Method of manufacturing end plugs for fuel elements

Abstract

The invention relates to a method of manufacturing end plugs for fuel elements. The invention provides a method of manufacturing end plugs for sealing composite tubular ceramic cladding of nuclear reactor fuel elements. The end plugs are manufactured on the basis of β-SiC and consist of two or three parts in the form of coaxial cylinders with different diameters. The diameter of the first part is equal to the outer diameter of the cladding. The diameter of the second part is 0.06-0.08 mm smaller than the inner diameter of the cladding. The diameter of the third part is 2-3 mm smaller than the inner diameter of the cladding. The method for manufacturing the end plugs includes preparing a powder mixture on the basis of β-SiC, AI2O3, Y2O3, taken in certain amounts and having certain particle sizes. The powder mixture is hot-pressed in a die unit using an upper punch and sintered at a temperature of 1850 ο °C in an inert gas atmosphere or in vacuum at a pressure of 0.1 MPa, the sintering mode being maintained for 120 minutes. The finished end plugs are demoulded from each die unit. The invention ensures improvement of the mechanical and thermophysical properties of the end plugs.

Description

[0001] This invention relates to the field of nuclear power engineering and can be used to manufacture end plugs for composite tubular ceramic cladding based on silicon carbide and designed to seal fuel elements.

[0002] The operational reliability of fuel elements is primarily determined by the quality of the connection provided between the cladding and the end plug.

[0003] When the internal volume of the fuel element is filled with an inert gas at a pressure up to 2.53 MPa, the connection should be hermetically sealed. Various methods are used to generate such pressure and seal the fuel element after it has been filled with gas.

[0004] The filling of the internal volume with gas and sealing of fuel elements made of zirconium alloy for water-moderated water-cooled reactors (VVERs) is carried out in a single cycle in a welding machine. The process flow and plug shape are presented in the book "Development, manufacture and operation of powerreactor fuel elements", ed. by Reshetnikov FG, Book 2, Energoizdat, 1995.

[0005] Furthermore, fuel elements for nuclear VVERs and methods for their manufacture are known in the art (see: Patent RU2481654, IPC G21C 3 / 00, published on 10.05.2013). This invention relates to nuclear power engineering and can be used to manufacture fuel elements primarily for nuclear VVERs. The tube cladding of the fuel element is made of alternating layers of nanocrystalline silicon carbide and separating layers of high-temperature materials that are structurally mismatched with silicon carbide; and the plugs at both ends of the tube are made of silicon carbide to prevent gas from passing through the end plugs. The method for manufacturing such a fuel element is based on heating graphite rods to temperatures ranging from 1300°C to 1600°C in a gas mixture corresponding to the tube layer material, and alternately replacing the mixture to form the next layer of the tube. To form the nanocrystalline silicon carbide layer, a gas mixture comprising hydrates and chlorides of Si and C is used.

[0006] The known disadvantages of the device are:

[0007] 1) Environmental risks, due to the formation of gaseous hydrogen chloride which is harmful to the environment, because the method uses a gas mixture including chlorine and hydrogen to form nanocrystalline silicon carbide layers.

[0008] 2) The patent specification lacks comprehensive data on the materials used to form the plug and the composition of the plug produced by the method.

[0009] Nuclear reactor fuel rods and fuel assemblies are known in the art (Patent EP 3226247, IPC G21C 3 / 10, G21C 3 / 06; published on 04.10.2017); the object of this invention is to provide nuclear reactor fuel rods in which SiC material is used as the material for the fuel cladding tube and end plug. Airtightness, heat resistance, and corrosion resistance are provided at the joint between the fuel cladding tube and the end plug. The nuclear reactor fuel rods are bundled into fuel assemblies. According to this invention, the nuclear reactor fuel rods are fuel rods for light water reactors. The nuclear reactor fuel rods include a fuel cladding tube and an end plug, both formed of silicon carbide material. The joint between the fuel cladding tube and the end plug is formed by brazing with an inserted predetermined metal bonding material and / or by diffusion bonding. The predetermined metal bonding material has a solidus temperature of 1200°C or higher. The outer surface of the joint and the portion of the outer surface of the fuel cladding tube and end plug adjacent to the outer surface of the joint are covered by a joint coating formed of a predetermined coating metal.

[0010] The drawback of this device is that the method for manufacturing the plug and the materials used to manufacture it are not disclosed; therefore, the manufacturability level and mechanical and thermophysical properties of the end plugs produced by this method cannot be assessed.

[0011] Methods for manufacturing SiC elements for nuclear fuel rods are known in the art (Patent GB 2553090, IPC G21C3 / 07, G21C 3 / 10, G21C 21 / 02; published on 28.02.2018). Such methods may include producing a SiC tube and SiC sealing devices (plugs) for one or both ends of the tube. The sealing device may provide an hermetically tight seal between the element on the end plug (in a cap shape) and a bonding intermediate material (such as titanium foil or silicon carbide slurry). Sealing methods may include applying current and pressure, for example using spark plasma sintering (SPS) or field-assisted sintering (FAST) technology. The plug may have a conical or truncated cone shape, and the element on the end plug may be formed into two semi-cylindrical portions. The tube may be rotated during the bonding process.

[0012] The disadvantage of this device is:

[0013] 1) The proposed end plug structure does not conform to the existing structure of typical plugs used to seal the tubes (cladding) of fuel rods used in VVER reactors. Therefore, it is not feasible to use this type of end plug as a replacement for existing plugs, as their use may lead to interference with coolant flow and may affect the heat transfer characteristics of fuel elements and fuel assemblies;

[0014] 2) The patent does not provide a method for manufacturing the plug or the materials used to manufacture the plug: therefore, it is impossible to assess the manufacturability level and mechanical and thermophysical properties of the end plug produced by the method.

[0015] Nuclear fuel rods are known in the art (US Patent Application 2017372802, IPC G21C3 / 10, G21C3 / 07; published 28.12.2017). The gland sealing end plug closure for nuclear fuel rod cladding is made of silicon carbide or other non-weldable materials. The sealant is preferably made of one or more forms of pure graphite, and the plunger, seat, and other components of the gland sealing end plug are formed of high-temperature metal or ceramic materials.

[0016] The disadvantage of this device is:

[0017] 1) The proposed end plug structure does not conform to the existing structure of typical plugs used to seal the tubes of fuel elements used in VVER-type reactors. Therefore, it is not feasible to use this type of end plug as a replacement for existing plugs, as their use may cause interference with coolant flow and may affect the heat transfer characteristics of fuel elements and fuel assemblies;

[0018] 2) The proposed structure of the end plug is technically complex, which may lead to defects in the fuel line containing fuel, since the process of sealing with the end plug is carried out in the final stage of assembling the fuel element.

