JPS6374916A - Manufacturing method of uranium dioxide powder - Google Patents

Abstract

PURPOSE:To obtain UO2 powder having an activity controlled to a prescribed level, by adding UN, HF and NHO3 to an aqueous solution of UO2F2 to adjust the U concentration, adding ammonia thereto and roasting and reducing the produced precipitate. CONSTITUTION:At least one component selected from UN, HF and HNO3 is added to an aqueous solution of UO2F2 to adjust the amounts of UO2F2 and the additive component in the aqueous solution to respective specific levels. The aqueous solution is added with ammonia water under agitation until the pH reaches about >=10 to precipitate ADU (ammonium diuranate). The ADU is filtered, dried and then converted to UO2 powder by roasting and reducing in H2 atmosphere. The activity of UO2 powder can be controlled to an arbitrary level by this process.

Description

[Detailed Description of the Invention] (Industrial Field) The present invention provides a method for converting hexafluoride (UF, ) into
Uranium dioxide (UOt) is suitable for producing F13 fuel for nuclear reactors.
) This paper relates to an improvement of the ammonium deuterate (ADU) method, which is one of the methods for converting powder to 1:11. More specifically, the present invention relates to a method of controlling the activity of UO1 powder obtained by controlling the conditions for producing ADU precipitation through a reaction between an aqueous solution containing uranyl fluoride (UOmFx) and ammonia.

(Prior art and its problems) The ADU method is widely known as a method for producing UO powder suitable for producing nuclear reactor fuel from UF6. A
There are two known methods for the DU method. Part 1
One method is to obtain Ut'a by the reaction of Ut'a gas with water.
In this method, OtF, an aqueous solution, and ammonia are reacted to precipitate ADU, and this ADU is filtered and dried, and then roasted and reduced to obtain UOz powder. In this method, A
The reaction in which DU is produced can be expressed as follows.

UFs+2HtO→U OIF! + 4 HF --
1----(1) UOt F*+ 4 HF' + 7
NH40H4(1/2) (NH4)ITJmO
Ma↓+6 N H4F + (11/2) H2O−
------- (2) Another method is to react UFa with a defrosting agent such as an aqueous solution of aluminum nitrate (uranyl nitrate).
In this method, the purified UN aqueous solution is converted into an aqueous solution, purified by solvent extraction, and then reacted with ammonia to produce ADU. The reaction in this case is as follows.

UF's +2 AJ (Now)s +2
H*04UOm (NOs)m+2AiF', ↓+4H
NOs −1−−−−−−−−(3) UOl (N0x
)t +4 HNOt+7 NH4OH→(1/2)(
NH4)I UtOy↓+6NHaNOs+(11/2
)t(O) In the first ADU method, UOIF, uranyl ion UO present in the aqueous solution, and fluorinated ranyl ion UO, F'+ are mainly involved in the ADU production reaction. In that case, the primary particles of ADU obtained are relatively large.Such ADU is also UO obtained through roasting and reduction operations.

The powder will have relatively low activity. On the other hand, in the second ADU method, among the UOI and uranyl nitrate ion UO1N Os+ present in the UN aqueous solution, UO1'+ is mainly involved in the ADU production reaction, and the ADU obtained in that case is The primary particles will be relatively small. UO and powder obtained from such ADU through roasting and reduction operations have a relatively high degree of activity.

When producing sintered pellets used as fuel for nuclear reactors from UO1 powder, the quality of the pellets depends on the raw material U.
O is greatly influenced by the quality of the powder. 4? In order to control the sintered density and crystal grain size, which are the most important factors in determining pellet quality, to the desired values, it is necessary to keep the activity of the UO8 powder used as the raw material appropriate. be. As long as UOI powder is produced using the conventional ADU method, there are major limitations in terms of control of UO8 powder activity. That is, in the first ADU method described above, only UO3 powder with relatively low activity can be obtained, and in the second ADU method, only UO3 powder with relatively high activity can be obtained.

(Object of the invention) The object of the present invention is to solve the problems of the above-mentioned prior art and
, Ft-containing aqueous solution via ADU to produce UO powder whose activity is controlled to a desired level.

