A method of manufacturing a shaped multi-leaf helical nuclear fuel element

Abstract

The application relates to a manufacturing method of a special-shaped multi-leaf spiral nuclear fuel element, and relates to a nuclear fuel element manufacturing method. The application is used to solve the problems of difficult operation and difficult guarantee of cross-section precision in the manufacturing process of the special-shaped multi-leaf spiral nuclear fuel element. The steps of the application comprise the following steps: step 1, mixing base powder and dispersion body simulated nuclear fuel; step 2, filling the mixed nuclear fuel powder into a preformed four-leaf cladding tube; step 3, placing the four-leaf preformed cladding tube filled with the nuclear fuel powder into a multi-roller rolling device, and gradually rolling the filled tube into a special-shaped multi-leaf fuel rod by means of each group of opposite rollers; step 4, pushing the rolled special-shaped multi-leaf fuel rod through a profiled guide tube to the outer mold spiral cavity of a twisting device by utilizing the friction force of a final rolling roller; and step 5, driving the right fuel rod of the twisting mold to do axial and rotary motion under the driving of a rotary motor and an axial motor. The application belongs to the technical field of nuclear fuel element manufacturing.

Description

Technical Field

[0001] This invention relates to a method for manufacturing nuclear fuel elements, belonging to the field of nuclear fuel element manufacturing technology. Background Technology

[0002] The high efficiency, economy, and cleanliness of nuclear energy have increasingly made it a focus of global energy development. To further improve the safety and efficiency of nuclear reactors, new nuclear fuel elements are required to possess characteristics such as large heat exchange area, good thermal conductivity, short refueling cycle, and high safety. Metallic nuclear fuel elements are better positioned to meet these requirements. Furthermore, traditional nuclear fuel elements, with their mostly circular outer shells, suffer from poor rigidity, small heat exchange area, and poor heat transfer performance. In recent years, a new type of fuel element has garnered increasing attention in the nuclear power industry, exhibiting a multi-bladed helical rod structure with two, three, or four blades.

[0003] Russia was the first country in the world to develop this type of multi-bladed spiral fuel element, with related reports appearing as early as the 1980s. Currently, the Russian company ZETM has developed it to its third generation, primarily used on icebreakers. Their patents disclose a four-bladed spiral fuel element rod with a pitch of 21.5 cm and an outer circle diameter of 12.6 mm. This four-bladed spiral fuel element rod has a replacement device at its center with a square area of ​​1.5–3.5 mm on each side. The American company Lightbridge has also published the processing of a similar multi-bladed spiral fuel element, explaining that this spiral shape enhances the overall rigidity of the element, reduces the positioning grid, and that the spiral ribs enhance the lateral mixing effect. Tsinghua University in China has also published a method for manufacturing similar multi-spiral twisted fuel elements through co-extrusion.

[0004] Currently, the internationally and domestically available patents related to multi-bladed spiral fuel rods only describe the filler type, element geometry, and fuel element arrangement. Reports on the processing methods of multi-bladed spiral fuel elements are scarce or vague. Research indicates that co-extrusion and drawing / twisting methods are the most common, but these methods present numerous technical challenges. During processing, ensuring the dimensional accuracy of the tube cross-section is difficult, and the mechanical bonding between the cladding and the powder is poor, indicating ongoing issues in the manufacturing process. Summary of the Invention

