Metallic components for aqueous environments

Abstract

Metallic components for aqueous environments 1. A metallic component for an aqueous environment, the metallic component comprising a protective coating applied to an outer surface of a metallic body and a zirconium alloy body, the metallic body being intended to come into contact with an aqueous working fluid in use, the metallic component comprising: 1. A metal component for use in an aqueous environment, wherein the protective coating comprises at least one oxide layer, the oxide layer comprising a matrix oxide and at least one doping element dispersed in the matrix oxide, the matrix oxide being selected from the group consisting of Y2O3, La2O3, Sc2O3, Yb2O3, CaO, MgO, Mg2Al2O4, or a combination thereof, and the doping element being selected from the group consisting of Ti, V, Cr, Fe, Ni, Cu, Zr, Nb, Sn, Ta, P, or an oxide thereof.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates generally to materials used in aqueous environments, particularly high temperature aqueous environments such as water-cooled nuclear reactors. [Background technology]

[0002] Thermonuclear power generation in water-cooled reactors has the potential to become safer and more efficient with the introduction of accident-tolerant fuels (ATFs). Global research and development efforts to utilize ATF technology were accelerated by the 2011 Fukushima Daiichi nuclear power plant accident, primarily focusing on the inherent limitations of fuel and cladding materials.

[0003] Considering cladding materials in particular, it is necessary to overcome the lack of resistance of zirconium-based alloys (Zircaloys) in terms of resistance to design-basis (DB) accidents, such as loss-of-coolant accidents (LOCAs). The main challenges to be addressed are their poor corrosion resistance in steam at temperatures above 1200 °C, hydrogen absorption in the cladding alloy matrix, and failure under combined mechanical and thermal loads. Additionally, these same materials must demonstrate excellent corrosion resistance in liquid or boiling water at temperatures between 270 and 360 °C and pressures between 7 and 187 MPa, to support the core fuel cycle during normal operation of light-water reactors (LWRs). The case of pressurized water reactors (PWRs) is particularly important because the majority of nuclear power plants in operation worldwide are based on this type of reactor.

[0004] In this regard, the best short-term option is to protect the metallic cladding tube by appropriate modification, including coating it with different materials. In the first case, ion implantation was proposed, but no significant improvement was detected. In the second case, various candidates have been investigated, including nitrides, carbides, oxides, and ceramic materials in MAX phases (pure metal, intermetallic compounds, or alloys), as well as metals. Limited research has also addressed the effect of multilayer coating structures on corrosion resistance, as an alternative to single-layer coatings. Prior art is represented by chromium (Cr) coatings fabricated using cold spray or magnetron sputtering methods. Such coatings provide excellent corrosion and wear resistance to zirconium alloys under both normal operation and LOCA conditions, at the expense of a small additional disadvantage in terms of the neutron balance of the core.

[0005] Despite these advantages, chromium coatings have inherent drawbacks that limit safety in the event of a severe accident. Indeed, chromium reacts with zirconium (Zr) in the cladding at high temperatures (T > 800 °C) to form an intermediate layer containing the intermetallic compound ZrCr2 and the eutectic Zr-Cr. The former exhibits embrittlement that reduces the mechanical properties of the coated cladding, while the latter causes a local melting point of 1332 °C (well below the melting point of zirconium alloys: about 1800 °C), leading to simultaneous consumption of both the coating and the cladding material.

[0006] For this reason, there are limits to the maximum allowable temperature and possible increase in mechanical strength after quenching.

[0007] To avoid interdiffusion at the Cr-Zr interface, an appropriate diffusion barrier should be designed. Alternatively, another material compatible with the primary coolant of the LWR and resistant to high-temperature steam (T > 1200 °C) could be selected. The material selected for the interdiffusion barrier should prevent outward diffusion of Zr from the cladding and inward diffusion of Cr from the coating material. Furthermore, interdiffusion between Zr or Cr and the diffusion barrier material should not be allowed. Furthermore, new eutectic reactions of Cr or Zr with the interlayer material should also be avoided.

