Method for closing an orifice of a silicon carbide-based container

Abstract

Method for closing an orifice of a silicon carbide-based container The invention relates to a method for closing an orifice of a container, the method comprising the following successive steps: a) providing a silicon carbide-based container comprising a cavity opened by an orifice, a silicon carbide-based plug and a solder carried by the plug and / or the container, a solid object being housed in the cavity, b) closing the orifice by soldering the plug to the container, the soldering comprising melting the solder by heating to a temperature above the melting temperature of the solder, followed by solidification of the solder so as to form a solid joint between the container and the plug, at least a part of the cavity, called the cold part, in which the solid object is housed, being maintained at a temperature below the degradation temperature of the solid object during the soldering. Figure for abstract: Fig.4.

Description

Title of the invention: Method for closing an orifice of a silicon carbide-based container Technical field

[0001] The present invention relates to the field of methods for assembling silicon carbide-based parts. In particular, the present invention relates to methods for closing an orifice of a silicon carbide-based container. Prior art

[0002] Silicon carbide-based containers have mechanical and thermal properties that make them suitable for a variety of applications, particularly in the nuclear, aeronautical, and space sectors. For example, silicon carbide-based containers, particularly composite containers comprising silicon carbide fibers incorporated into a silicon carbide matrix, are being considered as components in future nuclear reactors. In particular, they can help contain and protect nuclear fuel pellets while promoting heat exchange. Such containers can also be used in heat exchangers, gas turbines, or tanks.

[0003] To close containers based on silicon carbide, it is known to fill the opening orifice of the container with a stopper. Depending on the intended application, it is desired that the closure also has good mechanical and thermal properties. It is therefore advantageous for the stopper to also be based on silicon carbide. Also, it may be necessary for the stopper to be joined to the container securely and in a manner resistant to high temperatures.

[0004] However, conventional methods for securely joining two silicon carbide-based parts together often require the entire heating of said parts to high temperatures. Consequently, these methods are not suitable for closing a silicon carbide-based container in which an object is housed that deteriorates at said high temperatures.

[0005] Patent application US 2021 / 0166825 A1 describes a method for forming a tight seal between a silicon carbide structure and a plug having a central opening in order to fill the structure with gas during the process. However, this method is complex to implement.

[0006] There is therefore a need for a closure of a container based on silicon carbide which is robust and resistant to high temperatures, and which is simple to implement and guarantees the physical integrity and performance of an object enclosed in the container. Statement of the invention

[0007] The invention aims to meet at least part of this need and proposes a method for closing an orifice of a container, the method comprising the following successive steps: a) providing a silicon carbide-based container comprising a cavity and opened by the orifice, a silicon carbide-based plug and a solder carried by the plug and / or the container, a solid object being housed in the cavity, b) closing the orifice by soldering the plug to the container, the soldering comprising melting the solder by heating to a temperature above the melting temperature of the solder, followed by solidification of the solder so as to form a solid joint between the container and the plug, at least a part of the cavity, called the cold part, in which the solid object is housed, being maintained at a temperature below the degradation temperature of the solid object during the soldering.

[0008] The method according to the present invention is simple, quick to implement and does not degrade the mechanical and thermal properties of the container. In addition, since the brazing according to the invention only requires a localized supply of heat, the cold part of the cavity remains at a temperature guaranteeing the physical integrity, including the geometric shape, of any object deteriorating at high temperatures, for example at temperatures above 800°C, which could be placed in the cavity. In addition, the closure obtained by the method according to the invention is advantageously robust, leaktight, resistant to oxidation and resistant to temperatures ranging at least up to temperatures close to but strictly below the melting temperature of the brazing, typically up to 50°C below the melting temperature of the brazing, for example up to 1200°C, or even 1300°C, or even 1400°C.

[0009] A “silicon carbide-based” part is made of a material comprising at least 50% by mass of silicon carbide.

[0010] “The degradation temperature of the solid object” corresponds to the highest temperature at which the physical integrity of the object is preserved, i.e. at which the object does not deform substantially under its own weight and / or does not undergo a change in physical state, for example a phase change, and / or is not altered by a chemical reaction, and / or its mechanical properties, in particular its resistance to brittleness, are not reduced. Preferably, the degradation temperature of the solid object is equal to 0.5 times, or even 0.4 times, the melting temperature of said object.

