Nuclear fuel rods and manufacturing methods

Abstract

The nuclear fuel rod includes nuclear fuel contained within cladding (4), the cladding (4) including a tube (6) extending along a central axis (A) and having two ends, each plug (8) attached to a corresponding end of the tube (6) by sealing the end of the tube, and the tube (6) is covered by a tube coating (16) extending the entire length of the tube (16) from one end of the tube (6) to the other.

Description

[Technical Field]

[0001] The present invention relates to the field of nuclear fuel rods, in particular for light water reactors. [Background technology]

[0002] A nuclear fuel assembly used in a light water reactor generally comprises a bundle of nuclear fuel rods, each of which comprises cladding that contains the nuclear fuel, the cladding being made up of a cladding tube that is closed at each of its two ends by a plug.

[0003] Each plug is welded to a corresponding end of the tube, for example, to seal the tube. Various welding techniques can be used to attach each plug to the tube, such as TIG welding (arc welding in an inert atmosphere with a tungsten electrode), laser welding, or electron beam welding.

[0004] The tube and plug are generally made of metal, for example zirconium or a zirconium alloy, such as a Zircaloy type zirconium alloy.

[0005] In order to protect the cladding from the highly aggressive environment in which it finds itself during reactor operation, the tubes may be provided with an external protective coating, for example a protective coating made of chromium or a chromium alloy.

[0006] The presence of a protective coating on the tube can adversely affect the weld made between the tube and the plug, making the resulting weld appear to be weaker and / or more susceptible to corrosion.

[0007] To limit this risk, the protective coating is applied over most of the length of the tube without coating the end portions of the tube where the plugs are welded, so that the protective coating does not contaminate the welds made between the tube and each plug.

[0008] However, portions of the tubes not covered with a protective coating may be more susceptible to severe wear or corrosion, including high temperature oxidation under accident conditions, thereby forming weak areas of the tubes and rods. Summary of the Invention [Problem to be solved by the invention]

[0009] One of the aims of the invention is to propose a nuclear fuel rod that is easy to manufacture while being resistant, in particular resistant to corrosion and oxidation at high temperatures. [Means for solving the problem]

[0010] To this end, the present invention proposes a nuclear fuel rod comprising nuclear fuel contained in cladding, the cladding including a tube and two plugs, the tube extending along a central axis and having two ends, each plug being attached to a corresponding end of the tube by sealing said end, the tube being covered by a tube coating, the tube coating extending over the entire length of the tube from one end to the other.

[0011] According to particular embodiments, the nuclear fuel rod element comprises one or more of any of the following features taken individually or in all technically possible combinations: - one of the plugs or each plug is at least partially covered by a plug coating; - For each plug provided with a plug coating, the plug coating and the tube coating are distinct; - The pipe coating and plug coating are made of the same material; - the plug coating and tube coating of each plug with a plug coating are adjacent at the interface between the tube and the plug; - wherein each plug, whether coated or not, is welded onto the tube without affecting the shape of the interface between the tube and the plug and / or without reworking the interface between the tube and the plug by mechanical or chemical processes, in particular involving material removal; - the tube is made of zirconium-based material; - Each plug is made of zirconium-based material; - The tube coating is made of chromium-based materials; - Each plug is installed on a tube without the presence of a eutectic at the joint between the tube and the plug between the tube material, the tube coating material, the plug material, and, if applicable, the plug coating material covering the plug.

[0012] The invention further relates to a manufacturing method for a nuclear fuel rod as defined above, comprising the steps of producing tubes and plugs, each plug being coated, if applicable, with a plug coating, and welding at least one of the or each plug to the corresponding end of the tube by electric resistance welding.

