Preparation method of uranium nitride pellet and uranium nitride pellet

Abstract

The embodiment of the invention relates to the technical field of binary compounds of nitrogen and metal, in particular to a preparation method of a uranium nitride pellet and the uranium nitride pellet. The invention provides a uranium nitride pellet preparation method which comprises the following steps: arranging uranium nitride powder in a reaction region, and inputting a mixed gas containing a nitrogen element into the reaction region; heating the reaction area to a first preset value within first preset time, and enabling the uranium nitride powder to react with the mixed gas to obtain a reaction product; controlling the temperature of the reaction area, enabling the uranium nitride powder to fully react with the mixed gas, and enabling the nitrogen-uranium molar ratio of a reaction product to reach a preset value; and granulating and sintering the reaction product to obtain the uranium nitride pellet. The invention further provides the uranium nitride pellet. By using the method provided by the invention, the nitrogen-uranium molar ratio of the uranium nitride pellet can be accurately controlled, the crystal structure, heat conductivity and radiation stability of the uranium nitride pellet are optimized, and it is ensured that the uranium nitride pellet meets the performance requirements of serving in different nuclear reactors.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of binary compounds of nitrogen and metals, and more particularly to a method for preparing a uranium nitride pellet and a uranium nitride pellet. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Uranium nitride fuel has become an important form of fuel in nuclear reactors due to its excellent properties such as high uranium density, high thermal conductivity, high-temperature stability and good compatibility with liquid metal. The physical and chemical properties of uranium nitride fuel itself will affect its performance in nuclear reactors, thereby affecting the service performance, safety and stability of nuclear reactors.

[0004] However, the current uranium nitride fuel production and process technology still has many technical defects, which result in performance differences in the prepared uranium nitride fuel, thereby affecting its service performance in nuclear reactors. Summary of the Invention

[0005] A brief overview of the present application is provided below to provide a basic understanding of certain aspects of the present application. It should be understood that this overview is not an exhaustive overview of the present application. It is not intended to identify key or important portions of the present application, nor is it intended to limit the scope of the present application. Its purpose is simply to present certain concepts in a simplified form as a prelude to the more detailed description that will be discussed later.

[0006] In a first aspect, an embodiment of the present application provides a method for preparing a uranium nitride pellet, comprising the following steps: S10: placing a raw uranium nitride powder in a reaction area, and inputting a mixed gas including a nitrogen element into the reaction area; S20: heating the reaction area to a first predetermined value within a first predetermined time, so that the raw uranium nitride powder reacts with the mixed gas to obtain a reaction product; S30: controlling the temperature of the reaction area so that the raw uranium nitride powder and the mixed gas fully react, and the nitrogen-uranium molar ratio of the reaction product reaches a predetermined value; S40: pelletizing the reaction product obtained in step S30 to obtain uranium nitride pellets; and S50: sintering the uranium nitride pellets obtained in step S40 to obtain a uranium nitride pellet.

[0007] In a second aspect, an embodiment of the present application further provides a uranium nitride pellet, which is prepared using the method for preparing a uranium nitride pellet according to any embodiment of the first aspect of the present application.

[0008] The method for preparing uranium nitride pellets in the embodiments of the present application comprises: introducing a mixed gas including nitrogen into a reaction region, causing the raw uranium nitride powder to react with the mixed gas at a first predetermined temperature; controlling the temperature of the reaction region to achieve precise control of the nitrogen-uranium molar ratio in the reaction product; and stabilizing the nitrogen-uranium molar ratio at a predetermined value by pelletizing and sintering the reaction product. Thus, precise control of the nitrogen-uranium molar ratio of the obtained uranium nitride pellets is achieved, and the crystal structure, thermal conductivity, and radiation stability of the uranium nitride pellets are optimized, ensuring that the pellets meet the performance requirements for service in different nuclear reactors, and significantly improving the safety and stability of nuclear reactor operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other objects and advantages of the present application will become apparent from the following description of the embodiments of the present application with reference to the accompanying drawings, which will help to provide a comprehensive understanding of the present application.

[0010] Figure 1 4 is a flow chart of a method for preparing uranium nitride pellets according to an embodiment of the present application.

