Warm-pressing forming preparation method for preparing bent plate type fuel element by using flexible forming mold

Abstract

The invention relates to a warm-pressing forming preparation method for preparing a bent plate type fuel element through a flexible forming mold. The warm-pressing forming preparation method comprises the steps that a metal-based flat plate type fuel element is heated to the annealing temperature, and heat preservation is conducted for a first time under the condition of the annealing temperature; the upper die assembly is preheated, and heat preservation is conducted for a second duration under the condition of the preheating temperature; placing the annealed metal-based flat plate type fuel element on a flexible die body; the upper die assembly is pressurized, so that the metal-based flat plate type fuel element is formed into a bent plate type fuel element under the support of the flexible die body; the upper mold assembly is pressurized for a third time length, and the waste heat of the flexible forming mold in the pressurizing process is used for preserving the heat of the bent plate type fuel element. In the pressing process, the lower surface of the fuel element is completely attached to the upper surface of the flexible die body all the time, and local stress concentration is avoided. And the annealing temperature is in the lower limit interval of the recrystallization temperature, so that the yield strength of the fuel element is effectively reduced, and meanwhile, the mechanical property is prevented from being greatly reduced.

Description

Technical Field

[0001] This application relates to the field of reactor fuel element processing technology, and in particular to a thermoforming method for preparing curved plate-shaped fuel elements using flexible forming molds. Background Technology

[0002] To improve fuel performance and overcome the shortcomings of ceramic-type nuclear fuel in terms of thermal conductivity and ductility, high-uranium-density metal-based fuel elements have been adopted in some high-flux research reactors, high-power reactors, or long-life power reactors. These metal-based fuel elements include plate-shaped fuel elements. Plate-shaped fuel elements employ a sandwich structure of cladding + core plate + cladding, with a metallurgical bond between the cladding and core plate. This facilitates heat dissipation and reduces blistering, thus preventing fuel element failure due to cladding damage or pillow-like bulging of the cladding affecting coolant flow, thereby improving reactor safety. Plate-shaped fuel elements are divided into metal-based flat plate fuel elements and metal-based curved plate fuel elements. Among them, metal-based curved plate fuel elements, due to their high uranium loading and large heat dissipation area, are the preferred choice for ultra-high flux experimental reactors.

[0003] In related technologies, the molding and preparation of metal-based curved plate fuel elements generally involves first fully annealing a flat fuel element at a high temperature (e.g., 490°C) to reduce its yield strength. After the flat fuel element cools to ambient temperature, it is then pressed to form a curved plate fuel element. The pressing process consists of two steps: initial pressing and final pressing. Initial pressing forms the curved plate fuel element, but the resulting curved plate fuel element exhibits springback and cannot achieve the ideal size. Therefore, a final pressing is required, using a smaller final pressing head to compensate for the bending of the curved plate fuel element. This necessitates extensive experimentation to fit the bending compensation amount of the curved plate fuel element and, based on experience, determining the size of the final pressing head.

[0004] The purpose of the full annealing treatment in the above process is to reduce the yield strength of the fuel element, thereby reducing the springback. However, this also reduces the tensile strength and elongation at break of the fuel element, especially for fuel elements with high nuclear fuel content, where the reduction in mechanical properties is even greater. This has a potential impact on the operational safety of the fuel element in the reactor. In addition, in the final pressing step, a large number of experiments are required to fit the over-bending compensation of the curved plate-type fuel element, and the size of the final pressing head is determined empirically. If fuel elements of various sizes and nuclear fuel contents need to be prepared, it will result in huge time and economic costs.

[0005] In related technologies, metal-based curved plate fuel elements are generally prepared by pressing metal-based flat plate fuel elements with a forming mold. The forming mold includes an upper mold and a lower mold arranged opposite each other. The side of the upper mold facing the lower mold has a convex forming surface, and the side of the lower mold facing the upper mold has a concave forming surface. The convex and concave forming surfaces are used to press the metal-based flat plate fuel element into a curved plate fuel element.

[0006] However, when a metal-based flat fuel element is placed on the concave surface of the lower die, its two ends are supported on the concave surface, while the middle part is subjected to downward pressure from the upper die. This causes the metal-based flat fuel element to exhibit a typical three-point bending stress state during the compression process. As a result, stress concentration is likely to occur at the support points at both ends and at the contact point with the upper die, which affects the forming accuracy, damages the metallurgical bonding interface between the internal cladding and the core plate of the fuel element, and poses a potential threat to the service safety of the fuel element in the reactor. Summary of the Invention

[0007] Based on this, it is necessary to provide a warm-press molding method for preparing curved plate-shaped fuel elements using a flexible molding die, addressing at least one of the aforementioned technical problems in the related technologies.

[0008] A thermoforming method for preparing curved plate-shaped fuel elements using a flexible forming mold, wherein the flexible forming mold includes an upper mold assembly and a lower mold assembly, the lower mold assembly includes a lower mold frame and a flexible mold body installed in the lower mold frame, the flexible mold body being made of an elastic material;

[0009] The warm-press molding preparation method includes:

[0010] The metal-based flat fuel element is heated to the annealing temperature and held at the annealing temperature for a first time. During the heating process, the heating rate of the metal-based flat fuel element is 20℃ / min to 40℃ / min. The annealing temperature is set to be within the full range of recrystallization temperature of the metal material in the metal-based flat fuel element, starting from the lower limit of the full range and accounting for one-quarter of the lower limit interval.

[0011] The upper mold assembly is preheated and held at the preheated temperature for a second time, wherein the preheated temperature is lower than or equal to the annealing temperature and lower than the upper temperature resistance limit of the flexible mold.

[0012] The annealed metal-based flat fuel element is placed on the flexible mold;

[0013] Pressurize the upper mold assembly to press down on the metal-based flat fuel element, which is then shaped into a curved fuel element under the support of the flexible mold.

[0014] The upper mold assembly is kept under pressure for a third time, and the residual heat of the flexible molding die is used to keep the curved fuel element warm during the pressure-keeping process, so that the curved fuel element is kept in the molding space for a third time.

[0015] The curved fuel element is removed from the flexible molding die and cooled.

[0016] In one embodiment, the preheating temperature is 200°C to 350°C.

[0017] In one embodiment, if the annealing temperature is higher than the upper limit of the temperature resistance of the flexible mold, the annealed metal-based flat fuel element is cooled down. Once the temperature of the cooled metal-based flat fuel element is lower than the upper limit of the temperature resistance of the flexible mold, the metal-based flat fuel element is placed on the flexible mold.

[0018] In one embodiment, the temperature of the metal-based flat fuel element after cooling is equal to the preheating temperature, and then the metal-based flat fuel element is placed on the flexible mold.

[0019] In one embodiment, the temperature of the cooled metal-based flat-plate fuel element is between 250°C and 350°C.

[0020] In one embodiment, if the annealing temperature is lower than the upper limit of the temperature resistance of the flexible mold, the preheating temperature is made equal to the annealing temperature.

[0021] In one embodiment, in the step of preheating the upper mold assembly and holding it at the preheated temperature for a second time, the upper mold assembly is preheated by a first heating device, wherein the first heating device is a first heating furnace, or an electric heating rod that can be inserted into the upper mold assembly, or a covered heating shell woven from heating strips;

[0022] In the step of heating the metal-based flat fuel element to the annealing temperature and holding it at the annealing temperature for a first time, the metal-based flat fuel element is heated by a second heating device, which is a second heating furnace.

[0023] In one embodiment, the warm pressing molding preparation method further includes: spraying a release agent onto the convex molding surface before the step of preheating the upper mold assembly and holding it at the preheated temperature for a second time.

[0024] In one embodiment, the material of the flexible mold includes any one or more combinations of silicone rubber, fluororubber, perfluoroether rubber, or silicone rubber.

[0025] In one embodiment, the first duration is 20 min to 90 min; the second duration is not less than 1 h; and the third duration is 10 min to 1 h.

