Novel spiral ribbed fuel element enhanced heat exchange method, fuel element and assembly

Abstract

The invention relates to the technical field of heat transfer science and fluid mechanics, in particular to a novel spiral ribbed fuel element heat transfer enhancement method, a fuel element and an assembly. The enhanced heat exchange method comprises the steps that anticlockwise spiral fins and clockwise spiral fins are sequentially arranged on a fuel element body, and the anticlockwise spiral fins and the clockwise spiral fins are arranged in a twisted mode, so that the whole fuel element is covered with the inlet effect, and the heat exchange efficiency is improved; the adjacent fuel element bodies are arranged at intervals according to the rule that the initial spiral directions of the special-shaped fins are different, coolant stirring and mixing between the sub-channels are enhanced, it is ensured that the surface temperature of the fuel element bodies is evenly distributed, the overall heat exchange efficiency of the fuel assembly is improved, and the heat exchange enhancing effect is achieved. The heat exchange area of the fuel element can be increased through different numbers of special-shaped fins and different sizes of sectional areas.

Description

Technical Field

[0001] The invention relates to the technical field of heat transfer and fluid mechanics, and in particular to a novel method for enhancing heat exchange of a spiral ribbed fuel element, a fuel element and an assembly. Background Art

[0002] The core of a nuclear reactor is the energy source of a nuclear power plant and is therefore the core component of the primary circuit system. The core is composed of fuel assemblies, each of which is formed by fuel elements arranged in a certain pattern. The heat generated by the fission reaction inside the fuel element is transferred to the coolant on the surface of the cladding in the form of convection heat transfer. If effective heat transfer cannot be established between the fuel element and the coolant, the temperature of the fuel pellet will be too high, which is not conducive to the safe operation of the reactor. Therefore, the heat exchange capacity of the fuel element is an important guarantee for the safe operation of the reactor. In addition, enhancing the heat exchange capacity of the fuel element is also a necessary means to improve the economy of the reactor.

[0003] In the prior art, there are two main methods to enhance the heat exchange capacity of fuel elements. One is to change the shape of the core fuel elements, such as using annular or plate-shaped fuel elements; the other is to adjust the arrangement of fuel elements, such as compact arrangement. These methods have been applied in some reactors. For example, Japan's third-generation research reactor JRR-3 uses plate-shaped fuel elements and the coolant channels are narrow rectangles. When the fluid passes through the coolant channel, the boundary layer of the fluid will form near the channel wall. The fluid flow velocity is usually lower in the area close to the channel wall, and the flow velocity is higher in the area close to the center of the channel. When the fluid flows through a fuel element with a complex shape, it usually generates turbulence, resulting in turbulence of the boundary layer and enhancing the heat exchange effect. However, due to its relatively smooth and stable surface, the flow of the fluid in the annular or plate-shaped fuel element tends to be laminar, and no turbulence is formed in the coolant channel, which will not destroy the boundary layer of the coolant channel, and its heat exchange effect is limited. Compact arrangement, such as hexagonal arrangement, is commonly used in the physical design of the core. This design has strict restrictions on the requirements for the water-uranium ratio and has more stringent requirements on the shape and size of the coolant channel. Therefore, using existing solutions to improve the heat exchange capacity of fuel elements often faces many challenges and limitations in actual operations. Summary of the invention

[0004] Therefore, the present invention provides a novel method for enhancing heat exchange of a spiral ribbed fuel element, a fuel element and an assembly.

[0005] In order to solve the above technical problems, the present invention provides a novel method for enhancing heat exchange of spiral ribbed fuel elements, comprising: by sequentially arranging counterclockwise spiral fins and clockwise spiral fins along the fuel element body, and twisting the counterclockwise spiral fins and the clockwise spiral fins, so that the inlet effect covers the entire fuel element and improves the efficiency of heat exchange; by arranging adjacent fuel element bodies at regular intervals according to different initial spiral directions of the special-shaped fins, the mixing of the coolant between the sub-channels is enhanced, the uniform distribution of the surface temperature of the fuel element body is ensured, and the overall heat exchange efficiency of the fuel assembly is improved, so as to achieve the effect of enhancing heat exchange.

[0006] The present invention also provides a ribbed special-shaped fuel element used in the method of enhancing heat exchange using the new type of spiral ribbed fuel element, comprising: a fuel element main body, on which special-shaped fins are provided, the special-shaped fins include counterclockwise spiral fins and clockwise spiral fins, the counterclockwise spiral fins and the clockwise spiral fins are arranged in sequence along the extension direction of the fuel element main body, and the counterclockwise spiral fins and the clockwise spiral fins are twisted.