[0011] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner that does not affect the reader's understanding. DETAILED DESCRIPTION

[0012] Exemplary embodiments of the present application will be described below with reference to the accompanying drawings. For the sake of clarity and conciseness, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the process of developing any such actual implementation in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and these constraints may vary depending on the implementation. In addition, it should be understood that although the development work may be very complex and time-consuming, it is a routine task for those skilled in the art who benefit from the content of this application.

[0013] It is also necessary to explain here that, in order to avoid obscuring the present application due to unnecessary details, the accompanying drawings only show the device structure and / or processing steps that are closely related to the solution according to the present application, while other details that are not closely related to the present application are omitted.

[0014] The nitrogen-uranium molar ratio in uranium nitride fuel directly affects the microstructure, physical and chemical properties of the fuel. The inventors of the present application have discovered that in the current conventional production process of uranium nitride fuel, the nitrogen-uranium molar ratio in uranium nitride pellets is still controlled within a range, that is, the value of the nitrogen-uranium molar ratio is controlled within a range. As a result, the prepared uranium nitride pellets are difficult to meet the fuel performance requirements of different nuclear reactors, thereby affecting the safety and stability of nuclear reactor operation.

[0015] Based on this, the embodiment of the present application provides a method for preparing a uranium nitride pellet, such as Figure 1 As shown, Figure 1 A flow chart showing a method for preparing a uranium nitride pellet according to an embodiment of the present application is provided. The method comprises the following steps S10 to S50:

[0016] S10: placing raw material uranium nitride powder in a reaction area, and inputting a mixed gas including nitrogen into the reaction area.

[0017] S20: Raising the temperature of the reaction region to a first predetermined value within a first predetermined time, so that the raw material uranium nitride powder reacts with the mixed gas to obtain a reaction product.

[0018] S30: The temperature of the reaction area is controlled to allow the raw material uranium nitride powder to fully react with the mixed gas, and the nitrogen-uranium molar ratio of the reaction product to reach a predetermined value.

[0019] S40: Granulating the reaction product obtained in step S30 to obtain uranium nitride particles.

[0020] S50: Sintering the uranium nitride particles obtained in step S40 to obtain uranium nitride pellets.

[0021] The preparation method of uranium nitride pellets provided in the embodiments of the present application comprises: introducing a mixed gas including nitrogen into a reaction region, causing the raw material uranium nitride powder to react with the mixed gas at a first predetermined temperature; controlling the temperature of the reaction region to achieve precise control of the nitrogen-uranium molar ratio in the reaction product; and stabilizing the nitrogen-uranium molar ratio at a predetermined value by pelletizing and sintering the obtained reaction product. Thus, precise control of the nitrogen-uranium molar ratio of the obtained uranium nitride pellets is achieved, optimizing the crystal structure, thermal conductivity, and radiation stability of the uranium nitride pellets, ensuring that they meet the performance requirements for service in different nuclear reactors, and significantly improving the safety and stability of nuclear reactor operation.

[0022] In some embodiments, in step S10, the mixed gas includes nitrogen, hydrogen, and ammonia. In this embodiment, the nitrogen, hydrogen, and ammonia mixed gas is used to react with the uranium nitride powder to control the nitrogen partial pressure in the reaction region, thereby facilitating the regulation of the nitrogen-uranium molar ratio of the reaction product.

[0023] In some embodiments, the volume ratio of each component in the mixed gas is: nitrogen 85%-95%, hydrogen 2.5%-7.5%, and ammonia 2.5%-7.5%.

[0024] In this embodiment, a mixed gas containing 85% to 95% nitrogen, 2.5% to 7.5% hydrogen, and 2.5% to 7.5% ammonia by volume is fed into the reaction zone to increase the reactivity of nitrogen atoms in the mixed gas, accelerate the nitridation reaction of the uranium nitride powder, and facilitate control of the nitrogen-uranium molar ratio of the reaction product.

[0025] For example, the volume ratio of each component in the mixed gas is: nitrogen 90%, hydrogen 5%, and ammonia 5%.

