Intermixing vanes, positioning grid, fuel assembly and method of manufacture

Abstract

The application provides a mixing wing, a positioning grid, a fuel assembly and a preparation method, and relates to the technical field of nuclear reactions. The mixing wing is applied to the positioning grid of the fuel assembly, and the mixing wing is a shape memory alloy with double-path memory effect. The positioning grid comprises a grid body and the mixing wing, and the mixing wing is arranged on the end face of the grid body. The fuel assembly comprises a fuel rod bundle and the positioning grid, and a plurality of fuel rods of the fuel rod bundle correspondingly pass through a plurality of through holes of the positioning grid. The preparation method is used for preparing the positioning grid. The mixing wing is made of the shape memory alloy with double-path memory effect, the shape of the mixing wing can be self-adaptively adjusted according to the change of the reactor working condition and is located at different positions, different degrees of transverse disturbance flow of the coolant in the sub-channel of the fuel assembly rod bundle are generated, the best distribution of the bubble and the liquid film on the inner wall of the sub-channel of the fuel assembly rod bundle under different reactor working conditions is maintained, and therefore the economy and the safety of the fuel assembly are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear reaction, in particular to a mixing wing, a positioning grid, a fuel assembly and a preparation method. BACKGROUND

[0002] A nuclear reactor is also called an atomic energy reactor or a reactor, which is a device capable of maintaining a controllable self-sustaining chain nuclear fission reaction to achieve nuclear energy utilization. A fuel assembly is a unit of the reactor, which generally includes a fuel rod array and a positioning grid provided with a mixing wing. During the operation of the reactor, a rod bundle sub-channel is formed between adjacent fuel rods of the fuel rod array, and the coolant flows through the rod bundle sub-channel in the axial direction to exchange heat with the fuel rods, thereby taking out the heat energy generated by the fuel rods. During the flow of the coolant through the positioning grid, the coolant will generate a central large vortex in the central region of the rod bundle sub-channel of the fuel rod array under the disturbance of the mixing wing. The central large vortex can entrain wall surface bubbles of the fuel rod wall surface to strengthen heat transfer, while also reducing the thickness of the liquid film on the surface of the fuel rod, destroying the continuity of the liquid film and reducing the safety margin of the nuclear reactor. The orientation of the mixing wing directly determines the entrainment strength of the central large vortex on the wall surface bubbles. The existing mixing wing is generally fixedly arranged on the positioning grid and cannot be adaptively adjusted according to the core operating condition of the reactor. SUMMARY

[0003] The present application relates to the technical field of nuclear reaction, in particular to a mixing wing, a positioning grid, a fuel assembly and a preparation method.

[0004] To solve the above problems, the present application provides a mixing wing applied to a positioning grid of a fuel assembly, wherein the mixing wing is a shape memory alloy with double-path memory effect.

[0005] Optionally, the mixing wing includes a martensite shape and an austenite shape. In the martensite shape, the inclination angle of the mixing wing is θ1, and the range of θ1 is [30°, 45°]. In the austenite shape, the inclination angle of the mixing wing is θ2, and the range of θ2 is [0°, 15°].

[0006] Optionally, in the martensite shape, the azimuth angle of the mixing wing is Φ1, and the range of Φ1 is [0°, 5°]. In the austenite shape, the azimuth angle of the mixing wing is Φ2, and the range of Φ2 is [5°, 10°].

[0007] Optionally, the mixing wing is a TiNiZr alloy.

[0008] Optionally, the composition of the mixing wing is Ti50-xNi50Zrx (x=5, 10).

[0009] The application further provides a positioning grid, comprising a grid body and the mixing wing mentioned above, wherein the mixing wing is arranged on the end face of the grid body.

[0010] Optionally, the grid body and the mixing wing are integrally formed.

[0011] The application further provides a fuel assembly, comprising a fuel rod bundle and the positioning grid mentioned above, wherein the plurality of fuel rods of the fuel rod bundle correspond one by one to the plurality of through holes of the positioning grid.

