End plug for resistance welding of nuclear fuel rod and fuel rod

Abstract

The present invention discloses an end plug for resistance welding of nuclear fuel rods, wherein the middle part of the end plug body is provided with a welding zone for resistance welding with a cladding tube, and the welding zone is provided with a first truncated cone section, a second truncated cone section and a third truncated cone section which are coaxially connected in sequence in a direction away from the cladding tube; the outer diameter of the second truncated cone section is between the inner diameter and the outer diameter of the cladding tube; among the first truncated cone section, the second truncated cone section and the third truncated cone section, the outer diameter of the first truncated cone section is the smallest, and the outer diameter of the second truncated cone section is the largest; the inner end of the end plug body located in the cladding tube is also provided with a fourth truncated cone section which is coaxially connected with the first truncated cone section, and the outer diameter of the fourth truncated cone section is smaller than the inner diameter of the cladding tube, and is between the outer diameters of the first truncated cone section and the second truncated cone section. By adopting this scheme, the length and angle of the fusion line of the welding fusion zone and the protruding height of the weld can be effectively controlled, and the flow of the weld nodules during the welding process can be restricted to avoid the weld nodules from contacting the fuel column or the air cavity spring inside the fuel rod.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear reactor fuel elements, and in particular to an end plug used for resistance welding of nuclear fuel rods and a fuel rod. Background Art

[0002] Nuclear reactor fuel elements are generally formed by encapsulating fuel cores with cladding tubes and upper and lower end plugs. The single fuel rod formed is then loaded into a clamping support structure skeleton to form a fuel assembly. During the operation of the stack, the welding quality and integrity of the welds at the upper and lower ends of the fuel rods are key quality characteristics to ensure that the fission products inside the fuel rods do not leak. Since resistance welding uses a non-melting welding method, it has its own welding characteristics compared to traditional melting welding such as TIG or EB. Therefore, in order to ensure the quality of resistance welding welds and ensure the safety of operation in the fuel rod stack, it is necessary to design matching end plugs based on the resistance welding method and its welding and forming characteristics, and achieve reliable connection with the cladding through resistance welding.

[0003] A document that is relatively close to the present invention is "Resistance welding of end caps for nuclear fuel rods" (patent number CN104520936 A). The length of the weld fusion line formed in the later stage of welding the end plug and the cladding tube described in document 1 cannot be determined by visual inspection, and the weld strength after welding needs to be tested by destructive inspection.

[0004] Document 1 addresses the impact of weld nodules formed on the outside of the cladding tube during resistance welding by arranging an annular groove at the corresponding position of the end plug to accommodate the accumulation of weld nodules on the outside of the weld. As for the impact of weld nodule accumulation inside the cladding during resistance welding, Document 1 provides a certain accommodation space through an internal reduced diameter truncated cone. However, since there is only a reduced diameter truncated cone, the cone needs to have a certain height to ensure that the internal weld nodules do not contact other components in the axial direction. At the same time, since a certain space is required in the radial direction to accommodate the weld nodules, the internal cone must be reduced in diameter. This will weaken the support effect of the cone on components such as the internal fuel column or air cavity spring, or even make it impossible to provide support, such as placing a support tube inside. In addition, the contact part between the end plug and the cladding tube in Document 1 is provided with a chamfer or fillet for the purpose of top forging during the welding process, and the chamfer or fillet length is limited.

[0005] Therefore, there is an urgent need for an end plug for resistance welding of nuclear fuel rods that can improve welding quality. Summary of the invention

[0006] The present invention aims to solve the deficiencies of the prior art and to provide an end plug and a fuel rod for resistance welding of nuclear fuel rods. By adopting this solution, the length and angle of the fusion line in the welding fusion zone and the protruding height of the weld can be effectively controlled, and the flow of the weld nodule during the welding process can be restricted to avoid the weld nodule from contacting the fuel column or the air cavity spring inside the fuel rod.