[0007] The present invention also provides a ribbed special-shaped fuel element used in the method of enhancing heat exchange using the new type of spiral ribbed fuel element, comprising: a fuel element main body, on which special-shaped fins are arranged, and the special-shaped fins include counterclockwise spiral fins and clockwise spiral fins, and the counterclockwise spiral fins and clockwise spiral fins are arranged in sequence along the extension direction of the fuel element main body.

[0008] Furthermore, the counterclockwise spiral ribs and the clockwise spiral ribs are arranged in two ways: alternating or non-alternating.

[0009] Furthermore, there are two or more special-shaped fins.

[0010] The present invention also provides a fuel assembly for a nuclear reactor, comprising the ribbed special-shaped fuel element.

[0011] Furthermore, the cross-section of the fuel assembly is quadrilateral or hexagonal.

[0012] Furthermore, the initial spiral directions of any two adjacent special-shaped fins are arranged alternately clockwise and counterclockwise.

[0013] Furthermore, the initial spiral directions of the special-shaped fins of two adjacent layers are arranged alternately clockwise and counterclockwise.

[0014] Furthermore, the initial spiral directions of the special-shaped fins of two adjacent circles are arranged alternately clockwise and counterclockwise.

[0015] Furthermore, a plurality of counterclockwise shaped fins are arranged around each of the shaped fins whose initial spiral direction is clockwise.

[0016] The technical solution of the present invention has the following advantages:

[0017] The novel method for enhancing heat exchange of spiral ribbed fuel elements provided by the present invention comprises: sequentially arranging counterclockwise spiral fins and clockwise spiral fins along the main body of the fuel element, and twisting the counterclockwise spiral fins and the clockwise spiral fins so that the inlet effect covers the entire fuel element and improves the efficiency of heat exchange; arranging adjacent fuel element main bodies at regular intervals according to different initial spiral directions of the special-shaped fins, enhancing the mixing of coolant between sub-channels, ensuring uniform distribution of surface temperature of the fuel element main body, and improving the overall heat exchange efficiency of the fuel assembly, so as to achieve the effect of enhancing heat exchange.

[0018] The ribbed shaped fuel element can increase the surface area-total volume ratio of the fuel element through different numbers of shaped fins and cross-sectional areas of different sizes. At the same time, the alternating forward and reverse changes of the shaped fins can effectively make the inlet effect cover the entire fuel element, thereby greatly improving the heat exchange efficiency. The adjacent fuel elements are arranged at regular intervals according to the different initial spiral directions of the fins to enhance the mixing of the coolant between the sub-channels, thereby achieving the effect of enhancing heat exchange. Therefore, the ribbed shaped fuel element using this method can effectively improve the heat exchange capacity of the fuel element, can increase the reactor power while enhancing safety, and has important engineering application value.

[0019] The number and shape of special-shaped fins can be reasonably adjusted in the design of nuclear reactors to adapt to the type of coolant and the core operating environment, which helps to improve the heat exchange efficiency and ensure the safety and economy of the reactor. At the same time, the use of alternating fins in the forward and reverse directions on a single fuel element can make full use of the inlet effect and help improve the heat transfer performance.

[0020] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the disclosure, nor is it intended to limit the scope of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 A schematic diagram of the structure of a ribbed special-shaped fuel element provided by the present invention;

[0023] Figure 2 The ribbed special-shaped fuel element provided by the present invention is a cross-sectional view of four ribs;

[0024] Figure 3 The ribbed special-shaped fuel element provided by the present invention is a cross-sectional view of three ribs;

[0025] Figure 4 A cross-sectional view of a fuel assembly comprising four ribbed shaped fuel elements provided by the present invention;

[0026] Figure 5 A cross-sectional view of a fuel assembly comprising three ribs of a ribbed special-shaped fuel element provided by the present invention;

[0027] Figure 6 A schematic structural diagram of a first arrangement of fuel assemblies provided by the present invention;

[0028] Figure 7 A schematic structural diagram of a second arrangement of fuel assemblies provided by the present invention;

[0029] Figure 8 A schematic structural diagram of a third arrangement of fuel assemblies provided by the present invention;

[0030] Fig. 9 A schematic structural diagram of a fourth arrangement of fuel assemblies provided by the present invention;

[0031] Fig.10 A three-dimensional diagram of a first arrangement of fuel assemblies provided by the present invention.

