Method for closing orifice of silicon carbide-based container

Abstract

The invention relates to a method for closing an aperture of a silicon carbide-based container. The invention relates to a method for producing a solid object, comprising the following successive steps: a) providing a silicon carbide-based container, a silicon carbide-based stopper, and a brazing material carried by the stopper and / or the container, said container comprising a cavity open through an aperture in which the solid object is accommodated, b) closing the aperture by brazing the stopper onto the container, the brazing comprises melting the brazing material by heating to a temperature above the melting temperature of the brazing material and then solidifying the brazing material in order to form a solid joint between the container and the stopper, at least a portion of the cavity referred to as a cold portion in which the solid object is accommodated, the cold portion is maintained at a temperature lower than the degradation temperature of the solid object during brazing.

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 methods for closing an orifice of a silicon carbide based container. Background Art

[0002] Silicon carbide-based containers have mechanical and thermal properties that make them suitable for various applications, especially in the nuclear, aviation or aerospace fields. For example, silicon carbide-based containers, especially those made of composite materials containing silicon carbide fibers incorporated into a silicon carbide matrix, are envisioned as components in future nuclear reactors. Notably, they can help contain and protect nuclear fuel pellets while facilitating heat exchange. Such containers can also be used in heat exchangers, gas turbines or storage tanks.

[0003] In order to close containers based on silicon carbide, it is known that the open orifice of the container is blocked by a stopper. Depending on the envisaged application, it is desired that the closure also has good mechanical and thermal properties. It is therefore advantageous that the stopper is also based on silicon carbide. It may also be necessary for the stopper to be securely connected to the container in a high temperature resistant manner.

[0004] However, conventional methods that allow two silicon carbide-based parts to be firmly connected together generally require heating the parts as a whole to high temperatures. Therefore, these methods are not suitable for sealing silicon carbide-based containers that contain objects that deteriorate at such high temperatures.

[0005] Patent application US2021 / 0166825 A1 describes a method for forming a fluid-tight joint between a silicon carbide structure and a plug having a central opening to allow the structure to be filled with a gas during the method. However, this method is complex to implement.

[0006] Therefore, there is a need for a silicon carbide based container closure that is strong, resistant to high temperatures, easy to implement, and ensures the physical integrity and performance of the object enclosed in the container. Summary of the invention

[0007] The present invention aims to at least partially meet this need and proposes a method for closing an orifice of a container, the method comprising the following steps performed in sequence:

[0008] a) providing a silicon carbide based container, a silicon carbide based plug, and a brazing material carried by the plug and / or the container, the container comprising a cavity opened by an orifice, a solid object being accommodated in the cavity,

[0009] b) closing the orifice 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 and then solidifying the brazing material so as to form a solid joint between the container and the plug, at least a portion of the cavity (referred to as the cold portion) in which the solid object is accommodated being maintained at a temperature below the degradation temperature of the solid object during brazing.

[0010] The method according to the invention is simple, quick to implement and does not degrade the mechanical and thermal properties of the container. Moreover, since the brazing according to the invention requires only a local supply of heat, the cold part of the cavity is kept at a temperature that ensures the physical integrity (including the geometry) of any object that may be placed in the cavity and degraded at high temperatures, for example at temperatures above 800° C. Moreover, the closure obtained by the method of the invention is advantageously strong, impermeable to fluids, resistant to oxidation and resistant to temperatures at least in the range of: up to a temperature close to but strictly 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., or even 1300° C., or even 1400° C.

[0011] A "silicon carbide-based" component is made of a material comprising at least 50 mass % silicon carbide.

[0012] The "degradation temperature of a solid object" corresponds to the highest temperature at which the physical integrity of the object is preserved, that is, at which the object does not substantially deform under its own weight and / or does not undergo any change of physical state (e.g. phase transition), and / or is not modified by chemical reactions, and / or its mechanical properties, in particular its creep strength, are not reduced. Preferably, the degradation temperature of a solid object is equal to 0.5 times, or even 0.4 times, the melting temperature of said object.

[0013] Preferably, the solid object comprises at least one nuclear fuel pellet.Preferably, the gas tightness of the solid object is ensured by the presence of a metal lining made of a zirconium alloy.

[0014] Preferably, during brazing, the cold part is maintained at a temperature below 800°C.

