RU2415084C1 - Method of producing uranium dioxide powder - Google Patents

Abstract

FIELD: chemistry. ^ SUBSTANCE: invention can be used in preparing nuclear fuel for atomic power stations. Uranium dioxide powder is obtained through precipitation of uranium in form of dihydroxyaminate complexes of uranium or from nitrate, or chloride or sulphate solutions. The obtained precipitates are decomposed in an inert atmosphere at 200-500C. The uranium is precipitated with hydroxyl amine in molar ratio NH2OH: U ëÑ 2. ^ EFFECT: invention enables to obtain a product which is characterised by content of 7-10 vol % particles with size less than 100 nm in its granulometric composition at relatively low power consumption. ^ 2 dwg, 2 tbl, 8 ex

Description

The invention relates to nuclear energy and relates to a technology for producing uranium oxides for the manufacture of nuclear fuel for nuclear power plants.

In the known method for the manufacture of tablet fuel [patent RU 2158971, IPC G21C 3/62, G21C 21/10, C01G 43/025 1999] uranium dioxide is obtained by preliminary hydrolysis of uranium hexafluoride with the following stages: extraction of uranium from nitric acid solution of 30% TBP in an organic diluent; its re-extraction into an aqueous acidic solution; precipitation of ammonium polyuranate with ammonia water at a pH of 6.6-8; filtration, drying-calcination at 450 ÷ 600 ° С and reduction in hydrogen at 680 ÷ 720 ° С.

The disadvantages of this method include the following:

- the complexity of the process;

- the need to use high temperatures;

- the use of hydrogen for recovery.

In the closest to the proposed method technical solution [patent RU 2296106, IPC C01G 43/025 (2006.01), 2004], selected as a prototype, the following operations are proposed for obtaining powdered uranium dioxide:

- treatment with a 25% ammonia solution of a previously prepared aqueous solution of uranyl nitrate with a uranium content of 50 ÷ 100 g / dm ³ while maintaining the pH during precipitation of ammonium polyuranate (PUL) not less than 6.6;

- filtration, drying, thermal decomposition and reduction of the calcined product in a reducing atmosphere at a temperature of 660 ÷ 730 ° C.

The disadvantages of this method:

- high temperatures of thermal processes;

- the need to use a reducing environment;

- low content in the composition of the obtained powders of particles smaller than 100 nm (Table 1, line Prototype).

The invention is aimed at finding a method that allows to obtain uranium dioxide powder containing in its particle size distribution 7 ÷ 10 vol.% Particles less than 100 nm and less energy-intensive due to lower temperatures and elimination of the recovery stage. The presence of particles smaller than 100 nm with high surface energy, can improve the quality of the ceramic components of the fuel rods and optimize the technological parameters of the process of obtaining them - to reduce the sintering temperature of the tablets and increase the average grain size of the microstructure of sintered tablets [Kurina I.S. et al. // Atomic energy. - 2006. - T.101, No. 5. - S.347-352], [patent RU 2186431, IPC C01G 43/025 (2006.01), 2000].

The technical result is achieved by the fact that the proposed method for producing a powder of uranium oxide, characterized by the content in its particle size distribution of 7 ÷ 10 vol.% Particles smaller than 100 nm, including the deposition of uranium from nitrate, or chloride, or sulfate solutions and the decomposition of precipitates in an inert atmosphere at 200 ÷ 500 ° C, while the precipitation of uranium is carried out with hydroxylamine at a molar ratio of NH ₂ OH: U≥2.

The essence of the invention is illustrated by the following accompanying illustrations and tabular data:

Figure 1. Thermogram of uranyl dihydroxylaminate hydrate UO ₂ (NH ₂ O) ₂ · 3H ₂ O.

Figure 2. Thermogram of anhydrous uranyl dihydroxylaminate UO ₂ (NH ₂ O) ₂ .

