JPH0637306B2 - UO ▲ Lower 2 ▼ Production method of powder - Google Patents

Description

The present invention relates to a method for producing UO ₂ powder from UF ₆ and, in particular, to an improvement for improving the activity of the resulting UO ₂ powder.

"Prior Art" The ADU method is widely known as a method for converting UF ₆ into UO ₂ powder suitable for producing fuel pellets for nuclear reactors.

This ADU method generally involves reacting an aqueous UO ₂ F ₂ solution obtained by reacting UF ₆ gas with water with ammonia to produce ADU.
Is precipitated, the ADU is filtered and dried, and then roasted and reduced to convert it into UO ₂ powder.

However, the UO ₂ powder produced by this ADU method has a specific surface area of about 2 m ² / g and a relatively low activity, and it is usually necessary to sinter at a high temperature of about 1700 ° C. to process it into pellets. However, there is a drawback that the manufacturing cost is high.

Therefore, the present applicants previously filed Japanese Patent Application No. 62-197318.
UO, which has greater activity than the conventional ADU method in
_A method by which _two powders can be produced was proposed.

In this method, UO ₂ F ₂ powder produced by the reaction of UF ₆ gas and steam is dissolved in water, then reacted with ammonia to produce ADU, and this ADU is roasted and reduced to UO ₂ powder. It is characterized by converting,
By appropriately selecting the conditions for producing ADU, it becomes possible to obtain a UO ₂ powder having a large specific activity of 10 _m ² / g or more.

When pellets are manufactured using such highly active powders as raw materials, sintering at a low temperature of 1500 ° C or less is possible, which not only reduces manufacturing costs, but also controls the crystal structure such as crystal grain size and pore distribution. And the performance of the pellet can be improved.

"Problems to be solved by the invention" However, UO having a sufficiently high activity by the above method
_In order to obtain ₂ powders, manufacturing conditions from ADU generation to drying, for example, U concentration in UO ₂ F ₂ aqueous solution, NH ₃ / U
It is necessary to control the molar ratio, the amount of ADU cleaning water, etc. within a relatively narrow range, and UF ₆ is hydrolyzed at high temperature to produce UO ₂ F ₂
It is necessary to strictly control the reaction conditions so that tetravalent uranium is not generated as a by-product when producing
It had the drawbacks of low manufacturing flexibility and difficulty in control.

The present invention has been made in view of the above circumstances, and UF ₆
It is an object of the present invention to provide a method capable of increasing the degree of freedom in manufacturing conditions from high temperature hydrolysis to ADU production / drying, and more easily manufacturing UO ₂ powder having high activity.

"Means for Solving the Problem" Hereinafter, the method for producing the UO ₂ powder according to the present invention will be specifically described.

In this method, UO ₂ F ₂ powder is generated by a high-temperature hydrolysis reaction between UF ₆ gas and steam, the powder is dissolved in water to form a UO ₂ F ₂ aqueous solution, and then a hydrogen peroxide solution (H ₂
O ₂ ) is added to adjust the liquidity of the solution.

When performing high-temperature hydrolysis of UF ₆ gas, there is no problem if the reaction conditions are kept oxidative. However, if the reaction conditions are reducing, tetravalent uranium is produced as a by-product. May occur. Even if it does not occur at this point, tetravalent uranium may be produced in the subsequent process of dissolving the UO ₂ F ₂ powder in water.

In any case, when tetravalent uranium is mixed in the UO ₂ F ₂ aqueous solution, the tetravalent uranium acts as a major interfering factor in producing a highly active UO ₂ powder.

The first action of H ₂ O ₂ is to suppress such an interfering action of tetravalent uranium, and it is assumed that UO ₂ F ₂ powder is dissolved in water to obtain a UO ₂ F ₂ aqueous solution. Even if tetravalent uranium is present, it acts to convert the tetravalent uranium into a hexavalent uranium having no interfering action and detoxify it by the oxidizing action of H ₂ O ₂ .

Further, as a second action, H ₂ O is added to the UO ₂ F ₂ aqueous solution.
It was found from our experiments that the presence of ₂ increases the activity of the finally obtained UO ₂ powder.

That is, the ADU obtained by the reaction of the UO ₂ F ₂ aqueous solution with H ₂ O ₂ added and ammonia has smaller primary particles than those from the UO ₂ F ₂ aqueous solution without H ₂ O ₂ addition, and , The activity of UO ₂ powder is higher when H ₂ O ₂ is added. And this tendency is UO ₂
It becomes more remarkable by increasing the amount of H ₂ O ₂ added to the F ₂ aqueous solution.

