阅读说明：本技术 二氧化铀-石墨烯燃料芯块及其制备方法 (Uranium dioxide-graphene fuel pellet and preparation method thereof ) 是由 黄华伟 刘彤 廖业宏 孙茂州 严岩 任啟森 黄恒 许多挺 张永栋 肖玲 于 2020-11-06 设计创作，主要内容包括：本发明公开了一种二氧化铀-石墨烯燃料芯块及其制备方法,制备方法包括：S1、将重铀酸铵粉末在高温下煅烧,使重铀酸铵转化成U-3O-8；S2、用浓硝酸将U-3O-8溶解,获得缺酸硝酸铀酰溶液；S3、将获得的缺酸硝酸铀酰溶液制成溶胶溶液；S4、制备石墨烯悬浮液；S5、将溶胶溶液和石墨烯悬浮液混合,形成混合液；S6、将混合液进行加热使凝胶化,形成含水的铀化物-石墨烯混合物凝胶；S7、将含水的铀化物-石墨烯混合物凝胶进行洗涤并晾干,获得凝胶粉末；S8、依次将凝胶粉末进行干燥煅烧,还原烧结,获得二氧化铀-石墨烯复合粉末；S9、致密化烧结,制得二氧化铀-石墨烯燃料芯块。本发明的制备方法,提高燃料芯块的成分均匀性和热导率。(The invention discloses a uranium dioxide-graphene fuel pellet and a preparation method thereof, wherein the preparation method comprises the following steps: s1, calcining ammonium diuranate powder at high temperature to convert ammonium diuranate into U 3 O 8 (ii) a S2, adding U by concentrated nitric acid 3 O 8 Dissolving to obtain an acid-deficient uranyl nitrate solution; s3, preparing the obtained uranyl nitrate solution into sol solution; s4, preparing a graphene suspension; s5, mixing the sol solution and the graphene suspension to form a mixed solution; s6, heating the mixed solution to gelatinize to form aqueous uranium compound-graphene mixture gel(ii) a S7, washing and airing the hydrous uranium compound-graphene mixture gel to obtain gel powder; s8, drying and calcining the gel powder in sequence, and performing reduction sintering to obtain uranium dioxide-graphene composite powder; and S9, densifying and sintering to obtain the uranium dioxide-graphene fuel pellet. The preparation method of the invention improves the component uniformity and the thermal conductivity of the fuel pellet.)

1. A preparation method of a uranium dioxide-graphene fuel pellet is characterized by comprising the following steps:

s1, calcining ammonium diuranate powder at high temperature to convert the ammonium diuranate into U₃O₈；

S2, adding the U into concentrated nitric acid₃O₈Dissolving to obtain an acid-deficient uranyl nitrate solution;

s3, preparing the obtained uranyl nitrate solution into a sol solution;

s4, preparing a graphene suspension;

s5, mixing the sol solution and the graphene suspension, and stirring at low temperature to form a mixed solution;

s6, heating the mixed solution to gelatinize to form hydrous uranium compound-graphene mixture gel;

s7, washing and airing the aqueous uranium compound-graphene mixture gel to obtain gel powder;

s8, drying and calcining the gel powder in sequence, and performing reduction sintering to obtain uranium dioxide-graphene composite powder;

and S9, performing densification sintering on the uranium dioxide-graphene composite powder to obtain the uranium dioxide-graphene fuel pellet.

2. The method for producing a uranium dioxide-graphene fuel pellet according to claim 1, wherein in step S1, the ammonium diuranate powder is calcined at 800 to 900 ℃ for 2 to 4 hours to convert the ammonium diuranate into U₃O₈。

3. A method for the preparation of uranium dioxide-graphene fuel pellets according to claim 1, wherein in step S2, the U₃O₈The mass ratio of the concentrated nitric acid to the concentrated nitric acid is 1: 1.35-1.45;

at the U₃O₈Is dissolved inConcentrating the nitric acid, and filtering to obtain filtrate, namely the uranyl nitrate acid-deficiency solution.