[0026] The aforementioned warm-press forming method for preparing curved plate-shaped fuel elements using a flexible forming mold involves placing the annealed metal-based flat fuel element on a flexible mold. When the upper mold assembly presses down, the fuel element compresses the flexible mold. Throughout the pressing process, the flexible mold undergoes elastic deformation, ensuring that the lower surface of the fuel element remains completely in contact with the upper surface of the flexible mold. This transforms the concentrated load applied by the upper mold assembly into a full-area, quasi-isostatic uniform support for the entire lower surface of the fuel element. This support mode avoids localized stress concentration caused by point or line contact in traditional hard molds, effectively preventing shell breakage or interlayer separation during the bending forming process of the fuel element's sandwich structure. Simultaneously, the uniform stress distribution promotes plastic flow and stress relaxation of the material, significantly reducing springback after forming and ensuring the dimensional accuracy and shape stability of the curved plate-shaped fuel element.

[0027] The aforementioned warm-press forming method for preparing curved-plate fuel elements using flexible forming molds sets the annealing temperature within a quarter of the lower limit range of the full range of recrystallization temperatures of the metal material. This temperature range is significantly lower than the full annealing temperature used in the prior art. This allows the metal-based flat-plate fuel element to effectively reduce its yield strength while avoiding significant deterioration in mechanical properties, thereby significantly reducing damage to the overall performance of the fuel element. Moreover, the metal-based flat-plate fuel element can be precisely formed into a curved-plate fuel element in a single pressing operation, replacing the complex process of full annealing and two-step pressing in the prior art. It also avoids the need to rely on numerous experiments to fit the over-bending compensation amount of the curved-plate fuel element, significantly improving forming efficiency and reducing research and development and manufacturing costs. Attached Figure Description

[0028] Figure 1 This is a flowchart of a warm-press molding method for preparing curved fuel elements using a flexible molding die, according to one embodiment.

[0029] Figure 2 This is a schematic diagram of the upper mold assembly in one embodiment.

[0030] Figure 3 This is a schematic diagram of the lower mold frame in one embodiment.

[0031] Figure 4 This is a schematic diagram of the centering plate according to one embodiment.

[0032] Figure 5 This is a schematic diagram of the lower mold assembly in one embodiment.

[0033] Figure 6 This is a schematic diagram of the structure of a lower mold assembly in which a metal-based flat fuel element is placed, according to one embodiment.

[0034] Figure 7 This is a schematic diagram showing the disconnection of the upper mold assembly and the lower mold assembly during mold closing, according to one embodiment.

[0035] Figure 8 for Figure 7 A schematic diagram of the upper module component after it has been unloaded.

[0036] Explanation of reference numerals in the attached figures:

[0037] ZZ', First direction; YY', Second direction; XX', Third direction;

[0038] 10. Metal-based flat-plate fuel element; 20. Curved-plate fuel element;

[0039] 100. Upper mold assembly; 110. Upper mold base; 111. Centering hole; 120. Upper forming part; 121. Convex forming surface;

[0040] 200. Lower mold assembly; 210. Lower mold base; 211. Lower mold end plate; 212. First wall block; 213. Second wall block; 214. Centering column; 201. Mold cavity; 202. Stepped groove; 203. Slide groove; 220. Flexible mold body; 221. Upper flexible mold; 222. Lower flexible mold; 230. Limiting part; 240. Centering plate; 241. Slider; 242. Strip groove; 240a. First centering plate; 240b. Second centering plate; 250. Fastener. Detailed Implementation

[0041] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0042] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0043] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0044] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0045] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0046] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.

[0047] Please see Figure 1 This application provides a warm-press molding method for preparing curved-plate fuel elements using a flexible molding die. Please refer to [link to relevant documentation]. Figures 2 to 6 The flexible molding die includes an upper mold assembly 100 and a lower mold assembly 200. The upper mold assembly 100 includes an upper mold frame 110 and an upper forming part 120 connected to the lower side of the upper mold frame 110. The lower surface of the upper forming part 120 is a convex forming surface 121. The lower mold assembly 200 includes a lower mold frame 210 and a flexible mold body 220. The lower mold frame 210 is configured with a mold cavity 201. The flexible mold body 220 is installed in the mold cavity 201 and is made of an elastic material.

[0048] In actual use, the upper mold assembly 100 is positioned above the lower mold assembly 200, with the two facing each other, thus the convex forming surface 121 and the flexible mold body 220 are positioned opposite each other. The metal-based flat fuel element 10 is placed on the flexible mold body 220. Figures 6 to 8 By applying pressure to the flexible molding die, the upper mold assembly 100 moves downward to apply pressure to the metal-based flat fuel element 10, thereby pressing the metal-based flat fuel element 10 into a curved fuel element 20 under the elastic support of the flexible mold 220. The shape of the convex forming surface 121 matches the shape of the upper surface of the curved fuel element 20.

[0049] Please see Figure 1 The warm-press molding method for preparing curved fuel elements using flexible molding dies includes at least steps S100 to S600, and each step is described in detail below.

[0050] Step S100: Heat the metal-based flat fuel element 10 to the annealing temperature and hold it at the annealing temperature for a first time. During the heating process, the heating rate of the metal-based flat fuel element 10 is 20℃ / min to 40℃ / min. The annealing temperature is set to be within the full range of recrystallization temperature of the metal material in the metal-based flat fuel element 10, starting from the lower limit of the full range and accounting for one-quarter of the lower limit interval.

[0051] Specifically, the metal-based flat-plate fuel element 10 adopts a sandwich structure of cladding + core plate + cladding, that is, cladding is provided on both sides of the core plate, and metallurgical bonding is formed between the core plate and the cladding on both sides.

[0052] Understandably, the cladding is made of metal, while the core is made of a mixture of core material particles and metal matrix powder. The metal matrix powder in the core is made of the same metal as the cladding.

[0053] Optionally, the first duration can be 20 minutes to 90 minutes. The specific value of the first duration can be flexibly set according to actual needs.

[0054] Understandably, the metal material in the metal-based flat-plate fuel element 10 is the same metal material used for the cladding as the metal material corresponding to the metal matrix of the core plate.

[0055] The recrystallization temperature of the metal material in the metal-based flat-plate fuel element 10 is a temperature range, not a single value. In this step, the annealing temperature is set to a lower limit interval that accounts for one-quarter of the total recrystallization temperature range of the metal material in the metal-based flat-plate fuel element 10. In other words, the annealing temperature in this step can be any value within this lower limit interval.

[0056] For example, if the recrystallization temperature of the metal material in the metal-based flat plate fuel element 10 is in the full range of 250°C to 350°C, the lower limit of this full range is 250°C. Therefore, the lower limit range, which starts from the lower limit of this full range and accounts for one-quarter of the range, is 250°C to 275°C.

[0057] By annealing the metal-based flat fuel element 10 at its annealing temperature, the yield strength of the metal-based flat fuel element 10 can be reduced. In this step, during the annealing of the metal-based flat fuel element 10, by holding the metal-based flat fuel element 10 at the annealing temperature for a first time, the internal stress of the metal-based flat fuel element 10 can be effectively eliminated, the material plasticity can be improved, and the yield strength can be reduced.

[0058] Furthermore, in this step, during the heating of the metal-based plate-type fuel element 10, the heating rate of the metal-based plate-type fuel element 10 is 20℃ / min to 40℃ / min. This rapid heating rate quickly heats the metal-based plate-type fuel element 10 to the aforementioned annealing temperature, enabling it to quickly pass through the nucleation zone. Within this zone, if the heating is slow, the recrystallization nucleation rate is low while the grain growth driving force is high, easily leading to abnormal grain coarsening and grain boundary weakening. The rapid heating of 20℃ / min to 40℃ / min effectively shortens the residence time in this sensitive zone, thereby ensuring that the material is sufficiently softened to facilitate molding while maintaining a fine and uniform recrystallized structure. Ultimately, while ensuring molding accuracy, the strength, toughness, and service reliability of the fuel element are well maintained.

[0059] Step S200: Preheat the upper mold assembly 100 and keep it at the preheated temperature for a second time, wherein the preheated temperature is lower than or equal to the annealing temperature and the preheated temperature is lower than the upper temperature resistance limit of the flexible mold 220.

[0060] The specific value of the second duration can be flexibly set according to actual needs. Optionally, the second duration should not be less than 1 hour.

[0061] By preheating the upper mold assembly 100 in this step, when the upper mold assembly 100 applies pressure to the metal-based flat fuel element 10, the temperature of the upper mold assembly 100 can be approximately the same as or close to that of the metal-based flat fuel element 10. This avoids the rapid drop in temperature of the metal-based flat fuel element 10 due to an excessive temperature difference between the upper mold assembly 100 and the metal-based flat fuel element 10, which would affect the plastic state of the metal-based flat fuel element 10.

