Preparation method of fuel pellet

Abstract

The invention discloses a preparation method of a fuel pellet, by adopting a reasonable preparation method and tool design, the fuel pellet easy to oxidize is prepared in a low-oxygen and low-water environment, the fuel pellet is prevented from being oxidized in the preparation process, the density of the fuel pellet easy to oxidize can be effectively improved, the content of oxygen impurities in the pellet can be effectively reduced, and the fuel pellet can be used for preparing fuel pellets. And the safety of the fuel pellet in the preparation process is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear fuel, and particularly relates to a method for preparing fuel pellets. Background Art

[0002] Since the occurrence of the Fukushima accident in Japan, in order to improve the accident tolerance and inherent safety of fuels, the concept of accident tolerant fuel has been proposed in the international nuclear fuel field. Accident tolerant fuel is an innovative fuel aimed at improving the structural integrity of nuclear fuel under severe accidents. By adopting a new fuel / cladding material system and structural design, accident tolerant fuel can effectively reduce or avoid the generation of combustible gases under accident conditions, reduce the release of fission products, and thus reduce the risk of a large amount of radioactive material leakage in nuclear power plants.

[0003] The research and development of accident tolerant fuel mainly includes three aspects: improvement of cladding materials, research and development of advanced fuel pellets, and research and development of advanced claddings. Among them, the key point of the research and development of advanced fuel pellets lies in the development of new fuels with better thermal conductivity and fission product containment ability than UO2 fuel. UO2 fuel has performance advantages such as high melting point, corrosion resistance, low high-temperature creep, and good irradiation stability, and is widely used in commercial nuclear reactor fuels. However, UO2 fuel has a low thermal conductivity, which easily causes local overheating of the reactor core and affects the heat transfer from the pellets to the coolant. Under accident conditions, the low thermal conductivity of UO2 fuel leads to the ineffective removal of the residual heat of the reactor. Therefore, UO2 fuel has a potential risk of a reactor meltdown accident. In view of the above disadvantages of the currently used UO2 fuel, the next-generation advanced fuel pellets need to focus on improving the thermal conductivity of the fuel and reducing the temperature of the fuel during operation, so as to improve the inherent safety of the fuel.

[0004] UN fuel and U3Si2 fuel have become one of the potential materials for the next-generation advanced fuel pellets due to their high uranium density, high thermal conductivity, etc. However, UN fuel and U3Si2 fuel have high activity and are prone to react with oxygen, resulting in an increase in the UO2 phase in the pellets, which has an adverse impact on the density, thermal conductivity, and uranium density of the pellets. Summary of the Invention

[0005] The embodiments of the present application provide a method for preparing fuel pellets. By adopting a reasonable preparation method and tooling design, the easily oxidizable fuel pellets are prepared in a low-oxygen and low-water environment, avoiding the oxidation of the fuel pellets during the preparation process, effectively improving the density of the easily oxidizable fuel pellets, reducing the oxygen impurity content in the pellets, and ensuring the safety of the fuel pellets during the preparation process.

[0006] In a first aspect, the present application provides a method for preparing fuel pellets, including:

[0007] Steps of preparing powder, adding binder, ball milling the powder, pressing the green pellet of the fuel pellet, transferring the green pellet of the fuel pellet to a sintering furnace, and sintering the green pellet of the fuel pellet to obtain a fuel pellet with a density of more than 95% T.D., wherein all steps are carried out in an environment with a water content of a preset water content and an oxygen content of a preset oxygen content.

[0008] In some embodiments, the preset water content does not exceed 100 ppm, and the preset oxygen content does not exceed 200 ppm.

[0009] In some embodiments, the green pellet of the fuel pellet is transferred to the sintering furnace through a sealing device; or a sintering device capable of loading the green pellet of the fuel pellet under a protective atmosphere is used to transfer the green pellet of the fuel pellet to the sintering furnace.

[0010] In some embodiments, the preparation material of the sealing device includes graphite, tungsten, molybdenum, zirconia, alumina or silicon carbide.

