Method for preparing uranium dioxide microspheres through cutting and rounding

Abstract

The invention belongs to the technical field of uranium dioxide microspheres of spherical elements such as high-temperature gas cooled reactor elements and other experimental reactor dispersion elements, and discloses a method for preparing uranium dioxide microspheres by cutting and rounding, which comprises the following steps of: adding microcrystalline cellulose or polyvinyl alcohol or methyl cellulose into UO2 powder, U3O8 powder or ThO2 powder according to the mass ratio of 0.3-0.4%; adding 20-25% by mass of water and ethanol into the mixed powder to form a soft material with viscoelasticity and plasticity, putting the soft material into an extruder, extruding and cutting through a screen, immediately transferring the extrudate to a spheronization machine to prepare microspheres, putting the microspheres into a microwave drying furnace, and drying to remove moisture and organic matters, so as to obtain the composite material. And putting the microspheres into a sintering furnace, heating, introducing hydrogen, sintering, cooling and discharging from the furnace. According to the invention, efficient preparation under the condition of the same yield is realized by optimizing the process steps and reducing the emission of three wastes.

Description

Technical Field

[0001] The present application belongs to the technical field of uranium dioxide microspheres for spherical components such as high-temperature gas-cooled reactor components and other experimental reactor dispersed components, and in particular relates to a method for preparing uranium dioxide microspheres by cutting and rolling. Background Art

[0002] The high-temperature gas-cooled reactor is my country's fourth-generation advanced reactor-type nuclear power technology with independent intellectual property rights. Its outstanding feature is inherent safety. The all-ceramic TRISO coated fuel particles it uses are the first barrier to its inherent safety characteristics. Each spherical fuel element with a diameter of about 60 mm is pressed and loaded with nearly 12,000 coated fuel particles.

[0003] The existing microspheres are mainly prepared using sol-gel technology. The process includes dissolving uranium oxide in a low-acid state, boiling and preparing the gel, dispersion, aging and washing, drying, roasting, reduction, and sintering. The process is long and produces a certain amount of extremely low-level radioactive wastewater, which needs to be optimized. Summary of the Invention

[0004] The purpose of this application is to overcome the defects of the existing technology and provide a method for preparing uranium dioxide microspheres by cutting and rolling. By innovating and establishing a new process method, efficient preparation is achieved under the same output conditions.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] A method for preparing uranium dioxide microspheres by cutting and spheronization, comprising:

[0007] Step 1: Add microcrystalline cellulose or polyvinyl alcohol or methyl cellulose to UO2 powder, U3O8 powder or ThO2 powder at a mass ratio of 0.3% to 0.4% and mix evenly;

[0008] Step 2: Add water and ethanol in a mass ratio of 20% to 25% to the mixed powder and mix them evenly to make a soft material with viscoelasticity and plasticity;

[0009] Step 3: Place the soft material into the extruder and extrude and cut it through the screen;

[0010] Step 4: The extrudate is immediately transferred to a spheronizer to form microspheres;

[0011] Step 5: Place the microspheres in a microwave drying oven to dry and remove moisture and organic matter;

[0012] Step 6: Place the microspheres in a sintering furnace, heat to 1500℃~1600℃, and introduce hydrogen at a flow rate of 1.5Nm 3 / h~3Nm 3 / h, sintering, cooling and taking out of the furnace.

[0013] As an practicable method, in step 1, microcrystalline cellulose is added to U3O8 powder at a mass ratio of 0.4%, and the mixture is put into a three-dimensional mixer for mixing, and the uniformly mixed material is put into a container.

[0014] As an practicable method, the U3O8 microspheres formed in step 4 are placed in a microwave drying furnace and dried at 95°C for 25 min; the U3O8 microspheres are placed in a sintering furnace, heated to 1600°C, and hydrogen is introduced at a flow rate of 3 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0015] As an practicable method, in step 1, polyvinyl alcohol is added to UO2 powder at a mass ratio of 0.3%, and the mixture is placed in a three-dimensional mixer for mixing, and the uniformly mixed material is placed in a container.