[0062] Meanwhile, after the upper mold assembly 100 is preheated and kept at a certain temperature for a second time, the convex forming surface 121 can be stably maintained near the preheating temperature. In this way, in conjunction with the subsequent pressurization operation in step S400, the thermal creep of the material can be fully guaranteed, the stress can be effectively relaxed, and the springback of the component after molding can be reduced.

[0063] It should be noted that, in step S100, the heating rate of the metal-based flat fuel element 10 is relatively fast, while in step S200, the heating rate of the upper mold assembly 100 is slower than that of the metal-based flat fuel element 10. Therefore, the upper mold assembly 100 can be heated in advance, and after the upper mold assembly 100 has reached a certain temperature, the metal-based flat fuel element 10 can be heated further.

[0064] In this step, the preheating temperature should be lower than the upper temperature limit of the flexible mold 220. For example, if the upper temperature limit of the flexible mold 220 is 300°C, the preheating temperature should be lower than 300°C to prevent the flexible mold 220 from overheating and failing during pressing in step S400.

[0065] Since the flexible mold 220 is made of elastic materials (mostly polymeric materials, such as rubber), it is less resistant to prolonged high temperatures compared to rigid metal materials. Therefore, in this step, only the upper mold assembly 100 is preheated, and the lower mold assembly 200 is not preheated. After preheating, the upper mold assembly 100 (rigid metal material) has sufficient heat to maintain the temperature of the fuel element through heat conduction during pressing and holding. At the same time, the material used in the flexible mold 220 has low thermal conductivity, which also provides good insulation for the fuel element.

[0066] Step S300: Place the annealed metal-based flat fuel element 10 onto the flexible mold 220.

[0067] Step S400: Pressurize the upper mold assembly so that the upper mold assembly 100 presses down on the metal-based flat fuel element 10, thereby forming the metal-based flat fuel element 10 into a curved plate fuel element 20 under the elastic support of the flexible mold 220.

[0068] After step S100, the yield strength of the metal-based flat fuel element 10 has decreased. At this time, through steps S300 and S400, the annealed metal-based flat fuel element 10 is placed on the flexible mold 220. The upper mold assembly 100 applies pressure to the metal-based flat fuel element 10, forcing the metal-based flat fuel element 10 to undergo plastic deformation, thereby pressing the metal-based flat fuel element 10 into a curved plate fuel element 20.

[0069] like Figure 5 As shown, in its natural state (without the metal-based flat fuel element 10 placed), the upper surface of the flexible mold 220 is a plane perpendicular to the first direction ZZ'. Therefore, when the metal-based flat fuel element 10 is placed on the upper surface of the flexible mold 220, the lower surface of the metal-based flat fuel element 10 can completely fit against the upper surface of the flexible mold 220. Because the flexible mold 220 can elastically deform, the shape of the upper surface of the flexible mold 220 changes with the shape of the fuel element throughout the pressing process, thereby ensuring that the lower surface of the fuel element always remains completely fitted against the upper surface of the flexible mold 220.

[0070] Because the lower surface of the fuel element remains in complete contact with the upper surface of the flexible mold 220 throughout the entire pressing process, the concentrated load applied by the upper mold assembly 100 is transformed into a full-area, quasi-isostatic uniform support for the entire lower surface of the fuel element. This support mode avoids the local stress concentration caused by point or line contact in traditional hard molds, effectively preventing shell breakage or interlayer separation of the fuel element sandwich structure during bending and forming. At the same time, the uniform force distribution promotes the plastic flow and stress relaxation of the material, significantly reducing springback after forming and ensuring the dimensional accuracy and shape stability of the curved plate fuel element 20.

[0071] Step S500: The upper mold assembly 100 is kept under pressure for a third time, and the residual heat of the flexible molding die is used to keep the curved plate fuel element 20 warm during the pressure-keeping process, so that the curved plate fuel element 20 is kept in the molding space for a third time.

[0072] Optionally, the third duration is 10 minutes to 1 hour, and the specific value of the third duration can be flexibly set according to actual needs.

[0073] The upper mold assembly 100 is kept under pressure for a third duration, thereby allowing the upper mold assembly 100 and the flexible mold 220 to jointly confine the curved fuel element 20 within the forming space (the space between the convex forming surface 121 and the upper surface of the flexible mold 220) for a third duration. During this pressure-holding stage, the residual heat stored in the upper mold assembly 100 is continuously transferred to the curved fuel element 20 through the convex forming surface 121. At the same time, the flexible mold 220, due to its poor thermal conductivity, plays a role in heat preservation, together forming an environment that utilizes residual heat for heat preservation. This heat preservation process promotes creep and stress relaxation within the material of the curved fuel element 20, allowing the material more time for plastic rheology and internal stress release. The continuous elastic support of the flexible mold 220 during this period maintains the stability of the shape of the curved fuel element 20, thereby significantly reducing the springback of the curved fuel element 20 after the upper mold assembly 100 is unloaded, ensuring high precision and high stability of the final dimensions of the curved fuel element 20.

[0074] Step S600: Remove the curved fuel element 20 from the flexible molding die and cool it.

[0075] The upper mold assembly 100 can be removed from above the lower mold assembly 200, thereby removing the formed curved plate fuel element 20 and cooling it to finally obtain the desired curved plate fuel element 20. Optionally, step S600 involves air cooling the curved plate fuel element 20 after removing it from the flexible molding die.

[0076] The above-described warm-press molding method for preparing curved plate-shaped fuel elements using flexible molding dies involves annealing the metal-based flat plate-shaped fuel element 10 within the lower limit of its recrystallization temperature range, allowing it to retain higher mechanical properties while achieving the necessary plasticity. The upper mold assembly 100 is preheated to a preheating temperature not exceeding the annealing temperature and lower than the upper temperature resistance limit of the flexible mold 220, and held at this temperature for a second duration. This stabilizes the temperature of the convex forming surface 121, preventing excessive temperature difference between the convex forming surface 121 and the fuel element during pressing, which could lead to deterioration of its plasticity, while simultaneously protecting the flexible mold 220 from high-temperature damage. During pressing, the flexible mold 220 undergoes elastic deformation, providing uniform support across the entire surface of the fuel element's lower surface, thus allowing the upper mold to... The concentrated load of component 100 is transformed into a quasi-isostatic distribution, which effectively prevents the shell of the fuel element sandwich structure from breaking or separating due to local stress concentration, and promotes the plastic flow of materials to reduce springback. By maintaining pressure on the upper mold component 100 for a third time, the curved fuel element 20 is kept in the forming space for a third time. At the same time, the residual heat of the upper mold component 100 is used to transfer heat through the convex forming surface 121 and the heat insulation of the flexible mold 220 to keep it warm, promote the internal creep and stress relaxation of the fuel element. Combined with the continuous elastic support of the flexible mold 220, the internal stress is further released and the shape is stabilized, significantly reducing the amount of springback and ensuring the high precision and stability of the dimensions of the curved fuel element 20.

[0077] The above-described warm-press forming method for preparing curved plate-shaped fuel elements using flexible forming molds involves placing the annealed metal-based flat plate-shaped fuel element 10 on a flexible mold 220. When the upper mold assembly 100 presses down, the fuel element compresses the flexible mold 220. Throughout the pressing process, the flexible mold 220 undergoes elastic deformation, ensuring that the lower surface of the fuel element remains completely in contact with the upper surface of the flexible mold 220. This transforms the concentrated load applied by the upper mold assembly 100 into a full-area, quasi-isostatic uniform support for the entire lower surface of the fuel element. This support mode avoids localized stress concentration caused by point or line contact in traditional hard molds, effectively preventing shell breakage or interlayer separation during the bending forming process of the fuel element sandwich structure. Simultaneously, the uniform stress distribution promotes plastic flow and stress relaxation of the material, significantly reducing springback after forming and ensuring the dimensional accuracy and shape stability of the curved plate-shaped fuel element 20.