[0015] Preferably, the container is made of a sintered monolithic silicon carbide or of a composite material comprising ceramic fibers incorporated in a silicon carbide matrix, the ceramic fibers preferably being made of silicon carbide or of carbon. Preferably, the container is made of a composite material comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0016] Preferably, the container is in the shape of a hollow cylinder, one end of the cylinder is open by the orifice, and the end of the cylinder on the side opposite to the orifice is closed.

[0017] Preferably, the cold portion occupies at least 70%, or even at least 80%, or even at least 90% of the volume of the cavity.

[0018] Preferably, the cavity extends along a longitudinal axis (X) and the cold portion extends over at least 70%, or even at least 80%, or even at least 90% of the length of the cavity along the longitudinal axis (X).

[0019] Preferably, the cavity extends along the longitudinal axis (X) and the joint formed by brazing extends over at least 0.1% of the length of the cavity along the longitudinal axis (X), preferably over 0.1% to 10%, or even 0.1% to 5%, of the length of the cavity along the longitudinal axis (X).

[0020] Preferably, during brazing, the distance between the plug and the cold part is less than or equal to 10 mm, preferably less than 5 mm, preferably between 2 mm and 5 mm.

[0021] Preferably, the heating is performed by induction of a susceptor arranged near the orifice. Preferably, at least one thermal insulation is arranged between the susceptor and the cold part of the cavity. Advantageously, during step b), the heat is confined to the area where the plug is brazed to the container. Induction heating shortens the duration of heating during step b).

[0022] Preferably, during step b), the duration for which the brazing material is heated 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.

[0023] Preferably, during the melting of the brazing material in step b), the heating temperature of the brazing material is greater than or equal to 1250°C, or even greater than or equal to 1300°C, or even greater than or equal to 1400°C.

[0024] Preferably, during brazing, the brazing material is heated to a temperature lower than or equal to 1850° C., or even to a temperature lower than 1600° C. If the container and the stopper are made of a sintered monolithic piece of silicon carbide, the heating temperature of the brazing material during brazing may be between 1600° C. and 1850° C. If at least one of the container and the stopper is made of a composite material comprising ceramic fibers incorporated into a silicon carbide matrix, the heating temperature of the brazing material during brazing is preferably lower than 1600° C.

[0025] Preferably, during step b), solidification of the brazing material comprises gradually cooling the brazing material at a cooling rate between 1 K / min and 50 K / min.

[0026] Preferably, the method comprises cooling the cold portion during brazing by a cooling system extending along at least a portion of the cold portion, the portion comprising an end of the cold portion adjacent to the heated area of ​​the brazing material. Preferably, the cooling system comprises a fluid circuit in which a cooling fluid circulates during brazing.

[0027] Preferably, the plug is made of a sintered monolithic silicon carbide or of a composite material comprising ceramic fibers incorporated in a silicon carbide matrix, the ceramic fibers preferably being made of silicon carbide or of carbon. Preferably, the plug is made of a composite material comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0028] Preferably, the stopper is formed from the same material as the container.

[0029] Preferably, the plug provided in step a) comprises at least one cutout filled with brazing material. Advantageously, this ensures an adequate supply of brazing material during brazing, the one or more cutouts each constituting a reservoir of brazing material which may take the form of, for example, a hole filled with brazing material.

[0030] Preferably, at least a portion 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 the melting temperature of the brazing material, preferably to a temperature higher than or equal to 1250°C, or even higher than or equal to 1300°C, or even higher than or equal to 1400°C, during which the brazing material melts, followed by a step of solidifying the brazing material. Preferably, during the heating of the plug and the brazing material carried by the plug, the plug and the brazing material carried by the plug are placed in an environment under vacuum or inert gas. Preferably, the inert gas is argon or helium. Preferably, during brazing, the plug and the brazing material carried by the plug are heated to a temperature lower than or equal to 1850°C, or even to a temperature lower than 1600°C. If the plug is made of a sintered monolithic silicon carbide, the heating temperature of the brazing material during brazing may be between 1600°C and 1850°C. If the plug is made of a composite material comprising ceramic fibres incorporated in a silicon carbide matrix, the heating temperature of the brazing material during brazing is preferably below 1600°C.

[0031] Advantageously, such preheating of the plug and the brazing material carried by the plug evenly distributes the brazing material on the plug before brazing, so that a good supply of brazing material is obtained during brazing.

