Method for closing orifice of silicon carbide-based container

Abstract

To provide a method for closing a silicon carbide-based container.SOLUTION: The present invention relates to a method for closing an orifice of a container. The method includes the continuous steps of: a) providing a silicon carbide-based container comprising a cavity that is open by an orifice, a silicon carbide-based plug, and a brazing material borne by the plug and / or the container, with a solid object being housed in the cavity; and b) closing the orifice by brazing the plug onto the container, wherein the brazing involves melting the brazing material by heating to a temperature higher than the melting temperature of the brazing material, followed by solidification of the brazing material to form a solid joint between the container and the plug, such that at least a part of the cavity, referred to as a cold part, in which the solid object is housed, is maintained at a temperature lower than a degradation temperature of the solid object during the brazing.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to the field of methods for assembling silicon carbide-based components. In particular, the present invention relates to a method for closing an opening in a silicon carbide-based container. [Background technology]

[0002] Silicon carbide-based containers have mechanical and thermal properties that make them suitable for various applications, particularly in the nuclear, aviation or space fields. For example, silicon carbide-based containers, specifically made from composites including silicon carbide fibers incorporated in a silicon carbide matrix, are considered as components in future nuclear reactors. In particular, silicon carbide-based containers can help contain and protect nuclear fuel pellets while facilitating heat exchange. Such containers can also be used in heat exchangers, gas turbines or tanks.

[0003] It is known that in order to close silicon carbide-based containers, the open opening of the container is blocked by a plug. Depending on the intended application, it is desired that the closure also has good mechanical and thermal properties. It is therefore advantageous for the plug to also be silicon carbide-based. It may also be necessary for the plug to be firmly bonded to the container in such a way that it is resistant to high temperatures.

[0004] However, conventional methods for securely bonding two silicon carbide-based parts together often require the parts to be heated together to high temperatures, making these methods unsuitable for closing silicon carbide-based containers that contain objects that deteriorate at such high temperatures.

[0005] U.S. Patent Application Publication No. 2021 / 0166825(A1) describes a method for forming a fluid-tight bond between a silicon carbide structure and a plug having a central opening to seal the structure with a gas during the process. However, the method is complicated to implement. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 0166825(A1) Summary of the Invention [Problem to be solved by the invention]

[0007] Thus, there is a need for a silicon carbide based container closure that is robust, resistant to high temperatures, yet simple to implement, and that ensures the physical integrity and performance of objects enclosed in the container. [Means for solving the problem]

[0008] The present invention aims at least partially to meet this need and proposes a method for closing an opening of a container, said method comprising the following successive steps: a) providing a silicon carbide based container having a cavity opening by an opening, a silicon carbide based plug, and a braze material carried by the plug and / or the container, where a solid object is to be received in the cavity; b) a step of closing the opening by brazing the plug to the container, the brazing comprising melting the brazing material by heating to a temperature above the melting temperature of the brazing material followed by solidification of the brazing material so as to form a solid joint between the container and the plug, at least a part of the cavity in which the solid object is contained, referred to as the cold zone, being kept at a temperature below the degradation temperature of the solid object during the brazing; Includes.

[0009] The method according to the invention is simple and fast to carry out and does not degrade the mechanical and thermal properties of the container. Also, since the brazing according to the invention requires only a localized supply of heat, the cold parts of the cavity remain at a temperature that ensures the physical integrity, including the geometry of the objects that may be placed in the cavity, which deteriorates at higher temperatures, for example temperatures above 800° C. Furthermore, the closure obtained by the method according to the invention is advantageously robust, fluid-tight, resistant to oxides and resistant to temperatures at least in the range close to the melting temperature of the brazing material, but certainly below the melting temperature of the brazing material, typically up to 50° C. below the melting temperature of the brazing material, for example up to 1200° C., even 1300° C. or even 1400° C.

[0010] A "silicon carbide-based" part is made from a material that contains at least 50% silicon carbide by mass.

[0011] The "degradation temperature of a solid object" corresponds to the highest temperature at which the physical integrity of the object is maintained, i.e. the highest temperature at which the object does not substantially deform in its own weight, does not undergo a change in its physical state, such as a phase change, is not altered by chemical reactions, and / or the highest temperature at which the mechanical properties are not degraded, in particular the creep strength. Preferably, the degradation temperature of a solid object is equal to 0.5 or even 0.4 times the melting temperature of said object.

[0012] Preferably, the solid body comprises at least one nuclear fuel pellet. Preferably, the gas-tightness of the solid body is ensured by the presence of a metal liner made of a zirconium alloy.

[0013] Preferably, the cold section is maintained at a temperature below 800° C. during brazing.