[0019] The closest analogue considered to be the prototype is the fuel assembly and its manufacturing method (Patent JP 2012-233734, IPC G21C 21 / 02, published on 29.11.2012). This prototype aims to provide a fuel tube cladding assembly with corrosion resistance, radiation resistance, bonding strength, etc., under elevated temperatures and pressures in a reactor. The patent proposes end plugs made of a composite material reinforced with silicon carbide fibers.

[0020] The disadvantages of this device are: technical complexity, multi-stage manufacturing, and a large number of components with various configurations.

[0021] The technical objective of this invention is to develop the structure and manufacturing method of a SiC-based end plug for sealing fuel elements made of silicon carbide-based composite materials.

[0022] The technical effects of this invention are:

[0023] -For environmental safety,

[0024] - The possibility of using the developed end plug as a replacement for the plugs used in various reactors.

[0025] - The method for manufacturing end plugs has been simplified.

[0026] - Improvements in the mechanical and thermophysical properties of the end plug.

[0027] The essence of the proposed invention is that the end plug of the composite tubular ceramic cladding for sealing nuclear reactor fuel elements, according to a first variation, is made of β-SiC and consists of two parts in the form of two coaxial cylinders of different diameters. The first part of the end plug is located outside the cladding and is tail-shaped, configured to be mounted (assembled) to and fixed thereto on the end of the cladding to form a collar—a necessary protrusion—on the support portion. The second part of the end plug is configured to be disposed inside the cladding. The end of the cladding is made straight.

[0028] The diameter of the first portion of the end plug is equal to the outer diameter of the cladding. The diameter of the second portion of the end plug is 0.06-0.08 mm smaller than the inner diameter of the cladding so that the paste solder can be inserted into the gap therebetween. The paste solder is applied before assembly for brazing, and the capillary gap is required for brazing the end plug and the SiC cladding.

[0029] According to the second variant, the end plug of the composite tubular ceramic cladding for sealing nuclear reactor fuel elements is made of β-SiC and consists of two parts in the form of two coaxial cylinders of different diameters. The first part of the end plug is located outside the cladding and is tail-shaped, configured to be mounted (assembled) to and fixed thereto on the end of the cladding to form a collar—a necessary protrusion—on the support portion. The second part of the end plug is configured to be disposed inside the cladding. The end of the cladding is made straight.

[0030] The diameter of the first portion of the end plug is equal to the outer diameter of the cladding. The diameter of the second portion of the end plug is 2-3 mm smaller than the inner diameter of the cladding so that the foil solder can be inserted into the gap therebetween. The foil solder is arranged for brazing before assembly, and the capillary gap is required for brazing the end plug and the SiC cladding.

[0031] The end plug of the composite tubular ceramic cladding for sealing nuclear reactor fuel elements, according to the third variant, is made of β-SiC and consists of three parts in the form of three continuous cylinders of different diameters arranged coaxially. The first part of the end plug is located outside the cladding and is tail-shaped, configured to be mounted (assembled) to and fixed thereto on the end of the cladding to form a collar—a necessary protrusion—on the support portion. The second and third parts of the end plug are configured to be arranged inside the cladding and can be used to insert brazing filler metal into the gap between them and the cladding. The third part of the end plug is formed in the form of a groove or slot for inserting additional brazing filler metal. The cladding end is made straight.

[0032] The diameter of the first part of the end plug is equal to the outer diameter of the casing. The diameter of the second part of the end plug is 0.06-0.08 mm smaller than the inner diameter of the casing to allow for the insertion of paste solder. The diameter of the third part of the end plug is 2-3 mm smaller than the inner diameter of the casing to allow for the insertion of additional foil solder.

[0033] Therefore, the third variation of the end plug manufacturing process has two areas for simultaneously arranging two types of brazing filler metal—paste and foil. The paste and foil filler metals are arranged for brazing prior to assembly.

[0034] According to the first variant, a method for manufacturing end plugs for sealing composite tubular ceramic cladding of nuclear reactor fuel elements includes: preparing a silicon carbide-based powder mixture, hot-pressing the powder mixture, sintering it to produce end plugs of a predefined shape, and demolding the finished end plugs.

[0035] A powder mixture was prepared from β-SiC powder, Al2O3 powder, and Y2O3 powder. For this purpose, β-SiC powder was pulverized to produce 0.95 and 5.19 micrometer particles; then Al2O3 powder with 1.52 micrometer particles and Y2O3 powder with 1.01 micrometer particles were added. The content of the substances, in wt%, was as follows: β-SiC with 0.95 micrometer particles - 10.59%, β-SiC with 5.19 micrometer particles - 77.91%, Al2O3 with 1.52 micrometer particles - 10.0%, and Y2O3 with 1.01 micrometer particles - balance.

[0036] The composition of this powder mixture was selected based on the state diagram of the Al2O3-Y2O3 system.

[0037] After the powder mixture is prepared, a planetary ball mill can be used to mix the powder evenly.

[0038] The powder mixture is hot-pressed using specific tools (upper and lower punches and a die with units), the shape and size of which correspond to any of the three variations of end caps described above. A parallelepiped die with equal through-cylindrical units of the desired shape and cylindrical upper and lower punches are used. The lower punch is positioned below each unit on the lower side of the die, and the upper punch is positioned above each unit on the upper side of the die, allowing for movement of them into the die unit cavities.

[0039] Before hot pressing, the mold and punch can be annealed in a vacuum compression furnace. Possible variations of annealing may involve heating the mold and punch to a temperature of 200°C in a vacuum compression furnace, annealing for 60 minutes, cooling to room temperature at a rate not exceeding 50°C / hour, holding at room temperature for at least 12 hours, and maintaining the pressure in the chamber of the vacuum compression furnace at a level not exceeding 1 Pa.

[0040] For hot pressing, the powder mixture is loaded into the die unit cavity onto the lower punch, and the upper punch is placed in the die unit above the powder mixture; then the powder mixture is held at 1 Pa pressure without heating for more than 12 hours, pressed in the die unit using the upper punch, and pressed at 1850°C. ο Sintering is carried out at a temperature of C in an inert gas atmosphere or in a vacuum at a pressure of 0.1 MPa, with a pressing force of 22-25 MPa for each end plug. The sintering mode is maintained for 120 minutes. The finished end plugs are then demolded from each mold unit.