[0007] The present invention is achieved through the following technical solutions:

[0008] An end plug for resistance welding of nuclear fuel rods, comprising an end plug body;

[0009] The middle part of the end plug body is provided with a welding area for realizing resistance welding with the cladding tube, and the welding area is provided with a first truncated cone section, a second truncated cone section and a third truncated cone section which are coaxially connected in sequence in a direction away from the cladding tube; the outer diameter of the second truncated cone section is between the inner diameter and the outer diameter of the cladding tube;

[0010] Among the first truncated cone segment, the second truncated cone segment and the third truncated cone segment, the first truncated cone segment has the smallest outer diameter, and the second truncated cone segment has the largest outer diameter;

[0011] The inner end of the end plug body located in the cladding tube also has a fourth truncated cone segment coaxially connected to the first truncated cone segment. The outer diameter of the fourth truncated cone segment is smaller than the inner diameter of the cladding tube and is located between the outer diameters of the first and second truncated cone segments.

[0012] Compared with the prior art, the length of the weld fusion line formed in the later stage of welding the end plug and the cladding tube in Document 1 cannot be determined by visual inspection, and the strength of the weld after welding needs to pass destructive inspection; at the same time, since a certain space is required in the radial direction to accommodate the weld nodule, the internal cone shrinkage must be larger, which will cause the cone to weaken the supporting effect of the internal fuel column or air cavity spring and other components, or even fail to provide support, such as placing a support tube inside. The present invention provides an end plug for resistance welding of nuclear fuel rods. In a specific scheme, it includes a welding area located in the middle of the end plug body, and a stepped cone is used in the welding area, including a first cone segment, a second cone segment and a third cone segment. Among them, the outer diameter of the second frustum section is the largest, which is larger than the inner diameter of the cladding tube welded with it, and smaller than the outer diameter of the cladding tube welded with it. At the same time, the height of the second frustum section is determined according to the requirements of weld strength. In view of the problem that the length of the weld fusion line formed in the later stage of welding between the end plug and the cladding tube in document 1 cannot be determined by appearance inspection, and the weld strength after welding needs to be determined by destructive inspection, this scheme indirectly guarantees the length of the weld fusion line and the weld strength after welding by covering the height of the second frustum section of the entire welding area through the weld of the end plug. Under the premise of ensuring the quality of the weld, the production process is shortened, the relevant inspection equipment is saved, the production effect is improved, and the production cost is saved.

[0013] In order to address the influence of the end plug in Document 1 on the formation of weld nodules on the outside of the cladding tube during resistance welding, a design was adopted in which an annular groove was arranged at the corresponding position of the end plug to accommodate the accumulation of weld nodules on the outside of the welding. However, since there is only a reduced diameter cone, the cone needs to have a certain height to ensure that the internal weld nodules do not contact other components in the axial direction. At the same time, since a certain space is required in the radial direction to accommodate the weld nodule, the internal truncated cone must be greatly reduced in diameter, which will cause the support effect of the truncated cone on internal components such as the fuel column or the air cavity spring to be weakened, or even unable to provide support. For example, in order to solve the problem of placing a support tube inside, a groove of a certain depth is formed between the first truncated cone section and the second truncated cone section and the fourth truncated cone section in this scheme. The groove can provide a holding space for the weld nodule formed by top forging during resistance welding, that is, the excess weld nodule is allowed to flow under the step through the stepped truncated cone with a drop to avoid its accumulation, thereby preventing the outer diameter of the weld from being too large. A fourth truncated cone section with a diameter slightly smaller than the inner diameter of the cladding is provided at the end of the end plug. While providing sufficient support surface for components such as the fuel column or the air cavity spring inside the cladding tube, a groove is formed with the stepped truncated cone in the welding area to accommodate the internal weld nodule generated during the welding process. The truncated cone can also block the axial flow of the internal weld nodule to prevent the weld nodule from contacting components such as the fuel and the air cavity spring inside the cladding.

[0014] In view of the problem that the contact part between the end plug and the cladding tube in Document 1 is provided with a chamfer or fillet for upsetting during welding, and the length of the chamfer or fillet is limited, the contact part between the end plug and the cladding tube in this solution is a right angle, and the right-angle contact will not affect the contact pressure and upsetting forming of resistance welding. Secondly, the outer diameter of the third truncated cone is slightly smaller than that of the second truncated cone, so as to provide a certain space for upsetting deformation during resistance welding, and control the height of the outer diameter of the weld protruding from the outer diameter of the cladding tube due to upsetting deformation.