[0005] This invention addresses the problems of difficult operation and inability to guarantee cross-sectional accuracy in existing manufacturing processes for irregularly shaped multi-lobed helical nuclear fuel elements, and proposes a method for manufacturing irregularly shaped multi-lobed helical nuclear fuel elements. The technical solution adopted by the present invention to solve the above problems is as follows: The steps of the present invention include: Step 1: Mix the matrix powder and the dispersed material to simulate nuclear fuel; Step 2: Fill the mixed nuclear fuel powder into the pre-formed four-leaf cladding tube; Step 3: Place the four-lobed preformed cladding tube filled with nuclear fuel powder into a multi-roller pressing device, and use each set of rollers to gradually roll the powder-filled tube into an irregular multi-lobed fuel rod. Step 4: Using the friction of the final roll, the roll-formed irregular multi-leaf fuel rod is pushed forward through the contour guide tube into the outer mold spiral cavity of the twisting device, and then gradually pushed out in a spiral shape. The right end of the spiral section is then clamped by the spiral traction head. Step 5: Driven by the rotary motor and the axial motor, the helical traction head drives the fuel rod on the right side of the twisting mold to perform axial and rotational movements, causing it to twist into a helical angle along the axial direction of the irregularly shaped multi-lobed fuel rod. The process continues until all the irregularly shaped multi-lobed fuel rods, which have undergone multiple reduction rolling processes, are finally twisted into spiral irregularly shaped multi-lobed fuel rods.

[0006] Furthermore, the diameter of the blank is designed based on the circumference of the finished pipe: The circumference of the finished pipe is Based on the assumption that the circumference of the rolled tube remains unchanged, the radius of the billet is calculated. : ①, In formula ①, Indicates the radius of the round tube blank; After determining the pipe radius, calculate the density of the filler powder and the cross-sectional area of ​​the billet pipe. and core powder density There is a mathematical relationship between them. The cross-sectional area is calculated based on the shape and size requirements of the rolled filler rod. and core : ②, ③, In formula ③, the core filler rod density and cross-sectional area To determine the value, the rolling elongation factor Calculations based on actual processing and production show that the composition is related to the powder used. This invention uses an Al-WC mixed powder. v This represents the volume fraction of WC (when the volume fraction of WC is 30%, here...). v =0.3). Wherein, elongation coefficient... The value of and the volume of WC v The relationship exhibits a positive exponential correlation, as shown in formula ③. Based on formula ③, the cross-sectional area of ​​the round billet tube and its corresponding loose packing density are designed and determined. .

[0007] During processing, the filler rods are rolled to achieve density. Cross-sectional area of ​​filler rod It is certain. And the elongation coefficient... The cross-sectional area of ​​the billet tube is determined. With tap density The mathematical relationship between them allows for the design of the pipe cross-sectional area based on process requirements. Harmony and vibration density For example, when the cross-sectional area of ​​the self-designed billet drawn into the tube... It is certain, therefore the rolling elongation of the filler rod is... Become the vibration-tap density The determining factor. This invention, through rolling experiments on filler rods with different WC volumes, and by fitting and analyzing the experimental results, derives a highly accurate elongation coefficient. Based on the functional relationship between Al-WC volume and WC volume ③, a suitable tap density of Al-WC mixed powder can be calculated. ,vice versa.

[0008] Furthermore, in step 1, the matrix powder is either a single-element powder or a multi-element mixed powder. The single-element powder or the multi-element mixed powder is placed in a vacuum drying oven for drying, and the dried multi-element powder is then mixed evenly.

[0009] Furthermore, in step 2, the mixed nuclear fuel powder is filled into the pre-formed four-leaf cladding tube and then compacted. After compaction, both ends of the four-leaf cladding tube are sealed with hot melt adhesive.

[0010] Furthermore, the preformed four-leaf cladding tube filled with powder is placed in a multi-roller pressing device for multiple sets of rolling. The roll profile size of the rolls in the multi-roller pressing device gradually decreases, and the last two sets of roll grooves are the same as the cross-sectional shape and size of the finished simulated fuel element.

[0011] Furthermore, the multi-roll pressing device and the twisting device constitute a rolling-twisting equipment. The multi-roll pressing device consists of 10-24 sets of rolls, each set of rolls contains two rolling wheels, and the two rolling wheels are symmetrically distributed. The rolling wheel groove transitions from the pre-formed size to the irregular blade size. Under the action of the drive mechanism, the powder-filled pipe is rolled into shape. The twisting device consists of a twisting die and a traction device, and the multi-roller pressing device is connected to the twisting device through a contour guide tube.