[0026] In some embodiments, in step S20, the reaction area is heated to 1600° C. within 8-12 minutes to increase the activity of the nitriding reaction, allowing the mixed gas to diffuse rapidly in the reaction area and be rapidly absorbed by the raw uranium nitride powder, thereby completing the initial stage of the nitriding reaction in a short time.

[0027] For example, in step S20, the heating time of the reaction zone is controlled to 10 minutes to further improve the nitriding reaction activity and accelerate the reaction process.

[0028] In some embodiments, step S30 further includes steps S31 to S33:

[0029] S31: controlling the temperature of the reaction zone to drop from a first predetermined value to a second predetermined value, and maintaining the temperature for a second predetermined time.

[0030] S32: controlling the temperature of the reaction zone to rise from the second predetermined value to the first predetermined value, and maintaining the temperature for a third predetermined time.

[0031] S33: Repeat steps S31-S32 multiple times, and when the temperature of the reaction zone is controlled to rise from the second predetermined value to the first predetermined value for the last time, keep the temperature for a fourth predetermined time.

[0032] In this embodiment, the temperature of the reaction zone is controlled to cycle multiple times between a first predetermined value and a second predetermined value, and the temperature of the reaction zone is maintained for a fourth predetermined time when the temperature is last increased from the second predetermined value to the first predetermined value, thereby reducing the carbon and oxygen impurity content in the reaction product. In addition, the multiple cycles of temperature control change the structure of the reaction product, thereby facilitating the full progress of the nitridation reaction and ensuring that the raw material uranium nitride powder reacts completely with the mixed gas, thereby synergistically achieving control of the nitrogen-uranium molar ratio of the product obtained by the reaction.

[0033] In some embodiments, in step S31, the temperature of the reaction zone is controlled to drop from 1600°C to 500°C, and the insulation time is not less than 30 minutes; in step S32, the temperature of the reaction zone is controlled to rise from 500°C to 1600°C, and the insulation time is not less than 2 hours; in step S33, when the temperature of the reaction zone is controlled to rise from 500°C to 1600°C for the last time, the insulation time is adjusted to 1 hour.

[0034] In this embodiment, under the nitrogen partial pressure provided by the mixed gas, the temperature of the reaction zone is controlled to drop from 1600° C. to 500° C., and the holding time is not less than 30 minutes, so that the nitride phase structure undergoes a transformation from UN to U2N3, thereby achieving a change in the volume ratio of the reaction products and forming micropores, thereby increasing the contact area between the mixed gas and the solid phase. Similarly, the temperature of the reaction zone is controlled to rise from 500° C. to 1600° C., and the holding time is not less than 2 hours, so that the nitride phase structure undergoes a transformation from U2N3 to UN, thereby stabilizing the nitrogen-uranium molar ratio of the reaction products.

[0035] In some embodiments, step S40 further includes steps S41 to S43:

[0036] S41: Mixing the reaction product obtained in step S30 with a polyethylene glycol ethanol solution to obtain a mixture.

[0037] S42: Drying the mixture.

[0038] S43: The dried mixture is crushed under an argon atmosphere and sieved to obtain uranium nitride particles.

[0039] In this embodiment, the reaction product having a nitrogen-uranium molar ratio reaching a predetermined value obtained in step S30 is mixed with a polyethylene glycol ethanol solution, and the mixture is dried, crushed, and sieved to obtain uranium nitride particles. This refines the mixture, increases the contact area between the solid phase and the reaction gas in the subsequent solid-phase reaction, and accelerates the nitriding reaction. Furthermore, it is beneficial to achieve nitrogen balance between the solid phase and the sintering atmosphere during the subsequent sintering process, thereby stabilizing the nitrogen-uranium molar ratio of the uranium nitride particles at a predetermined value.

[0040] In some embodiments, in step S41, the reaction product obtained in step S30 is mixed with the polyethylene glycol ethanol solution by spraying to obtain a uniformly mixed mixture.

[0041] In some embodiments, in step S42, the vacuum degree is less than 1×10 -2 The mixture is dried in a vacuum environment of 1×10 Pa for a period of not less than 1 h. -2Pa environment can prevent the nitride from being oxidized and corroded by oxygen and water. Therefore, in this embodiment, the mixture is dried under this environment to prevent the uranium nitride powder from being oxidized and corroded, which would affect the control of the nitrogen-uranium molar ratio of the mixture.

