Nuclear fuel cladding and manufacturing process for such cladding

Abstract

Nuclear fuel cladding and method for manufacturing such cladding. The nuclear fuel cladding is manufactured with a substrate (14) made of pure zirconium or a zirconium-based alloy and a multilayer protective coating (16) covering a surface (14B) of the substrate (14), the protective coating (16) comprising a main layer (18) made of pure chromium and one or more additional layers (20), each additional layer (20) being made of pure chromium or of a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities. Figure for the abstract: Figure 2

Description

Title of the invention: Nuclear fuel cladding and method of manufacturing such 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] It is possible to provide a sheath comprising a substrate made of a zirconium-based alloy and covered with a protective coating made of chromium.

[0009] Such a protective chrome coating generally makes it possible to increase the tolerance of the sheath under normal and accident conditions. However, the wear resistance of such a protective chrome coating is relatively low.

[0010] 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.

[0011] To this end, the invention provides a nuclear fuel cladding manufactured with a substrate made of pure zirconium or a zirconium-based alloy and a multi-layer protective coating covering a surface of the substrate, the protective coating comprising a main layer made of pure chromium and one or more additional layers, each additional layer being made of pure chromium or a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities.

[0012] The addition of an additional layer made of pure chromium or of a material consisting of chromium and, in addition, oxygen and / or nitrogen, in particular a material consisting of chromium oxide, chromium nitride, chromium oxynitride or a combination of these compounds or made of chromium doped with oxygen and / or nitrogen, makes it possible to further improve the performance of the cladding covered with a main layer made of pure chromium, in particular in terms of wear resistance, scratch resistance and / or permeation to fission products and other products resulting from corrosion, resistance to hydriding and absorption of hydrogen by the substrate, depending on whether the additional layer is located on the main layer or under the main layer.

[0013] According to particular embodiments, the sheath comprises one or more of the following optional characteristics, taken individually or in all technically possible combinations:

[0014] - at least one additional layer is made of pure chromium, chromium oxide, of chromium nitride or chromium oxynitride or a combination of these materials;

[0015] - at least one additional layer is made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or in which oxygen atoms and / or nitrogen atoms are implanted;

[0016] - the sheath comprises a transition layer interposed between the main layer and an additional layer containing oxygen and / or nitrogen, the transition layer being made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or of metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted;

[0017] - the transition layer has an increasing rate of oxygen atoms progressively from the main layer to the additional layer and / or has a rate of nitrogen atoms progressively increasing from the main layer to the additional layer;

[0018] - the rate of oxygen atoms of the transition layer at its interface with the adjacent additional layer is substantially equal to the rate of oxygen atoms of the adjacent additional layer and / or the rate of nitrogen atoms of the transition layer at its interface with the adjacent additional layer is substantially equal to the rate of nitrogen atoms of the adjacent additional layer;

[0019] - the thickness of the main layer is between 3 pm and 30 pm;

[0020] - the thickness of each additional layer is between 10 nm and 5 pm;

[0021] - at least one additional layer is located on the main layer;

[0022] - at least one additional layer is located under the main layer.

[0023] The invention also relates to a method of manufacturing a nuclear fuel cladding, the manufacturing method comprising providing a substrate made of pure zirconium or a zirconium-based alloy, and depositing a multi-layer protective coating on a surface of the substrate, the deposition of the protective coating comprising the deposition of a main layer made of pure chromium by physical vapor deposition and the deposition of one or more additional layers, each additional layer being made of pure chromium or a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities.

[0024] According to examples of implementation, the manufacturing method comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0025] - at least one additional layer is made of pure chromium, chromium oxide, of chromium nitride or chromium oxynitride or a combination of these materials;

[0026] - at least one additional layer is made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted;

[0027] - an additional layer is deposited by physical vapor deposition;

[0028] - an additional layer is deposited by physical vapor deposition carried out in an atmosphere formed from a binary or ternary gas mixture containing a neutral gas and, in addition, dioxygen and / or dinitrogen;

[0029] - the manufacturing method comprises the formation of a transition layer interposed between the main layer and an additional layer, the transition layer being made of chromium doped with oxygen atoms;

[0030] - the transition layer has an increasing rate of oxygen atoms gradually from the main layer to the adjacent additional layer;

[0031] - the thickness of the main layer is between 3 pm and 30 pm;

[0032] - the thickness of each additional layer is between 10 nm and 5 pm;

[0033] - at least one additional layer is deposited after the main layer;

[0034] - at least one additional layer is deposited before the main layer.

