Nuclear fuel cladding and method of making such cladding - Patents.com

Abstract

The present invention relates to nuclear fuel cladding, the cladding being produced using a substrate (14) made of pure zirconium or a zirconium-containing alloy and a multi-layer protective coating (16) covering a surface (14B) of the substrate (14), the protective coating (16) having a main layer (18) made of pure chromium and one or more additional layers (20), each of which is made of pure chromium or a material made of chromium plus oxygen and / or nitrogen, and possibly the presence of unavoidable impurities.

Description

[Technical field]

[0001] The present invention relates to nuclear fuel cladding (hereinafter also referred to as "cladding") intended to contain nuclear fuel, and more particularly to nuclear fuel rod cladding, and to a method for producing same. [Background technology]

[0002] Nuclear fuel, which contains fissile material, is generally contained within a sealed cladding that prevents dispersion of the nuclear fuel.

[0003] A nuclear fuel assembly used in a light water or heavy water reactor generally comprises a bundle of nuclear fuel rods, each of which comprises a tubular cladding containing the nuclear fuel, the cladding being closed at each of its ends by a respective plug.

[0004] The cladding of the nuclear fuel assemblies is made, for example, of zirconium or zirconium alloys, which have high performance under normal operating conditions in a nuclear reactor.

[0005] However, these alloys may reach their limits, especially from a temperature standpoint, during severe accident conditions, such as during a loss of coolant accident (or LOCA).

[0006] During such an event, temperatures in the reactor core can reach over 800° C., and the cooling fluid is essentially in the form of water steam.

[0007] This can cause rapid degradation of the cladding of the nuclear fuel rods, in particular involving hydrogen release and rapid oxidation of the cladding, which can lead to weakening and even rupture of the cladding and thus the release of nuclear fuel outside the cladding.

[0008] It is possible to propose a coating comprising a substrate made of a zirconium alloy covered with a protective coating made of chromium.

[0009] Such protective chromium coatings generally enhance the durability of the coating under normal and accident conditions, however, the wear resistance of such protective chromium coatings is relatively low. Summary of the Invention [Problem to be solved by the invention]

[0010] One of the aims of the present invention is to propose a coating which exhibits improved behaviour under normal and accident conditions and at the same time exhibits improved wear resistance. [Means for solving the problem]

[0011] To this end, the invention proposes a nuclear fuel cladding, the cladding being manufactured using a substrate made of pure zirconium or a zirconium alloy and a multilayer protective coating covering the surface of the substrate, the protective coating having a main layer made of pure chromium and one or more additional layers, each additional layer being made of pure chromium or of a material composed of chromium furthermore of oxygen and / or nitrogen, with possible unavoidable impurities present.

[0012] By adding an additional layer made of pure chromium or an additional layer consisting of a material made of chromium and also oxygen and / or nitrogen, in particular chromium oxide, chromium nitride, chromium oxynitride or a combination of these compounds, or an additional layer made of chromium doped with oxygen and / or nitrogen, the performances of the coating covered with a main layer made of pure chromium are further improved, more particularly in terms of wear resistance, scratch resistance and / or permeability to fission products and other corrosion products, resistance to hydrogen absorption and hydriding by the substrate, depending on whether the additional layer is located above or below the main layer.

[0013] According to particular embodiments, the coating comprises one or more of the following optional features, considered individually or in all technically possible combinations: - at least one additional layer is made of pure chromium, chromium oxide, chromium nitride or chromium oxynitride or a combination of such materials; at least one additional layer is made of metallic chromium doped with oxygen and / or nitrogen atoms or of metallic chromium embedded with oxygen and / or nitrogen atoms; - the coating 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 and / or nitrogen atoms or metallic chromium in which oxygen and / or nitrogen atoms are embedded; - the transition layer has a concentration of oxygen atoms that gradually increases from the main layer to the additional layer and / or has a concentration of nitrogen atoms that gradually increases from the main layer to the additional layer; - the concentration of oxygen atoms in the transition layer at the interface with the adjacent additional layer is substantially equal to the concentration of oxygen atoms in the adjacent additional layer, and / or the concentration of nitrogen atoms in the transition layer at the interface with the adjacent additional layer is substantially equal to the concentration of nitrogen atoms in the adjacent additional layer; - the thickness of the main layer is 3μm-30μm; - the thickness of each additional layer is between 10 nm and 5 μm; - at least one additional layer is located above the main layer; At least one additional layer is located below the main layer.

[0014] The invention further relates to a method for producing nuclear fuel cladding comprising providing a substrate made of pure zirconium or a zirconium 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 of a material composed of chromium furthermore oxygen and / or nitrogen, with possible unavoidable impurities present.