[0015] Therefore, the above scheme aims to achieve: under the existing structural characteristics of fuel elements, a reliable connection between the cladding and the end plug by resistance welding is achieved, and the strength, sealing, corrosion resistance and other performance qualities of the weld formed between the two are ensured, so as to ensure the manufacturing quality of the fuel rods and their in-pile operating performance.

[0016] In a further solution, the portion of the end plug body located outside the cladding tube has a gripping area, and the gripping area has an annular groove for accommodating a gripper; the annular groove is used to cooperate with the gripper for gripping.

[0017] In a further solution, a gripping guide section is coaxially connected to one end of the annular groove facing the welding zone, and a gripping contact section is coaxially connected to the other end of the annular groove, and the outer diameters of the gripping guide section and the gripping contact section gradually increase in the direction away from the annular groove; wherein the gripping guide section and the gripping contact section are mainly cooperated with corresponding grippers to realize the gripping and pulling installation of the fuel rod; the gripping guide surface and the gripping contact surface have inclined surfaces with a certain inclination angle, which help the gripping head to retract and expand during the gripping process and play a guiding role.

[0018] In a further solution, a clamping area is coaxially connected between the gripping guide section of the gripping head and the third truncated cone section, and the clamping area includes a clamping section for clamping the electrode clamp; wherein the clamping section is used to provide a contact surface for the clamp during welding.

[0019] In a further solution, the clamping section is in a truncated cone shape, the outer diameter of the clamping section is smaller than the outer diameter of the third truncated cone section, and the end of the third truncated cone section facing the clamping section has a chamfered corner; wherein, the third truncated cone section is chamfered on a large size near the top end of the end plug to prevent hooking during the fuel rod grabbing process.

[0020] A further solution is that the clamping section is in the shape of a truncated cone, the large diameter end of the clamping section is connected to the third truncated cone section, and the small diameter end of the clamping section is connected to the grasping guide section of the gripping head; the outer diameter of the large diameter end of the clamping section is the same as the outer diameter of the third truncated cone section, and the outer diameter of the small diameter end of the clamping section is the same as the outer diameter of the large diameter end of the grasping guide section of the gripping head; wherein, the third truncated cone section in the stepped truncated cone of the resistance welding area is not chamfered on the side close to the top end of the end plug, but by directly chamfering the clamping section to the third truncated cone section, a conical chamfer is formed to play a guiding and anti-hooking role.

[0021] In a further solution, the outer end of the end plug body is also provided with a guide area, and the guide area includes a first frustoconical segment, the large diameter end of the first frustoconical segment is connected to the gripping contact segment of the gripping head through a transition cone; the small diameter end of the first frustoconical segment is provided with a spherical notch; wherein the guide area is mainly used for guiding and facilitating the inclusion of the gripper during the installation of the fuel rod.

[0022] In a further solution, a transition frustum of cone section is coaxially connected between the spherical segment and the small diameter end of the first frustum of cone section, the large diameter end of the transition frustum of cone section is connected to the small diameter end of the first frustum of cone section, and have the same outer diameter; the outer diameter size of the small diameter end of the transition frustum of cone section and the end face of the spherical segment is the same; wherein a transition frustum of cone with a shorter height is added between the first frustum of cone section and the spherical segment to make the transition between the two smooth.

[0023] In a further solution, a second truncated cone segment is coaxially connected between the first truncated cone segment and the second truncated cone segment, the large diameter end of the second truncated cone segment is connected to the end of the second truncated cone segment, and the outer diameters are the same; the small diameter end of the second truncated cone segment is connected to the end of the first truncated cone segment, and the outer diameters are the same; in this solution, in order to extend the length of the weld fusion line after welding, enhance the weld strength and guide the flow of the weld nodule, at the initial contact point between the end plug and the cladding tube in the present invention, the initial contact surface between the end plug and the cladding tube is a long inclined transition, and the entire surface is set as an inclined surface to help guide the flow of the weld nodule.