[0035] The invention also relates to a nuclear fuel cladding capable of being obtained by a method as defined above.

[0036] 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:

[0037] - [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;

[0038] - [Fig.2][Fig.3][Fig.4][Fig.5][Fig.6] Figures 2 to 6 are schematic views axial of nuclear fuel rod cladding;

[0039] - [Fig.7] [Fig.7] is a sectional view of a protective coating;

[0040] - [Fig.8] [Fig.8] is a schematic view of a deposition facility for a coating on a substrate by physical vapor deposition.

[0041] [Fig.l] illustrates 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.

[0042] The nuclear fuel rod 2 has the shape of an elongated rod along a longitudinal axis A.

[0043] The nuclear fuel rod 2 comprises a cladding 4 containing nuclear fuel. The cladding 4 is tubular and extends along the longitudinal axis A. The cladding 4 is sealed at each of its ends by a respective plug 6.

[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] [Fig.2] represents an axial view of a cladding 4 of a nuclear fuel rod 2, intended to contain nuclear fuel.

[0047] The sheath 4 comprises a substrate 14 provided with a protective coating 16.

[0048] The sheath 4 is tubular and extends along a longitudinal axis A.

[0049] Correspondingly, the substrate 14 is tubular and extends along the longitudinal axis A. The substrate 14 is a tube.

[0050] The substrate 14 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.

[0051] The substrate 14 is made of pure zirconium or a zirconium-based alloy.

[0052] The expression "pure zirconium" denotes a material containing at least 99% by weight of zirconium and the expression "zirconium-based alloy" denotes an alloy containing at least 95% by weight of zirconium. 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.

[0053] The substrate 14 has an internal surface 14A facing towards the inside of the cladding 4 and delimiting the space for receiving the nuclear fuel.

[0054] The substrate 14 has an external surface 14B intended to be turned towards the outside of the sheath 4. The external surface 14B is opposite the internal surface 14A.

[0055] The inner surface 14A is here the surface facing the inside of the tube-shaped substrate 14 and the outer surface 14B is the surface facing the outside of the tube-shaped substrate 14.

[0056] The protective coating 16 covers the outer surface 14B of the substrate 14. The protective coating 16 has the function of protecting the outer surface 14B of the substrate 14 from the external environment. In the absence of the protective coating 16, the outer surface 14B of the sheath 14 would be exposed to the external environment.

[0057] The protective coating 16 is multi-layered. The protective coating 16 comprises several superimposed layers.

[0058] The protective coating 16 comprises a main layer 18 and one or more additional layers 20.

[0059] The main layer 18 is made of pure chrome.

[0060] By "made from pure chromium" is meant made from a material comprising at least 99% by weight of chromium. The remainder of the material is made up of unavoidable impurities.

[0061] Each additional layer 20 is located on the main layer 18 or under the main layer 18. Each additional layer 20 located on the main layer 18 is located on the side of the main layer 18 opposite the substrate 14. Each additional layer 20 located under the main layer 18 is located between the main layer 18 and the substrate 14.

[0062] The protective coating 16 comprises for example one or more additional layers 20 located on the main layer 18. The main layer 18 is located between the substrate 14 and each additional layer 20 located on the main layer 18.

[0063] The protective coating 16 comprises for example one or more additional layers 20 located under the main layer 18. The main layer 18 is located between the substrate 14 and each additional layer 20 located under the main layer 18.

[0064] Preferably, the surface layer of the protective coating 16 is an additional layer 20. The surface layer of the protective coating 16 is the outermost layer of the protective coating 16. This surface layer is in contact with the external environment.

[0065] Each additional layer 20 is made of pure chromium or of a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities.

[0066] Preferably, the material of each additional layer 20 consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities, comprises at most 1% by weight of impurities, preferably at most 0.5% by weight of impurities.

[0067] The presence of impurities may be due, for example, to the presence of these impurities in the base material used to obtain the material of the additional layer 20.

[0068] For example, each additional layer 20 is made of pure chromium, chromium oxide, in particular Cr2O3 or an amorphous chromium oxide, chromium nitride, chromium oxynitride or a combination of these materials or is made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or is made of metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted.