[0041] When developing this method, the average size was 5.19 micrometers (r). п SiC particles (approximately 2.595 micrometers in diameter) are considered the main component (part) in the powder preparation. The powder amounts of the second, third, and fourth components are calculated using the data shown in Table 1.

[0042] Table 1. Calculation data for filling the gaps between particles of radius α with smaller particles.

[0043]

[0044]

[0045] Furthermore, when developing a method for selecting the composition of the powder mixture, the amounts of the second components—SiC, Al2O3, and Y2O3—of the pulverized SiC are calculated relative to the initial silicon carbide. The radii of the pulverized powder, as shown in Table 1, correspond to the values ​​of the second, third, and fourth components. Considering that the relative amount of the main component of the initial SiC is 77.91 wt%, the composition of the powder mixture according to the first variant will be as shown in Table 2.

[0046] Table 2. Composition of the powder mixture according to the first variant.

[0047]

[0048] According to the second variant, a method for manufacturing end plugs for sealing composite tubular ceramic cladding of nuclear reactor fuel elements includes: preparing a silicon carbide-based powder mixture, hot-pressing the powder mixture, sintering it to produce end plugs of a predefined shape, and demolding the finished end plugs.

[0049] A powder mixture was prepared from β-SiC powder, Al2O3 powder, and Y2O3 powder. For this purpose, β-SiC powder was pulverized to produce 0.95 and 5.19 micrometer particles; then Al2O3 powder with 1.52 micrometer particles and Y2O3 powder with 1.01 micrometer particles were added. The content of the substances, in wt%, was as follows: β-SiC with 0.95 micrometer particles - 10.78%, β-SiC with 5.19 micrometer particles - 79.22%, Al2O3 with 1.52 micrometer particles - 6.0%, and Y2O3 with 1.01 micrometer particles - balance.

[0050] The composition of this powder mixture was selected based on the state diagram of the Al2O3-Y2O3 system.

[0051] After the powder mixture is prepared, a planetary ball mill can be used to mix the powder evenly.

[0052] The powder mixture is hot-pressed using specific tools (upper and lower punches and a die with units), the shape and size of which correspond to any of the three variations of end caps described above. A parallelepiped die with equal through-cylindrical units of the desired shape and cylindrical upper and lower punches are used. The lower punch is positioned below each unit on the lower side of the die, and the upper punch is positioned above each unit on the upper side of the die, allowing for movement of them into the die unit cavities.

[0053] Before hot pressing, the mold and punch can be annealed in a vacuum compression furnace. Possible variations of annealing may involve heating the mold and punch to a temperature of 200°C in a vacuum compression furnace, annealing for 60 minutes, cooling to room temperature at a rate not exceeding 50°C / hour, holding at room temperature for at least 12 hours, and maintaining the pressure in the chamber of the vacuum compression furnace at a level not exceeding 1 Pa.

[0054] For hot pressing, the powder mixture is loaded into the die unit cavity onto the lower punch, and the upper punch is placed in the die unit above the powder mixture; then the powder mixture is held at 1 Pa pressure without heating for more than 12 hours, pressed in the die unit using the upper punch, and pressed at 1850°C. ο Sintering is carried out at a temperature of C in an inert gas atmosphere or in a vacuum at a pressure of 0.1 MPa, with a pressing force of 22-25 MPa for each end plug. The sintering mode is maintained for 120 minutes. The finished end plugs are then demolded from each mold unit.

[0055] When developing this method, the average size was 5.19 micrometers (r). п SiC particles (approximately 2.595 micrometers in diameter) are considered the main component in the powder preparation. The data shown in Table 1 above are used to calculate the powder amounts of the second, third, and fourth components.

[0056] Furthermore, when developing a method for selecting the composition of the powder mixture, the amounts of the second components—SiC, Al2O3, and Y2O3—of the pulverized SiC are calculated relative to the initial silicon carbide. The radii of the pulverized powder, as shown in Table 1, correspond to the values ​​of the second, third, and fourth components. Considering that the relative amount of the main component of the initial SiC is 79.22 wt%, the powder mixture composition according to the first variant will be as shown in Table 4.

[0057] Table 4. Composition of the powder mixture according to the second variant.

[0058]

[0059] The present invention is illustrated by the following figures.

[0060] Figure 1 A longitudinal section of the end plug structure according to the first variant is shown, wherein: 1-first part of the end plug; 2-second part of the end plug.

[0061] Figure 2 A longitudinal section of the end plug structure according to the second variant is shown, wherein: 3 - the first part of the end plug; 4 - the second part of the end plug.

[0062] Figure 3 A longitudinal section of the end plug structure according to the third variant is shown, wherein: 5 - the first part of the end plug; 6 - the second part of the end plug; 7 - the third part of the end plug.

[0063] Figure 4 A full view of a tube with a fuel element having an end plug according to a first variant is shown, wherein: 1-first portion of the end plug; 2-second portion of the end plug; 8-fuel element casing.

[0064] Figure 5 A full view of a tube with a fuel element having an end plug according to a second variant is shown, wherein: 3 - first part of the end plug; 4 - second part of the end plug; 8 - fuel element casing.

[0065] Figure 6 A full view of a tube with a fuel element having an end plug according to a third variant is shown, wherein: 5 - first part of the end plug; 6 - second part of the end plug; 7 - third part of the end plug; 8 - fuel element casing.

[0066] Figure 7 A top view of a mold for pressing plugs according to the first, second and third variations is shown, where: 9 - unit, 10 - mold.

[0067] Figure 8 A cross-sectional view AA of the mold used for pressing plugs according to the first and second variations is shown, where: 9 - unit, 10 - mold.

[0068] Figure 9 A cross-sectional view AA of the mold used for pressing the plug according to the third variant is shown, where: 9 - element, 10 - mold.

[0069] Figure 10 An external view of a die with a unit and an upper punch is shown, where: 9 - unit, 10 - die, 11 - upper punch.

[0070] Figure 11 The state diagram of the Al2O3-Y2O3 system is shown.

[0071] Figure 12 A photograph of a sample arranged in a furnace is shown.

[0072] Exemplary implementations are described below.

[0073] Example 1 - End plug of a composite tubular ceramic cladding for sealing nuclear reactor fuel elements according to a first variant.

[0074] The end plug intended for use with the fuel element casing 8 is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters – part 1 and part 2; see also Figure 1 and 4 For illustrative purposes, Figure 4 The fuel element cladding in fuel cells is typically shown as transparent.

[0075] The second part 2 of the end plug is configured to be arranged inside the fuel element housing 8; the first part 1, namely the collar in the form of a cylinder with a larger diameter—the tail, is configured to be arranged outside the fuel element housing 8.