[0011] 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 liner made of zirconium alloy.

[0012] Preferably, the cold part is maintained at a temperature below 800°C during brazing.

[0013] Preferably, the container is made of sintered monolithic silicon carbide or a composite comprising ceramic fibers incorporated in a silicon carbide matrix, preferably the ceramic fibers being made of silicon carbide or carbon. Preferably, the container is made of a composite comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0014] Preferably, the container is of cylindrical and hollow shape, one of the ends of the cylinder being open by the orifice, the end of the cylinder opposite the orifice being closed.

[0015] Preferably, the cold part represents at least 70%, or even at least 80%, or even at least 90%, of the volume of the cavity.

[0016] Preferably, the cavity extends along a longitudinal axis (X) and the cold portion extends along at least 70%, or even at least 80%, or even at least 90%, of the length of the cavity along the longitudinal axis (X).

[0017] Preferably, the cavity extends along a longitudinal axis (X) and the joint formed by the brazing extends along at least 0.1% of the length of the cavity along the longitudinal axis (X), preferably between 0.1% and 10%, or even between 0.1% and 5%, of the length of the cavity along the longitudinal axis (X).

[0018] Preferably, the distance between the plug and the cold part during brazing is less than or equal to 10 mm, preferably less than 5 mm, preferably between 2 and 5 mm.

[0019] Preferably, the heating is carried out by induction of a susceptor arranged near the orifice. Preferably, at least one thermal insulator is arranged between the susceptor and the cold part of the cavity. Advantageously, the heat is confined to the brazing zone of the cap on the container during step b). Induction heating makes it possible to shorten the heating time during step b).

[0020] Preferably, during step b), the duration of heating the solder to a temperature higher than the melting temperature of the solder is between a few seconds and 20 minutes, preferably between 30 seconds and 5 minutes.

[0021] Preferably, the heating temperature of the solder during its melting in step b) 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.

[0022] Preferably, the solder is heated to a temperature less than or equal to 1850°C, or even to a temperature less than 1600°C, during the soldering. In the case where the container and the stopper are made of sintered monolithic silicon carbide, the heating temperature of the solder may be between 1600°C and 1850°C during the soldering. In the case where at least one of the container and the stopper is made of a composite comprising ceramic fibers incorporated in a silicon carbide matrix, the heating temperature of the brazing is preferably less than 1600°C during brazing.

[0023] Preferably, during step b), the solidification of the solder comprises progressive cooling of the solder with a cooling rate of between 1 and 50 K / min.

[0024] Preferably, the method comprises cooling, during brazing, the cold part by a cooling system extending along at least a portion of the cold part, said portion comprising the end of the cold part adjacent to the heating zone of the brazing. Preferably, the cooling system comprises a fluid circuit in which a cooling fluid circulates during brazing.

[0025] Preferably, the plug is made of sintered monolithic silicon carbide or a composite comprising ceramic fibers incorporated in a silicon carbide matrix, preferably the ceramic fibers being silicon carbide or carbon. Preferably, the plug is made of a composite comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0026] Preferably, the stopper is formed from the same material as the container.

[0027] Preferably, the plug provided in step a) comprises at least one recess filled with solder. Advantageously, this guarantees a sufficient supply of solder during soldering, the recess(es) each forming a reservoir of solder which can take the form, for example, of holes filled with solder.

[0028] Preferably, at least a portion of the solder is carried by the plug, the closing step b) being preceded by a step of heating the plug and the solder carried by the plug to a temperature higher than the melting temperature of the solder, preferably at a temperature 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, during which the solder melts, then by a step of solidification of the solder. Preferably, the plug and the solder carried by the plug are placed in a vacuum or neutral gas environment during the heating of the plug and the solder carried by the plug. Preferably, the neutral gas is argon or helium. Preferably, the heating of the plug and the solder carried by the plug is carried out at a temperature lower than or equal to 1850°C, or even at a temperature lower than 1600°C, during the soldering.In the case where the plug is made of sintered monolithic silicon carbide, the heating temperature of the solder may be between 1600°C and 1850°C during soldering. In the case where the plug is made of a composite comprising ceramic fibers incorporated in a silicon carbide matrix, the heating temperature of the solder is preferably less than 1600°C during soldering.

