GB2581903A

GB2581903A - Uranium carbide pellet, preparation method thereof, and fuel rod

Info

Publication number: GB2581903A
Application number: GB2007032.2A
Authority: GB
Inventors: Xue Jiaxiang; Zhang Xiansheng; Liu Tong; Li Rui; Yan Yan; Li Sigong; Huang Huawei; gong Xing; Ren Qisen; Yan Jun; Lu Zhiwei
Original assignee: China General Nuclear Power Corp; China Nuclear Power Technology Research Institute Co Ltd; CGN Power Co Ltd
Current assignee: China General Nuclear Power Corp; China Nuclear Power Technology Research Institute Co Ltd; CGN Power Co Ltd
Priority date: 2017-08-21
Filing date: 2018-08-20
Publication date: 2020-09-02
Anticipated expiration: 2038-08-20
Also published as: CN107500767A; WO2019037688A1; CN107500767B; RO134863A2; GB2581903B; GB202007032D0

Abstract

A uranium carbide pellet, a preparation method therefor, and a fuel rod. The preparation method for the uranium carbide pellet comprises the following steps: S1, weighing a uranium nitride powder and a carbon source according to a molar ratio of 1:0.8-1.5 and adding them to a solvent, mixing the mixture uniformly to form a slurry; S2, drying the slurry to obtain a mixed powder; S3, pressing the mixed powder into green bodies with a density of 50% or more; and S4, carrying out high-temperature pressureless sintering, to give uranium carbide pellets with a density of ≥95%.

Description

Uranium Carbide Pellet, Preparation Method therefor, and Fuel Rod

Technical Field

[0001] The invention relates to the technical field of nuclear reactors, in particular to a uranium carbide pellet, a preparation method therefor and a fuel rod.

Background Art

[0002] The existing commercial PWR nuclear fuel is mainly uranium dioxide (UO2) pellets. However the UO2 pellet has low thermal conductivity and high central temperature, a large amount of decay heat is still stored in the pellets even if the reactor is shut down safely when an accident occures, waste heat is difficult to conduct out under a condition of loss of coolant, thus the cladding temperature of the fuel rod is rapidly increased to a dangerous level. The existing zirconium alloy material has an obvious zirconium-water reaction above 650°C due to the chemical property thereof. The reaction is an exothermic reaction, releasing a large amount of hydrogen, and seriously deteriorating the safety of a fuel assembly, which can cause catastrophic consequences such as reactor core melting, severe hydrogen explosion or the like.

[0003] If uranium carbide (UC) pellets are used, the thermal conductivity thereof is higher and the density of uranium is improved, which has obvious advantages in terms of economy and safety.

[0004] A conventional preparation of the uranium carbide pellet mainly includes two steps. Step one, uranium carbide powder is synthesized, and generally the uranium carbide powder is synthesized by carbothermic reduction of uranium dioxide at a high temperature; step two, the pellet is densified and sintered, and generally a pressureless sintering added with a sintering aid or a hot pressing sintering assisted by an external field is adopted.

[0005] The conventional preparation of the uranium carbide pellet has the following problems: [0006] 1, Oxygen atoms are easily dissolved in the uranium carbide powder, and the dissolved oxygen atoms can stabilize UC2 and decompose U2C3. The concentration of solid solution oxygen in the uranium carbide can reach 12.5 at,' which can reduce the thermal conductivity of uranium carbide. The uranium carbide is readily oxidized to UO2 or other oxide of uranium when the temperatures exceeds 200°C or the oxygen partial pressure exceeds 20 kPa. Therefore, the preparation and mixing of the uranium carbide need to be carried out in an argon-filled environment, and a high purity of argon is also required.

[0007] 2, Although adding the sintering aid to sinter the uranium carbide pellet is favorable for densification, the melting point of the pellet will be obviously reduced and the safety will be reduced.

[0008] 3, The densification of the uranium carbide pellet can be easily realized by adopting the hot pressing sintering assisted by an external field. However, only one pellet can be sintered at a time in each furnace by the method, with extremely low efficiency, large energy consumption, and high equipment requirement. Thus the method is not suitable for industrial mass production.