[0013] According to particular embodiments, the manufacturing method comprises one or more of any of the following features taken individually or in all technically possible combinations: - Each plug is welded to the pipe by electric resistance butt welding; - electric resistance welding of at least one of the plugs or of each plug is carried out with a current of 10 kA-20 kA; - electric resistance welding of at least one of the or each plug is carried out by applying the plug against the corresponding end of the pipe under a pressing force of 200 daN to 400 daN, preferably 250 daN to 350 daN; - electric resistance welding of at least one of the plugs or of each plug is carried out by applying an electric current for a duration of 10 ms to 30 ms; - the manufacturing method is carried out without reworking the interface between the tube and each plug welded to the tube by mechanical or chemical processes involving material removal; - Each plug is welded onto the tube without the formation of a eutectic at the joint between the tube and the plug between the tube material, the tube coating material, the plug material and, where applicable, the plug coating material covering the plug.

[0014] The invention and its advantages will be better understood upon reading the following description, given purely by way of non-limiting example, and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram of a nuclear fuel rod in longitudinal section; [Figure 2] 2A-2C are cross-sectional views illustrating a manufacturing method for a nuclear fuel rod such as that shown in FIG. 1. [Figure 3] 2A-2C are cross-sectional views illustrating a manufacturing method for a nuclear fuel rod such as that shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0016] FIG. 1 shows a nuclear fuel rod 2 intended for use in, for example, a light water reactor, in particular a pressurized water reactor (PWR) or a boiling water reactor (BWR), a "VVER" reactor, an "RBMK" reactor, or a heavy water reactor, for example a "CANDU" reactor.

[0017] The nuclear fuel rod 2 has the shape of a rod extending along a central axis A.

[0018] The nuclear fuel rod 2 includes cladding 4 which contains the nuclear fuel.

[0019] The cladding 4 includes a tube 6 and two plugs 8, each welded to a corresponding end of the tube 6 to seal that end. The tubes 6 extend along the central axis A of the nuclear fuel rod 2. The tubes 6 preferably have a circular cross section centered on the central axis A.

[0020] The nuclear fuel is, for example, in the form of pellet stacks 10 stacked axially inside the tubes 6. The pellet stacks 10 are also called "fissile columns."

[0021] The nuclear fuel rod 2 optionally includes a spring 12 disposed within the tube 6 between the pellet stack 10 and one of the plugs 8 to urge the pellet stack 10 toward the other plug 8. The spring 12 is compressed between the pellet stack 10 and the plug 8.

[0022] Between the pellet stack 10 and the plug 8 is a space or plenum 14 against which a spring 12 presses. The plenum 14 may be used for storing gases released from the nuclear fuel during reactor operation. The spring 12 is positioned within the plenum 14.

[0023] As shown in FIGS. 2 and 3, which illustrate the welding of plug 8 to one end of tube 6, tube 6 is provided with a tube coating 16.

[0024] The tube 6 has an inner surface 6B oriented towards the interior of the tube 6 and an outer surface 6A oriented towards the exterior of the tube 6 .

[0025] A tube coating 16 covers the outer surface 6A of the tube 6 to protect the tube from the external environment. During operation, the tube coating 16 is in contact with the environment.

[0026] The tube 6 is made of, for example, a zirconium-based material.

[0027] In this context, zirconium-based material means a material made of pure zirconium or a zirconium-based alloy. A pure zirconium material is a material that contains at least 99% by weight of zirconium.

[0028] A zirconium-based alloy is an alloy containing at least 95% by weight zirconium.

[0029] In one embodiment, the zirconium-based material of tube 6 is a quaternary zirconium alloy having a composition of 0.8-1.8 wt. % niobium, 0.2-0.6 wt. % tin, and 0.02-0.4 wt. % iron, with the remainder being zirconium and unavoidable impurities.

[0030] The tube 6 has a thickness of, for example, 0.4 mm to 1 mm. The thickness of the tube 6 is the distance between the inner surface 6B and the outer surface 6A of the tube 6.

[0031] The tube coating 16 is thin, for example having a thickness that is significantly less than the thickness of the tube 6 .