4. The method for preparing a uranium dioxide-graphene fuel pellet according to claim 1, wherein in step S3, urea and hexamethylenetetramine or ammonia water are added to the uranyl nitrate solution, and a sol solution is formed after complete dissolution;

wherein the molar ratio of the urea to the metal uranium in the uranyl nitrate acid-deficiency solution is 1: 1.2-1.6; the molar ratio of the hexamethylene tetramine or the ammonia water to the metal uranium in the uranyl nitrate starvation solution is 1: 1.2-1.6.

5. The method for preparing uranium dioxide-graphene fuel pellets according to claim 1, wherein step S4 comprises: adding graphene into deionized water by stirring according to the mass ratio of 2:8-4:6 to form a graphene mixed solution; and adding 0.5-2% of dispersant polyethyleneimine into the graphene mixed solution, and uniformly stirring to obtain the graphene suspension.

6. The method for preparing a uranium dioxide-graphene fuel pellet according to claim 1, wherein in step S5, the sol solution and the graphene suspension are mixed according to the volume percentage of graphene to uranium dioxide of 1-10: 100; stirring at a temperature below 5 deg.C to form a mixture.

7. The method for preparing a uranium dioxide-graphene fuel pellet according to claim 1, wherein in step S6, the mixed solution is put into an oven and heated at 80-90 ℃ for 48-96 hours to perform gelation.

8. The method of producing uranium dioxide-graphene fuel pellets according to claim 1, wherein in step S7, the aqueous uranium compound-graphene mixture gel is washed with dilute ammonia water to remove residual acid.

9. The method for the preparation of uranium dioxide-graphene fuel pellets according to claim 1, wherein in step S8, the dry calcination comprises: heating the mixture from room temperature for 1-2 hours to 110 ℃, and preserving heat for 3-4 hours; then heating to 200-220 ℃, and preserving heat for 2-2.5 hours; then heating to 300 ℃, and preserving the heat for 2-2.5 hours; finally cooling to room temperature;

the reduction sintering comprises the following steps: and (3) carrying out reduction calcination in the mixed gas atmosphere of argon and hydrogen, heating to 600 ℃ at the temperature of 5-10 ℃/min, preserving heat for 3-4 hours, and then cooling to room temperature.

10. The method for preparing the uranium dioxide-graphene fuel pellet as claimed in claim 1, wherein in the step S9, the densification sintering is performed by SPS sintering, the temperature is raised to 1200-1500 ℃, the temperature is kept for 5-30 minutes, and then the pellet is cooled to room temperature.

11. A uranium dioxide-graphene fuel pellet, characterized by being produced by the production method according to any one of claims 1 to 10.

Technical Field

The invention relates to the technical field of nuclear fuels, in particular to a uranium dioxide-graphene fuel pellet and a preparation method thereof.

Background

UO₂The high-melting-point nuclear fuel has the advantages of high melting point, good chemical stability, strong irradiation resistance and the like, and is widely used for nuclear fuel. However, UO₂The ceramic pellet has low heat conductivity coefficient, and the temperature difference of the fuel rod is large in the service process, so that the accident-resistant fault-tolerant capability of the fuel element is reduced. The addition of a certain volume content of a graphene phase to the pellet matrix can increase the thermal conductivity of the fuel pellet. However, due to the graphene particles and the UO₂The physical properties of the particles are different greatly, and agglomeration is easy to occur, so that the uniformity of the powder is poor. In addition, graphene and UO₂The reaction is easy to occur above 1300 ℃, which prevents the compact of the pellet.

At present, some carbon black C-UO is available at home and abroad₂Or diamond C-UO₂The literature on preparation relates to the traditional powder metallurgy preparation method. Mixing the C powder with UO₂The powder is mechanically mixed and then sintered by SPS, so that the sintering temperature can be reduced, and C and UO can be reduced₂But the powder uniformity is not ideal.

Disclosure of Invention

The invention aims to provide a preparation method of a uranium dioxide-graphene fuel pellet for improving component uniformity and thermal conductivity of the fuel pellet and the prepared uranium dioxide-graphene fuel pellet.