[0078] The aforementioned warm-press forming method for preparing curved-plate fuel elements using flexible forming molds sets the annealing temperature within a quarter of the lower limit range of the full range of recrystallization temperatures of the metal material. This temperature range is significantly lower than the full annealing temperature used in the prior art. This allows the metal-based flat-plate fuel element 10 to effectively reduce its yield strength while avoiding significant deterioration of its mechanical properties, thereby significantly reducing damage to the overall performance of the fuel element. Moreover, the metal-based flat-plate fuel element 10 can be precisely formed into a curved-plate fuel element 20 in a single pressing operation, replacing the complex process of full annealing and two-step pressing in the prior art. It also avoids the need to rely on numerous experiments to fit the over-bending compensation amount of the curved-plate fuel element, significantly improving forming efficiency and reducing research and development and manufacturing costs.

[0079] In one embodiment, the annealing temperature is lower than the temperature at which the metal matrix and nuclear fuel particles undergo an interfacial reaction, thereby preventing changes in core properties, particularly mechanical properties.

[0080] In one embodiment, the material of the flexible mold 220 includes any one or more combinations of silicone rubber, fluororubber, perfluoroether rubber, or silicone rubber.

[0081] The flexible mold 220 can be made of a variety of high-temperature resistant elastic materials, such as silicone rubber with a temperature resistance of about 300°C, fluororubber (such as FKM) with a temperature resistance of about 320°C, perfluoroether rubber (such as FFKM) with a temperature resistance of up to 330°C or higher, and silicone rubber with similar temperature resistance after special formulation optimization; for high-temperature pressing molding scenarios, special engineering elastomers such as polyimide with a temperature resistance exceeding 360°C can also be selected.

[0082] These elastic materials all maintain stable chemical properties and elastic modulus within a preheating and molding temperature range of 200°C to 350°C. By using these materials individually or in combination, the flexible mold 220 can continuously provide uniform and reliable full-area support during thermoforming, while ensuring no contamination or adhesion when in contact with the fuel element, thus guaranteeing the molding accuracy and surface quality of the curved fuel element 20.

[0083] In one embodiment, the preheating temperature is 200°C to 350°C.

[0084] The upper temperature resistance limit of commonly used materials for flexible molds (such as high-temperature resistant silicone rubber, fluororubber, etc.) is usually between 250℃ and 360℃.

[0085] In this embodiment, the preheating temperature is set to 200°C to 350°C. This ensures that the convex forming surface 121 of the upper mold assembly 100 has sufficient heat to effectively maintain the plastic forming conditions of the metal-based flat fuel element 10 during the pressing and holding process. It also avoids the risk of exceeding the upper temperature limit of the flexible mold 220, preventing permanent damage and elastic failure due to overheating. Thus, while ensuring the temperature requirements of the molding process, it ensures that the flexible mold 220 can stably and reliably provide elastic support function over the entire area.

[0086] In one embodiment, if the annealing temperature is higher than the upper limit of the temperature resistance of the flexible mold 220, the annealed metal-based flat fuel element 10 is cooled down. Once the temperature of the cooled metal-based flat fuel element 10 is lower than the upper limit of the temperature resistance of the flexible mold 220, the metal-based flat fuel element 10 is placed on the flexible mold 220.

[0087] In this embodiment, if the annealing temperature of the metal-based flat fuel element 10 is higher than the upper temperature resistance limit of the flexible mold 220, the annealed metal-based flat fuel element 10 is cooled to a temperature lower than the upper temperature resistance limit of the flexible mold 220. This prevents the overheated metal-based flat fuel element 10 from directly contacting and damaging the flexible mold 220, which has limited temperature resistance. Although the temperature of the metal-based flat fuel element 10 is reduced, its yield strength is significantly reduced due to the annealing process, and it still maintains good plasticity. This ensures both good deformation capability of the fuel element material during pressing and safe use of the flexible mold 220.

[0088] In one embodiment, the temperature of the cooled metal-based flat fuel element 10 can be the same as the preheating temperature of the upper mold assembly 100 before placing the metal-based flat fuel element 10 on the flexible mold 220. Alternatively, the temperature of the cooled metal-based flat fuel element 10 can be close to the preheating temperature of the upper mold assembly 100 (e.g., within 30°C higher or lower than the temperature of the upper mold assembly 100) before placing the metal-based flat fuel element 10 on the flexible mold 220.

[0089] In this embodiment, the temperature of the cooled metal-based flat fuel element 10 is the same as or close to the preheating temperature of the upper mold assembly 100, so that the temperature of the metal-based flat fuel element 10 and the preheated convex surface 121 is the same as or close, avoiding a large temperature difference between the two during pressing.

[0090] In one embodiment, when the temperature of the cooled metal-based flat fuel element 10 is in the temperature range of 240°C to 350°C, the metal-based flat fuel element 10 is then placed on the flexible mold 220.

[0091] In this embodiment, the metal-based flat fuel element 10 is cooled to a temperature range of 240°C to 350°C, which is the same as or close to the temperature of the preheated convex surface 121 to avoid excessive temperature difference between the two, and is below the upper limit of the temperature resistance of the flexible mold 220 to avoid damage to the flexible mold 220. At the same time, the metal-based flat fuel element 10 is in a temperature range of 240°C to 350°C, which is still within the temperature range suitable for plastic forming.

[0092] In other embodiments, the annealing temperature of the metal-based flat fuel element 10 is lower than the upper temperature limit of the flexible mold 220. Therefore, the preheating temperature of the upper mold assembly 100 is the same as the annealing temperature of the metal-based flat fuel element 10 (or the difference between the preheating temperature and the annealing temperature is within 30°C). This eliminates the need to cool the metal-based flat fuel element 10. After annealing and holding at that temperature for a first time, the metal-based flat fuel element 10 can be directly placed on the flexible mold 220. This avoids damage to the flexible mold 220, and ensures that the temperature of the metal-based flat fuel element 10 is the same as or close to that of the preheated convex surface 121, while also placing the metal-based flat fuel element 10 within a suitable temperature range for plastic forming.

[0093] In one embodiment, the arc length of the convex surface 121 is greater than the arc length of the designed arc-shaped plate fuel element, and the difference between the two is 10-50 mm.

[0094] In one embodiment, the axial length of the convex surface 121 is greater than the axial length of the designed arc-shaped plate fuel element, and the difference between the two is 20-100 mm.

[0095] In one embodiment, the length of the flexible phantom 220 is greater than the axial length of the designed arc-shaped plate-shaped fuel element, and the difference between the two is 10-100 mm.

[0096] In one embodiment, the width of the flexible mold 220 is greater than the width of the metal-based flat fuel element corresponding to the designed arc-shaped plate fuel element. Among all the arc-shaped plate fuel elements to be formed, the width of the metal-based flat fuel element corresponding to the arc-shaped plate fuel element with the largest width is 20-50 mm smaller than the width of the flexible mold 220.

[0097] In one embodiment, in step S200, the upper mold assembly 100 is preheated by a first heating device.

[0098] The first heating device can be a first heating furnace.

[0099] The first heating device can be an electric heating rod that can be inserted into the upper mold assembly 100. For example, the upper mold assembly 100 is provided with a socket, and the electric heating rod is inserted into the socket.

[0100] The first heating device can be a covered heating shell made of woven heating strips, which covers the upper mold assembly 100.

[0101] In one embodiment, in step S100, the metal-based flat-plate fuel element 10 is heated by a second heating device, which is a second heating furnace.

[0102] In this embodiment, the metal-based flat fuel element 10 is heated by a second heating device, and the upper mold assembly 100 is preheated by a first heating device. That is, the metal-based flat fuel element 10 and the upper mold assembly 100 are heated by different heating devices.

[0103] In one embodiment, the warm pressing molding preparation method further includes: spraying a release agent onto the convex forming surface 121 before step S200.

[0104] By spraying a release agent onto the convex surface 121, direct adhesion between the convex surface 121 and the metal-based flat fuel element 10 can be prevented, as well as adhesion between the convex surface 121 and the curved fuel element 20 can be prevented. This makes it easy to remove the curved fuel element 20 after it has been formed.

[0105] In one embodiment, the annealing process for the metal-based flat-plate fuel element 10 can be carried out in air or in a vacuum. If it must be carried out in a vacuum, the vacuum level must be no less than 10. -2 Pa.

[0106] Please see Figures 1 to 5 This application provides a flexible molding die, which includes an upper mold assembly 100 and a lower mold assembly 200 disposed opposite to each other along a first direction ZZ'.

