A method for rapid production of UN powder

Abstract

The application discloses a kind of UN powder's quick preparation method, solve the carbon-thermal reduction-nitriding reaction method in prior art difficult to obtain high-purity UN powder, arc smelting method high cost, long cycle problem.A kind of UN powder's quick preparation method of the application, UO2 powder is reduced into metal uranium using metal reduction method, then using reaction heat makes metal uranium and nitrogen gas nitriding reaction, obtains UN powder.The application is more efficient, the reaction process is faster, more sufficient, UN production cycle is compared with arc smelting method greatly shortened, even shorter than carbon-thermal reduction method, can realize the batch preparation of high-purity UN powder in very short time.

Description

Technical Field

[0001] This invention relates to the field of nuclear fuel technology, and in particular to a rapid method for preparing UN powder. Background Technology

[0002] Uranium dioxide (UO2) is currently the most widely used nuclear fuel in commercial nuclear reactors, possessing excellent thermal, chemical, and radiation stability, as well as advantages such as a high melting point, strong ability to retain solid fission products, and strong resistance to the diffusion of gaseous fission products. However, its reliance on phonon heat transfer causes its thermal conductivity to drop sharply under high temperatures and irradiation conditions, resulting in a rapid decline in its heat removal capacity. Therefore, the current UO2-Zr nuclear fuel system is only used at temperatures of 700-1200℃. In an accident scenario, the reactor cooling system fails, preventing heat dissipation and causing a rapid rise in core temperature. The Zr cladding reacts with water vapor at high temperatures, intensifying the exothermic oxidation and hydrogen release reactions, releasing large amounts of heat and hydrogen in a short time. The hydrogen explodes at high temperatures, the cladding tubes rupture due to various adverse reactions and fuel pellet deformation and compression, the pellets melt down due to excessive temperature, and the reactor pressure vessel is damaged due to excessive internal pressure, ultimately leading to a nuclear accident involving the leakage of radioactive materials (ROMeyer, Nucl. Technol., 155, 2006, 293). In all previous nuclear accidents, the leakage of radioactive materials was directly related to excessively high reactor core temperatures and fuel rod meltdown. Therefore, the intrinsic characteristic of UO2's extremely low thermal conductivity is one of the key factors causing nuclear leakage accidents. Furthermore, the uranium density in UO2 fuel is only 9.66 gU / cm³. 3 This results in low economic efficiency in the operation and management of nuclear power plants.

[0003] Uranium nitride (UN) has a melting point of 2600℃, comparable to UO2. However, UN exhibits superior thermal conductivity compared to UO2 (21.5 W·m³ at 600℃). -1 ·K -1 UO2: 3.89 W·m -1 ·K -1 Furthermore, the density of UN is 14.13 g / cm³. 3 ) and uranium density (13.55 gU / cm³) 3 All were higher than UO2 (10.96 g / cm³). 3 9.66 gU / cm 3For the same volume, UN fuel has a 40% higher uranium loading than UO2 (JHYang, J. Nucl. Mater., 465, 2015, 509). Therefore, compared to UO2, UN fuel achieves higher burnup, longer operating cycles, and less nuclear waste, demonstrating better operational and neutron economics. Furthermore, UN fuel exhibits good resistance to radiation and steam oxidation. UN nuclear fuel has significant advantages in improving the safety and economy of nuclear reactors. However, current UN powder is primarily prepared from highly reactive uranium oxide powder and high-purity carbon black, using a carbothermal reduction-nitridation reaction to synthesize uranium nitride powder. This method not only requires high reactivity of the UO2 powder and purity of the carbon black, but also imposes strict requirements on process parameters such as the carbon / uranium molar ratio, reaction atmosphere, reaction temperature, and time, making it difficult to obtain high-purity UN powder. Therefore, it also struggles to meet the purity requirements of nuclear fuel assemblies. Another method involves melting metallic uranium in a nitrogen atmosphere using an electric arc to prepare uranium nitride ingots, which are then pulverized or crushed to obtain UN powder. While this process can yield high-purity UN powder, it requires metallic uranium as a raw material, demands sophisticated equipment, has a long processing cycle, and incurs high production costs, making it unsuitable for industrial applications. Summary of the Invention

[0004] The purpose of this invention is to provide a rapid preparation method for UN powder, addressing the aforementioned problems and solving the issues of difficulty in obtaining high-purity UN powder using the carbothermic reduction-nitridation reaction method and the high cost and long cycle of the electric arc melting method.