The technical scheme adopted by the invention for solving the technical problems is as follows: the preparation method of the uranium dioxide-graphene fuel pellet comprises the following steps:

s1, calcining ammonium diuranate powder at high temperature to convert the ammonium diuranate into U₃O₈；

S2, adding the U into concentrated nitric acid₃O₈Dissolving to obtain an acid-deficient uranyl nitrate solution;

s3, preparing the obtained uranyl nitrate solution into a sol solution;

s4, preparing a graphene suspension;

s5, mixing the sol solution and the graphene suspension, and stirring at low temperature to form a mixed solution;

s6, heating the mixed solution to gelatinize to form hydrous uranium compound-graphene mixture gel;

s7, washing and airing the aqueous uranium compound-graphene mixture gel to obtain gel powder;

s8, drying and calcining the gel powder in sequence, and performing reduction sintering to obtain uranium dioxide-graphene composite powder;

and S9, performing densification sintering on the uranium dioxide-graphene composite powder to obtain the uranium dioxide-graphene fuel pellet.

Preferably, in step S1, the ammonium diuranate powder is calcined at 800 to 900 ℃ for 2 to 4 hours to convert the ammonium diuranate into U₃O₈。

Preferably, in step S2, the U₃O₈The mass ratio of the concentrated nitric acid to the concentrated nitric acid is 1: 1.35-1.45;

at the U₃O₈Dissolving in concentrated nitric acid, and filtering to obtain filtrate, namely the uranyl nitrate starved solution.

Preferably, in step S3, urea and hexamethylenetetramine or ammonia water are added to the uranyl nitrate deficient acid solution, and a sol solution is formed after complete dissolution;

wherein the molar ratio of the urea to the metal uranium in the uranyl nitrate acid-deficiency solution is 1: 1.2-1.6; the molar ratio of the hexamethylene tetramine or the ammonia water to the metal uranium in the uranyl nitrate starvation solution is 1: 1.2-1.6.

Preferably, step S4 includes: adding graphene into deionized water by stirring according to the mass ratio of 2:8-4:6 to form a graphene mixed solution; and adding 0.5-2% of dispersant polyethyleneimine into the graphene mixed solution, and uniformly stirring to obtain the graphene suspension.

Preferably, in step S5, mixing the sol solution and the graphene suspension according to the volume percentage of graphene to uranium dioxide of 1-10: 100; stirring at a temperature below 5 deg.C to form a mixture.

Preferably, in step S6, the mixed solution is placed in an oven and heated at 80 to 90 ℃ for 48 to 96 hours to gel.

Preferably, in step S7, the aqueous uranium compound-graphene mixture gel is washed with dilute ammonia water to remove the residual acid.

Preferably, in step S8, the dry calcination includes: heating the mixture from room temperature for 1-2 hours to 110 ℃, and preserving heat for 3-4 hours; then heating to 200-220 ℃, and preserving heat for 2-2.5 hours; then heating to 300 ℃, and preserving the heat for 2-2.5 hours; finally cooling to room temperature;

the reduction sintering comprises the following steps: and (3) carrying out reduction calcination in the mixed gas atmosphere of argon and hydrogen, heating to 600 ℃ at the temperature of 5-10 ℃/min, preserving heat for 3-4 hours, and then cooling to room temperature.

Preferably, in step S9, the densification sintering is performed by SPS sintering, the temperature is raised to 1200 ℃ to 1500 ℃, the temperature is maintained for 5 to 30 minutes, and then the temperature is cooled to room temperature.

The invention also provides a uranium dioxide-graphene fuel pellet which is prepared by adopting any one of the preparation methods.

The invention has the beneficial effects that: preparing uranium dioxide-graphene composite powder by a sol-gel process, and then preparing a uranium dioxide-graphene fuel pellet; the composite powder has the advantages of uniform component distribution and high powder activity, improves the uniformity of the components of the core block, is favorable for compactness of the core block, can obviously reduce the sintering temperature of a green body, and reduces the physical and chemical reactions of the interface of uranium oxide and graphene.

In addition, the thermal conductivity of graphene is superior to that of SiC powder, and the thermal conductivity improvement to the fuel pellets is also due to the SiC-added fuel pellets.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a flow chart of a preparation method of the present invention;

fig. 2 is a schematic structural view showing the distribution of graphene of the fuel pellets produced by the present invention.