[0012] Furthermore, based on the theoretical helix angle of the fuel rod... The requirement is to set the helix angle of the outer mold cavity during the twisting process to... This ensures that the final product is a uniquely shaped multi-bladed spiral simulated fuel element that meets the spiral angle requirements; The actual formula for calculating the torsion angle is:

[0013] In formula ④, Indicates the actual twist angle. Indicates the pipe pitch. In formula ⑤, the springback angle is represented. v The volume fraction of WC is used to represent the springback angle of Al-WC powder. Through extensive experimental testing, this angle was determined. It has a linear relationship with the volume fraction of WC.

[0014] The beneficial effects of this invention are as follows: This invention manufactures simulated fuel rods through a multi-segment rolling-twisting composite processing method, integrating multi-roll rolling and twisting processes into a single rolling-twisting integral forming device. This saves equipment costs, improves the continuity of the processing technology, and significantly increases the processing efficiency of the finished pipes. The step-by-step, tiered processing method makes the processing requirements of each step clearer. By reducing the processing difficulty of each step and improving the processing accuracy of each step, the overall manufacturing difficulty and the overall processing failure risk are reduced, and the overall dimensional accuracy of the simulated fuel rods is improved. The manufacturing of irregularly shaped multi-bladed spiral simulated fuel elements through multi-segment rolling and spiral twisting provides better process control. Furthermore, the multiple rolling and diameter reduction of the pipe significantly reduces the deformation difficulty and increases the cross-sectional dimensions of the element. The twisting spiral improves the uniformity, controllability, and yield of the pitch of the irregularly shaped multi-bladed spiral simulated fuel elements, while also significantly saving equipment costs and improving processing efficiency. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the powder filling process in a circular billet tube; Figure 2 This is a schematic diagram of the cross-sectional shape of the roll and the roll groove; Figure 3 This is a schematic diagram of the distribution of each group of rolls and the roll shape structure in a multi-roll pressing device; Figure 4 This is a schematic diagram of the cross-section and longitudinal section of the tube structure after the fuel rod has been rolled by a multi-roller pressing device. Figure 5 This is a schematic diagram of the rolling-twisting equipment. Figure 6 This is a longitudinal schematic diagram of a spiral simulated fuel rod after it has been twisted by a twisting device. Detailed Implementation

[0016] Specific Implementation Method 1: A method for manufacturing an irregularly shaped multi-leaf spiral nuclear fuel element, wherein the cross-section of the blades of the irregularly shaped multi-leaf spiral nuclear fuel element is irregularly shaped with multiple leaves or a plum blossom shape as shown in the figure, the pitch is 400mm, the total length of the simulated nuclear fuel region is 1000mm, the outer circle diameter is 5mm, the cladding tube wall thickness is 0.1mm, the core density is 95%, and the compacted cross-sectional area S is 9.5mm². 2 The perimeter is 16.57 mm, and the core powder is a mixture of aluminum powder and tungsten powder, with a particle size of [missing information]. The volume ratio of aluminum powder to tungsten powder is 6:4; the specific manufacturing steps include: Step 1: The target cross-section can be a standard irregular multi-leaf type, or the blades can be arc-shaped or cosine-shaped; based on the shape of the target product and the inner cross-sectional area and outer circumference of the pipe after compaction, the diameter of the round pipe blank and the compaction density of the powder filling are theoretically designed. The circumference of the finished pipe is Based on the assumption that the circumference of the rolled tube remains unchanged, the radius of the billet can be calculated: , in, Indicates the radius of the round tube blank; Once the pipe radius is determined, the density of the filler powder is calculated using the following formula:

