Fuel element and assembly based on spiral turbulent flow enhanced heat exchange and assembling method

Abstract

The invention provides a fuel element and assembly based on spiral turbulent flow enhanced heat exchange and an assembling method, belongs to the technical field of nuclear reactors, and aims to solve the technical problems of poor thermal hydraulic characteristics and large temperature difference between the center and the edge in a fuel assembly. The fuel element is of a tubular spiral structure with a water-drop-shaped section. The technical effects that the peak temperature of the fuel assembly is lower, and the temperature uniformity is better are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear reactors, in particular to a fuel element based on spiral disturbance flow enhanced heat transfer, an assembly and an assembling method. BACKGROUND

[0002] In the nuclear power plant reactor operation system, the performance of the fuel element is crucial, and is a key factor affecting the safety and economy of the reactor. Currently, common nuclear fuel is designed as a solid cylinder, and the coolant flows through the outer cladding to cool it. Some fuel elements also use stainless steel wire structures to assist cooling.

[0003] However, the existing fuel elements have exposed some problems in actual operation. Some fuel assemblies have unsatisfactory thermal hydraulic characteristics, which leads to a relatively obvious temperature difference between the center and the edge of the fuel core, which not only affects the overall thermal efficiency of the reactor, but also may bring potential risks to the long-term stable operation of the fuel element. To solve the above problems, some researchers have developed annular fuel elements, which have increased the heat transfer area, but the effect is still not ideal. SUMMARY

[0004] In view of the deficiencies in the prior art, the present application proposes a fuel element based on spiral disturbance flow enhanced heat transfer, an assembly and an assembling method, to solve the technical problems of poor thermal hydraulic characteristics and large temperature difference between the center and the edge in the fuel assembly.

[0005] The technical solution adopted by the present application is a fuel element based on spiral disturbance flow enhanced heat transfer, an assembly and an assembling method.

[0006] Among them, the fuel element based on spiral disturbance flow enhanced heat transfer is a tubular spiral structure with a water droplet-shaped cross section.

[0007] Optionally, the water droplet-shaped cross section includes a tail end circular arc segment and a head end V-shaped segment, the two sides of the circular arc segment and the two sides of the V-shaped segment are smoothly connected, the tip of the V-shaped segment is also smoothly connected, and the distance from the tip of the V-shaped segment to the center of the circular arc segment is greater than the radius of the circular arc segment.

[0008] Optionally, the fuel element includes an inner cladding located in the inner layer of the tubular structure, an outer cladding located in the outer layer of the tubular structure, and a fuel core filled between the two.

[0009] Among them, the fuel assembly based on spiral disturbance flow enhanced heat transfer includes the fuel element as described above, and further includes a lower tube seat and an upper tube seat; the two ends of a plurality of fuel elements are connected to the lower tube seat and the upper tube seat, respectively.

[0010] Optionally, the cross-sectional angles of the plurality of fuel elements are aligned in the same direction; one of the fuel elements is located at the center, and the remaining fuel elements are distributed around the central fuel element, with the outer surfaces of two adjacent fuel elements supporting each other.

[0011] Optionally, both ends of each fuel element are connected to the lower or upper tube seat via a connecting frame. The connecting frame includes: a fuel end cap for connecting the fuel element; a locating pin for connecting the mounting pin hole of the tube seat; and a claw-type support frame for connecting the fuel end cap and the locating pin. The inner cavity of the fuel element communicates with the outside through a through area on the fuel end cap.

[0012] Optionally, the fuel end cap is a fixed-shape integral part; or, the fuel end cap is an assembly whose thickness can be adaptively adjusted, the assembly including a fixed end plate, a movable end plate and an elastic element, the fixed end plate and the movable end plate being opposite to and slidably fitted, the elastic element being disposed between the fixed end plate and the movable end plate, and the movable end plate being connected to the fuel element.

[0013] Optionally, the fuel element is welded to the fuel end cap; or, the end face of the fuel end cap is provided with a protruding limiting profile plate, which can restrict the circumferential movement of the fuel element.

