JP2836711B2 - Method and apparatus for producing ammonium biuranate particles - 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 ammonium biuranate particles and an apparatus for producing ammonium biuranate particles used in the production method, and more particularly, to a method for producing ammonium biuranate having a high sphericity. The present invention relates to a method for producing ammonium biuranate particles which can be easily produced by a small apparatus, and an apparatus for producing ammonium biuranate particles having a simple structure used in the production method.

[0002]

2. Description of the Prior Art Generally, ammonium biuranate particles are produced by an external gelling method as shown in FIG. The droplet 2 of the uranyl nitrate solution formed by the droplet dropping means 1 becomes a true sphere due to its own viscosity and surface tension while falling down the droplet forming section 3. The sphere-shaped droplet falls from the droplet falling port 4 to the surface gelling section 6. Next, the droplets are completely gelled in an aqueous ammoniacal solution, which is a complete gelling section, to form ammonium biuranate particles.

[0003] The sphericity of ammonium biuranate particles is governed by the sphericity of a droplet of a uranyl nitrate solution immersed in an ammoniacal aqueous solution, and the sphericity of the deformed droplet is determined by the complete gelation interval. Will not be restored. Therefore, the purpose of the surface gelation section is to allow the droplet of the uranyl nitrate solution to withstand the impact when it lands in the aqueous ammoniacal solution and to maintain its sphericity, so that the surface of the droplet can be maintained. Is sufficiently gelled with ammonia gas.

As a general method for gelling the surface, a method is used in which the droplets are passed through a gelling agent atmosphere such as ammonia. Conventionally, as a specific method, a method of blowing ammonia gas as a jet from the ammonia gas supply port 16 into the air layer to promote the surface gelation of the droplet has been adopted. Under normal droplet formation conditions, the terminal drop speed of the droplet is about 0.5 m / sec or more.
At this speed, the falling droplets take in air (or an inert gas) around the droplet forming section, so that even during the surface gelling section, as shown in FIG. Layer 17 is formed. This layer of air hinders the reaction between the droplets and the ammonia gas, so it is necessary to blow the ammonia gas into the air layer as a jet.

A first disadvantage of the above method is that the ammonia gas is supplied in a jet state, which causes deformation of the droplet. Furthermore, since the amount of ammonia gas used increases, the size of the ammonia gas recovery device for preventing environmental pollution is increased, and accordingly, the entire device for manufacturing ammonium biuranate particles is increased in size.

The second disadvantage is that if the distance of the surface gelation section is increased in order to sufficiently gel the surface of the droplet, the terminal drop speed when the droplet lands on the ammoniacal aqueous solution also increases. The impact upon landing is increased. Therefore, even if the surface of the droplet is sufficiently gelled with ammonia gas, the sphericity is destroyed by the impact at the time of landing.

An object of the present invention is to solve the above problems. That is, an object of the present invention is to provide a method for producing ammonium biuranate particles and a method for producing ammonium biuranate particles which can be used for producing ammonium uranate particles having high sphericity with a small apparatus. It is to provide a manufacturing apparatus.

[0008]

Means for Solving the Problems As a result of diligent research conducted by the present inventors to solve the problems, the invention according to the first aspect is characterized in that ammonium diuranate particles are obtained from a uranyl nitrate solution by an external gelation method. In the method for producing
A method for producing ammonium biuranate particles, characterized by spraying a mist of an ammoniacal aqueous solution onto droplets of a uranyl nitrate solution.The invention according to claim 2, wherein the ammoniacal aqueous solution is a saturated aqueous ammonia solution. The method according to claim 1, wherein the mist is formed by an ultrasonic atomizer. The method according to claim 3, wherein the mist is formed by an ultrasonic atomizer. The invention according to claim 4 is a method for producing ammonium particles, wherein the mist has an average diameter of 30 μm or less, and the method according to claim 3, wherein the mist has an average diameter of 30 μm or less. The described invention is an ammonium biuranate particle production apparatus for producing ammonium biuranate particles from a uranyl nitrate solution by an external gelation method, A droplet dripping means for dripping the uranyl acid solution; and a precipitation tank having an aqueous ammoniacal solution for receiving droplets of the uranyl nitrate solution dropped from the droplet dripping means, wherein the droplet dripping means and the precipitation tank Between
An apparatus for producing ammonium biuranate particles, comprising an atomizer for spraying the mist of an ammoniacal aqueous solution, wherein the invention according to claim 6 is characterized in that ammonia is supplied from the sedimentation tank to the atomizer. The apparatus for producing ammonium biuranate particles according to claim 5, further comprising a means for sending a neutral aqueous solution.

