High-density single-phase UN fuel microsphere and preparation method thereof

Abstract

The invention relates to the technical field of UN nuclear fuel, and particularly discloses a high-density single-phase UN fuel microsphere and a preparation method thereof in order to solve the problem that existing uranium nitride fuel microsphere crystal structure phase composition is relatively complex, the preparation method comprises the following steps: S1, taking a uranyl nitrate solution, adding urea, urotropine and a carbon source, and mixing to prepare carbon-containing sol; s2, dispersing the carbon-containing sol into an organic solvent through a dispersion pore plate to form carbon-containing gel balls, and then washing, drying and calcining to obtain UO3-C dry calcined balls; s3, the UO3-C dry calcined pellets are sequentially subjected to carbon thermal reduction and nitriding sintering treatment, and the single-phase UN fuel microspheres are obtained. In the stage of preparing the uranyl nitrate solution, a special carbon source is added, so that the distribution uniformity of the carbon source in the UO3-C dry calcined ball is ensured; and in the later conversion processes of carbon thermal reduction, nitridation and the like, reducing gases with different proportions are introduced, and finally, the UN fuel microspheres composed of high-density and single-phase UN components are prepared.

Description

Technical Field

[0001] This invention relates to the field of UN nuclear fuel technology, and more specifically, to a high-density single-phase UN fuel microsphere and its preparation method. Background Technology

[0002] UN fuel, as a high-uranium-density ceramic fuel, possesses numerous advantages such as high uranium density and high thermal conductivity, which are beneficial for improving the heat transfer capacity of the pellets and increasing the uranium loading. Compared to the more traditional UO2 fuel, it can significantly reduce the operating temperature of the pellets, which is beneficial for energy extraction in the event of an accident. Based on the advantages of UN fuel, UN fuel microspheres are currently being developed as one of the fuel core options for ATF fuel CDM pellets, and as a UO2 alternative fuel.

[0003] Currently, the main method for preparing UN fuel microspheres is the sol-gel method. The sol preparation, carbon source selection, washing and drying / calcination processes, subsequent carbothermic reduction and nitriding, and sintering densification processes are all crucial technical aspects affecting the final fuel performance of the UN fuel microspheres. For example, patent CN120136045A proposes a method for preparing and applying uranium nitride spherical particles. This method involves mixing a carbon source including diamond powder with a solution to prepare gel particles, then pretreating the gel particles with carbothermic reduction and nitriding to obtain uranium nitride spherical particles. By controlling the C / U molar ratio, dense, smooth, and high-purity uranium nitride spherical particles are obtained.

[0004] However, existing uranium nitride fuels, such as those mentioned above, can improve the density and purity of uranium nitride particles to a certain extent. However, due to the influence of preparation processes or raw materials, there are problems such as uneven distribution of elemental components. As a result, the crystal structure of uranium nitride fuel microspheres has low uniformity, which affects the performance of uranium nitride fuel. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that the phase composition of existing uranium nitride fuel microsphere crystal structures is relatively complex.

[0006] This invention is achieved through the following technical solution: This invention provides a method for preparing high-density single-phase UN fuel microspheres, comprising the following steps: S1 Take uranyl nitrate solution, add urea, hexamethylenetetramine and carbon source, mix, and prepare carbon-containing sol; S2 The carbon-containing sol is dispersed into an organic solvent through a dispersion plate to form carbon-containing gel spheres, which are then washed, dried and calcined to obtain UO3-C dry calcined spheres; S3. The UO3-C dry-calcined balls are subjected to carbothermal reduction and nitriding sintering treatments in sequence to obtain the single-phase UN fuel microspheres.

[0007] Preferably, in step S1, the molar ratio of uranium metal to urea and hexamethylenetetramine is 1.2-1.7:1.

[0008] Preferably, the molar ratio of uranium metal to carbon source is 2-3:1.

[0009] Preferably, in step S1, the mixture is stirred at 0-10°C.