[0014] The fuel assembly method based on helical turbulence-enhanced heat transfer is applicable to the fuel assemblies described above and includes the following steps: Acquire the temperature distribution of the fuel assembly during operation and identify localized high-temperature zones; Assemble the lower tube seat, upper tube seat, and fuel element according to the structure of the fuel assembly, wherein, for the fuel element located in the high-temperature zone, at least one end is connected to the tube seat using a fuel end cap in the form of an assembly.

[0015] Optionally, the high-temperature zone of the fuel assembly during operation can be obtained through computer simulation; and / or, one end of the central fuel element can be installed into the lower tube seat first, then the outer peripheral fuel element can be installed, and finally the upper tube seat can be installed.

[0016] As can be seen from the above technical solution, the beneficial technical effects of the present invention are as follows: The fuel element proposed in this invention, based on helical turbulence-enhanced heat transfer, employs a tubular helical structure with a teardrop-shaped cross-section, effectively addressing the problems of poor thermal-hydraulic characteristics and large temperature differences between the center and edges in fuel assemblies. This unique structure increases the heat transfer area, enhancing the heat transfer effect between the coolant and the fuel core, and significantly reducing the peak temperature of the fuel assembly. Simultaneously, the helical structure promotes uniform coolant flow, resulting in a more even heat distribution and greatly improving the temperature uniformity of the fuel assembly, ensuring stable and efficient reactor operation. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0018] Figure 1 This is a schematic diagram of the fuel element's shape.

[0019] Figure 2 This is a schematic diagram of the cross-section of a fuel element.

[0020] Figure 3 This is a schematic diagram of the fuel element arrangement.

[0021] Figure 4 This is a three-dimensional schematic diagram of one type of support frame.

[0022] Figure 5 This is a three-dimensional schematic diagram of another type of support frame.

[0023] Figure 6 This is a cross-sectional view of the support frame.

[0024] Figure 7 This is a schematic diagram of the tail end of the lower tube seat.

[0025] Figure 8 This is a schematic diagram of the inner end of the lower tube seat.

[0026] Figure 9 This is a schematic diagram of the tail end of the upper tube seat.

[0027] Figure 10 This is a schematic diagram of the fuel element and the lower tube seat.

[0028] Figure 11 This is a schematic diagram of the fuel element and the upper tube seat.

[0029] Figure 12 This is a schematic diagram comparing it with existing technology structures.

[0030] Figure 13 A schematic diagram of cross-sectional temperature distribution for comparison with existing technologies.

[0031] Figure 14 A schematic diagram showing the highest temperature and pressure drop compared to existing technologies.

[0032] Figure 15 This is a diagram for comparison with several other existing technologies.

[0033] Figure 16 A schematic diagram of cross-sectional temperature distribution for comparison with several other existing technologies.

[0034] Figure 17This is a schematic diagram comparing temperature distribution from a three-dimensional perspective.

[0035] Figure 18 This is a schematic diagram comparing the secondary flow intensity with existing technologies.

[0036] Reference numerals: fuel element 4, inner shell 1, outer shell 3, fuel core 2, lower tube seat 11, mounting pin hole 12, compression spring 17, upper tube seat 14, fuel end cap 8, fixed end plate 80, movable end plate 81, elastic element 82, contour plate 83, notch 84, positioning pin 10, support frame 9, high temperature zone 90, point contact 92, inner flow channel 7, outer flow channel 6, filter screen 18, flow channel hole 13. Detailed Implementation

[0037] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0038] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0039] Among them, fuel element 4, which is based on spiral turbulence-enhanced heat transfer, please refer to the appendix. Figure 1 and Figure 4 One possible implementation of a single fuel element is as follows: the fuel element 4 is a tubular spiral structure with a teardrop-shaped cross-section. Specifically, as shown... Figure 2 As shown, the teardrop-shaped cross-section includes a rounded end segment and a V-shaped head segment. The two sides of the rounded end segment and the two sides of the V-shaped head segment are smoothly connected, and the tip of the V-shaped head segment is also smoothly connected. The distance from the tip of the V-shaped head segment to the center of the rounded end segment is greater than the radius of the rounded end segment. Since the fuel element 4 has a certain thickness, the distances mentioned above are all based on the center plane of the thickness. The fuel element 4 includes an inner shell 1 located in the inner layer of the tubular structure, an outer shell 3 located in the outer layer of the tubular structure, and a fuel core 2 filled between the two.

