Preparation method of fuel pellet and U3Si2 fuel pellet

Abstract

The invention discloses a preparation method of a fuel pellet and a U3Si2 fuel pellet. The method comprises the following steps: carrying out compression molding on U3Si2 powder containing a binder to obtain a U3Si2 green body; and after the U3Si2 green body is subjected to heat preservation at the target temperature for a target duration, the U3Si2 green body is sintered in a carbon-isolated environment, and the fuel pellet is obtained. According to the method disclosed by the invention, before the green body is sintered, heat preservation is performed on the green body at the temperature close to the melting point and the decomposition point of the binder to fully remove the binder in the pellet green body, so that the binder in the pellet is removed, and the carbon content in the U3Si2 green body is reduced. And sintering the U3Si2 green body in a carbon-isolated environment to further inhibit the reaction between the carbon in the environment and the green body. In this way, the carbon content in the U3Si2 pellet can be controlled to be 0.2 wt.% or below, then the problem of pellet cracking is solved, and the U3Si2 fuel pellet without cracks on the appearance is obtained.

Description

Technical Field

[0001] The present invention relates to the field of fuel pellet preparation technology, and more particularly to a method for preparing a fuel pellet and a method for preparing a fuel pellet. 3 Si 2 Fuel pellets. Background Art

[0002] U 3 Si 2 The fuel pellets have the characteristics of good thermal conductivity and high uranium density, and are one of the important candidates for the next generation of ATF fuel. 3 Si 2 During the preparation process of fuel pellets, macro cracks are easily generated on the surface, which has many adverse effects on the nuclear performance, safety and economy of nuclear reactors. Summary of the invention

[0003] In view of this, the present application provides a method for preparing a fuel pellet and a method for preparing a fuel pellet. 3 Si 2 The fuel pellets can be sintered in a carbon-isolated environment to effectively reduce the carbon content in the fuel pellets and prevent the generation of obvious cracks visible to the naked eye.

[0004] According to one aspect of the present application, there is provided a method for preparing a fuel pellet, comprising:

[0005] For U containing binder 3 Si 2 The powder is pressed into shape to obtain U 3 Si 2 Greenware;

[0006] The U 3 Si 2 After the green body is kept at the target temperature for the target time, the U 3 Si 2 The green body is sintered to obtain fuel pellets.

[0007] Optionally, the carbon content in the fuel pellet is less than or equal to 0.2wt.%;

[0008] The fuel pellets have no macro cracks on their surfaces, wherein the macro cracks have a width greater than 80 μm and a length greater than 200 μm.

[0009] Optionally, the target temperature is 200° C. to 700° C., and the target duration is 1 hour to 5 hours.

[0010] Optionally, the U 3 Si 2 The green body is kept at the target temperature for the target time, including:

[0011] According to the target temperature and the target duration, the U 3 Si 2 The green body is kept warm in sections;

[0012] Among them, the first stage target temperature is 250℃~400℃, the second stage target temperature is 500℃~650℃, the first stage target time or the second stage target time is 0.5h~4.5h, and the sum of the first stage target time and the second stage target time is less than or equal to 5h.

[0013] Optionally, the U 3 Si 2 The green body is sintered, including:

[0014] The sintering furnace constructed of non-carbon materials is used to 3 Si 2 The green body is sintered.

[0015] Optionally, the U 3 Si 2 The green body is sintered, including:

[0016] The U 3 Si 2 The green body is embedded in the embedding raw material for sintering, wherein the embedding raw material comprises at least one of the following: the U without a binder 3 Si 2 Powder, UN powder, W powder.

[0017] Optionally, the binder includes at least one of the following: polyvinyl alcohol, polyethylene glycol, polyvinyl butyral;

[0018] The binder is in the U 3 Si 2 The content in the powder is less than or equal to 1wt.%.

[0019] Optionally, the method for preparing the fuel pellets further comprises:

[0020] Using anhydrous ethanol as the medium 3 Si 2 The particles are ball milled to obtain the U 3 Si 2 Powder, wherein the U 3 Si 2 The particle size of the powder is less than 50 μm;

[0021] Prepare the binder solution according to the mass ratio;

[0022] Add the binder solution into the U 3 Si2 The powder is mixed and dried to obtain the U containing a binder. 3 Si 2 powder.