[0014] Preferably the container is made from sintered monolithic silicon carbide or from a composite comprising ceramic fibres, preferably made from silicon carbide or carbon, embedded in a silicon carbide matrix. Preferably the container is made from a composite comprising silicon carbide fibres embedded in a silicon carbide matrix.

[0015] Preferably, the container is of a hollow cylinder, one of its ends being open with an opening and the end of the cylinder opposite the opening being closed.

[0016] Preferably, the cold section represents at least 70%, or even at least 80%, or even at least 90% of the volume of the cavity.

[0017] Preferably, the cavity extends along a longitudinal axis (X) and the cold section extends along the longitudinal axis (X) over at least 70%, or even at least 80%, or even at least 90% of the length of the cavity.

[0018] Preferably, the cavity extends along a longitudinal axis (X) and the bond formed by brazing extends over at least 0.1% of the length of the cavity along the longitudinal axis (X), preferably extends over between 0.1% and 10%, or even extends over between 0.1% and 5% of the length of the cavity along the longitudinal axis (X).

[0019] Preferably the distance between the plug and the cold spot during the braze is equal to or less than 10mm, preferably less than 5mm, preferably between 2mm and 5mm.

[0020] Preferably, the heating is performed by induction with a susceptor placed in the vicinity of the opening. Preferably, at least one thermal insulator is placed between the susceptor and the cold part of the cavity. Advantageously, the heat is limited to the zone where the plug is brazed to the container during step b). Induction heating shortens the duration of heating during step b).

[0021] Preferably, during step b), the duration of heating of the brazing material to a temperature above the melting temperature of the brazing material is between a few seconds and 20 minutes, preferably between 30 seconds and 5 minutes.

[0022] Preferably, the heating temperature for the brazing material during melting in step b) is 1250°C or higher, or even 1300°C or higher, or even 1400°C or higher.

[0023] Preferably, the brazing material is heated during brazing to a temperature of 1850° C. or less, or even to a temperature below 1600° C. If the container and closure are made from sintered monolithic silicon carbide, the heating temperature for the brazing material may be between 1600° C. and 1850° C. during brazing. If at least one of the container and closure is made from a composite material including ceramic fibers incorporated in a silicon carbide matrix, the heating temperature for the brazing material is preferably less than 1600° C. during brazing.

[0024] Preferably, during step b), the solidification of the brazing material comprises a slow cooling of the brazing material at a cooling rate between 1 K / min and 50 K / min.

[0025] Preferably, the method includes cooling the cold section during brazing by a cooling system extending along at least a portion of the cold section, said portion including an end of the cold section adjacent the heating zone for the brazing material. Preferably, the cooling system comprises a fluid circuit through which a cooling fluid circulates during brazing.

[0026] Preferably the plug is made from sintered monolithic silicon carbide or from a composite including ceramic fibers incorporated in a silicon carbide matrix, the ceramic fibers preferably being made from silicon carbide or carbon. Preferably the plug is made from a composite including silicon carbide fibers incorporated in a silicon carbide matrix.

[0027] Preferably, the closure is formed from the same material as the container.

[0028] Preferably, the plug provided in step a) comprises at least one cutout which is filled with brazing material, advantageously this ensures a sufficient supply of brazing material during brazing, the cutout or cutouts each forming a reservoir of brazing material which may for example take the form of a hole filled with brazing material.

[0029] Preferably, at least a part of the brazing material is carried by the plug, and the closing step b) is preceded by a step of heating the plug and the brazing material carried by the plug to a temperature higher than the melting temperature of the brazing material, preferably to a temperature of 1250° C. or more, or even to a temperature of 1300° C. or more, or even to a temperature of 1400° C. or more, during which the brazing material melts, and then a step of solidifying the brazing material. Preferably, the plug and the brazing material carried by the plug are placed in an environment under vacuum or inert gas during the heating of the plug and the brazing material carried by the plug. Preferably, the inert gas is argon or helium. Preferably, the heating of the plug and the brazing material carried by the plug is performed to a temperature of 1850° C. or less, or even to a temperature below 1600° C., during brazing. If the plug is made from sintered monolithic silicon carbide, the heating temperature for the braze material can be between 1600° C. and 1850° C. during brazing. If the plug is made from a composite material including ceramic fibers incorporated in a silicon carbide matrix, the heating temperature for the braze material is preferably less than 1600° C. during brazing.

[0030] Advantageously, this preheating of the plug and the brazing material carried by the plug distributes the brazing material evenly on the plug prior to brazing so as to obtain a good supply of brazing material during brazing.

[0031] If the plug is a composite material including ceramic fibers incorporated in a matrix of silicon carbide, this preheating also causes the penetration of the brazing material in liquid state into the pores of the plug during melting of the brazing material. Thus, after the solidification step, the solidified brazing material covers the surface of the plug and at least partially or even completely closes the pores of the plug. Advantageously, such penetration of the brazing material into the plug improves the thermal diffusion, the hermeticity and the mechanical strength of the plug impregnated with the brazing material.