[0076] The fuel element housing 8 has an inner diameter of 7.72 mm and an outer diameter of 9.1 mm. The height of the second part of the end plug within the mating area is b2 = 10 mm, and the length of the first part 1 of the end plug is b1 = 7 mm. The diameter d1 of the second part 2 of the end plug is made 0.06 mm smaller than the inner diameter of the fuel element housing for the purpose of inserting the solder in the form of paste, and is equal to 7.66 mm. The diameter D of the first part 1 of the end plug is equal to the outer diameter of the fuel element housing minus 9.1 mm.

[0077] The diameter d1 of the second part 2 of the end plug, which is 0.06 mm smaller than the inner diameter of the fuel element casing, is determined by the thickness of the paste-like brazing filler layer that should be applied before assembly for brazing.

[0078] A paste-like brazing filler metal is applied before assembly to facilitate brazing; this capillary gap is necessary for brazing silicon carbide-based end plugs and cladding. Figure 4A full view of the fuel element casing 8 and the end plug consisting of a first part 1 and a second part 2 is shown, the surface of the second part 2 of the end plug being where the paste solder is applied.

[0079] This type of end plug is manufactured to a size suitable for use in VVER reactors.

[0080] Example 2 - End plug of a composite tubular ceramic cladding for sealing nuclear reactor fuel elements according to a first variant.

[0081] The end plug intended for use with the fuel element casing 8 is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters – part 1 and part 2; see also Figure 1 and 4 For illustrative purposes, Figure 4 The fuel element cladding in fuel cells is typically shown as transparent.

[0082] The second part 2 of the end plug is configured to be arranged inside the fuel element housing 8; the first part 1, namely the collar in the form of a cylinder with a larger diameter—the tail, is configured to be arranged outside the fuel element housing 8.

[0083] The fuel element housing 8 has an inner diameter of 9.31 mm and an outer diameter of 10.75 mm. The height of the second part of the end plug within the mating area is b2 = 10 mm, and the length of the first part 1 of the end plug is b1 = 5 mm. The diameter d1 of the second part 2 of the end plug is made 0.08 mm smaller than the inner diameter of the fuel element housing for the purpose of inserting the solder in the form of paste, and is equal to 9.23 mm. The diameter D of the first part 1 of the end plug is equal to the outer diameter of the fuel element housing minus 10.75 mm.

[0084] The diameter d1 of the second part 2 of the end plug, which is 0.08 mm smaller than the inner diameter of the fuel element casing, is determined by the thickness of the paste-like brazing filler metal layer that should be applied before assembly for brazing.

[0085] A paste-like brazing filler metal is applied before assembly to facilitate brazing; this capillary gap is necessary for brazing silicon carbide-based end plugs and cladding. Figure 4 A full view of the fuel element casing 8 and the end plug consisting of a first part 1 and a second part 2 is shown, the surface of the second part 2 of the end plug being where the paste solder is applied.

[0086] This type of end plug is manufactured to a size suitable for use in PWR reactors.

[0087] Example 3 - End plugs for composite tubular ceramic cladding used to seal nuclear reactor fuel elements according to a second variant.

[0088] The end plug intended for use with the fuel element casing 8 is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters – part 3 and part 4; see also Figure 2 and 5 For illustrative purposes, Figure 5 The fuel element cladding in fuel cells is typically shown as transparent.

[0089] The second part 4 of the end plug is configured to be arranged inside the fuel element housing 8; the first part 3, namely the collar in the form of a cylinder with a larger diameter—the tail, is configured to be arranged outside the fuel element housing 8.

[0090] The fuel element housing 8 has an inner diameter of 7.72 mm and an outer diameter of 9.1 mm. The height of the second portion 4 of the end plug within the mating area is b4 = 15 mm, and the length of the first portion 3 of the end plug is b3 = 5 mm. The diameter d2 of the second portion 4 of the end plug is made 2 mm smaller than the inner diameter of the fuel element housing 8 for the purpose of inserting foil-form brazing filler metal, and is equal to 5.72 mm. The diameter D of the first portion 3 of the end plug is equal to the outer diameter of the fuel element housing minus 9.1 mm.

[0091] The diameter d2 of the second part 4 of the end plug, which is 2 mm smaller than the inner diameter of the fuel element casing, is determined by the thickness of the foil filler metal that should be placed for brazing before assembly.

[0092] Foil is placed before assembly for brazing; this capillary gap is required for brazing silicon carbide-based end plugs and cladding. Figure 5 A full view of the fuel element housing 8 and the end plug consisting of a first part 3 and a second part 4 is shown, the surface of the second part 4 of the end plug being the place where the foil solder is inserted.

[0093] This type of end plug is manufactured to a size suitable for use in VVER reactors.

[0094] Example 4 - End plugs for composite tubular ceramic cladding used to seal nuclear reactor fuel elements according to a second variant.

[0095] The end plug intended for use with the fuel element casing 8 is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters – part 3 and part 4; see also Figure 2 and 5 For illustrative purposes, Figure 5 The fuel element cladding in fuel cells is typically shown as transparent.

[0096] The second part 4 of the end plug is configured to be arranged inside the fuel element housing 8; the first part 3, namely the collar in the form of a cylinder with a larger diameter—the tail, is configured to be arranged outside the fuel element housing 8.

[0097] The fuel element casing 8 has an inner diameter of 9.31 mm and an outer diameter of 10.75 mm. The height of the second portion 4 of the end plug within the mating area is b4 = 12 mm, and the length of the first portion 3 of the end plug is b3 = 6 mm. The diameter d2 of the second portion 4 of the end plug is made 3 mm smaller than the inner diameter of the fuel element casing 8 for the purpose of inserting foil-form brazing filler metal, and is equal to 6.31 mm. The diameter D of the first portion 3 of the end plug is equal to the outer diameter of the fuel element casing minus 10.75 mm.

[0098] The diameter d2 of the second part 4 of the end plug, which is 3 mm smaller than the inner diameter of the fuel element casing, is determined by the thickness of the foil filler metal that should be placed for brazing before assembly.

[0099] Foil is placed before assembly for brazing; this capillary gap is required for brazing silicon carbide-based end plugs and cladding. Figure 5 A full view of the fuel element housing 8 and the end plug consisting of a first part 3 and a second part 4 is shown, the surface of the second part 4 of the end plug being the place where the foil solder is inserted.

[0100] This type of end plug is manufactured to a size suitable for use in PWR reactors.

[0101] Example 5 - End plug of a composite tubular ceramic cladding for sealing nuclear reactor fuel elements according to a third variant.