[0032] If the plug is a composite material comprising ceramic fibers incorporated into a silicon carbide matrix, this preheating also results in the penetration of the brazing material in the liquid state into the pores of the plug during the 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 fills the pores of the plug. Advantageously, this penetration of the brazing material into the plug improves the thermal diffusivity, the sealing and the mechanical strength of the plug impregnated with the brazing material.

[0033] Preferably, the container, the stopper and the brazing material are placed in an environment under an inert gas or vacuum during the entire closing step b), or under vacuum during a portion of step b) and under an inert gas, preferably argon or helium, during another portion of step b). Advantageously, this limits undesired reactions during brazing.

[0034] "Vacuum environment" means a pressure below 10 -1 Pa environment. The environment can be in a higher vacuum, such as a pressure of 10 -3 Pa to 10 -5 Between Pa.

[0035] 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, or a silicide, or a mixture of silicon and silicide, or a mixture of silicides, or an oxide, or a mixture of oxides. Preferably, the binder is a hydrogel. Preferably, the evaporation temperature of the binder is lower than 500° C., or even lower than 400° C., preferably close to 300° C. Advantageously, this brazing material is non-reactive or not very reactive with silicon carbide, and therefore does not deteriorate the mechanical and thermal properties of the container and the stopper during the method.

[0036] According to a second variant, during step a), the brazing material is in the form of a plurality of solid particles. Preferably, the particles comprise a silicon alloy, or a silicide, or a mixture of silicon and a silicide, or a mixture of silicides, or an oxide, or a mixture of oxides.

[0037] According to a third variant, during step a), the brazing material is in the form of at least one sheet wrapped around the plug. Preferably, the sheet comprises a silicon alloy, or a silicide, or a mixture of silicon and silicide, or a mixture of silicides, or an oxide, or a mixture of oxides.

[0038] According to a fourth variant, during step a), the brazing material is in the form of a coating which, prior to step a), is deposited on the periphery of the stopper and / or the inner wall of the container by physical vapor deposition or chemical vapor deposition. This deposition enables better control of the thickness of the coating. Chemical vapor deposition may be plasma enhanced chemical vapor deposition, or may be atomic layer deposition. Preferably, the coating comprises a silicon alloy, or a silicide, or a mixture of silicon and silicide, or a mixture of silicides, or an oxide, or a mixture of oxides.

[0039] 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 contains at least 50 atomic % silicon. Preferably, the element is zirconium or chromium. Preferably, the silicon alloy or silicide contains 90 mass % to 42 mass % silicon and 10 mass % to 58 mass % zirconium.

[0040] Preferably, the oxide is selected from silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide and mixtures thereof.

[0041] Preferably, the brazing material further comprises carbon particles and / or silicon carbide particles.

[0042] Preferably, during step b), the carbon particles and / or silicon carbide particles are in the form of a powder in the gap between the container and the stopper.

[0043] Advantageously, the presence of carbon particles and / or silicon carbide particles in the brazing material and / or the gap between the container and the plug results in the joint formed by the solidification of the brazing material being a composite material comprising silicon carbide. If silicon carbide particles are involved, the silicide or oxide of the brazing material penetrates between the silicon carbide particles in the liquid phase during brazing, so that the joint formed by the solidification of the brazing material is a composite material comprising silicon carbide particles. If carbon particles are involved, the silicon alloy or silicide of the brazing powder reacts with the carbon particles during brazing, so that the joint formed by the solidification of the brazing material includes silicon carbide.

[0044] Other advantages and characteristics will emerge more clearly after reading the detailed description given by way of non-limiting illustration, with reference to the following figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] [ Figure 1 ] Figure 1 is a front schematic view of a silicon carbide container including an orifice open at one end thereof.

[0046] [ Figure 2 ] Figure 2 is based on Figure 1 Schematic diagram of a front view of a container with a plug inserted into the orifice.

[0047] [ Figure 3 ] Figure 3 is based on Figure 1 A front view of a container with a plug inserted into the orifice and solder paste carried by the plug and the container.

[0048] [ Figure 4 ] Figure 4 is based on Figure 3 A front view of a container, a plug and a solder paste which are locally heated at the end including the orifice.

[0049] [ Figure 5 ] Figure 5 is a schematic front view of a silicon carbide container including an orifice at one end thereof, the orifice being blocked by a plug brazed to the container.

[0050] [ Figure 6 ]、[ Figure 7 ]and[ Figure 8 ] Figures 6 to 8 is a schematic front view of a plug carrying solder paste.