[0012] The application further provides a preparation method for preparing the positioning grid mentioned above, comprising:

[0013] obtaining an initial base, wherein the initial base comprises a grid base and a wing base integrally formed on the end face of the grid base;

[0014] performing heat treatment on the initial base, wherein the grid base after heat treatment becomes a grid body, and the wing base after heat treatment becomes a wing body;

[0015] fixing the shape of the wing body using a mold, and performing heat treatment on the wing body after shape fixing to obtain a mixing wing with double-path memory effect.

[0016] Optionally, in the step of fixing the shape of the wing body using a mold, and performing heat treatment on the wing body after shape fixing to obtain a mixing wing with double-path memory effect, the step comprises:

[0017] martensite shape memory training: fixing the wing body to a preset martensite shape using a first mold, and keeping the wing body in a 423.15K cold environment for a first preset time;

[0018] austenite shape memory training: fixing the wing body to a preset austenite shape using a second mold, and keeping the wing body in a 523.15K hot environment for a second preset time;

[0019] alternately performing the martensite shape memory training and the austenite shape memory training for multiple times to obtain a mixing wing with double-path memory effect.

[0020] The hybrid vane provided by this invention is made of a shape memory alloy with a two-way memory effect. The hybrid vane can be positioned in a first orientation corresponding to the martensitic shape or a second orientation corresponding to the austenitic shape according to the reactor operating conditions and the temperature change of the coolant. This allows the shape of the hybrid vane to be adaptively adjusted to different orientations according to the changes in reactor operating conditions, generating different degrees of lateral turbulence in the coolant within the fuel assembly rod bundle sub-channels. This ensures that the vapor bubbles and liquid film on the inner wall of the rod bundle sub-channels are maintained optimally under different reactor operating conditions. Specifically, this results in higher heat output efficiency and economy of the fuel assembly during normal operation, and maintains the continuity of the liquid film on the surface of the fuel rods under abnormal operating conditions, thus providing a higher safety margin and improving the economy and safety of the fuel assembly.

[0021] The positioning grid, fuel assembly, and preparation method provided by this invention all possess all the beneficial effects of the aforementioned mixed-air blades, which will not be elaborated here. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 Axonometric view of the positioning grid provided by this invention;

[0024] Figure 2 A top view of a single rod bundle subchannel in the fuel assembly provided by the present invention;

[0025] Figure 3 for Figure 2 Front view of the two mixed airfoils;

[0026] Figure 4 A schematic diagram of the fluid flow within a single rod bundle channel when the interleaved vanes in the fuel assembly provided by the present invention are of a martensitic shape.

[0027] Figure 5 A schematic diagram of the fluid flow within a single rod bundle channel when the interleaving vanes in the fuel assembly provided by the present invention are austenitic.

[0028] Explanation of reference numerals in the attached figures:

[0029] 100 - Positioning grid; 110 - Grid body; 120 - Mixed airfoil; 200 - Fuel rod; 300 - Rod bundle channel; 410 - Central vortex; 420 - Wall bubble; 430 - Entrainment bubble. Detailed Implementation

[0030] In order to make the above objectives, characteristics and advantages of the present application more apparent, specific embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to explain the present application and not to limit the present application.

[0031] The present embodiment provides a mixing wing 120 which is a shape memory alloy with double memory effect.

[0032] The present embodiment also provides a spacer grid 100, as shown, comprising a grid body 110 and the mixing wing 120 described above, the mixing wing 120 being arranged at the end face of the grid body 110. Figure 1

[0033] The present embodiment also provides a fuel assembly comprising a fuel rod bundle and the spacer grid 100 described above, a plurality of fuel rods 200 of the fuel rod bundle corresponding one-to-one to a plurality of channel holes of the spacer grid 100.

[0034] The mixing wing 120, the spacer grid 100 and the fuel assembly provided by the present embodiment, wherein the mixing wing 120 is a shape memory alloy with double memory effect, and can deform to different orientations with the change of ambient temperature, and generate different degrees of transverse turbulence to the coolant in the rod bundle sub-channel 300 of the fuel assembly; wherein the spacer grid 100 comprises a grid body 110 for positioning the fuel rod bundle and the mixing wing 120 described above; wherein the fuel assembly comprises a fuel rod bundle for releasing heat energy outwardly and the spacer grid 100 described above.