[0029] Advantageously, this prior heating of the plug and the solder carried by the plug distributes the solder evenly over the plug before soldering so as to obtain a good supply of solder during soldering.

[0030] In the case where the plug is a composite comprising ceramic fibers incorporated in a silicon carbide matrix, this prior heating also induces infiltration of the solder in the liquid state, during its melting, into the porosities of the plug. Thus, after the solidification step, the solidified solder covers the surface of the plug and at least partially, or even completely, fills the porosities of the plug. Advantageously, such infiltration of the solder into the plug improves the thermal diffusivity, the sealing and the mechanical strength of the solder-impregnated plug.

[0031] Preferably, the container, the stopper and the solder are placed in an environment under neutral gas or under vacuum during the entirety of the closing step b) or under vacuum during a part of step b) and under neutral gas during the other part of step b), preferably the neutral gas being argon or helium. Advantageously, this limits undesirable reactions during soldering.

[0032] A “vacuum environment” is an environment with a pressure less than 10 1 Pa. The environment may be placed under a higher vacuum, for example with a pressure between 103 Pa and 105 Pa.

[0033] According to a first variant, during step a), the solder is in the form of a solder paste comprising a binder and a solder powder dispersed in the binder. Preferably, the solder 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 an aqueous gel. Preferably, the binder has an evaporation temperature of less than 500°C, or even less than 400°C, preferably close to 300°C. Advantageously, such a solder is non-reactive or only slightly reactive with silicon carbide and therefore does not degrade the mechanical and thermal properties of the container and the cap during the process.

[0034] According to a second variant, during step a), the brazing is in the form of a multitude of solid aggregates. Preferably, the aggregates comprise 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.

[0035] According to a third variant, during step a), the solder 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.

[0036] According to a fourth variant, during step a), the solder is in the form of a coating deposited, prior to step a), on the external periphery of the cap and / or on the internal wall of the container, by physical vapor deposition or by chemical vapor deposition. Such a deposition allows better control of the thickness of the coating. The chemical vapor deposition may be plasma-assisted or may be a deposition of atomic thin layers. 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.

[0037] Preferably, the silicon alloy or silicide is composed 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 atomic % silicon. Preferably, the element is zirconium or chromium. Preferably, the silicon alloy or silicide comprises between 90 and 42 mass % silicon and between 10 and 58 mass % zirconium.

[0038] Preferably, the oxide is chosen from silicon dioxide, alumina, calcium oxide, magnesium oxide and mixtures thereof.

[0039] Preferably, the solder also comprises carbon and / or silicon carbide particles.

[0040] Preferably, during step b), particles of carbon and / or silicon carbide are arranged in powder form in the gap between the container and the stopper.

[0041] Advantageously, the presence of carbon and / or silicon carbide particles in the solder and / or in the clearance between the container and the cap results in the joint formed by solidification of the solder being a composite comprising silicon carbide. In the case where these are silicon carbide particles, the silicide or oxide of the solder infiltrates in the liquid phase, during soldering, between the silicon carbide particles so that the joint formed by solidification of the solder is a composite comprising silicon carbide particles. In the case where these are carbon particles, the silicon alloy or the silicide of the solder powder reacts with the carbon particles, during soldering, so that the joint formed by solidification of the solder comprises silicon carbide.

[0042] Other advantages and characteristics will become more apparent upon reading the detailed description, given for illustrative and non-limiting purposes, with reference to the following figures. Brief description of the drawings

[0043] [Fig-1] [Fig. 1] is a schematic representation in front view of a silicon carbide container comprising an orifice open at one of its ends.

[0044] [Fig.2] [Fig.2] is a schematic representation in front view of the container according to [Fig.l], a stopper being inserted into the orifice.

[0045] [Fig.3] [Fig.3] is a schematic representation in front view of the container according to [Fig.l], a plug being inserted into the orifice and a solder paste being carried by the plug and the container.

[0046] [Fig.4] [Fig.4] is a schematic representation in front view of the container, the cap and the solder paste according to [Fig.3] undergoing localized heating at the end comprising the orifice.

[0047] [Fig.5] [Fig.5] is a schematic representation, seen from the front, of a silicon carbide container comprising an orifice at one of its ends, the orifice being blocked by a plug brazed to the container.