(Structure of the Invention) That is, according to the present invention, uranyl fluoride (UOl)
In the method of producing uranium dioxide powder from UO,F,) via ammonium deuterate (ADU), UO,F
', uranyl nitrate (UN),
At least one of the three components hydrogen fluoride (HF') and nitric acid (HNOs) is added to remove U in the aqueous solution.
By adjusting the OtF* and additive components to a predetermined ratio, A produced by the reaction between the aqueous solution and ammonia
A method for producing uranium dioxide powder is obtained, which is characterized by controlling the activity of uranium dioxide powder obtained by roasting and reducing DU to a predetermined level.

Thus, a feature of the present invention is to precipitate the ADU 1
This method differs greatly from the conventional ADU method. That is, in the conventional ADU method, ADU is produced from an aqueous solution containing UOtFt and HF, or from an aqueous solution containing UN and HNOs, whereas in the present invention, UN is produced in addition to UOtFt.

An aqueous solution containing at least one component of HF and HNOs is used as a raw material, and U contained in the aqueous solution is
ADU is produced by adjusting OtFt and additional components to a predetermined ratio. UOl, UO, F+
When the three ions U Ot N Os+ finally become ADU in the presence of ammonia, the primary particles of ADU tend to grow in the following order:

UOl ” <UOtNOs ” <UOtF”
(5) When UN is added to the UOzFt aqueous solution,
By increasing the proportion of "UOl", the generated ADU
The primary particles of become smaller. When HF' is added,
As the proportion of UOtF+ increases significantly, the primary particles of the ADU produced become significantly thicker.

When HNOs is added, the primary particles of ADU become larger due to the increase in the proportion of U Ot N Os+. Therefore, the addition of UO, F, UN to the aqueous solution is AD
UO obtained via U, the activity of the powder is increased (and
Addition of HF or HNos has the effect of reducing the activity of UO and powder.

HF has a greater activity suppression effect than HNOs.

EXAMPLES Next, the present invention will be specifically explained using Examples, but these Examples do not limit the scope of the present invention.

Example UORFt powder was dissolved in pure water to create a UOIFt aqueous solution, and this aqueous solution contained UN, HF' and t(No.

were added in the proportions shown in Table 1, and then pure water was further added to prepare an aqueous solution in which the temperature was adjusted to 200gU/J. Aqueous ammonia was added to these aqueous solutions while stirring until the pH reached 10 or higher to form a precipitate of ADU. After filtration and drying, ADU was heated to 650 ml in H8 atmosphere.
It was roasted and reduced at ℃ for 2 hours and converted into UOt powder.

UO! Was the powder molded at a molding pressure of 4t/cII? 1kH
The pellets were sintered at 1,750° C. for 4 hours in an atmosphere of 8 to form pellets. The BET specific surface area of the UO1 powder and the sintered density of the pellets are shown in Table 1.

From the results of 41.2 and 3 in Table i1, it can be seen that the greater the amount of UN added, the greater the activity of the obtained U O powder. From the comparison of 4'l, 4 and 5, the comparison of 1.6 and 7, and the comparison of 2.8 and 9, it is found that food with a large amount of HF and/or I (No) added, 1% UO, It can be seen that the activity of the powder decreases.When HF and HNOs are compared, HF has a large effect of decreasing the activity.In this way, the UO*Fx aqueous solution K U N ) HF
It can be seen that the activity of the obtained UOt powder can be controlled by adding at least one of the three components O, U HN Os, in a predetermined ratio.

taX table In addition to UOtF'l, UN, [(F' and H
Characteristics of 00m powder, UO, and pellets produced from an aqueous solution containing at least 1 component of NOs via ADU (effects of the invention) The present invention exhibits the following effects by adopting the above configuration.

(11 uo, the activity of the powder can be controlled to any desired size.

(2) Easily control the sintering density and pellet characteristics of 1N crystal grain when pelletizing at actual speed.

Claims (1)

[Claims] (1) In a method for producing uranium dioxide powder from uranyl fluoride (UO_2F_2) via ammonium deuterate (ADU), uranyl nitrate (UN), hydrogen fluoride (HF) are added to an aqueous solution containing UO_2F_2 in advance.
) and nitric acid (HNO_3) to adjust the ratio of UO_2F_2 and the added components in the aqueous solution to a predetermined ratio, thereby roasting the ADU produced by the reaction between the aqueous solution and ammonia. - A method for producing uranium dioxide powder, which is characterized by controlling the activity of the uranium dioxide powder obtained by reduction to a predetermined level.