[0069] A metallic chromium material doped with oxygen atoms and / or nitrogen atoms or in which oxygen atoms and / or nitrogen atoms are implanted means a material made of chromium whose atoms are arranged according to the crystalline structure of chromium, oxygen atoms and / or nitrogen atoms being inserted into this crystalline structure of chromium, and in particular replacing chromium atoms in this crystalline structure.

[0070] Doping with oxygen atoms and / or nitrogen atoms can be carried out for example during physical vapor deposition of the additional layer 20.

[0071] An implantation of oxygen atoms and / or nitrogen atoms is generally carried out after a deposition of chromium carried out for example by physical vapor deposition.

[0072] The thicknesses of the substrate 14 and of the layers of the protective coating 16 are taken perpendicular to the surface of the substrate 14 on which the protective coating 16 is deposited, here the external surface 14B.

[0073] The substrate 14 has, for example, a thickness of between 0.4 mm and 1 mm.

[0074] The main layer 18 has, for example, a thickness strictly less than that of the substrate 14.

[0075] The main layer 18 has, for example, a thickness of between 3 μm and 30 μm, in particular a thickness of between 5 μm and 20 μm.

[0076] Preferably, the thickness of each additional layer 20 is strictly less than the thickness of the main layer 18.

[0077] The thickness of each additional layer 20 is for example between 10 nm and 5 pm.

[0078] In Figures 2 to 6, the thickness of the substrate 14 and the thicknesses of the different layers of the protective coating 16 are not shown to scale for reasons of clarity of the drawings.

[0079] Optionally, the protective coating 16 comprises one or more transition layers 22, each transition layer 22 being interposed between the main layer 18 and an additional layer 20 located on the main layer 18 or under the main layer 18. Each transition layer 22 is in contact on one side with the main layer 18 and on the other side with an additional layer 20 located on the main layer 18 or under the main layer 18.

[0080] Each transition layer 22 is made of metallic chromium doped with oxygen and / or nitrogen atoms and / or of metallic chromium in which oxygen and / or nitrogen atoms are implanted.

[0081] The material of each transition layer 22 consists of metallic chromium doped with oxygen atoms and / or nitrogen atoms or metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted, with the possible presence of unavoidable impurities.

[0082] The material of the transition layer 22 is distinguished from a chromium oxide, a chromium nitride or a chromium oxynitride in that the material of the transition layer 22 is metallic chromium having the crystal structure of chromium and in which oxygen atoms and / or nitrogen atoms are included. The oxygen atoms and / or nitrogen atoms of the transition layer 22 are dispersed in the crystal structure of the metallic chromium of the transition layer 22.

[0083] The rate of oxygen atoms in the transition layer 22 is the number of oxygen atoms relative to the total number of atoms per unit volume. The rate of oxygen atoms is, for example, expressed as a percentage of oxygen atoms in the material.

[0084] Similarly, the nitrogen atom content of the transition layer 22 is the number of nitrogen atoms relative to the total number of atoms per unit volume. The nitrogen atom content is, for example, expressed as a percentage of oxygen atoms in the material.

[0085] Advantageously, the oxygen atom content of the transition layer 22 at its interface with the adjacent additional layer 20 is substantially equal to the oxygen atom content of this additional layer 20.

[0086] If the additional layer 20 adjacent to the transition layer 22 is made of Cr 2O3, the rate of oxygen atoms of the transition layer 22 at its interface with this additional layer 20 is for example 60%.

[0087] At least one transition layer 22, and in particular each transition layer 22 preferably has an oxygen atom content which increases, preferably progressively, according to the thickness of the transition layer 22, from the main layer 18 towards the adjacent additional layer 20.

[0088] In a preferred embodiment, the additional layer 20 adjacent to the transition layer 22 is made of chromium oxide Cr2O3 and the rate of oxygen atoms in the transition layer 22 increases, preferably progressively, from the main layer 18 to the adjacent additional layer 20 from a value of 0% up to a value of 60%.

[0089] In addition or as an option, the nitrogen atom rate of each transition layer 22 at its interface with the adjacent additional layer 20 is substantially equal to the nitrogen atom rate of this additional layer 20.

[0090] If the additional layer 20 adjacent to the transition layer 22 is made of chromium nitride (CrN), the rate of oxygen atoms in the transition layer 22 at its interface with this additional layer 20 is, for example, 50%.