[0015] According to example embodiments, the manufacturing method comprises one or more of any of the following features, considered individually or in all technically possible combinations: - at least one additional layer is made of pure chromium, chromium oxide, chromium nitride or chromium oxynitride or a combination of such materials; - at least one additional layer is made of metallic chromium doped with oxygen and / or nitrogen atoms or metallic chromium embedded with oxygen and / or nitrogen atoms; - the additive layer is deposited by physical vapor deposition; the additional layer is deposited by physical vapour deposition carried out in an atmosphere formed by a binary or ternary gas mixture containing a neutral gas and additionally oxygen and / or nitrogen; - the manufacturing method includes the formation of a transition layer interposed between the main layer and the additional layer, the transition layer being made of chromium doped with oxygen atoms; - the transition layer has a concentration of oxygen atoms that gradually increases from the main layer to the adjacent additional layer; - the thickness of the main layer is 3μm-30μm; - the thickness of each additional layer is between 10 nm and 5 μm; - at least one additional layer is applied after the main layer; At least one additional layer is applied before the main layer.

[0016] The invention further relates to a nuclear fuel cladding obtainable by a method as defined above.

[0017] The invention and its advantages can be better understood by reading the following description, given purely as a non-limiting example, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0018] [Figure 1] 1 is a schematic longitudinal cross-sectional view of a nuclear fuel rod showing the cladding of the nuclear fuel rod; [Diagram 2] 1 is a schematic axial view of the cladding of a nuclear fuel rod; [Diagram 3] 1 is a schematic axial view of the cladding of a nuclear fuel rod; [Figure 4] 1 is a schematic axial view of the cladding of a nuclear fuel rod; [Diagram 5] 1 is a schematic axial view of the cladding of a nuclear fuel rod; [Figure 6] 1 is a schematic axial view of the cladding of a nuclear fuel rod; [Figure 7] FIG. 2 is a schematic diagram of a protective coating. [Figure 8] 1 is a schematic diagram of an installation for depositing a coating on a substrate by physical vapor deposition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] FIG. 1 shows a nuclear fuel rod 2 intended for use in a light water reactor, in particular a pressurized water reactor (PWR) or boiling water reactor (BWR), a "VVER" reactor, a "RBMK" reactor or a heavy water reactor, for example a "CANDU" reactor.

[0020] The nuclear fuel rod 2 has a rod shape extending along a longitudinal axis A.

[0021] The nuclear fuel rod 2 comprises a cladding 4 which contains the nuclear fuel. The cladding 4 is tubular and extends along a longitudinal axis A. The cladding 4 is sealed at each of its ends by respective plugs 6.

[0022] 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".

[0023] The nuclear fuel rod 2 includes a spring 10 disposed within the cladding 4 between the stack of pellets 8 and one of the plugs 6 for urging the stack of pellets 8 towards the other plug 6. There is an empty space or plenum 12 between the stack of pellets 8 and the plug 6 against which the spring 10 bears.

[0024] FIG. 2 shows an axial view of the cladding 4 of a nuclear fuel rod 2 intended to contain nuclear fuel.

[0025] The covering 4 includes a substrate 14 having a protective coating 16 thereon.

[0026] The covering 4 is tubular and extends along a longitudinal axis A.

[0027] Correspondingly, the substrate 14 is tubular and extends along a longitudinal axis A. The substrate 14 is a tube.

[0028] Substrate 14 has, for example, an outer diameter of 8 mm to 15 mm, more specifically 9 mm to 13 mm, and / or a length of 1 m to 5 m, more specifically 2 m to 5 m.

[0029] The substrate 14 is made, for example, of pure zirconium or a zirconium alloy.

[0030] The expression "pure zirconium" refers to a material containing at least 99% by weight of zirconium, and the expression "zirconium alloy" refers to an alloy containing at least 95% by weight of zirconium, the zirconium alloy being selected from one of the known alloys, such as, for example, M5, ZIRLO, E110, HANA, N36, Zircaloy-2 and Zircaloy-4.

[0031] The substrate 14 has an inner surface 14A facing the interior of the cladding 4, which defines a space for containing nuclear fuel.

[0032] The substrate 14 has an outer surface 14B intended to be directed towards the exterior of the coating 4. The outer surface 14B is opposite the inner surface 14A.

[0033] The inner surface 14A here is the surface facing towards the inside of the tubular shaped substrate 14, and the outer surface 14B is the surface facing towards the outside of the tubular shaped substrate 14.

[0034] A protective coating 16 covers the outer surface 14B of the substrate 14. The function of the protective coating 16 is to protect the outer surface 14B of the substrate 14 from the external environment. Without the protective coating 16, the outer surface 14B of the cladding 14 would be exposed to the external environment.