[0032] Preferably, the container, the closure and the brazing material are in an environment under inert gas or vacuum throughout the closing step b), or in an environment under vacuum for one part of step b) and under inert gas for another part of step b), the inert gas being preferably argon or helium, which advantageously limits undesired reactions during brazing.

[0033] "Vacuum environment" is 10 -1 The environment is an environment with a pressure of less than 10 Pa. -3 Pa to 10 -5 It may also be placed under a higher vacuum, such as with a pressure of up to 10 Pa.

[0034] According to a first variant, during step a), the brazing material is in the form of a brazing paste comprising a binder and a brazing powder dispersed in the binder. Preferably, the brazing powder comprises a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides. Preferably, the binder is an aqueous gel. Preferably, the binder has an evaporation temperature below 500° C., or even below 400° C., preferably close to 300° C. Advantageously, such a brazing material does not or hardly reacts with silicon carbide, so that it does not degrade the mechanical and thermal properties of the container and the closure during the method.

[0035] According to a second variant, during step a), the brazing material is in the form of a multitude of solid granules, preferably comprising a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

[0036] According to a third variant, during step a), the brazing material is in the form of at least one sheet wound around the plug, preferably comprising a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

[0037] According to a fourth variant, during step a), the brazing material is in the form of a coating deposited by physical or chemical vapor deposition on the outer periphery of the plug and / or on the inner wall of the container before step a). Such a deposition allows a better control of the thickness of the coating. The chemical vapor deposition can be a plasma-enhanced chemical vapor deposition method or it can be an atomic layer deposition method. Preferably, the coating comprises a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

[0038] Preferably, the silicon alloy or silicide consists of silicon and at least one element selected from chromium, cobalt, cerium, titanium, vanadium, zirconium, neodymium, praseodymium, ruthenium, rhodium, rhenium, yttrium, iridium, nickel, platinum, palladium, silver, aluminum, molybdenum, and tungsten. Preferably, the silicon alloy or silicide comprises at least 50 at.% silicon. Preferably, the element is zirconium or chromium. Preferably, the silicon alloy or silicide comprises between 90% and 42% silicon by mass and 10% and 58% zirconium by mass.

[0039] Preferably, the oxide is selected from among silicon dioxide, alumina, calcium oxide, magnesium oxide, and mixtures thereof.

[0040] Preferably, the braze material also contains carbon particles and / or silicon carbide particles.

[0041] Preferably, during step b), the carbon particles and / or silicon carbide particles are located in the form of a powder in the clearance between the container and the bung.

[0042] Advantageously, the presence of carbon particles and / or silicon carbide particles in the brazing material and / or in the clearance between the container and the closure results in the bond formed by solidification of the brazing material being a composite containing silicon carbide. If silicon carbide particles are included, the silicide or oxide of the brazing material penetrates in liquid phase between the silicon carbide particles during brazing such that the bond formed by solidification of the brazing material is a composite containing silicon carbide particles. If carbon particles are included, the silicon alloy or silicide of the brazing powder reacts with the carbon particles during brazing such that the bond formed by solidification of the brazing material is a composite containing silicon carbide particles.

[0043] Other advantages and features will become more clearly apparent on reading the detailed description given by way of non-limiting illustration and with reference to the following figures, in which: [Brief description of the drawings]

[0044] [Figure 1] FIG. 1 is a schematic front view of a silicon carbide container with an opening at one of its ends. [Diagram 2] 2 is a schematic front view of the container according to FIG. 1 with a plug inserted in the opening. [Diagram 3] 2 is a schematic front view of the container according to FIG. 1 with the plug inserted in the opening and the brazing paste carried by the plug and the container; [Figure 4] FIG. 4 is a schematic front view of a container in which the plug and brazing paste according to FIG. 3 are subjected to localized heating at the end with the opening. [Diagram 5]FIG. 1 is a schematic front view of a silicon carbide container with an opening at one of its ends, the opening being plugged by a plug brazed to the container. [Figure 6] FIG. 2 is a schematic front view of a plug carrying brazing paste; [Figure 7] FIG. 2 is a schematic front view of a plug carrying brazing paste; [Figure 8] FIG. 2 is a schematic front view of a plug carrying brazing paste; [Figure 9] FIG. 2 is a schematic front view of a plug with a notch that is filled with brazing material. [Figure 10] 1 shows a schematic longitudinal section of an example of a device for implementing the method according to the invention by localized heating; [Figure 11] 1 is a graph showing measured and simulated changes in the temperature of the container at the opening and the temperature of the susceptor over time during a heating cycle for the brazing operation of a method according to the present invention, as well as the change in power sent to the coil over time during the heating cycle. [Figure 12] FIG. 2 shows a schematic longitudinal cross-section of a mechanical test in which a closure has been obtained by the method according to the invention and a pushing force is applied to a plug closing an opening of a container. [Figure 13] 13 is a graph showing the change in push force as a function of the placement of the load applying the push force measured during the mechanical testing shown in FIG. 12. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Figures 1 to 5 show an example of the implementation of the method according to the invention. The method comprises the step a) of providing a container 1, a plug 5 and a brazing material 6 carried by the container 1 and / or the plug 5. Figures 1 to 3 show different sub-steps of an example of the implementation of step a).