[0035] The rod bundle sub-channel 300 is formed between adjacent fuel rods 200 of the fuel rod bundle, Figure 2 The present application provides a top view of a single rod bundle sub-channel 300 in the fuel assembly; when the fuel assembly is in operation, the coolant flows through the rod bundle sub-channel 300 along its axial direction, the heat generated by the fuel rod 200 is transferred to the coolant and carried out of the fuel assembly by the coolant, thereby realizing the heat energy output of the fuel assembly outwardly; wherein when the coolant flows through the area where the spacer grid 100 is located, it needs to bypass the mixing wing 120, thereby generating a central large vortex 410 in the central area of the rod bundle sub-channel 300, and at the same time, the mixing wing 120 can exchange heat with the coolant during the process of being swept by the coolant, thereby changing the temperature.

[0036] The mixing wing 120 is a shape memory alloy with double memory effect, when the reactor is in normal operation, the temperature of the coolant is lower than the martensite finish temperature Mf of the mixing wing 120, the mixing wing 120 is cooled to below Mf under the action of coolant sweeping heat transfer, accordingly, Figure 3 ​As shown by the middle solid line, the mixing fins 120 are in martensite shape and located in the first orientation, the mixing fins 120 in the first orientation can produce strong lateral disturbance to the flowing coolant, as shown by the arrow, so that the central large vortex 410 has strong entrainment effect on the wall surface bubble 420 of the fuel rod 200, the wall surface bubble 420 gathers in the central region of the rod bundle sub-channel 300 to form an entrainment bubble 430, thereby strengthening the nucleate boiling heat transfer, Figure 4

[0037] The high fuel rod 200 has high heat transfer effect with the coolant, and the heat output power of the fuel assembly is correspondingly improved, and the economy is improved; when the reactor operating condition changes, such as positive reactivity introduction or loss of flow transient accident, the temperature of the coolant rises, when the temperature of the mixing fins 120 rises to the austenite starting temperature As to the austenite ending temperature Af under the heat transfer effect of the coolant, the mixing fins 120 are transformed from martensite to austenite, the shape and orientation of the mixing fins 120 change, and the mixing fins 120 are transformed to the second orientation,

[0038] Figure 3 As shown by the middle dashed line, the mixing fins 120 are transformed to austenite shape and located in the second orientation, the mixing fins 120 in the second orientation produce weakened lateral disturbance to the flowing coolant, as shown by the arrow, so that the central large vortex 410 and the lateral flow shear caused thereby are weakened, the entrainment bubble 430 in the rod bundle sub-channel 300 is dispersed to the periphery, correspondingly, the liquid droplets in the rod bundle sub-channel 300 can deposit to the surface of the fuel rod, thereby improving the continuity of the liquid film on the surface of the fuel rod 200, and the safety margin of the reactor is correspondingly ensured. Figure 5

[0039] 5Similarly, when the reactor operating condition returns to normal, as the temperature of the coolant decreases, the temperature of the mixing fins 120 decreases to below the martensite ending temperature, and the mixing fins 120 are again transformed to the first orientation in the martensite shape, the lateral disturbance of the mixing fins 120 to the coolant is again enhanced, the entrainment effect of the central large vortex 410 on the wall surface bubble 420 of the fuel rod 200 is correspondingly improved, thereby strengthening the nucleate boiling heat transfer, improving the heat output power of the fuel assembly and the economy, and the cycle is repeated.

[0040] 0The mixing fins 120 provided by the embodiment adopt a shape memory alloy having a double-path memory effect, the mixing fins 120 can be located in the first orientation in the martensite shape or the second orientation in the austenite shape according to the temperature change of the coolant under the reactor operating condition, so that the shape of the mixing fins 120 can be adaptively adjusted to be located in different orientations according to the change of the reactor operating condition, and the lateral disturbance of the mixing fins 120 to the coolant is adjusted to be enhanced or weakened,

[0041] ​​​The coolant in the fuel assembly rod bundle channel 300 generates lateral turbulence to varying degrees to ensure optimal distribution of vapor bubbles 420 and liquid film on the inner wall of the rod bundle channel 300 under different reactor operating conditions. Specifically, this enables the fuel assembly to have high heat output efficiency and economy during normal operation, and to maintain the continuity of the liquid film on the surface of the fuel rods 200 under abnormal operating conditions with a high safety margin, thereby improving the economy and safety of the fuel assembly.