[0051] [ Fig. 9 ] Fig. 9 is a schematic front view of a plug including a cutout filled with brazing material.

[0052] [ Fig.10 ] Fig.10 The present invention is a schematic longitudinal section of an embodiment of a device for carrying out the method according to the invention by local heating.

[0053] [ Fig.11 ] Fig.11 is a graph showing the measured and simulated variations with time of the temperature of the container at its orifice and of the temperature of the susceptor during a heating cycle of a brazing operation according to the method of the invention, the graph also showing the variation with time of the electrical power supplied to the coil during said heating cycle.

[0054] [ Fig.12 ] Fig.12 is a schematic longitudinal section of a mechanical test during which a thrust is applied to a plug closing the orifice of a container, the closure being obtained by the method according to the invention.

[0055] [ Fig.13 ] Fig.13 It is displayed in Fig.12 Shown is a graph of thrust force measured during mechanical testing versus displacement of the load applying the thrust. DETAILED DESCRIPTION

[0056] Figures 1 to 5An embodiment of implementing the method according to the invention is shown. The method comprises a 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 Different sub-steps of an embodiment for carrying out step a) are shown.

[0057] Figure 1 An embodiment of a container 1 is shown. The container has the shape of a hollow cylinder extending along a longitudinal axis X. The container comprises a cavity 2 extending along the longitudinal axis X, for example over a length between 5 cm and 400 cm. The cavity 2 is opened at one end of the container 1 by an orifice 3, the other end 4 of the container 1 being closed. Solid objects are accommodated in the cavity 2 of the container 1. The opening diameter of the orifice 3 may be between 0.5 cm and 50 cm. The container 1 is based on silicon carbide, preferably made of a composite material comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0058] Figure 2 The placement of a plug 5 in a cavity 2 is shown. The plug 5 has a shape complementary to the cavity 2 at the orifice 3 so as to be inserted therein with a small gap, preferably less than 100 μm, so that the plug 5 remains immobile when inserted into the orifice 3. Thus, there is a small gap between the wall 7 of the container 1 and the plug 5. At the end of the method according to the invention, the joint formed between the plug 5 and the container 1 will have a small thickness, which is mechanically advantageous. For example, the plug 5 is a rotating cylinder with a diameter between 0.4 cm and 5 cm. Once inserted in the container 1, the plug 5 extends along the longitudinal axis X, for example over a length of 0.5 cm to 5 cm. In particular, when the plug 5 is inserted in the container 1, the plug 5 occupies 0.1% to 10% of the length of the cavity 2 measured along the longitudinal axis X. The plug 5 is based on silicon carbide, preferably made of a composite material comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0059] The brazing material 6 is then deposited in the form of a paste on the plug 5 and / or the wall 7 . Figure 3 A container 1 is shown with a plug 5 inserted in an orifice 3 and a brazing paste 6 deposited on the plug 5 and the wall 7. The invention is not limited to brazing material 6 deposited in the form of a paste, other forms of brazing material and deposition methods are conceivable, for example the brazing material may be in the form of a mass of particles or sheets or a coating as described above.

[0060] Step a) is followed by step b) of closing the orifice 3 by brazing the plug 5 to the container 1. To this end, heating is carried out in a localized manner at the orifice 3 to heat the plug 5, the wall 7 close to the orifice 3 and the brazing material 6 to a temperature above 1250°C, or even above 1300°C, or even above 1400°C. Figure 4The local heating is shown, with lightning bolts 8 representing the targeted heat supply. The local 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 are indicated by arrows 9. If the container 1 and / or the plug 5 are made of a composite material comprising ceramic fibers incorporated into a silicon carbide matrix, the brazing material 6 penetrates into the pores of the container 1 and / or the plug 5.

[0061] During local heating, a portion of the cavity 2, called the cold portion 23, is kept at a temperature below 800° C. at a distance from the heating zone. The cold portion 23 extends over at least 70% of the length of the cavity 2 along the longitudinal axis X. In particular, the cold portion 23 corresponds to the entirety of the cavity 2 at least 1 cm, preferably at least 5 mm, preferably at least 2 mm from the plug 5 inserted into the orifice 3.

[0062] After heating, the plug 5, the container 1 and the brazing material 6 are cooled. During the cooling of the brazing material 6, the brazing material 6 solidifies, thereby forming a solid joint 10 between the plug 5 and the wall 7, as shown in FIG. Figure 5 Thus, the orifice 3 is blocked by a plug 5 fixed to the container 1 by brazing.