[0046] Figure 1 shows an example of a container 1. The container has a hollow cylindrical shape extending along a longitudinal axis X. The container comprises a cavity 2 extending along the longitudinal axis X over a length of, for example, between 5 cm and 400 cm. The cavity 2 is open at one of the two ends of the container 1 by an opening 3, the other end 4 of the container 1 being closed. A solid object is contained in the cavity 2 of the container 1. The opening 3 may have an opening diameter of between 0.5 cm and 50 cm. The container 1 is silicon carbide based and is preferably made of a composite material including silicon carbide fibers incorporated in a silicon carbide matrix.

[0047] FIG. 2 shows the arrangement of the plug 5 in the cavity 2. The plug 5 is of a shape complementary to the cavity 2 so that it is inserted with a small clearance in the cavity 2 at the opening 3, the clearance being preferably less than 100 μm so that the plug 5 remains stationary when inserted in the opening 3. There is therefore a small gap between the wall 7 of the container 1 and the plug 5. The bond formed between the plug 5 and the container 1 at the end of the method according to the invention therefore has a small thickness, which is mechanically advantageous. For example, the plug 5 is a rotating column and has a diameter between 0.4 cm and 5 cm. When mounted in the container 1, the plug 5 extends along the longitudinal axis X for a length between 0.5 cm and 5 cm, for example. In particular, the plug 5, when inserted in the container 1, occupies between 0.1% and 10% of the length of the cavity 2 measured along the longitudinal axis X. The plug 5 is silicon carbide based and is preferably made of a composite material including silicon carbide fibers incorporated in a silicon carbide matrix.

[0048] The brazing material 6 is therefore deposited in the form of a paste on the plug 5 and / or the walls 7. Figure 3 shows the container 1 with the plug 5 inserted in the opening 3 and the brazing paste 6 deposited on the plug 5 and the walls 7. The invention is not limited to the brazing material 6 being deposited in the form of a paste, other forms of brazing material and deposition methods are contemplated, for example the brazing material may be in the form of a number of granules, a sheet or a coating as described above.

[0049] Step a) is followed by step b) of closing the opening 3 by brazing the plug 5 to the container 1. For that purpose, heating is performed in a localized manner at the opening 3 so as to heat the plug 5, the wall 7 close to the opening 3 and the brazing material 6 to a temperature higher than 1250° C., or even higher than 1300° C., or even higher than 1400° C. FIG. 4 illustrates said localized heating, with a lightning bolt 8 symbolizing the targeted supply of heat. The localized heating melts the brazing material 6, which penetrates into the gap between the plug 5 and the wall 7. The melting and penetration of the brazing material 6 is marked by an arrow 9. If the container 1 and / or the plug 5 are made of a composite material including ceramic fibers incorporated in a matrix of silicon carbide, the brazing material 6 penetrates into the pores of the container 1 and / or the plug 5.

[0050] During localized heating, a part of the cavity 2 at a distance from the heating zone, referred to as cold zone 23, is kept at a temperature lower than 800° C. The cold zone 23 extends over at least 70% of the length of the cavity 2 along the longitudinal axis X. In particular, the cold zone 23 corresponds to the whole of the cavity 2 that is at least 1 cm, preferably at least 5 mm, preferably at least 2 mm, away from the plug 5 inserted in the opening 3.

[0051] After heating, the plug 5, the container 1 and the brazing material 6 are cooled. During the cooling, the brazing material 6 solidifies to form a solid bond 10 between the plug 5 and the wall 7, as shown in Figure 5. The opening 3 is thus plugged by the plug 5, which is fastened to the container 1 by brazing.

[0052] According to another example of implementation, the plug 5 provided in step a) at least partially carries the brazing material 6 before being inserted into the container 1. The plug 5 is therefore inserted into the opening 3 with the brazing material 6. This is followed by a step b) of closing the opening 3.