[0035] The protective coating 16 is multi-layered. The protective coating 16 has multiple stacked layers.

[0036] The protective coating 16 includes a main layer 18 and one or more additional layers 20 .

[0037] The main layer 18 is made of pure chromium.

[0038] "Made of pure chromium" means made of a material that contains at least 99% chromium by weight. The remainder of the material consists of unavoidable impurities.

[0039] Each additional layer 20 is located either above or below the main layer 18. Each additional layer 20 that is above the main layer 18 is located on the side of the main layer 18 opposite the substrate 14. Each additional layer 20 that is below the main layer 18 is located between the main layer 18 and the substrate 14.

[0040] The protective coating 16, for example, includes one or more additional layers 20 disposed over a primary layer 18. The primary layer 18 is disposed between the substrate 14 and each additional layer 20 disposed over the primary layer 18.

[0041] The protective coating 16, for example, includes one or more additional layers 20 that underlie the main layer 18. The main layer 18 is positioned between the substrate 14 and each additional layer 20 that underlies the main layer 18.

[0042] Preferably, the surface layer of the protective coating 16 is the additive layer 20. The surface layer of the protective coating 16 is the outermost layer of the protective coating 16. Such a surface layer is in contact with the external environment.

[0043] Each additional layer 20 is made of pure chromium or of a material composed of chromium with additional oxygen and / or nitrogen, possibly with unavoidable impurities present.

[0044] Preferably, the material of each additional layer 20, consisting of chromium and also oxygen and / or nitrogen and possibly present unavoidable impurities, contains a maximum of 1% by weight of impurities, preferably a maximum of 0.5% by weight of impurities.

[0045] The presence of impurities may for example result from the presence of impurities in the substrate used to obtain the material of the additional layer 20 .

[0046] For example, each additional layer 20 may be made of pure chromium, chromium oxide, more specifically Cr2O3 or amorphous chromium oxide, chromium nitride, chromium oxynitride or a combination of these materials, or may be made of metallic chromium doped with oxygen and / or nitrogen atoms or may be made of metallic chromium having embedded oxygen and / or nitrogen atoms.

[0047] Metallic chromium material doped with oxygen and / or nitrogen atoms or metal chromium material embedded with oxygen and / or nitrogen atoms means a material made of chromium whose atoms are arranged according to the crystal structure of chromium and in which oxygen and / or nitrogen atoms are inserted into this crystal structure of chromium, more specifically substituting chromium atoms in this crystal structure.

[0048] Doping with oxygen and / or nitrogen atoms can be performed, for example, during physical vapor deposition of the additional layer 20 .

[0049] The implantation of oxygen and / or nitrogen atoms is generally performed after chromium deposition, which is performed, for example, by physical vapor deposition.

[0050] The layer thicknesses of substrate 14 and protective coating 16 are taken perpendicular to the surface of substrate 14 onto which protective coating 16 is deposited, here outer surface 14B.

[0051] The substrate 14 has a thickness of, for example, 0.4 mm to 1 mm.

[0052] The main layer 18 has a thickness that is, for example, strictly less than the thickness of the substrate 14 .

[0053] The main layer 18 has a thickness of, for example, 3 μm to 30 μm, and more specifically, a thickness of 5 μm to 20 μm.

[0054] Preferably, the thickness of each additional layer 20 is strictly less than the thickness of the main layer 18 .

[0055] The thickness of each additional layer 20 is, for example, 10 nm to 5 μm.

[0056] 2-6, the thickness of the substrate 14 and the thicknesses of the various layers of the protective coating 16 are not shown to scale in order to maintain clarity of the drawings.

[0057] Optionally, protective coating 16 includes one or more transition layers 22, each interposed between main layer 18 and an additional layer 20 positioned above or below main layer 18. Each transition layer 22 contacts main layer 18 on one side and additional layer 20 positioned above or below main layer 18 on the other side.

[0058] Each transition layer 22 is made of metallic chromium doped with oxygen and / or nitrogen atoms and / or metallic chromium embedded with oxygen and / or nitrogen atoms.

[0059] The material of each transition layer 22 consists of metallic chromium doped with oxygen and / or nitrogen atoms or metallic chromium embedded with oxygen and / or nitrogen atoms, together with any unavoidable impurities that may be present.

[0060] The material of transition layer 22 differs from chromium oxide, chromium nitride, or chromium oxynitride in that the material of transition layer 22 is chromium metal, which has a chromium crystal structure and contains oxygen and / or nitrogen atoms. The oxygen and / or nitrogen atoms of transition layer 22 are dispersed within the chromium metal crystal structure of transition layer 22.