[0011] In some embodiments, the sealing device includes a cover body and a bearing member, and the cover body and the bearing member are sealed by a threaded manner or a sealing material.

[0012] In some embodiments, the fuel pellet includes a U3Si2 fuel pellet or a UN / U3Si2 composite fuel pellet.

[0013] In some embodiments, the fuel pellet includes a U3Si2 fuel pellet; the steps of preparing powder, adding binder, ball milling the powder, pressing the green pellet of the fuel pellet, transferring the green pellet of the fuel pellet to a sintering furnace, and sintering the green pellet of the fuel pellet include:

[0014] Dissolve polyethylene glycol in absolute ethanol to obtain a polyethylene glycol solution; in an atmosphere glove box, place the U3Si2 raw material and the polyethylene glycol solution in a zirconia ball milling tank, and place the zirconia ball milling tank in a sealed tank;

[0015] Take out the sealed tank from the atmosphere glove box, ball mill the U3Si2 raw material and the polyethylene glycol solution in the zirconia ball milling tank to obtain a first mixture, transfer the sealed tank to the atmosphere glove box after ball milling, and then take out the first mixture from the zirconia ball milling tank and dry it to obtain U3Si2 fuel powder containing polyethylene glycol;

[0016] Press the U3Si2 fuel powder containing polyethylene glycol into a shape to obtain a green pellet of the U3Si2 fuel pellet;

[0017] Transfer the green pellet of the U3Si2 fuel pellet to a sealing device, and transfer the sealing device to a vacuum sintering furnace; or, transfer the green pellet of the U3Si2 fuel pellet to a vacuum sintering furnace under a protective atmosphere;

[0018] Sinter the green body of U3Si2 fuel pellets in the vacuum sintering furnace to obtain U3Si2 fuel pellets.

[0019] In some embodiments, the fuel pellets include UN / U3Si2 composite fuel pellets; the steps of powder preparation, binder addition, powder ball milling, green body pressing of pellets, transferring the green body of pellets to the sintering furnace, and sintering the green body of pellets include:

[0020] Dissolve polyethylene glycol in absolute ethanol to obtain a polyethylene glycol solution; inside an atmosphere glove box, place the U3Si2 raw material, UN raw material, and the polyethylene glycol solution in a zirconia ball milling jar, and place the zirconia ball milling jar in a sealed jar;

[0021] Take out the sealed jar from inside the atmosphere glove box, in the zirconia ball milling jar, ball mill the U3Si2 raw material, UN raw material, and the polyethylene glycol solution to obtain a second mixture. After completing the ball milling, transfer the sealed jar to the atmosphere glove box, and then take out the second mixture from the zirconia ball milling jar and dry it to obtain a mixed powder of U3Si2 fuel and UN fuel containing polyethylene glycol;

[0022] Press the mixed powder of U3Si2 fuel and UN fuel containing polyethylene glycol into shape to obtain a green body of UN / U3Si2 composite fuel pellets;

[0023] Transfer the green body of UN / U3Si2 composite fuel pellets to a sealing device, and transfer the sealing device to a vacuum sintering furnace; or, under a protective atmosphere, transfer the green body of UN / U3Si2 composite fuel pellets to a vacuum sintering furnace;

[0024] Sinter the green body of UN / U3Si2 composite fuel pellets in the vacuum sintering furnace to obtain UN / U3Si2 composite fuel pellets.

[0025] In some embodiments, the step of sintering the U3Si2 fuel pellets in the vacuum sintering furnace includes: sintering the U3Si2 fuel pellets under vacuum or a flowing protective atmosphere, wherein when sintering the U3Si2 fuel pellets under a vacuum atmosphere, after the vacuum sintering furnace is evacuated, the vacuum degree is better than 5×10 -2 Pa.

[0026] In some embodiments, the step of sintering the UN / U3Si2 composite fuel pellets in the vacuum sintering furnace includes: sintering the UN / U3Si2 composite fuel pellets under vacuum or a flowing protective atmosphere, wherein when sintering the UN / U3Si2 composite fuel pellets under a vacuum atmosphere, after the vacuum sintering furnace is evacuated, the vacuum degree is better than 5×10 -2 Pa.