[0023] Optionally, the pair U 3 Si 2 The green body is sintered, including:

[0024] The U 3 Si 2 The green body is sintered, wherein the sintering temperature is 1200° C. to 1600° C. and the sintering time is 2 h to 4 h.

[0025] Optionally, the pressure of the press molding is 100 MPa to 350 MPa.

[0026] According to another aspect of the present application, there is provided a U 3 Si 2 The fuel pellets are prepared by using the above-mentioned method for preparing the fuel pellets.

[0027] By means of the above technical solution, the green body is kept warm at a temperature near the melting point and decomposition point of the binder before sintering to fully remove the binder in the green body of the core block, thereby removing the binder in the core block and reducing U 3 Si 2 The carbon content of the U(III) in the green body is then measured in a carbon-free environment. 3 Si 2 The green body is sintered to further inhibit the reaction of carbon in the environment with the green body. 3 Si 2 The carbon content in the pellet is controlled below 0.2wt.%, thereby solving the pellet cracking problem and obtaining a U 3 Si 2 Fuel pellets.

[0028] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0030] Figure 1 A schematic flow chart of a method for preparing a fuel pellet provided in an embodiment of the present application is shown;

[0031] Figure 2 The U provided in the embodiment of the present application is shown 3 Si 2 An image of the fuel pellets. DETAILED DESCRIPTION

[0032] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0033] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application.

[0034] Those skilled in the art will appreciate that, unless expressly stated, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, or there may be intermediate elements. In addition, the "connection" or "connection" used herein may include wireless connection or wireless fusion. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0035] Now, exemplary embodiments according to the present application will be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in a variety of different forms and should not be interpreted as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0036] In this embodiment, a method for preparing a fuel pellet is provided. Figure 1 As shown, the method includes:

[0037] Step 101, U containing a binder 3 Si 2 The powder is pressed into shape to obtain U 3 Si 2 Green body.

[0038] Wherein, the binder includes at least one of the following: polyvinyl alcohol (PVA), polyethylene glycol (PEG), and polyvinyl butyral (PVB).

[0039] It is worth mentioning that controlling the binder in U 3 Si 2 The content in the powder is less than or equal to 1wt.%, which can reduce the introduction of carbon elements due to the addition of binders on the basis of ensuring smooth molding of the green body, and is conducive to reducing the carbon content in the final fuel pellets.

[0040] It is understood that the U containing binder is subjected to the molding press with atmosphere protection. 3 Si 2 The powder is pressed and molded at a pressure of 100 MPa to 350 MPa to reduce oxidation of the core block.

[0041] In one embodiment, before step 101, the method for preparing the fuel pellets includes: using anhydrous ethanol as a medium to 3 Si 2 The particles were ball milled to obtain U 3 Si 2 powder; prepare a binder solution according to the mass ratio; add the binder solution to U 3 Si 2 The powder is mixed and dried to obtain U containing a binder. 3 Si 2 powder.

[0042] Among them, U 3 Si 2 The particle size of the powder is less than 50 μm.

[0043] In this embodiment, first weigh U according to the mass ratio. 3 Si 2 Particles and anhydrous ethanol were used to grind U 3 Si 2 The particles are ball-milled into fine U 3 Si 2 The binder is dissolved in the solvent according to the mass ratio to form a binder solution, and then the binder solution is added to the ball-milled U 3 Si 2 The powder is mixed and dried to make the binder and U 3 Si 2 The powders are better mixed together. So that the binder can be 3 Si 2 The bonding bridges are formed between the powders, which increases the contact area and friction between the powders, thereby improving the overall strength of the powders and promoting U 3 Si2 The sintering and densification of the green body improves the performance of the product and reduces the occurrence of cracks in the green body.

[0044] Step 102: 3 Si 2 After the green body is kept at the target temperature for the target time, the U 3 Si 2 The green body is sintered to obtain fuel pellets.

[0045] The target temperature is 200°C to 700°C, which can be reasonably set according to the melting point and decomposition point of the binder, such as 300°C, 450°C, 520°C, 650°C, etc. The target duration is 1h to 5h, which can be reasonably set according to the amount of binder added, such as 1.5h, 2h, 4h, etc. A carbon-isolating environment refers to reducing or eliminating carbon dioxide (CO 2 ) emissions and their impact on the environment.