[0102] The end plug intended for use with the fuel element casing 8 is based on β-SiC and consists of three parts in the form of three coaxial cylinders with different diameters—part 5, part 6, and part 7 (in the form of a groove); see also Figure 3 and 6 For illustrative purposes, Figure 6 The fuel element cladding in fuel cells is typically shown as transparent.

[0103] The second part 6 and the third part 7 of the end plug are configured to be arranged inside the fuel element housing 8; the first part 5, namely the collar in the form of a cylinder with a larger diameter—the tail, is configured to be arranged outside the fuel element housing 8.

[0104] The fuel element housing 8 has an inner diameter of 7.72 mm and an outer diameter of 9.1 mm. The height of the second part 6 of the end plug in the mating area is b6 = 10 mm, the length of the third part 7 of the end plug is b7 = 10 mm, and the length of the first part 5 of the end plug is b5 = 3 mm.

[0105] The diameter d1 of the second part 6 is 0.06 mm smaller than the inner diameter of the fuel element cladding for the purpose of inserting the solder in paste form and is equal to 7.66 mm. The diameter d2 of the third part 7 is 2 mm smaller than the inner diameter of the cladding for the purpose of inserting the solder in foil form and is equal to 5.72 mm, and the diameter of the first part 5 is equal to the outer diameter of the fuel element cladding.

[0106] This embodiment of the end plug has two areas for simultaneously inserting two types of solder: an area with diameter d1 and length b6, and an area with diameter d2 and length b7. The diameter d2 < d1 because the solder in paste form is inserted in the end plug area with diameter d1 and length b6, while the solder in foil form is inserted in the end plug area with diameter d2 and length b7.

[0107] Figure 6 A full view of the fuel element cladding 8 and the end plug consisting of the first part 5, the second part 6 and the third part 7 is shown. The surface of the second part 6 of the end plug is the place where the solder in paste form is inserted, and the surface of the third part 7 of the end plug is the place where the solder in foil form is inserted.

[0108] This type of end plug is manufactured to a size suitable for use in VVER reactors.

[0109] Example 6 - An end plug for a composite tubular ceramic cladding for sealing nuclear reactor fuel elements according to the third variant.

[0110] The end plug intended for use in combination with the fuel element cladding 8 is produced based on β-SiC and consists of three parts in the form of three coaxial cylinders with different diameters arranged in succession - the first part 5, the second part 6 and the third part 7 (in the form of a groove); see Figure 3 and 6 . For illustrative purposes, Figure 6 the fuel element cladding in

[0111] The second part 6 and the third part 7 of the end plug are configured to be arranged inside the fuel element cladding 8; the first part 5, i.e., the collar - the tail in the form of a cylinder with a larger diameter, is configured to be arranged outside the fuel element cladding 8.

[0112] The inner diameter of the fuel element cladding 8 is 9.31 mm and the outer diameter is 10.75 mm. The height of the second part 6 of the end plug is b6 = 7 mm, the length of the third part 7 of the end plug is b7 = 7 mm, and the length of the first part 5 of the end plug is b5 = 4 mm.

[0113] The diameter d1 of the second part 6 is 0.08 mm smaller than the inner diameter of the fuel element cladding for the purpose of inserting the solder in paste form and is equal to 9.23 mm. The diameter d2 of the third part 7 is 3 mm smaller than the inner diameter of the cladding for the purpose of inserting the solder in foil form and is equal to 6.31 mm. And the diameter of the first part 5 is equal to the outer diameter of the fuel element cladding and is 10.75 mm.

[0114] This embodiment of the end plug has two areas for simultaneously inserting two types of solder: an area with diameter d1 and length b6, and an area with diameter d2 and length b7. The diameter d2 < d1 because the solder in paste form is inserted in the end plug area with diameter d1 and length b6, while the solder in foil form is inserted in the end plug area with diameter d2 and length b7.

[0115] Figure 6 A full view of the fuel element cladding 8 and the end plug composed of the first part 5, the second part 6, and the third part 7 is shown. The surface of the second part 6 of the end plug is the place where the solder in paste form is inserted, and the surface of the third part 7 of the end plug is the place where the solder in foil form is inserted.

[0116] This type of end plug is manufactured to a size suitable for use in a PWR reactor.

[0117] Example 7 - A method for manufacturing an end plug for sealing a composite tubular ceramic cladding of a nuclear reactor fuel element according to the first variant.

[0118] The β-SiC powder is crushed to a particle size of 0.95 and 5.19 microns, and the Al2O3 powder with 1.52 micron particles and the Y2O3 powder with 1.01 micron particles are added.

[0119] A powder mixture is prepared from the β-SiC powder, the Al2O3 powder, and the Y2O3 powder. The substance content (wt%) is: β-SiC with 0.95 micron particles - 10.59, β-SiC with 5.19 micron particles - 77.91, Al2O3 with 1.52 micron particles - 10.0, Y2O3 with 1.01 micron particles - 1.5.

[0120] The composition of the above powder mixture was preselected based on the Al2O3 - Y2O3 system phase diagram, see Figure 11 .

[0121] After the powder mixture is prepared, they are mixed evenly using a planetary ball mill.

[0122] To manufacture end plugs using hot pressing technology, strength calculations were performed on the die and punch using the finite element method and Solidworks simulation software. As a result, PUS-1 graphite was selected, a model was developed, and a die 10 in the form of a parallelepiped with 12 equal through-cylinder elements 9 of the desired shape was manufactured, along with a cylindrical upper punch 11. See [link to relevant documentation]. Figure 7 , 8 10.

[0123] The shape of mold unit 9 corresponds to the end plug of the first variant disclosed in Embodiment 1, i.e., the diameter D of the upper cylindrical portion of the unit is 9.1 mm, and the height b1 of this portion is 7 mm. The diameter d1 of the lower cylindrical portion of the unit is 7.66 mm, which is 0.06 mm smaller than the inner diameter of the casing, and the height b2 of this portion is 10 mm. The upper punch 11 is manufactured with these dimensions properly taken into account. Figure 7 A top view of a mold 10 having a unit 9 for pressing a plug is shown; Figure 8 A cross-sectional view AA of a mold 10 having a unit 9 for pressing a plug is shown.

[0124] Immediately before hot pressing, the mold and punch are annealed in a vacuum compression furnace to remove moisture and various types of contaminants from the surface. To do this, the mold and punch are heated to 200°C in the furnace, annealed for 60 minutes, cooled to room temperature at a rate not exceeding 50°C per hour, and held at room temperature for at least 12 hours. Throughout the process, the pressure inside the furnace chamber is maintained at a level not exceeding 1 Pa.

