Method for producing a uranium nitride pellet and uranium nitride pellet

Abstract

Embodiments of the present application relate to the technical field of binary compounds of nitrogen and metal, and particularly relate to a preparation method of a uranium nitride pellet and the uranium nitride pellet. The present application provides a preparation method of a uranium nitride pellet, comprising: arranging uranium nitride powder in a reaction region, inputting a mixed gas containing nitrogen element into the reaction region; heating the reaction region to a first predetermined value within a first predetermined time, so that the uranium nitride powder reacts with the mixed gas to obtain a reaction product; controlling the temperature of the reaction region, so that the uranium nitride powder fully reacts with the mixed gas, and the nitrogen uranium molar ratio of the reaction product reaches a predetermined value; granulating and sintering the reaction product to obtain the uranium nitride pellet. The present application also provides a uranium nitride pellet. By using the method of the present application, the nitrogen uranium molar ratio of the uranium nitride pellet can be accurately controlled, the crystal structure, thermal conductivity and radiation stability of the uranium nitride pellet are optimized, and the performance requirements of the uranium nitride pellet serving in different nuclear reactors are ensured.

Description

Technical Field

[0001] The embodiments of this application relate to the field of binary compounds of nitrogen and metal, specifically to a method for preparing uranium nitride pellets and uranium nitride pellets. Background Technology

[0002] The statements herein are provided merely as background information in connection with this application and do not necessarily constitute prior art.

[0003] Uranium nitride fuel is 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 metals. The physical and chemical properties of uranium nitride fuel affect its performance in nuclear reactors, thereby affecting the service performance, safety, and stability of nuclear reactors.

[0004] However, current uranium nitride fuel production and processing technologies still have many technical defects, resulting in performance differences in the prepared uranium nitride fuel, which in turn affects its service performance in nuclear reactors. Summary of the Invention

[0005] A brief overview of this application is provided below to offer a basic understanding of certain aspects thereof. It should be understood that this overview is not an exhaustive summary of the application. It is not intended to identify key or essential parts of the application, nor is it intended to limit its scope. Its purpose is merely to present certain concepts in a simplified form as a prelude to the more detailed description that follows.

[0006] In a first aspect, embodiments of this application provide a method for preparing uranium nitride pellets, comprising the following steps: S10: placing raw uranium nitride powder in a reaction zone and introducing a mixed gas including nitrogen into the reaction zone; S20: heating the reaction zone to a first predetermined value within a first predetermined time, causing the raw uranium nitride powder to react with the mixed gas to obtain a reaction product; S30: controlling the temperature of the reaction zone to ensure that the raw uranium nitride powder and the mixed gas react fully, and to ensure that the nitrogen-uranium molar ratio of the reaction product reaches a predetermined value; S40: granulating the reaction product obtained in step S30 to obtain uranium nitride particles; S50: sintering the uranium nitride particles obtained in step S40 to obtain uranium nitride pellets.

[0007] Secondly, embodiments of this application also provide a uranium nitride pellet, which is prepared using the uranium nitride pellet preparation method of any embodiment of the first aspect of this application.

[0008] The method for preparing uranium nitride pellets in the embodiments of this application involves introducing a mixed gas containing nitrogen into a reaction zone, causing the raw material uranium nitride powder to react with the mixed gas at a first predetermined temperature. By controlling the temperature of the reaction zone, the molar ratio of nitrogen to uranium in the reaction product is precisely controlled. Then, by granulating and sintering the obtained reaction product, the molar ratio of nitrogen to uranium is stabilized at a predetermined value. Thus, the molar ratio of nitrogen to uranium in the obtained uranium nitride pellets is precisely controlled, the crystal structure, thermal conductivity, and radiation stability of the uranium nitride pellets are optimized, and their performance requirements for service in different nuclear reactors are ensured, significantly improving the safety and stability of nuclear reactor operation. Attached Figure Description

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

[0010] Figure 1 This is a flowchart of a method for preparing uranium nitride pellets according to an embodiment of this application.