[0046] In this embodiment, the green body is kept warm at a temperature near the melting point and decomposition point of the binder before sintering to fully remove the binder in the green body of the core block, thereby removing the binder in the core block and reducing U 3 Si 2 The carbon content of the U(III) in the green body is then measured in a carbon-free environment. 3 Si 2 The green body is sintered to further inhibit the reaction of carbon in the environment with the green body. 3 Si 2 The carbon content in the pellet is controlled below 0.2wt.%, thereby solving the pellet cracking problem and obtaining a U 3 Si 2 Fuel pellets.

[0047] It is worth mentioning that the carbon content of the fuel pellets prepared by the above method is less than or equal to 0.2 wt.%, and there are no macro cracks on the surface. The width of the macro cracks is greater than 80 μm and the length is greater than 200 μm.

[0048] In one embodiment, in step 102, U is subjected to a carbon-free environment. 3 Si 2 The green body can be sintered in the following ways:

[0049] Method 1: Use a non-carbon material sintering furnace to 3 Si 2 The green body is sintered.

[0050] It should be noted that the non-carbon material structure of the sintering furnace refers to the sintering furnace that can affect U 3 Si 2The structural parts of the green body are made of non-carbon materials. For example, the heating element of the sintering furnace is a non-carbon heating element, the insulation material in the sintering furnace is a non-carbon material, and the U 3 Si 2 The material of the green crucible is non-carbon material.

[0051] In this embodiment, a sintering furnace made of non-carbon material is used to heat U 3 Si 2 The green body can eliminate carbon and U 3 Si 2 The green body reaction ensures that the carbon content in the pellet does not increase, thereby reducing the risk of cracking.

[0052] Method 2: Use U 3 Si 2 The green body is embedded in the embedding raw material and sintered.

[0053] The embedding raw material should have a melting point higher than 1600°C and be easily reactive with carbon. 3 Si 2 Powder, UN (uranium nitride) fuel powder, W (tungsten) powder, the embedding material can also be other powders that react easily with carbon, or the above mixed powders.

[0054] In this embodiment, U 3 Si 2 The green body is completely embedded in the embedding raw material, which can isolate air or other substances during the sintering process to avoid U 3 Si 2 The green body is in contact with air or other substances. On the one hand, the coating of the embedding raw material can limit the U 3 Si 2 The fuel reacts with carbon-containing substances in the environment to reduce U 3 Si 2 The stress generated in the fuel pellets due to the above reaction can also reduce the various phases with different thermal expansion coefficients generated in the pellets due to the above reaction, which is beneficial to reduce U 3 Si 2 The risk of cracks in the fuel pellets during cooling is high. 3 Si 2 The green body can make it heated more evenly during the sintering process, which helps to avoid local overheating or overcooling, thereby promoting uniform sintering of the material and further improving the density and uniformity of the fuel pellets.

[0055] In one embodiment, in step 102, U 3 Si 2 The green body is kept at the target temperature for the target time, specifically including:3 Si 2 The green body is kept warm in sections;

[0056] Among them, the first stage target temperature is 250℃~400℃, the second stage target temperature is 500℃~650℃, the first stage target time or the second stage target time is 0.5h~4.5h, and the sum of the first stage target time and the second stage target time is less than or equal to 5h.

[0057] In this embodiment, the first heat preservation is performed at a lower temperature, and then the second heat preservation is performed at a higher temperature, or the first heat preservation is performed at a higher temperature, and then the second heat preservation is performed at a lower temperature. In this way, the different decomposition temperatures of the macromolecular structure and the small molecular structure of different binders can be fully considered, and the substances with different molecular structures can be volatilized in a targeted manner, which can not only save heating resources and improve the binder removal efficiency, but also the binder decomposition products generated by the first heating and heat preservation can be further reacted or volatilized through the second heating and heat preservation, effectively removing the binder in the core block, reducing the carbon content in the core block, and thus reducing the risk of cracking.

[0058] Furthermore, under vacuum or inert gas atmosphere, U 3 Si 2 The green body is sintered at a temperature of 1200°C to 1600°C and a sintering time of 2h to 4h.

[0059] It should be noted that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application. Specific embodiment 1:

[0061] Weigh U according to the mass ratio 3 Si 2 Fuel particles and anhydrous ethanol are used in a planetary ball mill to 3 Si 2 The fuel particles are ball-milled to obtain U 3 Si 2 Fuel powder.