[0048] [Fig.6], [Fig.7] and [Fig.8] Figures 6 to 8 are schematic representations in front view of a plug carrying solder paste.

[0049] [Fig.9] [Fig.9] is a schematic representation in front view of a plug having recesses filled with solder.

[0050] [Fig. 10] [Fig. 10] is a schematic representation in longitudinal section of an example of a device for implementing the method according to the invention, by heating in a localized manner.

[0051] [Fig. 11] [Fig. 11] is a graph representing the measured and simulated changes in the temperature of a container at its orifice and of a susceptor over time during a heating cycle for brazing using the method according to the invention, the graph also representing the change in the electrical power supplying the coil over time during said heating cycle.

[0052] [Fig. 12] [Fig. 12] is a schematic representation in longitudinal section of a mechanical test during which a pushing force is applied to a cap closing the orifice of a container, the closure being obtained by a method according to the present invention.

[0053] [Fig. 13] [Fig. 13] is a graph showing the evolution of the thrust force as a function of the displacement of the load applying the thrust force measured during the mechanical test illustrated by [Fig. 12]. Detailed description

[0054] Figures 1 to 5 illustrate an example of implementation of the method according to the invention. The method comprises a step a) of providing a container 1, a stopper 5 and a solder 6 carried by the container 1 and / or the stopper 5. Figures 1 to 3 represent different sub-steps of an example of implementation of step a).

[0055] An example of a container 1 is illustrated in [Fig. 1]. The container has a cylindrical and hollow shape extending along a longitudinal axis X. It comprises a cavity 2 extending along the longitudinal axis X, for example over a length of between 5 and 400 cm. The cavity 2 is open at one end of the container 1 by an orifice 3, the other end 4 of the container 1 being closed. A solid object is housed in the cavity 2 of the container 1. The orifice 3 may have an opening diameter of between 0.5 and 50 cm. The container 1 is based on silicon carbide, preferably a composite comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0056] [Fig. 2] illustrates the placement of a plug 5 in the cavity 2. The plug 5 is of a shape complementary to the cavity 2 at the orifice 3 so as to be inserted therein with a small clearance, preferably the clearance being less than 100 μm, so that the plug 5 remains immobile when inserted into the orifice 3. It then has a small gap between the wall 7 of the container 1 and the plug 5. The seal formed between the plug 5 and the container 1 at the end of the method according to the invention will then be of small thickness which is mechanically advantageous. For example, the plug 5 is cylindrical of revolution, with a diameter of between 0.4 and 5 cm. Once inserted into the container 1, the plug 5 extends along the longitudinal axis X, for example over a length of between 0.5 and 5 cm. In particular, when the stopper 5 is inserted into the container 1, it occupies between 0.1 and 10% of the length of the cavity 2, measured along the longitudinal axis X.The plug 5 is based on silicon carbide, preferably a composite comprising silicon carbide fibers incorporated in a silicon carbide matrix.

[0057] Then, the solder 6 is deposited, in the form of a paste, on the plug 5 and / or on the wall 7. [Fig. 3] illustrates the container 1 with the plug 5 inserted in the orifice 3 and the solder paste 6 deposited on the plug 5 and on the wall 7. The present invention is not limited to a solder 6 deposited in the form of a paste, other forms of solder and methods of deposition are conceivable, for example the solder can be in the form of a multitude of granules or a sheet or a coating as described previously.

[0058] Step a) is followed by a step b) of closing the orifice 3 by brazing the plug 5 onto the container 1. For this, heating is carried out in a localized manner at the orifice 3 so as to heat the plug 5, the wall 7 close to the orifice 3 and the solder 6 to a temperature above 1250°C, or even above 1300°C, or even above 1400°C. [Fig. 4] illustrates said localized heating, the flashes 8 symbolizing the targeted supply of heat. The localized heating melts the solder 6 which infiltrates into the gap between the plug 5 and the wall 7. The melting and infiltration of the solder 6 is symbolized by arrows 9. In the case where the container 1 and / or the cap 5 are made of a composite comprising ceramic fibers incorporated in a silicon carbide matrix, then the solder 6 infiltrates into the porosities of the container 1 and / or the cap 5.