[0032] The tube coating 16 has a thickness of, for example, 5 μm to 25 μm, in particular 10 μm to 20 μm. The thickness of the tube coating 16 is measured perpendicular to the outer surface 6A of the tube 6, i.e., in a radial direction relative to the central axis A of the tube 6.

[0033] The tube coating 16 is made of a chromium-based material.

[0034] In this context, chromium-based material means a pure chromium material or a chromium-based alloy.

[0035] A pure chromium material is a material that contains at least 99% chromium by weight. A chromium-based alloy is an alloy that contains at least 85% chromium by weight.

[0036] In one embodiment, the chromium-based material is a chromium-based alloy selected from binary chromium aluminum alloys, binary chromium nitrogen alloys, and binary chromium titanium alloys.

[0037] The tube coating 16 may include a single layer of a chromium-based material or multiple overlaying layers of a chromium-based material, preferably the same chromium-based material.

[0038] The structure of the tube coating 16 of multiple overlay layers results, for example, from the deposition process used to deposit the tube coating 16 onto the tube 6, particularly if the deposition is performed in multiple passes.

[0039] The tube coating 16 extends the entire length of the tube 6 from one end of the tube 6 to the other.

[0040] In a preferred embodiment, the tube coating 16 is continuous. The tube coating completely covers the outer surface 6A of the tube 6.

[0041] Each plug 8 includes an insertion portion 18 that is inserted into the tube 6 to attach the plug 8 to the corresponding end of the tube 6, and an exposed portion 20 that remains outside the tube 6 once the plug 8 is attached to the corresponding end of the tube 6.

[0042] Each plug 8 has an annular surface 22 that bears against the end of the tube 6 when the plug 8 is disposed therein. The annular surface 22 is centered about the central axis A. The annular surface 22 is positioned at the junction between the insert portion 18 and the exposed portion 20. As shown in FIG. 2 , the annular surface 22 may be, for example, a frustoconical shape that widens from the insert portion 18 toward the exposed portion 20.

[0043] Each plug 8 is made of, for example, a zirconium-based material.

[0044] In one embodiment, the zirconium-based material of the plug 8 is a quaternary zirconium alloy having a composition including 0.8 to 1.8 wt. % niobium, 0.2 to 0.6 wt. % tin, and 0.02 to 0.4 wt. % iron, with the remainder being zirconium and unavoidable impurities.

[0045] In one embodiment, the tube 6 and each plug 8 are made of the same material.

[0046] Optionally, each plug 8 of the nuclear fuel rod 2 is provided with a plug coating 24. The plug coating 24 extends over the exposed portion 20 of the plug 8.

[0047] In a preferred embodiment, the plug coating 24 is continuous, for example, completely covering the exposed portion 20.

[0048] The plug coating 24 preferably extends to the outer edge of the annular surface 22 .

[0049] The plug coating 24 is made of, for example, a chromium-based material.

[0050] In one embodiment, the chromium-based material of the plug coating 24 is a chromium-based alloy selected from a binary chromium-aluminum alloy, a binary chromium-nitrogen alloy, and a binary chromium-titanium alloy.

[0051] The plug coating 24 of each plug 8 provided with a plug coating 24 is distinct from the tube coating 16 .

[0052] In one embodiment, the plug coating 24 and the tube coating 16 of each plug 8 are made of the same material.

[0053] If the plug 8 is provided with a plug coating 24, the plug coating 24 is provided in such a manner that the tube coating 16 and the plug coating 24 are adjacent when the plug 8 is disposed in the end of the tube 6.

[0054] More specifically, the plug coating 24 extends over the exposed portion 20 so as to be adjacent to the tube coating 16 when the plug 8 is disposed in the end of the tube 6 .

[0055] The insert portion 18, and, if applicable, the annular surface 22, are completely free of the plug coating 24. The plug coating 24 does not cover the insert portion 18, and, if applicable, the annular surface 22.