Summary of the Invention

Technical Problem [0009] A technical problem to be solved in the invention is to provide a preparation method of a uranium carbide pellet wherein a reaction synthesis and a sintering densification are completed in one step and the products can be industrially produced in batch, and a prepared uranium carbide pellet and a fuel rod with the uranium carbide pellet.

Solutions to the Problem Technical Solutions [0010] A technical solution adopted by the invention to solve the technical problem is to provide a preparation method for a uranium carbide pellet, wherein the preparation method includes the following steps: [0011] S1, weighing uranium nitride powder and carbon source according to a molar ratio of 1:0.8-1.5, adding the uranium nitride powder and the carbon source into a solvent, and mixing uniformly to form a slurry; [0012] S2, drying the slurry to obtain mixed powder; [0013] S3, pressing the mixed powder into a green body with a density of 50% or more; [0014] S4, carrying out a high-temperature pressureless sintering to obtain the uranium carbide pellet with a density > 95%.

[0015] In the preparation method of the present invention, in the step Si, the uranium nitride powder has a purity of more than 95% and a particle size of 0.1-50 gm; [0016] the carbon source is carbon black and/or graphite, having a purity of more than 95% and a particle size of 0.1-50 gm.

[0017] In the preparation method of the present invention, in step SI, the solvent is ethanol or acetone.

[0018] In the preparation method of the invention, the step S3 includes the following steps: [0019] S3.1, pre-pressing and molding the mixed powder under a pressure of 5-30 Mpa; [0020] S3.2, vacuum sealing a pre-pressed and molded green body, carrying out a high-pressure pressing on a sealed green body under a pressure of 150-300 Mpa, and obtaining a green body with a density of 50% or more after pressure maintaining.

[0021] In the preparation method of the invention, in the step S3.1, the mixed powder is put into a pellet steel mold for pre-pressing and molding; and [0022] in the step S3.2, the pre-pressed and molded green body is vacuum sealed with an oilpaper, and the sealed green body is subjected to the high-pressure pressing using a cold i so stab c press.

[0023] In the preparation method of the invention, the step S4 includes the following steps: [0024] S4.1, putting the green body obtained in the step S3 into a high-temperature pressureless furnace, heating to 1300°C-1600°C at a rate of 5-30°C/min under a vacuum environment, and maintaining the temperature for 0.5-4h; and [0025] S4.2, heating to 1700°C-2000°C at a rate of 5-30°C/min under an inert atmosphere, and maintaining the temperature for 1-14 hours to obtain the uranium carbide pellet.

[0026] In the preparation method of the present invention, in step S4.2, an argon gas is introduced into the high-temperature pressureless furnace and is maintained at one atmospheric pressure to form the inert atmosphere.

[0027] According to the preparation method, the atomic ratio of uranium, carbon and nitrogen in the obtained uranium carbide pellet is 1: (0.8-1.5):(0-0.2).

[0028] The invention further provides a uranium carbide pellet prepared by the preparation method of any one of the above.

[0029] The invention further provides a fuel rod including the uranium carbide pellet above.

Beneficial Effects of the Invention Beneficial Effects [0030] The invention has the following beneficial effects: by using the uranium nitride and the carbon source as raw materials, and the two processes of carbothermic reduction reaction and densification sintering are achieved under the high-temperature pressureless sintering, so that a hot-pressing sintering process with low production efficiency is not required, and a sintering aid is not required to be introduced, thus avoiding the problem of reducing the melting point of a pellet; batch sintering can be achieved, the energy consumption is low, and the method is suitable for industrial production of fuel pellets.

Detailed Description of the Present Invention Embodiments [0031] A preparation method of uranium carbide pellets includes the following steps: [0032] S1, weighing uranium nitride powder and carbon source according to a molar ratio of 1:0.8-1.5, adding them into a solvent, and mixing the mixture uniformly to form a slurry.