[0040] The fuel element proposed in this scheme, based on helical turbulence-enhanced heat transfer, is a tubular helical structure with a teardrop-shaped cross-section, which has many significant advantages over existing technologies.

[0041] In terms of heat exchange capacity, this fuel element features a double-sided cooling annular design, increasing the heat exchange area by approximately 50% compared to traditional solid fuel elements, significantly improving heat exchange efficiency. Simultaneously, its axial spiral structure mixes the coolant, enhancing the heat exchange effect. Furthermore, this fuel element is circumferentially asymmetrical, unlike circumferentially symmetrical petal-shaped fuel elements. Figure 15 and Figure 16Compared to other fuels, it has a stronger mixing ability, which can more effectively promote heat transfer and make the heat distribution of the fuel assembly more uniform.

[0042] In terms of structural support, the fuel element relies on its own spiral structure, which enables it to achieve self-support during arrangement, eliminating the need for additional wire winding supports or grid support structures. (See [reference needed]) Figure 12 The two adjacent fuel elements 4 can contact and support each other, and the contact is point contact. This not only simplifies the overall structure of the fuel assembly and reduces the complexity of manufacturing and installation, but also reduces the potential failure points and maintenance costs caused by the additional support structure, thereby improving the reliability and stability of reactor operation.

[0043] For information on thermal-hydraulic performance, please refer to [link / reference]. Figure 18 , Figure 18 The comparison of secondary flow intensity for four fuel elements is shown. Secondary flow intensity characterizes the lateral mixing intensity of the fuel element, and is defined as S: In the formula, V x V y and V z These represent the velocities in the x, y, and z directions (axial directions), respectively. From... Figure 18 It can be seen that the fuel element in this design has a better secondary flow intensity distribution, meaning it can better mix the coolant to enhance heat transfer. Although the wire-wound structure also has high secondary flow intensity, this structure causes a larger flow pressure drop, which is not conducive to saving pump power. (See [reference needed]). Figure 14 .

[0044] In specific application scenarios, fuel elements 4 need to be used in groups.

[0045] This solution is based on a fuel assembly that enhances heat transfer through helical turbulence. One possible implementation is as follows (see attached document). Figure 10 and Figure 11 , Figure 10 The lower end of the fuel assembly, Figure 11 The fuel assembly consists of multiple fuel elements 4 vertically connected between its upper and lower ends. Specifically, this fuel assembly includes the aforementioned fuel elements 4, as well as a lower tube seat 11 and an upper tube seat 14; the two ends of the multiple fuel elements 4 are respectively connected to the lower tube seat 11 and the upper tube seat 14.

[0046] Regarding the arrangement shape, see Figure 3 The cross-sectional tips of multiple fuel elements 4 all point in the same direction. Within different height ranges of the fuel assembly, since the initial angle and helix angle of each fuel element 4 are the same, the tips of each fuel element 4 will also point in the same direction at any height, only differing in orientation. Figure 3When the cross-section reaches the indicated height, the sharp corners of each fuel element 4 face to the right, and two adjacent fuel elements 4 can support each other laterally. Specifically, one fuel element 4 is located in the center, and the remaining fuel elements 4 are distributed around it, with the outer surfaces of adjacent fuel elements 4 supporting each other. Specifically, the helical high point at the tip of the V-shaped segment of one fuel element 4 supports the arc segment of another fuel element 4, forming a local point contact 92 and support. That is, along the height direction of the fuel element 4, when the helix of the fuel element 4 on the left rotates to the right, it contacts the middle of the arc segment of the fuel element 4 on the right, forming a point contact 92. This means that there is a point contact 92 every other helix pitch of the fuel element 4.