[0056] Preferably, each plug 8 is mounted, and in particular welded, onto the tube 6 without the presence of a eutectic at the junction between the tube 6 and the plug 8 between the material of the tube 6, the material of the tube coating 16, the material of the plug 8, and, if applicable, the material of the plug coating 24 covering the plug 8.

[0057] In particular, if the tube 6 and / or plug 8 are made of a zirconium-based material and the tube coating 16 and / or possible plug coating 24 are made of a chromium-based material, the nuclear fuel rod 2 does not have any chromium-zirconium eutectic (Cr—Zr) at the joint between the tube 6 and the plug 8.

[0058] It is believed that the presence of eutectics, particularly chromium-zirconium eutectic (Cr-Zr), at the joint between the tube 6 and the plug 8 may weaken the nuclear fuel rod 2 and reduce its resistance to oxidation, especially at high temperatures (typically above 350°C).

[0059] As shown in Figures 2 and 3, the method of manufacturing a nuclear fuel rod 2 includes providing a tube 6 coated with its tube coating 16 and, if applicable, a plug 8 coated with a plug coating 24 (Figure 2), followed by attaching the plug 8 to one end of the tube 6, which attachment step is performed by electric resistance welding or "resistance butt welding" (Figure 3).

[0060] To attach the plug 8 onto the tube 6 by resistance welding, the plug 8 is positioned at the end of the tube 6 and an electric current is applied between the tube 6 and the plug 8 to weld the plug 8 to the tube 6. While the electric current is flowing, the tube 6 and the plug 8 are heated by the Joule effect, and thus their surfaces in contact are welded together under the combined effect of the welding force and the heat.

[0061] More specifically in this case, the plug 8 is arranged at the end of the tube 6 so that the annular surface 22 presses axially against the end of the tube 6, after which an electric current is applied (see Figure 3).

[0062] Electric resistance welding is performed without the addition of material.

[0063] Preferably, the attachment is carried out by electric resistance butt welding, also known as "resistance butt welding".

[0064] To attach each plug 8 to the tube 6 by electric resistance welding, the plug 8 is positioned at the end of the tube 6, the plug 8 and the tube 6 are pressed against each other with a specified pressure (arrow F in Figure 3), and while maintaining the pressure, an electric current is applied between the tube 6 and the plug 8 to weld the plug 8 to the tube 6.

[0065] More specifically in this case, the plug 8 is arranged at the end of the tube 6 in such a way that the annular surface 22 presses axially against the end of the tube 6 under a defined compressive force, which is maintained during the application of an electric current (see FIG. 3).

[0066] As shown in FIG. 3, electric resistance welding is performed, for example, using a welding machine 26 including gripping members 28, one of which is provided for gripping the plug 8 and the other of which is provided for gripping the tube 6 near the end of the tube 6 to which the plug 8 is attached, wherein the gripping members 28 are preferably provided for pressing the tube 6 and the plug 8 together under a predetermined pressing force, and the welding machine 26 includes a power source 30 for applying an electric current between the tube 6 and the plug 8 via the gripping members 28.

[0067] Electric resistance welding is carried out by applying a direct current, an alternating current or a pulsed current. Preferably, resistance welding is carried out by applying an alternating current. The use of a direct current or a pulsed current (obtained, for example, by discharging a capacitor) can also be envisaged.

[0068] Preferably, the electric resistance welding of each plug 8 is carried out by applying a current at a value between 10 kA and 20 kA.

[0069] Preferably, the electric resistance welding of each plug 8 is carried out under a pressing force of 200 daN to 400 daN, more preferably 250 daN to 350 daN.

[0070] Preferably, the electric resistance welding of each plug 8 is carried out by applying a current for a duration of 10 ms to 30 ms.

[0071] Preferably, the electric resistance welding of each plug 8 is carried out in such a way that the temperature at the interface between the tube 6 and the plug 8 is between 1300°C and 1600°C.

[0072] Advantageously, the welding by electric resistance is carried out in such a way that at the end of the weld the tube 6 and the plug 8 have a weld bead whose dimensional characteristics are controlled and checked.