[0033] Wherein, the purity of the uranium nitride (UN) powder is more than 95%, and the particle size of the UN powder is 0.1-50 pm. The carbon source (C) is carbon black and/or graphite, the purity of the carbon source is more than 95% and the particle size of the carbon source is 0.1-50 pm.

[0034] The solvent may be ethanol or acetone. The uranium nitride powder and the carbon source are added to the solvent, so that the uranium nitride powder and the carbon source are fully mixed and uniformly distributed.

[0035] S2, drying the slurry to obtain mixed powder [0036] The obtained slurry can be dried by rotary evaporation to obtain the dried mixed powder. The evaporation drying time can be regulated and controlled according to actual conditions.

[0037] S3, pressing the mixed powder into a green body with a density of 50% or more.

[0038] The step S3 can further include the following steps: [0039] S3.1, pre-pressing and molding the mixed powder under a pressure of 5-30Mpa.

[0040] S3.2, vacuum sealing the pre-pressed and molded peen body, carrying out a high-pressure pressing on the sealed green body under a pressure of 150-300 Mpa, and obtaining the green body with a density of 50% or more after pressure maintaining.

[0041] The pressure maintaining time may depend on circumstances, such as 5 minutes, with a primary purpose of stabilizing the shape of the pressed green body.

[0042] Specifically, in the step S3.1, the mixed powder is placed in a pellet steel mold, and a pressure of 10 MPa can be applied to perform the pre-pressing and molding. In the step S3.2, the pre-pressed and molded green body is vacuum sealed with an oilpaper, and the pre-pressed and molded green body is subjected to a high-pressure pressing such as 200 Mpa using a cold isostatic press.

[0043] S4, carrying out a high-temperature pressureless sintering to obtain the uranium carbide pellet with a density of >95%.

[0044] The step S4 can further include the following steps: [0045] S4.1, putting the green body obtained in the step S3 into a high-temperature pressureless furnace, heating it to 1300 °C-1600°C at a rate of 5-30°C/min under a vacuum environment, and maintaining the temperature for 0.5-4h, wherein the vacuum is maintained throughout the whole period.

[0046] The carbothermic reduction reaction of the green body is mainly realized in the step, and the reaction is fully carried out and completed by temperature maintaining so as to form uranium carbide.

[0047] S4.2, heating to 1700°C-2000°C at a rate of 5-30°C/min under an inert atmosphere, and maintaining the temperature for 1-14 hours to obtain the uranium carbide pellet.

[0048] After the temperature maintaining is finished, the uranium carbide pellet can be taken out after cooling to a room temperature.

[0049] This step primarily achieves densification of the green body to form a pellet having a predetermined density.

[0050] Alternatively, in step S4.2, an argon gas may be introduced into the high-temperature pressureless furnace, and be maintained at one atmospheric pressure to form the inert atmosphere.

[0051] In the preparation method in the present invention, the pressureless sintering is achieved through an in-situ reaction of the uranium nitride and the carbon source, and the densification is achieved through solid solution and carbon nitrogen vacancy defect migration mass transfer.

[0052] In the uranium carbide pellet obtained by the invention, the atomic ratio of uranium, carbon and nitrogen is 1:(0.8-1.5):(0-0.2), and the ratio can be adjusted. The adjusting modes of the uranium carbon atom ratio and the solid solution nitrogen include changing a particle size and a constituent distribution ratio of the raw material, changing a reaction temperature and a reaction holding time, changing a sintering temperature and a sintering temperature-maintaining time, changing a sintering atmosphere, etc. [0053] The uranium carbide pellet in the present invention is prepared by adopting the preparation method above.

[0054] The fuel rod in the present invention includes the uranium carbide pellet above.

[0055] The invention is further illustrated by the following specific embodiments.

[0056] Embodiment 1 [0057] Prepare the uranium carbide pellet with a density of 98%, weighing according to a molar ratio of UN:C of 1:1.2, with 249 g of the UN powder and 14.4 g of the carbon black.