[0047] In the above embodiments, this scheme is based on a fuel assembly with enhanced heat transfer through helical turbulence. Multiple teardrop-shaped cross-section tubular helical fuel elements 4 are vertically connected between the lower tube seat 11 and the upper tube seat 14. In terms of arrangement, the pointed corners of the multiple fuel elements 4 face the same direction. Although the overall direction of the pointed corners differs at different heights, they remain consistent. One fuel element 4 is centrally located, with the others distributed around it. Adjacent fuel elements 4 are supported by point contacts 92, that is, the V-shaped tip of one fuel element 4 supports the arc segment of another fuel element 4, forming point contacts 92. There is one point contact every one pitch. This structure not only continues the advantages of enhanced heat transfer and self-support of a single fuel element, but also further enhances the overall stability of the fuel assembly through a reasonable arrangement. It also optimizes the flow path of the coolant within the assembly, making heat transfer more uniform and efficient, effectively reducing the peak temperature of the fuel assembly, improving temperature uniformity, ensuring the safe and stable operation of the reactor, and improving economic efficiency.

[0048] Furthermore, both ends of each fuel element 4 are connected to the lower tube seat 11 or the upper tube seat 14 via a connecting frame. The connecting frame includes: a fuel end cap 8 connecting the fuel element 4; a positioning pin 10 connecting the mounting pin hole 12 of the tube seat; and a claw-type support frame 9 connecting the fuel end cap 8 and the positioning pin 10. The inner cavity of the fuel element 4 communicates with the outside through a through area on the fuel end cap 8. Both the lower tube seat 11 and the upper tube seat 14 are provided with flow channel holes 13, through which coolant can enter the area of ​​the claw-type support frame 9. The structure of the claw-type support frame 9 does not obstruct the flow of coolant. The coolant can enter the inner flow channel 7 of a single fuel element 4 after passing through the claw-type support frame 9, and can also flow through the outer flow channel 6 between adjacent fuel elements 4. When the coolant flows through the outer flow channel 6 between the fuel elements 4, it is agitated by the spiral cross-section of the fuel element 4, thereby generating lateral flow.

[0049] In the above embodiment, each fuel element 4 is connected to the lower tube seat 11 and the upper tube seat 14 by connecting brackets at both ends. The connecting bracket consists of a fuel end cap 8, a positioning pin 10, and a claw-type support frame 9. The inner cavity of the fuel element 4 communicates with the outside through the through area of ​​the fuel end cap 8. The lower and upper tube seats are provided with flow channel holes 13, through which coolant enters the area of ​​the claw-type support frame 9. Its special structure does not obstruct the flow of coolant. The coolant can enter the inner flow channel 7 of a single fuel element 4 through it, and can also flow through the outer flow channel 6 between adjacent fuel elements 4. When the coolant flows through the outer flow channel 6, it is agitated by the spiral cross section of the fuel element 4, resulting in lateral flow. This not only ensures the stable connection of the fuel element 4, but also optimizes the coolant flow path, enhances the heat exchange effect, makes the heat distribution more uniform, further reduces the peak temperature of the fuel assembly, improves temperature uniformity, and at the same time reduces flow resistance, saves pump power consumption, and improves the safety and economy of reactor operation.

[0050] In one possible implementation, see Appendix Figure 6 The fuel end cap 8 is either a fixed-shape integral piece or a thickness-adjustable assembly. The assembly includes a fixed end plate 80, a movable end plate 81, and an elastic element 82. The fixed end plate 80 and movable end plate 81 are opposite and slidably fitted. The elastic element 82 is located between the fixed end plate 80 and the movable end plate 81. The movable end plate 81 connects to the fuel element 4. Generally, the integral fuel end cap 8 is used for fuel assemblies located at the edge, while the assembled fuel end cap 8 is used for fuel assemblies located at the center. In a more preferred embodiment, the fixed end plate 80 and the movable end plate 81 are connected by a locally located piston, with the elastic element 82 located inside the piston. The position and number of piston structures correspond to the claw points of the claw support frame 9. When installing the fuel element 4 between the upper and lower tube seats, the distance between the two opposing movable end plates 81 can be slightly less than the length of the fuel element 4, thus allowing the elastic element 82 to have a certain initial pressure and compression. This is because, during the operation of the fuel assembly, due to temperature inhomogeneity and differences in consistency among the fuel elements 4, the fuel elements 4 will experience asynchronous microscopic losses, or inconsistent thermal expansion due to temperature differences, resulting in changes in the length of each fuel element 4. If both ends are fixed, these changes must be absorbed by the bending deformation of the fuel elements 4; however, in this solution, the elastic element 82 can absorb these changes, and the fuel elements 4 will not bend or deform, nor will internal stress be generated.