[0059] During localized heating, a part of the cavity 2, called the cold part 23, at a distance from the heating zone is maintained at a temperature below 800°C. The cold part 23 extends over at least 70% of the length of the cavity 2 along the longitudinal axis X. In particular, the cold part 23 corresponds to the whole of the cavity 2 at a distance of at least 1 cm, preferably at least 5 mm, preferably at least 2 mm, from the plug 5 inserted into the orifice 3.

[0060] After heating, the plug 5, the container 1 and the solder 6 are cooled. The solder 6 is solidified during its cooling, thus forming a solid seal 10 between the plug 5 and the wall 7, as shown in [Fig. 5]. The orifice 3 is thus blocked by the plug 5 fixed to the container 1 by soldering.

[0061] According to another example of implementation, the plug 5 provided in step a) carries at least a part of the solder 6 before its insertion into the container 1. Then, the plug 5 is inserted with the solder 6 into the orifice 3. Step b) of closing the orifice 3 follows.

[0062] Figures 6, 7 and 8 illustrate different methods of depositing the solder 6 on the plug 5. For example, the solder 6 can be deposited on and carried by the lateral surface of the plug 5, the bases of the plug 5 not being covered with the solder 6, as illustrated in [Fig. 6]. Alternatively, the solder 6 can be deposited on and carried by the lateral surface of the plug 5 and the upper base of the plug 5, as illustrated in [Fig. 7]. Alternatively, the solder 6 can be deposited on and carried by the upper base of the plug 5, the lateral surface of the plug 5 not being covered with solder 6, as illustrated in [Fig. 8].

[0063] Furthermore, the plug 5 may also comprise at least one recess 31 filled with solder 6, as illustrated in [Fig. 9]. The recesses 31 thus form solder reservoirs 6 which increases the supply of solder 6 during the soldering of step b). For example, the recesses 31 may be blind holes dug in the side wall of the plug 5. The recess(es) 31 may also be radial grooves or grooves.

[0064] Prior to the insertion of the plug 5 and to step b), the solder 6 carried by the plug 5 can be heated to a temperature above its melting temperature. The solder 6 then flows so as to cover at least the lateral surface of the plug 5, or even the entire plug 5. The heating can be carried out in a furnace, preferably under secondary vacuum or under neutral gas, the neutral gas preferably being argon or helium. Then, a solidification of the solder 6 by cooling is carried out after said heating. Thus, the solidified solder 6 is uniformly distributed over the cap 5 ensuring a good supply of solder 6 when soldering cap 5 to container 1.

[0065] In the case where the plug 5 is made of a composite comprising ceramic fibers incorporated in a silicon carbide matrix, this prior heating induces infiltration of the solder into the porosities of the plug 5, followed by solidification upon cooling. Such infiltration improves the thermal diffusivity, the sealing and the mechanical strength of the plug 5 impregnated with solder 6.

[0066] The inventors carried out tensile tests at room temperature in order to compare the differences in mechanical behavior between a tensile specimen not impregnated with brazing 6 and a tensile specimen whose porosities were infiltrated by brazing 6. The tensile specimens were all made of a composite comprising silicon carbide fibers in a silicon carbide matrix. The tensile specimens were cylindrical specimens with a length equal to 75 mm and a central section with a diameter equal to 9.50 mm. The brazing 6 used was in the form of a paste comprising a powder, consisting of a silicon alloy composed of 88% by mass of silicon and 12% by mass of zirconium, mixed with an aqueous gel as a binder. During tensile tests, a breaking stress of the order of 240 MPa for a deformation of the order of 0.8 to 0.9% was measured for the non-impregnated tensile specimen.A breaking stress of the order of 280 MPa for a deformation greater than 1.1% was measured for the tensile specimen whose porosities were infiltrated by brazing 6. These tensile tests therefore show a significant improvement in the mechanical strength of the tensile specimen when it is impregnated with brazing 6.

[0067] If the solder 6 is not distributed sufficiently uniformly on the plug 5 after heating, an additional deposit of solder 6 on the plug 5, in particular on the areas lacking solder 6, can be carried out. This deposit is preferably followed by additional heating of the plug 5 and the solder 6 carried by the plug 5 similarly to the previous paragraph. If necessary, this additional deposit advantageously fills the disparities in the coverage of the solder 6 on the plug 5 caused by the infiltration of the solder 6 into the porosities of the plug 5.