[0058] Adopt the ethanol as the solvent, mix the mixture through a roll-type mixing using a Si3N4 ball for 24 hours at a speed of 120 revolutions per minute, and dry the obtained slurry by rotary evaporation to obtain a uniformly mixed mixed powder. Put the mixed powder into a pellet steel mold, pre-press the mixed powder under a pressure of 10 MPa, then vacuum seal the pre-formed green body with an oilpaper, then use a cold isostatic press to apply an isobaric load of 200 MPa to the green body vacuum sealed with the oilpaper, and maintain the pressure at 200 MPa for 5 minutes, enabling an initial density of the pellet green body to reach 50% or more.

[0059] Take out the green body and put it into a high-temperature pressureless furnace for reaction sintering. With the pressureless sintering, in the first reaction stage, the heating rate is 10°C/min, the temperature is raised to 1400°C and maintained for 1 hour. In this stage, the vacuum environment must be maintained. After the temperature maintaining is finished, stop vacuumizing, introduce a high-purity argon gas into the furnace and keep it at one atmospheric pressure. Heat to 1800°C at a heating rate of 10°C/min, and maintain the temperature for 4 hours. After the temperature maintaining is finished, taken out the pellet after cooling to the room temperature.

[0060] X-ray diffraction analysis shows that the phase of the sintered pellet is uranium carbide, and the diffraction peak has no significant shift. The test shows that the uranium carbide pellet prepared by sintering at a maintaining temperature of 1800°C for 4 hours has a density of 98%, a porosity of 2%, and a pore diameter of 100 nm, and pores are open pores. [0061] Embodiment 2 [0062] Prepare the uranium carbide pellet with a density of 95%. Change the carbon source from the carbon black in Embodiment 1 to the graphite. Weigh according to a molar ratio of UN:C of 1:0.8, with 249 g of UN powder and 9.6 g of graphite.

[0063] Prepare the green body in the same manner as in Embodiment 1, the in-situ reaction temperature is 1500°C and is maintained for 2 hours, and the sintering temperature is 1900°C and is maintained for 1 hour. [0064] By X-ray diffraction analysis, the phase of the sintered pellet is uranium carbide, and the diffraction peak has a slight shift to the left, indicating the existence of the nitrogen solid solution. The test shows that the uranium carbide pellet prepared by sintering at a maintaining temperature of 1900°C for 1 hour has a density of 95%, a porosity of 5%, and a pore diameter of 500 nm, and the pores are open pores.

[0065] Embodiment 3 [0066] Prepare the uranium carbide pellet with a density of 99%. Weigh according to a molar ratio UN:C of 1:1, with 249 g of UN powder and 12 g of graphite.

[0067] Prepare the green body in the same manner as in Embodiment 1, with the same in-situ reaction as in Embodiment 1, and prepare the pellet by pressureless sintering at 2000°C for 3 hours.

[0068] X-ray diffraction analysis shows that the phase of the sintered pellet is uranium carbide, and the diffraction peak has no significant shift. The test shows that the density of the uranium carbide pellet prepared by sintering maintained at a temperature of 2000°C for 14 hours is 99%, and no open pore exists.

[0069] Embodiment 4 [0070] Prepare the uranium carbide pellet with a density of 95%. Change the carbon source from carbon black in Embodiment 1 to graphite. Weigh according to a molar ratio UN:C of 1:1.5, with 249 g of UN powder and 18 g of graphite.

[0071] Prepare the green body in the same manner as in Embodiment 1, the in-situ reaction temperature is 1600°C and is maintained for 1.5 hours, and the sintering temperature is 1700°C and is maintained for 10 hours. [0072] By X-ray diffraction analysis, the phase of the sintered pellet is uranium carbide, and the diffraction peak has a slight shift to the right, indicating the existence of rich carbon. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1700°C for 10 hours has a density of 95%, a porosity of 5%, and a pore diameter of 200 nm, and the pores are open pores.

[0073] Embodiment 5 [0074] Prepare the uranium carbide pellet with a density of 97%. Use the carbon black as a raw material. Weigh according to a molar ratio UN:C of 1:0.9, with 249 g of UN powder and 10.8 g of carbon black.

