to the reduction device 7,
Roasting with H ₂ , N ₂ and steam introduced from the conduit 12,
It is reduced to form UO ₂ and is received in container 8 as the product uranium dioxide powder. Reference numeral 13 is an exhaust treatment system.

As described above, according to the present invention, the hydrolysis step of the conventional ADU method (hereinafter, referred to as a conventional method) can be applied to a fluidized bed reactor or the like by UF _{6 process.}
It was converted into a process to obtain UO ₂ F ₂ particles by blowing gas and water vapor.

That is, the merits of the present invention are
In point.

(1) It is possible to reduce the amount of ammonia water used and the generation of by-product NH ₄ F as compared with the conventional method. In the method of the present invention, by introducing a dry hydrolysis step into a wet hydrolysis step, HF produced as a by-product in the hydrolysis step is converted into UO ₂ gas.
It becomes possible to separate from F ₂ powder, which reduces the amount of ammonia water used in the ADU process to about 40% compared to the conventional method, and the amount of NH ₄ F generated is 1 / It will be about 3.

Further, in the method of the present invention, the HF gas generated from the hydrolysis step is condensed and recovered, and the recovered HF aqueous solution is converted into H ₂ SO ₄
It can be recovered as hydrofluoric acid by adding the operation of extractive distillation with the action of. This hydrofluoric acid anhydride can be reused as a raw material for a manufacturing plant of UF ₆ , which is a raw material for uranium enrichment.

In contrast, Hutu oxygen partial in the conventional method is in the form of all NH ₄ F, but in order to obtain the anhydrous hydrofluoric acid from the NH ₄ F There are several ways, for example, the NH ₄ F Ca (O
H) ₂ reacted with, after collecting the ammonia partial, but recovery of HF becomes possible in a method for recovering anhydrous HF by the action of H ₂ SO ₄ in ZanTsuta CaF _2, a by-product of CaSO ₄ Will occur.

(2) The concentration of uranium in the uranyl ion-containing solution is significantly increased, which makes it possible to make the related equipment compact.

According to the method of the present invention, a uranyl ion-containing solution (UO ₂₎ obtained by hydrolyzing UF ₆ gas is used as compared with the conventional method.
F ₂ solution: In the present invention, the uranium concentration in the solution obtained by dissolving UO ₂ F ₂ in the second step described in claim (b) can be greatly increased practically.

In the conventional method, since UF ₆ gas is blown directly into water (liquid state) for reaction, HF remains in addition to UO ₂ F _{2 in} the produced uranyl ion-containing liquid. Are produced as HF gas and separated from UO ₂ F ₂ .

When HF is contained in the uranyl ion-containing liquid, the following problems occur.

(a) Uranyl ion-containing liquid containing HF has a lower solubility of uranium than liquid containing no HF, (b) Uranyl ion-containing liquid containing HF increases the uranium concentration, and then UO ₂ is added by a step. When produced, the activity of UO ₂ produced is lower than that of a liquid containing no HF, and the reactor fuel has a activity of 100 to 250 gU /
Is the limit.

According to the method of the present invention, the UO ₂ F ₂ particles are separated from the generated HF gas and then dissolved, so that the HF concentration in the liquid becomes small. Therefore, the dissolution concentration should be increased to about 1200 gU /. It is possible to obtain a uranium concentration of 400 in the liquid containing uranyl ions under the condition that the produced UO ₂ satisfies the required standard as a reactor fuel even in the practical operation range.
It is possible to increase up to ~ 900 gU /. Therefore, according to the method of the present invention, the related apparatus can be made compact by about 1/2 to 1/5 as compared with the conventional method.

This means that when the same amount of U is supplied and the same size of tank and reaction device are used after the dissolution step, the method of the present invention has a processing speed several times that of the conventional method. And bring great effects. On the contrary, in order to keep the processing speed at the same level, the conventional method must increase the volume of the equipment and tanks.

Further, according to the present invention, the physical properties of the UO ₂ powder obtained are shown in Table 2 of the Example in comparison with the physical properties in the conventional method, but almost the same values were obtained, which is problematic as a fuel for a nuclear reactor. There is no. That is, the present invention provides a method for converting UF ₆ into UO ₂ powder, which reduces by-products (NH ₄ F) as compared with the conventional method and enables the related apparatus to be made compact. .

Next, the present invention will be described more specifically by way of examples, but the following examples do not limit the scope of the present invention.

Example The diameter of the reaction part of the fluidized bed reactor used in this example is 8.
It is 3 cm, and the main operating conditions are as follows.

Operating conditions: Treatment rate (UF ₆ ) 8 kg-mol / hr Reaction temperature 280 ° C. Fluidized gas velocity 15 cm / S (H ₂ O used as gas, linear velocity) Table 1 shows typical methods of the present invention and conventional methods. Comparison with other methods is shown. For the conventional method, typical data of the ADU method is converted into the same processing speed.

As described above, according to the method of the present invention, the amount of ammonia water used at the time of the third step (ADU conversion) in the claims is reduced to about 40% as compared with the conventional method, and the amount of NH ₄ F The amount generated is about 1/3. In the conventional method, NH ₄ F produced in the subsequent process
Ammonia is recovered from the liquid and the F component is fixed as CaF ₂ . Therefore, according to the method of the present invention, A
Not only the DU part but also a part of the device in the subsequent step can be made compact.

Table 2 shows UO ₂ produced by the method of the present invention and the conventional method.
A comparison of typical physical properties of particles is shown. As is clear from Table 2, UO ₂ produced by the method of the present invention has no particular difference in physical properties as compared with UO ₂ produced by the conventional method, and the UO ₂ satisfying the required standard as a raw material for reactor fuel is sufficiently satisfied. You can see that

(Effects of the Invention) As described above, the present invention has the following effects by changing the hydrolysis process of the conventional ADU method to the dry process.

(1) Since the uranium concentration in the uranyl ion-containing solution obtained by hydrolysis of UF ₆ gas can be greatly increased practically, the processing capacity is increased.

(2) The amount of ammonia water used in the ADU process is reduced to about 40% compared to the conventional method.

(3) The amount of NH ₄ F produced as a by-product is about 1/3 that of the conventional method.

[Brief description of drawings]

The drawing is a system diagram of an apparatus used in one embodiment of the present invention. In the figure, 1 ... Vaporizer 2 ... Fluidized bed reactor 2a ... HF condenser 2b ... HF aqueous solution receiver 3 ... Dissolving device 4 ... ADU converting device 5 ... Passing device 6 ... Drying device 7 …… Roasting reduction device 8 …… Product receiver 9 …… Steam supply pipe 10 …… Water supply pipe 11 …… Ammonia water supply pipe 12 …… H ₂ , N ₂ , steam supply pipe 13 …… Exhaust treatment system

Claims (1)

[Claims] 1. A method for converting uranium hexafluoride into uranium dioxide powder, comprising: (a) UO ₂ F ₂ by a gas phase reaction between UF ₆ gas and steam.
First step for separating particles and HF gas, (b) Second step for dissolving UO ₂ F ₂ particles from the first step in water, (c) Add aqueous ammonia solution to UO ₂ F ₂ aqueous solution for second step Third to precipitate ammonium diuranate
Step 4, (d) Separate the precipitation of ammonium biuranate from the third step and dry it, and step (e) Roast and reduce the dried ammonium heavy uranate of the fourth step to convert it into UO ₂ powder. A fifth step, a method for producing uranium dioxide, characterized in that