[0107] The upper mold assembly 100 includes an upper mold base 110 and an upper forming part 120. The upper forming part 120 is connected to the lower side of the upper mold base 110. The lower surface of the upper forming part 120 is a convex forming surface 121. The length direction of the upper forming part 120 is the second direction YY', and the width direction of the upper forming part 120 is the third direction XX'. The second direction YY', the third direction XX', and the first direction ZZ' are perpendicular to each other.

[0108] The lower mold assembly 200 includes a lower mold frame 210 and a flexible mold body 220. The lower mold frame 210 includes a lower mold end plate 211 and a first wall block 212 and a second wall block 213 disposed on the lower mold end plate 211 and spaced apart along the third direction XX'. A mold cavity 201 is constructed between the first wall block 212 and the second wall block 213. The flexible mold body 220 is installed in the mold cavity 201 and is disposed opposite to the convex forming surface 121. The flexible mold body 220 is made of elastic material and is used to provide support for the fuel element plate.

[0109] The upper forming part 120 and the upper mold frame 110 can be connected by bolts or integrally formed.

[0110] The first wall block 212, the second wall block 213, and the lower mold end plate 211 can be integrally formed.

[0111] The flexible mold 220 has its length direction along the second direction YY' and its width direction along the third direction XX'. The thickness direction of the flexible mold 220 is along the first direction ZZ'. The mold cavity 201 has its length direction along the second direction YY' and its width direction along the third direction XX'.

[0112] The aforementioned flexible forming mold, by setting a flexible mold 220 made of elastic material in the mold cavity 201 of the lower mold frame 210, is positioned opposite to the convex forming surface 121 of the upper mold assembly 100. When the upper mold assembly 100 presses down on the metal-based flat fuel element 10, the flexible mold 220 can undergo elastic deformation, ensuring that its upper surface remains in contact with the lower surface of the fuel element. This transforms the concentrated load applied by the upper mold assembly 100 into a full-area, quasi-isostatic uniform support for the entire lower surface of the fuel element. This support mode avoids localized stress concentration caused by point or line contact in traditional hard molds during the bending forming process of the fuel element, effectively preventing shell breakage or interlayer separation in the sandwich structure of the fuel element. At the same time, the uniform stress distribution promotes plastic flow and stress relaxation of the material, significantly reducing springback after forming and ensuring the dimensional accuracy and shape stability of the curved plate fuel element 20.

[0113] In one embodiment, the flexible mold 220 includes an upper flexible mold 221 and a lower flexible mold 222 stacked together. The thickness of the upper flexible mold 221 is less than the thickness of the lower flexible mold 222, and the upper flexible mold 221 is detachably installed in the mold cavity 201.

[0114] The upper flexible mold 221 and the lower flexible mold 222 do not require any connecting structure (screws, adhesives, etc.) to be strongly fixed to the mold cavity 201; they only need to be placed inside the mold cavity 201. The flexible mold 220 and the mold cavity 201 can have a clearance fit. The upper flexible mold 221 and the lower flexible mold 222 also do not require any connecting structure to be fixed together; the upper flexible mold 221 can simply be stacked on top of the lower flexible mold 222.

[0115] In the above embodiments, the flexible mold 220 is designed to include an upper flexible mold 221 and a lower flexible mold 222 stacked together, with the thickness of the upper flexible mold 221 being less than the thickness of the lower flexible mold 222. Simultaneously, the upper flexible mold 221 is detachably installed within the mold cavity 201. This structural arrangement allows the upper flexible mold 221, which directly contacts the fuel element and bears the main wear and deformation, to be replaced individually after reaching its service life, without replacing the entire flexible mold 220. The lower flexible mold 222 serves as the main elastic support base, providing stable and sufficient elastic deformation space and recovery force through its greater thickness. This significantly reduces the long-term use and maintenance costs of the mold while ensuring the durability and stability of the overall support performance of the flexible mold 220.

[0116] Please see Figure 7 In one embodiment, the width of the upper flexible mold 221 is greater than the width of the lower flexible mold 222, and the shape of the mold cavity 201 matches the shape of the flexible mold 220.

[0117] In the above embodiments, by setting the width of the upper flexible mold 221 to be greater than the width of the lower flexible mold 222, the flexible mold 220 forms a structure that is wider at the top and narrower at the bottom in cross-section. Simultaneously, the shape of the mold cavity 201 matches the shape of the flexible mold 220. This structure allows the force to be transmitted through the upper flexible mold 221 to its wider sides when the upper mold assembly 100 presses down on the fuel element, and is constrained by the side walls of the mold cavity 201. This effectively converts the downward pressure into a lateral clamping force on the entire flexible mold 220, preventing displacement or warping within the mold cavity 201. This wider-at-the-top, narrower-at-the-bottom structure, combined with the matching mold cavity 201, ensures that the flexible mold 220 maintains a stable installation position and shape even under significant pressure and complex deformation, thus providing continuous, uniform, and reliable full-area elastic support for the fuel element and avoiding molding defects caused by support instability.

[0118] Please see Figure 7 In one embodiment, the flexible mold 220 has inclined surfaces on both sides along the third direction XX', so that the width of the flexible mold 220 gradually increases from bottom to top. The upper flexible mold 221 has inclined surfaces on both sides along the third direction XX', and the lower flexible mold 222 has inclined surfaces on both sides along the third direction XX'. The sides of the upper flexible mold 221 and the lower flexible mold 222 are coplanar.

[0119] In the above embodiments, by setting both sides of the upper flexible mold 221 and the lower flexible mold 222 along the third direction XX' as coplanar inclined surfaces, the flexible mold body 220 as a whole forms a continuous inclined surface structure with the width gradually increasing from bottom to top. This continuous inclined structure, in conjunction with the shape-matched mold cavity 201, ensures that when the flexible mold 220 is pressed down by the upper mold assembly 100, its lateral deformation is uniformly constrained by the inner wall of the inclined surface of the mold cavity 201. This effectively converts the vertical downward pressure into a lateral clamping force on the entire flexible mold 220, avoiding stress concentration or relative misalignment at the interlayer joint between the upper flexible mold 221 and the lower flexible mold 222. At the same time, this continuous inclined structure ensures that the upper flexible mold 221 and the lower flexible mold 222 can work together as a whole when deformed under stress, enhancing the structural stability and overall stiffness of the flexible mold 220 under complex loads. This provides a more uniform, stable, and reliable full-area elastic support for the fuel element, ensuring the accuracy and repeatability of the molding process.

[0120] In other embodiments, the width of the upper flexible mold 221 may be uniform from bottom to top, and the width of the lower flexible mold 222 may be uniform from bottom to top.

[0121] Optionally, the width of the upper flexible mold 221 is 10-30 mm larger than the width of the lower flexible mold 222.

[0122] In the above embodiments, by setting the widths of the upper flexible mold 221 and the lower flexible mold 222 to be uniform from bottom to top, a stepped structure is formed at the joint between the upper flexible mold 221 and the lower flexible mold 222, thereby forming a stepped structure inside the mold cavity 201. This stepped structure provides a clear positioning reference for the upper flexible mold 221, ensuring that it can be quickly and accurately reset during repeated disassembly and assembly.

[0123] Please see Figure 3 In one embodiment, two stepped grooves 202 are also constructed between the first wall block 212 and the second wall block 213, and the two stepped grooves 202 are respectively located at both ends of the mold cavity 201 along the second direction YY'.

[0124] Combination Figure 5 and Figure 6 The flexible molding die also includes two limiting parts 230, which correspond one-to-one with two stepped grooves 202. The shape of the limiting part 230 is adapted to the shape of the stepped groove 202, and the limiting part 230 is detachably connected to the first wall block 212 and the second wall block 213. The two limiting parts 230 are used to limit the two ends of the flexible mold body 220 along the second direction YY'.

[0125] In the above embodiment, by providing stepped grooves 202 at both ends of the mold cavity 201 along the second direction YY' and configuring detachable limiting parts 230 with adapted shapes, when the flexible mold 220 is placed in the mold cavity 201, its two ends are constrained by the limiting parts 230 respectively. This mechanically restricts the displacement of the flexible mold 220 at both ends along the second direction YY' when it undergoes elastic deformation under the pressure of the upper mold assembly 100, effectively preventing excessive expansion or slippage of the flexible mold 220 in the length direction. Simultaneously, the detachable limiting parts 230 facilitate assembly and disassembly operations during the installation or replacement of the flexible mold 220 and provide a precise positioning reference in the length direction for the flexible mold 220. This end-limiting structure ensures that the flexible mold 220 maintains a stable working position when repeatedly subjected to pressing loads, thereby providing continuous and stable full-area support for the fuel element and ensuring the repeatability and reliability of the molding process.