[0011] It should be noted that the accompanying drawings are not necessarily drawn to scale, but are shown only in a schematic manner without affecting the reader's understanding. Detailed Implementation

[0012] Exemplary embodiments of this application will be described below with reference to the accompanying drawings. For clarity and brevity, 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 development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0013] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the equipment structure and / or processing steps closely related to the solution according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0014] The nitrogen-uranium molar ratio in uranium nitride fuel directly affects the fuel's microstructure, physical, and chemical properties. The inventors of this application have discovered that in current traditional uranium nitride fuel production processes, the nitrogen-uranium molar ratio in uranium nitride pellets is still controlled within a range, i.e., the value of the nitrogen-uranium molar ratio is controlled within a certain range. This makes it difficult for the prepared uranium nitride pellets to meet the fuel performance requirements of different nuclear reactors, thereby affecting the safety and stability of nuclear reactor operation.

[0015] Based on this, embodiments of this application provide a method for preparing uranium nitride pellets, such as... Figure 1 As shown, Figure 1 The flowchart illustrates a method for preparing uranium nitride pellets according to an embodiment of this application, the method comprising the following steps S10 to S50:

[0016] S10: Place the raw material uranium nitride powder in the reaction zone and introduce a mixed gas containing nitrogen into the reaction zone.

[0017] S20: The reaction zone is heated 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 the reaction product.

[0018] S30: Temperature control is applied to the reaction zone to ensure that the raw material uranium nitride powder reacts fully with the mixed gas and that the nitrogen-uranium molar ratio of the product obtained from the reaction reaches a predetermined value.

[0019] S40: Granulate 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 method for preparing uranium nitride pellets provided in the embodiments of this application involves introducing a mixed gas containing nitrogen into a reaction zone, causing the raw material uranium nitride powder to react with the mixed gas at a first predetermined temperature. By controlling the temperature of the reaction zone, the molar ratio of nitrogen to uranium in the reaction product is precisely controlled. Then, by granulating and sintering the obtained reaction product, the molar ratio of nitrogen to uranium is stabilized at the predetermined value. Thus, the molar ratio of nitrogen to uranium in the obtained uranium nitride pellets is precisely controlled, 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, a mixed gas of nitrogen, hydrogen, and ammonia is used to react with uranium nitride powder to control the nitrogen partial pressure in the reaction zone, thereby facilitating the control of the nitrogen-uranium molar ratio of the reaction products.

[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 with a volume ratio of 85%-95% nitrogen, 2.5%-7.5% hydrogen, and 2.5%-7.5% ammonia is introduced into the reaction zone to enhance the reactivity of nitrogen atoms in the mixed gas, accelerate the nitridation reaction process of uranium nitride powder, and facilitate the control of the nitrogen-uranium molar ratio of the reaction products.

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

[0026] In some embodiments, in step S20, the reaction zone is heated to 1600°C within 8-12 minutes to improve the activity of the nitriding reaction, so that the mixed gas can diffuse rapidly in the reaction zone and be rapidly absorbed by the raw material 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 at 10 min 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: Control the temperature of the reaction zone to drop from a first predetermined value to a second predetermined value, and maintain the temperature for a second predetermined time.

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

[0031] S33: Repeat steps S31-S32 multiple times, and when the temperature of the control reaction zone rises from the second predetermined value to the first predetermined value in the last control reaction, keep it at that temperature for a fourth predetermined time.

[0032] In this embodiment, the temperature of the reaction zone is controlled to cycle between a first predetermined value and a second predetermined value multiple times, and the temperature is maintained for a fourth predetermined time when the temperature of the reaction zone rises from the second predetermined value to the first predetermined value for the last time. This reduces the carbon and oxygen impurity content in the reaction products. Furthermore, the temperature is controlled in multiple cycles to change the structure of the reaction products, which is conducive to the full progress of the nitriding reaction and ensures that the raw material uranium nitride powder reacts completely with the mixed gas. Thus, the nitrogen-uranium molar ratio of the products obtained from the reaction is controlled in a coordinated manner.

[0033] In some embodiments, in step S31, the temperature of the reaction zone is controlled to decrease from 1600°C to 500°C, and the holding time is not less than 30 min; in step S32, the temperature of the reaction zone is controlled to increase from 500°C to 1600°C, and the holding time is not less than 2 h; in step S33, when the temperature of the reaction zone is controlled to increase from 500°C to 1600°C for the last time, the holding time is adjusted to 1 h.

