Nuclear fuel rod cladding and manufacturing process for such cladding

Abstract

Nuclear fuel rod cladding and method for manufacturing such cladding. The cladding comprises a tube (14) extending along a longitudinal axis and a tubular inner lining (18) received inside the tube (14), the tube (14) comprising at least one reinforced layer (16) made of a composite material comprising a ceramic matrix reinforced with ceramic reinforcing fibers, the thickness of the tube (14) being between 280 µm and 600 µm. Figure for the abstract: Figure 1

Description

Title of the invention: Nuclear fuel rod cladding and method for manufacturing such a cladding

[0001] The present invention relates to the field of nuclear fuel claddings (hereinafter also referred to as "claddings") intended to contain nuclear fuel, in particular nuclear fuel rod claddings, and their manufacturing method.

[0002] Nuclear fuel including fissile material is generally contained in a sealed sheath which prevents the dispersion of the nuclear fuel.

[0003] Nuclear fuel assemblies used in light water or heavy water reactors generally comprise a bundle of nuclear fuel rods, each nuclear fuel rod comprising a tubular sheath containing nuclear fuel, the sheath being closed at each of its two ends by a respective plug.

[0004] The cladding of nuclear fuel assemblies is made, for example, of a zirconium-based alloy. Such zirconium-based alloys exhibit high performance under normal conditions of use in nuclear reactors.

[0005] However, they can reach their limits, particularly in terms of temperature, during severe accident conditions, such as during a loss of coolant accident (or LOCA for “Loss Of Coolant Accident” in English).

[0006] During such an event, the temperature in the core of the nuclear reactor can reach more than 800°C and the cooling fluid is essentially in the form of water vapor.

[0007] This can cause rapid degradation of the cladding of a nuclear fuel rod, with in particular the release of hydrogen and rapid oxidation of the cladding leading to its embrittlement or even its bursting, and therefore to the release of nuclear fuel from the cladding.

[0008] One of the aims of the invention is to propose a sheath which exhibits improved behavior under normal conditions and accident conditions, while exhibiting improved wear resistance.

[0009] To this end, the invention provides a nuclear fuel rod cladding, the cladding comprising a tube extending along a longitudinal axis and a tubular internal lining received inside the tube, the tube comprising at least one reinforced layer made from a composite material comprising a ceramic matrix reinforced with ceramic reinforcing fibers, the thickness of the tube being comprised between 280 pm and 600 pm.

[0010] The tube made of ceramic matrix composite material reinforced with ceramic fibers makes it possible to obtain a cladding which is very resistant, particularly in accident conditions. The risk of rupture of the cladding and, in doing so, of release of nuclear fuel from the cladding, is therefore reduced. For example, a silicon carbide matrix reinforced with silicon carbide and / or carbon reinforcing fibers is particularly resistant.

[0011] The internal lining provided in the tube makes it possible to improve the sealing and in particular to prevent the release of fission gases outside the sheath.

[0012] According to particular embodiments, the sheath comprises one or more of the following optional characteristics, taken individually or in all technically possible combinations:

[0013] - the tube comprises a single reinforced layer, the thickness of the tube being comprised between 280 pm and 340 pm;

[0014] -the tube comprises exactly two reinforced layers, the thickness of the tube being between 450 pm and 600 pm;

[0015] - the ceramic matrix is ​​made of silicon carbide and / or the reinforcing fibers ceramics are made of silicon carbide and / or carbon;

[0016] - one or each reinforced layer is formed with filament winding of the ceramic reinforcing fibers;

[0017] - one or each reinforced layer is formed with filament winding of the ceramic reinforcing fibers without interlacing of ceramic reinforcing fibers;

[0018] - one or each reinforced layer is formed with filament winding of the ceramic reinforcing fibers with interlacing of the ceramic reinforcing fibers, for example by braiding the ceramic reinforcing fibers;

[0019] - the tube comprises at least one non-reinforced layer, preferably made in the same material as the ceramic matrix;

[0020] - the sheath comprises an internal non-reinforced layer covering the layer(s) reinforced on the inner side of the tube and / or an external unreinforced layer covering the reinforced layer(s) on the outer side of the tube and / or an intermediate unreinforced layer inserted between two reinforced layers of the tube;