[0010] Preferably, in step S2, the pressure is controlled to be 0.05-0.2 MPa when passing through the dispersion orifice plate.

[0011] Preferably, the organic solvent is heated to 60-100°C before dispersion.

[0012] Preferably, in step S2, the drying and calcining temperature is 280-350℃, and the drying and calcining time is 2-5h.

[0013] Preferably, in step S3, during the carbothermic reduction treatment, the temperature is raised to 1600-1700℃, and argon gas containing 5-10% hydrogen by volume is introduced, and the carbothermic reduction is carried out for 5-15 hours.

[0014] Preferably, in step S3, during the nitriding sintering treatment, after heating to 1750-1850℃, nitrogen gas containing 5-10% hydrogen by volume is introduced, and sintering is carried out for 5-15 hours.

[0015] The technical solution of the present invention has the following beneficial effects: This invention belongs to the field of nuclear fuel preparation, and relates to the preparation of micron-sized fuel microspheres, the synthesis and conversion of UN fuel phases, and their sintering densification methods. Specifically, this invention ensures the uniform distribution of C source in UO3-C dry-calcined spheres by adding a specially formulated liquid C source during the preparation of uranyl nitrate solution; and by introducing reducing gases in different proportions during subsequent carbothermic reduction and nitriding conversion processes, ultimately preparing high-density, single-phase UN fuel microspheres composed of UN components. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0017] This invention provides a high-density single-phase UN fuel microsphere, the preparation method of which includes the following steps: (1) Take a high concentration of uranyl nitrate solution, add urea, hexamethylenetetramine and C source, stir and mix at a low temperature of 0-10℃ to prepare a C-containing sol.

[0018] In this process, the molar ratio of uranium metal to urea and hexamethylenetetramine is 1.2-1.7:1, and the molar ratio of uranium metal to carbon source is 2-3:1. The introduction of carbon source in this process can ensure the uniformity of carbon source distribution in the subsequently prepared UO3-C dry-calcined balls.

[0019] (2) The C-containing sol is dispersed through a dispersion plate under a pressure of 0.05-0.2 MPa into an organic solvent heated to 60-100℃, which allows the C-containing sol to form C-containing gel spheres through gelation in the organic solvent; then it is washed, dried and calcined in sequence at a temperature of 280-350℃ for 2-5 hours to form C-containing UO3-C dry calcined spheres.

[0020] (3) The UO3-C dry-calcined balls are first subjected to high-temperature carbothermic reduction. The temperature is raised to 1600-1700℃, and argon gas containing 5-10% hydrogen by volume is introduced. The carbothermic reduction lasts for 5-15 hours. Then, the nitriding sintering treatment is carried out. The temperature is raised to 1750-1850℃, and nitrogen gas containing 5-10% hydrogen by volume is introduced. The sintering lasts for 5-15 hours, and high-density single-phase UN fuel microspheres are obtained.

[0021] During high-temperature carbothermic reduction and other conversion processes, different proportions of reducing gas (H2) are added, which can significantly improve the sintering density of single-phase UN fuel microspheres, obtain a single-phase UN composition, and reduce the content of impurities such as carbon and oxygen in the product.

[0022] The UN fuel microspheres proposed in this invention can be used as fuel cores for preparing CDM pellets. The processing method and process conditions of each step in the preparation process directly affect the sintering density, uranium content, nitrogen content and other composition of the final single-phase UN fuel microsphere product, as well as the content of impurities such as carbon and oxygen, and thus affect its performance. Therefore, the above-mentioned preparation method and its parameter conditions are important factors affecting the performance of the single-phase UN fuel microspheres proposed in this invention.

[0023] Example 1 Step 1: Take 100gU of a 600gU / L uranyl nitrate solution, add urea and hexamethylenetetramine at a uranium metal molar ratio of 1.4:1, then add liquid C source at a uranium metal molar ratio of 2.7:1, stir at 5℃ to prepare a C-containing sol.