[0063] According to another embodiment, the plug 5 provided in step a) is at least partially loaded with brazing material 6 before inserting the plug 5 into the container 1. The plug 5 is then inserted into the orifice 3 together with the brazing material 6. This is followed by step b) of closing the orifice 3.

[0064] Figure 6 , Figure 7 and Figure 8 Different methods of depositing the brazing material 6 on the plug 5 are shown. For example, the brazing material 6 can be deposited on and carried by the side surface of the plug 5, with the base of the plug 5 not being covered by the brazing material 6, such as Figure 6 As an alternative, the brazing material 6 may be deposited on and carried by the side surfaces of the plug 5 and the upper base of the plug 5, as shown in FIG. Figure 7 As an alternative, the brazing material 6 may be deposited on and carried by the upper base of the plug 5, with the side surface of the plug 5 not being covered by the brazing material 6, as shown in FIG. Figure 8 shown.

[0065] In addition, the plug 5 may also include at least one cutout 31 filled with the brazing material 6, such as Fig. 9 Thus, the cutouts 31 form a reservoir for the brazing material 6, thereby increasing the supply of the brazing material 6 during the brazing of step b). For example, the cutouts 31 may be blind holes recessed into the side wall of the plug 5. One or more cutouts 31 may also be radial grooves or slots.

[0066] Before inserting the plug 5 and in step b), the brazing material 6 carried by the plug 5 can be heated to a temperature above its melting temperature. Then, the brazing material 6 flows to cover at least the side surface of the plug 5, or even the entire plug 5. The heating can be carried out in a furnace, preferably under high vacuum or inert gas, preferably argon or helium. Then, after the heating, the brazing material 6 is solidified by cooling. Therefore, the solidified brazing material 6 is evenly distributed on the plug 5, ensuring a good supply of the brazing material 6 during the brazing of the plug 5 to the container 1.

[0067] If the plug 5 is made of a composite material comprising ceramic fibers incorporated into a silicon carbide matrix, this preheating also causes the brazing material to penetrate into the pores of the plug 5 and then solidify when cooled. This penetration improves the thermal diffusion, sealing and mechanical strength of the plug 5 impregnated with the brazing material 6.

[0068] The inventors conducted tensile tests at ambient temperature to compare the difference in mechanical properties between tensile specimens that were not impregnated with brazing material 6 and tensile specimens whose pores had been infiltrated with brazing material 6. The tensile specimens were all made of a composite material containing silicon carbide fibers in a silicon carbide matrix. The tensile specimens were cylindrical specimens 75 mm long with a central portion diameter of 9.50 mm. The brazing material 6 used was in the form of a paste, which contained a powder made of a silicon alloy consisting of 88% by mass of silicon and 12% by mass of zirconium, and mixed with a hydrogel as a binder. In the tensile test, for the unimpregnated tensile specimen, a fracture stress of about 240 MPa was measured, and the deformation was about 0.8% to 0.9%. For the tensile specimen whose pores had been infiltrated with brazing material 6, a fracture stress of about 280 MPa was measured, and the deformation was greater than 1.1%. Therefore, these tensile tests show that the mechanical strength of the tensile specimen is significantly improved when impregnated with brazing material 6.

[0069] If the brazing material 6 is not sufficiently evenly distributed on the plug 5 after heating, additional deposition of the brazing material 6 can be performed on the plug 5, in particular on the areas lacking the brazing material 6. Similar to the previous paragraph, after such deposition, the plug 5 and the brazing material 6 carried by the plug 5 are preferably additionally heated. Where appropriate, such additional deposition advantageously fills in the differences in coverage of the brazing material 6 on the plug 5, which differences are caused by the penetration of the brazing material 6 into the pores of the plug 5.

[0070] Machining can be performed after the brazing material 6 on the plug 5 has solidified to reduce the surface micro-protrusions formed by the brazing material 6 on the plug 5. Advantageously, this facilitates the insertion of the plug 5 into the container 1. In addition, once the orifice 3 is closed by the plug 5, the plug 5 has few or even no surface micro-protrusions on its surface facing the object contained in the cavity. If the brazing material 6 is in the form of a coating deposited by physical vapor deposition or chemical vapor deposition before step a), performing the above-mentioned mechanical processing is disadvantageous because the surface micro-protrusions can be ignored.