[0021] - the tube is formed exclusively from the ceramic matrix and the reinforcing fibers ceramics;

[0022] - the internal lining has a thickness of between 50 pm and 200 pm, in par particularly between 50 pm and 150 pm;

[0023] - the internal lining is metallic;

[0024] - the internal lining is made of pure zirconium or an alloy based on zirconium containing at least 95% by weight of zirconium;

[0025] - the internal lining is pre-oxidized;

[0026] - the sheath comprises an outer protective layer covering an outer surface of the tube;

[0027] - the outer protective layer is metallic;

[0028] - the outer protective layer is made of pure chrome or an alloy based on chromium containing at least 85% by weight of chromium or pure zirconium or zirconium-based alloy containing at least 85% by weight of zirconium or pure titanium or titanium-based alloy containing at least 80% by weight of titanium;

[0029] - the outer protective layer has a thickness of between 5 pm and 40 pm.

[0030] The invention also relates to a nuclear fuel rod comprising a cladding according to any one of the preceding claims, nuclear fuel received inside the inner lining of the cladding, and two plugs, each plug closing a respective axial end of the cladding.

[0031] According to particular embodiments, the nuclear fuel rod comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0032] - each cap is made of composite material comprising a matrix ceramic reinforced with ceramic reinforcing fibers, in particular a silicon carbide matrix reinforced with silicon carbide and / or carbon reinforcing fibers;

[0033] - the nuclear fuel rod comprising two internal elements sealing, each closing a respective end of the internal lining;

[0034] - the gas contained in the inner lining is helium and / or the pressure of the gas at the interior of the inner lining is equal to or less than 200 bars, preferably equal to or less than 100 bars, more preferably equal to or less than 20 bars.

[0035] The invention and its advantages will be better understood on reading the following description, given solely as a non-limiting example, and made with reference to the appended drawings, in which:

[0036] - [Fig.l] [Fig.l] is a schematic view in longitudinal section of a pencil of nuclear fuel illustrating a cladding of the nuclear fuel rod;

[0037] - [Fig.2] [Fig.2] is a schematic sectional view of the fuel rod nuclear of [Fig.l], according to II - II on [Fig.l].

[0038] [Fig.l] illustrates an example of a nuclear fuel rod 2 intended to be used in a light water reactor, in particular a pressurized water reactor (or PWR for "Pressurized Water Reactor") or a boiling water reactor (or BWR for "Boiling Water Reactor"), a "VVER" type reactor, a "RBMK" type reactor, or a heavy water reactor, for example of the "CANDU" type.

[0039] The nuclear fuel rod 2 has the shape of an elongated rod along a longitudinal axis A.

[0040] The nuclear fuel rod 2 comprises a cladding 4 containing nuclear fuel. The cladding 4 is tubular and extends along the longitudinal axis A.

[0041] The sheath 4 is for example closed at its axial ends by two plugs 6, each plug 6 closing a respective axial end of the sheath 4, preferably in a sealed manner.

[0042] One of the two stoppers 6 or, preferably, each stopper 6 has a gripping finger 6A

[0043] Each gripping finger 6A allows the nuclear fuel rod 2 to be gripped, for example during the manufacture of the nuclear fuel rod 2, during the insertion of the nuclear fuel rod 2 into a nuclear fuel assembly, or even for the extraction of the nuclear fuel rod 2 from a nuclear fuel assembly.

[0044] The nuclear fuel is for example in the form of a stack of pellets 8 stacked axially inside the cladding 4, each pellet 8 containing fissile material. The stack of pellets 8 is also called a “fissile column”.

[0045] The nuclear fuel rod 2 comprises a spring 10 arranged inside the cladding 4, between the stack of pellets 8 and one of the plugs 6, to push the stack of pellets 8 towards the other plug 6. A vacuum or plenum 12 is present between the stack of pellets 8 and the plug 6 on which the spring 10 bears.

[0046] The sheath 4 has, for example, an external diameter of between 8 mm and 15 mm, in particular between 9 mm and 13 mm, and / or a length of between 1 m and 5 m, in particular between 2 m and 5 m.