[0091] At least one transition layer 22, and in particular each transition layer 22, preferably has an oxygen atom content which increases, preferably progressively, according to the thickness of the transition layer 22, from the main layer 18 towards the adjacent additional layer 20.

[0092] In a preferred embodiment, the additional layer 20 adjacent to the transition layer 22 is made of chromium oxide CrO and the rate of oxygen atoms in the transition layer 22 increases, preferably progressively, from the main layer 18 to the adjacent additional layer 20 from a value of 0% up to a value of 50%.

[0093] In a particular embodiment, at least one transition layer 22, and in particular each transition layer 22, preferably has a rate of oxygen atoms and a rate of nitrogen atoms which increase, preferably progressively, according to the thickness of the transition layer 22, from the main layer 18 towards the adjacent additional layer 20.

[0094] The thickness of each transition layer 22 is for example between 10 nm and 1 pm.

[0095] As illustrated in [Fig.2], in an exemplary embodiment, the protective coating 16 comprises the main layer 18 and an additional layer 20 located on the main layer 18, a transition layer 22 being interposed between the main layer 18 and the additional layer 20.

[0096] The main layer 18 is for example immediately adjacent to the substrate 14. The main layer 18 is in contact with the substrate 14. The main layer 18 is deposited directly on the substrate 14.

[0097] The additional layer 20 is made for example of pure chromium, chromium oxide and / or chromium oxynitride or metallic chromium doped with oxygen and / or nitrogen or chromium in which oxygen atoms and / or nitrogen atoms are implanted. In a particular embodiment, the additional layer 20 is made of chromium oxide, preferably Cr2O3 or an amorphous chromium oxide.

[0098] The additional layer 20 is preferably the surface layer of the protective coating 16 (i.e. the layer in contact with the external environment).

[0099] The protective coating 16 here consists of the main layer 18, the additional layer 20 located on the main layer 18 and the transition layer 22 interposed between the main layer 18 and the additional layer 20.

[0100] Other embodiments are conceivable, as illustrated in Figures 3 to 6 in which the numerical references to the analogous elements have been repeated.

[0101] The sheath 4 of [Fig.3] differs from that of [Fig.2] in that an additional layer 20 is applied directly onto the main layer 18. The additional layer 20 is in contact with the main layer 18. The sheath 4 is devoid of a transition layer 22 between the main layer 18 and the additional layer 20 located on the main layer 18.

[0102] The protective coating 16 is for example made up of the main layer 18 and the additional layer 20 located on the main layer 18.

[0103] The sheath 4 of [Fig.4] differs from that of [Fig.2] in that an additional layer 20 is located under the main layer 18, a transition layer 22 being interposed between the additional layer 20 and the main layer 18.

[0104] The additional layer 20 is for example deposited directly on the substrate 14, here on the external surface 14B of the substrate 14.

[0105] The protective coating 16 is for example made up of the additional layer 20, the main layer 18 located on the additional layer 20, and the transition layer 22 interposed between the additional layer 20 and the main layer 18.

[0106] The sheath 4 of [Fig.5] differs from that of [Fig.4] in that the main layer 18 is applied directly onto the additional layer 20. The additional layer 20 is in contact with the main layer 18. The sheath 4 is devoid of a layer of transition 22 between the additional layer 20 and the main layer 18 located on the additional layer 20.

[0107] The protective coating 16 is for example made up of the additional layer 20 deposited on the external surface 14B of the substrate 14 and the main layer 18 located on the additional layer 20.

[0108] The sheath 4 of [Fig.6] differs from that of [Fig.2] in that the protective coating 16 comprises an additional layer 20 located under the main layer 18 and an additional layer 20 located on the main layer 18. Optionally, a transition layer 22 is interposed between the main layer 18 and the additional layer 20 located under the main layer 18. Also optionally, a transition layer 22 is interposed between the main layer 18 and the additional layer 20 located on the main layer 18.

[0109] The protective coating 16 is for example made up of the main layer 18, an additional layer 20 located under the main layer 18, an additional layer 20 located on the main layer 18, a transition layer 22 inserted between the main layer 18 and the additional layer 20 located under the main layer 18 and a transition layer 22 inserted between the main layer 18 and the additional layer 20 located on the main layer 18.