Hereinafter, the present invention will be described in more detail. (1) Uranyl nitrate solution The uranyl nitrate solution is prepared from a uranyl nitrate stock solution, pure water, a thickener, and the like. Uranyl nitrate stock solution is U ₃ O
₈ It can be obtained by dissolving powder in nitric acid.
The uranium concentration in the uranyl nitrate stock solution is usually 465 to 4
75 gU / liter.

The thickener is added so that the dropped uranyl nitrate solution becomes a true sphere due to its own surface tension and viscosity during dropping. Examples of the thickener include a polyvinyl alcohol resin or a resin having a property of coagulating under alkaline conditions, polyethylene glycol, and Metroose. As the resin having a property of coagulating under alkaline conditions, a resin having a coagulating property in an alkali atmosphere by itself, for example, polyvinyl acetal / N; neutralized product of N-dimethylaminoacetate acid (trade name: AEA, Sankyo Pharmaceutical Co., Ltd.) ))). As the thickener, one kind can be used alone, or two or more kinds can be used in combination.

The uranium concentration in the uranyl nitrate solution is
It is usually from 100 gU / liter to 400 gU / liter, preferably from 120 to 250 gU / liter. The general content of the thickener is 2 g / l to 50 g / l, but when using Metroose as the thickener, the concentration is usually 4 to 10 g / l. The uranyl nitrate solution may appropriately contain an additive such as a photodegradation terminator or a surfactant for adjusting the surface tension of the stock solution. As the photodecomposition terminator, a substance having an effect of preventing photodecomposition of the binder resin (uranium becomes a catalyst), for example, tetrahydrofuryl alcohol (4HF) can be used.

The method of preparing the uranyl nitrate solution is not particularly limited, but in a usual case, a thickener aqueous solution is prepared in advance by mixing a thickener with pure water. It is prepared by mixing with uranyl and then adding pure water to adjust the concentration or viscosity.

(2) Method of forming uranyl nitrate solution droplets The uranyl nitrate solution prepared as described above is cooled to a predetermined temperature to adjust its viscosity, and is dropped from a dropping nozzle into an aqueous ammonia solution. You. At this time, the cooling temperature of the uranyl nitrate solution dropped from the dropping nozzle is determined by how the viscosity is adjusted. For example, the viscosity of uranyl nitrate solution is set to 70 to 100 cp.
(Centipoise), the cooling temperature is preferably 18 to 20 ° C.

The method of forming the uranyl nitrate solution into droplets is not particularly limited. For example, it can be realized by oscillating a small-diameter dropping nozzle by an appropriate means.
When the dropping nozzle is vibrated, the dropping nozzle may be vibrated in the axial direction thereof, or may be vibrated in the diameter direction of the dropping nozzle. The frequency is usually 40-200 Hz, but about 150 Hz is most common. The diameter of the dropping nozzle can be usually 0.4 to 1.5 mm. The delivery rate of the uranyl nitrate solution delivered from the dropping nozzle is usually 15 to 30 cc / min. Under such dripping conditions of uranyl nitrate, about 1.2 to 2.8.
Droplets of a uranyl nitrate solution having a diameter of mm are formed by the dropping nozzle. The dripping nozzle is arranged so that its opening is directed downward and faces the aqueous ammonia solution described later.

(3) Surface gelation method of uranyl nitrate solution droplet The droplet of the uranyl nitrate solution formed by the vibration of the dropping nozzle is a space until it lands on the surface of the aqueous ammonia solution in a precipitation tank having an aqueous ammonia solution described later. In the above, it is necessary that the surface of the droplet is sufficiently gelled in order to prevent deformation at the time of landing. However, since the droplet immediately after dropping from the vibrating nozzle is not yet a true sphere, when the vibrating nozzle tip comes into contact with ammonia gas, the vibrating nozzle tip is instantaneously closed, so that it is placed in a certain space downward from the dropping nozzle. Is desirably kept in an atmosphere of air or an inert gas such as nitrogen.