[0125] After cooling and unloading from the furnace, mold 10 is prepared for pressing as follows:

[0126] - The lower punch is arranged at the bottom of each mold unit 9 (not shown in the figure);

[0127] -Then, the powder mixture is placed into each of the 12 mold units in an amount of 2.5 ± 0.002 g, onto the lower punch;

[0128] -Then, the upper punches 11 are arranged above the powder mixture so that they cover each unit 9 on the upper part of the mold 10.

[0129] The prepared mold 10 containing the powder mixture was placed in the furnace and held without heating at a pressure of ~1 Pa for more than 12 hours. The ceramic plugs were sintered in an inert gas (argon) atmosphere at a temperature of 1850 °C and a pressure of approximately 0.1 MPa. The sintering method of the end plugs is shown in Table 3. The arrangement of the samples in the furnace is as follows: Figure 12 As shown in the image.

[0130] Table 3. Methods of using end plugs for sintering in the furnace.

[0131]

[0132]

[0133] After sintering, the end plug sample is removed from the mold and cleaned.

[0134] The produced end plug samples were transported for study of their mechanical and thermophysical properties. The results showed that the produced end plugs possess high mechanical characteristics and good thermophysical properties, allowing them to be used under the required conditions.

[0135] Example 8 - A method for manufacturing end plugs for sealing composite tubular ceramic cladding for nuclear reactor fuel elements, according to a first variation.

[0136] This method is carried out in a similar manner to that described in Example 7, but with the use of a mold unit and other dimensions of the upper punch corresponding to the end plug of the second embodiment disclosed in Example 3.

[0137] That is, the diameter D of the upper cylindrical portion of the unit is 9.1 mm, and the height b3 of this portion is 5 mm. The diameter d2 of the lower cylindrical portion of the unit is 5.72 mm, which is 2 mm smaller than the inner diameter of the casing, and the height b4 of this portion is 15 mm. The upper punch 11 is manufactured with these dimensions properly taken into account. Figure 7 A top view of a mold 10 having a unit 9 for pressing a plug is shown; Figure 8 A cross-sectional view AA of a mold 10 having a unit 9 for pressing a plug is shown.

[0138] The results show that the produced end plugs have high mechanical characteristics and good thermophysical properties, allowing them to be used under the required conditions.

[0139] Example 9 - A method for manufacturing end plugs for sealing composite tubular ceramic cladding for nuclear reactor fuel elements, according to a first variation.

[0140] This method is performed similarly to that described in Example 7, but with different dimensions for the mold unit and upper punch corresponding to the end plug of the third embodiment disclosed in Example 5. Furthermore, the resulting powder mixture is hot-pressed in a vacuum furnace instead of in an inert gas atmosphere.

[0141] The upper cylindrical portion of the unit has a diameter D of 9.1 mm and a height b3 of 5 mm. The middle cylindrical portion of the unit has a diameter d1 of 7.66 mm, which is 0.06 mm smaller than the inner diameter of the casing, and a height b6 of 10 mm. The lower cylindrical portion of the unit has a diameter d2 of 5.72 mm, which is 2 mm smaller than the inner diameter of the casing, and a height b7 of 10 mm. The upper punch 11 is manufactured with these dimensions properly taken into account. Figure 7 A top view of a mold 10 having a unit 9 for pressing a plug is shown; Figure 9 A cross-sectional view AA of a mold 10 having a unit 9 for pressing a plug is shown.

[0142] The results show that the produced end plugs have high mechanical characteristics and good thermophysical properties, allowing them to be used under the required conditions.

[0143] Example 10 - A method for manufacturing end plugs for sealing composite tubular ceramic cladding for nuclear reactor fuel elements, according to a second variation.

[0144] β-SiC powder was pulverized to particle sizes of 0.95 and 5.19 micrometers, and Al2O3 powder with 1.52 micrometer particles and Y2O3 powder with 1.01 micrometer particles were added.

[0145] A powder mixture was prepared from β-SiC powder, Al2O3 powder, and Y2O3 powder. The content (wt%) of the substances was: β-SiC with 0.95 μm particles - 10.78%, β-SiC with 5.19 μm particles - 79.22%, Al2O3 with 1.52 μm particles - 6.00%, and Y2O3 with 1.01 μm particles - 4.00%.

[0146] The composition of the above powder mixture is based on a pre-selected state diagram of the Al2O3-Y2O3 system, see [link / reference]. Figure 11 .

[0147] After the powder mixture is prepared, it is mixed evenly using a planetary ball mill.

[0148] To manufacture end plugs using hot pressing technology, strength calculations were performed on the die and punch using the finite element method and Solidworks simulation software. As a result, PUS-1 graphite was selected, a model was developed, and a die 10 in the form of a parallelepiped with 12 equal through-cylinder elements 9 of the desired shape was manufactured, along with a cylindrical upper punch 11. See [link to relevant documentation]. Figure 7 , 8 10.

[0149] The shape of mold unit 9 corresponds to the end plug of the first variant disclosed in Embodiment 1, i.e., the diameter D of the upper cylindrical portion of the unit is 9.1 mm, and the height b1 of this portion is 7 mm. The diameter d1 of the lower cylindrical portion of the unit is 7.66 mm, which is 0.06 mm smaller than the inner diameter of the casing, and the height b2 of this portion is 10 mm. The upper punch 11 is manufactured with these dimensions properly taken into account. Figure 7 A top view of a mold 10 having a unit 9 for pressing a plug is shown; Figure 8A cross-sectional view AA of a mold 10 having a unit 9 for pressing a plug is shown.

[0150] Immediately before hot pressing, the mold and punch are annealed in a vacuum compression furnace to remove moisture and various types of contaminants from the surface. To do this, the mold and punch are heated to 200°C in the furnace, annealed for 60 minutes, cooled to room temperature at a rate not exceeding 50°C per hour, and held at room temperature for at least 12 hours. Throughout the process, the pressure inside the furnace chamber is maintained at a level not exceeding 1 Pa.

[0151] After cooling and unloading from the furnace, mold 10 is prepared for pressing as follows:

[0152] - The lower punch is arranged at the bottom of each mold unit 9 (not shown in the figure);

[0153] -Then, the powder mixture is placed into each of the 12 mold units in an amount of 2.5 ± 0.002 g, onto the lower punch;

[0154] -Then, the upper punches 11 are arranged above the powder mixture so that they cover each unit 9 on the upper part of the mold 10.