[0024] A further solution is a fuel rod, comprising a cladding tube, wherein end plugs are resistance-welded at the port positions of the cladding tube, and the fourth conical section at the inner end of the end plug is supported on the fuel column or the end of the air cavity spring inside the cladding tube; in this solution, the above end plug is used, and the fuel core block and the air cavity spring are encapsulated in the space formed by the end plug and the cladding by pressure resistance welding, thereby finally forming a rod-shaped fuel element.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] 1. The middle welding part of the end plug of the present invention adopts a stepped cone, and the outer diameter of the second cone section welded to the cladding tube is larger than the outer diameter of the third cone section that accommodates the upsetting deformation during the resistance welding process and provides an auxiliary function. Therefore, the length of the fusion zone formed after welding can be easily checked and controlled indirectly through the height of the upsetting deformation of the second cone section, thereby realizing the monitoring of the weld strength. Compared with the welds formed by the end plugs used for pressure resistance welding of existing fuel rods, the strength of the weld can be guaranteed without checking the weld width and height. At the same time, by adopting a bevel chamfer connection between the first cone section and the second cone section, the fusion length of the weld after welding can be changed, which plays a certain role in improving the weld strength;

[0027] 2. The middle welding part of the end plug of the present invention adopts a stepped truncated cone, and the outer diameter of the third truncated cone section is slightly smaller than that of the second truncated cone section, so that a certain drop depth is formed between the two, which can provide a certain flow space for the weld nodule formed during the resistance welding process, so as to control the height of the outer diameter of the weld protruding from the outer diameter of the cladding tube caused by the upsetting deformation;

[0028] 3. The middle welding part of the end plug of the present invention adopts a stepped truncated cone, and the end of the third truncated cone section close to the top of the end plug adopts a large-size chamfer, which plays a role in guiding and preventing the fuel rod from being hooked during the fuel rod pulling process; the self-welding clamping section can also be directly chamfered to the third truncated cone section, and the formed conical chamfer plays a role in guiding and preventing the fuel rod from being hooked;

[0029] 4. The end of the end plug of the present invention adopts a short truncated cone design, namely the fourth truncated cone section, which forms a groove of a certain depth with the first truncated cone section and the second truncated cone section. Compared with the end plug used for the existing fuel rod pressure resistance welding, while providing a certain accommodation space for the weld nodules formed during the resistance welding process, the fourth truncated cone section can block the weld nodules formed during the resistance welding process to prevent the weld nodules from contacting the fuel column or the air cavity spring. Its end plane can also provide support for the fuel column or the air cavity spring in the fuel rod cladding;

[0030] 5. The top end of the end plug of the present invention comprises two parts, one of which is composed of an annular groove containing a gripper, a gripping guide surface of a gripper head, and a gripping contact surface of a gripper head. This part of the structure mainly cooperates with the corresponding gripper to realize the gripping, pulling and installation of the fuel rod; the other part is composed of a first frustum section, a spherical notch formed by the rounded top end, and a transition frustum section therebetween. This part of the structure mainly plays a role of guiding and being easily contained by the gripper during the installation of the fuel rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0032] Figure 1 A schematic diagram of the structure of the end plug of Example 1 provided by the present invention;

[0033] Figure 2 A schematic diagram of the structure of the end plug of Example 2 provided by the present invention;

[0034] Figure 3 A schematic diagram of the structure of the end plug of Example 3 provided by the present invention;

[0035] Figure 4 A schematic structural diagram of a fuel rod according to an embodiment of the present invention.

[0036] Marks and corresponding parts names in the attached drawings:

[0037] 1-guide area, 11-spherical segment, 12-first frustum section, 13-transition frustum section, 2-gripping area, 21-annular groove, 22-gripping head grabbing guide section, 23-gripping head grabbing contact section, 3-clamping section, 4-welding area, 41-first frustum section, 42-second frustum section, 43-third frustum section, 5-fourth frustum section. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0039] Embodiment 1:

[0040] like Figure 1 As shown, an end plug for resistance welding of nuclear fuel rods comprises a guide area 1 with a guide function at the top of the end plug, a gripping area 2, a clamping section 3 for clamping an electrode chuck in the middle of the end plug, a welding area 4 for resistance welding, and a fourth truncated cone section 5 with a gas support function at the end of the end plug. The end plug is made of the same type of zirconium alloy material as the cladding.

