Manufacturing method of special-shaped multi-blade spiral nuclear fuel element

Abstract

The invention relates to a manufacturing method of a nuclear fuel element, in particular to a manufacturing method of a special-shaped multi-blade spiral nuclear fuel element. The problems that an existing special-shaped multi-blade spiral nuclear fuel element manufacturing process is difficult to operate, and the section precision is difficult to guarantee are solved. The method comprises the following steps: step 1, mixing matrix powder and a dispersion simulated nuclear fuel; step 2, filling the mixed nuclear fuel powder into a preformed four-blade cladding tube; 3, placing the four-blade preformed cladding tube filled with the nuclear fuel powder into a multi-roller rolling device, and gradually rolling the tube filled with the powder into a special-shaped multi-blade fuel rod by using each group of rollers; 4, the special-shaped multi-blade fuel rod formed through rolling is forwards pushed into an outer mold spiral cavity of a twisting device through a profiling guide pipe by means of the friction force of a final roller; and 5, the spiral traction head is driven by a rotating motor and an axial motor to drive the fuel rod on the right side of the twisting die to do axial and rotating motion. The invention belongs to the technical field of nuclear fuel element manufacturing.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a nuclear fuel element, and belongs to the technical field of nuclear fuel element manufacturing. Background Art

[0002] Nuclear energy, with its advantages of efficiency, economy, and cleanliness, is increasingly becoming a key focus of global energy development. To further improve the safety and efficiency of nuclear reactors, new nuclear fuel elements are required to possess large heat exchange areas, good thermal conductivity, short refueling cycles, and high safety. Metallic nuclear fuel elements are more likely to meet these requirements. Traditional nuclear fuel elements, however, are mostly circular in shape, resulting in poor rigidity, a small heat exchange area, and poor thermal conductivity. In recent years, a new type of fuel element, a multi-lobed, spiral rod-like structure with two, three, or four lobes, has garnered increasing attention within the nuclear power industry.

[0003] Russia was the first country to develop this type of multi-lobed spiral fuel element, with related reports appearing in the 1980s. Currently, Russia's ZETM company has developed it to the third generation, primarily for use on icebreakers. Its patent discloses a four-lobed spiral fuel element rod with a pitch of 21.5 cm and a circumscribed diameter of 12.6 mm. The rod features a displacer in the center of a square area with sides of 1.5 to 3.5 mm. LightBridge Corporation in the United States has also announced the processing of similar multi-lobed spiral fuel elements, explaining that this spirally mounted fuel element enhances overall rigidity, reduces the need for spacers, and that the spiral ribs enhance lateral mixing. Tsinghua University in China has also announced the manufacture of similar multi-lobed twisted fuel elements through co-extrusion.

[0004] Currently available international and domestic patents for multi-lobed spiral fuel rods describe only the filler type, geometry, and fuel element arrangement. There are few reports on the processing methods for multi-lobed spiral fuel elements, or the process descriptions are vague. Research has revealed that co-extrusion and drawing and twisting are the most common methods, but these methods present numerous technical challenges. During processing, the cross-sectional dimensional accuracy of the tube is difficult to ensure, and the mechanical bond between the cladding and powder is poor, leaving many process challenges. Summary of the Invention

[0005] The present invention aims to solve the problems of difficult operation and difficult to ensure cross-sectional accuracy in the existing manufacturing process of special-shaped multi-lobed spiral nuclear fuel elements, and further proposes a manufacturing method of special-shaped multi-lobed spiral nuclear fuel elements.

[0006] The technical solution adopted by the present invention to solve the above problems is: the steps of the present invention include:

[0007] Step 1: Mixing the matrix powder and the dispersion simulating nuclear fuel;

[0008] Step 2: Filling the mixed nuclear fuel powder into the preformed four-leaf cladding tube;

[0009] Step 3: Place the four-lobed preformed cladding tube filled with nuclear fuel powder in a multi-roller rolling device, and use each set of rollers to gradually roll the powder-filled tube into a special-shaped multi-lobed fuel rod;

[0010] Step 4: Using the friction force of the final rolling roller, the roll-formed special-shaped multi-lobed fuel rod is pushed forward through the contoured guide tube into the spiral cavity of the outer mold of the twisting device, and is gradually pushed out in a spiral shape, and then the spiral traction head clamps the right end of the spiral segment;

[0011] Step 5: The spiral traction head drives the fuel rod on the right side of the twisting die to perform axial and rotational motion under the drive of the rotary motor and the axial motor, so that it is twisted into a spiral angle ω along the axial direction of the special-shaped multi-lobed fuel rod, until the special-shaped multi-lobed fuel rods that have been rolled through multiple reducing passes are finally twisted into spiral special-shaped multi-lobed fuel rods.