[0032] Description of reference numerals:

[0033] 1. Fuel element body; 2. Special-shaped fins; 3. Counterclockwise spiral fins; 4. Clockwise spiral fins; 5. Fuel assembly. DETAILED DESCRIPTION

[0034] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present disclosure. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0035] In the description of the present disclosure, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present disclosure, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0036] In the description of the present disclosure, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0037] In the present disclosure, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] The disclosure below provides many different embodiments or examples to realize different structures of the present disclosure. In order to simplify the disclosure of the present disclosure, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present disclosure. In addition, the present disclosure can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present disclosure provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0039] The preferred embodiments of the present disclosure are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0040] Traditional fuel elements include circular fuel elements, wire-wound fuel elements, etc. Among them, the most widely used are circular fuel elements. The technology of circular fuel elements is mature, but the contact area between the surface of the fuel element and the coolant is small, and the heat exchange capacity is poor. The wire in the wire-wound type is a metal material, does not contain nuclear fuel, and mainly plays a supporting role. The wire-wound fuel assembly can be designed and optimized according to the specific needs of the reactor. It has greater flexibility, but the enhanced heat exchange effect is limited, and the production process is relatively complicated. The existing spiral ribbed fuel assembly is improved on the basis of the circular fuel element, which increases the heat exchange area and enhances the heat exchange efficiency, but there is still a problem of uneven heat exchange, resulting in the enhanced heat exchange effect is not obvious.

[0041] See also Figures 1 to 10 As shown, the present invention provides a novel method for enhancing heat exchange of spiral ribbed fuel elements, which is an improvement and innovation made to the prior art; the novel method for enhancing heat exchange of spiral ribbed fuel elements involved comprises: by sequentially arranging counterclockwise spiral fins 3 and clockwise spiral fins 4 along the fuel element body 1, and the counterclockwise spiral fins 3 and the clockwise spiral fins 4 are twisted, so that the inlet effect covers the entire fuel element and improves the efficiency of heat exchange; by arranging adjacent fuel element bodies 1 at regular intervals according to different initial spiral directions of the special-shaped fins 2, the mixing of the coolant between the sub-channels is enhanced, the uniform distribution of the surface temperature of the fuel element body 1 is ensured, and the overall heat exchange efficiency of the fuel assembly is improved, so as to achieve the effect of enhancing heat exchange.

[0042] The surface area-total volume ratio of the fuel element can be increased by using different numbers of special-shaped fins 2 and cross-sectional areas of different sizes. At the same time, the alternating forward and reverse changes of the special-shaped fins 2 can effectively make the inlet effect cover the entire fuel element, thereby greatly improving the heat exchange efficiency. The arrangement of adjacent fuel elements in a regular interval according to the different initial spiral directions of the fins can enhance the mixing of the coolant between the sub-channels, thereby achieving the effect of enhancing heat exchange. Therefore, the ribbed special-shaped fuel element using this method can effectively improve the heat exchange capacity of the fuel element, can improve the reactor power while enhancing safety, and therefore has important engineering application value.

[0043] The number and shape of the special-shaped fins 2 can be reasonably adjusted in the design of a nuclear reactor to adapt to the type of coolant and the core operating environment, which helps to improve the heat exchange efficiency and ensure the safety and economy of the reactor. At the same time, the use of alternating fins in the forward and reverse directions on a single fuel element can make full use of the inlet effect and help improve the heat transfer performance.

[0044] In a nuclear reactor, nuclear fuel such as uranium or plutonium undergoes fission reaction under the action of neutrons, releasing heat energy. The reactor core transfers heat to the surface of the cladding through heat transfer. The reactor core usually contains fuel elements and coolant (such as water, liquid metal or gas). When the coolant flows, it absorbs the heat released from the surface of the cladding in the form of convection heat transfer.

[0045] The heat transfer process of a reactor is a vital part of nuclear power generation and involves multiple steps, each of which ensures the efficient transfer and use of the heat generated by the nuclear reaction. The following is a detailed expansion of each step of the heat transfer process:

[0046] 1. Nuclear reactions generate heat:

[0047] In the reactor core, the nuclear fuel used is usually uranium-235. Neutrons bombard uranium-235 to produce a chain fission nuclear reaction, which continuously releases heat energy, which is the main source of energy when the reactor is running.

[0048] 2. Heat conduction:

[0049] The fission reaction occurs in the pellets in the fuel element, and the heat generated causes the pellet temperature to rise. The heat is transferred to the fins of the fuel cladding through the pellets, air gaps and cladding in turn, and then the heat is taken out through convection heat exchange between the special-shaped fins and the coolant.