[0008] WO 2018067425 A2 and WO 2016042262 A1 describe the use of interdiffused layers of refractory metals, preferably molybdenum (Mo) and tantalum (Ta), respectively. However, Mo and Ta have higher neutron absorption capabilities than Zr and Cr, which would penalize the neutron balance and cause increased fuel costs.

[0009] The use of Mo layers investigated by CEA and Framatome could lead to the formation of new interdiffusion layers at the interface with Cr and Zr, forming a eutectic with a melting point near 1332°C, even though this would increase resistance to LOCA events. Furthermore, Mo oxides are not stable in water and would dissolve on contact with liquid water or volatilize into steam at high temperatures if the outer Cr layer were to be damaged and oxidizing species penetrated the outer coating layer.

[0010] The use of nitride diffusion barriers has also been proposed to prevent Cr-Zr interdiffusion in Cr / CrN multilayer structures. The formation of a ZrN interlayer at the coating / substrate interface could potentially retard the diffusion of Cr into the Zr matrix of the substrate. However, each nitride layer can be easily oxidized when exposed to vapors of oxygen-containing species, while CrN itself is unstable and subject to decomposition at high temperatures (T > 1000 °C). The consequences of the oxidation reaction and the accompanying volume changes represent a potential problem and a serious limitation to the effectiveness of the nitride barrier concept.

[0011] With regard to oxides, the inventors believe (or strongly believe) that they provide the greatest stability under the combined influence of an oxidizing environment and high temperatures. WO 2020018361 A1 describes a zirconium-based cladding tube coated with an intermediate layer and a first coating layer (in particular chromium oxide or niobium oxide) formed by ceramic fiber yarns and an outer chromium layer.

[0012] Yttrium oxide (YO), in particular, has been widely studied in the field of corrosion protection due to its high stability and inertness to various environments. In particular, the application of this material as a corrosion-resistant barrier in plasma reactors and interconnections in solid oxide fuel cells has been reported. Furthermore, WO 2018017145 A1 and US 2013344348 A1 describe the application of oxide-based corrosion barriers, particularly yttrium oxide, to zirconium alloy substrates. In the specific context of ATF-coated cladding, YO will not be reduced by Zr because its standard free energy of formation is lower than that of Zr. Furthermore, there is no interaction at the interface with Cr. As a result, during a LOCA event, the thickness of the Cr coating is not reduced by the aforementioned mechanism, thus ensuring the protection of Zr from corrosion. At the same time, the formation of new interfaces is suppressed, thus preventing the formation of brittle intermetallic compounds. However, in the YO-HO system, yttrium hydroxide (Y(OH)) and YOOH are believed to be more stable than YO under LWR operating conditions. Thus, an unprotected layer of pure YO would react with water to form hydroxides, causing changes in the coating microstructure and leading to film wear and possible mechanical failure. On the other hand, Cr, when in contact with water, will form a stable film of CrO, which may prevent further oxidation of the underlying layer.

[0013] From a broader perspective, the use of oxide-based ceramics has been proposed for both corrosion protection in high-temperature water and as a diffusion barrier at coating / coating interfaces. While Al2O3 and ZrO2 fabricated as single-layer coatings did not provide any improvement in high-temperature water, the improved corrosion resistance in high-temperature steam provided by the ZrO2 diffusion barrier in Zr / ZrO2 / FeCrAl and Zr / ZrO2 / Cr systems has only been demonstrated up to 1100 °C, still below the LOCA threshold. Furthermore, because oxygen atoms can dissolve in the Zr matrix of fuel cladding, diffusion processes at the Zr / ZrO2 interface would lead to depletion and reduction of the ZrO2 layer, reducing its barrier effectiveness and allowing Zr atoms to re-expose the outer interface.