[0110] As illustrated in [Fig.7], in an exemplary embodiment, a protective coating 16 comprises at least one group of several adjacent additional layers 20. Each additional layer 20 of this group is in contact with the next in the stack of layers of the protective coating 16. In [Fig.7], three adjacent additional layers 20 are shown.

[0111] Preferably, each additional layer 20 adjacent to another additional layer 20 is made of a material different from that of this other additional layer 20. In an exemplary embodiment, an additional layer 20 made of pure chromium is adjacent to another additional layer 20 made of a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities, in particular in a material made of chromium oxide, chromium nitride, chromium oxynitride, metallic chromium doped with oxygen atoms and / or nitrogen atoms or metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted.

[0112] Advantageously, the group of several adjacent additional layers 20 comprises at least one additional layer 20 made of pure chromium which is interposed between two other additional layers 20, each of these two other additional layers 20 being made of a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities, in particular in a material made of chromium oxide, chromium nitride, oxynitride of chromium, metallic chromium doped with oxygen atoms and / or nitrogen atoms or metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted.

[0113] In this case, the two other additional layers 20 located on either side of each additional layer 20 made of pure chrome are made of the same material or of different materials.

[0114] In an exemplary embodiment, each of these two other additional layers 20 is made of a material consisting of chromium and oxide, for example chromium oxide, or of a material consisting of chromium and nitrogen, for example chromium nitride.

[0115] In a particular embodiment, the additional layer 20 made of pure chromium is interposed between two other additional layers 20 made of chromium nitride.

[0116] In an exemplary embodiment, the group of several adjacent additional layers 20 comprises at least one additional layer 20 made of pure chromium arranged alternately with other additional layers 20, each of these other additional layers 20 being made of a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities, in particular in a material made of chromium oxide, chromium nitride, chromium oxynitride, metallic chromium doped with oxygen atoms and / or nitrogen atoms or metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted.

[0117] These other additional layers 20 which are arranged alternately with the additional layer(s) 20 made of pure chrome, are made of the same material or of at least two different materials.

[0118] In a particular embodiment, the group of adjacent additional layers 20 comprises one or more additional layers made of pure chromium alternating with other additional layers 20 made of chromium nitride.

[0119] A protective coating 16 may comprise such a group of adjacent additional layers 20 located on the main layer 18 and / or such a group of adjacent additional layers 20 located under the main layer 18.

[0120] A method of manufacturing a sheath 4 will now be described with reference to [Fig.8].

[0121] The manufacturing method comprises a step of obtaining the substrate 14. When the substrate 14 is a tube, it is for example obtained in a known manner by pilgrim rolling, from a tubular blank of diameter larger than that of the substrate 14, the blank being deformed so that its diameter is progressively reduced and its length gradually increased, before possibly being cut to the desired length to obtain the substrate 14.

[0122] The manufacturing method comprises depositing the main layer 18 on the external surface 14B of the substrate 14 by physical vapor deposition.

[0123] As illustrated in [Fig.8], the physical vapor deposition of the main layer 18 is for example carried out under a controlled atmosphere in a chamber 24 of a physical vapor deposition installation 26, and in particular under a rarefied atmosphere formed for example by a neutral gas, such as argon.

[0124] The neutral gas is chosen to avoid oxidation phenomena during the phase of deposition of a layer of the protective coating 16 on the substrate 14.

[0125] Physical vapor deposition is carried out for example by cathodic sputtering or by evaporation.

[0126] In an exemplary embodiment, the main layer 18 is deposited by physical vapor deposition by cathodic sputtering.

[0127] To do this, the substrate 14 and a target 28 made of chromium are placed in the chamber 24 in which a rarefied atmosphere is generated, formed for example of a neutral gas, such as argon, and an electric field is generated in the rarefied atmosphere, resulting in the appearance of a plasma containing atoms and electrically charged particles (electrons, ions, etc.), which are precipitated onto the target 28 under the effect of the electric field and detach atoms from the target 28 (i.e. the target 28 is sputtered, hence the term cathode sputtering), these atoms detached from the target 28 then being deposited on the substrate 14.

[0128] The physical vapor deposition installation 26 comprises the chamber 24, the target 28 arranged inside the chamber 24, a pump 30 whose inlet is fluidly connected to the chamber 24 to generate a rarefied atmosphere in the chamber 24, an electrical generator 32 connected to the target 28, optionally, an electrical generator 34 connected to the substrate 14, and a gas supply device 36 fluidly connected to the chamber 24, for example to supply the neutral gas (e.g. argon), dioxygen and / or dinitrogen.