[0073] In other words, at the end of the weld, the tube 6 and plug 8 have a shape that matches the structural elements of the fuel assembly.

[0074] This is achieved, for example, by controlling the type of current applied (direct current, alternating current or pulsed current), the amperage of the current, the duration of application of the current and the compressive force used to press the tube 6 and plug 8 together and, if applicable, maintained during application of the current, as well as the nature and geometry of the gripping member 28.

[0075] The ranges of values ​​as mentioned above, in particular in combination, make it possible to maintain the desired temperature range and thus to achieve electric resistance welding.

[0076] Controlling the dimensions of the weld bead along the weld line avoids the need to perform operations to rework the weld line, particularly by mechanical or chemical processes involving material removal, such as deburring and grinding, and allows the pipe coating 16 and, if applicable, the plug coating 24 to be preserved.

[0077] It is therefore possible to obtain a rod having a tube 6 provided with a tube coating 16 over the entire length of the tube 6, from one end of the tube 6 to the other. If applicable, and if each plug 8 is provided with a plug coating 8, the entire cladding 4 (i.e. the tube 6 and each plug 8) is thus coated and is effectively protected from the external environment.

[0078] In particular, the plug coating 24 and the tube coating 16 of each plug 8 provided with the plug coating 24 are adjacent at the interface between the tube 6 and the plug 8 .

[0079] In embodiments where the tube coating 16 and the plug coating 24 are continuous, after welding, the plug coating 24 and the tube coating 16 together form a continuous coating that extends continuously over the tube 6 and plug 8, particularly at the interface between the tube 6 and plug 8.

[0080] When the tube coating 16 is continuous and each plug 8 is provided with a continuous plug coating 24, the tube coating 16 and plug coating 24 form a cladding coating that continuously covers the cladding 4 over the entire length of the tube 6 and on the plug 8, with coating continuity at the interface between the tube 6 and each plug 8.

[0081] Each plug 8 provided with the plug coating 24 is welded onto the tube 6 without affecting the geometry of the interface between the tube 6 and the plug 8 and / or without reworking the interface between the tube 6 and the plug 8, particularly by mechanical or chemical processes involving the removal of material.

[0082] Moreover, the manufacturing method can be used to attach each plug 8 to a tube 6 without forming a eutectic at the junction between the tube 6 and the plug 8 between the material of the tube 6, the material of the tube coating 16, the material of the plug 8, and, if applicable, the material of the plug coating 24 covering the plug 8.

[0083] In particular, if the tube 6 and / or plug 8 are made of a zirconium-based material and the tube coating 16 and / or possible plug coating 24 are made of a chromium-based material, the nuclear fuel rod 2 does not have any chromium-zirconium eutectic (Cr-Zr) at the junction between the tube 6 and the plug 8. Preferably, two plugs 8 are installed on the tube 6 as described above to form the nuclear fuel rod 2.

[0084] The installation of the plug 8, the insertion of the nuclear fuel, here in the form of pellets 10, and, if applicable, the insertion of the spring 12, are carried out sequentially.

[0085] For example, one of the plugs 8 is mounted on the tube 6 , after which the nuclear fuel and, if applicable, the spring 12 are inserted into the tube 6 , and then the other plug 8 is mounted on the tube 6 .

[0086] Preferably, the first plug 8 to be installed is the plug 8 located opposite the spring 12. The nuclear fuel and then the spring 12 are then inserted into the tube 6, after which the other plug 8 is installed in the tube 6.

[0087] Optionally, an additional element is inserted into the tube 6. An additional element that can be inserted into the tube 6 is a tubular shim intended to be positioned between the plug 8, located at the end of the tube 6 opposite the end at which the spring 12 is located, and the pellet column 10. In particular, the shim makes it possible to form a second plenum at the end of the rod opposite the spring 12.