[0053] 6, 7 and 8 show different ways of depositing the brazing material 6 on the plug 5. For example, the brazing material 6 can be deposited on and carried by the side of the plug 5, as shown in FIG. 6, and the base of the plug 5 is not covered with the brazing material 6. Alternatively, the brazing material 6 can be deposited on and carried by the side of the plug 5 and the upper base of the plug 5, as shown in FIG. 7. Alternatively, the brazing material 6 can be deposited on and carried by the upper base of the plug 5, as shown in FIG. 8, and the side of the plug 5 is not covered with the brazing material 6.

[0054] Furthermore, the plug 5 may also comprise at least one notch 31 which is filled with the brazing material 6, as shown in Fig. 9. The notch 31 thus forms a reservoir for the brazing material 6, thereby increasing the supply of the brazing material 6 during brazing in step b). For example, the notch 31 may be a blind hole recessed into the side wall of the plug 5. The one or more notches 31 may also be radial grooves or slots.

[0055] Prior to the insertion of the plug 5, in step b), the brazing material 6 carried by the plug 5 can be heated to a temperature higher than its melting temperature so that the brazing material 6 flows over at least the sides of the plug 5, or even over the entire plug 5. The heating can be carried out in a furnace, preferably under high vacuum or inert gas, which is preferably argon or helium. The solidification of the brazing material 6 by cooling is then carried out after said heating. The solidified brazing material 6 is thus distributed evenly over the plug 5, ensuring a good supply of the brazing material 6 during the brazing of the plug 5 into the container 1.

[0056] If the plug 5 is made from a composite material including ceramic fibers incorporated in a silicon carbide matrix, this preheating also causes the braze material to penetrate into the pores of the plug 5, followed by solidification upon cooling. Such penetration improves the thermal diffusion, hermeticity, and mechanical strength of the plug 5 impregnated with the braze material 6.

[0057] The present invention carried out tensile tests at ambient temperature to compare the difference in mechanical behavior between tensile test specimens that were not impregnated with the brazing material 6 and those in which the holes were impregnated with the brazing material 6. The tensile test specimens were all made of a composite material containing silicon carbide fibers in a silicon carbide matrix. The tensile test specimens were cylindrical specimens of 75 mm length with a central section having a diameter of 9.50 mm. The brazing material 6 used was in the form of a paste containing a powder made of a silicon alloy consisting of 88% silicon by mass and 12% zirconium by mass, mixed with an aqueous gel as a binder. In the tensile tests, a fracture stress of the order of 240 MPa was measured for the non-impregnated tensile test specimens for deformations of the order of 0.8% to 0.9%. A fracture stress of the order of 280 MPa was measured for the tensile test specimens in which the holes were infiltrated with the brazing material 6 for deformations of more than 1.1%. Therefore, these tensile tests show a significant improvement in the mechanical strength of the tensile test specimens when they are impregnated with the braze material 6.

[0058] If the brazing material 6 is not sufficiently uniformly distributed over the plug 5 after heating, an additional deposition of the brazing material 6 on the plug 5 may be performed, in particular on the zones free of brazing material 6. This deposition is preferably followed by an additional heating of the plug 5 and of the brazing material 6 carried by the plug 5, as in the previous paragraph. Where appropriate, the additional deposition advantageously compensates for imbalances in the coverage of the brazing material 6 on the plug 5 caused by the penetration of the brazing material 6 into the pores of the plug 5.

[0059] Machining may be performed after solidification of the brazing material 6 on the plug 5 in order to reduce the roughness formed by the brazing material 6 on the plug 5. Advantageously, this facilitates the insertion of the plug 5 into the container 1. Also, once the opening 3 is closed by the plug 5, the plug 5 has little or even no roughness on the surface facing the object contained in the cavity. If the brazing material 6 was in the form of a coating deposited by physical or chemical vapour deposition before step a), the roughness is negligible, making it unprofitable to perform said machining.

[0060] Furthermore, the container 1 provided in step a) also carries at least a portion of the brazing material 6 prior to the insertion of the plug 5 into the container 1. In particular, the brazing material 6 may cover a portion of the wall 7 to which the plug 5 is brazed.

[0061] Figure 10 shows a device 11 configured to perform the heating of the brazing material in step b) of the method according to the invention. The device 11 comprises a hermetic enclosure 12 for containing the vessel 1 with the plug 5 inserted in the opening 3 and the brazing material 6 carried by the plug 5 and / or the vessel 1. Preferably, the enclosure 12 is a quartz tube.

[0062] An inlet pipe 13 leads to the enclosure 12. The inlet pipe 13 is adapted to inject an inert gas into the enclosure 12. The inert gas can be argon or helium. The device 11 comprises an outlet pipe 14 for exhausting the gas present in the enclosure 12. This pipe 14 can also make it possible to create a vacuum in the enclosure 12. Preferably, the inlet pipe 13 and the outlet pipe 14 are configured so that the inert gas circulates continuously in the enclosure 12.