[0017] The target product requires a core density of not less than 95% and a compacted cross-sectional area S of 9.5 mm². 2 The circumference is 16.57mm. The value is 1.2. The WC content is 40%, therefore here... v The value is 0.4. Based on the above formula, the diameter of the pipe blank is 5mm, and the loose packing density is 0.46. Step 2: Mix the metal matrix powder and the simulated fuel powder (tungsten powder, etc.); In the simulated fuel powder core 2, the metal matrix powder is selected as aluminum powder matrix, and the simulated fuel powder is a powder with the same density as nuclear fuel powder, such as tungsten powder, tungsten carbide powder or tungsten-molybdenum alloy powder. The aluminum powder matrix and the simulated fuel powder can be mixed at a volume ratio of 10% to 50%. In the embodiment, there are no restrictions on the volume ratio and mixing method of the metal matrix powder and the simulated fuel powder. Tungsten powder was selected as the simulated fuel powder, and the theoretical density of the Al-WC mixed powder (volume ratio = 6:4) was 7.87 g / cm³. 3 The total weight of the filler powder is 142.41g, aluminum powder is 29.31g, and tungsten powder is 113.10g; In this step, before mixing the metal powder and the simulated fuel powder, the powder is vacuum-dried in a vacuum drying oven at a temperature of 60-100°C and a vacuum degree of not less than 10. -3 MPa, drying time not less than 1 hour, to ensure the drying of metal matrix powder and simulated fuel powder; Step 3: Fill the outer casing 1 with the mixed simulated fuel core 2; The mixed simulated nuclear fuel powder is filled into a round billet tube. During the filling process, the tube is vibrated to ensure that the powder is distributed in a certain density in the pre-drawn tube. Step 4: Place the pipe 3, after being filled with simulated fuel powder, at the inlet end of the multi-roll rolling device of the multi-roll rolling-twisting equipment for multi-roll rolling, such as... Figure 2 As shown; Based on the cross-sectional shape and dimensions of the final formed simulated fuel rod, a 20-roll rolling mill was designed, with the rolls arranged as follows: Figure 3 As shown, the distribution of the rolls in each pass is rotated by 90°, and the distribution pattern is longitudinal-transverse-longitudinal. The distance D between the front and rear rolls is the same. Each group of rolls is distributed in a relative manner. Each roll rotates around its own axis, and the fuel rod to be rolled moves along the axis under the action of the roll friction force. The rollers of group 4 are distributed in the same way as the rollers 5 and 6, forming roller grooves 8. The groove size of each group of rollers gradually transitions from the tube 3 after filling with powder to the final forming size 9. The main forming process during rolling is the roll forming by 8a and 8b acting on the outer wall of the simulated fuel rod. During the progressive roll forming process of multiple rollers, the gradual deformation of the outer shell causes the core to gradually deform into a standard irregular multi-leaf simulated fuel rod 9. Key parts 9c and 9d are formed to the target size under the action of roll grooves 8a and 8b. The mixed fuel powder 12a aluminum powder and 12b mixed simulated fuel powder are denser under the force of roll grooves 8a and 8b, and are formed together with the shell into an irregular multi-leaf simulated fuel rod. Step 5: After the multi-leaf simulated fuel rod is formed by multi-roll rolling 16, it enters the twisting die of the twisting device through the conformal guide tube 15. The end of the formed tube is clamped by the traction end 14 of the twisting device, and under the action of the traction device 14, it moves in a spiral motion along the motion axis, such as... Figure 5 As shown; Step 6: The rolled finished pipe passes through the spiral die inlet transition zone 12a, then through the spiral region 12b. Under the traction force of the spiral device, the simulated fuel rod 12 passes through the spiral region 12b and forms four-petal petals 13d and spiral grooves 13c axially. The spiral angle is... The irregularly shaped, multi-lobed, spiral-shaped simulated fuel rod 13, such as Figure 6 As shown; Design the helix angle of the twisting mold. ,in The springback angle needs to be determined based on the pitch of the target product. Through theoretical calculations and repeated experimental verification and iterations, the helix angle of the twisting die was finally determined. The actual helix angle of the mold is calculated according to the following formula;

[0018] In the formula, This is the actual twist angle. For pipe thread pitch, For the rebound angle, v The volume fraction of WC is represented by the spring angle, which has a linear relationship with the volume fraction of WC.

[0019] In this embodiment, the pipe pitch is 400 mm and the volume fraction of WC is 40%. v =0.4. Therefore, the springback angle Δω in this case is 0.184, and the calculated actual helix angle is 1.122°.