[0129] Preferably, the physical vapor deposition is carried out by magnetron sputtering. In this case, a magnetic field is generated, preferably at least in the vicinity of the target 28.

[0130] The provision of a magnetic field makes it possible to better control the trajectory of the electrically charged particles reaching the target 28, which allows a better controlled deposition rate of the main layer 18, in particular a higher deposition rate.

[0131] The magnetic field is generated for example by one or more permanent magnets 38, as illustrated in [Fig.3], and / or one or more electromagnets.

[0132] The manufacturing method comprises the deposition of at least one additional layer 20, also by physical vapor deposition.

[0133] The deposition of each additional layer 20 is for example carried out in the same physical vapor deposition installation 26 as the deposition of the main layer 18.

[0134] The deposition of each additional layer 20 is carried out for example using the same physical vapor deposition technique as that used to carry out the physical vapor deposition of the main layer 18.

[0135] The deposition of each additional layer 20 is carried out for example by physical vapor deposition by cathode sputtering, in particular by magnetron cathode sputtering.

[0136] The deposition of each additional layer 20 is carried out according to the same technique as the deposition of the main layer 18, but differs in that it is carried out, when necessary, in a controlled atmosphere containing, in addition to the neutral gas, dioxygen and / or dinitrogen for the formation of an additional layer formed of chromium oxide, chromium nitride, chromium oxynitride or a combination of these compounds.

[0137] The oxygen and nitrogen are for example introduced into the chamber 24 using the gas supply device 36.

[0138] In an exemplary embodiment, only dioxygen is introduced into the controlled atmosphere in addition to the neutral gas. The controlled atmosphere is a binary gas mixture containing the neutral gas and dioxygen. This makes it possible to obtain an additional layer 20 of chromium oxide.

[0139] In an exemplary embodiment, only nitrogen is introduced into the controlled atmosphere. The controlled atmosphere is a binary gas mixture containing the neutral gas and nitrogen. This makes it possible to obtain an additional layer 20 of chromium nitride.

[0140] In an exemplary embodiment, dioxygen and dinitrogen are introduced into the controlled atmosphere in addition to the neutral gas. The controlled atmosphere is a ternary gas mixture containing the neutral gas, dioxygen and dinitrogen. This makes it possible to obtain an additional layer containing chromium oxide, chromium nitride and / or chromium oxynitride.

[0141] In an exemplary embodiment, only the neutral gas is introduced into the controlled atmosphere. This makes it possible to obtain an additional layer 20 of pure chromium.

[0142] The layers of the protective coating 16 are deposited successively from the closest to the furthest from the substrate 14.

[0143] Each additional layer 20 located under the main layer 18 is deposited before the main layer 18 and / or each additional layer 20 located on the main layer 18 is deposited after the main layer 18.

[0144] After deposition of the main layer 18 and each additional layer 20, the sheath 4 comprises the substrate 14 whose external surface 14B is covered by the protective coating 16.

[0145] Where appropriate, the manufacturing method comprises forming each transition layer 22.

[0146] Each transition layer 22 is for example produced by depositing a layer of chromium by physical vapor deposition while introducing gaseous oxygen into the atmosphere of the chamber 24.

[0147] The formation of a transition layer 22 on the main layer 18 is for example carried out following the deposition of the main layer 18, by continuing the physical vapor deposition of the chromium while introducing gaseous oxygen into the atmosphere of the chamber 24.

[0148] To produce a transition layer 22 having an increasing, preferably progressive, rate of oxygen atoms, the rate of dioxygen in the atmosphere of the chamber 24 is for example increased or decreased over time, preferably progressively.

[0149] Alternatively, instead of introducing gaseous oxygen into the atmosphere of the chamber 24, it is possible to introduce an oxygenated product which decomposes or evaporates by releasing oxygen into the controlled atmosphere.

[0150] Alternatively, the transition layer 22 is obtained after the deposition of chromium by physical vapor deposition over a thickness corresponding to that desired for the transition layer 22, then by carrying out an ionic implantation of oxygen in this layer of chromium.