[0075] Use the acetone as the solvent, mix the mixture through a roll-type mixing using a SiC ball for 12 hours at the speed of 120 revolutions per minute, and dry the obtained slurry by rotary evaporation to obtain the mixed powder which is uniformly mixed. Put the mixed powder into a pellet steel mold, firstly pre-press the mixed powder under the pressure of 201\4Pa, then vacuum seal the pre-formed green body by the oilpaper, then use a cold isostatic press to apply an isobaric load of 250MPa to the green body vacuum sealed by the oilpaper, and maintain the pressure at 250 MPa for 5 minutes, enabling an initial density of the pellet green body to reach 50% or more.

[0076] Take out the green body and put it into a high-temperature pressureless furnace for reaction sintering. With the pressureless sintering, in the first reaction stage, the heating rate is 20°C/min, raise the temperature to 1550°C and maintain it for 0.5 hour. In this stage, the vacuum environment must be maintained. After the temperature maintaining is finished, stop the vacuumizing, introduce a high-purity argon gas into the furnace and keep it at one atmospheric pressure. Heat to 1900°C at a heating rate of 20°C/min, and maintain the temperature for 8 hours. After the temperature maintaining is finished, taken out the pellet after cooling to the room temperature.

[0077] X-ray diffraction analysis shows that the phase of the sintered pellet is uranium carbide, and the diffraction peak has no significant shift. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1900°C for 8 hours has a density of 97%, a porosity of 3%, and a pore diameter of 300 nm, and the pores are open pores.

[0078] Embodiment 6 [0079] Prepare the uranium carbide pellet with a density of 100%. Use the carbon black as the raw material. Weigh according to a molar ratio UN:C of 1:1.1, with 249 g of UN powder and 13.2 g of carbon black. [0080] Prepare the green body in the same manner as in Embodiment 5, the in-situ reaction temperature is 1600°C and maintained for 2 hours, and the sintering temperature is 1950°C and maintained for 12 hours. [0081] X-ray diffraction analysis shows that the phase of the sintered pellet is uranium carbide, and the diffraction peak has no significant shift. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1950°C for 12 hours has a density of 100%, and a porosity of 0%.

[0082] Embodiment 7 [0083] Prepare the uranium carbide pellet with a density of 95.5%. Use the carbon black as the raw material. Weigh according to a molar ratio UN:C of 1:1.5, with 249 g of UN powder and 18 g of carbon black.

[0084] Use the acetone as the solvent, mix the mixture through a roll-type mixing using a SiC ball for 24 hours at the speed of 120 revolutions per minute, and dry the obtained slurry by rotary evaporation to obtain the mixed powder which is uniformly mixed. Put the mixed powder into a pellet steel mold, firstly pre-press under the pressure of 15 MPa, then vacuum seal the pre-formed green body by the oilpaper, then use a cold isostatic press to apply an isobaric load of 150 MPa to the green body vacuum sealed by the oilpaper, and maintain the pressure at 150 MPa for minutes, enabling an initial density of the pellet green body to reach 50% or more.

[0085] Take out the green body and put it into a high-temperature pressureless furnace for reaction sintering. With the pressureless sintering, in the first reaction stage, the heating rate is 30°C/min, the temperature is raised to 1600°C and maintained for 2 hour. In this stage, the vacuum environment must be maintained. After the temperature maintaining is finished, stop the vacuumizing, introduce a high-purity argon gas into the furnace and keep it at one atmospheric pressure. Heat to 1850 °C at a heating rate of 30°C/min, and maintain the temperature for 6 hours. After the temperature maintaining is finished, taken out the pellet after cooling to the room temperature.

[0086] By X-ray diffraction analysis, the phase of the sintered pellet is uranium carbide, and the diffraction peak shifts slightly to the right, indicating the existence of rich carbon. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1850°C for 6 hours has a density of 95.5%, and a porosity of 4.5%.