[0016] As an practicable method, the ThO2 microspheres formed in step 4 are placed in a microwave drying furnace and kept at 120°C for 20 min; the ThO2 microspheres are placed in a sintering furnace, heated to 1600°C, and hydrogen is introduced at a flow rate of 3 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0017] As an practicable method, in step 1, microcrystalline cellulose is added to ThO2 powder at a mass ratio of 0.4%, and the mixture is placed in a three-dimensional mixer for mixing, and the uniformly mixed material is placed in a container.

[0018] As an practicable method, in step 1, microcrystalline cellulose is added to UO2 powder at a mass ratio of 0.4%, and the mixture is put into a three-dimensional mixer for mixing, and the uniformly mixed material is put into a container.

[0019] As an practicable method, in step 1, polyvinyl alcohol auxiliary material is added to UO2 powder at a mass ratio of 0.3%, and the mixture is placed in a three-dimensional mixer for mixing, and the uniformly mixed material is placed in a container.

[0020] As an practicable method, the UO2 microspheres formed in step 4 are placed in a calcination drying furnace, an oxygen flow rate of 0.5 Nm3 / h is introduced, and the temperature is kept at 320°C for 6 hours to dry and remove moisture and organic matter to obtain UO3 microspheres;

[0021] The UO3 microspheres were placed in the reduction furnace and a mixture of 10% hydrogen and 90% argon was introduced at a gas flow rate of 0.5 Nm 3 / h, keep at 750℃ for 2h, UO3 microspheres are reduced to UO2 microspheres;

[0022] The UO2 microspheres were placed in a sintering furnace, heated to 1550°C, introduced with a hydrogen flow rate of 1.5 Nm3 / h, sintered for 48 hours, and then cooled and taken out of the furnace.

[0023] As an practicable method, in step 3, a screen with an aperture of 0.4 mm to 0.5 mm is selected for extrusion and cutting, and the length of the long strip is 2 to 3 times the diameter.

[0024] Compared with the prior art, the method for preparing uranium dioxide microspheres by cutting and spheronization provided in this application has the following beneficial effects:

[0025] The present application provides a non-liquid phase process for preparing uranium oxide microspheres for nuclear fuel. Specifically, a method for preparing microspheres by using a uranium oxide cutting and spheronization process is designed. This method achieves efficient preparation under the same output conditions by optimizing process steps and reducing the emission of three wastes.

[0026] Experimental results show that the uranium oxide microspheres prepared in this application achieve the same quality as existing products. While eliminating the numerous chemical conversion processes, associated operating equipment, and raw materials required during the liquid-phase preparation process, this significantly reduces production and human resource costs. Furthermore, this process is environmentally friendly, providing a more economical and environmentally friendly solution for the industrialized production of nuclear fuel microspheres and contributing to the advancement of high-temperature gas-cooled reactor component manufacturing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings required for the technical description.

[0028] Figure 1 Flowchart of the method for preparing uranium dioxide microspheres by cutting and spheronization provided in this application. DETAILED DESCRIPTION

[0029] The following is further explained in detail through specific implementation methods.

[0030] like Figure 1 As shown, the present application provides a method for preparing uranium dioxide microspheres by cutting and rolling, comprising the following steps:

[0031] Step 1: Homogenize the materials: Add microcrystalline cellulose (MCC) or polyvinyl alcohol, methyl cellulose and other auxiliary materials to the UO2 powder at a mass ratio of 0.3% to 0.4%, mix in a mixer for 20 to 30 minutes, and then put the mixed materials into a container. The container is the container for holding the mixed powder and preparing the soft material in the cutting and spheronization equipment.

[0032] Step 2: Making a soft material: Evenly add water and ethanol (20% to 25% by mass) to the mixed uranium dioxide powder, mix well, and make it into a soft material with moderate viscoelasticity and plasticity.

[0033] Step 3: Soft material extrusion: Place the soft material into the extruder and select a screen with a pore size of 0.4mm to 0.5mm for extrusion and cutting. The length of the long strip is 2 to 3 times the diameter.