[0024] Step 2: The C-containing sol was dispersed through a dispersion plate at a pressure of 0.1 MPa into silicone oil heated to 80°C to form C-containing gel spheres. Then, the sol was washed three times with 3.00 mol / L ammonia and 50 v% ethanol, and then dried and calcined at 300°C for 3 h to obtain C-containing UO3-C dry calcined spheres.

[0025] Step 3: Place the UO3-C dry-calcined balls into a 2000℃ tungsten wire heating furnace, and at around 1650℃, introduce argon gas containing 8% hydrogen by volume for carbothermic reduction for 10 hours; then raise the temperature to around 1800℃, introduce nitrogen gas containing 8% hydrogen by volume, and sinter for 10 hours. After cooling, remove from the furnace to obtain 100gU of UN fuel microspheres.

[0026] The UN fuel microspheres prepared in this embodiment are composed of single-phase UN and have a density of 12.95 g / cm³. 3 .

[0027] Example 2 Step 1: Take 100gU of a 600gU / L uranyl nitrate solution, add urea and hexamethylenetetramine at a uranium metal molar ratio of 1.4:1, then add liquid C source at a uranium metal molar ratio of 2.7:1, stir at 5℃ to prepare a C-containing sol.

[0028] Step 2: The C-containing sol was dispersed through a dispersion plate at a pressure of 0.1 MPa into silicone oil heated to 80°C to form C-containing gel spheres. Then, the sol was washed three times with 3.00 mol / L ammonia and 50 v% ethanol, and then dried and calcined at 300°C for 3 h to obtain C-containing UO3-C dry calcined spheres.

[0029] Step 3: Place the UO3-C dry-calcined balls into a 2000℃ tungsten wire heating furnace, and at around 1650℃, introduce argon gas containing 4% hydrogen by volume for carbothermic reduction for 10 hours; then raise the temperature to around 1800℃, and introduce nitrogen gas containing 4% hydrogen by volume for sintering for 10 hours. After cooling, remove from the furnace to obtain 100gU of UN fuel microspheres.

[0030] The UN fuel microspheres prepared in this embodiment are composed of single-phase UN and have a density of 13.10 g / cm³. 3 .

[0031] Example 3 Step 1: Take 100gU of a 600gU / L uranyl nitrate solution, add urea and hexamethylenetetramine at a uranium metal molar ratio of 1.4:1, then add liquid C source at a uranium metal molar ratio of 2.7:1, stir at 5℃ to prepare a C-containing sol.

[0032] Step 2: The C-containing sol was dispersed through a dispersion plate at a pressure of 0.1 MPa into silicone oil heated to 80°C to form C-containing gel spheres. Then, the sol was washed three times with 3.00 mol / L ammonia and 50 v% ethanol, and then dried and calcined at 300°C for 3 h to obtain C-containing UO3-C dry calcined spheres.

[0033] Step 3: Place the UO3-C dry-calcined balls into a 2000℃ tungsten wire heating furnace, and at around 1650℃, introduce argon gas containing 8% hydrogen by volume for carbothermic reduction for 10 hours; then raise the temperature to around 1850℃, introduce nitrogen gas containing 8% hydrogen by volume, and sinter for 10 hours. After cooling, remove from the furnace to obtain 100g of UN fuel microspheres.

[0034] The UN fuel microspheres prepared in this embodiment are composed of single-phase UN and have a density of 13.25 g / cm³. 3 .

[0035] Example 4 Step 1: Take 100gU of a 550gU / L uranyl nitrate solution, add urea and hexamethylenetetramine at a uranium metal molar ratio of 1.3:1, then add liquid C source at a uranium metal molar ratio of 2.2:1, stir at 5℃ to prepare a C-containing sol.

[0036] Step 2: The C-containing sol was dispersed through a dispersion plate at a pressure of 0.1 MPa into silicone oil heated to 80°C to form C-containing gel spheres. Then, the sol was washed three times with 3.00 mol / L ammonia and 50 v% ethanol, and then dried and calcined at 300°C for 3 h to obtain C-containing UO3-C dry calcined spheres.