[0051] In the above embodiments, the fuel end cap 8 has two forms: one is a fixed-shape integral part, mostly used for edge fuel elements, which has better heat dissipation and regulation, and its thermal expansion is less than that of the central area; the other is an assembly with self-adjustable thickness, consisting of a fixed end plate 80, a movable end plate 81, and an elastic element 82, commonly used for central fuel elements. In a more preferred embodiment, the fixed end plate 80 and the movable end plate 81 are connected by a local piston, and the elastic element 82 is located inside the piston, with the piston structure position and number of sets corresponding to the claw points of the claw support frame 9. During installation, the distance between the relative movable end plates 81 is slightly less than the length of the fuel element 4, so that the elastic element 82 has initial pressure and compression. During operation, due to uneven temperature and differences in the consistency of the fuel elements 4, length changes will occur. The traditional two-end fixing method will cause the fuel element 4 to bend and deform and generate internal stress, and the length changes of each fuel element 4 will be inconsistent. However, the elastic element 82 in this embodiment can absorb these changes, avoid bending deformation and internal stress of the fuel element 4, effectively extend the service life of the fuel element 4, ensure stable operation of the fuel assembly, and improve the safety and reliability of the reactor.

[0052] In one possible implementation, see Appendix Figure 4 and Figure 5 The fuel element 4 is welded to the fuel end cap 8; or, the end face of the fuel end cap 8 is provided with a protruding limiting profile plate 83, which can restrict the circumferential movement of the fuel element 4. The inner cavity cross section of the limiting profile plate 83 is consistent with the outer periphery of the teardrop-shaped cross section, but the tip of the limiting profile plate 83 is provided with a notch 84 to accommodate the helical torsion of the teardrop-shaped cross section of the fuel element 4.

[0053] In the above embodiments, there are two ways to connect the fuel element 4 to the fuel end cap 8. One method is to directly weld the fuel element 4 to the fuel end cap 8. This connection method is stable and reliable, ensuring that the fuel element 4 and fuel end cap 8 are tightly connected during reactor operation, preventing loosening or detachment and ensuring the integrity of the fuel assembly structure. The second method involves a protruding limiting profile plate 83 on the end face of the fuel end cap 8. Its inner cavity cross-section matches the outer periphery of the teardrop-shaped cross-section of the fuel element 4, effectively restricting the circumferential movement of the fuel element 4. Simultaneously, the limiting profile plate 83 has a notch 84 at its tip to accommodate the helical twisting of the teardrop-shaped cross-section of the fuel element 4 during initial installation. This design not only simplifies the installation process, reduces installation difficulty and cost, but also makes the replacement of the fuel element 4 more convenient, allowing for rapid replacement, reducing reactor downtime, improving reactor operating efficiency and economic benefits, and ensuring the safe and stable operation of the reactor.

[0054] One possible implementation of the fuel assembly method based on helical turbulence-enhanced heat transfer is as follows, applicable to the above-mentioned fuel assembly, and includes the following steps: Acquire the temperature distribution of the fuel assembly during operation, and identify localized high-temperature zones, such as...Figure 13 The 90°C high-temperature zone is a relative concept. Taking the temperature cloud map simulation results as an example, it refers to the area where the temperature is significantly higher than other areas, and it is generally shown in red in the temperature cloud map. Assemble the lower tube seat 11, upper tube seat 14 and fuel element 4 according to the structure of the fuel assembly. For the fuel element 4 located in the high temperature zone 90, at least one end is connected to the tube seat using a fuel end cap 8 in the form of an assembly. At least one of the tube seats, the lower tube seat 11 or the upper tube seat 14, is provided with a compression spring 17 at its outer end, which can adjust the axial height of the entire fuel assembly. The entire fuel assembly abuts against the external structure through the compression spring 17, which can generate preload and improve stability and adaptability.

[0055] In a more specific embodiment, the high-temperature zone 90 during the operation of the fuel assembly is obtained by computer simulation; and / or, one end of the central fuel element 4 is first installed into the lower tube seat 11, then the outer peripheral fuel element 4 is installed, and finally the upper tube seat 14 is installed.