[0042] In some embodiments, step S50 further includes steps S51 to S54:

[0043] S51: Pressing the uranium nitride particles obtained in step S40 into a compact to obtain a green compact.

[0044] S52: The compact is placed in a sintering area, and nitrogen is introduced into the sintering area so that a trace amount of nitrogen is contained in the sintering area.

[0045] S53: Sintering the compact in a sintering area.

[0046] S54: Evacuate the sintering area and keep the sintered product in a vacuum for a predetermined time to obtain a uranium nitride pellet.

[0047] In this embodiment, the uranium nitride particles obtained in step S40 are pressed into green compacts, and the green compacts are sintered in a slight nitrogen atmosphere. After sintering, the sintered product is kept warm for a predetermined time in a vacuum environment to prevent the ambient temperature from decreasing during the holding process, causing the uranium nitride to react with nitrogen to form a U2N3 phase, thereby affecting the nitrogen-uranium molar ratio control of the uranium nitride pellets.

[0048] In some embodiments, in step S51, the uranium nitride particles obtained in step S40 are placed in a mold and compacted at a pressure between 350 MPa and 500 MPa to obtain a compact having a green density of 45% to 55% TD%.

[0049] In some embodiments, in step S52, the partial pressure of nitrogen is maintained between 10 Pa and 50 Pa to maintain the sintering area in a slight nitrogen atmosphere, thereby preventing the tendency of UN phase decomposition under high temperature conditions of 1700-1900° C. during the sintering process, thereby affecting the molar ratio control of the uranium nitride pellets.

[0050] In some embodiments, in step S53, the sintering temperature is controlled between 1700-1900° C., and the sintering process lasts for 2-3 hours to achieve densification and grain growth of the sintered product, thereby obtaining a high-density uranium nitride pellet.

[0051] In some embodiments, in step S54, the vacuum degree of the vacuum environment is maintained at 10 -2Pa, and the holding temperature is controlled between 1000-1200°C for 1-2 hours. By evacuating and storing the sintered product at a temperature below 1200°C, the uranium nitride is further prevented from reacting with nitrogen at low temperatures to form the U2N3 phase, which would affect the nitrogen-uranium molar ratio. Setting the holding period to 1-2 hours further stabilizes the nitrogen-uranium molar ratio of the sintered uranium nitride pellets.

[0052] An embodiment of the present application further provides a uranium nitride pellet, which is prepared using the method for preparing a uranium nitride pellet according to any embodiment of the first aspect of the present application.

[0053] The process of preparing uranium nitride pellets in this application is further described below.

[0054] The raw material uranium nitride powder is placed in a reaction area, and a mixed gas of 90% nitrogen, 5% hydrogen, and 5% ammonia is introduced into the reaction area; the reaction area is heated to 1600° C. within 10 minutes to react the raw material uranium nitride powder with the mixed gas to obtain a reaction product; the temperature of the reaction area is controlled to drop from 1600° C. to 500° C., and the holding time is not less than 30 minutes; the temperature of the reaction area is then controlled to rise from 500° C. to 1600° C., and the holding time is not less than 2 hours; the above cooling and heating steps are repeated three times; when the temperature of the reaction area is controlled to rise from 500° C. to 1600° C. for the third time, the holding time is adjusted to 1 hour, so that the raw material uranium nitride powder and the mixed gas fully react, and the nitrogen-uranium molar ratio of the reaction product reaches a predetermined value; the obtained reaction product is mixed with a 0.5wt% polyethylene glycol ethanol solution by spraying to obtain a mixture, and the mixture is heated under a vacuum degree of less than 1×10 -2 Pa vacuum environment, drying the mixture for 1 hour, crushing the dried mixture in an oxygen-free argon atmosphere, and passing it through an 80-100 mesh sieve to obtain uranium nitride particles; placing the obtained uranium nitride particles into a mold, pressing and molding them at a pressure between 350-500 MPa to obtain a compact with a green density of 45-55% TD%, placing the compact in a sintering area, inputting nitrogen into the sintering area to maintain the nitrogen partial pressure in the sintering area between 10 Pa and 50 Pa, sintering the compact at a temperature of 1700-1900 ° C, and the sintering process lasting 2-3 hours, evacuating the sintering area, and sintering the compact at a vacuum degree of 10 -2 Pa environment, and keep the temperature at 1000-1200°C for 1-2 hours to obtain uranium nitride pellets.