[0027] A preparation method of fuel pellets provided by the present application, through adopting a reasonable preparation method and tooling design, enables the preparation of easily oxidizable fuel pellets in a low-oxygen and low-water environment, avoids the oxidation of fuel pellets during the preparation process, can effectively improve the density of easily oxidizable fuel pellets, reduce the oxygen impurity content in the pellets, and ensure the safety of fuel pellets during the preparation process. Description of the Drawings

[0028] Figure 1 An actual diagram of a sealing device provided according to some embodiments is exemplarily shown;

[0029] Figure 2 A macroscopic morphology diagram of a U3Si2 fuel pellet provided according to some embodiments is exemplarily shown;

[0030] Figure 3 A macroscopic morphology diagram of a UN / U3Si2 composite fuel pellet provided according to some embodiments is exemplarily shown. Detailed Description of the Embodiments

[0031] In order to better understand the above technical solutions, the technical solutions of the present application will be described in detail below through specific embodiments.

[0032] When adopting the powder metallurgy process route to prepare U3Si2 fuel pellets or UN / U3Si2 composite fuel pellets, in order to prepare high-density U3Si2 fuel pellets or UN / U3Si2 composite fuel pellets, the raw materials need to be ball-milled to obtain powders with finer particle sizes. However, the U3Si2 fuel powder, UN fuel powder and their mixed powders with finer particle sizes are extremely easy to react with oxygen in the environment (when the above powders are exposed to air, the powders will spontaneously combust), resulting in more UO2 phases in the fuel pellets. These UO2 phases will hinder the densification of fuel pellets (U3Si2 fuel, UN / U3Si2 composite fuel pellets) during the sintering process, making it difficult to obtain high-density fuel pellets. Therefore, when preparing U3Si2 fuel and UN / U3Si2 composite fuel pellets, special processes and tooling are needed to solve the above problems.

[0033] The embodiment of the present application provides a preparation method of fuel pellets. The method includes steps of powder preparation, binder addition, powder ball-milling, green pellet pressing of the pellets, transferring the green pellets of the pellets to a sintering furnace, and sintering the green pellets of the pellets to obtain fuel pellets with a density reaching above 95% T.D., wherein all steps are carried out in an environment with a water content of a preset water content and an oxygen content of a preset oxygen content.

[0034] In the embodiment of the present application, by adopting a reasonable preparation method and tooling design, the easily oxidizable fuel pellets are prepared in a low-oxygen and low-water environment to avoid oxidation of the fuel pellets during the preparation process, which can effectively increase the density of the easily oxidizable fuel pellets, reduce the oxygen impurity content in the pellets, and ensure the safety of the fuel pellets during the preparation process. The water-oxygen control value is to reduce the generation of UO2 phase in the fuel pellets. When the water-oxygen content in the environment is high, the particle size of the fuel powder after ball milling is small and the specific surface area is high. It is very easy to react with the water-oxygen in the environment to form UO2 phase, resulting in a high content of UO2 phase in the pellets; the UO2 in the pellets has an adverse effect on the densification process of the pellets, making it difficult to obtain high-density fuel pellets.

[0035] In some embodiments, the preset water content does not exceed 100 ppm, and the preset oxygen content does not exceed 200 ppm.

[0036] In some embodiments, the green pellets are transferred to a sintering furnace through a sealing device; or a sintering device capable of loading the green pellets into a furnace under a protective atmosphere is used to transfer the green pellets to a sintering furnace.

[0037] In the embodiment of the present application, the sealing device and the sintering device capable of loading green pellets into a furnace under a protective atmosphere are used to transfer the green pellets to a sintering furnace, thereby solving the problem of green fuel pellets being oxidized during transfer. Figure 1 A physical diagram of a sealing device provided according to some embodiments is exemplarily shown. Figure 1 The material of the sealing device is graphite, and the sealing device is sealed by thread sealing.

[0038] In some embodiments, the sealing device is made of a material including graphite, tungsten, molybdenum, zirconium oxide, aluminum oxide or silicon carbide.