[0050] 3. Coolant flow:

[0051] The flow of coolant in the core often adopts a forced circulation system. Depending on the reactor design, the coolant can be water (such as light water reactors), heavy water, liquid sodium or gas (such as helium). The coolant is pumped to the core and absorbs heat through convection heat exchange with the surface of the fuel elements. Setting different numbers of special-shaped fins on the fuel elements can increase the surface area-total volume ratio of the fuel elements. At the same time, the alternating forward and reverse changes of the special-shaped fins can effectively make the inlet effect cover the entire fuel element, thereby greatly improving the heat exchange efficiency. The arrangement of adjacent fuel elements at regular intervals according to the different initial spiral directions of the fins can enhance the mixing of the coolant between the sub-channels, thereby achieving the effect of enhancing heat exchange.

[0052] 4. Heat exchange:

[0053] As the coolant flows through the core and absorbs heat, its temperature rises and it then flows into the steam generator, where it exchanges heat with the fluid in the secondary circuit (usually water), heating the water in the secondary circuit into steam.

[0054] 5. Coolant circulation:

[0055] After being cooled by the steam generator, the coolant flows out and re-enters the core. This cycle is continuous, ensuring the continuous and safe operation of the reactor.

[0056] The present invention also provides a ribbed special-shaped fuel element used in the method of enhancing heat exchange using the novel spiral ribbed fuel element, the ribbed special-shaped fuel element comprising: a fuel element body 1, the fuel element body 1 being provided with special-shaped fins 2, the special-shaped fins 2 comprising counterclockwise spiral fins 3 and clockwise spiral fins 4, the counterclockwise spiral fins 3 and the clockwise spiral fins 4 being arranged in sequence along the extension direction of the fuel element body 1, and the counterclockwise spiral fins 3 and the clockwise spiral fins 4 being twisted.

[0057] The ribbed shaped fuel element can increase the surface area-total volume ratio of the fuel element by using different numbers of shaped fins 2 and cross-sectional areas of different sizes. At the same time, the alternating forward and reverse changes of the shaped fins 2 can effectively make the inlet effect cover the entire fuel element, thereby greatly improving the heat exchange efficiency. The adjacent fuel elements are arranged at regular intervals according to the different initial spiral directions of the fins to enhance the mixing of the coolant between the sub-channels, thereby achieving the effect of enhancing the heat exchange.

[0058] The heat exchange process of the fuel assembly composed of the ribbed special-shaped fuel element is as follows: in a nuclear reactor, the fuel element serves as the heat source of the reactor, and the heat generated by the fission reaction inside the fuel element is first transferred to the surface of the cladding in the form of heat conduction. Then, it is transferred to the coolant in the form of convection heat transfer on the surface of the cladding, and the coolant (such as water, liquid metal, gas, etc.) flows through the channels between the fuel elements to take away the heat. The speed, flow rate and temperature of the coolant flow have an important influence on the heat exchange efficiency.

[0059] The number and shape of the special-shaped fins 2 on the fuel element required in different situations are different. In this embodiment, the counterclockwise spiral fins 3 and the clockwise spiral fins 4 have two arrangements: alternating and non-alternating. That is, each fuel element in the fuel assembly 5 includes multiple forms of clockwise and counterclockwise alternating twisting and non-alternating twisting, and the fuel elements have multiple arrangements.

[0060] The number of the special-shaped fins 2 is two or more. Specifically, the number of the special-shaped fins 2 can be set according to actual conditions.

[0061] The present invention also provides a fuel assembly for a nuclear reactor, comprising the ribbed special-shaped fuel assembly 5.

[0062] Specifically, the cross section of the fuel assembly 5 is quadrilateral or hexagonal.

[0063] Figure 1 The counterclockwise spiral fins 3 and the clockwise spiral fins 4 appear alternately. The length l in the spiral direction is calculated based on the operating conditions of the reactor core. The formula l / d≤0.005RePr is used to make l equal to the length of the inlet section, where d is the hydraulic diameter of the fuel bundle channel, Re is the Reynolds number, and Pr is the Prandtl number. This keeps the inlet effect covering the entire axial range. This structure destroys the boundary layer, makes the boundary layer thinner, reduces thermal resistance, and enhances heat transfer.

[0064] In this embodiment, the fuel element 5 takes a square arrangement of four fin fuel elements alternating in a clockwise and counterclockwise direction as an example. For fuel elements with other numbers of special-shaped fins 2, fuel elements with other twisting patterns, and fuel assemblies with different arrangements, the application principles are the same and also fall within the protection scope of the present invention.