[0071] Furthermore, the container 1 provided in step a) may also carry at least a portion of the brazing material 6 before the plug 5 is inserted into the container 1. In particular, the brazing material 6 may cover that portion of the wall 7 to which the plug 5 is to be brazed.

[0072] Fig.10 An apparatus 11 is shown which is configured to heat the brazing material in step b) of the method according to the invention. The apparatus 11 comprises a sealed housing 12 for accommodating a container 1 having a plug 5 inserted into an orifice 3 and brazing material 6 carried by the plug 5 and / or the container 1. Preferably, the housing 2 is a quartz tube.

[0073] A feed line 13 leads to the housing 12. The feed line 13 is suitable for injecting an inert gas into the housing 12. The inert gas may be argon or helium. The device 11 comprises a discharge line 14 for discharging the gas present in the housing 12. The line 14 may also form a vacuum in the housing 12. Preferably, the feed line 13 and the discharge line 14 are configured so that the inert gas circulates continuously in the housing 12.

[0074] The device 11 further comprises a coil 16 comprising at least one turn around the housing 12. Preferably, the one or more turns are made of copper. The coil 16 is electrically connected to a high frequency generator 17. A susceptor 18 is housed in the housing 12 and is surrounded by the coil 16. Preferably, the susceptor 18 is made of graphite. The susceptor 18 comprises a central channel for accommodating the container 1 placed in the housing 12, the susceptor 18 then surrounding the container 1 in the region of the orifice 3 and the stopper 5. Preferably, the coil 16 and the susceptor 18 are concentric, so that the central channel of the susceptor 18 is centered on the center of the coil 16.

[0075] The device 11 further comprises a cooling system 19 arranged in the housing 12 so as to extend along the cold portion 23 of the container 1. In particular, the cooling system 19 may comprise a central channel into which the container 1 is inserted so that the cooling system 19 faces the cold portion 23 over its entire length. Preferably, the cooling system 19 comprises a fluid circuit wound around the channel housing the container 1, a cooling fluid (preferably water) being used to circulate in the fluid circuit. Preferably, the pipes 22 of the fluid circuit are made of copper or brass.

[0076] The cooling system 19 does not have to extend over the entire length of the cold portion 23. The cold portion 23 may include a portion remote from the heating zone, such that this portion is not significantly affected by the heating during step b), that is, this portion is kept at ambient temperature even without cooling. Where appropriate, the cooling system 19 does not have to extend along the remote portion. Furthermore, a first thermal insulation member 20 is arranged between the wall of the housing 12 and the susceptor 18 and between the susceptor 18 and the cooling system 19. Preferably, the first thermal insulation member 20 is made of insulating graphite, for example, fiber graphite. Furthermore, a second thermal insulation member 21 is arranged between the first thermal insulation member 20 and the cooling system 19. The second thermal insulation member 21 may be made of an oxide, for example, aluminum oxide.

[0077] The heating performed by the device 11 is local induction heating. First, the container 1 is placed in the housing 12, the plug 5 is inserted into the orifice 3, and the brazing material 6 is carried by the plug 5 and / or the container 1. Once the container 1 has been placed, the susceptor 18 surrounds the wall 7 in the region of the orifice 3, the plug 5 and the brazing material 6, and the cooling system 19 extends along the cold portion 23.

[0078] Then, the inert gas is injected into the housing 12. Before the inert gas is injected, a vacuum may be formed in the housing 12. Preferably, the injection of the inert gas causes the housing 12 to be at atmospheric pressure. Preferably, the inert gas is injected through a feed line 13 and then discharged through a discharge line 14 to maintain continuous circulation of the inert gas in the housing 12. The circulation direction of the inert gas in the housing 12 is shown by an arrow 15.

[0079] Thereafter, the cooling system 19 is activated to cool the cold portion 23. In particular, a cooling fluid, preferably water, may be circulated in the fluid circuit.

[0080] Then, the high-frequency generator 17 supplies electric power to the coil 16, which then generates a magnetic field. The susceptor 18 converts the energy of the magnetic field into heat by induction, and heats the wall 7, the plug 5 and the brazing material 6 in the region of the orifice 3 of the container 1 in a localized manner by conduction. The electric power supplied by the high-frequency generator 17 is gradually increased 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 conduction, the first thermal insulation 20 and the second thermal insulation 21 limit the heat generated by the susceptor 18 to the region where the plug 5 is brazed to the container 1, thereby increasing the localization of the heating. During heating, the cooling system 19 continuously cools the cold portion 23 to keep it at a temperature below 800° C.