[0151] Each physical vapor deposition (deposition of the main layer 18, deposition of each additional layer 20 and, where appropriate, deposition of each transition layer 22) can be carried out with a continuous current density (i.e. by applying a continuous electric current to the target 28) or a pulsed current density (i.e. by applying a pulsed electric current comprising pulses).

[0152] Each physical vapor deposition by magnetron sputtering can be carried out according to one of the following techniques or a combination of at least two of the following techniques: direct current magnetron sputtering (in English "Direct Current" or "DC"), pulsed direct current magnetron sputtering (in English "Pulsed Direct Current" or "DC pulsed"), high power pulsed magnetron sputtering (in English "High Power Impulse Magnetron Sputtering" (HiPIMS or HPMS), cathode sputtering Magnetron Sputtering Bipolar (MSB), Dual Magnetron Sputtering (DMS), Unbalanced Magnetron Sputtering (UBM).

[0153] Deposition of the protective coating 16 by physical vapor deposition by magnetron sputtering is preferred, but the invention is not limited to such a deposition technique.

[0154] Alternatively, the deposition of each layer of the protective coating 16 may be carried out using another technique, for example by physical vapor deposition by evaporation, in particular by physical vapor deposition by electric arc, or by physical deposition by cold spray.

[0155] The addition of a main layer 18 of chromium on the substrate 14 makes it possible to improve the wear resistance of the sheath 4 compared to a sheath 4 made of pure zirconium or a zirconium-based alloy and not coated.

[0156] The addition in addition of an additional layer 20 made of pure chromium or of a material consisting of chromium oxide, chromium nitride, chromium oxynitride or a combination of these compounds or made of chromium doped with oxygen and / or nitrogen, makes it possible to further improve the performance of the cladding 4, in particular in terms of wear resistance, scratch resistance and / or permeation to fission products.

[0157] Each additional layer 20 deposited by physical vapor deposition can be deposited in a controlled manner, with a chosen thickness, and in particular sufficient to obtain the desired performance.

[0158] The addition of an additional layer 20 on the main layer 18 is likely to improve the resistance to wear and scratches, due to an increased hardness compared to the main layer 18. The wear resistance makes it possible to limit the sensitivity of the cladding 4 to wear by vibration (or "fretting" in English). The scratch resistance makes it possible to limit the risk of scratches forming on the external surface of the cladding 4 when inserting the nuclear fuel rod 2 through the spacer grids of a nuclear fuel assembly.

[0159] Each additional layer 20 located on the main layer 18 or under the main layer 18, in particular when it contains Cr2O3, makes it possible to limit the permeation through the cladding 4 of fission products such as tritium coming from the inside of the cladding or of corrosion products such as hydrogen coming from the external surface.

[0160] Hydrogen is likely to increase the fragility of the substrate 14 made of zirconium-based alloy and tritium can pollute the coolant circulating in the core of the nuclear reactor.

[0161] An additional layer 20 located on the main layer 18 and containing chromium oxide, and in particular Cr2O3, can also take on a black coloring even before its insertion into a core of a nuclear reactor, which can be favorable to thermal transfers during transient phases of the nuclear reactor, in particular during start-up of the nuclear reactor.

[0162] An additional layer 20 located under the main layer 18, between the substrate 14 and the main layer 20, is capable of reducing the formation of a Cr-Zr eutectic for high temperatures, typically for temperatures above 1330°C. The resistance of the sheath in the event of LOCA is thereby improved.

[0163] It will be noted that the natural formation of an oxide on a zirconium-based alloy cladding occurs within a few days after water is placed on the surface of the cladding. For example, the natural formation of an oxide on a zirconium-based alloy cladding of a nuclear fuel rod occurs within approximately five days after the nuclear fuel assembly is inserted into the core of a nuclear reactor. The thickness of zirconium oxide thus formed on the cladding quickly reaches approximately 100 nm and quickly provides protection to the zirconium alloy substrate.

[0164] On the contrary, the natural formation of a chromium oxide on a protective chromium coating in the presence of water on the coating is slow, for example by a factor of 10 to 20 times slower than for a zirconium-based alloy, and insufficient to provide protection to the coating as soon as the cladding is used in a nuclear reactor core. A chromium oxide thickness of 100 nm is reached only after 500 days in the reactor.

[0165] The deposition of a protective coating comprising at least one additional layer during the manufacture of the cladding makes it possible to ensure protection from the start of use of the cladding in a nuclear reactor core.

