Batch preparation method of large-grain UO2 pellets
Through the processes of batch mixing, dry granulation, pressing, wet hydrogen sintering and grinding, the problem of large-grain UO2 core pellets being difficult to produce on a large-grain UO2 core pellets in the prior art is solved, and the batch preparation of large-grain UO2 core pellets is realized, and the potential for a larger production scale is achieved.
Patent Information
- Application Number
- CN202510485383.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-17
- Publication Date
- 2025-06-17
AI Technical Summary
The existing large-grain UO2 core pellet preparation is mainly concentrated in the laboratory preparation stage and is difficult to apply to large-scale and batch industrial production.
UO2 powder, Cr2O3, Al2O3, pore-forming agent and lubricant are used to batch mix, and batch preparation of large-grain UO2 core pellets is achieved through dry granulation, pressing, wet hydrogen sintering and grinding.
The batch preparation of large-grain UO2 core pellets has been realized, the overall process flow is smooth, and it has the potential to be promoted to a larger production scale (100 kg level).
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Figure CN120164641A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of nuclear fuel pellets, and particularly relates to a method for batch preparation of large-grain UO2 pellets. Background Art
[0002] UO2 ceramic pellets are currently widely used nuclear fuels in nuclear reactors, and have significant advantages such as good high-temperature stability, radiation resistance, corrosion resistance, good dimensional stability under irradiation, and good compatibility with cladding materials. However, UO2 ceramic pellets still have some disadvantages, such as low thermal conductivity, and swelling during irradiation will inhibit the deepening of burnup.
[0003] Large-grain UO2 pellets not only possess the basic physical and chemical properties of traditional UO2 pellets (high melting point, high chemical stability, etc.), but also have better fission gas containment ability, can effectively reduce the fission gas release rate, relieve the PCI effect (pellet-cladding interaction) caused by too high temperature to a certain extent, and can effectively prevent accidents such as pellet cracking and cladding damage. It has unique advantages in improving the economy of fuel pellets and enhancing the safety of fuel pellets during operation.
[0004] However, the existing preparation of large-grain UO2 pellets mainly focuses on the laboratory preparation stage, and uses methods such as ball mills for material mixing, and only has the ability to prepare large-grain UO2 pellets in the order of hundreds of grams, making it difficult to be applied to large-scale and batch industrial production. Summary of the Invention
[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for batch preparation of large-grain UO2 pellets.
[0006] The present invention provides a method for batch preparation of large-grain UO2 pellets, comprising the following steps:
[0007] S1) Intermittently mixing UO2 powder, Cr2O3, Al2O3, pore-forming agent and a first lubricant to obtain a mixed material;
[0008] S2) Granulating the mixed material by dry granulation to obtain particulate matter;
[0009] S3) Mixing the particulate matter with a second lubricant to obtain a particulate matter mixture;
[0010] S4) Pressing the particulate matter mixture to obtain green pellets;
[0011] S5) High-temperature sintering the green pellets in a wet hydrogen atmosphere to obtain sintered pellets;
[0012] S6) Grinding the sintered pellets to obtain large-grain UO2 pellets.
[0013] Preferably, the mass of Cr2O3 is 0.1% - 0.12% of the mass of the UO2 powder;
[0014] The mass of Al2O3 is 0.01% - 0.02% of the mass of the UO2 powder.
[0015] Preferably, the pore-forming agent is selected from ammonium oxalate;
[0016] The first lubricant and the second lubricant are each independently selected from Acker wax and / or zinc stearate.
[0017] Preferably, the mass of the pore-forming agent is 0.3% - 0.4% of the mass of the UO2 powder;
[0018] The mass of the first lubricant is 0.04% - 0.06% of the mass of the UO2 powder;
[0019] The mass of the second lubricant is 0.3% - 0.4% of the mass of the particulate matter.
[0020] Preferably, the intermittent mixing in step S1) is specifically: mixing for 3 - 5 min, stopping for 3 - 5 min, repeating the mixing and stopping process, and the cumulative effective mixing time is not less than 60 min;
[0021] The intermittent mixing is carried out by a plowshare mixer; the rotation speed of the crushing knife of the plowshare mixer is 3000 - 3300 rpm; the rotation speed of the mixing knife of the plowshare mixer is 100 - 120 rpm;
[0022] The intermittent mixing is carried out in a protective atmosphere.