[0062] Weigh polyethylene glycol (PEG) and anhydrous ethanol according to the mass ratio, and dissolve polyethylene glycol in anhydrous ethanol to obtain a 2wt.% polyethylene glycol solution. 3 Si 2 Powder) weighed U 3 Si 2 Powder and polyethylene glycol solution. 3 Si 2The powders were fully mixed and the anhydrous ethanol in the mixture was dried at 50°C to obtain U 3 Si 2 Fuel powder.

[0063] The U containing binder was pressed by a molding machine at 200 MPa for 30 seconds. 3 Si 2 The fuel powder is pressed into shape to obtain U 3 Si 2 The fuel pellets are green and have a relative density of about 53% TD.

[0064] Vacuum sintering furnace for U 3 Si 2 The fuel pellets are sintered to obtain U 3 Si 2 Fuel pellets. The vacuum sintering furnace uses tungsten as the heating element, tungsten / molybdenum / stainless steel as the insulation layer material, the sintering crucible is made of tungsten, the sintering temperature is 1500℃, and the sintering time is 2.5h.

[0065] After the oxide layer on the surface of the core block was processed by a centerless grinder, the U 3 Si 2 The carbon content in the fuel pellets is less than 0.16wt.%, and the pellet density is 11.83g / cm 3 , the relative density is 96.7% TD, and there are no cracks visible to the naked eye on the surface of the core block. Specific embodiment 2:

[0067] Weigh U according to the mass ratio 3 Si 2 Fuel particles and anhydrous ethanol are used in a planetary ball mill to 3 Si 2 The fuel particles are ball-milled to obtain U 3 Si 2 Fuel powder.

[0068] Weigh polyethylene glycol (PEG) and anhydrous ethanol according to the mass ratio, and dissolve polyethylene glycol in anhydrous ethanol to obtain a 2wt.% polyethylene glycol solution. 3 Si 2 Powder) weighed U 3 Si 2 Powder and polyethylene glycol solution. 3 Si 2 The powders were fully mixed and the anhydrous ethanol in the mixture was dried at 50°C to obtain U 3 Si 2Fuel powder.

[0069] The U containing binder 3 Si 2 The fuel powder is pressed into shape to obtain U 3 Si 2 The fuel pellets are green, and the green relative density is about 52% TD.

[0070] At 200℃, U 3 Si 2 The green fuel pellets were kept at 500°C for 1.5 hours and then kept at 500°C for 0.5 hours.

[0071] Weigh a certain mass of U 3 Si 2 fuel powder and spread it evenly in the crucible. 3 Si 2 The green fuel pellets are placed inside the crucible and then 3 Si 2 Fuel powder will U 3 Si 2 The embedded fuel pellets are then sintered in a vacuum furnace. 3 Si 2 The fuel core block green body is sintered, wherein the vacuum sintering furnace uses graphite as the heating element, carbon felt as the insulation layer material, the sintering crucible is made of high-purity graphite, the sintering temperature is 1400°C, and the sintering time is 3 hours.

[0072] After the oxide layer on the surface of the core block is processed by a centerless grinder, it is tested 3 Si 2 The carbon content in the fuel pellets is less than 0.14wt.%, and the pellet density is 10.97g / cm 3 , the relative density is 89.6% TD, and there are no cracks visible to the naked eye on the surface of the core block. Specific embodiment 3:

[0074] Weigh U according to the mass ratio 3 Si 2 Fuel particles and anhydrous ethanol are used in a planetary ball mill to 3 Si 2 The fuel particles are ball-milled to obtain U 3 Si 2 Fuel powder.

[0075] Weigh polyethylene glycol (PEG) and anhydrous ethanol according to the mass ratio, and dissolve polyethylene glycol in anhydrous ethanol to obtain a 2wt.% polyethylene glycol solution. 3 Si 2 Powder) weighed U3 Si 2 Powder and polyethylene glycol solution. 3 Si 2 The powders were fully mixed and the anhydrous ethanol in the mixture was dried at 50°C to obtain U 3 Si 2 Fuel powder.

[0076] The U containing binder was pressed by a molding machine at 200 MPa for 30 seconds. 3 Si 2 The fuel powder is pressed into shape to obtain U 3 Si 2 The fuel pellets are green and have a relative density of about 53% TD.

[0077] For U 3 Si 2 In order to fully remove the binder in the green fuel pellets, the green fuel pellets were sintered at 350°C for 1 hour and then at 600°C for 1 hour. 3 Si 2 The fuel pellets are sintered to obtain U 3 Si 2 Fuel pellets. The vacuum sintering furnace uses tungsten as the heating element, tungsten / molybdenum / stainless steel as the insulation layer material, the sintering crucible is made of tungsten, the sintering temperature is 1600℃, and the sintering time is 2h.

