JPH0470243B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention uses UF ₆ produced from natural uranium or recovered uranium in a uranium enrichment plant as a raw material to
This invention relates to a method for recovering and reusing hydrofluoric anhydride from degraded UF ₆ with a low concentration of 235 that remains in large amounts when concentrating UF6.

Conventional technology and its problems The amount of degraded UF ₆ remaining in uranium enrichment plants reaches nearly 90% of the raw material UF ₆ . Although all sorts of possible uses for this depleted uranium have been considered, there is currently no use for much of the generated amount, and the majority of it is simply stored.

Even in Europe and the United States, which have long experience operating commercial uranium enrichment plants, large amounts of degraded UF ₆ are stored in cylinders, and they are having trouble dealing with it. In Japan, as the development of uranium enrichment plants progresses, the amount of degraded UF ₆ stored is increasing, and it is clear that the amount will become enormous if commercial uranium enrichment plants are built.

Degraded UF ₆ is currently stored in steel cylinders weighing between several and 10 tons each, but this substance, which has no use, must be stored almost permanently. Since UF ₆ is a chemically unstable volatile substance that exhibits significant corrosive properties,
Storing large amounts of this material has extremely serious problems, including the long-term integrity of the containers, safety in the event of a disaster, protection of nuclear materials, and the sentiments of local residents. In addition to these management problems, there is also the resource-economic drawback that storing UF ₆ in the form of fluorine leaves a huge amount of unused fluorine resources.

Against this background, it is desired to establish a method that can store degraded UF ₆ in a chemically safe form and recover and effectively utilize the fluorine content.

The most preferable storage form for depleted uranium is U ₃ O ₈ , which is the most stable of all uranium compounds and from the viewpoint of recovering the fluorine content. UF ₆ U ₃ O ₈
There are wet methods and dry methods for converting. In the wet method, UF ₆ is hydrolyzed in a liquid phase reaction to obtain a uranyl ion-containing solution, and ammonia is added to this to precipitate ammonium deuterate, or hydrogen peroxide is added to the solution to precipitate uranium peroxide. U ₃ O ₈ is obtained by precipitating, separating and drying these precipitates, and then thermally decomposing them. On the other hand, in the dry method, for example, UO ₂ F ₂ is obtained by a gas phase reaction by reacting steam with UF ₆ , and U ₃ O ₈ is obtained by further reacting with steam.

The wet method has many steps and uses a large amount of reagents, so it generates a lot of secondary waste, whereas the dry method has a simple manufacturing process and uses almost no reagents, so it generates a lot of secondary waste. It is suitable for low-cost, large-scale processing.

The dry method also has the advantage that the fluorine content can be easily recovered as dilute HF.

The by-product rare HF is a chemical that is normally used in general industry, but under the current situation in Japan, rare HF generated at nuclear facilities is not accepted by general industry as a national sentiment. Therefore, in order to make effective use of the fluorine content without turning it into waste, it is essential to recycle it within nuclear _facilities . must be recovered in the form of anhydrous HF, which can be recycled to In addition, the treatment method must generate less secondary waste and be able to process large quantities at low cost.

As a method for recovering anhydrous HF from dilute HF, there is a method of distilling dilute HF with a high concentration higher than the azeotropic composition, but this is not preferred because dilute HF with the azeotropic composition remains. Other methods include a combination of distillation and electrodialysis, and a distillation method in which organic matter is added to dilute HF, but the sulfuric acid extractive distillation method, in which sulfuric acid is added to dilute HF, increases the purity of hydrofluoric anhydride and It is suitable for low-cost mass processing because it can reduce the amount of waste.

Under the circumstances of the prior art as described above, the present inventors converted degraded UF ₆ to U ₃ O ₈ by a dry method,
At the same time, the by-product dilute HF is dehydrated by sulfuric acid distillation method.
It has been found that the problem can be solved by recovering it as HF.