[0047] As seen in Figures 1 and 2, the sheath 4 comprises a tube 14 having an inner surface 14A and an outer surface 14B. The inner surface 14A faces the inside of the tube 14 and the outer surface faces the outside of the tube 14. The tube 14 extends along the longitudinal axis A.

[0048] The tube 14 is for example closed at its axial ends by the two plugs 6, each plug 6 closing a respective axial end of the tube 14, preferably in a sealed manner.

[0049] The tube 14 is at least partly made of a ceramic matrix composite material reinforced with ceramic reinforcing fibers.

[0050] The ceramic reinforcing fibers are for example made of carbon or silicon carbide (SiC), preferably of nuclear quality. Nuclear quality silicon carbide reinforcing fibers are silicon carbide fibers with high crystallinity and / or stoichiometric or quasi-stoichiometric, i.e. with a C / Si ratio in atomic percentage (at%) of between 1.00 and 1.10 (i.e. 1.00 < C%at / Si%at < 1.10) and an oxygen content of less than 1 percent by mass (%mass), in particular so-called third-generation silicon carbide fibers. Such silicon carbide reinforcing fibers have a high radiation tolerance.

[0051] The ceramic matrix is ​​for example made of silicon carbide. The tube 14 is in this case made at least in part of a composite material with a ceramic matrix of silicon carbide reinforced with silicon carbide fibers (SiC / SiCf) or carbon fibers (SiC / C).

[0052] The sheath 4 comprises a tubular inner lining 18 received inside the tube 14. The inner lining 18 is preferably in contact with the inner surface 14A of the tube 14.

[0053] The tube 14 is formed from one or more superimposed layers. The superimposed layers are concentric.

[0054] The tube 14 comprises a reinforced layer 16 or several reinforced layers 16.

[0055] Each reinforced layer 16 is made from the composite material comprising the ceramic matrix reinforced with ceramic reinforcing fibers.

[0056] Each reinforced layer 16 is made of the ceramic matrix composite material, for example silicon carbide (SiC), reinforced with ceramic reinforcing fibers, preferably silicon carbide (SiC) and / or carbon (C).

[0057] The tube 14 comprises for example a single reinforced layer 16 or exactly two reinforced layers 16.

[0058] The thickness of the tube 14, taken between its internal surface 14A and its external surface 14B, is between 280 pm and 600 pm.

[0059] The provision of a single reinforced layer 16 makes it possible to obtain a sheath 4 having sufficient mechanical strength, while limiting the thickness of the sheath 4. The provision of two superimposed reinforced layers 16 makes it possible to improve the mechanical strength of the sheath 4, while having a sheath 4 whose thickness is contained.

[0060] In each reinforced layer 16, the reinforcing fibers are for example arranged in a two- or three-dimensional arrangement.

[0061] The reinforcing fibers of one or each reinforced layer 16 are for example deposited by filament winding (winding of a wire under tension around a rotating mandrel).

[0062] This makes it possible to achieve a good surface condition and a high volume fraction of fibers to obtain a tube having the mechanical characteristics required for a nuclear fuel rod cladding.

[0063] In each reinforced layer 16, the reinforcing fibers are for example wound helically around the longitudinal axis A, preferably making a winding angle ±0 of between 30° and 60° with the direction of the longitudinal axis A, in in particular a winding angle ±0 of approximately 45° with the direction of the longitudinal axis A.

[0064] The filament winding is carried out without interlacing the reinforcing fibers, in particular without braiding the reinforcing fibers, and / or with interlacing the reinforcing fibers, for example with braiding the reinforcing fibers.

[0065] Advantageously, the reinforcing fibers are previously coated with a fiber / matrix interphase (intermediate thin layer with a “mechanical fuse” role) before being incorporated into a ceramic matrix, for example by chemical vapor infiltration (or CVI). This makes it possible to improve the damage tolerance of the composite material of the tube 14.

[0066] Optionally, the tube 14 comprises at least one unreinforced layer 20.

[0067] Each non-reinforced layer 20 is preferably made in the ceramic matrix not reinforced by ceramic reinforcing fibers, or in other words in the same material as the ceramic matrix of the reinforced layer(s) 16 not reinforced by ceramic reinforcing fibers.