[0155] The prepared mold 10 containing the powder mixture was placed in the furnace and held without heating at a pressure of ~1 Pa for more than 12 hours. The ceramic plugs were sintered in an inert gas (argon) atmosphere at a temperature of 1850 °C and a pressure of approximately 0.1 MPa. The sintering method of the end plugs is shown in Table 5. The arrangement of the samples in the furnace is as follows: Figure 12 As shown in the image.

[0156] Table 5. Methods of using end plugs for sintering in the furnace.

[0157]

[0158]

[0159] After sintering, the end plug sample is removed from the mold and cleaned.

[0160] The produced end plug samples were transported for study of their mechanical and thermophysical properties. The results showed that the produced end plugs possess high mechanical characteristics and good thermophysical properties, allowing them to be used under the required conditions.

[0161] Example 11 - A method for manufacturing end plugs for sealing composite tubular ceramic cladding for nuclear reactor fuel elements, according to a second variation.

[0162] This method is performed similarly to that described in Example 10, but with different dimensions of the mold unit and upper punch corresponding to the end plug of the second embodiment disclosed in Example 3. Furthermore, the resulting powder mixture is hot-pressed in a vacuum furnace instead of in an inert gas atmosphere.

[0163] The upper cylindrical portion of the unit has a diameter D of 9.1 mm and a height b3 of 5 mm. The lower cylindrical portion of the unit has a diameter d2 of 5.72 mm, which is 2 mm smaller than the inner diameter of the casing, and a height b4 of 15 mm. The upper punch 11 is manufactured with these dimensions properly taken into account. Figure 7 A top view of a mold 10 having a unit 9 for pressing a plug is shown; Figure 8 A cross-sectional view AA of a mold 10 having a unit 9 for pressing a plug is shown.

[0164] The results show that the produced end plugs have high mechanical characteristics and good thermophysical properties, allowing them to be used under the required conditions.

[0165] Example 12 - A method for manufacturing end plugs for sealing composite tubular ceramic cladding for nuclear reactor fuel elements, according to a second variation.

[0166] This method is carried out in a similar manner to that described in Example 10, but with the use of a different size of the mold unit and upper punch corresponding to the end plug of the third embodiment disclosed in Example 5.

[0167] The upper cylindrical portion of the unit has a diameter D of 9.1 mm and a height b5 of 3 mm. The middle cylindrical portion of the unit has a diameter d1 of 7.66 mm, which is 0.06 mm smaller than the inner diameter of the casing, and a height b6 of 10 mm. The lower cylindrical portion of the unit has a diameter d2 of 5.72 mm, which is 2 mm smaller than the inner diameter of the casing, and a height b7 of 10 mm. The upper punch 11 is manufactured with these dimensions properly taken into account. Figure 7 A top view of a mold 10 having a unit 9 for pressing a plug is shown; Figure 9 A cross-sectional view AA of a mold 10 having a unit 9 for pressing a plug is shown.

[0168] The results show that the produced end plugs have high mechanical characteristics and good thermophysical properties, allowing them to be used under the required conditions.

[0169] Therefore, the developed end plug structure and its manufacturing method can seal fuel elements made of silicon carbide, including in cases where inert gas pressure exists within the internal volume of the fuel element. This invention provides:

[0170] - For environmental safety, by preventing the formation of compounds harmful to the ecosystem,

[0171] - The possibility of using the developed end plug as a replacement for the plugs used in various VVER reactors, due to its shape and size being suitable for typical structures.

[0172] - A simplified method for manufacturing end plugs, due to the smaller number of manufacturing stages.

[0173] - Improved mechanical and thermophysical properties of the end plugs due to the developed method for manufacturing the end plugs, which takes into account the particle size of the material used and the parameters of the process performed.

Claims

1. A method of manufacturing an end plug of a composite tubular ceramic can for sealing a nuclear reactor fuel element, wherein the end plug is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters, wherein the diameter of the first part made in the form of a tail configured to be mounted onto the end of the can is equal to the outer diameter of the can and the diameter of the second part configured to be arranged inside the can is smaller than the inner diameter of the can by 0.06-0.08 mm, the method comprising: preparing a powder mixture from β-SiC powder, AI2O3 powder and Y2O3 powder taken in the following amounts in wt%: β-SiC with 0.95 micron particles - 10.59, β-SiC with 5.19 micron particles - 77.91, AI2O3 with 1.52 micron particles - 10.0, Y2O3 with 1.01 micron particles - balance; hot-pressing the powder mixture using an upper punch and a lower punch and a die having a cell shaped and sized to correspond to the end plug; to this end, loading the powder mixture into the internal cavity of the die cell onto the lower punch; placing the upper punch into the die cell above the powder mixture; holding the powder mixture for more than 12 hours without heating at 1 Pa pressure; pressing the powder mixture in the die cell using the upper punch and sintering the pressed powder mixture at a temperature of 1850 ο 0.1 MPa pressure in an inert gas atmosphere or in vacuum; the duration of the holding in the sintering mode is 120 minutes, and the finished end plug is ejected from each die cell.

2. A method of manufacturing an end plug of a composite tubular ceramic can for sealing a nuclear reactor fuel element, wherein the end plug is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters, wherein the diameter of the first part made in the form of a tail configured to be mounted onto the end of the can is equal to the outer diameter of the can and the diameter of the second part configured to be arranged inside the can is smaller than the inner diameter of the can by 2-3 mm, the method comprising: preparing a powder mixture from β-SiC powder, AI2O3 powder and Y2O3 powder taken in the following amounts in wt%: β-SiC with 0.95 micron particles - 10.59, β-SiC with 5.19 micron particles - 77.91, AI2O3 with 1.52 micron particles - 10.0, Y2O3 with 1.01 micron particles - balance; hot-pressing the powder mixture using an upper punch and a lower punch and a die having a cell shaped and sized to correspond to the end plug; to this end, loading the powder mixture into the internal cavity of the die cell onto the lower punch; placing the upper punch into the die cell above the powder mixture; holding the powder mixture for more than 12 hours without heating at 1 Pa pressure; pressing the powder mixture in the die cell using the upper punch and sintering the pressed powder mixture at a temperature of 1850 ο 0.1 MPa pressure in an inert gas atmosphere or in vacuum; the duration of the holding in the sintering mode is 120 minutes, and the finished end plug is ejected from each die cell.