According to the present invention, as a means for gelling the surface of the droplet, a mist of an aqueous ammoniacal solution is sprayed on the droplet. The aqueous ammoniacal solution as a gelling agent is not particularly limited as long as it generates ammonia gas.
Aqueous ammonia or a heated hydrazine aqueous solution is preferred, and saturated aqueous ammonia is particularly preferred. The concentration of the aqueous ammonia solution is usually from 20% by weight to a saturated concentration.

The mist of the ammoniacal aqueous solution is taken into a layer of air or an inert gas, adheres to the droplet while generating ammonia gas, and gels the surface of the droplet. The gel-like surface is formed by the conversion of a metal salt, for example uranyl nitrate, to an ammonium compound such as ammonium biuranate (ADU) by reaction of the heavy uranic acid solution with ammonia. The surface gelling action of the droplets is much more efficient with mist than with only ammonia gas.

The smaller the diameter of the mist, the better. this is,
Small mist adheres more uniformly to the droplet surface,
This is because the specific surface area of the mist increases and ammonia gas evaporating from the mist increases. The diameter of the mist is
If it is about 30 μm or less, it is sufficiently effective.

As the atomizer for generating the mist, any of a compressed gas atomizer and an ultrasonic atomizer can be used. In the compressed gas method, the droplet may be deformed by the jet of the compressed gas. On the other hand, when an ultrasonic atomizer is used, there is some heat generation at the tip of a nozzle that oscillates ultrasonic waves. For this reason, if the ammoniacal aqueous solution is supplied to the ultrasonic atomizer, more ammonia gas evaporates from the mist, and the efficiency of the surface gelling action is further improved. Therefore, in the present invention, an ultrasonic atomizer is more preferably used.

The flow rate of the aqueous ammoniacal solution sprayed as a mist is usually 1 to 3 times, preferably 2 to 2.5 times the amount of liquid droplets per vibrating nozzle. If the amount of the mist is less than 1 time, the sphericity of the droplet cannot be sufficiently secured, and if the amount is more than 3 times, the loss of the mist is large.

In the method of the present invention, there is no deformation of the droplet by the surface gelling means, for the following reason.
The layer of air or inert gas flows downward at approximately the same speed as the droplet. Therefore, the mist taken in the layer of air or inert gas also flows downward together with the flow of air or inert gas. That is, since the droplets pass through the position of the atomizer and fall together with the gas-liquid two-phase flow of the ammonia gas and the mist of the ammoniacal aqueous solution, there is no deformation due to surface gelation.

(4) A precipitation tank having an aqueous ammonia solution The liquid whose surface has been gelled immerses in the aqueous ammonia solution stored in the precipitation tank and completely settles down to the bottom of the precipitation tank. Gelled. The aqueous ammonia in the precipitation tank is preferably the same as that used when generating the mist. This is because it is possible to circulate and pump out the sedimentation tank using a transport pipe and a pump, spray it as a mist, and collect the mist in the sedimentation tank.

The ammonium biuranate particles completely gelled in the sedimentation tank as described above are washed with pure water and ethanol or methanol, and further subjected to drying, roasting and sintering steps to obtain spherical UO ₂ nuclear fuel particles. become. Each of these processes can be performed by a known method.

(5) Apparatus for producing ammonium biuranate particles The apparatus for producing ammonium biuranate particles of the present invention is for carrying out the production method described above. FIG.
Figure 1 shows the outline of the device. The following will be described with reference to FIG.

As shown in FIG. 1, the apparatus for producing ammonium biuranate particles includes a dropping means and a settling tank 13. The droplet dropping means includes a dropping nozzle 1 for dropping a uranyl nitrate solution supplied from a uranyl nitrate solution supply unit (not shown) for storing the uranyl nitrate solution. The dripping nozzle 1 has an opening that opens downward, and is disposed vertically above the sedimentation tank 13. Vibration is applied to the dripping nozzle 1 by, for example, an appropriate means in the horizontal direction, so that the droplet adhering to the opening can be dropped.

The sedimentation tank 13 is a bottomed cylindrical body having a droplet drop port 4 at the top. A predetermined amount of the ammoniacal aqueous solution 12 is stored in the sedimentation tank 13. A pair of exhaust ports 5 are provided opposite to each other on the peripheral side surface of the sedimentation tank 13, below the droplet dropping port 4 and above the liquid level in the sedimentation tank 13. The exhaust port 5 is connected to a pipe that collects ammonia gas with an exhaust amount that does not disturb the atmosphere when the droplet 2 falls. In addition, an exhaust pump (not shown) is attached to the pipe to exhaust ammonia gas through the pipe.