[0014] It is therefore an object of the present invention to provide a coating, particularly for zirconium alloy-based metal components, that is stable under the normal operating conditions of a water-cooled reactor. Another object of the present invention is to provide a coating, particularly for zirconium alloy-based metal components, that is sufficiently resistant to the severe conditions that may occur in the event of a coolant leak accident. Summary of the Invention

[0015] For the above purposes, the subject of the present invention is 1. A metallic component for an aqueous environment, comprising a metallic body and a protective coating applied to an outer surface of the metallic body, the metallic body being intended to come into contact with an aqueous working fluid in use, the metallic component comprising: the protective coating comprises at least one oxide layer, the oxide layer comprising a matrix oxide and at least one doping oxide dispersed in the matrix oxide, the matrix oxide being selected from the group consisting of Y2O3, La2O3, Sc2O3, Yb2O3, CaO, MgO, Mg2Al2O4 or a combination thereof, and the at least one doping oxide being selected from the group consisting of oxides of Ti, V, Cr, Fe, Ni, Cu, Zr, Nb, Sn, Ta and P; The at least one doping oxide is A single doped oxide, wherein the oxidized element of the single doped oxide can form a ternary compound with the matrix oxide, and the concentration of the single doped oxide is C d is 0.1 mol% (%mol)≦C d <C T So, C T is the maximum concentration of the single doping oxide, defined as the single doping oxide concentration in the ternary compound associated with the highest matrix oxide concentration in the matrix oxide-single doping oxide phase diagram, or a first doping oxide and at least one second doping oxide, wherein an oxidized element of the first doping oxide is capable of forming a ternary compound with the matrix oxide, and the concentration of the first doping oxide is C d is 0.1 mol% or less C d <C T So, C T is a maximum concentration defined as the first doping oxide concentration in the ternary compound associated with the highest matrix oxide concentration in the matrix oxide-first doping oxide phase diagram; Including, The concentration of each second doping oxide is C d The following is a metal component for use in an aqueous environment.

[0016] Furthermore, an object of the present invention is a method for producing a metallic component according to the present invention, comprising a step of depositing said at least one oxide layer on an alloy body of metallic material by physical vapor deposition, wherein said metallic material body is maintained at a deposition temperature of less than 300°C during deposition.

[0017] The inventors have discovered that doping Y2O3 with selected elements improves corrosion resistance during normal PWR operation. Furthermore, high temperature tests performed by the inventors on the Zr / Y2O3 / Cr system demonstrated that diffusion of Zr into Cr and vice versa was prevented even at 1200°C for 1 hour. It is believed that doping may also have a positive effect on the other claimed oxides. [Brief explanation of the drawings]

[0018] Detailed Description of the Invention Further features and advantages of the present invention will become more apparent from the following detailed description of embodiments of the invention, given with reference to the accompanying drawings, which are provided purely for illustrative and non-limiting purposes. [Figure 1] Figure 1 shows SEM images of a pure YO-coated Zr sheet sample (left panel) and a CrO-doped YO-coated sample (center and right panels) after 14 days of exposure in a static autoclave simulating the primary coolant of a pressurized water reactor (360 °C, saturation pressure, [Li] = 2 ppm (as LiOH), [B] = 1000 ppm (as HBO)). [Figure 2] Figure 2 shows a cross-sectional BSE-SEM image of a Zr-4 / 1 μm Y2O3 / 10 μm Cr sample after exposure in Ar flow at 1200 °C for 1 hour. The inward diffusion of Cr and outward diffusion of Zr are prevented by the presence of the Y2O3 layer, which was deposited on the Zircaloy-4 cladding by PLD before the deposition of a thick Cr film by magnetron sputtering (MS). [Figure 3]Figures 3 and 4 show Ellingham diagrams for several oxides. (NN Greenwood and A. Earnshaw, "The Chemistry of the Elements (2nd Edition)", Butterworth-Heinemann, 1997, ISBN 0080379419; M. Musaddique, A. Rafique (2023), "Pyrometallurgy and Electrometallurgy of Rare Earths - Part A: Analysis of Metallothermic Reduction and Its Variants", Mineral Processing and Extractive Metallurgy Review, DOI: 10.1080 / 08827508.2022.2164576) [Figure 4] Figures 3 and 4 show Ellingham diagrams for several oxides. (NN Greenwood and A. Earnshaw, "The Chemistry of the Elements (2nd Edition)", Butterworth-Heinemann, 1997, ISBN 0080379419; M. Musaddique, A. Rafique (2023), "Pyrometallurgy and Electrometallurgy of Rare Earths - Part A: Analysis of Metallothermic Reduction and Its Variants", Mineral Processing and Extractive Metallurgy Review, DOI: 10.1080 / 08827508.2022.2164576)