[0068] The production of an unreinforced layer 20 in the same material as that of the matrix of the reinforced layers 16 allows good cohesion between the layers of the tube 14.

[0069] The tube 14 comprises for example an internal non-reinforced layer 20 covering the reinforced layer(s) 16 on the side of the internal surface 14A of the tube 14, and preferably defining the internal surface 14A of the tube 14, and / or an external non-reinforced layer 20 covering the reinforced layer(s) 16 on the side of the external face 14B of the tube 14, and preferably defining the external surface 14B of the tube 14.

[0070] Internal and external non-reinforced layers 20 make it possible to control the dimensions of the tube 14, in particular the internal diameter of the tube 14 and the external diameter of the tube 14, and the surface conditions of the internal 14A and external 14B surfaces of the tube 14, for example by machining and / or lapping the non-reinforced layers 22 to form the internal 14A and external 14B surfaces of the tube 14.

[0071] When the tube 14 comprises two reinforced layers 16, optionally, the tube 14 comprises an intermediate unreinforced layer 20 interposed between the two reinforced layers 16.

[0072] Preferably, the tube 14 is formed exclusively from the ceramic matrix and the ceramic reinforcing fibers. The tube 14 comprises at least one reinforced layer 16 in which the ceramic matrix is ​​reinforced by the ceramic reinforcing fibers, thereby forming a composite material, and, optionally, at least one unreinforced layer 20 made with the ceramic matrix not reinforced by the ceramic reinforcing fibers.

[0073] A method of manufacturing the tube 14 comprises, for example, the production of the or reinforced layers 16 by filament winding of the reinforcing fibers then infiltration of the reinforcing fibers with the matrix, for example by chemical vapor infiltration, then deposition of an internal non-reinforced layer 20 and / or an external non-reinforced layer 20, then, preferably, the reworking of the internal surface 14A and / or the external surface 14B of the tube 14, for example by machining and / or lapping.

[0074] To provide an intermediate non-reinforced layer 20, the manufacturing method comprises, for example, producing a reinforced layer 16, then depositing the intermediate non-reinforced layer 20 over said reinforced layer 16, then producing the other reinforced layer 16 over the intermediate non-reinforced layer 20.

[0075] In the following, the thicknesses are taken radially relative to the longitudinal axis A.

[0076] In particular, the tube 14 has a thickness (El in [Fig.2]) taken between the internal surface 14A and the external surface 14B of the tube 14, including the reinforced layer(s) 16, and the possible non-reinforced layer(s) 20.

[0077] In exemplary embodiments, the tube 14 comprises a single reinforced layer 16, the thickness E1 of the tube 14 being between 280 μm and 340 μm.

[0078] In exemplary embodiments, the tube 14 comprises exactly two reinforced layers 16, the thickness E2 of the tube 14 being between 450 μm and 600 μm.

[0079] The inner liner 18 is preferably in contact with the inner surface 14A of the tube 14.

[0080] The sheath 4 is free of radial play between the tube 14 and the internal lining 18.

[0081] The inner lining 18 is preferably solid. The inner lining 18 is fluid-tight, particularly gas-tight.

[0082] The internal lining 18 is for example metallic, i.e. made of metal.

[0083] The internal lining 18 is for example made of pure zirconium or of an alloy with zirconium base containing at least 95% by weight of zirconium.

[0084] The term "pure zirconium" means a material containing at least 99% by weight of zirconium. The remainder of the material consists of unavoidable impurities.

[0085] The zirconium-based alloy is for example chosen from one of the known alloys such as M5, ZIRLO, El 10, HANA, N36, Zircaloy-2 and Zircaloy 4.

[0086] The internal lining 18 has a thickness (E2 in [Fig.2]) of between 50 pm and 200 pm, in particular between 50 pm and 150 pm.

[0087] The internal lining 18 is for example pre-oxidized in a controlled environment to optimize its sealing characteristics against gases such as tritium.

[0088] The pre-oxidized inner liner 18 is intentionally fabricated with an oxide layer. The oxide layer is present on the inner liner 18 prior to use of the nuclear fuel rod, particularly in a nuclear reactor.