[0087] Embodiment 8 [0088] Prepare the uranium carbide pellet with a density of 96.5%. Use the carbon black as the raw material. Weigh according to a molar ratio UN:C of 1:1.3, with 249 g of UN powder and 15.6 g of carbon black. [0089] Use the acetone as the solvent, and mix the mixture through a roll-type mixing using a Si3N4 ball for 18 hours at the speed of 120 revolutions per minute, and dry the obtained slurry by rotary evaporation to obtain the mixed powder which is uniformly mixed. Put the mixed powder into a pellet steel mold, firstly pre-press under the pressure of 30 MPa, then vacuum seal the pre-formed green body by the oilpaper, then use a cold isostatic press to apply an isobaric load of 300 MPa to the green body vacuum sealed by the oilpaper, and maintain the pressure at 300 MPa for 5 minutes, enabling an initial density of the pellet green body to reach 50% or more.

[0090] Take out the green body and put it into a high-temperature pressureless furnace for reaction sintering. With the pressureless sintering, in the first reaction stage, the heating rate is 15°C/min, the temperature is raised to 1450°C and maintained for 2.5 hour. In this stage, the vacuum environment must be maintained. After the temperature maintaining is finished, stop the vacuumizing, introduce the high-purity argon gas into the furnace and keep it at one atmospheric pressure. Heat to 1950 °C at a heating rate of 15°C/min, and maintain the temperature for 2 hours. After the temperature maintaining is finished, taken out the pellet after cooling to the room temperature.

[0091] By X-ray diffraction analysis, the phase of the sintered pellet is uranium carbide, and the diffraction peak shifts slightly to the right, indicating the existence of rich carbon. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1950°C for 2 hours has a density of 96.5%, and a porosity of 3.5%.

[0092] Embodiment 9 [0093] Prepare the uranium carbide pellets with a density of 96%. Use the carbon black as the raw material. Weigh according to a molar ratio UN:C of 1:0.8, with 249 g of UN powder and 9.6 g of carbon black.

[0094] Use the acetone as the solvent, and mix the mixture through a roll-type mixing using Si3N4 ball for 20 hours at the speed of 120 revolutions per minute, and dry the obtained slurry by rotary evaporation to obtain the uniformly mixed mixed powder. Put the mixed powder into a pellet steel mold, firstly pre-press under the pressure of 5 Wifia, then vacuum seal the pre-formed green body by the oilpaper, then use a cold isostatic press to apply an isobaric load of 150 MPa to the green body vacuum sealed by the oilpaper, and maintain the pressure at 150 MPa for 5 minutes, enabling an initial density of the pellet green body to reach 50% or more.

[0095] Take out the green body and put it into a high-temperature pressureless furnace for reaction sintering. With the pressureless sintering, in the first reaction stage, the heating rate is 5°C/min, the temperature is raised to 1300°C and maintained for 4 hour. In this stage, the vacuum environment must be maintained. After the temperature maintaining is finished, stop the vacuumizing, introduce the high-purity argon gas into the furnace and keep it at one atmospheric pressure. Heat to 1850 °C at a heating rate of 5°C/min, and maintain the temperature for 5 hours. After the temperature maintaining is finished, taken out the pellet after cooling to the room temperature.

[0096] By X-ray diffraction analysis, the phase of the sintered pellet is uranium carbide, and the diffraction peak shifts slightly to the left, indicating the existence of solid solution nitrogen. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1850°C for 5 hours has a density of 96%, and a porosity of 4%.

[0097] Embodiment 10 [0098] Prepare the uranium carbide pellet with a density of 98.5%. Use the carbon black as the raw material. Weigh according to a molar ratio UN:C of 1:1.1, with 249 g of UN powder and 13.2 g of carbon black.

[0099] Use the acetone as the solvent, and mix the mixture through the roll-type mixing using the Si3N4 ball for 24 hours at the speed of 240 revolutions per minute, and dry the obtained slurry by rotary evaporation to obtain the mixed powder which is uniformly mixed. Put the mixed powder the pellet steel mold, firstly pre-press under the pressure of 10 MPa, then vacuum seal the pre-formed green body by the oilpaper, then use the cold isostatic press to apply an isobaric load of 200 MPa to the green body vacuum sealed by the oilpaper, and maintain the pressure at 200 MPa for 5 minutes, enabling an initial density of the pellet green body to reach 50% or more.