[0023] Preferably, the pressure of the dry granulation does not exceed 50 bar; the loose bulk density of the particulate matter is 2.0 - 2.5 g / cm 3 。
[0024] Preferably, the rotation speed of the mixing in step S3) is 10 - 30 rpm; the mixing time is 20 - 40 min.
[0025] Preferably, the density of the green pellet in step S4) is 5.8 - 6.2 g / cm 3 ; the height of the green pellet is 15 - 16.5 mm; the pressing pressure is 25 - 40 kN.
[0026] Preferably, the temperature of the high-temperature sintering in step S5) is 1740 °C - 1750 °C; the high-temperature sintering time is 6 - 8 h; the dew point of the wet hydrogen atmosphere is 15 °C - 25 °C.
[0027] Preferably, the average grain size of the large-grain UO2 pellets is 30 - 80 μm;
[0028] The sintering density of the large-grain UO2 pellets is 95-97% T.D.
[0029] The present invention provides a batch preparation method for large-grain UO2 pellets, comprising the following steps: S1) intermittently mixing UO2 powder, Cr2O3, Al2O3, a pore-forming agent and a first lubricant to obtain a mixed material; S2) granulating the mixed material by dry granulation to obtain particulate matter; S3) mixing the particulate matter with a second lubricant to obtain a particulate mixture; S4) pressing the particulate mixture to obtain green pellet cores; S5) performing high-temperature sintering on the green pellet cores in a wet hydrogen atmosphere to obtain sintered pellet cores; S6) grinding the sintered pellet cores to obtain large-grain UO2 pellets. Compared with the prior art, the present invention uses Cr2O3 and Al2O3 as grain growth aids, adds a pore-forming agent and a lubricant, adopts a plowshare mixing and wet hydrogen sintering method, and realizes the batch preparation of large-grain UO2 pellets through processes such as mixing, granulation, spheroidization, pressing, sintering, and grinding. The overall process flow is smooth and has the potential to be extended to the preparation of large-grain UO2 pellets on a larger production scale (hundred-kilogram level). Description of the Drawings
[0030] Figure 1 It is a process schematic diagram of the batch preparation method for large-grain UO2 pellets provided by the present invention.
[0031] Figure 2 It is a metallographic diagram of the ordinary UO2 pellets prepared in Comparative Example 1;
[0032] Figure 3 It is a metallographic diagram of the large-grain UO2 pellets prepared in Example 1 of the present invention;
[0033] Figure 4 It is a metallographic diagram of the large-grain UO2 pellets prepared in Example 2 of the present invention. Detailed Embodiments
[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.
[0035] The present invention provides a method for batch preparation of large-grained UO2 pellets, comprising the following steps: S1) intermittently mixing UO2 powder, Cr2O3, Al2O3, a pore-forming agent and a first lubricant to obtain a mixed material; S2) subjecting the mixed material to dry granulation to obtain particulate matter; S3) mixing the particulate matter with a second lubricant to obtain a particulate matter mixture; S4) pressing the particulate matter mixture to obtain green pellets; S5) performing high-temperature sintering on the green pellets in a wet hydrogen atmosphere to obtain sintered pellets; S6) grinding the sintered pellets to obtain large-grained UO2 pellets.
[0036] The present invention uses Cr2O3 and Al2O3 as grain growth aids, adds a pore-forming agent and a lubricant, and adopts the methods of plowshare mixing and wet hydrogen sintering. Through the processes of mixing, granulation, spheroidization, pressing, sintering, and grinding, the batch preparation of large-grained UO2 pellets is realized. The overall process flow is smooth, and it has the potential to be extended to the preparation of large-grained UO2 pellets on a larger production scale (hundred-kilogram level).
[0037] See Figure 1 , Figure 1 which is a schematic flow diagram of the method for batch preparation of large-grained UO2 pellets provided by the present invention.
[0038] Among them, the present invention has no special restrictions on the sources of all raw materials, and they can be commercially available.