[0012] Furthermore, the diameter of the blank is designed according to the circumference of the finished pipe:

[0013] The circumference of the finished pipe is L 成品 , based on the fact that the circumference of the rolled tube remains unchanged, the radius r of the billet is calculated:

[0014] L 成品 =L 坯料 =2πr 坯料 ①,

[0015] In formula ①, r 坯料 Indicates the radius of the round tube blank;

[0016] After the tube radius is determined, calculate the density of the powder filling and the cross-sectional area S of the blank tube. 坯料 and core powder density η 松装 There is a mathematical relationship between the cross-sectional area S and the cross-sectional area S. 拉拔 and core η 振实 :

[0017] η 松装 ×S 拉拔 =η 轧实 ×S 轧实 ×γ②,

[0018] γ=1.02+0.0072*exp(8.0×v)③,

[0019] In formula ③, the density of the core rod η 轧实 and cross-sectional area S 轧实To determine the value, the rolling elongation coefficient γ is calculated through actual processing and production and is related to the powder filled. The present invention uses an Al-WC powder mixture, where v represents the volume fraction of WC (when the WC volume fraction is 30%, here v = 0.3). Among them, the value of the elongation coefficient γ is exponentially positively correlated with the volume v of WC. The functional relationship is shown in Formula ③. Based on Formula ③, the cross-sectional area of ​​the round billet tube and the corresponding delivery density η are designed and determined. 送装 .

[0020] The density of the core rod during the processing is η 轧实 , cross-sectional area of ​​core filling rod S 轧实 The elongation coefficient γ determines the cross-sectional area S of the blank tube. 轧实 and tap density η 振实 The mathematical relationship between them can be used to design the pipe cross-sectional area S according to the process requirements. 轧实 and tap density η 振实 For example, when the cross-sectional area of ​​the self-designed billet drawn tube is S 拉拔 is determined, so the rolling elongation γ of the core-filled rod becomes the tap density η 振实 The present invention conducts rolling experiments on cored rods with different WC volumes and performs fitting analysis on the experimental results to obtain a functional relationship between the elongation coefficient γ and the WC volume with high accuracy ③, and then calculates a more appropriate Al-WC mixed powder tap density η 振实 ,vice versa.

[0021] Furthermore, in step 1, the base powder is a single substance powder or a multi-component mixed powder, the single substance powder or the multi-component mixed powder is placed in a vacuum drying oven for drying, and the dried multi-component powder is mixed evenly.

[0022] Furthermore, in step 2, the mixed nuclear fuel powder is filled into the preformed four-leaf cladding tube and then vibrated, and after vibrating, both ends of the four-leaf cladding tube are sealed with hot melt adhesive.

[0023] Furthermore, the powder-filled four-leaf preformed cladding tube is placed in a multi-roller rolling device for multiple sets of rolling. The roller profile size of the rollers in the multi-roller rolling device gradually decreases, and the last two sets of roller profiles have the same shape and size as the cross-section of the finished simulated fuel element.

[0024] Furthermore, a multi-roller rolling device and a twisting device form a rolling-twisting device. The multi-roller rolling device is composed of 10-24 groups of rollers. Each group of rollers includes two rolling wheels, and the two rolling wheels are symmetrically distributed. The rolling wheel groove transitions from the pre-formed size to the size of the special-shaped blade. Under the action of the driving mechanism, the powder-filled tube is rolled into shape.

[0025] The twisting equipment consists of a twisting die and a traction device, and the multi-roller pressing device is connected to the twisting device through a contoured guide tube.

