JPH0224767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field) The present invention relates to a method for producing uranium dioxide powder with good fluidity from uranium hexafluoride or uranyl nitrate via ammonium diurate (ADU).

(Prior art and its problems) In the case of a wet method, uranium dioxide powder, which is a raw material for electric power generation electric furnace fuel, is usually produced by the following process. That is, solid uranium hexafluoride (UF ₆ ) is heated and vaporized, this uranium hexafluoride is brought into contact with pure water and hydrolyzed to form a dilute aqueous solution of uranyl fluoride (UO ₂ F ₂ ). An aqueous ammonia solution is added to form a precipitate of ammonium diuranate (ADU), this slurry solution is filtered, the resulting cake is washed, dried, and pulverized.The resulting ADU powder is subjected to roasting and reduction, followed by reduction of carbon dioxide. This is a method for producing uranium powder, and is generally referred to as the ADU method among wet conversion methods. However, the uranium dioxide powder produced by this method has poor fluidity, and the process for producing the powder has had problems such as clogging in the hopper and difficulty in quantitatively feeding the powder.

In addition, in the pellet forming process using the uranium dioxide powder as a raw material, in order to improve the fluidity of the powder, it was necessary to provide a rough compacting process to form a green compact using a rotary press and a granulation process to size the green compact.

(Object of the Invention) Therefore, the present inventors provide a method for producing uranium dioxide powder with good fluidity in the above-mentioned conventional method of producing uranium dioxide powder from uranium hexafluoride or uranyl nitrate by the wet ADU method. As a result of investigation, it was discovered that the above object can be achieved by adjusting the moisture content of ADU, which is an intermediate product, and the present invention was achieved.

(Structure of the Invention) That is, according to the present invention, uranium hexafluoride (UF ₆ ) is heated and vaporized, and the uranium hexafluoride is brought into contact with pure water and hydrolyzed to produce uranyl fluoride (UO ₂ F ₂ ) Prepare an aqueous solution and add an ammonia aqueous solution to this aqueous solution or to a uranyl nitrate aqueous solution to generate a precipitate of ammonium deuterate (ADU),
Next, this precipitate is separated, washed, dried, and then ground to obtain ADU powder, and the ADU powder is roasted and reduced in a method for producing uranium dioxide powder,
In the drying process of the ADU precipitation, the moisture content of the dried ADU powder is adjusted to 20 to 35% by weight, and in the granulation process of the ADU powder following the drying process, an ammonium salt is mixed into the ADU powder as a binder. The ADU powder was granulated using
Good fluidity characterized by ~1500μm
A method for producing UO ₂ powder is obtained.

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a flow sheet of one embodiment of the present invention.

In the present invention, it is important to adjust the moisture content of ADU powder from the drying process to 20 to 35% by weight on a dry weight basis, and the subsequent processing is performed using conventional mechanical methods to reduce ADU powder to a thickness of 50 to 1500 μm. granulate into particles with a particle size of . This granulation process normally requires a binder such as polyvinyl alcohol (PVA), but we found that NH ₄ F or
Since we discovered that ammonium salts such as NH ₄ NO ₃ act as an effective binder, there is no need to add or mix a new binder, and the ADU powder can be produced relatively easily by simply adjusting the water content. It was confirmed that grains could be formed.

The ADU powder granulated in this way is dried,
When the granulated ADU powder is then roasted and reduced for 30 to 60 minutes at a temperature of 600 to 800°C, the particle size of the granulated ADU powder shrinks by about 10 to 20%, but the shape of the granulated ADU powder is maintained and the fluidity is improved. It was found that good uranium dioxide powder could be obtained.

In the method of the present invention, if the moisture content of the ADU powder is less than 20% by weight on a dry weight basis, granulation will not occur, and if it exceeds 35% by weight, the powder will become sticky, and both are unsuitable.

Further, the particle size of the granulated ADU powder is in the range of 50 to 1500 μm, and any particle size outside this range is unfavorable for pellet formation.

Furthermore, the temperature at which the granulated ADU is roasted and reduced is 600~
It is in the range of 800℃. If this temperature is less than 600℃, the fluorine content in the uranium dioxide powder will increase, while if it exceeds 800℃, the activity of the uranium dioxide powder will decrease, making it impossible to obtain pellets with the required density (around 95%). .