[0037] Step 3: Place the UO3-C dry-calcined balls into a 2000℃ tungsten wire heating furnace, and reduce them for 3 hours by introducing pure hydrogen at around 550℃; then raise the temperature to around 1600℃, and introduce argon gas containing 8% hydrogen by volume for carbothermic reduction for 10 hours; finally raise the temperature to around 1800℃, introduce nitrogen gas containing 8% hydrogen by volume, and sinter for 10 hours. After cooling, remove the balls from the furnace to obtain 100g of UN fuel microspheres.

[0038] The UN fuel microspheres prepared in this embodiment are composed of single-phase UN and have a density of 13.30 g / cm³. 3 .

[0039] Example 5 Step 1: Take 100gU of a 550gU / L uranyl nitrate solution, add urea and hexamethylenetetramine at a uranium metal molar ratio of 1.3:1, then add liquid C source at a uranium metal molar ratio of 2.2:1, stir at 5℃ to prepare a C-containing sol.

[0040] Step 2: The C-containing sol was dispersed through a dispersion plate at a pressure of 0.1 MPa into silicone oil heated to 80°C to form C-containing gel spheres. Then, the sol was washed three times with 3.00 mol / L ammonia and 50 v% ethanol, and then dried and calcined at 300°C for 3 h to obtain C-containing UO3-C dry calcined spheres.

[0041] Step 3: Place the UO3-C dry-calcined balls into a 2000℃ tungsten wire heating furnace, and reduce them for 3 hours by introducing pure hydrogen at around 550℃; then raise the temperature to around 1600℃, and introduce argon gas containing 4% hydrogen by volume for carbothermic reduction for 10 hours; finally raise the temperature to around 1850℃, introduce nitrogen gas containing 4% hydrogen by volume, and sinter for 10 hours. After cooling, remove the balls from the furnace to obtain 100g of UN fuel microspheres.

[0042] The UN fuel microspheres prepared in this embodiment are composed of single-phase UN and have a density of 13.35 g / cm³. 3 .

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for the preparation of high density, single phase UN fuel microspheres, characterized by, The method comprises the following steps: S1: taking a uranyl nitrate solution, adding urea, urotropin and a carbon source, mixing to prepare a carbon-containing sol; S2: dispersing the carbon-containing sol into an organic solvent through a dispersion hole plate to form carbon-containing gel balls, and then washing, drying and calcining to obtain UO3-C dry calcined balls; S3: sequentially performing carbonthermal reduction and nitriding sintering treatment on the UO3-C dry calcined balls to obtain the single-phase UN fuel microspheres.

2. The method of claim 1, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: In step S1, the molar ratio of the amount of uranium metal to the amount of urea and urotropin is 1.2-1.7:

1.

3. The method of claim 2, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: The molar ratio of the amount of uranium metal to the amount of carbon source is 2-3:

1.

4. The method of claim 1, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: In step S1, the stirring and mixing are performed at 0-10℃.

5. The method of claim 1, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: In step S2, the pressure is controlled to be 0.05-0.2 MPa when passing through the dispersion hole plate.

6. The method of claim 5, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: Before dispersion, the organic solvent is heated to 60-100℃.

7. The method of claim 1, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: In step S2, the drying and calcining temperature is 280-350℃, and the drying and calcining time is 2-5h.

8. The method of claim 1, wherein the high-density, single-phase UN fuel microspheres are characterized by: In step S3, the heating temperature is raised to 1600-1700℃ during the carbonthermal reduction treatment, argon containing 5-10% hydrogen is introduced, and the carbonthermal reduction is performed for 5-15h.

9. The method of claim 1, wherein the high-density, single-phase UN fuel microspheres are prepared by the process of: In step S3, the heating temperature is raised to 1750-1850℃ during the nitriding sintering treatment, nitrogen containing 5-10% hydrogen is introduced, and the sintering is performed for 5-15h.

10. High-density single-phase UN fuel microspheres prepared by the preparation method in any one of claims 1-9.