[0039] UO2 powder, Cr2O3, Al2O3, a pore-forming agent and a first lubricant are intermittently mixed to obtain a mixed material; the mass of the Cr2O3 is preferably 0.1% - 0.12% of the mass of the UO2 powder; the mass of the Al2O3 is preferably 0.01% - 0.02% of the mass of the UO2 powder; the pore-forming agent is preferably ammonium oxalate; the mass of the pore-forming agent is preferably 0.3% - 0.4% of the mass of the UO2 powder; the first lubricant is preferably Acker wax and / or zinc stearate; the mass of the first lubricant is preferably 0.04% - 0.06% of the mass of the UO2 powder, more preferably 0.05%; the intermittent mixing is specifically: mixing for 3 - 5 min, stopping for 3 - 5 min, repeating the mixing and stopping process, and the cumulative effective mixing time is preferably not less than 60 min, more preferably not less than 100 min; in some embodiments provided by the present invention, the cumulative effective mixing time is 105 min or 150 min; the intermittent mixing is preferably carried out by a plowshare mixer; the rotation speed of the crushing knife of the plowshare mixer is preferably 3000 - 3300 rpm; the rotation speed of the mixing knife of the plowshare mixer is preferably 100 - 120 rpm; the intermittent mixing is preferably carried out in a protective atmosphere; the protective atmosphere can be a protective atmosphere well-known to those skilled in the art without special limitations, and nitrogen is preferably used in the present invention; mixing in a protective atmosphere can prevent the oxidation of UO2 powder.
[0040] The mixed material is granulated by dry granulation to obtain particulate matter; the dry granulation is specifically: the mixed material is pressed into flakes by a roll device, and these flakes enter a sizing device, are broken into small particles by a rotating sizing roll and flow out through a sieve with a set aperture to obtain qualified particles; the pressure of the dry granulation is preferably not more than 50 bar, more preferably 30 - 50 bar, still more preferably 35 - 45 bar, and most preferably 40 - 45 bar; the loose bulk density of the particulate matter is preferably 2.0 - 2.5 g / cm 3 , more preferably 2.2 - 2.4 g / cm 3 , still more preferably 2.2 - 2.3 g / cm 3 . Dry granulation can increase the fluidity of the mixed material and facilitate the automatic filling of the press to prepare green compact cores.
[0041] Adopting the plowshare mixing method and combining with the dry granulation process, kilogram-level material mixing is realized, the fluidity of the material is improved, batch mixing and pressing capabilities are available, and large-grain UO2 core blocks can be prepared in batches.
[0042] Mix the particulate matter with a second lubricant to obtain a particulate matter mixture; the second lubricant is preferably Acker wax and / or zinc stearate; the mass of the second lubricant is 0.3% to 0.4% of the mass of the particulate matter; the mixing is preferably carried out in a double-cone mixer; the rotation speed of the mixing is preferably 10 to 30 rpm; the mixing time is preferably 20 to 40 min, more preferably 20 to 30 min; through this step, a material with better fluidity can be obtained.
[0043] Press the particulate matter mixture to obtain a green compact core; the pressure of the pressing is preferably 25 to 40 kN, more preferably 25 to 35 kN, and still more preferably 29 to 32 kN; the density of the green compact core is preferably 5.8 to 6.2 g / cm 3 , more preferably 5.8 to 6.0 g / cm 3 ; the height of the green compact core is preferably 15 to 16.5 mm.
[0044] Subject the green compact core to high-temperature sintering in a wet hydrogen atmosphere to obtain a sintered core; the dew point of the wet hydrogen atmosphere is preferably 15°C to 25°C, more preferably 17°C to 25°C; the temperature of the high-temperature sintering is preferably 1740°C to 1750°C; the time of the high-temperature sintering is preferably 6 to 8 h.
[0045] Grind the sintered core to obtain a large-grain UO2 core; the grinding is preferably carried out in a centerless grinder; the grinding is preferably external cylindrical grinding, and the diameter of the large-grain UO2 core is made to meet the specified requirements through grinding.
[0046] According to the present invention, the average grain size of the large-grain UO2 core is preferably 30 to 80 μm; the sintered density of the large-grain UO2 core is 95 to 97% T.D; the mass content of uranium in the large-grain UO2 core is not less than 87.7%; the oxygen-to-uranium ratio of the large-grain UO2 core is preferably 1.99 to 2.02, more preferably 2 to 2.02; the total hydrogen content of the large-grain UO2 core is not higher than 0.8 μg / g UO2; the equivalent boron content of the large-grain UO2 core does not exceed 4 μg / g U; the Cr content of the large-grain UO2 core prepared by this method does not exceed 900 μg / g U; when the core conducts a thermal stability test, under the conditions of a holding temperature of 1715°C, a holding time of greater than or equal to 24 hours, and a test atmosphere of H2, the density increment of the core is less than 1% T.D.