[0078] After the oxide layer on the surface of the core block is processed by a centerless grinder, the following Figure 2 U shown 3 Si 2 Fuel pellets. 3 Si 2 The carbon content in the fuel pellets is less than 0.1wt.%, and the pellet density is 11.53g / cm 3 , the relative density is 94.2%TD, and there are no cracks visible to the naked eye on the surface of the core block.

[0079] Those skilled in the art will appreciate that the accompanying drawings are only schematic diagrams of a preferred implementation scenario, and the modules or processes in the accompanying drawings are not necessarily necessary for implementing the present application. Those skilled in the art will appreciate that the modules in the devices in the implementation scenario can be distributed in the devices of the implementation scenario according to the description of the implementation scenario, or can be changed accordingly and located in one or more devices different from the present implementation scenario. The modules of the above-mentioned implementation scenario can be combined into one module, or can be further split into multiple submodules.

[0080] The above serial numbers of this application are only for description and do not represent the advantages and disadvantages of the implementation scenarios. The above disclosure is only a few specific implementation scenarios of this application, but this application is not limited to them, and any changes that can be thought of by technicians in this field should fall within the scope of protection of this application.

Claims

1. A method for preparing a fuel pellet, characterized in that: The method comprises: The U3Si2 powder containing the binder is pressed and molded to obtain a U3Si2 green body; After the U3Si2 green compact is kept at a target temperature for a target time, the U3Si2 green compact is sintered in a carbon-free environment to obtain a fuel pellet.

2. The method for preparing a fuel pellet according to claim 1, characterized in that: The carbon content of the fuel pellets is less than or equal to 0.2 wt.%; The fuel pellets have no macro cracks on their surfaces, wherein the macro cracks have a width greater than 80 μm and a length greater than 200 μm.

3. The method for preparing a fuel pellet according to claim 1, characterized in that: The target temperature is 200° C. to 700° C., and the target duration is 1 hour to 5 hours.

4. The method for preparing a fuel pellet according to claim 1, characterized in that: The step of keeping the U3Si2 green compact at a target temperature for a target period of time comprises: Insulating the U3Si2 green compact in sections according to the target temperature and the target duration; Among them, the first stage target temperature is 250℃~400℃, the second stage target temperature is 500℃~650℃, the first stage target time or the second stage target time is 0.5h~4.5h, and the sum of the first stage target time and the second stage target time is less than or equal to 5h.

5. The method for preparing a fuel pellet according to claim 1, characterized in that: The step of sintering the U3Si2 green compact in a carbon-isolated environment comprises: Using a sintering furnace made of non-carbon material to sinter the U3Si2 green compact; or, The U3Si2 green body is embedded in an embedding raw material for sintering, wherein the embedding raw material comprises at least one of the following: the U3Si2 powder without a binder, UN powder, and W powder.

6. The method for preparing a fuel pellet according to claim 1, characterized in that: The binder comprises at least one of the following: polyvinyl alcohol, polyethylene glycol, polyvinyl butyral; The content of the binder in the U3Si2 powder is less than or equal to 1 wt.%.

7. A method for preparing a fuel pellet according to any one of claims 1 to 6, characterized in that: The method further comprises: Using anhydrous ethanol as a medium to ball-mill U3Si2 particles to obtain the U3Si2 powder, wherein the particle size of the U3Si2 powder is less than 50 μm; Prepare the binder solution according to the mass ratio; The binder solution is added into the U3Si2 powder, mixed and dried to obtain the U3Si2 powder containing the binder.

8. The method for preparing a fuel pellet according to any one of claims 1 to 6, characterized in that: The step of sintering the U3Si2 green compact comprises: The U3Si2 green body is sintered in a vacuum or inert gas atmosphere, wherein the sintering temperature is 1200° C. to 1600° C. and the sintering time is 2 h to 4 h.

9. The method for preparing a fuel pellet according to any one of claims 1 to 6, characterized in that: The pressure of the press molding is 100 MPa to 350 MPa.

10. A U3Si2 fuel pellet, characterized in that: The fuel pellets are prepared by the method for preparing fuel pellets according to any one of claims 1 to 9.

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