[0034] Step 4: Spheronization: The extrudate is immediately transferred to a spheronization machine and rolled into a spherical shape under the action of friction and centrifugal force.

[0035] Step 5: Drying: Place the uranium dioxide microspheres in a microwave drying oven to dry and remove most of the moisture and organic matter.

[0036] Step 6: Reduction sintering: Place the uranium dioxide microspheres in a sintering furnace, heat to 1500-1600°C, and introduce hydrogen at a flow rate of 1.5 Nm 3 / h~3.0Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0037] This application uses a "non-liquid phase" process, while the existing sol-gel process, from nitric acid dissolution to gel boiling, gel preparation, dispersion, and aging, is all carried out in liquid. This process requires oxidizing uranium dioxide powder to uranium trioxide octoxide powder, then dissolving the uranium trioxide octoxide powder in an acid-free solution to form uranyl nitrate. Urea, ammonium nitrate, polyvinyl alcohol, tetrahydrofurfuryl alcohol, and other auxiliary materials are then added through gel boiling and gel preparation to produce a sol solution. The sol solution is then dispersed to create tiny droplets that react with ammonia gas and aqueous ammonia and age to form solid ammonium diuranate particles. The ammonium diuranate particles are then washed, dried, roasted, and reduced to uranium dioxide particles to be sintered.

[0038] The cutting and spheronization process employed in this application uses solids for preparation. Uranium dioxide powder is used as the primary material, combined with auxiliary materials such as a binder, and then directly cut and spheronized. After drying, the uranium dioxide particles to be sintered are obtained. This process eliminates the liquid-phase chemical conversion process, as well as steps such as roasting and reduction. It differs fundamentally from the sol-gel process in terms of operational complexity and the input of primary and auxiliary materials.

[0039] This application adopts the cutting and spheronization technology to prepare uranium dioxide (uranium trioxide, uranium octoxide, thorium dioxide, etc.) powder and auxiliary materials (microcrystalline fiber, methyl cellulose, polyvinyl alcohol, alcohol, water, etc.) into a wet material with a certain plasticity. After being extruded through an extruder, the material is subjected to self-rotation and friction rolling on a spheronization machine to prepare uranium-containing microspheres that meet the requirements of nuclear fuel.

[0040] The present application prepares uranium-containing microspheres for use in the reactor component manufacturing field by a cutting and spheronization method, and the raw materials thereof include but are not limited to uranium dioxide, uranium trioxide, uranium trioxide, ammonium diuranate, as well as thorium dioxide, lithium aluminate, lithium titanate, and other raw materials that can be used for nuclear fuel elements and targets.

[0041] Example 1

[0042] Step 1: Add microcrystalline cellulose (MCC) to U3O8 powder at a mass ratio of 0.4%, put it into a three-dimensional mixer, mix it for 25 minutes, and then put the mixed material into a special container.

[0043] Step 2: Evenly add water and ethanol (25% by mass) to the above-mentioned mixed U3O8 powder and mix them evenly to form a soft material with moderate viscoelasticity and plasticity.

[0044] Step 3: Place the soft material into the extruder, select a mesh size of 0.4mm to 0.5mm, and extrude and cut it. The length of the long strip is 2.5 times the diameter.

[0045] Step 4: The extrudate is immediately transferred to a spheronizer and rolled into a spherical shape under the action of friction and centrifugal force.

[0046] Step 5: Place the U3O8 microspheres in a microwave drying oven and dry them at 95°C for 25 minutes to remove most of the moisture and organic matter.

[0047] Step 6: Place the above U3O8 microspheres into a sintering furnace, heat it to 1600℃, and introduce hydrogen at a flow rate of 3.0Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0048] Example 2

[0049] Step 1: Add polyvinyl alcohol auxiliary material to UO2 powder at a mass ratio of 0.3%, put it into a three-dimensional mixer, mix it for 30 minutes, and then put the evenly mixed material into a special container.

[0050] Step 2: Add water and ethanol (25% by mass) to the above-mentioned mixed UO2 powder and mix them evenly to form a soft material with moderate viscoelasticity and plasticity.