[0063] The device 11 also comprises a coil 16 comprising at least one turn around the enclosure 12. Preferably, the turn or turns are made of copper. The coil 16 is electrically connected to a radio frequency generator 17. A susceptor 18 is housed in the enclosure 12 and surrounded by the coil 16. Preferably, the susceptor 18 is made of graphite. The susceptor 18 comprises a central passage for receiving the vessel 1 housed in the enclosure 12, such that the susceptor 18 surrounds the vessel 1 in the region of the opening 3 and the plug 5. Preferably, the coil 16 and the susceptor 18 are concentric such that the central passage of the susceptor 18 is centered in the middle of the coil 16.

[0064] The device 11 also comprises a cooling system 19 arranged in the enclosure 12 so as to extend along the cold part 23 of the container 1. In particular, the cooling system 19 may comprise a central passageway into which the container 1 is inserted so as to face the cold part 23 over the entire length of the cold part 23. Preferably, the cooling system 19 comprises a fluid circuit that winds around the passageway that receives the container 1, a cooling fluid, preferably water, is intended to circulate in the fluid circuit. Preferably, the ducts 22 of the fluid circuit are made from copper or brass.

[0065] It is not essential that the cooling system 19 extends over the entire length of the cold section 23. The cold section 23 may comprise a part remote from the heating zone so that it is not significantly affected by heating during step b), i.e. remains at ambient temperature without cooling. If appropriate, it is not essential that the cooling system 19 extends along said remote part. Furthermore, a first insulation 20 is arranged between the wall of the enclosure 12 and the susceptor 18, and between the susceptor 18 and the cooling system 19. Preferably, the first insulation 20 is made of insulating graphite, for example fibrous graphite. Also, a second insulation 21 is arranged between the first insulation 20 and the cooling system 19. The second insulation 21 may be made of an oxide, for example alumina.

[0066] The heating performed by the device 11 is localized and is inductive heating. Firstly, the vessel 1 is placed in the enclosure 12 with the plug 5 inserted in the opening 3 and the brazing material 6 carried by the plug 5 and / or the vessel 1. When the vessel 1 is placed, a susceptor 18 surrounds the wall 7 in the area of ​​the opening 3, the plug 5 and the brazing material 6, and a cooling system 19 extends along the cold section 23.

[0067] Inert gas is then injected into the enclosure 12. Prior to the injection of the inert gas, a vacuum may be created in the enclosure 12. Preferably, the injection of the inert gas is such that the enclosure 12 is at ambient pressure. Preferably, the inert gas is injected through an inlet pipe 13 and then exhausted through an exhaust pipe 14 to maintain a continuous circulation of the inert gas in the enclosure 12. The direction of circulation of the inert gas in the enclosure 12 is indicated by arrow 15.

[0068] The cooling system 19 is then activated to cool the cold section 23. In particular, a cooling fluid, preferably water, may be circulated in the fluid circuit.

[0069] The high frequency generator 17 then delivers power to the coil 16, which generates a magnetic field. The susceptor 18 converts the energy from the magnetic field into heat by induction, which heats the wall 7 of the vessel 1 in a localized manner by induction in the area of ​​the opening 3, the plug 5 and the brazing material 6. The power delivered by the high frequency generator 17 is gradually increased so as to gradually increase the heating temperature to at least 1250°C, or even at least 1300°C, or even at least 1400°C. During heating by induction, the first insulation 20 and the second insulation 21 increase the localization of the heating by limiting the heat generated by the susceptor 18 to the zone where the plug 5 is brazed to the vessel 1. During heating, the cooling system 19 continuously cools the cold section 23, which is kept at a temperature below 800°C.

[0070] The device 11 shown in Fig. 10 thus makes it possible to carry out step b) of closing the opening 3 by brazing the plug 5 to the container 1. The device 11 locally heats, by induction, the brazing material 6 carried by the plug 5 and / or the container 1, causing said brazing material 6 to melt in order to braze the plug 5 to the container 1. Furthermore, the device 11 keeps the cold section 23 at a low temperature during heating. The keeping at a low temperature is achieved by insulation between the cold section 23 and the zone where the plug 5 is brazed to the container 1 and by cooling of the cold section 23 by the cooling system 19.