Table 1. The content of particles with a size of less than 100 nm in uranium dioxide powders obtained by the proposed method and the prototype according to the results of particle size analysis using mercury porosimeters "PASCAL 140" and "PASCAL 440".

Table 2. Interplanar distances d (Å) and relative intensities (Int) of thermal decomposition products according to examples 1 and 4 (DRON-3M, CuKα radiation).

A distinctive feature of the proposed method for producing uranium oxide powder is that the precipitation of uranium from uranium-containing solutions is carried out using hydroxylamine. In this case, UO ₂ (NH ₂ O) ₂ · H ₂ O molecular complexes that are stable in air are formed (n = 3 during precipitation under normal conditions; n = 0 during precipitation from hot solutions), which are poorly soluble in water and ordinary organic solvents. Such properties of dihydroxylaminate complexes make it possible to use uranium chloride, nitrate, sulfate solutions for their preparation without preliminary purification of cations.

Precipitation at a molar ratio of NH ₂ OH: U of less than 2 is impractical, since it does not lead to the complete separation of uranium from solutions.

The use of an inert atmosphere is due to the fact that the presence of atmospheric oxygen at the decomposition stage of the resulting precipitation affects the composition of the final product.

The claimed temperature range is determined experimentally and is optimal to achieve a maximum content of particles with a size of less than 100 nm in the particle size distribution of the obtained uranium dioxide powder. The minimum decomposition temperature is due to the nature of the thermolysis of uranyl dihydroxylaminate complexes, which ends at ~ 200 ° C for both UO ₂ (NH ₂ O) ₂ · 3H ₂ O (Fig. 1) and UO ₂ (NH ₂ O) ₂ (Fig. .2). It is not advisable to carry out decomposition at temperatures above 500 ° C, since the content of particles less than 100 nm in the obtained uranium oxide does not exceed 6 vol.% (Table 1, example 8).

The invention is implemented as follows. A solution of hydroxylamine in water, obtained by neutralization of hydroxylammonium salts with bases, is added to an aqueous solution of a uranyl salt. The molar ratio of NH ₂ OH: U is not less than 2. For the complete precipitation of uranium, it is necessary to maintain a pH in the range of 6–8 using a solution of hydroxylamine or another base. The precipitate formed is filtered off, washed (if necessary) with water, dried and placed in a furnace for decomposition in an inert atmosphere. Depending on the decomposition temperature, uranium dioxide powder is characterized by a content of 7 ÷ 10 vol.%, Particles less than 100 nm in size.

Below are examples and test results of the obtained samples. The examples illustrate but do not limit the proposed method. The test results for the content of particles less than 100 nm in powders of uranium dioxide are summarized in Table 1.

Example 1

To an aqueous solution of uranyl nitrate with a mass concentration of uranium of 47.4 g / dm ^{3 was} added an aqueous solution of hydroxylamine with a mass concentration of NH ₂ OH of 26.3 g / dm ³ , which corresponds to a molar ratio of NH ₂ OH: U = 4: 1. The precipitate was filtered off, dried, decomposed in an inert atmosphere at a temperature of 300 ° C. The data of x-ray phase analysis are given in Table 2. The content of particles less than 100 nm in size is 8.96 vol.%.

Example 2

To an aqueous solution of uranyl chloride with a mass concentration of uranium of 60.3 g / dm ^{3 was} added an aqueous solution of hydroxylamine with a mass concentration of NH ₂ OH of 33.4 g / dm ³ , which corresponds to a molar ratio of NH ₂ OH: U = 4: 1. The precipitate was filtered off, dried, decomposed in an inert atmosphere at a temperature of 200 ° C. The content of particles less than 100 nm in size is 7.17 vol.%.

Example 3

To an aqueous solution of uranyl sulfate with a mass concentration of uranium of 48.4 g / dm ^{3 was} added an aqueous solution of hydroxylamine with a mass concentration of NH ₂ OH of 26.8 g / dm ³ , which corresponds to a molar ratio of NH ₂ OH: U = 4: 1. The precipitate was filtered off, dried, decomposed in an inert atmosphere at a temperature of 300 ° C. The content of particles less than 100 nm in size is 8.96 vol.%.