[0126] Please see Figures 3 to 6 In one embodiment, the tops of the first wall block 212 and the second wall block 213 are respectively provided with grooves 203 extending along a third direction XX'. The flexible molding die also includes two centering plates 240, which are respectively disposed on the tops of the first wall block 212 and the second wall block 213. The bottoms of the two centering plates 240 are respectively provided with sliders 241, which slide in cooperation with the grooves 203 along a third direction XX' to adjust the distance between the two centering plates 240.

[0127] In the above embodiment, by providing grooves 203 extending along the third direction XX' on the top of the first wall block 212 and the second wall block 213 respectively, and providing sliders 241 that slide in cooperation with the grooves 203 on the bottom of the two centering plates 240 respectively, the two centering plates 240 can precisely and smoothly adjust the distance between them along the grooves 203 according to the width of the metal-based flat fuel element 10. This structure ensures that the centering plates 240 maintain linear motion without deviation during movement. When the fuel element is placed on the flexible mold 220, by adjusting the centering plates 240 to contact the sides of the fuel element, the fuel element can be quickly and accurately positioned at the center of the width direction of the lower mold assembly 200. This ensures that the fuel element is subjected to symmetrical and uniform force during the pressing process, effectively avoiding defects such as twisting of the molded part, uneven wall thickness, or stress concentration caused by placement deviation, which is beneficial to obtaining high-quality and dimensionally accurate curved plate fuel element 20.

[0128] In one embodiment, the two centering plates 240 extend along the third direction XX' towards each other to the upper surface of the flexible mold 220 to limit the two edges of the upper surface of the flexible mold 220.

[0129] In the above embodiment, by extending the two centering plates 240 along the third direction XX' towards each other to the upper surface of the flexible mold 220, this structure allows the centering plates 240 to reliably limit the two sides of the upper surface of the flexible mold 220 after centering the fuel element in the width direction. When the upper mold assembly 100 presses down on the fuel element, the upward bulging trend of the two sides of the flexible mold 220 during elastic deformation is rigidly constrained by the centering plates 240, preventing uneven distribution of support force due to excessive expansion of the edge area. At the same time, this limiting effect, together with the constraint of the limiting part 230 at the stepped groove in the length direction, constitutes a complete constraint system for the three-dimensional deformation of the flexible mold 220, ensuring that it always maintains a regular deformation shape during the pressing process, thereby providing the fuel element with clear boundaries, stable and controllable full-area elastic support, effectively ensuring the molding accuracy and dimensional consistency of the curved plate fuel element 20.

[0130] It should be noted that when the two centering plates 240 are aligned with the metal-based flat fuel element 10 along the width direction, the sides of the two centering plates 240 that are closest to each other abut against the two sides of the metal-based flat fuel element 10 along the width direction. After the two centering plates 240 have completed the alignment of the metal-based flat fuel element 10 along the width direction, the two centering plates 240 need to be moved appropriately along the third direction XX' in a direction away from each other by a clearance distance to ensure that there is no interference between the upper mold assembly 100 and the two centering plates 240 when it is pressed down. Please also refer to... Figure 7 After the two centering plates 240 move away from each other by the clearance distance along the third direction XX', the edge of the two centering plates 240 that is close to each other along the third direction XX' is still above the upper surface of the flexible mold 220, thereby forming a reliable limit on both sides of the upper surface of the flexible mold 220 during the pressing down of the upper mold assembly 100, and suppressing the edge bulging of the flexible mold 220.

[0131] See Figure 7 In one embodiment, the centering plate 240 at the top of the first wall block 212 is the first centering plate 240a, and the centering plate 240 at the top of the second wall block 213 is the second centering plate 240b.

[0132] After the two centering plates 240 are aligned with the metal-based flat fuel element 10 along the width direction, the two centering plates 240 are moved appropriately along the third direction XX' in a direction away from each other by a certain clearance distance. The side of the first centering plate 240a away from the second centering plate 240b along the third direction XX' is aligned with the edge of the first wall block 212, and the side of the second centering plate 240b away from the first centering plate 240a along the third direction XX' is aligned with the edge of the second wall block 213.

[0133] In the above embodiments, by setting the clearance positions of the first centering plate 240a and the second centering plate 240b after centering to be aligned with the edges of the first wall block 212 and the second wall block 213 respectively, this design establishes a clear and fixed mechanical positioning reference. When moving the centering plates, operators do not need to use measuring tools for precise distance measurement; they only need to visually observe whether the outer side of the centering plate is flush with the edge of the wall block to quickly and accurately complete the positioning operation. This visual alignment method not only significantly simplifies the operation process and improves production efficiency, but also completely eliminates the risk of insufficient or excessive clearance distance caused by human measurement errors. It ensures that the two centering plates 240 can stably remain in the predetermined safe position, providing reliable clearance space for the downward pressing movement of the upper mold assembly 100 while maintaining the effective limiting function of the flexible mold body 220's edge.

[0134] Combination Figures 4 to 5 In one embodiment, both centering plates 240 are provided with strip grooves 242 extending along a third direction XX'. Fasteners 250 are provided on the top of the first wall block 212 and the top of the second wall block 213.

[0135] Fasteners 250 on the top of the first wall block 212 pass through the corresponding slot 242 to lock the centering plate 240 to the first wall block 212. Fasteners 250 on the top of the second wall block 213 pass through the corresponding slot 242 to lock the centering plate 240 to the second wall block 213.

[0136] The fastener 250 can be fixed at the top of the first wall block 212 / second wall block 213. For example, a threaded hole can be provided at the top of the first wall block 212 / second wall block 213, and the fastener 250 is a bolt. It can be made to engage with the threaded hole by tightening the fastener 250, or it can be removed from the threaded hole.

[0137] In the above embodiment, by providing strip grooves 242 extending along the third direction XX' on the two centering plates 240, and by providing corresponding fasteners 250 on the top of the first wall block 212 and the second wall block 213, the centering plates 240 can be reliably fixed after position adjustment through the cooperation of the fasteners 250 and the strip grooves 242. This structural design allows the operator to slide the centering plates 240 along the slide groove 203 to a suitable position according to fuel elements of different widths, and then lock the centering plates 240 stably in the predetermined position by tightening the fasteners 250. The extension length of the strip grooves 242 provides sufficient travel range for the position adjustment of the centering plates 240, ensuring that it can adapt to the centering requirements of various fuel element specifications. This adjustable and lockable positioning mechanism ensures both the flexibility of the centering operation and the stability of the position of the centering plates 240 during the pressing process, enabling it to continuously provide reliable edge limiting function for the flexible mold 220.

[0138] It should be noted that after centering is completed, the two centering plates 240 should be moved appropriately along the third direction XX' in a direction away from each other by a certain distance to ensure that the upper mold assembly 100 does not interfere with the two centering plates 240 when it is pressed down, and then the two centering plates 240 should be locked.

[0139] In one embodiment, the lower mold end plate 211 has centering posts 214 at both ends along the second direction YY'. The upper mold frame 110 has centering holes 111, and the centering posts 214 are correspondingly arranged with the centering holes 111. The centering posts 214 and the corresponding centering holes 111 are inserted and engaged along the first direction ZZ'.

[0140] In the above embodiment, by setting centering pillars 214 at both ends of the lower mold end plate 211 along the second direction YY', and setting corresponding centering holes 111 at the corresponding positions of the upper mold frame 110, the centering pillars 214 can accurately guide the centering holes 111 to complete the insertion and engagement along the first direction ZZ' during the pressing process of the upper mold assembly 100. This structure ensures that the convex forming surface 121 of the upper mold assembly 100 and the mold cavity 201 of the lower mold assembly 200 always maintain a precise coaxial alignment relationship during the mold closing process, effectively preventing problems such as unilateral pressure on the fuel element, uneven wall thickness, or local stress concentration caused by mold misalignment; at the same time, this rigid alignment mechanism provides a stable guiding reference for the entire forming system, ensuring that the pressure applied by the upper mold assembly 100 can be evenly transmitted to the entire support surface of the flexible mold 220, so that the fuel element obtains a symmetrical force environment during the pressing process, thereby significantly improving the forming accuracy, dimensional consistency, and structural integrity of the curved plate fuel element 20.