[0071] The inventors have carried out simulations and measurements to determine the change over time in the temperature involved during the brazing operation of the method according to the invention. For that purpose, the device 11 comprises a pyrometer 24 which measures the temperature of the susceptor 18 and of the vessel 1 in the region of the opening 3. The device 11 also comprises a thermocouple (not shown here) which measures the temperature of the susceptor 18 and of the vessel 1 in the region of the opening 3. The measurements made by the pyrometer 24 were compared with the measurements made by the thermocouple. Figure 11 shows the results of these simulations and of these measurements. The simulations and measurements were carried out for a heating cycle in which the average power fed into the coil 16 reaches a first level at 15 kW for 10 minutes and then reaches 17 kW for 10 minutes. Curve 25 shows the change in the average power fed into the coil 16 during the heating cycle.

[0072] Curve 26 shows the change in the simulated temperature of the susceptor 18 during the heating cycle. Curve 27 shows the change in the measured temperature of the susceptor 18 during the heating cycle. Curves 26 and 27 show that the susceptor 18 reaches a temperature of 1560° C. during a first level and then reaches a temperature of 1620° C. during a second level.

[0073] Curve 28 shows the change in the simulated temperature of the container 1 in the region of the opening 3 during the heating cycle. It shows that the temperature of the container 1 in the region of the opening 3 reaches a temperature of 1300° C. during the first level and then a temperature of 1420° C. during the second level. Curve 29 shows the change in the measured temperature of the container 1 in the region of the opening 3 during the heating cycle. Curve 29 shows that the temperature of the container 1 in the region of the opening 3 reaches a temperature of 1320° C. during the first level and then a temperature of 1480° C. during the second level. The simulated or measured temperature of the container 1 in the region of the opening 3 during each of the first and second levels is therefore above 1300° C., as is desired for the brazing in step b) of the method according to the invention.

[0074] The inventors have also simulated the change in temperature of the cold section 23 during the heating cycle described above. The maximum temperature of the cold section 23 obtained by this simulation is 725° C., which is therefore well below 800° C.

[0075] The inventors have tested the mechanical strength of the closure obtained according to the invention. To that end, they have closed a container 1 using the method according to the invention. The container 1 and the plug 5 provided were made of a composite material comprising silicon carbide fibres incorporated in a matrix of silicon carbide. The brazing material 6 used was in the form of a paste comprising a powder made of a silicon alloy consisting of 88.5% silicon by mass and 11.5% zirconium by mass, mixed with an aqueous gel as binder, for example the commercially available gel "Vitta Braz-Binder Gel Grade ST" or the cement "Nicrobraz". Approximately 400 mg of brazing paste 6 were deposited on the plug 5. The plug 5 and the brazing paste 6 carried by it were then heated to 1420°C under argon in a brazing furnace so as to melt the brazing material 6 which completely covered the plug 5 and closed the notch recessed into the plug 5. The brazing material 6 carried by the plug 5 was then solidified by cooling and machined to eliminate roughness formed by the brazing material 6 on the plug 5 that would hinder the insertion of the plug 5 into the container 1. The plug 5 was then brazed to the container 1 in order to close the opening 3 of the container 1. The brazing was carried out in the device 11 shown in FIG. 10 as previously indicated. The brazing involved heating the opening 3, the plug 5 and the wall 7 of the container 1 in the region of the brazing material 6 at a temperature of 1420° C. for 10 minutes, followed by slow cooling of the brazing material 6.

[0076] To test the robustness of the closure of the container 1 obtained according to the previous paragraph, the inventors carried out a mechanical test of the "pull-out" type, as shown in Figure 12. This mechanical test involved the application of a pushing force F to the plug 5 with the aid of a piston 32, the container 1 being supported by a frame 33 during the mechanical test, in order to generate shear stresses in the joint 10 between the plug 5 and the wall 7.

[0077] Figure 13 shows the results of this mechanical test. Curve 30 shows the pushing force F as a function of the displacement of the piston 32 during this mechanical test. The maximum pushing force applied before the closure breaks is 3925 N. The closure of the container 1 therefore has a breaking strength of 221 MPa, a nominal shear strength of 30.4 MPa and a burst pressure of 736 bar. Furthermore, the break does not occur at the joint 10, but rather it is the wall 7 of the container 1 beyond the joint 10 that breaks. The joint 10 formed by the method according to the invention is therefore stronger than the container 1.

[0078] Other variations and improvements are contemplated without departing from the scope of the invention as defined by the following claims. [Explanation of symbols]

[0079] 1 container 2 cavities 3 Opening 4 The other end 5. Stopper 6 Brazing materials, brazing pastes 7. Wall 8 Targeted supply of heat 9 Melting and penetration of brazing material 6 10 Solid Joints 11 Devices 12 Sealed Enclosure 13 Inlet piping 14 Discharge piping 15 Direction of inert gas circulation 16 Coils 17 High Frequency Generator 18 Susceptor 19 Cooling System 20 First Insulation Material 21 Secondary Insulation 23 Low temperature section 24 Pyrometer 25 Change in average power delivered to coil 16 26 Change in simulated temperature of susceptor 18 27 Change in measured temperature of susceptor 18 28 Change in simulated temperature of container 1 in the area of ​​opening 3 29 Change in the measured temperature of the container 1 in the area of ​​the opening 3 30 Pushing force F as a function of the displacement of the piston 32 31 Cutout 32 Piston 33 Frame F Pushing force X Longitudinal Axis