[0056] This method first obtains the temperature distribution of the fuel assembly during operation, identifying localized high-temperature zones 90. Based on the assembly structure, the lower tube seat 11, upper tube seat 14, and fuel element 4 are assembled. For the fuel element 4 in the high-temperature zone 90, at least one end is connected to the tube seat using a modular fuel end cap 8. Simultaneously, a compression spring 17 is installed at the outer end of at least one tube seat (either the lower or upper tube seat 11) to adjust the axial height of the entire fuel assembly. This spring generates pre-tightening force through contact with the external structure, improving stability and adaptability. This method can identify high-temperature zones in advance and employs a flexible installation structure. When temperature changes cause the fuel element 4 to lengthen during operation, the elastic element deforms to absorb the length change, preventing internal stress and bending of the fuel element 4, ensuring safe and stable operation of the assembly, and extending its service life.

[0057] To compare the differences between this solution and existing technologies, Figure 12 to Figure 14 Two alternative solutions, differing from this one, are listed: one is a hollow cylindrical tube, and the other is a hollow cylindrical tube with a spiral winding. All other parameters being equal, from... Figure 13 It can be seen that the hollow cylindrical tube with spiral winding and the teardrop-shaped design in this scheme have a significant advantage in temperature uniformity compared to the simple hollow cylindrical tube. The simple hollow cylindrical tube has obvious high-temperature and low-temperature zones, and the temperature distribution is extremely uneven. The spiral winding scheme and the teardrop-shaped design have better overall temperature uniformity.

[0058] Combination Figure 14It can be observed that regardless of the pitch of the fuel element 4, the teardrop-shaped design of this scheme has a lower maximum temperature compared to the spiral winding design. For example, when the pitch of both the spiral winding and the teardrop-shaped design is around 300 mm, the maximum temperature of the teardrop-shaped fuel element 4 in this scheme is approximately 516 K, while the maximum temperature of the spiral winding fuel element 4 is closer to 518 K, which is about 2 K higher. Meanwhile, see also... Figure 14 As shown in the chart on the right, the pressure drop of the teardrop-shaped fuel element 4 on the coolant in this design is consistently lower than that of the spiral-wound fuel element 4. Figure 14 It can be seen that in the preferred scheme, the pitch of the teardrop-shaped fuel element 4 can be selected in the range of 300mm to 400mm. At this time, the highest temperature of the teardrop-shaped fuel element 4 is close to that of the hollow circular tube and lower than that of the spiral winding scheme. At the same time, the pressure drop of the teardrop-shaped fuel element 4 is close to that of the hollow circular tube and lower than that of the spiral winding scheme. However, the temperature uniformity of the teardrop-shaped fuel element 4 is much higher than that of the hollow circular tube scheme.

[0059] Figure 15 to Figure 18 Several other schemes different from this one are listed. It can be seen that when the petal shape is 4 (cross-shaped) and 2 (straight-shaped), the teardrop-shaped fuel element 4 has better temperature uniformity, a smaller temperature difference between the center and the edge, and the high-temperature zone is located in the center and is lower than the high-temperature zone of the other schemes. This is because the teardrop-shaped fuel element is not essentially the same type as the petal-shaped fuel element. The teardrop-shaped fuel element has asymmetrical characteristics in the circumferential direction, and it is precisely because of this asymmetry that the teardrop-shaped fuel element has a stronger lateral mixing ability than the symmetrical petal-shaped fuel element, resulting in more complete mixing of the coolant and thus enhanced heat transfer.

[0060] In summary, structurally, this design employs a teardrop-shaped fuel element 4, which differs from common hollow cylindrical tubes, hollow cylindrical tubes with spiral winding, and petal-shaped (cross-shaped, straight-lined) structures. In terms of performance, compared to hollow cylindrical tubes and spiral winding schemes, this design exhibits superior temperature uniformity. At different pitches, the maximum temperature is lower; for example, at a pitch of approximately 300mm, the maximum temperature is about 2K lower than the spiral winding scheme, and the pressure drop to the coolant is consistently lower. The overall performance is even better when the pitch is preferably in the range of 300mm to 400mm. Compared to petal-shaped fuel elements, this design, due to the circumferential asymmetry of the teardrop-shaped fuel element, has stronger lateral mixing capabilities, allowing for more thorough coolant mixing, enhanced heat transfer, smaller temperature difference between the center and edge, and lower temperatures in the high-temperature zone. These innovative designs effectively improve the heat transfer performance and stability of the fuel assembly.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A fuel element (4) based on helical turbulence-enhanced heat transfer, characterized in that, The fuel element (4) is a tubular spiral structure with a teardrop-shaped cross-section.