Detailed Description

Referring to fig. 1, the method for preparing a uranium dioxide-graphene fuel pellet according to the present invention may include the following steps:

s1, preprocessing: calcining ammonium diuranate powder at 800-900 ℃ for 2-4 hours to convert the ammonium diuranate into U at high temperature₃O₈。

S2, dissolving: using concentrated nitric acid to react U₃O₈Dissolving to obtain acid-deficient uranyl nitrate (UO)₂(NO₃)₂) And (3) solution.

Wherein, the mass ratio of the solid to the liquid is 1:1.35-1.45(g/ml) to the U₃O₈Dissolved in concentrated nitric acid.

At U₃O₈Dissolving in concentrated nitric acid, filtering to remove incompletely dissolved U₃O₈(deslagging), and obtaining filtrate, namely the uranyl nitrate acid-deficiency solution.

S3, preparing glue: preparing the obtained uranyl nitrate acid-deficient solution into a sol solution.

Specifically, urea and hexamethylenetetramine or ammonia water are added into the uranyl nitrate solution for acid shortage, and a sol solution is formed after complete dissolution.

Wherein the molar ratio of the urea to the metal uranium in the uranyl nitrate acid-deficiency solution is 1: 1.2-1.6; the molar ratio of hexamethylene tetramine or ammonia water to the metal uranium in the uranyl nitrate starvation solution is 1: 1.2-1.6.

S4, preparing a graphene suspension;

the step S4 includes: adding graphene into deionized water by stirring according to the mass ratio of 2:8-4:6 of the graphene to the deionized water to form a graphene mixed solution; and adding 0.5-2% (accounting for the total mass fraction of the graphene mixed solution) of dispersant Polyethyleneimine (PEI) into the graphene mixed solution, and uniformly stirring to obtain the graphene suspension.

S5, mixing materials: and mixing the sol solution and the graphene suspension, and stirring at a low temperature to form a mixed solution.

And mixing the sol solution and the graphene suspension according to the volume percentage of 1-10:100 of graphene and uranium dioxide. Stirring and cooling at the temperature of lower than 5 ℃ to form a mixed solution.

And S6, heating the mixed solution to gelatinize, and forming aqueous uranium compound-graphene mixture gel.

Alternatively, the mixed solution is put into an oven and heated at 80-90 ℃ for 48-96 hours to carry out gelation.

And S7, washing and airing the aqueous uranium compound-graphene mixture gel to obtain gel powder.

And washing the hydrous uranium compound-graphene mixture gel by using dilute ammonia water to remove residual acid.

And S8, sequentially drying and calcining the gel powder, and performing reduction sintering to obtain uranium dioxide-graphene composite powder.

The drying and calcining comprises the following steps: heating the gel powder from room temperature for 1-2 hours to 110 ℃, and preserving heat for 3-4 hours; then heating to 200-220 ℃, and preserving heat for 2-2.5 hours; then heating to 300 ℃, and preserving the heat for 2-2.5 hours; and finally cooling (naturally cooling) to room temperature.

The reduction sintering comprises the following steps: and (3) carrying out reduction calcination on the dried and calcined gel powder in the mixed gas atmosphere of argon and hydrogen, heating to 600 ℃ at the temperature of 5-10 ℃/min, preserving the heat for 3-4 hours, and then cooling (naturally cooling) to room temperature to obtain the uranium dioxide-graphene composite powder.

S9, compacting and sintering the uranium dioxide-graphene composite powder to obtain a uranium dioxide-graphene fuel pellet (UO)₂-graphene fuel pellets).

And adopting SPS sintering for densification sintering, heating to 1200-1500 ℃, preserving heat for 5-30 minutes, and then cooling to room temperature.

As shown in fig. 1, the uranium dioxide-graphene fuel pellets prepared by the present invention have graphene 10 uniformly distributed in the pellet matrix 20, and specifically may be distributed in the pellet matrix 20 in a mesh shape as shown in the figure.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.