[0141] In one embodiment, the thickness of the flexible mold 220 along the first direction ZZ' is designed to satisfy the following: the flexible mold 220 can allow the maximum elastic deformation along the first direction ZZ' to be greater than the maximum chord height of all the arc-shaped fuel element plates to be formed.

[0142] Optionally, the maximum elastic deformation allowed by the flexible mold 220 along the first direction ZZ' should be 20%-30% greater than the maximum chord height of all the arc-shaped fuel element plates to be formed. The maximum elastic deformation allowed by the flexible mold 220 along the first direction ZZ' should be 2mm-10mm greater than the maximum chord height of all the arc-shaped fuel element plates to be formed.

[0143] Optionally, the flexible mold 220 can allow the maximum elastic deformation along the first direction ZZ' not to exceed 25% of the total thickness of the flexible mold 220.

[0144] In the above embodiments, by specifically designing the thickness of the flexible mold 220 along the first direction ZZ', the maximum allowable elastic deformation is greater than the maximum chord height of all the curved fuel element plates to be formed. This design principle ensures that the flexible mold 220 has sufficient elastic deformation space. When the upper mold assembly 100 presses down on the fuel element to the maximum designed chord height, the flexible mold 220 can provide continuous and stable full-area support for its lower surface while maintaining a fully elastic deformation state, effectively avoiding support failure or local stress concentration due to insufficient deformation. At the same time, this design ensures that the flexible mold 220 can still fully recover its initial shape after experiencing maximum compression deformation, preventing permanent deformation. This ensures that the mold maintains stable support performance and forming accuracy during long-term repeated use, providing reliable elastic support for high-quality forming of curved fuel elements of different specifications.

[0145] In one embodiment, the convex surface 121 is a convex arc-shaped surface, the outer diameter of which is equal to or slightly smaller than the inner diameter of the designed arc-shaped fuel element plate.

[0146] In the above embodiments, by designing the convex forming surface 121 as a convex arc surface, and making its outer diameter equal to or slightly smaller than the inner diameter of the designed arc-shaped fuel element plate, this dimensional design enables the upper mold assembly 100 to perform over-bending compensation on the fuel element during the pressing process. When the convex forming surface 121 is pressed down with a size slightly smaller than the target radius of curvature, the fuel element is forced to bend to a greater degree than the final designed curvature under the elastic support of the flexible mold 220; after the pressure is removed after the holding stage, the amount of springback generated by the elasticity of the material in the fuel element restores it to the precise designed curvature. This preset over-bending compensation amount, combined with the uniform support provided by the flexible mold 220, effectively offsets the dimensional deviation caused by the elastic recovery of the material, ensuring that the curved plate fuel element 20 can stably achieve the designed radius of curvature and geometric accuracy after molding, realizing the technical effect of obtaining a high-precision molded part through a single pressing.

[0147] In other embodiments, the curved plate fuel element 20 may also be an involute plate fuel element or a plate fuel element with other curved shapes. Correspondingly, the convex surface 121 may also be an involute convex surface.

[0148] In one embodiment, the upper mold assembly 100 is made of high-temperature stable chromium-based or nickel-based alloy steel or austenitic stainless steel that has undergone high-temperature stabilization treatment, specifically including ferritic stainless steels 430, 441, and 409L, nickel-based alloy steels GH600, GH3030, and GH4169, and austenitic stainless steels S310 and 321, etc. The surface roughness of the convex forming surface 121 is not higher than 1.8 μm. The lower mold base 210 can be made of the same material as the upper mold assembly 100, or it can be ordinary stainless steel. The center plate 240 can be made of the same material as the upper mold assembly 100.

[0149] In one embodiment, the above-described warm compression molding preparation method and flexible molding die can be used for Al-based, Zr-based dispersed fuels or UMo. x Preparation of metal-based arc plate type fuel element with alloy sheet coated with Zr coating.

[0150] The following are some more specific implementation examples:

[0151] First embodiment: The curved plate type fuel element is an arc-shaped plate-shaped U3Si2-Al based dispersion fuel element. The warm pressing preparation method of the arc-shaped plate-shaped U3Si2-Al based dispersion fuel element includes the following steps:

[0152] (1) Install the upper mold assembly 100 on the upper worktable of the press, install the lower mold frame 210 on the lower worktable of the press, and spray the release agent evenly on the convex forming surface 121.

[0153] (2) Place the two layers of silicone rubber mold (the upper flexible mold and the lower flexible mold respectively) into the mold cavity 201.

[0154] (3) Adjust the spacing between the two centering plates 240 according to the width of the U3Si2-Al based flat plate type dispersed fuel element.

[0155] (4) The upper mold assembly 100 is placed in the first heating furnace for preheating and heat preservation. The preheating temperature is 300±5℃ and the heat preservation time is not less than 1h. The first heating furnace is a heating furnace that can be opened in the horizontal direction.

[0156] (5) The cold-rolled U3Si2-Al-based flat fuel element is placed in the second heating furnace for annealing. The annealing temperature is 350±5℃ and the holding time is 20min~1.5h.

[0157] (6) Use a fixture to place the annealed U3Si2-Al-based flat fuel element on the upper silicone rubber mold and ensure alignment.

[0158] (7) Move the two centering plates 240 away from each other along the third direction so that the two centering plates 240 are aligned with the top edges of the corresponding wall blocks (first wall block 212 / second wall block 213) respectively, and then fix them with fasteners.

[0159] (8) Open the first heating furnace and position the heating components inside the first heating furnace so as not to affect the up-and-down movement of the upper mold assembly 100.

[0160] (9) Start the press so that the upper mold assembly 100 moves down and the convex surface 121 contacts the U3Si2-Al based flat plate fuel element and then slowly descends (5mm / min) until the upper mold assembly reaches the end position of the predetermined stroke; continue to pressurize the upper mold assembly 100 and maintain the pressure for not less than 30min.

[0161] (10) Start the compressor to lift the upper mold assembly 100 so that the upper mold assembly 100 does not affect the subsequent unloading operation of the fuel element.

[0162] (11) Use a fixture to transfer the obtained arc-shaped plate-shaped U3Si2-Al based dispersed fuel element to the product rack, and let it cool naturally to obtain the U3Si2-Al based dispersed fuel element of the designed size.

[0163] In this embodiment, the target dimensions of the arc-shaped U3Si2-Al based dispersion fuel element are: thickness 2.0 mm, inner radius 110 mm, arc length 60 mm, and length 500 mm. The radius of the convex surface 121 can be designed to be 105 mm, arc length 100 mm, and length 600 mm. The material of the upper mold assembly 100 can be ferritic stainless steel 430, 441, 409L, etc.

[0164] Second embodiment: The curved plate type fuel element is an arc-shaped plate-shaped UO2-Zr based dispersion fuel element. The warm pressing preparation method of the arc-shaped plate-shaped UO2-Zr based dispersion fuel element includes the following steps:

[0165] (1) Install the upper mold assembly 100 on the upper worktable of the press, install the lower mold frame 210 on the lower worktable of the press, and spray the release agent evenly on the convex forming surface 121.

[0166] (2) Place the two layers of perfluoroether rubber molds (the upper flexible mold and the lower flexible mold, respectively) into the mold cavity 201.

[0167] (3) Adjust the spacing between the two centering plates 240 according to the width of the UO2-Zr-based flat plate type dispersed fuel element.

[0168] (4) The upper mold assembly 100 is wrapped with a heating shell woven with heating tape to preheat and keep the upper mold assembly 100 warm. The preheating temperature is 300±5℃ and the heat preservation time is not less than 1h.

[0169] (5) The cold-rolled UO2-Zr-based flat fuel element is placed in the second heating furnace for annealing. The annealing temperature is 475±5℃ and the holding time is 20min~1.5h.

[0170] (6) Take the annealed UO2-Zr-based flat fuel element out of the second heating furnace and place it on the product rack to cool it to 300°C in the air. Then use a clamp to place the UO2-Zr-based flat fuel element on the upper perfluoroether rubber mold and ensure alignment.

[0171] (7) Move the two centering plates 240 away from each other along the third direction so that the two centering plates 240 are aligned with the top edges of the corresponding wall blocks (first wall block 212 / second wall block 213) respectively, and then fix them with fasteners.