[0088] During operation, the nuclear fuel rods 2 inserted in the nuclear fuel assemblies are oriented substantially vertically within the core of the nuclear reactor.

[0089] One of the plugs 8, called the upper plug 8, is intended to be positioned at the top, and the other plug, called the lower plug 8, is intended to be positioned at the bottom.

[0090] The upper plug 8 is the plug adjacent to the spring 12. If a tubular shim is provided, the shim is adjacent to the lower plug 8.

[0091] As can be seen in Figure 1, one or each of the plugs 8 advantageously comprises a gripping member 32 intended to be able to grasp a nuclear fuel rod, for example, to extract it from a nuclear fuel assembly. In Figure 1, each of the plugs 8 has such a gripping member 32.

[0092] Therefore, preferably, the manufacturing method includes the steps of first attaching a lower plug 8 to one end of the tube 6, then inserting nuclear fuel and a spring 12 inside the tube 6, and then attaching an upper plug 8 onto the other end of the tube.

[0093] During the manufacturing process, the tube 6 is provided with a tube coating 16 before each plug 8 is mounted on the tube 6, and each plug 8 having a plug coating 24 is provided with a plug coating 24 before it is mounted on the tube 6.

[0094] Although each plug 8 is then welded to the tube 6, it is possible to obtain a continuous coating of the tube 6 and each plug 8 coated with the plug coating 24, with the tube coating 16 and the plug coating 24 being adjacent.

[0095] The manufacturing method comprises the steps of producing a tube 6, for example by a pilgering process.

[0096] The manufacturing method includes the steps of applying a tube coating 16 onto the tube 6 and, where applicable, applying a plug coating 24 onto each plug 8 provided with such a coating 8 .

[0097] The tube coating 16 and / or each plug coating 24 is applied by physical vapor deposition, for example by cathodic sputtering, and even more particularly by magnetron sputtering, thereby providing a durable tube coating 16.

[0098] The physical vapor deposition by magnetron sputtering of the tube coating 16 and / or each plug coating 24 can be carried out according to one or a combination of at least two of the following techniques: direct current (DC) magnetron sputtering, pulsed direct current (or DC pulsed) magnetron sputtering, high power impulse magnetron sputtering (HiPIMS or HPPMS), magnetron sputtering bipolar (MSB), dual magnetron sputtering (DMS), unbalanced magnetron sputtering (UBM), for example.

[0099] The nuclear fuel rod 2 is not limited to the above-described embodiment.

[0100] In the embodiment shown in FIGS. 1-3, each plug 8 is provided with a plug coating 24 that covers the exposed portion 20 of the plug 8 .

[0101] In one variant, neither of the two plugs 8 is provided with a plug coating 24, or only one of the two plugs 8 is provided with a plug coating 24. In the latter case, either the lower plug 8 or the upper plug 8 is involved. The lower plug 8 and the upper plug 8 are not subjected to exactly the same thermal, chemical, and neutron stresses, and therefore it may be advantageous to coat only one of the two plugs 8.

[0102] If at least one of the plugs 8 does not have any coating (i.e., "uncoated"), each uncoated plug 8 is attached to, and particularly welded onto, the tube 6 without affecting the shape of the interface between the tube 6 and the plug 8 and / or without reworking the interface between the tube 6 and the plug 8 by mechanical or chemical processes, particularly involving material removal.

[0103] In the embodiment of Figures 1 to 3, nuclear fuel is provided in the form of pellet stacks 10 which contain fissile material.