[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℃ to 500℃, and the holding time is not less than 30 minutes, so that the nitride phase structure changes from UN to U2N3, thereby changing the volume ratio of the reaction products and forming micropores, thus 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℃ to 1600℃, and the holding time is not less than 2 hours, so that the nitride phase structure changes 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: Mix the reaction product obtained in step S30 with a polyethylene glycol ethanol solution to obtain a mixture.

[0037] S42: Dry 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 obtained in step S30 with a predetermined nitrogen-uranium molar ratio is mixed with a polyethylene glycol ethanol solution, and the mixture is dried, crushed, and sieved to obtain uranium nitride particles. This process refines the mixture, increases the contact area between the solid phase and the reactant gas in the subsequent solid-phase reaction, and accelerates the nitriding reaction. Furthermore, it facilitates the achievement of 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 the predetermined value.

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

[0041] In some embodiments, in step S42, when the vacuum degree is less than 1×10 -2 The mixture is dried in a vacuum environment of Pa for at least 1 hour. This is because the vacuum level is less than 1 × 10⁻⁶ Pa. -2Only under Pa environmental conditions can nitrides be prevented from being oxidized and corroded by oxygen and water. Therefore, in this embodiment, the mixture is dried under this environment to avoid the uranium nitride powder 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: Press the uranium nitride particles obtained in step S40 into a compact.

[0044] S52: Place the compact in the sintering zone and introduce nitrogen into the sintering zone to make the sintering zone contain trace amounts of nitrogen.

[0045] S53: The compact is sintered in the sintering zone.

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

[0047] In this embodiment, the uranium nitride particles obtained in step S40 are pressed into a compact, and the compact is sintered in a micro-nitrogen atmosphere. After sintering, the sintered product is kept at a predetermined temperature in a vacuum environment for a certain time to prevent the ambient temperature from dropping during the holding process, which would cause the uranium nitride to react with nitrogen to form the U2N3 phase, thereby affecting the control of the nitrogen-uranium molar ratio of the uranium nitride pellet.

[0048] In some embodiments, in step S51, the uranium nitride particles obtained in step S40 are loaded into a mold and pressed under a pressure between 350-500 MPa to obtain a compact with a green density of 45-55% TD%.

[0049] In some embodiments, in step S52, the partial pressure of nitrogen is maintained between 10 Pa and 50 Pa to keep the sintering region in a micro-nitrogen atmosphere to prevent the tendency of UN phase decomposition during the sintering process at high ambient temperatures of 1700-1900°C, thereby affecting the molar ratio control of 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 of the sintered product and grain growth, thereby obtaining a high-density uranium nitride pellet.

[0051] In some embodiments, in step S54, the vacuum level of the vacuum environment is maintained at 10. -2Pa, the holding temperature is controlled between 1000-1200℃, and the holding process lasts for 1-2 hours. By storing the sintered product under vacuum at a temperature below 1200℃, it is possible to further prevent uranium nitride from reacting with nitrogen at low temperature to form the U2N3 phase, which would affect the control of the nitrogen-uranium molar ratio. Setting the holding process to last for 1-2 hours is beneficial to further stabilize the nitrogen-uranium molar ratio of the sintered uranium nitride pellets.

[0052] The embodiments of this application also provide a uranium nitride pellet, which is prepared using the uranium nitride pellet preparation method of any embodiment of the first aspect of this application.