[0068] Machining may be carried out after the solder 6 has solidified on the plug 5 in order to reduce the roughness formed by the solder 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 latter has few, if any, roughnesses on its surface facing the object housed in the cavity. In the case where the solder 6 was in the form of a coating deposited, prior to step a), by physical vapor deposition, or chemical vapor deposition, it is not interesting to carry out the aforementioned machining because the roughness is negligible.

[0069] Furthermore, the container 1 provided in step a) may also carry at least a portion of the solder 6 before the insertion of the plug 5 therein. In particular, the solder 6 may cover the portion of the wall 7 onto which the plug 5 will be soldered.

[0070] [Fig. 10] illustrates a device 11 configured to carry out the heating of the brazing of step b) of the method according to the present invention. The device 11 comprises a hermetic enclosure 12 for housing the container 1 with the stopper 5 inserted in the orifice 3 and the brazing 6 carried by the stopper 5 and / or the container 1. Preferably, the enclosure 2 is a quartz tube.

[0071] A supply conduit 13 opens into the enclosure 12. The supply conduit 13 is adapted to inject a neutral gas into the enclosure 12. The neutral gas may be argon or helium. The device 11 comprises an evacuation conduit 14 for evacuating the gases present in the enclosure 12. This conduit 14 may also allow a vacuum to be created in the enclosure 12. Preferably, the supply conduit 13 and the evacuation conduit 14 are configured so that the neutral gas circulates continuously in the enclosure 12.

[0072] The device 11 also comprises a coil 16 comprising at least one turn around the enclosure 12. Preferably, the turn(s) are made of copper. The coil 16 is electrically connected to a high-frequency generator 17. A susceptor 18 is housed in the enclosure 12 and encircled by the coil 16. Preferably, the susceptor 18 is made of graphite. The susceptor 18 comprises a central passage for receiving the container 1 housed in the enclosure 12, the susceptor 18 then surrounding the container 1 at the orifice 3 and the cap 5. Preferably, the coil 16 and the susceptor 18 are concentric so that the central passage of the susceptor 18 is centered in the middle of the coil 16.

[0073] 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 passage in which the container 1 is inserted, so that the cooling system 19 is opposite the cold part 23 over its entire length. Preferably, the cooling system 19 comprises a fluid circuit winding around the passage receiving the container 1, a cooling fluid, preferably water, being intended to circulate in the fluid circuit. Preferably, the channels 22 of the fluid circuit are made of copper or brass.

[0074] It is not necessary for the cooling system 19 to extend over the entire length of the cold portion 23. The cold portion 23 may comprise a portion remote from the heating zone so that it is not significantly affected. by heating during step b), i.e. it would remain at room temperature even without cooling. Where appropriate, it is not necessary for the cooling system 19 to extend along the aforementioned remote portion. Furthermore, a first thermal insulator 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 thermal insulator 20 is made of insulating graphite, for example fibrous graphite. In addition, a second thermal insulator 21 is arranged between the first thermal insulator 20 and the cooling system 19. The second thermal insulator 21 may be made of oxide, for example alumina.

[0075] The heating carried out by the device 11 is a localized and inductive heating. First of all, the container 1 is placed in the enclosure 12 with the plug 5 inserted in the orifice 3 and the solder 6 carried by the plug 5 and / or by the container 1. Once the container 1 is placed, the susceptor 18 surrounds the wall 7 at the orifice 3, the plug 5 and the solder 6, and the cooling system 19 extends along the cold part 23.

[0076] Then, the neutral gas is injected into the enclosure 12. A vacuum can be created in the enclosure 12 prior to the injection of the neutral gas. Preferably, the injection of the neutral gas is such that the enclosure 12 is at atmospheric pressure. Preferably, the neutral gas is injected through the supply conduit 13 and then discharged through the discharge conduit 14 so as to maintain a continuous circulation of the neutral gas in the enclosure 12. The direction of circulation of the neutral gas in the enclosure 12 is represented by the arrows 15.

[0077] Subsequently, the cooling system 19 is started to cool the cold part 23. In particular, a cooling fluid, preferably water, can be circulated in the fluid circuit.