Claims

1. 1. A method for closing an opening in a container, comprising the steps of: a) providing a silicon carbide based container (1) with a cavity (2) opening by an opening (3), a silicon carbide based plug (5) and a brazing material (6) carried by said plug and / or said container, wherein a solid object is to be accommodated in said cavity; b) a step of closing of said opening by brazing said plug to said container, said brazing comprising melting of said brazing material by heating to a temperature higher than its melting temperature, followed by solidification of said brazing material so as to form a solid joint (10) between said container and said plug, at least a part of said cavity in which said solid object is contained, called cold section (23), is kept at a temperature lower than the degradation temperature of said solid object during said brazing; Including, The brazing includes cooling the cold section by a cooling system (19) extending along at least a portion of the cold section, the portion including an edge of the cold section adjacent a heating zone for the braze material.

2. The method of claim 1 , wherein the solid object comprises at least one nuclear fuel pellet.

3. 3. The method of claim 1 or 2, wherein the container is made from sintered monolithic silicon carbide or from a composite comprising ceramic fibres incorporated in a silicon carbide matrix, the ceramic fibres preferably being made from silicon carbide or carbon.

4. 4. The method according to claim 1, wherein the container is of a hollow cylindrical shape, one of the ends of the cylinder being open by the opening and the end (4) of the cylinder opposite the opening being closed.

5. 5. The method according to any one of claims 1 to 4, wherein the cold section represents at least 70%, or even at least 80%, or even at least 90% of the volume of the cavity.

6. 6. The method according to any one of claims 1 to 5, wherein the distance between the plug and the cold part during the braze is equal to or less than 10 mm, preferably less than 5 mm, preferably between 2 mm and 5 mm.

7. 7. The method according to claim 1, wherein the heating is performed by induction through a susceptor (18) arranged in the vicinity of the opening, and wherein at least one thermal insulator (20, 21) is preferably arranged between the susceptor and the cold part of the cavity.

8. 8. The method according to any one of the preceding claims, wherein the brazing material is heated during the brazing to a temperature of 1250°C or higher, or even to a temperature of 1300°C or higher, or even to a temperature of 1400°C or higher.

9. 9. The method according to any one of the preceding claims, wherein the brazing material is heated to a temperature of up to 1850°C, or even below 1600°C, during the brazing.

10. 10. The method of claim 1, wherein the cooling system comprises a fluid circuit through which a cooling fluid circulates during the brazing.

11. 11. A method according to any one of claims 1 to 10, wherein the plug is made from sintered monolithic silicon carbide or from a composite comprising ceramic fibres incorporated in a silicon carbide matrix, the ceramic fibres preferably being made from silicon carbide or carbon.

12. 12. The method according to any one of the preceding claims, wherein the plug provided in step a) comprises a notch (31) which is filled with the brazing material.

13. 13. The method according to any one of the preceding claims, wherein at least a part of the brazing material is carried by the plug and the closing step b) is preceded by a step of heating the plug and the brazing material carried by the plug to a temperature above a melting temperature of the brazing material, preferably to a temperature of 1250°C or more, or even to a temperature of 1300°C or more, or even to a temperature of 1400°C or more, during which the brazing material melts, and then a step of solidifying the brazing material.

14. 14. The method according to any one of claims 1 to 13, wherein the container, the closure and the brazing material are in an environment under vacuum or inert gas throughout the closing step b), or in an environment under vacuum for a part of step b) and under inert gas for another part of step b), the inert gas being preferably argon or helium.

15. 15. The method according to any one of claims 1 to 14, wherein during step a) the brazing material is in the form of a brazing paste comprising a binder and a brazing powder dispersed in the binder, the brazing powder preferably comprising a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

16. 15. The method according to any one of claims 1 to 14, wherein during step a) the brazing material is in the form of a multiplicity of solid granules, said granules preferably comprising a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

17. 15. The method according to any one of claims 1 to 14, wherein during step a) the brazing material is in the form of at least one sheet wrapped around the plug, said sheet preferably comprising a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

18. 15. The method according to any one of claims 1 to 14, wherein during step a), the brazing material is in the form of a coating deposited by physical or chemical vapour deposition on the outer periphery of the plug and / or on the inner wall of the container before step a), the coating preferably comprising a silicon alloy, a silicide, a mixture of silicon and silicide, a mixture of silicides, an oxide or a mixture of oxides.

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