[0104] In one variant, the nuclear fuel is provided in another form, for example in the form of a powder. [Explanation of symbols]

[0105] 2 nuclear fuel rods 4. Covering 6 tubes 6A outer surface 6B Inner surface 8 plugs 10 pellet stacks 12 Spring 14 Plenum 16 Pipe Coating 18 Insertion 20 Exposed part 22 Annular Surface 24 Spark Plug Coating 26 Welding machine 28 Gripping member 30 power supply

Claims

1. 1. A nuclear fuel rod comprising nuclear fuel contained within cladding (4), the cladding (4) comprising a tube (6) and two plugs (8), the tube (6) extending along a central axis (A) and having two ends, each plug (8) attached to a corresponding end of the tube (6) by sealing its end, the tube (6) covered by a tube coating (16), the tube coating (16) extending the entire length of the tube (16) from one end of the tube (6) to the other, and each plug attached on the tube without the presence of a eutectic at the junction between the tube and the plug among the tube material, the tube coating material, the plug material, and, if applicable, the plug coating material covering the plug.

2. 2. Nuclear fuel rod according to claim 1, wherein the or each plug (8) is at least partially covered by a plug coating (24).

3. 3. The nuclear fuel rod of claim 2, wherein the tube coating (16) and the plug coating (24) are made of the same material.

4. 4. A nuclear fuel rod according to claim 2 or 3, wherein the plug coating (24) and the tube coating (16) of each plug (8) provided with the plug coating (24) are adjacent at the interface between the tube (6) and the plug (8).

5. 2. Nuclear fuel rod according to claim 1, characterized in that the tube (6) is made of a zirconium-based material.

6. 2. Nuclear fuel rod according to claim 1, wherein each plug (8) is made of a zirconium-based material.

7. 2. The nuclear fuel rod of claim 1, wherein the tube coating (16) is made of a chromium-based material.

8. A method for manufacturing a nuclear fuel rod comprising nuclear fuel stored in cladding (4), the cladding (4) comprising a tube (6) and two plugs (8), the tube (6) extending along a central axis (A) and having two ends, each plug (8) being attached to a corresponding end of the tube (6) by sealing its end, the tube (6) being covered by a tube coating (16), wherein the tube coating (16) extends over the entire length of the tube (16) from one end of the tube (6) to the other, the method comprising producing the tube (6) and the plugs (8) and welding by electric resistance welding of at least one of the or each plug (8) to the corresponding end of the tube (6), the method being carried out without reworking the interface between the tube (6) and each plug (8) welded onto the tube (6) by mechanical or chemical processes involving material removal.

9. 9. A method according to claim 8, wherein each plug (8) is welded onto the tube (6) by electric resistance butt welding.

10. The method of claim 8, wherein the electric resistance welding of at least one of the or each plug (8) is performed with a current of between 10 kA and 20 kA.

11. 9. A method according to claim 8, wherein the welding by electrical resistance of the or each plug (8) is carried out by applying the plug (8) to the corresponding end of the tube (6) under a pressing force of between 200 daN and 400 daN.

12. 9. A method according to claim 8, wherein the welding by electrical resistance of the or each plug (8) is carried out by applying the plug (8) to the corresponding end of the tube (6) under a pressing force of between 250 daN and 350 daN.

13. 9. A method according to claim 8, wherein the electric resistance welding of at least one of the or each plug (8) is carried out by applying an electric current for a duration of between 10 ms and 30 ms.

14. 9. The method of claim 8, wherein each plug (8) is welded onto the tube (6) without forming a eutectic at the joint between the tube (6) and the plug (8) between the material of the tube (6), the material of the tube coating (16), the material of the plug (8) and, if applicable, the material of the plug coating (24) covering the plug (8).

15. A manufacturing method as described in claim 8, wherein one or each of the plugs (8) is at least partially covered by a plug coating (24).

16. A manufacturing method as described in claim 15, wherein the tube coating (16) and the plug coating (24) are made of the same material.

17. A manufacturing method as described in claim 15, wherein the plug coating (24) and the tube coating (16) of each plug (8) provided with the plug coating (24) are adjacent at the interface between the tube (6) and the plug (8).

18. The manufacturing method of claim 8, wherein the tube (6) is made of a zirconium-based material.

19. The manufacturing method of claim 8, wherein each plug (8) is made of a zirconium-based material.

20. A manufacturing method as described in claim 8, wherein the pipe coating (16) is made of a chromium-based material.

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