[0026] Furthermore, according to the theoretical helix angle ω0 of the fuel rod, the helix angle of the twisted outer model cavity is set to ω1 = ω0 + Δω during the twisting process to ensure that the final formed special-shaped multi-leaf spiral simulated fuel element meets the helix angle requirements;

[0027] The actual calculation formula for the twisting angle is:

[0028] ω1=360° / P+Δω④,

[0029] Δω=0.038+0.46*v⑤

[0030] In formula ④, ω1 represents the actual twisting angle, P represents the pipe pitch, Δω represents the rebound angle, and in formula ⑤, v represents the volume fraction of WC. After a large number of experimental tests, it was found that the rebound angle Δω of Al-WC powder and the WC volume fraction have a linear functional relationship.

[0031] The beneficial effects of the present invention are as follows: the present invention manufactures simulated fuel rods through a multi-stage rolling-twisting composite processing method, integrates the multi-roll rolling process and the twisting process into a rolling-twisting integral forming device, saves equipment costs, not only improves the continuity of the processing technology, but also greatly improves the processing efficiency of the finished pipe. The step-by-step processing method makes the processing requirements of each step clearer, reduces the processing difficulty of each step, improves the processing accuracy of each step, thereby reducing the overall manufacturing difficulty and the overall risk of processing failure, and improves the overall dimensional accuracy of the simulated fuel rod. The special-shaped multi-leaf spiral simulated fuel element is manufactured by a multi-stage rolling and spiral twisting forming method, which has better process controllability, and the pipe is rolled and reduced for multiple times, which greatly reduces the difficulty of deformation and improves the cross-sectional size of the element. The twisting spiral improves the uniformity of the pitch, controllable accuracy and yield of the special-shaped multi-leaf spiral simulated fuel element, and greatly saves equipment costs and improves processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the powder filling process of a round billet tube;

[0033] Figure 2 Schematic diagram of the cross-sectional shape of the roller and the roller groove;

[0034] Figure 3 It is a schematic diagram of the distribution of each group of rollers in the multi-roller rolling device and the roller shape structure;

[0035] Figure 4 It is a schematic diagram of the cross-section and longitudinal section of the tube structure after simulating the fuel rod being rolled by the multi-roller rolling device;

[0036] Figure 5 It is a schematic diagram of the rolling-twisting equipment structure;

[0037] Figure 6 This is a longitudinal schematic diagram of the spiral simulated fuel rod after being twisted by the twisting device. DETAILED DESCRIPTION

[0038] Specific embodiment 1: A method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element, wherein the blade cross section of the special-shaped multi-lobed spiral nuclear fuel element is special-shaped multi-lobed or plum blossom-shaped as shown in the figure, the pitch is 400mm, the total length of the simulated nuclear fuel area is 1000mm, the circumscribed circle diameter is 5mm, the cladding tube wall thickness is 0.1mm, the core density is 95%, and the rolled cross-sectional area S is 9.5mm 2 The circumference is 16.57mm. The core powder is a mixed powder of aluminum powder and tungsten powder. The particle size of the powder is 250-300μm, and the volume ratio of aluminum powder to tungsten powder is 6:4. The specific manufacturing steps include:

[0039] Step 1: The target cross section can be a standard special-shaped multi-lobed shape, or the blades can be arc-shaped or cosine-shaped. The round tube billet diameter and powder filling tap density are theoretically designed based on the target product shape and the designed inner cross-sectional area and outer tube circumference after rolling.

[0040] The circumference of the finished pipe is L 成品 , then according to the unchanged circumference of the rolled tube, the radius of the billet is calculated:

[0041] L 成品 =L 坯料 =2πr 坯料 ,

[0042] Among them, r 坯料 Indicates the radius of the round tube blank;

[0043] After the pipe radius is determined, the density of the filling powder is calculated by the formula:

[0044] η 松装 ×S 拉拔 =η 轧实 ×S 轧实 ×γ,

[0045] γ=1.02+0.0072*exp(8.0×v)

[0046] The target product requires the core density to be no less than 95% and the rolled cross-sectional area S to be 9.5mm 2 , the circumference is 16.57mm, here γ is 1.2. The WC content is 40%, so here v is 0.4. According to the above formula, the diameter of the pipe blank is 5mm and the loose density is 0.46;

[0047] Step 2: Mixing the metal matrix powder and the simulated fuel powder (tungsten powder, etc.);

[0048] In the simulated fuel powder core 2, the metal matrix powder is an aluminum powder matrix, and the simulated fuel powder is a powder with the same density as the nuclear fuel powder, and tungsten powder, tungsten carbide powder, or tungsten-molybdenum alloy powder can be selected. The aluminum powder matrix and the simulated fuel powder can be mixed at a volume ratio of 10% to 50%. In the embodiment, there is no restriction on the volume ratio and mixing method of the metal matrix powder and the simulated fuel powder.