[0172] (8) Remove the heating shell woven with heating tape that covers the upper mold assembly 100.

[0173] (9) Start the press so that the upper mold assembly 100 moves down and the convex forming surface 121 contacts the UO2-Zr based flat plate fuel element and then slowly descends (5mm / min) until the upper mold assembly reaches the end position of the predetermined stroke; hold the pressure on the upper mold assembly 100 for a time of not less than 30min, wherein the predetermined stroke of the upper mold assembly 100 causes the deformation of the flexible mold 220 along the first direction ZZ' to be between 15 and 20mm.

[0174] (10) Start the compressor to lift the upper mold assembly 100 so that the upper mold assembly 100 does not affect the subsequent unloading operation of the fuel element.

[0175] (11) Use a fixture to transfer the obtained arc-shaped plate-shaped UO2-Zr-based dispersed fuel element to the product rack, and let it cool naturally to obtain the UO2-Zr-based dispersed fuel element of the designed size.

[0176] In this embodiment, the target dimensions of the arc-shaped plate-like UO2-Zr-based dispersed fuel element are: thickness 2.0 mm, inner radius 85 mm, arc length 120 mm, and length 500 mm. The radius of the convex surface 121 can be designed to be 85 mm, arc length 200 mm, and length 600 mm. The surface roughness of the convex surface 121 is not higher than 1.8 μm.

[0177] The upper mold assembly 100 and the lower mold base 210 are made of austenitic stainless steel 321 that has undergone high-temperature stabilization treatment. The center plate is made of stainless steel.

[0178] Third embodiment: The curved plate type fuel element is an arc-shaped UMo. x -Al-based dispersed fuel element, arc-shaped UMo x - The warm-press forming method for preparing Al-based dispersed fuel elements includes the following steps:

[0179] The curved plate type fuel element is an arc-shaped plate-shaped UMo x -Al-based dispersed fuel element, arc-shaped UMo x - The warm-press forming method for preparing Al-based dispersed fuel elements includes the following steps:

[0180] (1) Install the upper mold assembly 100 on the upper worktable of the press, install the lower mold frame 210 on the lower worktable of the press, and spray the release agent evenly on the convex forming surface 121.

[0181] (2) Place the two silicone rubber molds (the upper flexible mold and the lower flexible mold) into the mold cavity 201.

[0182] (3) According to UMo x - The width of the Al-based flat-plate type dispersed fuel element is adjusted by the spacing between the two centering plates 240.

[0183] (4) The upper mold assembly 100 is preheated and kept warm using a first heating furnace. The preheating temperature is 250±5℃ and the holding time is not less than 1h. The first heating furnace has a bottom-mounted sliding furnace door.

[0184] (5) The cold-rolled UMo x -Al-based flat-plate fuel elements are annealed in a second heating furnace at a temperature of 420±5℃ for 20 min to 1.5 h.

[0185] (6) Anneal the UMo x -Al-based flat-plate fuel elements are removed from the second heating furnace and placed on a product rack to cool to 270°C in air. Then, a clamp is used to hold the UMo... x - The Al-based flat-plate fuel element is placed on the upper silicone rubber mold, ensuring alignment.

[0186] (7) Move the two centering plates 240 away from each other along the third direction so that the two centering plates 240 are aligned with the top edges of the corresponding wall blocks (first wall block 212 / second wall block 213) respectively, and then fix them with fasteners.

[0187] (8) Push or pull the furnace door of the first heating furnace to a region that does not affect the up-and-down movement of the upper mold assembly 100.

[0188] (9) Start the press, causing the upper mold assembly 100 to move down, and the convex forming surface 121 and UMo x -The Al-based flat fuel element slowly descends (5mm / min) after contact until the upper mold assembly reaches the end position of the predetermined stroke; the upper mold assembly 100 is pressurized for a time of not less than 30min, wherein the predetermined stroke of the upper mold assembly 100 causes the deformation of the flexible mold 220 along the first direction ZZ' to be between 15 and 20mm.

[0189] (10) Start the compressor to lift the upper mold assembly 100 so that the upper mold assembly 100 does not affect the subsequent unloading operation of the fuel element.

[0190] (11) Use a clamp to hold the obtained arc-shaped plate-shaped UMo x -Al-based dispersed fuel elements are transferred to the product rack and allowed to cool naturally, resulting in UMo of the designed dimensions. x -Al-based dispersed fuel elements.

[0191] In this embodiment, the target dimensions of the arc-shaped plate-like UO2-Zr-based dispersed fuel element are: thickness 2.0 mm, inner radius 85 mm, arc length 120 mm, and length 500 mm. The radius of the convex surface 121 can be designed to be 85 mm, arc length 200 mm, and length 600 mm. The surface roughness of the convex surface 121 is not higher than 1.8 μm.

[0192] The upper mold assembly 100 and the lower mold base 210 are made of chromium-based or nickel-based alloy steel. The center plate is made of stainless steel.

[0193] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0194] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A warm compaction manufacturing method for manufacturing a curved plate type fuel element using a flexible forming mold, characterized by, The flexible forming die comprises an upper die assembly and a lower die assembly, the lower die assembly comprises a lower die frame and a flexible die body installed in the lower die frame, and the flexible die body is made of elastic material; The warm compaction forming preparation method comprises: The metal-based flat fuel element is heated to an annealing temperature, and is kept at the annealing temperature for a first time length, the heating rate of the metal-based flat fuel element during the heating process is 20-40 ℃ / min, the annealing temperature is set to be in a full range of recrystallization temperature of the metal material in the metal-based flat fuel element, and is in a lower limit interval of the full range from the lower limit to one fourth of the full range; The upper die assembly is preheated and kept at the preheating temperature for a second time length, wherein the preheating temperature is lower than or equal to the annealing temperature and is lower than the upper limit of the temperature resistance of the flexible die body; The annealed metal-based flat fuel element is placed on the flexible die body; The upper die assembly is pressurized to make the upper die assembly press down the metal-based flat fuel element, and the metal-based flat fuel element is formed into a curved plate type fuel element under the support of the flexible die body; The upper die assembly is kept pressurized for a third time length, and the temperature of the flexible forming die keeps the curved plate type fuel element in the forming space for the third time length during the keeping pressurized process; The curved plate type fuel element is taken out of the flexible forming die and cooled.

2. The warm compaction manufacturing method according to claim 1, characterized in that, The preheating temperature is 200-350 ℃.

3. The warm compaction manufacturing method according to claim 1, wherein If the annealing temperature is higher than the upper limit of the temperature resistance of the flexible die body, the annealed metal-based flat fuel element is cooled, and the temperature of the cooled metal-based flat fuel element is lower than the upper limit of the temperature resistance of the flexible die body, and then the metal-based flat fuel element is placed on the flexible die body.

4. The warm compaction manufacturing method according to claim 3, wherein The temperature of the cooled metal-based flat fuel element is equal to the preheating temperature, and then the metal-based flat fuel element is placed on the flexible die body.

5. The warm compaction manufacturing method according to claim 3, wherein The temperature of the cooled metal-based flat fuel element is 250-350 ℃.

6. The warm compaction manufacturing method according to claim 1, wherein If the annealing temperature is lower than the upper limit of the temperature resistance of the flexible die body, the preheating temperature is equal to the annealing temperature.

7. The warm compaction manufacturing method according to claim 1, wherein In the step of preheating the upper die assembly and keeping it at the preheating temperature for a second time length, the upper die assembly is preheated by a first heating device, wherein the first heating device is a first heating furnace, or an electric heating rod capable of being inserted into the upper die assembly, or a cladding type heating shell woven by a heating belt; In the step of heating the metal-based flat fuel element to an annealing temperature and keeping it at the annealing temperature for a first time length, the metal-based flat fuel element is heated by a second heating device, and the second heating device is a second heating furnace.

8. The warm compaction manufacturing method according to claim 1, wherein Further comprising: Before the step of preheating the upper die assembly and keeping it at the preheating temperature for a second time length, a release agent is sprayed on the convex forming surface of the upper die assembly.

9. The warm compaction manufacturing method according to claim 1, wherein The material of the flexible mold body includes any one or a combination of silicone rubber, fluororubber, perfluoroether rubber, or silicone rubber.

10. The warm compaction manufacturing method according to claim 1, wherein The first time length is 20 min to 90 min; the second time length is not less than 1 h; and the third time length is 10 min to 1 h.

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