[0061] The concentration of oxygen atoms in the transition layer 22 is the number of oxygen atoms relative to the total number of atoms per unit volume, expressed, for example, as a percentage of oxygen atoms in the material.

[0062] Similarly, the nitrogen atomic concentration of the transition layer 22 is the number of nitrogen atoms relative to the total number of atoms per unit volume, for example expressed as a percentage of nitrogen atoms in the material.

[0063] Advantageously, the concentration of oxygen atoms in the transition layer 22 at the interface with the adjacent additional layer 20 is substantially equal to the concentration of oxygen atoms in this additional layer 20 .

[0064] If the additional layer 20 adjacent to the transition layer 22 is made of Cr2O3, the concentration of oxygen atoms in the transition layer 22 at the interface with the additional layer 20 is, for example, 60%.

[0065] At least one transition layer 22, and more particularly each transition layer 22, preferably has a concentration of oxygen atoms that preferably increases gradually from the main layer 18 to the adjacent additional layer 20 depending on the thickness of the transition layer 22.

[0066] In a preferred embodiment, the additional layer 20 adjacent to the transition layer 22 is made of chromium oxide Cr2O3, and the concentration of oxygen atoms in the transition layer 22 increases, preferably gradually, from a value of 0% to a maximum value of 60% from the main layer 18 toward the adjacent additional layer 20.

[0067] Additionally or alternatively, the concentration of nitrogen atoms in each transition layer 22 at its interface with an adjacent additional layer 20 is substantially equal to the concentration of nitrogen atoms in that additional layer 20 .

[0068] If the additional layer 20 adjacent to the transition layer 22 is made of chromium nitride (CrN), the concentration of oxygen atoms in the transition layer 22 at its interface with the additional layer 20 is, for example, 50%.

[0069] At least one transition layer 22, and more particularly each transition layer 22, preferably has a concentration of oxygen atoms that preferably increases gradually from the main layer 18 to the adjacent additional layer 20 depending on the thickness of the transition layer 22.

[0070] In a preferred embodiment, the additional layer 20 adjacent to the transition layer 22 is made of chromium oxide CrO, and the concentration of oxygen atoms in the transition layer 22 increases, preferably gradually, from a value of 0% to a maximum value of 50% from the main layer 18 towards the adjacent additional layer 20.

[0071] In one particular example embodiment, at least one transition layer 22, and more specifically each transition layer 22, preferably has a concentration of oxygen atoms and a concentration of nitrogen atoms that preferably increase gradually from the main layer 18 to the adjacent additional layer 20 depending on the thickness of the transition layer 22.

[0072] The thickness of each transition layer 22 is, for example, 10 nm to 1 μm.

[0073] As shown in FIG. 2, in one example embodiment, the protective coating 16 has a primary layer 18 and an additional layer 20 positioned over the primary layer 18, with a transition layer 22 interposed between the primary layer 18 and the additional layer 20.

[0074] 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.

[0075] The additional layer 20 is made of, for example, pure chromium, chromium oxide and / or chromium oxynitride, or metallic chromium doped with oxygen and / or nitrogen, or chromium with embedded oxygen and / or nitrogen atoms. In one particular embodiment, the additional layer 20 is made of chromium oxide, preferably Cr2O3 or amorphous chromium oxide.

[0076] Additional layer 20 is preferably a surface layer of protective coating 16 (ie, the layer in contact with the external environment).

[0077] The protective coating 16 here comprises a primary layer 18 , an additional layer 20 overlying the primary layer 18 , and a transition layer 22 interposed between the primary layer 18 and the additional layer 20 .

[0078] Alternative embodiments may be contemplated, as shown in Figures 3-6, in which reference numbers for similar elements are repeated.

[0079] The coating 4 shown in Figure 3 differs from the coating shown in Figure 2 in that the additional layer 20 is applied directly over the primary layer 18. The additional layer 20 is in contact with the primary layer 18. The coating 4 does not have a transition layer 22 between the primary layer 18 and the additional layer 20 that is located over the primary layer 18.

[0080] The protective coating 16 may, for example, be comprised of a primary layer 18 and an additional layer 20 disposed over the primary layer 18 .

[0081] The coating 4 shown in FIG. 4 differs from the coating shown in FIG. 2 in that an additional layer 20 is located below the main layer 18, with a transition layer 22 interposed between the additional layer 20 and the main layer 18.

[0082] Additional layer 20 is, for example, deposited directly on substrate 14, here on outer surface 14B of substrate 14.

[0083] The protective coating 16 may, for example, be comprised of an additional layer 20 , a primary layer 18 overlying the additional layer 20 , and a transition layer 22 interposed between the additional layer 20 and the primary layer 18 .