[0047] To further illustrate the present invention, the following is a detailed description of a batch preparation method for a large-grain UO2 core provided by the present invention in conjunction with embodiments.
[0048] All reagents used in the following examples are commercially available.
[0049] Comparative Example 1
[0050] 1.1 Mixing
[0051] A certain mass of UO2 powder was placed in a plowshare mixer. Based on the mass of the UO2 powder, ammonium oxalate as a pore-forming agent and Acker wax as a lubricant were added. The addition ratio of ammonium oxalate as the pore-forming agent was 0.2%, and the addition ratio of Acker wax as the lubricant was 0.05%.
[0052] The plowshare mixer was started, and an intermittent mixing process was adopted. It was mixed for 3 minutes, stopped for 3 minutes, and repeated 35 mixing cycles. The cumulative effective mixing time was 105 minutes. The speed of the crushing knife was 3000 rpm, and the speed of the mixing knife was 100 rpm to make the materials mixed evenly. During the stirring and mixing process, nitrogen gas was filled at a certain pressure to prevent the oxidation of UO2 powder.
[0053] 1.2 Pelletizing
[0054] The above-mentioned mixed materials were pelletized using a dry granulator to increase the fluidity of the mixed materials and facilitate automatic feeding of the press. The pelletizing pressure was 45 bar, and the loose bulk density of the powder after pelletizing was about 2.2 g / cm 3 .
[0055] During dry granulation, the mixed powder was first pressed into flakes by a roller device. These flakes entered the sizing device, were broken into small particles by a rotating sizing roller, and flowed out through a sieve with a set aperture (1.5 mm) to obtain qualified particles.
[0056] 1.3 Spheroidizing
[0057] The pelletized powder was loaded into the barrel of a spheroidizing mixer. Based on the mass of the spheroidizing materials, 0.3% Acker wax as a lubricant was added. The spheroidizing mixer was started, and the mixing time was 30 minutes with a speed of 10 rpm to obtain materials with better fluidity.
[0058] 1.4 Pressing
[0059] The spheroidized powder was put into a press to press green compact cores. The density of the green compact cores was controlled at 5.8 g / cm 3 ~6.0 g / cm 3 , and the height of the green compact cores was controlled at 15.8 mm - 16.0 mm, and the pressing pressure was controlled at 35 kN.
[0060] 1.5 Sintering
[0061] The green compact cores were sent into a high-temperature sintering furnace for high-temperature sintering. The sintering temperature was 1750 °C, the high-temperature sintering time was 8 hours, and the sintering atmosphere was dry hydrogen.
[0062] 1.6 Grinding
[0063] The sintered core blocks are placed in a centerless grinder for cylindrical grinding, so that the diameter of the core blocks after grinding meets the specified requirements, thereby obtaining the final finished core blocks.
[0064] The finished core block obtained in Comparative Example 1 was analyzed using a microscope, and its metallographic image was obtained as follows: Figure 2 shown.
[0065] Example 1
[0066] 1.1 Mixing
[0067] A certain mass of UO2 powder is put into a plowshare mixer, and the grain growth aid Cr2O3, Al2O3, pore former ammonium oxalate, and lubricant aker wax are added based on the mass of UO2 powder. Among them, the addition ratio of Cr2O3 is 0.12%, the addition ratio of Al2O3 is 0.02%, the addition ratio of ammonium oxalate, the addition ratio of pore former, and the addition ratio of aker wax is 0.05%.
[0068] Start the plowshare mixer, use intermittent mixing process, mix for 3 minutes, stop for 3 minutes, repeat 35 mixing cycles, cumulative effective mixing time 105 minutes, crusher speed 3000rpm, mixer speed 100rpm, so that the materials are mixed evenly. A certain pressure of nitrogen is filled during the mixing process to prevent UO2 powder from oxidation.