[0100] Take out the green body and put it into a high-temperature pressureless furnace for reaction sintering. With the pressureless sintering, in the first reaction stage, the heating rate is 10°C/min, the temperature is raised to 1350°C and maintained for 4 hours. In this stage, the vacuum environment must be maintained. After the temperature maintaining is finished, stop the vacuumizing, introduce the high-purity argon gas into the furnace and keep it at one atmospheric pressure. Heat to 1750 °C at a heating rate of 10°C/min, and maintain the temperature for 13 hours. After the temperature maintaining is finished, taken out the pellet after cooling to the room temperature.

[0101] After X-ray diffraction analysis, the phase of the sintered pellet is uranium carbide, and the diffraction peak has no significant shift. The test shows that the uranium carbide pellet prepared by sintering maintained at a temperature of 1750°C for 13 hours has a density of 98.5%, and a porosity of 1.5%.

[0102] The above described is merely an embodiment of the invention and is not intended to limit the scope of the invention. Any equivalent structure or equivalent process transformation made by the description of the present invention, or the application directly or indirectly used in other related technical fields, are also included in the scope of patent protection of the present invention.

Claims

Claims 1. A preparation method for a uranium carbide pellet, comprising the following steps: S1, weighing uranium nitride powder and carbon source according to a molar ratio of 1:0.8-1.5 adding the uranium nitride powder and the carbon source into a solvent, and mixing uniformly to form a slurry; S2, drying the slurry to obtain mixed powder; S3, pressing the mixed powder into a green body with a density of 50% or more; and S4, carrying out a high-temperature pressureless sintering to obtain the uranium carbide pellet with a density of > 95%.
2. The preparation method for the uranium carbide pellet according to claim 1, wherein in the step S1, the uranium nitride powder has a purity of more than 95% and a particle size of 0.1-50!An; the carbon source is carbon black and/or graphite, having a purity of more than 95% and a particle size of 0.1-50 p.m.
3. The preparation mcthod for the uranium carbide pellet according to claim 1, wherein in the step SI, the solvent is ethanol or acetone.
4. The preparation method for the uranium carbide pellet according to claim 4, wherein the step S3 comprises the following steps: S3.1, pre-pressing and molding the mixed powder under a pressure of 5-30 Mpa; and S3.2, vacuum sealing the pre-pressed and molded green body, pressing on the sealed green body under a pressure of 150-300 MPa, and obtaining a green body with a density of 50% or more after pressure maintaining.
5. The preparation method for the uranium carbide pellet according to claim 4, wherein, in the step S3.1, put the mixed powder into a pellet steel mold for pre-pressing and molding; and in the step S3.2, vacuum seal the pre-pressed and molded green body with an oilpaper, and carry out the high-pressure pressing on the sealed green body using a cold isostatic press.
6. The preparation method for the uranium carbide pellet according to claim 1, wherein the step S4 comprises the following steps: S4.1, putting the green body obtained in the step S3 into a high-temperature pressureless furnace, heating to 1300°C-1600°C at a rate of 5-30°C/min under a vacuum environment, and maintaining the temperature for 0.5-4h; and S4.2, heating to 1700°C-2000°C at a rate of 5-30°C/min under an inert atmosphere, and maintaining the temperature for 1-14 hours to obtain the uranium carbide pellet.
7. The preparation method for the uranium carbide pellet according to claim 6, wherein in the step S4.2, introduce an argon gas into the high-temperature pressureless furnace and maintain at one atmospheric pressure to form the inert atmosphere.
8. The preparation method for the uranium carbide pellet according to any one of claims 1-7, wherein the atomic ratio of uranium, carbon and nitrogen in the obtained uranium carbide pellet is 1:(0.8-1.5):(0-0.2).
9. A uranium carbide pellet, characterized by being prepared by the preparation method of any one of claims 1 to 8.
10. A fuel rod, characterized by comprising the uranium carbide pellet of claim 9.