[0084] The coating 4 shown in Figure 5 differs from the coating shown in Figure 4 in that the primary layer 18 is applied directly over the additional layer 20. The additional layer 20 is in contact with the primary layer 18. The coating 4 does not have a transition layer 22 between the additional layer 20 and the primary layer 18 that is located above the additional layer 20.

[0085] The protective coating 16 may be comprised of an additional layer 20 disposed, for example, on the outer surface 14 B of the substrate 14 , and a main layer 18 disposed on the additional layer 20 .

[0086] The coating 4 shown in Figure 6 differs from the coating shown in Figure 2 in that the protective coating 16 has an additional layer 20 that is located below the main layer 18 and an additional layer 20 that is located above the main layer 18. Optionally, a transition layer 22 is interposed between the main layer 18 and the additional layer 20 that is located below the main layer 18. Also optionally, a transition layer 22 is interposed between the main layer 18 and the additional layer 20 that is located above the main layer 18.

[0087] The protective coating 16 is, for example, composed of a main layer 18, an additional layer 20 located below the main layer 18, and an additional layer 20 located above the main layer 18, with a transition layer 22 interposed between the main layer 18 and the additional layer 20 located below the main layer 18, and with the transition layer 22 interposed between the main layer 18 and the additional layer 20 located above the main layer 18.

[0088] As shown in Figure 7, in one example embodiment, the protective coating 16 has at least one group of a plurality of adjacent additive layers 20. Each additive layer 20 of a group is in contact with an adjacent layer in the stack of layers of the protective coating 16. In Figure 7, three adjacent additive layers 20 are shown.

[0089] 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 one embodiment, adjacent to an additional layer 20 made of pure chromium is another additional layer 20 made of a material composed of chromium and also oxygen and / or nitrogen with possible unavoidable impurities, more specifically a material made of chromium oxide, chromium nitride, chromium oxynitride, metallic chromium doped with oxygen and / or nitrogen atoms, or metallic chromium with embedded oxygen and / or nitrogen atoms.

[0090] Advantageously, a group of several adjacent additional layers 20 comprises at least one additional layer 20 made of pure chromium, interposed between two further additional layers 20, each of which is made of a material composed of chromium and also of oxygen and / or nitrogen and possibly also of unavoidable impurities, more particularly a material made of chromium oxide, chromium nitride, chromium oxynitride, or of metallic chromium doped with oxygen and / or nitrogen atoms, or of metallic chromium in which oxygen and / or nitrogen atoms are embedded.

[0091] In such a case, the two further additional layers 20 on either side of each additional layer 20 made of pure chromium may be made of the same or different materials.

[0092] In one embodiment, each of the two further additional layers 20 is made of a material composed of chromium and an oxide, for example chromium oxide, or a material composed of chromium and nitrogen, for example chromium nitride.

[0093] In one particular embodiment, an additional layer 20 made of pure chromium is sandwiched between two other additional layers 20 made of chromium nitride.

[0094] In one embodiment, the group of adjacent additional layers 20 comprises at least one additional layer 20 made of pure chromium, alternated with other additional layers 20, each of which is made of a material consisting of chromium and also oxygen and / or nitrogen and possibly unavoidable impurities, more particularly a material made of chromium oxide, chromium nitride, chromium oxynitride, or metallic chromium doped with oxygen and / or nitrogen atoms, or metallic chromium in which oxygen and / or nitrogen atoms are embedded.

[0095] The additional layer(s) 20 alternating with the pure chromium layer(s) may be made of the same material or at least two different materials.

[0096] In one particular embodiment, a group of adjacent additive layers 20 includes one or more additive layers made of pure chromium alternating with another additive layer 20 made of chromium nitride.

[0097] The protective coating 16 may include a group of such adjacent additional layers 20 positioned above the main layer 18 and / or a group of such adjacent additional layers 20 positioned below the main layer 18 .

[0098] Next, a method for producing the coating 4 will be described with reference to FIG.

[0099] The manufacturing method includes a step of obtaining a substrate 14. If the substrate 14 is a tube, it is obtained in a known manner, for example by pilger rolling, from a tubular blank having a diameter greater than that of the substrate 14, the blank being deformed so that its diameter is gradually reduced and its length is gradually increased and then, if appropriate, cut to the desired length to obtain the substrate 14.

[0100] The manufacturing method next includes depositing a main layer 18 on the outer surface 14B of the substrate 14 by physical vapor deposition.