[0078] Then, the high-frequency generator 17 electrically powers the coil 16 which then generates a magnetic field. The susceptor 18 converts the energy of the magnetic field into heat by induction, which heats by conduction and in a localized manner the wall 7 of the container 1 at its orifice 3, the cap 5 and the solder 6. The electrical power supplied by the high-frequency generator 17 is progressively increased so as to gradually raise 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 and second thermal insulators 20 and 21 confine the heat produced by the susceptor 18 at the soldering zone of the cap 5 on the container 1 which thus improves the localization of the heating. The cooling system 19 continuously cools, during heating, the cold part 23, which is maintained at a temperature below 800°C.

[0079] Thus, the device 11 illustrated in [Fig. 10] makes it possible to carry out step b) of closing the orifice 3 by brazing the plug 5 onto the container 1. The device 11 locally heats by induction the solder 6 carried by the plug 5 and / or by the container 1 and melts said solder 6 to braze the plug 5 onto the container 1. In addition, the device 11 keeps the cold part 23 at a low temperature during heating. The low temperature is maintained by thermal insulation between the cold part 23 and the brazing zone of the plug 5 onto the container 1 and by cooling the cold part 23 by the cooling system 19.

[0080] The inventors carried out simulations and measurements in order to determine the evolution over time of the temperatures involved during brazing of the method according to the present invention. For this, the device 11 comprises a pyrometer 24 measuring the temperature of the susceptor 18 and the temperature of the container 1 at the orifice 3. The device 11 also comprises a thermocouple, not shown here, measuring the temperature of the susceptor 18 and the temperature of the container 1 at the orifice 3. The measurements carried out by the pyrometer 24 were compared with the measurements carried out by the thermocouple. The results of these simulations and these measurements are illustrated in [Fig.l 1]. The simulations and measurements were carried out for a heating cycle during which the average electrical power supplying the coil 16 reaches a first level at 15 kW for 10 minutes and then a second level at 17 kW for 10 minutes.Curve 25 represents the evolution of the average electrical power supplying the coil 16 during the heating cycle.

[0081] Curve 26 represents the evolution of the simulated temperature of the susceptor 18 during the heating cycle. Curve 27 represents the evolution 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 stage and then a temperature of 1620°C during the second stage.

[0082] Curve 28 represents the evolution of the simulated temperature of the container 1 at the orifice 3 during the heating cycle. It shows that the temperature of the container 1 at the orifice 3 reaches a temperature of 1300°C during the first stage and then a temperature of 1420°C during the second stage. Curve 29 represents the evolution of the measured temperature of the container 1 at the orifice 3 during the heating cycle. Curve 29 shows that the temperature of the container 1 at the orifice 3 reaches a temperature of 1320°C during the first stage and then a temperature of 1480°C during the second stage. Also, the simulated or measured temperature of the container 1 at the orifice 3 during each of the first and second stages is greater than or equal to 1300°C, as desired for the brazing of step b) of the method according to the invention.

[0083] The inventors also simulated the evolution of the temperature of the cold part 23 during the heating cycle described above. The maximum temperature of the cold part 23 obtained by this simulation is 725°C. This temperature is therefore well below 800°C.

[0084] The inventors tested the mechanical strength of a closure obtained according to the present invention. For this, they closed a container 1 using the method according to the present invention. The container 1 and the cap 5 provided were made of a composite comprising silicon carbide fibers incorporated in a silicon carbide matrix. The brazing agent 6 used was in the form of a paste comprising a powder, consisting of a silicon alloy composed of 88.5% by mass of silicon and 11.5% by mass of zirconium, mixed with an aqueous gel, for example the gel called “Vitta Braz-Binder Gel Grade ST” or the cement “Nicrobraz” commercially available, as binders. Approximately 400 mg of the brazing agent paste 6 was deposited on the cap 5.Then the plug 5 and the solder paste 6 carried by the plug were heated under argon in a soldering furnace at 1420°C so as to melt the solder 6 which completely covered the plug 5 and filled a recess dug in the plug 5. The solder 6 carried by the plug 5 was then solidified by cooling and machining was carried out to remove the asperities formed by the solder 6 on the plug 5 and likely to hinder the insertion of the plug 5 into the container 1. Subsequently, the plug 5 was soldered onto the container 1 to close the orifice 3 of the container 1. The soldering was carried out in the device 11 illustrated in [Fig. 10] as explained previously. The brazing included heating the wall 7 of the container 1 at its orifice 3, the cap 5 and the brazing 6 to a temperature of 1420°C for 10 minutes followed by gradual cooling of the brazing 6.