[0039] In the embodiment of the present application, the sealing device is made of high temperature resistant materials such as graphite, tungsten, molybdenum, zirconium oxide, aluminum oxide or silicon carbide.

[0040] In some embodiments, the sealing device comprises a cover body and a bearing component, and the cover body and the bearing component are sealed by threads or sealing materials. Exemplarily, the sealing material can be sealing materials such as paraffin or sealing grease.

[0041] In some embodiments, the fuel pellets include U3Si2 fuel pellets or UN / U3Si2 composite fuel pellets.

[0042] In some embodiments, the fuel pellets include U3Si2 fuel pellets; the steps of powder preparation, binder addition, powder milling, pellet green body pressing, pellet green body transfer to a sintering furnace, and pellet green body sintering include:

[0043] Dissolve polyethylene glycol in absolute ethanol to obtain a polyethylene glycol solution; inside an atmosphere glove box, place the U3Si2 raw material and the polyethylene glycol solution in a zirconia ball milling jar, and place the zirconia ball milling jar in a sealed jar;

[0044] Take out the sealed jar from inside the atmosphere glove box, and in the zirconia ball milling jar, ball mill the U3Si2 raw material and the polyethylene glycol solution to obtain a first mixture. After completing the ball milling, transfer the sealed jar to the atmosphere glove box, then take out the first mixture from the zirconia ball milling jar and dry it to obtain U3Si2 fuel powder containing polyethylene glycol;

[0045] Press the U3Si2 fuel powder containing polyethylene glycol into a shape to obtain a green body of U3Si2 fuel pellets;

[0046] Transfer the green body of U3Si2 fuel pellets to a sealing device, and transfer the sealing device to a vacuum sintering furnace; or, under a protective atmosphere, transfer the green body of U3Si2 fuel pellets to a vacuum sintering furnace; in this embodiment, after obtaining the green body of U3Si2 fuel pellets, the green body of U3Si2 fuel pellets can be transferred to a vacuum sintering furnace by using a sealing device, or the green body of U3Si2 fuel pellets can be transferred to a vacuum sintering furnace under a protective atmosphere.

[0047] Sinter the green body of U3Si2 fuel pellets in the vacuum sintering furnace to obtain U3Si2 fuel pellets.

[0048] In some embodiments, the fuel pellets include UN / U3Si2 composite fuel pellets; the steps of powder preparation, binder addition, powder ball milling, green body pressing of pellets, transfer of the green body of pellets to a sintering furnace, and sintering of the green body of pellets include:

[0049] Dissolve polyethylene glycol in absolute ethanol to obtain a polyethylene glycol solution; inside an atmosphere glove box, place the U3Si2 raw material, UN raw material and the polyethylene glycol solution in a zirconia ball milling jar, and place the zirconia ball milling jar in a sealed jar;

[0050] Take out the sealed jar from inside the atmosphere glove box, and in the zirconia ball milling jar, ball mill the U3Si2 raw material, UN raw material and the polyethylene glycol solution to obtain a second mixture. After completing the ball milling, transfer the sealed jar to the atmosphere glove box, then take out the second mixture from the zirconia ball milling jar and dry it to obtain a mixed powder of U3Si2 fuel and UN fuel containing polyethylene glycol;

[0051] Press the mixed powder of U3Si2 fuel and UN fuel containing polyethylene glycol into a shape to obtain a green body of UN / U3Si2 composite fuel pellets;

[0052] Transfer the green body of the UN / U3Si2 composite fuel pellet to a sealing device and transfer the sealing device to a vacuum sintering furnace; or, under a protective atmosphere, transfer the green body of the UN / U3Si2 composite fuel pellet to a vacuum sintering furnace; in this embodiment, after obtaining the green body of the UN / U3Si2 composite fuel pellet, the green body of the UN / U3Si2 composite fuel pellet can be transferred to a vacuum sintering furnace by using a sealing device, or the green body of the UN / U3Si2 composite fuel pellet can be transferred to a vacuum sintering furnace under a protective atmosphere.