To date, there is no known treatment method in which waste degraded UF ₆ is converted into U ₃ O ₈ by a dry gas phase method and stored, and at the same time, by-product HF is recovered in the form of anhydrous HF.

Structure of the Invention That is, according to the present invention, degraded UF ₆ is converted to U 3 O 8 by a dry gas phase reaction method, and at the same time diluted HF as a by-product is converted into U ₃ O ₈ .
A method for treating degraded UF 6 is provided, which comprises recovering UF ₆ as anhydrous HF by a sulfuric acid extractive distillation method.

Conversion of UF ₆ to U ₃ O ₈ by a dry method can be carried out using a fluidized bed reactor, a rotary kiln, a reaction tube equipped with a screw conveyor, etc.; is advantageous. According to this device, high-density storage suitable for storage
This is because U ₃ O ₈ powder is obtained, and high-concentration dilute HF is produced as a by-product, increasing the efficiency of processing into anhydrous HF, and at the same time suppressing the amount of secondary waste generated.

Embodiment The present invention is specifically carried out, for example, as follows.

The attached drawing shows a plant used for converting waste degraded UF ₆ into U ₃ O ₈ by gas phase reaction using a fluidized bed reactor, and in combination with this to obtain anhydrous HF by sulfuric acid extractive distillation method. An example concept is shown.

The waste degraded UF ₆ is vaporized in a vaporizer 1 and introduced into the fluidized bed reactor 2 through a nozzle provided at a suitable position within the reactor. At the same time, water vapor as a reaction gas and a fluidizing gas is injected into the furnace from the bottom through a conduit 11. Here, a gas phase reaction between UF ₆ and water vapor occurs.
A fluidized bed is formed, producing particles of UO ₂ F ₂ .

In this case, the formation of UO ₂ F ₂ particles is due to the coating granulation mechanism on the surface of the initially generated fine particles, which is the purpose of this method to form high-density U ₃ particles suitable for storage.
Very suitable for obtaining _O8 .

The generated UO ₂ F ₂ particles are discharged from the upper part of the fluidized bed by overflow and sent to the second fluidized bed reactor 3, and then in the exhaust gas of the third fluidized bed reactor 4 installed. Atte 2nd fluidized bed reactor 3
Due to the large amount of water vapor contained in the reactant gas and fluidizing gas introduced at the bottom of the
Converts to U ₃ O ₈ . This U ₃ O ₈ is sent to the third fluidized bed reactor 4 by overflow as described above, where it undergoes a final deF treatment using steam introduced from the conduit 12, and is received in the container 5 as a product.

By-product HF discharged from the fluidized bed reactors 2 and 3 is collected together in a condenser 6 and recovered as highly concentrated dilute HF, which is sent to an extractive distillation column 7.
Sulfuric acid is supplied to the extractive distillation column 7 through a conduit 14, and anhydrous HF is recovered from the top of the column by extractive distillation, liquefied in a condenser 8, and received in a container 9. Dilute sulfuric acid is recovered from the bottom of the tower, but this is carried through conduit 13.
The sulfuric acid is sent to the sulfuric acid concentration column 10, and the evaporated water is condensed in the condenser 15 and sent to the wastewater treatment system.
This is the only secondary waste. Concentrated sulfuric acid is discharged from the bottom of the column and recycled to the extractive distillation column.

Since the individual devices mentioned above and their operation are known, they will not be described in detail.

Example The diameter of the reaction section of the fluidized bed reactor in which the method of the present invention was carried out using the apparatus described above was 8.3 cm, and the diameters of the extractive distillation column and the sulfuric acid concentration column were also 8.3 cm.

The operating conditions were as follows.