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

[0054] Uranium nitride powder was placed in the reaction zone, and a mixed gas of 90% nitrogen, 5% hydrogen, and 5% ammonia was introduced into the reaction zone. The temperature of the reaction zone was raised to 1600°C within 10 minutes to allow the uranium nitride powder to react with the mixed gas and obtain the reaction product. The temperature of the reaction zone was then controlled to decrease from 1600°C to 500°C and held for at least 30 minutes. The temperature was then controlled to increase from 500°C to 1600°C and held for at least 2 hours. This cooling and heating cycle was repeated three times. During the third temperature increase from 500°C to 1600°C, the holding time was adjusted to 1 hour to ensure sufficient reaction between the uranium nitride powder and the mixed gas, and to achieve a predetermined nitrogen-uranium molar ratio in the obtained product. The obtained reaction product was mixed with a 0.5 wt% polyethylene glycol ethanol solution using a spray method to obtain a mixture. The mixture was then subjected to a vacuum of less than 1 × 10⁻⁶. -2 In a vacuum environment of Pa, the mixture is dried for 1 hour. The dried mixture is then crushed under an oxygen-free argon atmosphere and passed through an 80-100 mesh sieve to obtain uranium nitride particles. These particles are then placed into a mold and pressed under a pressure of 350-500 MPa to obtain a compact with a green density of 45-55% TD%. The compact is placed in a sintering zone, and nitrogen is introduced into the zone to maintain a nitrogen partial pressure between 10 Pa and 50 Pa. The compact is sintered at 1700-1900 °C for 2-3 hours. The sintering zone is then evacuated to a vacuum of 10 Pa. -2 Uranium nitride pellets were obtained by holding the pellet at 1000-1200℃ for 1-2 hours in an environment of Pa.

[0055] Regarding the embodiments of this application, it should also be noted that, without conflict, the embodiments of this application and the features in the embodiments can be combined with each other to obtain new embodiments.

[0056] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. The scope of protection of this application shall be determined by the scope of the claims.

Claims

1. A method for preparing uranium nitride pellets, characterized in that, It includes the following steps: S10: Place the raw material uranium nitride powder in the reaction zone and introduce a mixed gas including nitrogen into the reaction zone; S20: The reaction zone is heated 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 the reaction product; S30: The temperature of the reaction zone is controlled to ensure that the raw material uranium nitride powder reacts fully with the mixed gas, and the nitrogen-uranium molar ratio of the reaction product reaches a predetermined value. S40: Granulate 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 core; Step S30 also includes the following steps: S31: Control the temperature of the reaction zone to drop from a first predetermined value to a second predetermined value, and maintain the temperature for a second predetermined time; S32: Control the temperature of the reaction zone to rise from a second predetermined value to a first predetermined value, and maintain the temperature for a third predetermined time; S33: Repeat steps S31-S32 multiple times, and when the temperature of the reaction zone is raised from the second predetermined value to the first predetermined value for the last time, keep it warm for a fourth predetermined time. 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 raised from 500°C to 1600°C for the last time, the holding time is adjusted to 1 hour. In step S10, the mixed gas includes nitrogen, hydrogen, and ammonia; 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%.

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

3. The method according to claim 1, characterized in that, Step S40 also includes the following steps: S41: Mix the reaction product obtained in step S30 with a polyethylene glycol ethanol solution to obtain a mixture; S42: The mixture is dried; S43: The dried mixture is crushed under an argon atmosphere and sieved to obtain the uranium nitride particles.

4. The method according to claim 3, characterized in that, In step S42, the vacuum level is less than 1×10⁻⁶. -2 The mixture is dried in a vacuum environment of Pa for a time of not less than 1 hour.

5. The method according to claim 1, characterized in that, The S50 step also includes the following steps: S51: Press the uranium nitride particles obtained in step S40 into a compact; S52: The pressed blank is placed in the sintering zone, and nitrogen gas is introduced into the sintering zone so that the sintering zone contains a trace amount of nitrogen gas; S53: Sinter the pressed blank in the sintering zone; S54: Evacuate the sintering region and keep the sintering product in the vacuum for a predetermined time to obtain the uranium nitride pellet.

6. The method according to claim 5, characterized in that, In step S52, the partial pressure of nitrogen is maintained between 10 Pa and 50 Pa.

7. The method according to claim 5, characterized in that, In step S53, the sintering temperature is controlled between 1700-1900℃, and the sintering process lasts for 2-3 hours.

8. The method according to claim 5, characterized in that, In step S54, the vacuum level of the vacuum environment is maintained at 10. -2 Pa, the insulation temperature is controlled between 1000-1200℃, and the insulation process lasts for 1-2 hours.

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