Next, the present invention will be explained in more detail with reference to examples, but the scope of the present invention is not limited by the following examples.

Example 1 Gasify UF ₆ and absorb it into water to produce 145g
Make a ₂ -solution UO ₂ F, add 28% by weight ammonia water to it, and stir until the pH becomes 10.
An ADU slurry was made, 10% of this slurry was taken and passed through paper to obtain an ADU cake. The cake was dried without washing at a temperature of 120° C. for about 1 hour to a moisture content of 28% by weight on a dry weight basis. In this state, it contained 6% by weight of NH ₄ F salt. This ADU powder was granulated to an average particle size of about 500 μm using a rolling type general granulation method.
900 g of this granulated ADU powder was dried at a temperature of 120° C. for about 5 hours, and then roasted and reduced at a temperature of 670° C. for about 90 minutes in a hydrogen reducing atmosphere containing a stream of water vapor to obtain UO ₂ powder. This UO ₂ powder had an average particle diameter of approximately 400 μm, had a high apparent density, and had a nearly spherical particle shape, so it had good fluidity, and the residual fluorine in the UO ₂ powder was 10 ppm or less. This UO ₂ powder did not need to be granulated again before processing into pellets.

Example 2 Uranyl nitrate UO ₂ with a uranium concentration of 100 gU/
(NO ₃ ) ₂ aqueous solution was prepared, 28% by weight ammonia water was added to it, and the mixture was stirred until the pH reached 10.
An ADU slurry was made, 12 of this slurry was taken and passed through paper to obtain an ADU cake. The cake was dried without washing at a temperature of 120° C. for approximately 1 hour to a moisture content of 30% by weight on a dry weight basis. In this state, it contained 5% by weight of NH ₄ NO ₃ salt. This ADU powder was granulated to an average particle size of about 1000 μm using a rolling type general granulation method. After drying 800 g of the obtained granulated ADU powder at a temperature of 120°C for about 5 hours, it was dried for 700 g in a hydrogen reducing atmosphere containing a stream of water vapor.
Roast reduction was performed at a temperature of ℃ for about 90 minutes to obtain _UO2 powder. This UO ₂ powder had an average particle size of about 800 μm, a high apparent density, and a nearly spherical particle shape, so it had good fluidity, and it was not necessary to granulate it again before forming into pellets.

(Effects of the Invention) By adopting the above configuration, the present invention can achieve the following effects.

(1) The obtained uranium dioxide powder has a high apparent density and the particle shape is close to spherical, so it has very good fluidity, eliminates the problem of clogging in the powder hopper, and is easy to granulate during the pellet forming process. The process is no longer necessary.

(2) Since granulation is carried out in the ammonium deuterate process, in the subsequent processes, such as drying, roasting and reduction, filling, and mixing,
There is less dusting and uranium loss is reduced compared to conventional methods.

(3) Since ammonium salts such as NH ₄ F and NH ₄ NO ₃ can be used as binders, uranium dioxide powder with extremely low fluorine content can be obtained, which is extremely useful in the production of nuclear fuel.

[Brief explanation of drawings]

FIG. 1 is a flow sheet diagram of an embodiment of the present invention;
FIG. 2 is a flow sheet diagram of an example of a conventional method.

Claims (1)

[Claims] 1 Heating and vaporizing uranium hexafluoride (UF ₆ ),
Contact with pure water and hydrolyze to obtain a uranyl fluoride (UO ₂ F ₂ ) aqueous solution, and add an ammonia aqueous solution to the aqueous solution or to the uranyl nitrate aqueous solution to generate a precipitate of ammonium deuterate (ADU),
In the method for producing uranium dioxide powder, which comprises separating the precipitate, washing and drying, pulverizing the precipitate to obtain ADU powder, and further roasting and reducing the ADU powder, the drying step of the ADU precipitate involves Applicable
Adjust the moisture content of ADU powder to 20-35% by weight,
In the granulation process of the ADU powder following the drying process, the ADU powder is granulated using ammonium salt accompanying the ADU powder as a binder, and furthermore, in the drying process following the granulation process, the drying temperature is adjusted.
A method for producing UO ₂ powder with good fluidity, characterized in that the temperature is in the range of 110 to 180°C, and the particle size of the granulated ADU powder after drying is 50 to 1500 μm.