[0019] The component according to the present invention comprises a body made of a metallic material, in particular a zirconium alloy, with an oxide-based protective coating (especially deposited by physical vapor deposition (PVD)). This component may be, for example, a fuel cladding tube for a nuclear reactor. The protective coating is characterized by a specific chemical composition, consisting of atoms of a suitable dopant contained in a matrix of a specific oxide material, in a single layer or multilayer structure, or a combination thereof. These characteristics allow the coating to provide protection for the underlying metallic substrate under environmental conditions typical of normal PWR operation, since the layer suitable for contact with the coolant is essentially thermodynamically stable with respect to water at the temperatures and operating pressures of a PWR. Furthermore, the same characteristics characterizing the coatings described herein allow for the extension of protective capabilities to environmental conditions typical of a LOCA. In this case, the material in contact with steam will not be depleted by evaporation or volatilization of hydroxide species, which typically results from interaction with water steam at high temperatures (T > 1200°C).

[0020] Interaction with Zr from the metal substrate is hindered (or prevented) by the excellent thermodynamic stability towards Zr that characterizes the specific oxides that make up the matrix of the coatings proposed herein.

[0021] In certain formulations described in the following paragraphs, the coating may be easily implemented as an interdiffusion barrier layer, coated with an outer layer of Cr, with the goal of preventing out-diffusion of Zr and in-diffusion of Cr atoms and the resulting formation of harmful Zr-Cr compounds. According to one embodiment, the oxide-based coating may be made to provide anti-corrosion protection even in the absence of an outer layer made of a metal or metal alloy.

[0022] The selection of materials is bounded by the following criteria: a. Chemical compatibility with water under PWR operating conditions: The selected material should form a passive film in pressurized water at a temperature of 270-360°C, pH 6.9-7.4, and the concentrations of added elements are [Li+] 2.2-6 ppm and [10-B] 1200-1800 ppm. b. Suppression of hydrolysis and volatilization in steam at 1200°C; c. Stability to contact with Zr in the temperature range from room temperature to the melting point of Zr (1855°C) by having a standard Gibbs free energy value of less than -1092 kJ / mol; d. Thermal expansion coefficient of zirconium alloy (5.8~6.0×10 at room temperature) -6 ) and minimize the difference between e. The neutron absorption cross section at thermal energy is low, otherwise in the range of 0.1 to 4 b (or barn).

[0023] Y2O3 meets all these criteria except for its stability in water, where hydroxide formation is expected over the PWR operating parameter range (temperature = 270–360 °C, pH = 6.9–7.4, [Li+] = 2.2–6 ppm, [10-B] = 1200–1800 ppm). Applying an outer layer of Cr coating over the inner layer of Y2O3 could theoretically avoid direct contact between Y2O3 and water, but would require a very high coating thickness to avoid microscopic defects that could cause catastrophic failure of the entire barrier layer, thus exposing the underlying Zr. This is undesirable because Cr absorbs more thermal neutrons than Zr or ZrO2, thus necessitating enrichment of the fuel in fissile material to maintain neutron balance in the uncoated fuel cladding. On the other hand, if the Cr thickness is kept below 10 μm to limit the neutron penalty in the reactor core, residual cracks and micropores in the Cr layer increase the short-circuit paths for the diffusion of oxidizing species. In this case, the interaction of YO with water or OH groups leads to microstructural changes in the diffusion barrier layer, eventually leading to mechanical failure and subsequent oxidation of the Zr substrate.

[0024] To address and mitigate this potential risk, the present invention involves fine-tuning material properties by introducing appropriate doping materials to improve corrosion resistance and overall diffusion barrier performance. A suitable material or combination of materials may be introduced as a dispersion in a material matrix with a uniform concentration along the coating thickness. In certain cases where the coating results in a nanocrystalline or monocrystalline film structure, as described in more detail below, the doping element may be preferentially distributed at the grain boundaries. Furthermore, the doping material may be introduced in a concentration that varies with thickness, in a manner described in more detail below.