[0089] The sheath 4 and / or its caps 6 optionally comprise an external protective layer 22. The protective layer 22 covers the external surface 14B of the tube 14.

[0090] The external protective layer 22 is for example metallic.

[0091] The outer protective layer 22 is made of pure chromium or an alloy based on chromium containing at least 85% by weight of chromium or pure zirconium or zirconium-based alloy containing at least 85% by weight of zirconium or pure titanium or titanium-based alloy containing at least 80% by weight of titanium.

[0092] The term "pure chromium" means a material comprising at least 99% by weight of chromium. The remainder of the material consists of unavoidable impurities.

[0093] The term "pure titanium" means a material comprising at least 99% by weight of titanium. The remainder of the material consists of unavoidable impurities.

[0094] Preferably, the external protective layer 22 has a thickness (E3 in [Fig.2]) of between 5 μm and 40 μm.

[0095] As visible in [Fig. 1], the sheath 4 preferably comprises two closure elements 24 each closing a respective axial end of the internal lining 14, preferably in a fluid-tight manner, in particular gas-tight.

[0096] Each closure element 24 is for example fixed to the internal lining 18 by being welded and / or brazed and / or glued and / or inserted by force at the corresponding axial end of the internal lining 18.

[0097] Preferably, when closing the inner lining 18, the nature and pressure of the gas contained in the inner lining 18 are controlled, for example by using a valve. The gas is for example helium. The pressure is advantageously equal to or less than 200 bars, preferably equal to or less than 100 bars, more preferably equal to or less than 20 bars. The pressure is for example 15 bars.

[0098] In exemplary embodiments, each closure element 24 is metallic. In particular, each closure element 24 is made of the same material as the inner lining 18 and is preferably welded thereto, and also, optionally, welded, brazed, glued and / or force-fitted.

[0099] The closure elements 24 closing the internal lining 18 are for example distinct from the plugs 6 closing the axial ends of the tube 14.

[0100] In exemplary embodiments, each plug 6 is made of composite material comprising a matrix reinforced with reinforcing fibers, in particular a ceramic matrix reinforced with reinforcing fibers, even more in particular a silicon carbide matrix reinforced with silicon carbide fibers.

[0101] Each plug 6 is for example fixed to the tube 14 by being brazed and / or glued and / or inserted by force and / or pinned to the corresponding axial end of the tube 14. In advantageous embodiments, each plug 6 is brazed or pinned and brazed.

[0102] When an external protective layer 22 is provided, this covers the tube 14 over its entire length, and preferably partially or completely covers each plug 6, in particular at the junction between the plug 6 and the tube 14.

[0103] According to a method of manufacturing the nuclear fuel rod 2, the tube 14 and the internal lining 18 are for example manufactured separately, then the internal lining 18 is closed, its gas tightness preferably being checked, then the previously closed internal lining 18 is inserted into the tube 14.

[0104] In particular, the manufacturing method comprises manufacturing the tube 14, obtaining the inner lining 18, filling the inner lining 18 with nuclear fuel, for example by inserting the pellets 8 into the inner lining 18, closing the inner lining 18 at its axial ends using the sealing elements 24, preferably checking the gas tightness of the closed inner lining 18, inserting the filled and closed inner lining 18 into the tube 14, then closing the tube 14 at its axial ends by the plugs 6.

[0105] The manufacture of the tube 14 comprises the production of the reinforced layer(s) 16, in particular by filament winding of reinforcing fibers, for example on a cylindrical shape (or mandrel). The filament winding is carried out without interlacing of the reinforcing fibers and / or with interlacing of the reinforcing fibers, for example by braiding.

[0106] The reinforcing fibers are for example impregnated before deposition by filament winding, for example by passing through an impregnation bath, and / or after their filament winding, for example by infiltration, in particular by chemical vapor infiltration.

[0107] The method of manufacturing the tube 14 comprises the production of a single reinforced layer 16 or exactly two reinforced layers 16.