Example 4

To an aqueous solution of uranyl nitrate with a mass concentration of uranium of 47.4 g / dm ^{3 was} added an aqueous solution of hydroxylamine with a mass concentration of NH ₂ OH of 78.9 g / dm ³ , which corresponds to a molar ratio of NH ₂ OH: U = 12: 1 and heated to boiling. The precipitate was filtered off, dried, decomposed in an inert atmosphere at a temperature of 300 ° C. The data of x-ray phase analysis are given in Table 2. The content of particles less than 100 nm in size is 8.96 vol.%.

Example 5

The processes of examples 1-4 with the decomposition of the obtained precipitation in an inert atmosphere at a temperature of 400 ° C. The content of particles less than 100 nm in size was 9.56 vol.%.

Example 6

The processes of examples 1-4 with the decomposition of the obtained precipitation in an inert atmosphere at a temperature of 450 ° C. The content of particles less than 100 nm in size was 9.79 vol.%.

Example 7

The processes of examples 1-4 with the decomposition of the obtained precipitation in an inert atmosphere at a temperature of 500 ° C. The content of particles less than 100 nm in size was 9.14 vol.%.

Example 8

The processes of examples 1-4 with the decomposition of the obtained precipitation in an inert atmosphere at a temperature of 600 ° C. The content of particles less than 100 nm in size was 5.61% vol.

As can be seen from the examples, obtaining a powder of uranium dioxide of the desired particle size distribution does not depend on the composition of the initial uranium-containing solution.

Table 1 Example No. The temperature of the oxide, ° C The content of particles less than 100 nm in fractions, vol.% fraction, microns Sum of fractions 0.10-0.08 0.08-0.06 0.06-0.04 0.04-0.02 0.02-0.01 Received by the proposed method 2 200 0.58 1,2 1.83 3.46 0.1 7.17 1,3,4 300 1,04 1,6 2.21 4.05 0.06 8.96 5 400 0.94 1.78 2.44 4.31 0.09 9.56 6 450 1.49 2.14 2.78 3.33 0.05 9.79 7 500 1.16 1.88 2,55 3.38 0.17 9.14 8 600 0.98 1.31 1.31 2.01 0 5.61 Prototype Obtained from ammonium polyuranate (PUA) precipitated at pH 6.8 PUA source 0.94 0.47 0 0 0 1.41 500 0.54 0.59 0.35 0 0 1.48 Obtained from ammonium polyuranate (PUA) precipitated at pH 7.2 PUA source 0.84 0.29 0 0 0 1.23 500 0.08 0 0 0 0 0.08

table 2 UO ₂ [JCPDS - lnt. Center of Diffraction Data, 1999, N 05-0550] The decomposition products obtained by examples one four d (Å) Int.,% d (Å) Int.,% d (Å) Int.,% 3,156 100.0 3.132 one hundred 3.162 one hundred 2,733 34.7 2.714 35.0 2,714 32,7 1,932 40.9 1.922 40,0 1,922 43.9 1,648 35.0 1.635 31,0 1,642 33.7 1,578 7.6 1.559 8.0 1,577 8.2

The inventive method allows to obtain a powder of uranium dioxide of the desired particle size distribution at relatively low energy consumption due to the use of hydroxylamine as a precipitant.

Claims (1)

A method of producing a powder of uranium dioxide, characterized in its particle size distribution of 7 ÷ 10 vol.% Particles less than 100 nm in size, including the deposition of uranium in the form of dihydroxyaminate complexes from either nitrate or chloride or sulfate solutions, decomposition of the obtained precipitates in an inert atmosphere at 200 ÷ 500 ° C, while the precipitation of uranium is carried out with hydroxylamine at a molar ratio of NH ₂ OH: U≥2.

Images