[0005] The technical solution adopted in this invention is as follows: a rapid preparation method for UN powder, comprising the following steps: reducing UO2 powder to metallic uranium using a metallothermic reduction method, and then using the heat of reaction to cause the metallic uranium to undergo a nitriding reaction with nitrogen gas to obtain UN powder.

[0006] Furthermore, the rapid preparation method of UN powder of the present invention includes the following steps:

[0007] A. Mix UO2 powder and metal reducing agent evenly at a mass ratio of 1:0.1-20 (e.g., 1:0.1, 1:1, 1:5, 1:10, 1:20, etc., depending on the type and particle size of the metal reducing agent and the particle size of the UO2 powder). Then, heat the mixture under the protection of high-purity nitrogen gas and cool it to room temperature after the reaction is complete to obtain the product.

[0008] B. After removing impurities by acid immersion, the product obtained in step A is washed and dried to obtain UN powder.

[0009] Furthermore, the metal reducing agent is selected from any one of magnesium, lithium, sodium, and potassium metal powders.

[0010] Furthermore, the particle size of the UO2 powder is 100nm-200μm, for example, it can be 100nm, 1μm, 100μm, 200μm, etc. The particle size of the UO2 powder should not be too large or too small. If it is too large, the reduction efficiency will be reduced, the reduction cycle will be prolonged, and it will be difficult to achieve full reduction. If it is too small, powder agglomeration will easily occur, and it will be more difficult to mix the UO2 powder and the metal reducing agent evenly, which will also make it difficult to achieve full reduction.

[0011] Furthermore, the particle size of the metal powder is 0.5-200μm, for example, it can be 0.5μm, 1μm, 100μm, 200μm, etc. The particle size of the metal powder should not be too large or too small. If it is too large, the contact area between the metal reducing agent and the UO2 powder is small, and the UO2 powder that is not in sufficient contact is difficult to be fully reduced. If it is too small, powder agglomeration is likely to occur, and it will be more difficult to mix the metal reducing agent and the UO2 powder evenly, and it will also be difficult to achieve full reduction.

[0012] Furthermore, in step A, the heating temperature is 65-900℃, for example, it can be 65℃, 100℃, 500℃, 900℃, etc. The specific heating temperature is mainly related to the melting point of the metal reducing agent, but it should not be too low or too high. If the heating temperature is too low, the reduction reaction will not proceed sufficiently, the reduction efficiency will be reduced, and it will be difficult to achieve complete reduction. If the heating temperature is too high, the reduction reaction will be too violent, and the metal reducing agent will easily clump together, hindering the further progress of the reduction reaction, and it will also be difficult to achieve complete reduction.

[0013] Furthermore, in step A, the reaction time is 1-8 hours, for example, it can be 1 hour, 2 hours, 3 hours, 8 hours, etc.

[0014] Furthermore, in step B, the acid is hydrochloric acid or sulfuric acid with a mass concentration of 1-50%, and the specific choice can be determined according to the actual situation.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0016] 1. This invention employs a metallothermic reduction method, using magnesium, lithium, sodium, potassium, and other powders as metal reducing agents to directly reduce UO2 powder into highly active metallic uranium powder in a nitrogen atmosphere. Simultaneously, the heat generated by the metallothermic reduction promotes the reaction of metallic uranium with nitrogen to generate UN powder. Finally, impurities are removed by washing with hydrochloric acid or sulfuric acid. High-purity UN micro powder can be prepared in batches within a very short period of time, with a purity of over 90%.

[0017] 2. Compared with the carbothermic reduction method, the method of the present invention is easier to carry out, releases more heat, and has a better reduction effect on UO2 to metallic uranium. Therefore, it is easier to achieve full reduction of UO2 and the requirements for the activity of UO2 raw materials are also reduced.

[0018] 3. In order to ensure that UO2 is completely converted into metallic uranium or uranium nitride, the reducing agent must be in excess. The carbon black or carbides remaining in the carbothermic reduction method are difficult to separate from UN, while the metal or metal oxides remaining in the metallothermic reduction method are easily dissolved in hydrochloric acid or sulfuric acid, thereby achieving efficient analysis with UN and obtaining high-purity UN.

[0019] 4. The metal thermal reduction-nitriding reaction method of the present invention has higher thermal efficiency, faster and more complete reaction process, and the production cycle of UN is significantly shortened compared with the electric arc melting method, and even shorter than the carbothermal reduction method. It can achieve the mass production of high-purity UN powder in a very short time. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Example 1

[0022] This embodiment provides a rapid preparation method for UN powder, including the following steps:

[0023] S1. Mix UO2 powder with a particle size of 100μm and magnesium metal powder with a particle size of 50μm at a mass ratio of 1:1 to obtain a mixed powder.