[0069] 1.2 Granulation
[0070] The mixed materials were granulated using a dry granulator to increase the fluidity of the mixed materials and facilitate automatic filling of the press. The granulation pressure was 45 bar, and the loose density of the powder after granulation was about 2.3 g / cm 3 .
[0071] During dry granulation, the mixed powder is first pressed into flakes by a roller device, and these flakes enter the granulation device, where they are broken into fine particles by the rotating granulation rollers and flow out through a sieve with a set aperture (1.5 mm) to obtain qualified granules.
[0072] 1.3 Spherification
[0073] The granulated powder was loaded into the barrel of a double cone mixer, 0.4% lubricant Aker wax was added based on the mass of the spheroidized material, and the double cone mixer was started with a mixing time of 30 min and a rotation speed of 10 rpm to obtain a material with better fluidity.
[0074] 1.4 Suppression
[0075] The spheronized powder is put into a press to press the green pellets. The density of the green pellets is controlled at 5.8 g / cm 3 ~6.0g / cm 3, the height of the green compact is controlled at 15.7 mm to 16.1 mm, and the pressing pressure is controlled at 32 kN.
[0076] 1.5 Sintering
[0077] The green compact is sent into a high-temperature sintering furnace for high-temperature sintering. The sintering temperature is 1750 °C, the high-temperature sintering time is 8 hours, and the sintering atmosphere is wet hydrogen with a dew point of 25 °C.
[0078] 1.6 Grinding
[0079] The sintered compact is put into a centerless grinder for external cylindrical grinding so that the diameter of the ground compact meets the specified requirements, and the final finished compact is obtained.
[0080] The finished compact obtained in Example 1 is analyzed using a microscope, and its metallographic diagram is as Figure 3 shown.
[0081] The finished compact obtained in Example 1 is analyzed. Its sintered density is 96.02% T.D; its uranium mass content is 88.07%; its oxygen-to-uranium ratio is 2.004; its total hydrogen content is 0.126 μg / g UO2; its equivalent boron content is 0.92 μg / g U; its Cr content is 644 μg / g U; when the compact is subjected to a thermal stability test, under the conditions of a holding temperature of 1715 °C, a holding time of 24 hours, and a test atmosphere of H2, the density increment of the compact is 0.01% T.D.
[0082] Example 2
[0083] 2.1 Mixing
[0084] A certain mass of UO2 powder is put into a plowshare mixer. Based on the mass of the UO2 powder as the reference mass, the grain growth aids Cr2O3, Al2O3, the pore-forming agent ammonium oxalate, and the lubricant Aklax are added. Among them, the addition ratio of Cr2O3 is 0.12%, the addition ratio of Al2O3 is 0.01%, the addition ratio of the pore-forming agent ammonium oxalate is 0.4%, and the addition ratio of the lubricant Aklax is 0.05%.
[0085] The plowshare mixer is started, and an intermittent mixing process is adopted. Mix for 5 min, stop for 3 min, and repeat 30 mixing cycles. The cumulative effective mixing time is 150 min. The speed of the crushing knife is 3000 rpm, and the speed of the mixing knife is 100 rpm to make the materials mix evenly. During the stirring and mixing process, nitrogen is filled at a certain pressure to prevent the oxidation of the UO2 powder.
[0086] 2.2 Pelletizing
[0087] Use a dry granulator to granulate the above-mentioned mixed materials to increase the fluidity of the mixed materials and facilitate automatic filling of the press. The granulation pressure is 40 bar, and the loose bulk density of the powder after granulation is about 2.2 g / cm 3 。
[0088] During dry granulation, the mixed powder is first pressed into flakes by a roller device. These flakes enter the sizing device, are broken into fine particles by a rotating sizing roller, and flow out through a sieve with a set aperture (1.5 mm) to obtain qualified particles.
[0089] 2.3 Spheroidization
[0090] Load the granulated powder into the barrel of a double-cone mixer, add 0.3% lubricant Acker wax based on the mass of the spheroidized material, start the double-cone mixer, with a mixing time of 20 min and a rotation speed of 10 rpm to obtain materials with better fluidity.
[0091] 2.4 Pressing
[0092] Put the spheroidized powder into a press to press green compact cores. The density of the green compact cores is controlled at 5.8 g / cm 3 ~5.9 g / cm 3 ,and the height of the green compact cores is controlled at 15.6 mm - 16.0 mm, and the pressing pressure is controlled at 29 kN.