[0041] The top guide area 1 of the end plug is composed of the top spherical segment 11, the first truncated cone section 12 and the transition truncated cone section 13 between the two. The gripping area 2 is composed of an annular groove 21 for accommodating the gripper, the gripper head guide surface and the gripping contact surface. The gripper head gripping guide surface and the gripper head gripping contact surface are inclined surfaces with a certain inclination angle, which help the gripper head to retract and expand during the gripping process and play a guiding role. The middle clamping section 3 of the end plug is formed by a truncated cone of a certain height, which provides a contact surface for the clamp during welding. The welding area 4 is composed of a stepped frustum, wherein the first frustum section 41 has the smallest outer diameter, the second frustum section 42 is the welding implementation part and has the largest outer diameter, and the third frustum section 43 is the stepped frustum auxiliary welding part; the groove formed between the first frustum section 41 and the second frustum section 42 can provide a space for accommodating the weld nodules formed during the welding process; the size of the outer diameter of the second frustum section 42 is between the inner diameter and the outer diameter of the cladding tube, and the height of the second frustum section 42 can monitor the length of the weld fusion zone formed after welding; in order to control the height of the weld nodules during the auxiliary welding process, the outer diameter of the third frustum section 43 is slightly smaller than that of the second frustum section 42, which can provide a certain flow space for the weld nodules, and at the same time, the third frustum section 43 is treated with a large-size chamfer near the top end of the end plug to prevent hooking during the fuel rod grabbing process; therefore, the end welding area 4 can be used to judge whether the weld strength after welding is qualified, and at the same time ensure that the welding will not affect the fuel and air cavity spring inside the fuel rod. The fourth conical section 5 at the end of the end plug is formed by a conical section with a diameter slightly smaller than the inner diameter of the cladding and a smaller height. The side thereof in contact with the fuel column or the air cavity spring is a horizontal plane, which can provide stable axial support, and the side thereof connected to the stepped conical section can block the weld nodules formed during the welding process, thereby preventing the weld nodules from contacting the fuel column or the air cavity spring.

[0042] The height of the second truncated cone section 42 is greater than the minimum requirement for the length of the fusion line of the weld fusion zone. The difference in outer diameter between the second truncated cone section 42 and the first truncated cone section 41 is greater than 1 mm. The outer diameter of the fourth truncated cone section 5 is less than the inner diameter of the cladding tube matched with the end plug by no more than 1 mm, and a groove is formed between the fourth truncated cone section 5 and the welding zone 4.

[0043] Embodiment 2:

[0044] like Figure 2 As shown, the only difference between this embodiment and embodiment 1 is that the third truncated cone section 43 in the stepped truncated cone of the resistance welding area 4 is not rounded near the top end of the end plug, but the clamping section 3 is directly beveled to the third truncated cone section 43 to form a conical bevel to play a guiding and anti-hooking role.

[0045] Embodiment 3:

[0046] like Figure 3 As shown, the difference between this embodiment and embodiment 1 is that: the first truncated cone section 41 and the second truncated cone section 42 in the step truncated cone of the resistance welding area 4 are connected by a bevel transition, so that the fusion line of the weld after welding has a certain inclination angle, so as to increase the fusion line length, enhance the weld strength, and guide the flow of the weld nodule during welding. The end plug is made of a zirconium alloy material different from that of the cladding tube.

[0047] Example 4

[0048] like Figure 4 As shown, this embodiment further provides a fuel rod, which includes a cladding tube, and end plugs are resistance-welded at the port positions of the cladding tube, and the fourth conical segment 5 at the inner end of the end plug is supported on the fuel column or the end of the air cavity spring inside the cladding tube; this embodiment adopts the end plug for resistance welding of nuclear fuel rods of Examples 1 to 3, and encapsulates the fuel core block and the air cavity spring in the space formed by the end plug and the cladding by performing pressure resistance welding, so as to finally form a rod-shaped fuel element.