[0051] Step 3: Place the soft material into the extruder, select a mesh size of 0.4mm, and extrude and cut it. The length of the long strip is twice the diameter.

[0052] Step 4: The extrudate is immediately transferred to a spheronizer and rolled into a spherical shape under the action of friction and centrifugal force.

[0053] Step 5: Place the uranium dioxide microspheres into a roasting and drying furnace and introduce nitrogen at a flow rate of 0.5 Nm 3 / h, keep warm at 500℃ for 2h, and dry to remove most of the moisture and organic matter.

[0054] Step 6: Place the uranium dioxide microspheres in a sintering furnace, heat to 1550°C, and introduce hydrogen at a flow rate of 1.5 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0055] Example 3

[0056] Step 1: Add microcrystalline cellulose (MCC) to ThO2 powder at a mass ratio of 0.4%, put it into a three-dimensional mixer, mix it for 30 minutes, and then put the mixed material into a special container.

[0057] Step 2: Add water and ethanol at a mass ratio of 25% to the above-mentioned evenly mixed ThO2 powder, and mix them evenly to form a soft material with moderate viscoelasticity and plasticity.

[0058] Step 3: Place the soft material into the extruder, select a screen aperture of 0.4mm to 0.5mm, and extrude and cut it. The length of the long strip is 2 to 3 times the diameter.

[0059] Step 4: The extrudate is immediately transferred to a spheronizer and rolled into a spherical shape under the action of friction and centrifugal force.

[0060] Step 5: Place the ThO2 microspheres in a microwave drying oven and keep them at 120°C for 20 minutes to dry and remove most of the moisture and organic matter.

[0061] Step 6: Place the above ThO2 microspheres into a sintering furnace, heat it to 1600°C, and introduce hydrogen at a flow rate of 2.0 Nm 3 / h, sinter for 24 hours, cool down and take out of the furnace.

[0062] Example 4

[0063] Step 1: Add 0.4% by mass of microcrystalline cellulose (MCC) to UO2 powder, put it into a three-dimensional mixer, mix it for 25 minutes, and then put the mixed material into a special container.

[0064] Step 2: Add water and ethanol at a mass ratio of 25% to the above-mentioned mixed UO2 powder, and mix them evenly to form a soft material with moderate viscoelasticity and plasticity.

[0065] Step 3: Place the soft material into the extruder, select a mesh size of 0.4mm to 0.5mm, and extrude and cut it. The length of the long strip is 2.5 times the diameter.

[0066] Step 4: The extrudate is immediately transferred to a spheronizer and rolled into a spherical shape under the action of friction and centrifugal force.

[0067] Step 5: Place the UO2 microspheres in a microwave drying oven and dry them at 95°C for 25 minutes to remove most of the moisture and organic matter.

[0068] Step 6: Place the uranium dioxide microspheres in a sintering furnace, heat to 1550°C, and introduce hydrogen at a flow rate of 1.5 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0069] Example 5

[0070] Step 1: Add polyvinyl alcohol auxiliary material to UO2 powder at a mass ratio of 0.3%, put it into a three-dimensional mixer, mix it for 30 minutes, and then put the evenly mixed material into a special container.

[0071] Step 2: Add water and ethanol (25% by mass) to the above-mentioned mixed UO2 powder and mix them evenly to form a soft material with moderate viscoelasticity and plasticity.

[0072] Step 3: Place the soft material into the extruder, select a mesh size of 0.4mm, and extrude and cut it. The length of the long strip is twice the diameter.

[0073] Step 4: The extrudate is immediately transferred to a spheronizer and rolled into a spherical shape under the action of friction and centrifugal force.

[0074] Step 5: Place the uranium dioxide microspheres into a roasting and drying furnace and introduce oxygen at a flow rate of 0.5 Nm 3 / h, and kept at 320℃ for 6h to dry and remove most of the water and organic matter to obtain uranium trioxide microspheres.

[0075] Step 6: Place the uranium trioxide microspheres into the reduction furnace and introduce a mixture of hydrogen (10%) and argon (90%) at a flow rate of 0.5 Nm 3 / h, and kept at 750℃ for 2h, the uranium trioxide microspheres were reduced to uranium dioxide microspheres and were preliminarily sintered.