[0065] See also Figure 6 As shown, Figure 6In a fuel assembly including a square arrangement of four-fin fuel elements, the initial spiral directions of any two adjacent special-shaped fins 2 in the fuel assembly are arranged alternately clockwise and counterclockwise, satisfying the condition that the spiral directions of the fins of adjacent fuel elements are opposite. The spiral directions of the fins of adjacent fuel elements are opposite, which can effectively enhance the mixing of coolant between sub-channels, reduce the circumferential distribution unevenness, and promote heat transfer. This arrangement of adjacent fuel elements with alternating initial spiral directions in clockwise and counterclockwise directions can be applied to a variety of arrangements, such as quadrilateral arrangement, hexagonal arrangement, etc. The special-shaped fuel elements under different arrangements have different degrees of improvement in enhancing the ability to mix coolant between sub-channels.

[0066] Adjacent fuel elements are arranged at intervals according to different rules of the initial spiral directions of the special-shaped fins, which can enhance the coolant mixing ability between sub-channels and thus improve the heat exchange efficiency.

[0067] See also Figure 7 As shown, the initial spiral directions of the special-shaped fins 2 of two adjacent layers are arranged alternately clockwise and counterclockwise.

[0068] See also Figure 8 As shown, the initial spiral directions of two adjacent circles of the special-shaped fins 2 are arranged alternately clockwise and counterclockwise.

[0069] See also Fig. 9 As shown, a plurality of counterclockwise shaped fins 2 are arranged around each shaped fin 2 whose initial spiral direction is clockwise.

[0070] Figure 7 , Figure 8 , Fig. 9 They are different new arrangements, placing fuel elements twisted in opposite directions in the special-shaped fuel assembly to further enhance the mixing of the coolant between the sub-channels, and enhance the coolant flow on the leeward side of the fuel element, thereby improving the convective heat transfer capacity of the concave arc and the leeward side of the fuel element. The spiral directions of the fins of adjacent fuel elements are opposite, which can effectively enhance the mixing of the coolant between the sub-channels, reduce the unevenness of the circumferential heat transfer distribution, and greatly improve the heat transfer efficiency.

[0071] The present invention also provides a variety of new arrangements, including the fuel assembly of the nuclear reactor.

[0072] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A novel method for enhancing heat exchange of a spiral ribbed fuel element, characterized in that: include: By sequentially arranging counterclockwise spiral fins (3) and clockwise spiral fins (4) along the fuel element body (1), and the counterclockwise spiral fins (3) and the clockwise spiral fins (4) are twistedly arranged, the inlet effect covers the entire fuel assembly (5), and the efficiency of heat exchange is improved; By arranging adjacent fuel element bodies (1) at regular intervals according to different initial spiral directions of the special-shaped fins (2), the mixing of coolant between the sub-channels is enhanced, the uniform distribution of the surface temperature of the fuel element body (1) is ensured, and the overall heat exchange efficiency of the fuel assembly (5) is improved, thereby achieving the effect of enhancing heat exchange.

2. A ribbed special-shaped fuel element used in the method for enhancing heat exchange using the novel spiral ribbed fuel element according to claim 1, characterized in that: include: A fuel element body (1), wherein the fuel element body (1) is provided with special-shaped fins (2), wherein the special-shaped fins (2) include counterclockwise spiral fins (3) and clockwise spiral fins (4), and the counterclockwise spiral fins (3) and the clockwise spiral fins (4) are sequentially arranged along the extension direction of the fuel element body (1).

3. The ribbed special-shaped fuel element according to claim 2, characterized in that: The counterclockwise spiral ribs (3) and the clockwise spiral ribs (4) have two arrangement modes: alternating or non-alternating.

4. The ribbed special-shaped fuel element according to claim 2, characterized in that: The number of the special-shaped fins (2) is two or more.

5. A fuel assembly for a nuclear reactor, characterized in that: A ribbed special-shaped fuel element comprising any one of claims 2-4.

6. The fuel assembly for a nuclear reactor according to claim 5, characterized in that: The cross section of the fuel assembly (5) is quadrilateral or hexagonal.

7. The fuel assembly for a nuclear reactor according to claim 5, characterized in that: The initial spiral directions of any two adjacent special-shaped fins (2) are arranged alternately clockwise and counterclockwise.

8. The fuel assembly for a nuclear reactor according to claim 5, characterized in that: The initial spiral directions of the special-shaped fins (2) of two adjacent layers are arranged alternately clockwise and counterclockwise.

9. The fuel assembly for a nuclear reactor according to claim 5, characterized in that: The initial spiral directions of two adjacent circles of the special-shaped fins (2) are arranged alternately clockwise and counterclockwise.

10. The fuel assembly for a nuclear reactor according to claim 5, characterized in that: A plurality of counterclockwise shaped fins (2) are arranged around each of the shaped fins (2) with an initial clockwise spiral direction.

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