[0085] 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, as illustrated by [Fig. 12]. This mechanical test comprises the application of a thrust force F on the cap 5 using a piston 32 in order to generate a shear stress on the seal 10 between the cap 5 and the wall 7, the container 1 being carried by a frame 33 during the mechanical test.

[0086] The result of this mechanical test is illustrated in [Fig. 13]. Curve 30 represents the thrust force F as a function of the displacement of the piston 32 during this mechanical test. The maximum thrust force applied before rupture of the closure 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 rupture did not occur on the seal 10 but it is the wall 7 of the container 1 beyond the seal 10 which has broken. Thus, the seal 10 formed by the method according to the present invention is stronger than the container 1.

[0087] Other variants and improvements may be envisaged without departing from the scope of the invention as defined by the claims below.

Claims

Claims

1. A method of closing an orifice of a container, the method comprising the following successive steps: a) providing a container (1) based on silicon carbide comprising a cavity (2) opened by an orifice (3), a plug (5) based on silicon carbide and a solder (6) carried by the plug and / or the container, a solid object being housed in the cavity, b) closing the orifice by soldering the plug to the container, the soldering comprising melting the solder by heating to a temperature above the melting temperature of the solder, followed by solidification of the solder so as to form a solid joint (10) between the container and the plug, at least a part of the cavity, called the cold part (23), in which the solid object is housed, being maintained at a temperature below the degradation temperature of the solid object during the soldering,the brazing comprising cooling the cold part by a cooling system (19) extending along at least a portion of the cold part, said portion comprising the end of the cold part adjacent to the brazing heating zone.,

2. A method according to claim 1, the solid object comprising at least one nuclear fuel pellet.

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

4. Method according to the preceding claim, the container being of hollow cylindrical shape, one of the ends of the cylinder being open by the orifice, the end (4) of the cylinder opposite the orifice being closed.

5. Method according to one of the preceding claims, the cold part representing at least 70%, or even at least 80%, or even at least 90%, of the volume of the cavity.

6. Method according to one of the preceding claims, the distance between the plug and the cold part during brazing being less than or equal to 10 mm, preferably less than 5 mm, preferably between 2 and 5 mm.

7. Method according to one of the preceding claims, the heating being carried out by induction of a susceptor (18) arranged near the orifice, preferably at least one thermal insulator (20, 21) being arranged between the susceptor and the cold part of the cavity.

8. Method according to one of the preceding claims, the solder being heated to a temperature 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, during the soldering.

9. Method according to one of the preceding claims, the solder being heated to a temperature less than or equal to 1850°C, or even less than 1600°C, during the soldering.

10. Method according to one of the preceding claims, the cooling system comprising a fluid circuit in which a cooling fluid circulates during brazing.

11. Method according to one of the preceding claims, the plug being made of sintered monolithic silicon carbide or of a composite comprising ceramic fibers incorporated in a silicon carbide matrix, preferably the ceramic fibers being made of silicon carbide or carbon.

12. Method according to one of the preceding claims, the plug provided in step a) comprising a recess (31) filled with the solder.

13. Method according to one of the preceding claims, at least part of the solder being carried by the plug, the closing step b) being preceded by a step of heating the plug and the solder carried by the plug to a temperature higher than the melting temperature of the solder, preferably at a temperature 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, during which the solder melts, then by a step of solidification of the solder.

14. Method according to one of the preceding claims, the container, the stopper and the solder being placed in a vacuum or neutral gas environment during the entirety of the closing step b), or in a vacuum during part of step b) and in a neutral gas during the other part of step b), preferably the neutral gas being argon or helium.

15. Method according to one of the preceding claims, during step a), the solder being in the form of a solder paste comprising a binder and a solder powder dispersed in the binder, preferably the solder powder 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. Method according to one of claims 1 to 14, during step a), the brazing being in the form of a multitude of solid aggregates, preferably the aggregates 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.

17. Method according to one of claims 1 to 14, during step a), the solder being in the form of at least one sheet wrapped around the plug, preferably the sheet 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. Method according to one of claims 1 to 14, during step a), the solder being in the form of a coating deposited, prior to step a), on the external periphery of the cap and / or on the internal wall of the container, by physical vapor deposition or by chemical vapor deposition, preferably the coating 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.

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