3. A method of manufacturing an end plug of a composite tubular ceramic can for sealing a nuclear reactor fuel element, wherein the end plug is based on β-SiC and consists of three parts in the form of three coaxially arranged cylinders with different diameters, wherein the diameter of the first part made in the form of a tail configured to be mounted onto the end of the can is equal to the outer diameter of the can, the diameter of the second part configured to be arranged inside the can is smaller than the inner diameter of the can by 0.06-0.08 mm and the diameter of the third part configured to be arranged inside the can is smaller than the inner diameter of the can by 2-3 mm, the method comprising: preparing a powder mixture from β-SiC powder, AI2O3 powder and Y2O3 powder taken in the following amounts in wt%: β-SiC with 0.95 micron particles - 10.59, β-SiC with 5.19 micron particles - 77.91, AI2O3 with 1.52 micron particles - 10.0, Y2O3 with 1.01 micron particles - balance; hot-pressing the powder mixture using an upper punch and a lower punch and a die having a cell shaped and sized to correspond to the end plug; to this end, loading the powder mixture into the internal cavity of the die cell onto the lower punch; placing the upper punch into the die cell above the powder mixture; holding the powder mixture for more than 12 hours at 1 Pa pressure without heating; pressing the powder mixture in the die cell using the upper punch and sintering the pressed powder mixture at a temperature of 1850 ο 0.1 MPa pressure in an inert gas atmosphere or in vacuum; the duration of the holding in the sintering mode is 120 minutes, and the finished end plug is ejected from each die cell.

4. The method according to any one of claims 1 to 3, characterized in that, when preparing the powder mixture, it is mixed uniformly using a planetary ball mill.

5. The method according to any one of claims 1 to 3, characterized in that, the die and the punch are annealed in a vacuum compression furnace before hot pressing.

6. The method of claim 5, wherein, heating the mold and the punch to a temperature of 200°C in a vacuum compression furnace, annealing for 60 minutes, cooling to room temperature at a rate of no more than 50°C per hour, holding at room temperature for at least 12 hours, while maintaining the pressure in the chamber of the vacuum compression furnace at a level of no more than 1 Pa.

7. A method of manufacturing an end plug for a composite tubular ceramic can of a nuclear reactor fuel element, wherein the end plug is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters, wherein the diameter of the first part, made in the form of a tail, configured to be mounted onto the end of the can, is equal to the outer diameter of the can, and the diameter of the second part, configured to be arranged inside the can, is smaller than the inner diameter of the can by 0.06-0.08 mm, The method comprises: preparing a powder mixture from β-SiC powder, AI2O3 powder and Y2O3 powder taken in the following amounts in wt%: β-SiC - 10.78 with 0.95 micron particles, β-SiC - 79.22 with 5.19 micron particles, AI2O3 - 6.0 with 1.52 micron particles, Y2O3 - balance with 1.01 micron particles; hot-pressing the powder mixture using an upper punch and a lower punch and a die having a cell shaped and sized to correspond to the end plug; to this end, loading the powder mixture into the internal cavity of the die cell onto the lower punch; placing the upper punch into the die cell above the powder mixture; holding the powder mixture for more than 12 hours without heating at 1 Pa pressure; pressing the powder mixture in the die cell using the upper punch and sintering the pressed powder mixture at a temperature of 1850 ο 0.1 MPa pressure in an inert gas atmosphere or in vacuum; the duration of the holding in the sintering mode is 90 minutes, and the finished end plug is ejected from each die cell.

8. A method of manufacturing an end plug for a composite tubular ceramic can of a nuclear reactor fuel element, wherein the end plug is based on β-SiC and consists of two parts in the form of two coaxial cylinders with different diameters, wherein the diameter of the first part, made in the form of a tail, configured to be mounted onto the end of the can, is equal to the outer diameter of the can, and the diameter of the second part, configured to be arranged inside the can, is smaller than the inner diameter of the can by 2-3 mm, the method comprising: preparing a powder mixture from β-SiC powder, AI2O3 powder and Y2O3 powder taken in the following amounts in wt%: β-SiC - 10.78 with 0.95 micron particles, β-SiC - 79.22 with 5.19 micron particles, AI2O3 - 6.0 with 1.52 micron particles, Y2O3 - balance with 1.01 micron particles; hot-pressing the powder mixture using an upper punch and a lower punch and a die having a cell shaped and sized to correspond to the end plug; to this end, loading the powder mixture into the internal cavity of the die cell onto the lower punch; placing the upper punch into the die cell above the powder mixture; holding the powder mixture for more than 12 hours at 1 Pa pressure without heating; pressing the powder mixture in the die cell using the upper punch and sintering the pressed powder mixture at a temperature of 1850 ο 0.1 MPa pressure in an inert gas atmosphere or in vacuum; the duration of the holding in the sintering mode is 90 minutes, and the finished end plug is ejected from each die cell.

9. A method of manufacturing an end plug for a composite tubular ceramic can of a nuclear reactor fuel element, wherein the end plug is based on β-SiC and consists of three parts in the form of three coaxial cylinders with different diameters arranged one inside the other, wherein the diameter of the first part, made in the form of a tail, configured to be mounted onto the end of the can, is equal to the outer diameter of the can, the diameter of the second part, configured to be arranged inside the can, is smaller than the inner diameter of the can by 0.06-0.08 mm, and the diameter of the third part, configured to be arranged inside the can, is smaller than the inner diameter of the can by 2-3 mm, The method comprises: preparing a powder mixture from β-SiC powder, AI2O3 powder and Y2O3 powder taken in the following amounts in wt%: β-SiC - 10.78 with 0.95 micron particles, β-SiC - 79.22 with 5.19 micron particles, Al203-6.0 with 1.52 micron particles, Y203-remainder with 1.01 micron particles; hot-pressing the powder mixture using an upper punch and a lower punch and a die having a cell shaped and sized to correspond to the end plug; to this end, loading the powder mixture into the internal cavity of the die cell onto the lower punch; placing the upper punch into the die cell above the powder mixture; holding the powder mixture for more than 12 hours without heating at 1 Pa pressure; pressing the powder mixture in the die cell using the upper punch and sintering the pressed powder mixture at a temperature of 1850 ο 0.1 MPa pressure in an inert gas atmosphere or in vacuum; the duration of the holding in the sintering mode is 90 minutes, and the finished end plug is ejected from each die cell.

10. The method according to any one of claims 7 to 9, characterized in that, When preparing the powder mixture, it is mixed homogeneously using a planetary ball mill.

11. The method according to any one of claims 7 to 9, characterized in that, The mold and the punch are annealed in a vacuum compression furnace before hot pressing.

12. The method of claim 11, wherein, The mold and the punch are heated in a vacuum compression furnace to a temperature of 200°C, annealed for 60 minutes, cooled to room temperature at a rate not exceeding 50°C per hour, and held at room temperature for at least 12 hours, while the pressure in the chamber of the vacuum compression furnace is maintained at a level not higher than 1 Pa.

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