[0076] Step 7: Place the above uranium dioxide microspheres into a sintering furnace, heat it to 1550°C, and introduce hydrogen at a flow rate of 1.5 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

[0077] The above description is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in this application should be covered by the scope of protection of the present application.

Claims

1. A method for preparing uranium dioxide microspheres by cutting and spheronization, characterized in that: include: Step 1: Add microcrystalline cellulose or polyvinyl alcohol or methyl cellulose to UO2 powder, U3O8 powder or ThO2 powder at a mass ratio of 0.3% to 0.4% and mix evenly; Step 2: Add water and ethanol in a mass ratio of 20% to 25% to the mixed powder and mix them evenly to make a soft material with viscoelasticity and plasticity; Step 3: Place the soft material into the extruder and extrude and cut it through the screen; Step 4: The extrudate is immediately transferred to a spheronizer to form microspheres; Step 5: Place the microspheres in a microwave drying oven to dry and remove moisture and organic matter; Step 6: Place the microspheres in a sintering furnace, heat to 1500℃~1600℃, and introduce hydrogen at a flow rate of 1.5Nm 3 / h~3Nm 3 / h, sintering, cooling and taking out of the furnace.

2. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 1, characterized in that: In step 1, microcrystalline cellulose is added to U3O8 powder at a mass ratio of 0.4%, and the mixture is put into a three-dimensional mixer for mixing, and the uniformly mixed material is put into a container.

3. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 2, characterized in that: The U3O8 microspheres formed in step 4 were placed in a microwave drying furnace and dried at 95°C for 25 min. The U3O8 microspheres were placed in a sintering furnace, heated to 1600°C, and hydrogen was introduced at a flow rate of 3 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

4. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 1, characterized in that: In step 1, polyvinyl alcohol is added to UO2 powder at a mass ratio of 0.3%, and the mixture is placed in a three-dimensional mixer for mixing, and the uniformly mixed material is placed in a container.

5. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 4, characterized in that: The ThO2 microspheres formed in step 4 were placed in a microwave drying furnace and kept at 120°C for 20 min; the ThO2 microspheres were placed in a sintering furnace, heated to 1600°C, and hydrogen was introduced at a flow rate of 3 Nm 3 / h, sinter for 48 hours, cool down and take out of the furnace.

6. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 1, characterized in that: In step 1, microcrystalline cellulose is added to ThO2 powder at a mass ratio of 0.4%, and the mixture is placed in a three-dimensional mixer for mixing, and the uniformly mixed material is placed in a container.

7. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 1, characterized in that: In step 1, 0.4% microcrystalline cellulose is added to UO2 powder, the mixture is put into a three-dimensional mixer for mixing, and the uniformly mixed material is put into a container.

8. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 1, characterized in that: In step 1, 0.3% by mass of polyvinyl alcohol auxiliary material is added to the UO2 powder, the mixture is put into a three-dimensional mixer for mixing, and the evenly mixed material is put into a container.

9. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 8, characterized in that: The UO2 microspheres formed in step 4 were placed in a calcination and drying furnace, oxygen flow rate was 0.5 Nm3 / h, and the temperature was kept at 320°C for 6 hours to dry and remove moisture and organic matter to obtain UO3 microspheres; The UO3 microspheres were placed in the reduction furnace and a mixture of 10% hydrogen and 90% argon was introduced at a gas flow rate of 0.5 Nm 3 / h, keep at 750℃ for 2h, UO3 microspheres are reduced to UO2 microspheres; The UO2 microspheres were placed in a sintering furnace, heated to 1550°C, introduced with a hydrogen flow rate of 1.5 Nm3 / h, sintered for 48 hours, and then cooled and taken out of the furnace.

10. The method for preparing uranium dioxide microspheres by cutting and spheronization according to claim 1, characterized in that: In step 3, a screen with an aperture of 0.4 mm to 0.5 mm is selected for extrusion and cutting, and the length of the long strip is 2 to 3 times the diameter.

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