Therefore, when generating the ADU, _UO 2 _{F 2} aqueous H
By adding ₂ O ₂ , the activity of the UO ₂ powder can be increased, and the allowable range of manufacturing conditions can be expanded correspondingly, and the degree of freedom in manufacturing can be increased to facilitate the control of conditions. Therefore, the manufacturing cost can be reduced.

However, if the amount of H ₂ O ₂ added is too large, UO ₂ F
_{2 It} has been found that a precipitate of uranyl peroxide (UPO) is deposited in the aqueous solution, which is not preferable because it leads to non-uniformity of the product.

When the present inventors examined this problem, they found that the UPO
If precipitation of H ₂ O ₂ occurs, hydrofluoric acid (H ₂ O ₂
It has been found effective to add F) and redissolve the UPO. However, also in this case, since the primary particles of the ADU that are produced become inactive when HF is added in excess, the amount of HF added should be kept to the minimum amount necessary to redissolve UPO.

"Examples" Next, the effects of the present invention will be demonstrated with reference to Examples.

UF ₆ gas is hydrolyzed at high temperature in an oxidizing and reducing atmosphere, and the produced UO ₂ F ₂ powder is dissolved in water to form an aqueous solution having a uranium concentration of 300 gU /
0.01% of ₂ O ₂ per 1 mol of uranium in this aqueous solution
Was added at a ratio of 0.10 mol. At this time, if a UPO precipitate was precipitated, HF was further added to redissolve the UPO.

Ammonia water was rapidly added to the UO ₂ F ₂ aqueous solution thus prepared with stirring until the pH exceeded 10, and AD
U was generated. Next, this ADU was filtered and dried, then roasted and reduced to obtain UO ₂ powder.

On the other hand, for comparison, UO ₂ F without addition of H ₂ O ₂ etc.
₂ ADU is produced from the stock solution of the aqueous solution under the same conditions as above,
Further, UO ₂ powder was obtained.

Table 1 shows the atmosphere during high-temperature hydrolysis of UF ₆ and U
H ₂ O per mol of uranium in O ₂ F ₂ aqueous solution
₂ shows the added amount of ₂ / HF and the specific surface area of the finally obtained UO ₂ powder.

As is clear from Table 1, H _{2 in} UO ₂ F ₂ aqueous solution
As the amount of added O ₂ was increased, the specific surface area of the UO ₂ powder increased regardless of the atmosphere of UF ₆ high temperature hydrolysis.

Further, when UF ₆ high temperature hydrolysis is carried out in a reducing atmosphere (Nos. 4 to 7), tetravalent uranium is mixed in the obtained UO ₂ F ₂ , and in this case, No. AD as it is like 4
Conversion to UO ₂ powder via U resulted in less activity. On the other hand, No. H ₂ O like 5-7
_{When 2} (and HF) was added, it was possible to obtain UO ₂ powder as active as UF ₆ high temperature hydrolysis was performed in an oxidizing atmosphere.

"Effects of the Invention" As described above, according to the method for producing UO ₂ powder according to the present invention, the following excellent effects are obtained.

By adding H ₂ O ₂ to the UO ₂ F ₂ aqueous solution before ADU generation, even when tetravalent uranium is mixed in the UO ₂ F ₂ aqueous solution, this can be made harmless, and the generated AUU primary particles It is possible to make UO ₂ powder that can be made small and has a large specific surface area and high activity. As a result, the allowable range of production conditions becomes wider than that in the conventional method, and the control of reaction conditions can be facilitated.

When HF is added together with H ₂ O ₂ , the precipitation of uranyl peroxide (UPO) caused by excess H ₂ O ₂ is prevented and the heterogeneity of UO ₂ powder can be prevented.

Claims (2)

[Claims] 1. A method for producing UO ₂ powder to produce a UO ₂ powder by way of the ADU from _{UO 2 F} 2, _H 2 O the _UO 2 _{F 2} in an aqueous solution was prepared by dissolving in water
_A method for producing a UO ₂ powder, which comprises adding ₂ and then adding ammonia to produce ADU. _2. The method for producing a UO ₂ powder according to claim 1, wherein HF is added together when the H ₂ O ₂ is added.