[0108] Optionally, the method of manufacturing the tube 14 comprises the deposition of an intermediate non-reinforced layer 20 between the two reinforced layers 16. In this case, the manufacturing method comprises for example the production of a reinforced layer 16, then the deposition of a non-reinforced layer 20 on the reinforced layer 16, then the production of another reinforced layer over the non-reinforced layer 20 which is interposed between the two reinforced layers 16.

[0109] Optionally, the production of the reinforced layer(s) 16 is followed by deposition of an internal non-reinforced layer 20 and / or an external non-reinforced layer 20.

[0110] Optionally, the manufacturing method comprises the deposition of an external protective layer 22 on the external surface 14B of the tube, for example by very low pressure plasma projection (or VLPPS from the English “Vacuum Low Pressure Plasma”). Spraying”) or by physical vapor deposition (or PVD from the English “Physical Vapor Deposition”).

[0111] The deposition of the external protective layer 22 is for example carried out when the internal lining 18 containing the fuel is present inside the tube 14, and preferably after the tube 14 has been closed using the plugs 6.

[0112] In embodiments, as described above, the tube 14 is formed to a cylindrical shape before inserting the filled and sealed inner liner 18 inside the tube 14.

[0113] In other embodiments, the inner liner 18 is filled with the nuclear fuel and closed at its axial ends by the sealing elements 24, then the tube 14 is formed around the inner liner 18. The inner liner 18 serves as a form for the production of the tube 14.

[0114] The proposed sheath 4 exhibits improved behavior under normal conditions of use and under accident conditions.

[0115] The tube 14 made of a ceramic matrix composite material reinforced with silicon carbide fibers makes it possible to obtain a cladding 6 which is very resistant, particularly in accident conditions. The risk of rupture of nuclear fuel release from the cladding is therefore reduced. A silicon carbide matrix reinforced with silicon carbide reinforcing fibers is particularly resistant.

[0116] The internal lining 18 provided in the tube 14 makes it possible to improve the sealing and in particular to prevent the release of fission gases outside the sheath 6.

[0117] The addition of a protective coating covering the external surface of the tube 14 of the cladding 4, and preferably also on the plugs 6, makes it possible to limit the risk of hydrothermal corrosion by the fluid circulating in the nuclear reactor around the nuclear fuel rod. In particular, it makes it possible to avoid or at least limit the erosion of the composite material of the tube 14 and / or to limit the release of silicon into the primary fluid (when the tube 14 comprises silicon) and / or to avoid or at least limit deposits, in particular CRUD (Chalk River Unidentified Deposits) deposits.

[0118] The thickness E1 of the tube 14, between 280 pm and 340 pm if the tube 14 comprises a single reinforced layer 16 or between 450 pm and 600 pm if the tube 14 comprises exactly two reinforced layers 16, makes it possible to form a cladding 4 having dimensions (in particular internal diameter and external diameter) compatible with existing nuclear fuel pellets.

[0119] The thickness El of the tube 14 between 280 pm and 340 pm if the tube 14 comprises a single reinforced layer 16 or between 450 pm and 600 pm if the tube 14 comprises exactly two reinforced layers 16 allows, with the tube 14 made at least partly of composite material, in particular of the SiC / SiCf or SiC / Cf type, a compromise satisfactory between thermal transfer and mechanical resistance in normal operation and in accidental operation, with good tolerance to damage that may be suffered by the sheath 4.

[0120] The tube 14 closed at its axial ends by the plugs 6 and, preferably provided with the external protective layer 22, protects the internal lining 18 from the external environment under normal operating conditions and under accident conditions.

[0121] The thickness range provided for the internal lining 18 allows sufficient mechanical strength before insertion into the tube 14, limited neutron absorption and satisfactory heat transfer.

[0122] The internal lining 18 ensures gas tightness with limited impact on the internal diameter of the sheath 4.

[0123] The material of the liner 18 must have low interaction with the material of the tube 14 and with the nuclear fuel for the temperature conditions of severe accident conditions.

[0124] The thickness range provided for the outer protective layer 22 allows limited neutron absorption and satisfactory heat transfer, and ensures a good service life, with a controlled risk of delamination. It makes it possible to produce an outer protective layer 22 which remains protective despite swelling of the tube 14 under irradiation, which is generally less than 2%.