[0101] As shown in FIG. 8, physical vapor deposition of the main layer 18 is performed, for example, in a chamber 24 of a physical vapor deposition system 26 under a controlled atmosphere, more specifically, under a rarefied atmosphere of a neutral gas, such as argon.

[0102] The neutral gas is selected so as to prevent oxidation phenomena during the step of depositing the layer of protective coating 16 on the substrate 14 .

[0103] Physical vapor deposition is carried out, for example, by sputtering or evaporation.

[0104] In one example embodiment, the main layer 18 is deposited by physical vapor deposition by sputtering.

[0105] For this purpose, the substrate 14 and a target 28 made of chromium are placed in a chamber 24, in which a rarefied atmosphere of a neutral gas, for example argon, is created, in which an electric field is created, which leads to the creation of a plasma containing charged particles (electrons, ions, etc.), which precipitate on the target 28 under the action of the electric field and detach atoms from the target 28 (i.e. the target 28 is subjected to sputtering, hence the term sputtering), and the atoms detached from the target 28 are then deposited on the substrate 14.

[0106] The physical vapor deposition system 26 includes a chamber 24, a target 28 disposed within the chamber 24, a pump 30 having an inlet fluidly connected to the chamber 24 to generate a rarefied atmosphere within the chamber 24, a generator 32 connected to the target 28, optionally a generator 34 connected to the substrate 14, and a gas supply 36 fluidly connected to the chamber 24 for supplying, for example, a neutral gas (e.g., argon), oxygen and / or nitrogen.

[0107] Preferably, physical vapor deposition is performed by magnetron sputtering. In such a case, a magnetic field is preferably generated at least near target 28.

[0108] The provision of a magnetic field allows for better control of the trajectories of the charged particles reaching the target 28, thus leading to a better controlled deposition rate of the main layer 18, and more specifically, a faster deposition rate.

[0109] The magnetic field is generated, for example, by one or more permanent magnets 38 as illustrated in FIG. 3 and / or by one or more electromagnets.

[0110] The manufacturing method includes the deposition of at least one additional layer 20, also by physical vapor deposition.

[0111] The deposition of each additional layer 20 is performed, for example, in the same physical vapor deposition facility 26 as the physical vapor deposition of the main layer 18 .

[0112] The deposition of each additional layer 20 is performed, for example, using the same physical vapor deposition techniques used to perform the physical vapor deposition of the main layer 18 .

[0113] The deposition of each additional layer 20 is carried out by physical vapor deposition by sputtering, and more particularly by magnetron sputtering.

[0114] The deposition of each additional layer 20 is performed using the same techniques as the deposition of the main layer 18, except that it is performed in a controlled atmosphere containing oxygen and / or nitrogen, in addition to a neutral gas, to form an additional layer of chromium oxide, chromium nitride, chromium oxynitride, or combinations thereof, as desired.

[0115] Oxygen gas and nitrogen gas are supplied into chamber 24 by, for example, gas supply 36 .

[0116] In one embodiment, only oxygen is provided in the controlled atmosphere in addition to the neutral gas, the controlled atmosphere being a binary gas mixture containing the neutral gas and oxygen, which makes it possible to obtain an additional layer 20 of chromium oxide.

[0117] In one embodiment, only nitrogen is provided in the controlled atmosphere, which is a binary gas mixture containing a neutral gas and nitrogen, making it possible to obtain an additional layer 20 of chromium nitride.

[0118] In one example embodiment, oxygen gas and nitrogen gas are provided in the controlled atmosphere in addition to the neutral gas. The controlled atmosphere is a ternary gas mixture containing the neutral gas, oxygen and nitrogen. This allows for an additive layer containing chromium oxide, chromium nitride and / or chromium oxynitride to be obtained.

[0119] In one embodiment, only neutral gas is supplied in the controlled atmosphere, which makes it possible to obtain an additive layer 20 of pure chromium.

[0120] The layers of protective coating 16 are deposited in sequence from the layer closest to substrate 14 to the layer furthest away.

[0121] Each additional layer 20 located below the main layer 18 is applied before the main layer 18 and / or each additional layer 20 located above the main layer 18 is applied after the main layer 18 .

[0122] After deposition of the main layer 18 and each additional layer 20, the coating 4 comprises a substrate 14 having an outer surface 14B covered by a protective coating 16.

[0123] Where appropriate, the manufacturing method includes forming each transition layer 22 .

[0124] Each transition layer 22 is fabricated, for example, by depositing a layer of chromium by physical vapor deposition while introducing gaseous oxygen into the atmosphere within chamber 24 .

[0125] Formation of transition layer 22 on main layer 18 is accomplished, for example, after deposition of main layer 18, by continuing the physical vapor deposition of chromium while introducing gaseous oxygen into the atmosphere of chamber 24.