On the peripheral side of the settling tank 13, an atomizer 7 for spraying a mist of an aqueous ammonia solution on droplets is provided between the exhaust port 5 and the surface of the aqueous ammonia solution 12 in the settling tank 13. is set up. In addition, this atomizer 7
The method described in the section of “(2) Method of forming uranyl nitrate solution droplet” can be suitably used. In the apparatus shown in FIG. 1, the mist is removed by using ultrasonic waves. Is generated. A transport pipe 10 is attached to a wall surface of a portion of the settling tank 13 which is in contact with the aqueous ammonia solution, so that the aqueous ammonia solution 12 can be supplied to the atomizer 7 by the pump 11. A transport pipe 19 is attached so as to connect the bottom of the sedimentation tank 13 and the upper wall surface of the portion in contact with the aqueous ammonia solution, and the aqueous ammonia solution is pumped upward from the bottom by the aqueous ammonia circulation pump 18. It is circulating.

In the apparatus shown in FIG. 1, the area from the dropping nozzle 1 to the vicinity of the droplet dropping port 4 is a droplet forming section 3, and the area from the vicinity of the dropping port 4 to the ammoniacal aqueous solution surface 12 is a surface gel. And the ammoniacal aqueous solution 12
The inside is the complete gelation section 14.

The operation of the apparatus for producing ammonium biuranate particles shown in FIG. 1 will be described below. First, the drop 2 of the ammonium biuranate solution is dropped from the dropping nozzle 1 by vibration. The droplet formation section 3 has a sufficient distance for the droplet 2 to become a true sphere, and is disposed in the air or in an inert gas atmosphere. However, the droplet 2 becomes a true sphere while dropping in the droplet forming section 3 even if it does not. Sufficient exhaust is performed from the exhaust port 5 so that the ammonia gas does not leak from the droplet drop port 4 to the droplet forming section 3. Therefore, even in this case, in the droplet forming section 3, there is no deformation of the droplet shape due to the fact that the ammonia gas acts on the non-spherical droplet to gel the surface. In addition, the opening of the dropping nozzle is not blocked by the ammonia gas acting on the opening.

A mist 8 of an aqueous ammoniacal solution is sprayed from an atomizer 7 onto the droplet 2 entering the surface gelling section 6 from the droplet dropping port 4. Since two atomizers 7 are installed, the mist 8 can be sprayed uniformly over the entire droplet 2. Next, the droplets 9 whose surface has been gelled land on the liquid surface of the ammoniacal aqueous solution 12 which is the complete gelling section 14. At this time, since the surface of the droplet 2 is gelled by the mist 8 of the ammoniacal aqueous solution,
There is no damage to the droplets during landing. Settling tank 1
The droplet 9 whose surface has been gelled while falling in the ammoniacal aqueous solution 12 in 3 is completely gelled to become ammonium biuranate particles 15.

In the present invention, the ammoniacal aqueous solution 12 in the sedimentation tank 13 is collected and sent to the atomizer 7 by the transport pipe 10 and the pump 11. The mist 8 of the sprayed ammoniacal aqueous solution is collected in the precipitation tank 13. Therefore, according to the present invention, there is no need to newly supply ammonia gas as in the conventional method, so that the ammonia gas recovery device connected to the end of the exhaust port 5 can be downsized. Also,
Ammoniacal aqueous solution circulating pump 18 causes sedimentation tank 13
Since the aqueous ammoniacal solution is circulated upward from the bottom, it is possible to prevent the ammonium biuranate particles 15 from staying at the bottom of the precipitation tank 13 and being deformed by its own weight.

The length of the droplet forming section 3, the surface gelling section 6, the length of the complete gelling section 14, and the position of the atomizer 7 are determined in consideration of the size of the droplet, the diameter and amount of the mist, and the like. ,
It can be determined appropriately by experiment.

The apparatus for producing ammonium biuranate particles of the present invention is not limited to that shown in FIG.
Various design changes can be made within the scope of the present invention. For example, a plurality of droplet drop nozzles may be provided, and the number of atomizers may be increased accordingly.

[0034]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited thereto.

Example 1 Uranium concentration 250 g / l, polyvinyl alcohol resin 3 as a polymer compound
A uranyl nitrate solution having a viscosity of 92 cp (30 ° C.) was prepared at 0 g / liter. Using this uranyl nitrate solution, droplets having a diameter of 2.1 mm were formed under the conditions of a vibration nozzle having a vibration frequency of 100 Hz and an amplitude of 0.36 mm.