[0053] Sinter the green body of the UN / U3Si2 composite fuel pellet in the vacuum sintering furnace to obtain a UN / U3Si2 composite fuel pellet.

[0054] In some embodiments, the step of sintering the U3Si2 fuel pellet in the vacuum sintering furnace includes: sintering the U3Si2 fuel pellet under vacuum or a flowing protective atmosphere, wherein when sintering the U3Si2 fuel pellet under a vacuum atmosphere, after the vacuum sintering furnace is evacuated, the vacuum degree is better than 5×10 -2 Pa.

[0055] In some embodiments, the step of sintering the UN / U3Si2 composite fuel pellet in the vacuum sintering furnace includes: sintering the UN / U3Si2 composite fuel pellet under vacuum or a flowing protective atmosphere, wherein when sintering the UN / U3Si2 composite fuel pellet under a vacuum atmosphere, after the vacuum sintering furnace is evacuated, the vacuum degree is better than 5×10 -2 Pa.

[0056] Example 1

[0057] During the preparation of the U3Si2 fuel pellet, the control of the water and oxygen content in the preparation environment of the U3Si2 fuel pellet is realized by using an atmosphere glove box. In this embodiment, the water content in the atmosphere glove box is controlled at (10-20) ppm and the oxygen content is controlled at (10-20) ppm.

[0058] When ball-milling U3Si2 raw materials, first weigh polyethylene glycol (PEG) and absolute ethanol according to the mass ratio, and dissolve polyethylene glycol in absolute ethanol to obtain a 2.5 wt.% polyethylene glycol solution. Inside the atmosphere glove box, weigh U3Si2 raw materials and the polyethylene glycol solution according to the ratio of m(polyethylene glycol):m(U3Si2 raw materials) of 0.3 wt.%, put the above-mentioned mixture into a zirconia ball-milling jar, and then place the zirconia ball-milling jar in a sealable stainless steel sheath, that is, a sealed jar. Then, take out the stainless steel sheath with the zirconia ball-milling jar from the atmosphere glove box, and ball-mill the U3Si2 raw materials and the polyethylene glycol solution in the zirconia ball-milling jar to ensure that the U3Si2 raw materials are not oxidized during the ball-milling process.

[0059] After ball-milling is completed, transfer the stainless steel sheath with the zirconia ball-milling jar to the atmosphere glove box, and ensure that the water content in the atmosphere glove box is (10 - 20) ppm and the oxygen content is (10 - 20) ppm. Take out all the substances in the zirconia ball-milling jar, that is, the first mixture, inside the atmosphere glove box, and dry the absolute ethanol in the above-mentioned first mixed material at 70 °C to obtain U3Si2 fuel powder containing a binder. The average particle size of the U3Si2 fuel powder containing a binder is about 5 μm. The binder is polyethylene glycol.

[0060] Use a molding press to press the U3Si2 fuel powder containing a binder into shape to obtain a green body of U3Si2 fuel pellets, where the relative density of the green body is about 52% T.D. The molding process should be carried out inside the atmosphere glove box, and ensure that the water content in the atmosphere glove box is (10 - 20) ppm and the oxygen content is (10 - 20) ppm.

[0061] After obtaining the green body of U3Si2 fuel pellets, transfer the green body of U3Si2 fuel pellets to a sealing device made of graphite. The morphology of the sealed graphite device is as Figure 1 shown. Quickly transfer the sealed device containing the green body of U3Si2 fuel pellets to a vacuum sintering furnace, and immediately evacuate to minimize the exposure time of the sealed device in the air.

[0062] Use a vacuum sintering furnace to sinter the green body of U3Si2 fuel pellets. The sintering temperature is 1550 °C and the sintering time is 2 h. Among them, during the sintering process, the vacuum degree of the vacuum sintering furnace is better than 5×10 -2 Pa. The macroscopic morphology after sintering of the pellets is as Figure 2 shown, and U3Si2 fuel pellets with a density of about 11.83 g / cm 3 can be obtained, and the relative theoretical density is about 96.7% T.D.