[0093] 2.5 Sintering
[0094] Send the green compact cores into a high-temperature sintering furnace for high-temperature sintering. The sintering temperature is 1750 °C, the high-temperature sintering time is 8 hours, and the sintering atmosphere is wet hydrogen with a dew point of 17 °C.
[0095] 2.6 Grinding
[0096] Put the sintered cores into a centerless grinder for external cylindrical grinding so that the diameter of the ground cores meets the specified requirements to obtain the final finished cores.
[0097] Analyze the finished cores obtained in Example 2 using a microscope, and obtain their metallographic diagrams as Figure 4 shown.
[0098] Analyze the finished cores obtained in Example 2, and obtain their sintered density of 96.8% T.D.; obtain the mass content of uranium in them as 88.14%; obtain the oxygen-to-uranium ratio as 2.00; obtain the total hydrogen content as 0.5 μg / UO2; obtain the equivalent boron content as 1.06 μg / gU; obtain the Cr content as 787 μg / gU.
[0099] When conducting the thermal stability test on the pellet, under the conditions of a holding temperature of 1715 °C, a holding time of 24 hours, and a test atmosphere of H2, the density increment of the pellet is less than 0.13% T.D.
[0100] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.
Claims
1. A method for batch preparation of large-grain UO2 pellets, characterized in that: The following steps are involved: S1) intermittently mixing UO2 powder, Cr2O3, Al2O3, a pore former and a first lubricant to obtain a mixed material; S2) granulating the mixture by dry granulation to obtain granules; S3) mixing the particulate matter with a second lubricant to obtain a particulate matter mixture; S4) pressing the particle mixture to obtain a green pellet; S5) sintering the green pellets at high temperature in a wet hydrogen atmosphere to obtain sintered pellets; S6) Grinding the sintered pellets to obtain large-grain UO2 pellets.
2. The batch preparation method according to claim 1, characterized in that: The mass of the Cr2O3 is 0.1% to 0.12% of the mass of the UO2 powder; The mass of the Al2O3 is 0.01% to 0.02% of the mass of the UO2 powder.
3. The batch preparation method according to claim 1, characterized in that: The pore-forming agent is selected from ammonium oxalate; The first lubricant and the second lubricant are each independently selected from aker wax and / or zinc stearate.
4. The batch preparation method according to claim 1, characterized in that: The mass of the pore former is 0.3% to 0.4% of the mass of the UO2 powder; The mass of the first lubricant is 0.04% to 0.06% of the mass of the UO2 powder; The mass of the second lubricant is 0.3% to 0.4% of the mass of the particulate matter.
5. The batch preparation method according to claim 1, characterized in that: The intermittent mixing in step S1) is specifically: mixing for 3 to 5 minutes, stopping for 3 to 5 minutes, repeating the mixing and stopping process, and the cumulative effective mixing time is not less than 60 minutes; The intermittent mixing is carried out by a ploughshare mixer; the rotation speed of the pulverizing blade of the ploughshare mixer is 3000-3300 rpm; the rotation speed of the mixing blade of the ploughshare mixer is 100-120 rpm; The intermittent mixing is carried out in a protective atmosphere.
6. The batch preparation method according to claim 1, characterized in that: The dry granulation pressure does not exceed 50 bar; the bulk density of the granules is 2.0 to 2.5 g / cm 3 .
7. The batch preparation method according to claim 1, characterized in that: The mixing speed in step S3) is 10-30 rpm; the mixing time is 20-40 min.
8. The batch preparation method according to claim 1, characterized in that: The density of the green pellet in step S4) is 5.8-6.2 g / cm 3 ; The height of the green core block is 15 to 16.5 mm; and the pressing pressure is 25 to 40 kN.
9. The batch preparation method according to claim 1, characterized in that: The temperature of the high temperature sintering in step S5) is 1740°C to 1750°C; the time of the high temperature sintering is 6 to 8 hours; and the dew point of the wet hydrogen atmosphere is 15°C to 25°C.
10. The batch preparation method according to claim 1, characterized in that: The average grain size of the large-grain UO2 pellets is 30 to 80 μm; The sintering density of the large-grain UO2 pellet is 95-97% TD.