[0020] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for manufacturing an irregularly shaped, multi-lobed, spiral nuclear fuel element, characterized in that, The specific steps include: Step 1: Mix the matrix powder and the dispersed material to simulate nuclear fuel; Step 2: Fill the mixed nuclear fuel powder into the pre-formed four-leaf cladding tube; Step 3: Place the four-lobed preformed cladding tube filled with nuclear fuel powder into a multi-roller pressing device, and use each set of rollers to gradually roll the powder-filled tube into an irregular multi-lobed fuel rod. Step 4: Using the friction of the final roll, the roll-formed irregular multi-leaf fuel rod is pushed forward through the contour guide tube into the outer mold spiral cavity of the twisting device, and gradually pushed out in a spiral shape. The right end of the spiral section is then clamped by the spiral traction head. Step 5: Driven by the rotary motor and the axial motor, the helical traction head drives the fuel rod on the right side of the twisting mold to perform axial and rotational movements, causing it to twist into a helical angle along the axial direction of the irregularly shaped multi-lobed fuel rod. Until the multi-stage diameter reduction rolling process is completed, the irregularly shaped multi-leaf fuel rods are finally twisted and formed into spiral irregularly shaped multi-leaf fuel rods. The diameter of the blank is designed based on the circumference of the finished pipe: The circumference of the finished pipe is Based on the assumption that the circumference of the rolled tube remains unchanged, the radius of the billet is calculated. : ①， In formula ①, Indicates the radius of the round tube blank; After determining the pipe radius, calculate the density of the filler powder and the cross-sectional area of ​​the billet pipe. and core powder density There is a mathematical relationship between them. The cross-sectional area is calculated based on the shape and size requirements of the rolled filler rod. and core : ②， ③， In formula ①, This indicates the rolling density of the filler rod. This represents the cross-sectional area of ​​the filler rod. This represents the rolling elongation coefficient, with a value between 1.02 and 1.3, depending on the powder used. v This represents the volume fraction of WC.

2. The method for manufacturing an irregularly shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that, In step 1, the matrix powder is either a single-element powder or a multi-element mixed powder. The single-element powder or the multi-element mixed powder is placed in a vacuum drying oven for drying, and the dried multi-element powder is then mixed evenly.

3. The method for manufacturing an irregularly shaped multi-lobed helical nuclear fuel element according to claim 1, characterized in that, In step 2, the mixed nuclear fuel powder is filled into the pre-formed four-leaf cladding tube and then compacted. After compaction, the two ends of the four-leaf cladding tube are sealed with hot melt adhesive.

4. The method for manufacturing an irregularly shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that, The preformed four-leaf cladding tube filled with powder is placed in a multi-roller pressing device for multiple sets of rolling. The roll profile size of the rolls in the multi-roller pressing device gradually decreases, and the last two sets of roll grooves are the same as the cross-sectional shape and size of the finished simulated fuel element.

5. The method for manufacturing an irregularly shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that, The rolling-twisting equipment consists of a multi-roll pressing device and a twisting device. The multi-roll pressing device consists of 10-24 sets of rolls. Each set of rolls contains two rolling wheels, which are symmetrically distributed. The rolling wheel groove transitions from the pre-formed size to the size of the irregular blade. Under the action of the drive mechanism, the powder-filled pipe is rolled into shape. The twisting device consists of a twisting die and a traction device, and the multi-roller pressing device is connected to the twisting device through a contour guide tube.

6. The method for manufacturing an irregularly shaped multi-lobed helical nuclear fuel element according to claim 1, characterized in that, Based on the theoretical helix angle of the fuel rod The requirement is to set the helix angle of the outer mold cavity during the twisting process to... This ensures that the final product is a uniquely shaped multi-bladed spiral simulated fuel element that meets the spiral angle requirements; The actual formula for calculating the torsion angle is: In formula ④, Indicates the actual twist angle. Indicates the pipe pitch. In formula ⑤, the springback angle is represented. v The volume fraction of WC is used to represent the springback angle of Al-WC powder. Through extensive experimental testing, this angle was determined. It has a linear relationship with the volume fraction of WC.

Images