[0042] Specifically, in this embodiment, as Figure 3 As shown, the mixed-phase vane 120 includes a martensitic shape (shown by solid lines) and an austenitic shape (shown by dashed lines). In the martensitic shape, the inclination angle of the mixed-phase vane 120 is θ1, ranging from [30° to 45°]. In the austenitic shape, the inclination angle of the mixed-phase vane 120 is θ2, ranging from [0° to 15°]. The inclination angle is the angle of inclination of the mixed-phase vane 120 relative to the vertical direction towards the bar bundle channel 300. When the temperature of the mixed-phase vane 120 is below Mf under the grazing heat transfer effect of the coolant, it is in a martensitic shape, corresponding to the... Figure 3 The first position, indicated by the solid line, has an inclination angle of [30°, 45°]. This inclination angle allows the mixed-phase vane 120 to generate strong lateral disturbances to the flowing coolant, resulting in a strong entrainment effect of the central vortex 410 on the surface bubbles 420 of the fuel rod 200. This enhances nucleus boiling heat transfer, improves the heat transfer effect between the fuel rod 200 and the coolant, and correspondingly increases the heat output power of the fuel assembly, thereby improving its economic efficiency. When the temperature of the mixed-phase vane 120 is higher than Af under the grazing heat transfer effect of the coolant, it is in an austenitic shape, correspondingly located... Figure 3 In the second orientation shown by the dashed line, the tilt angle of the mixing vane 120 is [0°, 15°]. As the tilt angle of the mixing vane 120 decreases, the effective turbulence area of ​​the mixing vane 120 on the coolant decreases, correspondingly weakening the lateral disturbance to the flowing coolant. The central vortex 410 and the resulting lateral flow shear force are thus weakened, allowing droplets in the rod bundle sub-channel 300 to deposit on the surface of the fuel rod 200, thereby improving the continuity of the liquid film on the surface of the fuel rod 200 and ensuring the safety margin of the fuel assembly. Specifically, θ1 is preferably 30°, and θ2 is preferably 15°.

[0043] Optionally, the orientation of the mixing vane 120 includes an azimuth angle in addition to the above-mentioned tilt angle, and specifically, the azimuth angle is a twist angle of the mixing vane 120 in the counterclockwise direction; in this embodiment, the azimuth angle of the mixing vane 120 in the martensite shape is Φ1, and the range of Φ1 is [0°, 5°]; the azimuth angle of the mixing vane 120 in the austenite shape is Φ2, and the range of Φ2 is [5°, 10°]. When the mixing vane 120 is in the first orientation of the martensite shape, the mixing vane 120 has a smaller azimuth angle Φ1 in addition to the tilt angle θ1, that is, the twist angle of the mixing vane 120 is smaller, thereby ensuring the effective disturbance area of the mixing vane 120 to the coolant, and accordingly ensuring the transverse disturbance intensity of the mixing vane 120 to the coolant, thereby strengthening the nucleate boiling heat transfer to ensure the heat output power of the fuel assembly; when the mixing vane 120 is in the second orientation of the austenite shape, the mixing vane 120 has the azimuth angle Φ2 in addition to the tilt angle θ2, and the tilt angle is reduced while the azimuth angle is increased, and the twist angle of the mixing vane 120 is further reduced to further reduce the effective disturbance area of the mixing vane 120 to the coolant, and accordingly further reduce the transverse disturbance of the mixing vane 120 to the coolant in the rod bundle sub-channel 300, thereby further improving the deposition of liquid droplets on the surface of the fuel rod 200 in the rod bundle sub-channel 300, ensuring the continuity of the liquid film on the surface of the fuel rod 200, and further ensuring the safety margin of the fuel assembly.