[0063] Example 2

[0064] During the preparation of UN / U3Si2 composite fuel pellets, an atmosphere glove box is also used to control the water and oxygen contents in the preparation environment of UN / U3Si2 composite fuel pellets. In this embodiment, the water content in the atmosphere glove box is controlled at (0.1 - 10) ppm, and the oxygen content is controlled at (0.1 - 10) ppm.

[0065] When ball milling the UN raw material and U3Si2 raw material, first weigh polyethylene glycol (PEG) and absolute ethanol according to the mass ratio, and dissolve the polyethylene glycol in absolute ethanol to obtain a 2.5 wt.% polyethylene glycol solution. Inside the atmosphere glove box, weigh the UN raw material and U3Si2 raw material according to the ratio of m(UN raw material) : m(U3Si2 raw material) = 7:3, and then weigh the raw materials and the polyethylene glycol solution according to the ratio of m(polyethylene glycol) : m(UN raw material, U3Si2 raw material) = 0.3 wt.%. Load the above mixture into a zirconia ball milling jar, and then place the zirconia ball milling jar in a sealable stainless steel jacket, i.e., a sealed jar. Then, take out the stainless steel jacket with the zirconia ball milling jar from the atmosphere glove box, and ball mill the UN raw material, U3Si2 raw material and polyethylene glycol solution in the zirconia ball milling jar to ensure that the UN raw material and U3Si2 raw material are not oxidized during the ball milling process.

[0066] After ball milling is completed, transfer the stainless steel jacket with the zirconia ball milling jar to the atmosphere glove box, ensuring that the water content in the atmosphere glove box is (0.1 - 10) ppm and the oxygen content is (0.1 - 10) ppm. Take out all the substances in the zirconia ball milling jar, i.e., the second mixture, inside the atmosphere glove box, and dry the absolute ethanol in the above second mixture at 50 °C to obtain a mixed powder of UN fuel and U3Si2 fuel containing a binder. The average particle size of the mixed powder of UN fuel and U3Si2 fuel containing a binder is less than 10 μm. The binder is polyethylene glycol.

[0067] Use a molding press to press the mixed powder of UN fuel and U3Si2 fuel containing a binder into shape to obtain a green body of UN / U3Si2 composite fuel pellets, where the relative density of the green body is about 51% T.D. The molding process should be carried out inside the atmosphere glove box, and ensure that the water content in the atmosphere glove box is (0.1 - 10) ppm and the oxygen content is (0.1 - 10) ppm.

[0068] After obtaining the green body of UN / U3Si2 composite fuel pellets, transfer the green body of UN / U3Si2 composite fuel pellets to a sealing device made of zirconia. Quickly transfer the sealing device containing the green body of UN / U3Si2 composite fuel pellets to a vacuum sintering furnace, and immediately evacuate the air to minimize the exposure time of the sealing device in the air.

[0069] The green body of the UN / U3Si2 composite fuel pellet is sintered using a vacuum sintering furnace. The sintering temperature is 1700 °C and the sintering time is 2 h. During the sintering process, the vacuum degree of the vacuum sintering furnace is about 3×10 -2 Pa. The macroscopic morphology of the pellet after sintering is as shown in Figure 3 , and a UN / U3Si2 composite fuel pellet with a density of about 13.08 g / cm 3 can be obtained, with a relative theoretical density of about 96.0%T.D.

[0070] Example 3

[0071] During the preparation of the UN / U3Si2 composite fuel pellet, the control of the water and oxygen content in the preparation environment of the UN / U3Si2 composite fuel pellet is also achieved using an atmosphere glove box. In this example, the water content in the atmosphere glove box is controlled at (15 - 25) ppm and the oxygen content is controlled at (30 - 60) ppm.