[0081] therefore, Fig.10The device 11 shown can perform step b of closing the orifice 3 by brazing the plug 5 to the container 1. The device 11 locally heats the brazing material 6 carried by the plug 5 and / or the container 1 by induction and melts the brazing material 6 to braze the plug 5 to the container 1. In addition, the device 11 keeps the cold portion 23 at a low temperature during heating. The keeping at a low temperature is achieved by thermal insulation between the cold portion 23 and the area where the plug 5 is brazed to the container 1 and cooling the cold portion 23 by the cooling system 19.

[0082] The inventors have carried out simulations and measurements to determine the evolution of the temperatures involved over time during a brazing operation according to the method of the invention. To this end, the device 11 comprises a pyrometer 24 which measures the temperature of the susceptor 18 and the temperature in the region of the orifice 3 of the container 1. The device 11 also comprises a thermocouple (not shown here) which measures the temperature of the susceptor 18 and the temperature in the region of the orifice 3 of the container 1. The measurements made by the pyrometer 24 are compared with the measurements made by the thermocouple. Fig.11 The results of these simulations and these measurements are shown. A heating cycle has been simulated and measured during which the average electric power supplied to the coil 16 reaches a first level of 15 kW for 10 minutes and then reaches a second level of 17 kW for 10 minutes. Curve 25 shows the variation of the average electric power supplied to the coil 16 during the heating cycle.

[0083] Curve 26 shows the variation of the simulated temperature of the susceptor 18 during the heating cycle. Curve 27 shows the variation of 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 the first level and then reaches a temperature of 1620°C during the second level.

[0084] Curve 28 shows the variation of the simulated temperature of the container 1 in the region of the orifice 3 during the heating cycle. It shows that the temperature of the container 1 in the region of the orifice 3 reaches a temperature of 1300° C. during the first level and then reaches a temperature of 1420° C. during the second level. Curve 29 shows the variation of the measured temperature of the container 1 in the region of the orifice 3 during the heating cycle. Curve 29 shows that the temperature of the container 1 in the region of the orifice 3 reaches a temperature of 1320° C. during the first level and then reaches a temperature of 1480° C. during the second level. Thus, during each of the first and second levels, the simulated or measured temperature of the container 1 in the region of the orifice 3 is greater than or equal to 1300° C., as desired for brazing in step b) of the method according to the invention.

[0085] The inventors also simulated the temperature change of the cold portion 23 during the above-mentioned heating cycle. The highest temperature of the cold portion 23 obtained by the simulation was 725° C. Therefore, the temperature is much lower than 800° C.

[0086] The inventors tested the mechanical strength of the closure obtained according to the invention. To this end, the inventors used the method according to the invention to close the container 1. The provided container 1 and the plug 5 are made of a composite material containing silicon carbide fibers incorporated into a silicon carbide matrix. The brazing material 6 used is in the form of a paste, which contains a powder made of a silicon alloy consisting of 88.5% by mass of silicon and 11.5% by mass of zirconium and is mixed with a hydrogel as a binder, such as a commercially available gel "Vitta Braz-Binder Gel Grade ST" or cement "Nicrobraz". Approximately 400 mg of brazing paste 6 is deposited on the plug 5. Then, in a brazing furnace, the plug 5 and the brazing paste 6 carried by the plug are heated to 1420°C under argon to melt the brazing material 6, which completely covers the plug 5 and fills the cutout recessed in the plug 5. Then, the brazing material 6 carried by the plug 5 is solidified by cooling, and mechanical processing is performed to eliminate surface micro-protrusions formed on the plug 5 by the brazing material 6, which are likely to hinder the plug 5 from being inserted into the container 1. Subsequently, the plug 5 is brazed to the container 1 to close the orifice 3 of the container 1. As described above, brazing is performed on the Fig.10 The brazing is carried out in the device 11 shown. The brazing consists in heating the wall 7 of the container 1 in the region of its orifice 3, the plug 5 and the brazing material 6 to a temperature of 1420° C. for 10 minutes and then gradually cooling the brazing material 6.

[0087] In order to test the robustness of the closure of the container 1 obtained according to the preceding paragraph, the inventors carried out a mechanical test of the "pull-out" type, such as Fig.12 This mechanical test consists in applying a thrust F to the stopper 5 by means of a piston 32 so as to generate shear stresses at the joint 10 between the stopper 5 and the wall 7 , during which the container 1 is carried by the frame 33 .