[0166] In this respect, it should be noted that the deposition of the chromium layers of the protective chromium coating is generally carried out in an inert medium (with rare gas such as argon) to avoid oxidation phenomena during the deposition of the chromium layer coating.

Claims

Claims

1. Nuclear fuel cladding, manufactured with a substrate (14) made of pure zirconium or a zirconium-based alloy and a multi-layer protective coating (16) covering a surface (14B) of the substrate (14), the protective coating (16) comprising a main layer (18) made of pure chromium and one or more additional layers (20), each additional layer (20) being made of pure chromium or a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities, in which at least one additional layer (20) is made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or in which oxygen atoms and / or nitrogen atoms are implanted.

2. A sheath according to claim 1, wherein at least one additional layer (20) is made of pure chromium, chromium oxide, chromium nitride or chromium oxynitride or a combination of these materials.

3. Sheath according to claim 1 or claim 2, comprising a transition layer (22) interposed between the main layer (18) and an additional layer (20) containing oxygen and / or nitrogen, the transition layer (22) being made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or of metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted.

4. Sheath according to claim 3, in which the transition layer (22) has a rate of oxygen atoms progressively increasing from the main layer (18) towards the additional layer (20) and / or has a rate of nitrogen atoms progressively increasing from the main layer (18) towards the additional layer (20).

5. Sheath according to claim 3 or claim 4, in which the rate of oxygen atoms of the transition layer (22) at its interface with the adjacent additional layer (20) is substantially equal to the rate of oxygen atoms of the adjacent additional layer (20) and / or the rate of nitrogen atoms of the transition layer (22) at its interface with the adjacent additional layer (20) is substantially equal to the rate of nitrogen atoms of the adjacent additional layer (20).

6. A sheath according to any preceding claim, wherein the thickness of the main layer (18) is between 3 pm and 30 pm.

7. A sheath according to any preceding claim, wherein the thickness of each additional layer (20) is between 10 nm and 5 pm.

8. A sheath according to any preceding claim, wherein an additional layer (20) is located on the main layer (18).

9. A sheath according to any preceding claim, wherein an additional layer (20) is located beneath the main layer (18).

10. A method of manufacturing a nuclear fuel cladding, the manufacturing method comprising: - providing a substrate (14) made of pure zirconium or a zirconium-based alloy; and - depositing a multi-layer protective coating (16) on a surface (14B) of the substrate (14), the deposition of the protective coating (16) comprising the deposition of a main layer (18) made of pure chromium by physical vapor deposition and the deposition of one or more additional layers (20), each additional layer (20) being made of pure chromium or a material consisting of chromium and, in addition, oxygen and / or nitrogen, with the possible presence of unavoidable impurities, in which at least one additional layer is made of metallic chromium doped with oxygen atoms and / or nitrogen atoms or of metallic chromium in which oxygen atoms and / or nitrogen atoms are implanted.

11. A manufacturing method according to claim 10, wherein an additional layer (20) is made of pure chromium, chromium oxide, chromium nitride or chromium oxynitride or a combination of these materials.

12. A manufacturing method according to claim 10 or claim 11, wherein at least one additional layer (20) is deposited by physical vapor deposition.

13. Manufacturing method according to any one of claims 10 to 12, in which at least one additional layer (20) is deposited by physical vapor deposition carried out in an atmosphere formed of a binary or ternary gas mixture containing a neutral gas and, in addition, dioxygen and / or dinitrogen.

14. A manufacturing method according to any one of claims 10 to 13, comprising the formation of a transition layer (22) interposed between the main layer (18) and an additional layer (20), the transition layer (22) being made of chromium doped with oxygen atoms.

15. A manufacturing method according to claim 14, wherein the transition layer (22) has a progressively increasing oxygen atom content from the main layer (18) to the adjacent additional layer (20).

16. A manufacturing method according to any one of claims 10 to 15, wherein the thickness of the main layer (18) is between 3 pm and 30 pm.

17. A manufacturing method according to any one of claims 10 to 16, wherein the thickness of each additional layer (20) is between 10 nm and 5 pm.

18. A manufacturing method according to any one of claims 10 to 17, wherein at least one additional layer (20) is deposited after the main layer (18).

19. A manufacturing method according to any one of claims 10 to 18, wherein at least one additional layer (20) is deposited before the main layer (18).

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