[0072] When ball milling the UN raw material and U3Si2 raw material, first weigh polyethylene glycol and absolute ethanol according to the mass ratio, and dissolve the polyethylene glycol in absolute ethanol to obtain a 2.5 wt.% polyethylene glycol solution. Inside the atmosphere glove box, weigh the UN raw material and U3Si2 raw material according to the ratio of m(UN raw material):m(U3Si2 raw material) of 9:1, and then weigh the raw materials and the polyethylene glycol solution according to the ratio of m(polyethylene glycol):m(UN raw material, U3Si2 raw material) of 0.1 wt.%, and then load the above mixture into a zirconia ball milling jar. Then, place the zirconia ball milling jar in a sealable stainless steel jacket, and then take out the stainless steel jacket with the zirconia ball milling jar from the atmosphere glove box to ensure that the UN raw material and U3Si2 raw material are not oxidized during the ball milling process.

[0073] After ball milling is completed, transfer the stainless steel jacket with the zirconia ball milling jar to the atmosphere glove box to ensure that the water content in the atmosphere glove box is (15 - 25) ppm and the oxygen content is (30 - 60) ppm. Take out all the substances in the zirconia ball milling jar, that is, the second mixture, inside the atmosphere glove box, and dry the absolute ethanol in the above second mixture at 60 °C to obtain a mixed powder of UN fuel and U3Si2 fuel containing a binder. The average particle size of the mixed powder of UN fuel and U3Si2 fuel containing a binder is less than 10 μm. The binder is polyethylene glycol.

[0074] Using a molding press, press the mixed powder of UN fuel and U3Si2 fuel containing a binder into a shape to obtain a green body of the UN / U3Si2 composite fuel pellet, where the relative density of the green body is about 50%T.D. The molding process should be carried out inside the atmosphere glove box, and ensure that the water content in the atmosphere glove box is (15 - 25) ppm and the oxygen content is (30 - 60) ppm.

[0075] Use a sintering device capable of loading the green pellets of fuel pellets in a protective atmosphere to sinter the green pellets of UN / U3Si2 composite fuel pellets. The sintering device connects an atmosphere glove box with a sintering furnace, and uses the atmosphere glove box to control the water and oxygen content in the environment for loading the green pellets of UN / U3Si2 composite fuel pellets. In this embodiment, the water content in the atmosphere glove box is controlled at (15 - 25) ppm, and the oxygen content is controlled at (30 - 60) ppm. After obtaining the green pellets of UN / U3Si2 composite fuel pellets, transfer the green pellets of UN / U3Si2 composite fuel pellets into the sintering device under an atmosphere protection environment, and then use the sintering device to sinter the green pellets of UN / U3Si2 composite fuel pellets. The sintering temperature is 1650 °C, and the sintering time is 4 h. Among them, during the sintering process, the vacuum degree of the vacuum sintering furnace is about 8×10 -3 Pa. UN / U3Si2 composite fuel pellets with a density of about 13.59 g / cm 3 can be obtained, and the relative theoretical density is about 96.5% T.D.

[0076] In summary, a method for preparing fuel pellets provided by the present invention, through the adoption of a reasonable preparation method and tooling design, enables the preparation of easily oxidized fuel pellets in a low-oxygen and low-water environment, avoids the oxidation of fuel pellets during the preparation process, can effectively increase the density of easily oxidized fuel pellets, reduce the oxygen impurity content in the pellets, and ensure the safety of fuel pellets during the preparation process.

[0077] It is easy for those skilled in the art to understand that, on the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed. The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only the preferred implementation manner of the present application. It should be noted that for those of ordinary skill in the art in this technical field, several improvements and modifications can be made without departing from the technical principle of the present application, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A method for preparing a fuel pellet, characterized in that: include: The steps of powder preparation, binder addition, powder ball milling, green pellet pressing, green pellet transfer to a sintering furnace, and green pellet sintering are used to obtain fuel pellets with a relative theoretical density of more than 95% TD, wherein all steps are carried out under an environment with a preset water content and a preset oxygen content.

2. The method according to claim 1, characterized in that The preset water content does not exceed 100 ppm, and the preset oxygen content does not exceed 200 ppm.

3. The method according to claim 1, characterized in that: The green pellets are transferred to a sintering furnace through a sealing device; or a sintering device capable of loading the green pellets into a furnace under a protective atmosphere is used to transfer the green pellets to a sintering furnace.