[0088] Fig.13 The results of this mechanical test are shown. Curve 30 shows the variation of the thrust F with the displacement of the piston 32 during this mechanical test. The maximum thrust applied before the closure ruptures is 3925 N. Thus, the closure of the container 1 has a fracture strength of 221 MPa, a nominal shear strength of 30.4 MPa and a burst pressure of 736 bar. Furthermore, the rupture does not occur at the joint 10, but rather the wall 7 of the container 1 outside the joint 10. Thus, the joint 10 formed by the method according to the invention is stronger than the container 1.

[0089] Other variations and modifications can be envisaged without departing from the scope of the invention as defined by the claims.

Claims

1. A method for closing an orifice of a container, the method comprising the following steps performed in sequence: a) providing a silicon carbide based container (1), a silicon carbide based plug (5), and a brazing material (6) carried by the plug and / or the container, the container comprising a cavity (2) opened by an orifice (3), a solid object being accommodated in the cavity, b) closing the orifice 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 and then solidifying the brazing material so as to form a solid joint (10) between the container and the plug, at least a portion of the cavity being referred to as a cold portion (23) in which the solid object is accommodated, the cold portion being maintained at a temperature below the degradation temperature of the solid object during the brazing, The brazing includes cooling the cold portion by a cooling system (19) extending along at least a portion of the cold portion, including an end of the cold portion adjacent to a heated area of ​​the brazing material.

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

3. A method according to any one of the preceding claims, the container being made of a sintered monolithic silicon carbide or of a composite material comprising ceramic fibers incorporated in a silicon carbide matrix, the ceramic fibers preferably being made of silicon carbide or of carbon.

4. The method according to the preceding claim, the container being in the shape of a hollow cylinder, one end of which is open through the orifice, the end (4) of the cylinder on the side opposite to the orifice being closed.

5. A method as claimed in any preceding claim, the cold portion occupying at least 70%, or even at least 80%, or even at least 90% of the volume of the cavity.

6. Method according to any of the preceding claims, wherein during the brazing, the distance between the plug and the cold portion is less than or equal to 10 mm, preferably less than 5 mm, preferably between 2 mm and 5 mm.

7. A method as claimed in any one of the preceding claims, the heating being performed by induction of a susceptor (18) arranged near the orifice, preferably with at least one thermal insulation (20, 21) arranged between the susceptor and a cold part of the cavity.

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

9. The method according to any of the preceding claims, during the brazing, the brazing material is heated to a temperature lower than or equal to 1850°C, or even lower than 1600°C.

10. A method as claimed in any preceding claim, the cooling system comprising a fluid circuit in which a cooling fluid is circulated during the brazing.

11. A method as claimed in any one of the preceding claims, the plug being made of a sintered monolithic silicon carbide or of a composite material comprising ceramic fibres incorporated in a silicon carbide matrix, the ceramic fibres preferably being made of silicon carbide or of carbon.

12. Method according to any of the preceding claims, the plug provided in step a) comprising a cutout (31 ) filled with the brazing material.

13. A method according to any one of the preceding claims, at least a portion of the brazing material being carried by the plug, the closing step b) being preceded by a step of heating the plug and the brazing material carried by the plug to a temperature above the melting temperature of the brazing material, preferably to a temperature higher than or equal to 1250° C., or even higher than or equal to 1300° C., or even higher than or equal to 1400° C., during which the brazing material melts, followed by a step of solidifying the brazing material.

14. A method as claimed in any one of the preceding claims, wherein the container, the stopper and the brazing material are placed in an environment under vacuum or inert gas throughout the closing step b), or in an environment under vacuum in one part of step b) and in an environment under inert gas in another part of step b), the inert gas being preferably argon or helium.

15. A method as claimed in any one of the preceding claims, 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, or a silicide, or a mixture of silicon and silicide, or a mixture of silicides, or an oxide, or a mixture of oxides.

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

17. 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, the sheet preferably comprising a silicon alloy, or a silicide, or a mixture of silicon and silicide, or a mixture of silicides, or an oxide, or a mixture of oxides.

18. 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, which is deposited on the periphery of the plug and / or the inner wall of the container by physical vapor deposition or chemical vapor deposition before step a), and the coating preferably comprises a silicon alloy, or a silicide, or a mixture of silicon and silicide, or a mixture of silicides, or an oxide, or a mixture of oxides.

Images