[0049] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An end plug for resistance welding of nuclear fuel rods, characterized in that: including an end plug body; The middle part of the end plug body is provided with a welding area (4) for realizing resistance welding with the cladding tube, and the welding area (4) is provided with a first truncated cone section (41), a second truncated cone section (42) and a third truncated cone section (43) which are coaxially connected in sequence in a direction away from the cladding tube; the outer diameter of the second truncated cone section (42) is between the inner diameter and the outer diameter of the cladding tube; Among the first truncated cone section (41), the second truncated cone section (42) and the third truncated cone section (43), the first truncated cone section (41) has the smallest outer diameter, and the second truncated cone section (42) has the largest outer diameter; The inner end of the end plug body located in the cladding tube also has a fourth truncated cone section (5) coaxially connected to the first truncated cone section (41); the outer diameter of the fourth truncated cone section (5) is smaller than the inner diameter of the cladding tube and is located between the outer diameters of the first truncated cone section (41) and the second truncated cone section (42); A second truncated cone section is coaxially connected between the first truncated cone section (41) and the second truncated cone section (42); the large diameter end of the second truncated cone section is connected to the end of the second truncated cone section (42) and have the same outer diameter; the small diameter end of the second truncated cone section is connected to the end of the first truncated cone section (41) and have the same outer diameter; The height of the second truncated cone section (42) is greater than the minimum requirement for the length of the fusion line of the weld fusion zone; and the difference in outer diameter between the second truncated cone section (42) and the first truncated cone section (41) is greater than 1 mm.

2. An end plug for resistance welding of nuclear fuel rods according to claim 1, characterized in that: The portion of the end plug body located outside the cladding tube has a gripping area (2), and the gripping area (2) has an annular groove (21) for accommodating a gripper.

3. An end plug for resistance welding of nuclear fuel rods according to claim 2, characterized in that: One end of the annular groove (21) facing the welding zone (4) is coaxially connected to a gripping head grabbing guide section (22), and the other end of the annular groove (21) is coaxially connected to a gripping head grabbing contact section (23), and the outer diameters of the gripping head grabbing guide section (22) and the gripping head grabbing contact section (23) both gradually increase in a direction away from the annular groove (21).

4. An end plug for resistance welding of nuclear fuel rods according to claim 3, characterized in that: A clamping area is also coaxially connected between the gripping head gripping guide section (22) and the third truncated cone section (43), and the clamping area includes a clamping section (3) for clamping the electrode clamp.

5. The end plug for resistance welding of nuclear fuel rods according to claim 4, characterized in that: The clamping section (3) is in the shape of a truncated cone, the outer diameter of the clamping section (3) is smaller than the outer diameter of the third truncated cone section (43), and the end of the third truncated cone section (43) facing the clamping section (3) has a rounded corner.

6. The end plug for resistance welding of nuclear fuel rods according to claim 4, characterized in that: The clamping section (3) is in the shape of a truncated cone, the large diameter end of the clamping section (3) is connected to the third truncated cone section (43), and the small diameter end of the clamping section (3) is connected to the grasping guide section (22) of the grasping head; The outer diameter of the large diameter end of the clamping section (3) is the same as the outer diameter of the third truncated cone section (43), and the outer diameter of the small diameter end of the clamping section (3) is the same as the outer diameter of the large diameter end of the grasping guide section (22) of the grasping head.

7. The end plug for resistance welding of nuclear fuel rods according to claim 3, characterized in that: The outer end of the end plug body is also provided with a guide area (1), the guide area (1) comprising a first truncated cone section (12), the large diameter end of the first truncated cone section (12) being connected to the gripping contact section (23) via a transition cone; the small diameter end of the first truncated cone section (12) is provided with a spherical segment (11).

8. The end plug for resistance welding of nuclear fuel rods according to claim 7, characterized in that: A transitional frustum section (13) is coaxially connected between the spherical segment (11) and the small diameter end of the first frustum section (12); the large diameter end of the transitional frustum section (13) is connected to the small diameter end of the first frustum section (12) and has the same outer diameter; the small diameter end of the transitional frustum section (13) and the end face of the spherical segment (11) have the same outer diameter.

9. A fuel rod, characterized in that: It comprises a cladding tube, each of which is provided with an end plug by resistance welding at the port position of the cladding tube, and a fourth truncated cone section (5) at the inner end of the end plug is supported on a fuel column or an end of an air cavity spring inside the cladding tube; the end plug is the end plug according to any one of claims 1 to 8.

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