4. The method according to claim 3, characterized in that The sealing device is made of graphite, tungsten, molybdenum, zirconium oxide, aluminum oxide or silicon carbide.

5. The method according to claim 3, characterized in that: The sealing device comprises a cover body and a bearing component, and the cover body and the bearing component are sealed by threads or sealing materials.

6. The method according to claim 1, characterized in that The fuel pellets include U3Si2 fuel pellets and UN / U3Si2 composite fuel pellets.

7. The method according to claim 6, characterized in that The fuel pellets include U3Si2 fuel pellets; The steps of preparing powder, adding binder, ball milling powder, pressing green pellets, transferring green pellets to a sintering furnace, and sintering green pellets include: dissolving polyethylene glycol in anhydrous ethanol to obtain a polyethylene glycol solution; In an atmosphere glove box, the U3Si2 raw material and the polyethylene glycol solution are placed in a zirconia ball mill, and the zirconia ball mill is placed in a sealed tank; The sealed can is taken out from the atmosphere glove box, and the U3Si2 raw material and the polyethylene glycol solution are ball-milled in the zirconia ball mill to obtain a first mixture. After the ball milling is completed, the sealed can is transferred to the atmosphere glove box, and the first mixture is taken out from the zirconia ball mill and dried to obtain U3Si2 fuel powder containing polyethylene glycol; Pressing the U3Si2 fuel powder containing polyethylene glycol into a green U3Si2 fuel pellet; Moving the U3Si2 fuel pellet green body to a sealing device, and transferring the sealing device to a vacuum sintering furnace; or, in a protective atmosphere, transferring the U3Si2 fuel pellet green body to a vacuum sintering furnace; The U3Si2 fuel pellet green body in the vacuum sintering furnace is sintered to obtain U3Si2 fuel pellets.

8. The method according to claim 6, characterized in that The fuel pellets include UN / U3Si2 composite fuel pellets; The steps of preparing powder, adding binder, ball milling powder, pressing green pellets, transferring green pellets to a sintering furnace, and sintering green pellets include: dissolving polyethylene glycol in anhydrous ethanol to obtain a polyethylene glycol solution; In an atmosphere glove box, U3Si2 raw material, UN raw material and the polyethylene glycol solution are placed in a zirconia ball mill jar, and the zirconia ball mill jar is placed in a sealed jar; The sealed can is taken out from the atmosphere glove box, and the U3Si2 raw material, the UN raw material and the polyethylene glycol solution are ball-milled in the zirconia ball mill to obtain a second mixture. After the ball milling is completed, the sealed can is transferred to the atmosphere glove box, and the second mixture is taken out from the zirconia ball mill and dried to obtain a mixed powder of U3Si2 fuel and UN fuel containing polyethylene glycol; Pressing the U3Si2 fuel containing polyethylene glycol and the UN fuel mixed powder into a shape to obtain a UN / U3Si2 composite fuel pellet green body; Moving the UN / U3Si2 composite fuel pellet green body to a sealing device, and transferring the sealing device to a vacuum sintering furnace; or, in a protective atmosphere, transferring the UN / U3Si2 composite fuel pellet green body to a vacuum sintering furnace; The UN / U3Si2 composite fuel pellet green body in the vacuum sintering furnace is sintered to obtain UN / U3Si2 composite fuel pellet.

9. The method according to claim 7, characterized in that: The step of sintering the U3Si2 fuel pellets in the vacuum sintering furnace comprises: sintering the U3Si2 fuel pellets in a vacuum or flowing protective atmosphere, wherein when the U3Si2 fuel pellets are sintered in a vacuum atmosphere, the vacuum sintering furnace is evacuated to a vacuum degree of better than 5×10 -2 Pa.

10. The method according to claim 8, characterized in that The step of sintering the UN / U3Si2 composite fuel pellets in the vacuum sintering furnace comprises: sintering the UN / U3Si2 composite fuel pellets in a vacuum or flowing protective atmosphere, wherein when the UN / U3Si2 composite fuel pellets are sintered in a vacuum atmosphere, the vacuum sintering furnace is evacuated to a vacuum degree of better than 5×10 -2 Pa.

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