[0126] To produce a transition layer 22 having a preferably gradually increasing proportion of oxygen atoms, the proportion of oxygen in the atmosphere of chamber 24 is preferably gradually increased or decreased, for example, over time.

[0127] In one variation, instead of introducing gaseous oxygen into the atmosphere of chamber 24, it is possible to introduce oxidation products that decompose or evaporate by releasing oxygen into the controlled atmosphere.

[0128] In one variant, the transition layer 22 is obtained by depositing chromium by physical vapor deposition to a thickness corresponding to the thickness desired for the transition layer 22, followed by ion implantation of oxygen into the chromium layer.

[0129] Each physical vapor deposition (deposition of the main layer 18, each additional layer 20, and, where appropriate, each transition layer 22) can be performed with a direct current density (i.e., by applying a direct current to the target 28) or with a pulsed current density (i.e., by applying a pulsed current including pulses).

[0130] Each physical vapor deposition by magnetron sputtering can be carried out according to one of the following techniques or according to a combination of at least two of the following techniques: direct current (DC) magnetron sputtering, direct current pulse (or DC pulse) magnetron sputtering, high power pulse magnetron sputtering (HiPIMS or HPMS), two-pole magnetron sputtering (MSB), dual magnetron sputtering (DMS), unbalanced magnetron (UBM) sputtering.

[0131] Although deposition of protective coating 16 by physical vapor deposition using magnetron sputtering is preferred, the invention is not limited to such deposition techniques.

[0132] As a variant, each layer of protective coating 16 may be deposited by another technique, for example physical vapour deposition by evaporation, more particularly by arc, or by cold spray.

[0133] The addition of a primary layer 18 of chromium on the substrate 14 helps to improve the wear resistance of the coating 4 compared to a coating 4 made of uncoated pure zirconium or a zirconium alloy.

[0134] By adding an additional layer 20 made of pure chromium or of a material consisting of chromium oxide, chromium nitride, chromium oxynitride or a combination of such compounds, or of chromium doped with oxygen and / or nitrogen, the performance of the coating 4, more particularly in terms of wear resistance, scratch resistance and / or permeability to fission products, can be further improved.

[0135] Each additional layer 20 deposited by physical vapor deposition can be deposited in a controlled manner with a selected thickness, and more specifically, a thickness sufficient to obtain the desired performance.

[0136] The addition of the additional layer 20 on top of the main layer 18 provides increased hardness compared to the main layer 18, thereby improving wear and scratch resistance. Wear resistance reduces the susceptibility of the cladding 4 to fretting. Scratch resistance reduces the risk of scratching the outer surface of the cladding 4 when the nuclear fuel rods 2 are inserted through the grid spacers of the nuclear fuel assembly.

[0137] Each additional layer 20 located above or below the main layer 18, more particularly if it comprises Cr2O3, serves to limit the permeation through the cladding 4 of fission products such as tritium coming from inside the cladding or corrosion products such as hydrogen coming from the outer surface.

[0138] Hydrogen can increase the vulnerability of the zirconium alloy substrate 14, and tritium can contaminate the coolant circulating within the reactor core.

[0139] The additional layer 20, located on top of the main layer 18 and containing chromium oxide, in particular Cr2O3, may also have a black color even before it is inserted into the reactor core, which may be advantageous for heat transfer during the transient phase of the reactor, more particularly during the start-up of the reactor.

[0140] The additional layer 20, located below the main layer 18 and between the substrate 14 and the main layer 20, can reduce the formation of Cr-Zr eutectic at high temperatures, typically above 1330° C. The cladding is more resistant to LOCA events.

[0141] It should be noted that the spontaneous formation of oxides on zirconium alloy cladding occurs within a few days of exposure to the presence of water on the cladding surface. For example, the spontaneous formation of oxides on the zirconium alloy cladding of nuclear fuel rods occurs approximately 5 days after the fuel assembly is inserted into the reactor core. The thickness of zirconium oxide thus formed on the cladding rapidly reaches approximately 100 nm, quickly protecting the zirconium alloy substrate.

[0142] In contrast, the spontaneous formation of chromium oxide on chromium protective coatings in the presence of water on the coating is slower, 10 to 20 times slower than for example zirconium alloys, and is insufficient to protect the coating as soon as it is used in the reactor core: a chromium oxide thickness of 100 nm is reached only after 500 days in the reactor.

[0143] A protective coating including at least one additional layer is applied during manufacture of the covering.

[0144] Depositing a protective coating including at least one additive layer during manufacture of the cladding provides protection from the start of use of the cladding in the reactor core.