[0049] Tungsten powder was selected as the simulated fuel powder, and the theoretical density of Al-WC mixed powder (volume ratio = 6:4) was 7.87 g / cm 3 The total weight of the filling powder is 142.41g, aluminum powder is 29.31g, and tungsten powder is 113.10g;

[0050] In this step, before the metal powder and the simulated fuel powder are mixed, the powder is vacuum-heated and dried in a vacuum drying oven at a temperature of 60 to 100°C and a vacuum degree of not less than 10 -3 MPa, the drying time is not less than 1h, to ensure that the metal matrix powder and simulated fuel powder are dry;

[0051] Step 3: Fill the mixed simulated fuel core 2 into the outer cladding 1;

[0052] The mixed simulated nuclear fuel powder is filled into the round billet tube. During the powder filling process, the tube is vibrated to ensure that the filled powder has a certain density distribution in the pre-drawn tube.

[0053] Step 4: Place the tube 3 filled with simulated fuel powder at the inlet of the multi-roll rolling device of the multi-roll rolling-twisting equipment and perform multi-roll rolling. Figure 2 As shown;

[0054] According to the cross-sectional shape and size of the final simulated fuel rod, a 20-roll rolling device is developed, and the rolls are arranged as follows: Figure 3 As shown, the roller distribution of each previous and next pass is rotated 90 degrees, showing a longitudinal-transverse-longitudinal distribution pattern. The distance D between the front and rear rollers is the same. Each group of rollers 4 is relatively distributed. Each roller rotates around its own axis, and the fuel rods to be rolled move along the axis driven by the friction of the rollers.

[0055] The rollers of group 4 are arranged in a similar manner to the relative distribution of rollers 5 and 6, forming roller grooves 8. The groove size of each group of rollers gradually transitions from the tube 3 after powder filling to the final formed 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 rolling process of multiple rollers, the gradual deformation of the outer cladding causes the core to gradually deform into a standard special-shaped multi-lobed simulated fuel rod 9.

[0056] Key parts 9c and 9d are formed to target dimensions under the action of roller grooves 8a and 8b. The density of the mixed fuel powder 12a (aluminum powder) and the mixed simulated fuel powder 12b increases under the action of roller grooves 8a and 8b, and the mixed fuel powder is formed into a multi-lobed simulated fuel rod with a special shape along with the cladding.

[0057] 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 profiling guide tube 15. The traction end 14 of the twisting device clamps the end of the formed tube and performs a spiral motion along the moving axis under the action of the traction device 14. Figure 5 As shown;

[0058] Step 6: The finished tube after rolling passes through the spiral die entrance transition zone 12a and the spiral area 12b. Under the action of the traction force of the spiral device, the simulated fuel rod 12 passes through the spiral area 12b and forms four-leaf petals 13d and spiral grooves 13c along the axial direction. The special-shaped multi-leaf spiral simulated fuel rod 13 with a spiral angle of ω0 is formed. Figure 6 As shown;

[0059] The twisting die's helical angle ω1 is designed to be ω0+Δω, where Δω is the springback angle. This needs to be determined based on the target product's pitch M through theoretical calculations and repeated experimental verification and iteration. The actual die's helical angle ω1 is then calculated using the following formula:

[0060] ω1=360° / P+Δω,

[0061] Δω=0.038+0.46*v

[0062] Where ω1 is the actual twisting angle, P is the pipe pitch, Δω is the springback angle, and v represents the volume fraction of WC. The springback angle and the WC volume fraction are in a linear function relationship.

[0063] The pipe pitch in this embodiment is 400 mm, the volume fraction of WC is 40%, and v = 0.4. Therefore, the springback angle Δω in this case is 0.184, and the calculated actual helix angle is 1.122°.