[0055] Regarding the embodiments of the present application, it should also be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other to obtain new embodiments.

[0056] The above are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. The protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preparing uranium nitride pellets, characterized in that: It includes the following steps: S10: placing raw uranium nitride powder in a reaction area, and inputting a mixed gas including nitrogen into the reaction area; S20: raising the temperature of the reaction region to a first predetermined value within a first predetermined time, so that the raw material uranium nitride powder reacts with the mixed gas to obtain a reaction product; S30: controlling the temperature of the reaction area so that the raw material uranium nitride powder and the mixed gas fully react and the nitrogen-uranium molar ratio of the reaction product reaches a predetermined value; S40: pelletizing the reaction product obtained in step S30 to obtain uranium nitride particles; S50: Sintering the uranium nitride particles obtained in step S40 to obtain the uranium nitride pellets.

2. The method according to claim 1, characterized in that In step S10, the mixed gas includes nitrogen, hydrogen and ammonia.

3. The method according to claim 2, characterized in that The volume ratio of each component in the mixed gas is: nitrogen 85%-95%, hydrogen 2.5%-7.5%, and ammonia 2.5%-7.5%.

4. The method according to claim 1, wherein In step S20, the reaction zone is heated to 1600° C. within 8-12 minutes.

5. The method according to claim 1, characterized in that In step S30, the following steps are also included: S31: controlling the temperature of the reaction zone to drop from a first predetermined value to a second predetermined value, and maintaining the temperature for a second predetermined time; S32: controlling the temperature of the reaction zone to rise from the second predetermined value to the first predetermined value, and maintaining the temperature for a third predetermined time; S33: Repeat steps S31-S32 multiple times, and when the temperature of the reaction zone is controlled to rise from the second predetermined value to the first predetermined value for the last time, keep the temperature for a fourth predetermined time.

6. The method according to claim 5, characterized in that In step S31, the temperature of the reaction zone is controlled to drop from 1600° C. to 500° C., and the holding time is not less than 30 minutes; In step S32, the temperature of the reaction zone is controlled to rise from 500° C. to 1600° C., and the holding time is not less than 2 hours; In step S33, when the temperature of the reaction zone is controlled to rise from 500°C to 1600°C for the last time, the holding time is adjusted to 1 hour.

7. The method according to claim 1, characterized in that In step S40, the following steps are also included: S41: mixing the reaction product obtained in step S30 with a polyethylene glycol ethanol solution to obtain a mixture; S42: drying the mixture; S43: crushing the dried mixture under an argon atmosphere, and sieving to obtain the uranium nitride particles.

8. The method according to claim 7, characterized in that In step S42, the vacuum degree is less than 1×10 -2 The mixture is dried in a vacuum environment of 0.1 Pa for a time of not less than 1 h.

9. The method according to claim 1, characterized in that In step S50, the following steps are also included: S51: pressing the uranium nitride particles obtained in step S40 into a compact to obtain a green compact; S52: placing the compact in a sintering area, and introducing nitrogen into the sintering area so that a trace amount of nitrogen is contained in the sintering area; S53: sintering the compact in the sintering area; S54: evacuating the sintering area and keeping the sintered product in a vacuum for a predetermined time to obtain the uranium nitride pellets.

10. The method according to claim 9, characterized in that In step S52, the partial pressure of nitrogen is maintained between 10Pa and 50Pa.

11. The method according to claim 9, characterized in that In step S53, the sintering temperature is controlled between 1700-1900°C, and the sintering process lasts for 2-3 hours.

12. The method according to claim 9, characterized in that In step S54, the vacuum degree of the vacuum environment is maintained at 10 -2 Pa, the insulation temperature is controlled between 1000-1200℃, and the insulation process lasts for 1-2h.

13. A uranium nitride pellet, characterized in that: The uranium nitride pellets are prepared by the method for preparing uranium nitride pellets according to any one of claims 1 to 12.

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