Next, the droplets were dropped on the surface gel section where the mist was sprayed under the following conditions. Ultrasonic atomizer (manufactured by Sonotec, nozzle inner diameter: 1.32 mm, frequency: 12
0 KHz), and the feed rate of the ammoniacal aqueous solution is 30
Mist was generated under operating conditions of cc / min. The average diameter of the mist was 18 μm. Since two ultrasonic atomizers were used, the total mist generation amount was 60 cc / min.

The droplet dropped at a distance of 35 cm from the lower end of the vibrating nozzle to the surface of the aqueous ammoniacal solution, and the terminal drop velocity upon landing was 3.5 m / sec. The droplet of this embodiment is:
Its sphericity was maintained by sufficiently withstanding the impact of landing. Further, the final drop speed was changed to 8.7 m by changing the droplet forming conditions.
/ S, the sphericity could be maintained. The allowable limit of the terminal drop speed when the surface of the droplet is gelled by blowing ammonia gas as a jet is
Usually, it was about 4 m / sec. This result indicates that the method using the mist of the ammoniacal aqueous solution is more efficient in gelling the surface of the droplet than the conventional method using ammonia gas.

After the ammonium biuranate particles produced by using the apparatus for producing ammonium biuranate particles of the present invention were washed with pure water and ethanol, their sphericity was evaluated. The sphericity was evaluated by the following method. That is, the diameter of one particle is randomly measured 50 times using a particle size analyzer. The sphericity is represented by the ratio of the maximum value to the minimum value of the measured diameter (sphericity = maximum diameter / minimum diameter). In other words, the true sphere becomes 1. Table 1 shows a comparison of the sphericity of the particles of the present invention and the conventional method.

[0039]

[Table 1]

Further, in the method of the present invention, it is not necessary to supply a new ammonia gas in the surface gelation section.
The processing amount of the ammonia gas recovery device for the purpose of preventing environmental pollution can be reduced to about 40%.

[0041]

According to the present invention, a method for producing ammonium biuranate particles, which can produce ammonium uranate particles having high sphericity with a small apparatus, and a heavy uranic acid used in the production method. An apparatus for producing ammonium particles can be provided.

[0042]

[Brief description of the drawings]

FIG. 1 is an explanatory view of an apparatus for producing ammonium biuranate particles according to the present invention.

FIG. 2 is an explanatory view of a conventional apparatus for producing ammonium biuranate particles by an external gelation method.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Dropping nozzle 2 Droplet 3 Droplet formation section 4 Droplet drop 5 Exhaust port 6 Surface gelation section 7 Atomizer 8 Mist of ammoniacal aqueous solution 9 Droplet whose surface is gelled 10 Transport pipe 11 Pump 12 Ammonia Aqueous aqueous solution 13 Precipitation tank 14 Complete gelation section 15 Ammonium biuranate particles 16 Ammonia gas supply port 17 Air layer 18 Ammonia aqueous solution circulation pump 19 Transport pipe

Claims (6)

(57) [Claims] 1. A method for producing ammonium biuranate particles from a uranyl nitrate solution by an external gelation method, wherein a mist of an ammoniacal aqueous solution is sprayed on droplets of the uranyl nitrate solution. Method for producing particles. 2. The method according to claim 1, wherein the aqueous ammoniacal solution is saturated aqueous ammonia. 3. The method for producing ammonium biuranate particles according to claim 1, wherein the mist is formed by an ultrasonic atomizer. 4. The method according to claim 3, wherein the mist has an average diameter of 30 μm or less. 5. An ammonium biuranate particle producing apparatus for producing ammonium biuranate particles from a uranyl nitrate solution by an external gelation method, wherein the uranyl nitrate solution is dropped and a droplet is dropped from the droplet dropping means. A precipitation tank having an aqueous ammoniacal solution for receiving droplets of the uranyl nitrate solution, and an atomizer for spraying the mist of the aqueous ammoniacal solution is provided between the droplet dropping means and the precipitation tank. An apparatus for producing ammonium biuranate particles, comprising: 6. The apparatus for producing ammonium biuranate particles according to claim 5, comprising means for sending an aqueous ammoniacal solution from the precipitation tank to the atomizer.