[0064] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element, characterized in that: The specific steps include: Step 1: Mixing the matrix powder and the dispersion simulating nuclear fuel; Step 2: Filling the mixed nuclear fuel powder into the preformed four-leaf cladding tube; Step 3: Place the four-lobed preformed cladding tube filled with nuclear fuel powder in a multi-roller rolling device, and use each set of rollers to gradually roll the powder-filled tube into a special-shaped multi-lobed fuel rod; Step 4: Using the friction force of the final rolling roller, the roll-formed special-shaped multi-lobed fuel rod is pushed forward through the contoured guide tube into the spiral cavity of the outer mold of the twisting device, and is gradually pushed out in a spiral shape, and then the spiral traction head clamps the right end of the spiral segment; Step 5: The spiral traction head drives the fuel rod on the right side of the twisting die to perform axial and rotational motion under the drive of the rotary motor and the axial motor, so that it is twisted into a spiral angle ω along the axial direction of the special-shaped multi-lobed fuel rod, until the special-shaped multi-lobed fuel rods that have been rolled through multiple reducing passes are finally twisted into spiral special-shaped multi-lobed fuel rods.

2. The method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that: The diameter of the blank is calculated from the circumference of the finished tube: The circumference of the finished pipe is L 成品 , based on the fact that the circumference of the rolled tube remains unchanged, the radius r of the billet is calculated: L 成品 =L 坯料 =2πr 坯料 ①, In formula ①, r 坯料 Indicates the radius of the round tube blank; After the tube radius is determined, calculate the density of the powder filling and the cross-sectional area S of the blank tube. 坯料 and core powder density η 松装 There is a mathematical relationship between the cross-sectional area S and the cross-sectional area S. 拉拔 and core η 振实 : or 松装 ×S 拉拔 =the 轧实 ×S 轧实 ×γ②, γ=1.02+0.0072*exp(8.0×v)③, In formula ①, η 轧实 Indicates the density of the core rod rolled, S 轧实 It represents the cross-sectional area of ​​the core rod, and γ represents the rolling elongation coefficient, which is between 1.02 and 1.3 and is related to the filled powder.

3. The method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that: In step 1, the base powder is a single substance powder or a multi-component mixed powder. The single substance powder or the multi-component mixed powder is placed in a vacuum drying oven for drying, and the dried multi-component powders are mixed evenly.

4. The method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that: In step 2, the mixed nuclear fuel powder is filled into the preformed four-leaf cladding tube and then vibrated. After vibrating, both ends of the four-leaf cladding tube are sealed with hot melt adhesive.

5. The method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that: The powder-filled four-leaf preformed cladding tube is placed in a multi-roller rolling device for multiple sets of rolling. The roller profile size of the rollers in the multi-roller rolling device gradually decreases, and the last two sets of roller profiles have the same shape and size as the cross-section of the finished simulated fuel element.

6. The method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that: The multi-roller rolling device and the twisting device form a rolling-twisting device. The multi-roller rolling device consists of 10-24 groups of rollers. Each group of rollers contains two rolling wheels, and the two rolling wheels are symmetrically distributed. The rolling wheel groove transitions from the pre-formed size to the size of the special-shaped blade. Under the action of the driving mechanism, the powder-filled tube is rolled into shape. The twisting equipment consists of a twisting die and a traction device, and the multi-roller pressing device is connected to the twisting device through a contoured guide tube.

7. The method for manufacturing a special-shaped multi-lobed spiral nuclear fuel element according to claim 1, characterized in that: According to the theoretical helical angle ω0 of the fuel rod, the helical angle of the twisted outer model cavity is set to ω1 = ω0 + Δω during the twisting process to ensure that the final formed special-shaped multi-leaf spiral simulated fuel element meets the helical angle requirements; The actual calculation formula for the twisting angle is: ω1=360° / P+Δω④, Δω=0.038+0.46*v⑤ In formula ④, ω1 represents the actual twisting angle, P represents the pipe pitch, Δω represents the springback angle, and in formula ⑤, v represents the volume fraction of WC. After a large number of experimental tests, the springback angle and the WC volume fraction have a linear functional relationship.

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