First fluidized bed reactor Reaction temperature 300℃ UF ₆ supply rate 100g/min Fluidizing gas (steam) introduction rate 45cm/sec H ₂ O/U 5.5 Production UO ₂ F ₂ 87.5g/min Second fluidized bed reactor Reaction Temperature 700℃ UO ₂ F ₂ Feed rate 87.5g/min Fluidizing gas rate 45cm/sec H ₂ O/U 5.0 Production U ₃ O ₈ /UO ₂ F ₂ 67.8/13.1g/min Third fluidized bed reactor Temperature 700 ℃ U ₃ O ₈ / UO ₂ F ₂ supply rate 67.8 / 13.1 g / min Fluidization gas velocity 24 cm / sec H ₂ O / U 5.0 produced U ₃ O ₈ 79.7 g / min Extractive distillation column HF (46 wt% HF) supply Speed 4/hour Sulfuric acid (80wt% H ₂ SO ₄ ) supply rate 10/hour Produced anhydrous HF 2/hour Sulfuric acid concentration tower Sulfuric acid (70wt%) supply rate 12/hour Concentrated sulfuric acid (80wt%) recovery rate 10/hour Waste water volume 2.5/hour The physical properties of the U ₃ O ₈ powder obtained in this way are 1
An example was as follows.

Bulk density: 4.0 g/cm ³ Particle density (He gas replacement method): 8.0 g/cm ³ Specific surface area (BET method): 1.6 m ² /g The recovered anhydrous HF had a purity of 99.98% or more.

Effects of the Invention As described above, the present invention can produce the following excellent effects.

(1) Among the methods for converting degraded UF ₆ to U ₃ O ₈ , the dry gas phase reaction method and sulfuric acid extraction produce no secondary waste, are suitable for inexpensive large-scale processing, and can easily obtain dilute hydrofluoric acid. Degraded UF ₆ using a method combined with distillation method
By recovering hydrofluoric anhydride from UF ₆ manufacturing plants, it is possible to obtain high-purity hydrofluoric anhydride with a purity of 99.98% or higher, which can be used at UF 6 manufacturing plants, at low cost and with almost no secondary waste. This makes it possible to economically and effectively utilize the degraded UF ₆ fluorine resources. Furthermore, converting degraded UF ₆ to U ₃ O ₈ increases storage safety compared to conventional storage of degraded UF ₆ .

(2) By converting degraded UF ₆ to U ₃ O ₈ using a fluidized bed reactor, the unique granulation function of the reactor eliminates the need for secondary treatment in other conversion methods. U ₃ O ₈ with a high bulk density of approximately 4.0 g/cm ³ suitable for storage, which is difficult to obtain, can be obtained at low cost, in large quantities, and with almost no secondary waste. In addition, according to this method, a higher concentration of dilute hydrofluoric acid is produced as a by-product compared to other methods, increasing the processing efficiency of hydrofluoric anhydride in the HF treatment system, and reducing the amount of secondary waste generated in the same treatment system. It also has the advantage of being able to keep it low.

[Brief explanation of the drawing]

The accompanying drawings illustrate the concept of an apparatus for carrying out the method of the invention. 1... UF ₆ vaporizer, 2... first fluidized bed reactor,
3... Second fluidized bed reactor, 4... Third fluidized bed reactor, 5... U ₃ O ₈ receiver, 6... Hydrofluoric acid condenser, 7
...Extractive distillation column, 8...Fluoric anhydride condenser, 9...
... Fluoric anhydride receiver, 10 ... Sulfuric acid concentration column, 11,
12...Steam supply pipe, 13...Dilute sulfuric acid transfer pipe,
14... Concentrated sulfuric acid transfer pipe, 15... Waste water condenser.

Claims (1)

[Claims] 1. Degraded UF ₆ is converted to U ₃ O ₈ by a dry gas phase reaction method, and at the same time dilute HF as a by-product is converted to anhydrous UF 6 that can be used at a UF ₆ manufacturing plant by a sulfuric acid extractive distillation method. A method for recovering and reusing hydrofluoric anhydride from degraded UF ₆ , which consists of recovering and reusing it as HF. 2. A method for recovering and reusing hydrofluoric anhydride from degraded UF ₆ as set forth in claim 1, which converts depleted uranium to U ₃ O ₈ by a dry gas phase reaction method using a fluidized bed reactor. and how to implement it.