[0145] It should therefore be noted that the deposition of the chromium layer of the chromium protective coating is generally carried out in an inert medium (including noble gases such as argon) to prevent oxidation phenomena during the deposition of the chromium layer coating. [Explanation of symbols]

[0146] 14 Substrate 14A inner surface 14B Outer surface 16 Protective Coating 18 Main layer 20 Additive Layer 22 Transition layer

Claims

1. 1. Nuclear fuel cladding, the cladding being manufactured using a substrate (14) made of pure zirconium or a zirconium alloy, and a multi-layer protective coating (16) covering a surface (14B) of the substrate (14), the protective coating (16) having 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 composed of chromium and additionally oxygen and / or nitrogen, with possible unavoidable impurities present.

2. 2. The coating of claim 1, wherein the at least one additional layer (20) is made of pure chromium, chromium oxide, chromium nitride or chromium oxynitride or a combination of such materials.

3. 3. The coating according to claim 1 or 2, wherein the at least one additional layer (20) is made of metallic chromium doped with oxygen and / or nitrogen atoms or metallic chromium embedded with oxygen and / or nitrogen atoms.

4. 4. The coating according to claim 1, further comprising a transition layer (22) interposed between the main layer (18) and the additional layer (20) containing oxygen and / or nitrogen, the transition layer (22) being made of metallic chromium doped with oxygen and / or nitrogen atoms or of metallic chromium in which oxygen and / or nitrogen atoms are embedded.

5. 5. The coating of claim 4, wherein the transition layer (22) has a concentration of oxygen atoms that gradually increases from the main layer (18) to the additional layer (20) and / or a concentration of nitrogen atoms that gradually increases from the main layer (18) to the additional layer (20).

6. 6. The coating of claim 4 or 5, wherein a concentration of oxygen atoms in the transition layer (22) at the interface with an adjacent additional layer (20) is substantially equal to a concentration of oxygen atoms in the adjacent additional layer (20) and / or a concentration of nitrogen atoms in the transition layer (22) at the interface with an adjacent additional layer (20) is substantially equal to a concentration of nitrogen atoms in the adjacent additional layer (20).

7. The coating according to any one of the preceding claims, wherein the thickness of the main layer (18) is between 3 μm and 30 μm.

8. A coating according to any one of the preceding claims, wherein the thickness of each additional layer (20) is between 10 nm and 5 μm.

9. The coating of any one of claims 1 to 8, wherein an additional layer (20) is located on the main layer (18).

10. 10. The coating of any one of claims 1 to 9, wherein the additional layer (20) is located below the main layer (18).

11. 1. A method for manufacturing nuclear fuel cladding, comprising: - providing a substrate (14) made of pure zirconium or a zirconium alloy, and - deposition of a multilayer protective coating (16) on the surface (14B) of the substrate (14), the deposition of the protective coating (16) comprising a main layer (18) made of pure chromium by physical vapor deposition and the deposition of one or more additional layers (20), each of which is made of pure chromium or of a material composed of chromium and also of oxygen and / or nitrogen, with possible unavoidable impurities present; A method for producing nuclear fuel cladding comprising:

12. The method of claim 11, wherein the additional layer (20) is made of pure chromium, chromium oxide, chromium nitride or chromium oxynitride or a combination of such materials.

13. 13. The method according to claim 11 or 12, wherein the additional layer is made of metallic chromium doped with oxygen and / or nitrogen atoms or metallic chromium embedded with oxygen and / or nitrogen atoms.

14. The method according to any one of claims 11 to 13, wherein the additional layer (20) is applied by physical vapor deposition.

15. 15. The method according to any one of claims 11 to 14, wherein the additional layer (20) is deposited by physical vapor deposition carried out in an atmosphere composed of a binary or ternary gas mixture containing a neutral gas and further oxygen and / or nitrogen.

16. 16. The method of claim 11, further comprising the formation of a transition layer (22) interposed between the main layer (18) and the additional layer (20), the transition layer (22) being made of chromium doped with oxygen atoms.

17. The method of claim 16, wherein the transition layer (22) has a concentration of oxygen atoms that gradually increases from the main layer (18) to the adjacent additive layer (20).

18. The method according to any one of claims 11 to 17, wherein the thickness of the main layer (18) is between 3 μm and 30 μm.

19. A method according to any one of claims 11 to 18, wherein the thickness of each additional layer (20) is between 10 nm and 5 μm.

20. The method according to any one of claims 11 to 19, wherein at least one additional layer (20) is applied after the main layer (18).

21. The method according to any one of claims 11 to 20, wherein at least one additional layer (20) is applied before the main layer (18).

22. Nuclear fuel cladding obtainable by the method according to any one of claims 11 to 21.

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