[0044] Optionally, in this embodiment, the mixing vane 120 can be a TiNiZr alloy. On the one hand, the TiNiZr shape memory alloy has a relatively narrow phase transition hysteresis (10K-20K), and can realize the transition between the martensite shape and the austenite shape in a small temperature range, which can meet the working condition requirements of the coolant in the fuel assembly from the subcooled boiling to the saturated boiling in a small temperature span; on the other hand, the TiNiZr alloy is easy to be formed and processed, and accordingly, the processing convenience and cost of the mixing vane 120 are relatively low.

[0045] Specifically, in this embodiment, the composition of the mixing vane 120 is Ti50-xNi50Zrx (x = 5, 10). Of course, in other embodiments, the mixing vane 120 can also use other components of shape memory alloy, as long as the phase transition temperature meets the working condition temperature change in the fuel assembly.

[0046] Optionally, in the embodiment, the lattice body 110 and the mixing fin 120 are integrally formed. The lattice body 110 and the mixing fin 120 are made of the same material, integrally formed, and the lattice body 110 and the mixing fin 120 are subjected to different heat treatments, so that the lattice body 110 is a rigid body with a fixed shape, and the mixing fin 120 is a shape memory alloy with a two-way memory effect. On the basis of realizing the shape change of the mixing fin 120 with temperature, the connection firmness and stability of the mixing fin 120 and the lattice body 110 are improved, and the poor processability and weldability of the shape memory alloy are correspondingly reduced, which leads to the difficulty of connecting the mixing fin 120 to the lattice body 110 and the poor connection firmness.

[0047] The embodiment also provides a preparation method for preparing the positioning lattice 100. The preparation method comprises the following steps: obtaining an initial base body, the initial base body comprising a lattice base body and a fin base body integrally formed on an end face of the lattice base body; and performing heat treatment on the initial base body, so that the lattice base body becomes a lattice body and the fin base body becomes a fin body after the heat treatment; using a mold to fix the shape of the fin body, and performing heat treatment on the fixed shape of the fin body to obtain a mixing fin with a two-way memory effect. First, the initial base body is prepared. In the initial base body, the lattice base body and the fin base body are an integral part, and the fin base body is coplanar with the side wall of the connected lattice base body, that is, the fin base body is not bent and twisted relative to the corresponding side wall of the lattice base body, and the inclination angle and the azimuth angle of the fin base body are both 0°. Then, the initial base body is subjected to heat treatment as a whole to improve the strength of the initial base body. After the heat treatment, the lattice base body becomes the lattice body 110, and the fin base body becomes the fin body, and the shapes of the two are not changed and the strength is enhanced. Subsequently, the martensite shape and the austenite shape of the fin body are fixed in shape by the mold, and the fixed martensite shape and austenite shape are subjected to different heat treatment respectively, so that the fin body is converted into the mixing fin 120 capable of shape conversion between the preset martensite shape and austenite shape, thereby obtaining the lattice body 110 with a fixed shape and the mixing fin 120 integrally formed on the lattice body 110 and having a reversible shape memory effect. Not only can the connection firmness of the mixing fin 120 and the lattice body 110 be ensured, but also the processing convenience of the positioning lattice 100 can be improved.

[0048] Specifically, the step of obtaining the initial base body, the initial base body comprising the grid base body and the fin base body integrally formed on the end face of the grid base body, comprises: preparing an alloy ingot, specifically, the alloy ingot can be prepared by a non-consumable vacuum arc furnace. Hot-rolling the alloy ingot into a first plate material of a first preset thickness, such as 3.5 mm; cold-rolling the first plate material into a second plate material of a second preset thickness, such as 1.2 mm-1.4 mm; and polishing the second plate material into a third plate material of a third preset thickness, such as 1 mm. Cutting a fourth plate material of a preset shape from the third plate material. Bending the fourth plate material and laser welding the interface of the fourth plate material to obtain the initial base body.

[0049] Alternatively, the step of obtaining the initial base body, the initial base body comprising the grid base body and the fin base body integrally formed on the end face of the grid base body, can also comprise: preparing an alloy ingot. Rolling the alloy ingot into a square rod of a preset size. Cutting a channel hole of the grid body along the length direction of the square rod to obtain a grid-shaped hollow rod body, and then cutting the side wall of the hollow rod body to obtain the fin base body, thereby obtaining the initial base body.