[0024] S2. Under the protection of high-purity nitrogen gas (nitrogen gas integral of more than 99%), the temperature is raised to 900℃ and reduced for 6 hours, and then cooled to room temperature to obtain the product;

[0025] S3. The obtained product is soaked in an 8% hydrochloric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of over 90%.

[0026] Example 2

[0027] This embodiment provides a rapid preparation method for UN powder, including the following steps:

[0028] S1. Mix UO2 powder with a particle size of 100 nm and sodium metal powder with a particle size of 500 nm at a mass ratio of 1:0.1 to obtain a mixed powder;

[0029] S2. Under the protection of high-purity nitrogen gas (nitrogen gas integral of more than 99%), the temperature is raised to 100℃ and reduced for 8 hours, and then cooled to room temperature to obtain the product;

[0030] S3. The obtained product is soaked in a 1% hydrochloric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of over 90%.

[0031] Example 3

[0032] This embodiment provides a rapid preparation method for UN powder, including the following steps:

[0033] S1. Mix UO2 powder with a particle size of 1μm and potassium metal powder with a particle size of 5μm at a mass ratio of 1:3 to obtain a mixed powder;

[0034] S2. Under the protection of high-purity nitrogen gas (nitrogen gas integral of 99% or more), the temperature is raised to 65°C and reduced for 4 hours, then cooled to room temperature to obtain the product;

[0035] S3. The obtained product is soaked in a 15% hydrochloric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of over 90%.

[0036] Example 4

[0037] This embodiment provides a rapid preparation method for UN powder, including the following steps:

[0038] S1. Mix UO2 powder with a particle size of 200μm and magnesium metal powder with a particle size of 200μm at a mass ratio of 1:20 to obtain a mixed powder;

[0039] S2. Under the protection of high-purity nitrogen gas (nitrogen gas integral of more than 99%), the temperature is raised to 650℃ and reduced for 2 hours, and then cooled to room temperature to obtain the product;

[0040] S3. The obtained product is soaked in a 50% sulfuric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of over 90%.

[0041] Example 5

[0042] This embodiment provides a rapid preparation method for UN powder, including the following steps:

[0043] S1. Mix UO2 powder with a particle size of 50 μm and sodium metal powder with a particle size of 10 μm at a mass ratio of 1:5 to obtain a mixed powder.

[0044] S2. Under the protection of high-purity nitrogen gas (nitrogen gas integral of more than 99%), the temperature is raised to 150°C and reduced for 1 hour, and then cooled to room temperature to obtain the product.

[0045] S3. The obtained product is soaked in a 10% sulfuric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of over 90%.

[0046] Comparative Example 1

[0047] Comparative Example 1 is the same as Example 4, except that the particle size of the UO2 powder is 300 μm.

[0048] Experimental results: The obtained product was soaked in a 50% sulfuric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of about 76%.

[0049] Comparative Example 2

[0050] Comparative Example 2 is the same as Example 4, except that the particle size of the magnesium metal powder is 250 μm.

[0051] Experimental results: The obtained product was soaked in a 50% sulfuric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of about 82%.

[0052] Comparative Example 3

[0053] Comparative Example 3 is the same as Example 4, except that the heating temperature is 700°C.

[0054] Experimental results: The obtained product was soaked in a 50% sulfuric acid solution to remove impurities, and then washed and dried to obtain UN powder with a purity of about 64%.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rapid preparation method for UN powder, characterized in that, The process includes the following steps: reducing UO2 powder to metallic uranium using a metallothermic reduction method, and then using the heat of reaction to cause the metallic uranium to undergo a nitriding reaction with nitrogen gas to obtain UN powder. Specifically, the steps are as follows: A. After mixing UO2 powder and metal reducing agent at a mass ratio of 1:0.1-20, the mixture is heated and reacted under the protection of high-purity nitrogen gas. After the reaction is completed, the mixture is cooled to room temperature to obtain the product. The particle size of the UO2 powder is 100nm-200μm, and the particle size of the metal powder is 0.5-200μm. B. After removing impurities by acid immersion, the product obtained in step A is washed and dried to obtain UN powder.

2. The rapid preparation method as described in claim 1, characterized in that, The metal reducing agent is selected from any one of magnesium, lithium, sodium, and potassium metal powders.

3. The rapid preparation method as described in claim 2, characterized in that, In step A, the temperature for heating is 65-900℃.

4. The rapid preparation method as described in claim 3, characterized in that, In step A, the reaction time is 1-8 hours.

5. The rapid preparation method as described in claim 1, characterized in that, In step B, the acid is hydrochloric acid or sulfuric acid with a mass concentration of 1-50%.