Claims

Claims

1. A nuclear fuel rod cladding, comprising a tube (14) extending along a longitudinal axis and a tubular inner liner (18) received inside the tube (14), the tube (14) comprising at least one reinforced layer (16) made of a composite material comprising a ceramic matrix reinforced with ceramic reinforcing fibers, the thickness of the tube (14) being between 280 μm and 600 μm.

2. A sheath according to claim 1, wherein the tube (14) comprises a single reinforced layer (16), the thickness of the tube (14) being between 280 pm and 340 pm.

3. A sheath according to claim 1, wherein the tube (14) comprises exactly two reinforced layers, the thickness of the tube (14) being between 450 pm and 600 pm.

4. A sheath according to any one of the preceding claims, wherein the ceramic matrix is ​​made of silicon carbide and / or the ceramic reinforcing fibers are made of silicon carbide and / or carbon.

5. A sheath according to any preceding claim, wherein one or each reinforced layer (16) is formed with filament winding of the ceramic reinforcing fibers.

6. A sheath according to any preceding claim, wherein one or each reinforced layer (16) is formed with filament winding of the ceramic reinforcing fibers without interlacing of the ceramic reinforcing fibers.

7. A sheath according to any preceding claim, wherein one or each reinforced layer (16) is formed with filament winding of the ceramic reinforcing fibers with interlacing of the ceramic reinforcing fibers, for example by braiding the ceramic reinforcing fibers.

8. A sheath according to any preceding claim, wherein the tube (14) comprises at least one unreinforced layer (20), preferably made of the same material as the ceramic matrix.

9. Sheath according to claim 8, comprising an internal non-reinforced layer (20) covering the reinforced layer(s) (16) on the side of the internal face of the tube (14) and / or an external non-reinforced layer (20) covering the reinforced layer(s) (16) on the side of the external face of the tube (14) and / or an intermediate unreinforced layer (20) interposed between two reinforced layers (16) of the tube (14).

10. A sheath according to any preceding claim, wherein the tube (14) is formed exclusively from the ceramic matrix and the ceramic reinforcing fibers.

11. A sheath according to any preceding claim, wherein the inner lining has a thickness of between 50 pm and 200 pm, in particular between 50 pm and 150 pm.

12. A sheath according to any preceding claim, wherein the inner liner (18) is metallic.

13. A sheath according to any preceding claim, wherein the inner liner (18) is made of pure zirconium or a zirconium-based alloy containing at least 95% by weight zirconium.

14. A sheath according to any preceding claim, wherein the inner liner (18) is pre-oxidized.

15. A sheath according to any preceding claim, comprising an outer protective layer (22) covering an outer surface of the tube (14).

16. A sheath according to claim 15, wherein the outer protective layer (22) is metallic.

17. A sheath according to claim 15 or 16, wherein the outer protective layer (22) is made of pure chromium or a chromium-based alloy containing at least 85% by weight of chromium or of pure zirconium or a zirconium-based alloy containing at least 85% by weight of zirconium or of pure titanium or a titanium-based alloy containing at least 80% by weight of titanium.

18. Sheath according to any one of claims 15 to 17, in which the outer protective layer (22) has a thickness of between 5 pm and 40 pm.

19. A nuclear fuel rod comprising a cladding according to any one of the preceding claims, nuclear fuel received within the inner lining (18) of the cladding, and two plugs (6), each plug (6) closing a respective axial end of the cladding.

20. Nuclear fuel rod according to claim 19, in which each plug (6) is made of composite material comprising a ceramic matrix reinforced with ceramic reinforcing fibers, in par- in particular a silicon carbide matrix reinforced with silicon carbide and / or carbon reinforcing fibers.

21. A nuclear fuel rod according to claim 19 or claim 20, comprising two internal sealing elements (24), each closing a respective end of the internal liner (18).

22. A nuclear fuel rod according to any one of claims 19 to 21, wherein the inner liner (18) contains a gas, and the gas is helium and / or the pressure of the gas inside the inner liner (18) is equal to or less than 200 bars, preferably equal to or less than 100 bars, more preferably equal to or less than 20 bars.