2. The fuel element (4) based on helical turbulence-enhanced heat transfer as described in claim 1, characterized in that: The teardrop-shaped cross-section includes a rounded end segment and a V-shaped end segment. The two sides of the rounded end segment and the two sides of the V-shaped end segment are smoothly connected. The tip of the V-shaped end segment is also smoothly connected. The distance from the tip of the V-shaped end segment to the center of the rounded end segment is greater than the radius of the rounded end segment segment.

3. The fuel element (4) based on helical turbulence-enhanced heat transfer as described in claim 1, characterized in that: The fuel element (4) includes an inner shell (1) located in the inner layer of the tubular structure, an outer shell (3) located in the outer layer of the tubular structure, and a fuel core (2) filled between the two.

4. A fuel assembly based on helical turbulence-enhanced heat transfer, characterized in that, It includes the fuel element (4) as described in any one of claims 1-3, and also includes a lower tube seat (11) and an upper tube seat (14); the two ends of the plurality of fuel elements (4) are respectively connected to the lower tube seat (11) and the upper tube seat (14).

5. The fuel assembly based on helical turbulence-enhanced heat transfer as described in claim 4, characterized in that: The cross-sectional angles of the multiple fuel elements (4) are aligned; one of the fuel elements (4) is located at the center, and the remaining fuel elements (4) are distributed around the central fuel element (4), with the outer surfaces of two adjacent fuel elements (4) supporting each other.

6. The fuel assembly based on helical turbulence-enhanced heat transfer as described in claim 4, characterized in that, Each of the fuel elements (4) is connected at both ends to the lower tube seat (11) or the upper tube seat (14) via a connecting bracket, the connecting bracket comprising: Fuel end cap (8) connecting to fuel element (4); The locating pin (10) of the mounting pin hole (12) of the connecting pipe seat; In addition, a claw-type support frame (9) connects the fuel end cap (8) and the positioning pin (10), and the inner cavity of the fuel element (4) communicates with the outside through the through area on the fuel end cap (8).

7. The fuel assembly based on helical turbulence-enhanced heat transfer as described in claim 6, characterized in that: The fuel end cap (8) is a single piece with a fixed shape; Alternatively, the fuel end cap (8) is an assembly with an adaptively adjustable thickness. The assembly includes a fixed end plate (80), a movable end plate (81), and an elastic element (82). The fixed end plate (80) and the movable end plate (81) are opposite to each other and slidably engaged. The elastic element (82) is located between the fixed end plate (80) and the movable end plate (81). The movable end plate (81) is connected to the fuel element (4).

8. The fuel assembly based on helical turbulence-enhanced heat transfer as described in claim 6, characterized in that: The fuel element (4) is welded to the fuel end cap (8); Alternatively, the end face of the fuel end cap (8) is provided with a protruding limiting profile plate (83) which can restrict the circumferential movement of the fuel element (4).

9. A fuel assembly method based on helical turbulence-enhanced heat transfer, characterized in that, Applicable to the fuel assembly as described in claim 7, comprising the following steps: The temperature distribution of the fuel assembly during operation is obtained, and local high-temperature areas are identified (90); Assemble the lower tube seat (11), upper tube seat (14) and fuel element (4) according to the structure of the fuel assembly, wherein, for the fuel element (4) located in the high temperature zone (90), at least one end is connected to the tube seat using a fuel end cap (8) in the form of an assembly.

10. The fuel assembly method based on helical turbulence-enhanced heat transfer as described in claim 9, characterized in that: The high-temperature zone (90) of the fuel assembly during operation was obtained through computer simulation; And / or, first install one end of the middle fuel element (4) into the lower pipe seat (11), then install the outer peripheral fuel element (4), and finally install the upper pipe seat (14).

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