[0050] Specifically, the step of heat-treating the initial base body, the grid base body becoming the grid body and the fin base body becoming the fin body after heat-treatment, can comprise: maintaining the initial base body at 773.15 K in a hot environment for 2 h, so that the grid base body becomes the grid body and the fin base body becomes the fin body.

[0051] Optionally, in the embodiment, the step of using a mold to fix the shape of the fin body and heat-treating the fixed shape of the fin body to obtain the hybrid fin 120 with a double-way memory effect, comprises: martensite shape memory training: using a first mold to fix the fin body into a preset martensite shape, and maintaining at 423.15 K in a cold environment for a first preset time, specifically, the first preset time can be 10 min. Austenite shape memory training: using a second mold to fix the fin body into a preset austenite shape, and maintaining at 523.15 K in a hot environment for a second preset time, specifically, the second preset time can be 10 min; alternately operating the martensite shape memory training and the austenite shape memory training multiple times to obtain the hybrid fin 120 with a double-way memory effect.

[0052] Finally, it should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations.

[0053] and the term "comprises" or "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements,

[0054] but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. The terms an or a as used herein in the context of claiming a genus of claim 1 are intended to include both a and at least one, and thus should be construe to be consistent with the definition of the more general term "comprising." The terms "about" and "substantially" as used herein refer to ± 10 %.

[0055] 0The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and are within the scope of the application as defined by the appended claims. The actual scope of the application is defined by the appended claims.

[0056] These embodiments, while including the best mode known to the inventors at this time, are to be used as illustrative only and are not to be taken in a limiting sense as to the scope of the present application. The application is therefore to be understood in all its aspects as not limited to the embodiments described herein, but only by reference to the appended claims, the true scope of which is to be determined by their fair meaning and the equivalents thereof.

Claims

1. A method of manufacture, characterized by, A method for preparing a positioning grid (100), the method comprising: obtaining an initial base body, the initial base body comprising a grid base body and a wing base body integrally formed on an end face of the grid base body; subjecting the initial base body to heat treatment, the grid base body after heat treatment becoming a grid body (110), and the wing base body becoming a wing body; using a mold to fix the shape of the wing body, and subjecting the wing body after shape fixation to heat treatment to obtain a hybrid wing (120) having a two-way memory effect: martensite shape memory training: using a first mold to fix the wing body into a preset martensite shape, and keeping the wing body in a 423.15K cold environment for a first preset time; austenite shape memory training: using a second mold to fix the wing body into a preset austenite shape, and keeping the wing body in a 523.15K hot environment for a second preset time; alternately operating the martensite shape memory training and the austenite shape memory training multiple times to obtain a hybrid wing (120) having a two-way memory effect.

2. A positioning lattice, characterized in that The positioning grid prepared by the method of claim 1, comprising an integrally formed grid body (110) and a hybrid wing (120), the hybrid wing (120) being arranged on an end face of the grid body (110), and the hybrid wing being a shape memory alloy having a two-way memory effect.

3. The positioning grid according to claim 2, characterized in that The hybrid wing (120) comprises a martensite shape and an austenite shape, in the martensite shape, an inclination angle of the hybrid wing (120) is θ1, and θ1 is in the range of [30°, 45°]; in the austenite shape, an inclination angle of the hybrid wing (120) is θ2, and θ2 is in the range of [0°, 15°].

4. The positioning grid according to claim 3, characterized in that In the martensite shape, an azimuth angle of the hybrid wing (120) is Φ1, and Φ1 is in the range of [0°, 5°]; in the austenite shape, an azimuth angle of the hybrid wing (120) is Φ2, and Φ2 is in the range of [5°, 10°].

5. The positioning grid according to any one of claims 2-4, characterized in that, The hybrid wing (120) is a TiNiZr alloy.

6. The positioning grid according to any one of claims 2-4, characterized in that, The hybrid wing (120) has a composition of Ti50-xNi50Zrx (x = 5, 10).

7. A fuel assembly characterized by, A fuel rod bundle and the positioning grid (100) of claim 2, a plurality of fuel rods (200) of the fuel rod bundle one-to-one correspond to a plurality of through holes of the positioning grid (100).

Images