[0025] The present invention includes a protective coating comprising at least one ceramic layer applied to a metallic component, which may be, for example, a fuel rod cladding tube for a PWR, and which comprises an atomic dispersion of metal cations of a suitable dopant in a matrix of metal oxide.

[0026] The matrix is ​​composed of metal oxides that can withstand reduction by Zr metal, and therefore the metal oxides are selected from the group including Y2O3, La2O3, Sc2O3, Yb2O3, CaO, MgO, Mg2Al2O4, or combinations thereof. Analysis of the neutron absorption cross sections of these materials reveals that MgO, CaO, Mg2Al2O4, and Y2O3 will have a lower detrimental effect on the neutron balance of the core, while the detrimental effect introduced by Y2O3 is higher than that of MgO, CaO, and Mg2Al2O4. On the other hand, the use of La2O3, Sc2O3, and Yb2O3 will cause an increased detrimental effect on neutrons because their thermal neutron absorption cross sections are 18 to 70 times greater than that of zirconium alloys.

[0027] Furthermore, when considering MgO, CaO, Mg2Al2O4, and Y2O3 from a thermodynamic point of view, Y2O3 would be the most stable with respect to Zr. Over a wide temperature range, the Gibbs free energy change of Y2O3 is smaller than that of MgO and CaO. Furthermore, because the slope of the Gibbs free energy change curve of Zr during oxidation is smaller than that of the formation of Mg2Al2O4, as the temperature increases, the oxidation curve of Zr will intersect with the formation curve of Mg2Al2O4. As a result, in the Zr / Mg2Al2O4 system, above a certain temperature, ZrO2 will be thermodynamically favored, and Zr will reduce the spinel oxide to Mg and Al metals.

[0028] From these considerations, the preferred material for the matrix is ​​Y2O3.

[0029] Doping elements selected from the group consisting of Ti, V, Cr, Fe, Ni, Cu, Zr, Nb, Sn, Ta, and P are added to enhance the stability of the matrix oxide against corrosion and dissolution of the ceramic layer under normal reactor operating conditions or accident conditions. The doping elements are added to the matrix oxide in the form of their more stable oxides. One or more doping elements may be added to the matrix oxide. These elements are selected from metals that, in the pH and electrochemical potential ranges typical of the primary coolant of a PWR, form a passivating layer of their own oxide, if possible, and are resistant to dissolution and hydrolysis.

[0030] The oxides of the doping elements and the matrix oxides can react to form ternary oxide compounds, so the doping oxide concentration C characterizing the aforementioned ternary oxides T is defined. In order to prevent the growth of a second ternary oxide compound phase within the matrix oxide, C d The doping oxide concentration, expressed as C T It should be less than.

[0031] In conclusion, the concentration of doping oxide C d 0.1 mol%≦C d <C T The concentration of doping oxide C is chosen in the range d is preferably 5 mol% <C d <C T In a preferred embodiment of the present invention, the doping element is Cr, and the concentration of the doping oxide Cr2O3 is 5 mol%. <C d <C T range, preferably 10 mol%≦C d <C T The ternary oxide compound formed by the reaction of Y2O3 with Cr2O3 is YCrO3, and its C T The concentration is 50 mol %.

[0032] In a preferred embodiment of the present invention, the matrix oxide is Y2O3, and the metal element selected as the dopant is an element capable of forming a trivalent ion. As a result, the Y in the matrix oxide 3+ Direct ion substitution does not lead to a disruption of the charge balance, e.g., by the creation of oxygen holes. A low oxygen conductivity is an advantage, since the substrate material, Zr, must be protected from oxidation during the entire life of the coated metal component and in the event of an accident. Therefore, doping Y2O3 with trivalent cations does not lead to an increase in the oxygen conductivity of the matrix oxide due to the introduction of dopants.

[0033] The ceramic layer may have one of the following structures: 1. In the matrix oxide, a uniform dispersion of the doping element along the thickness direction of the layer and at the atomic level is achieved with 0.1 mol % ≦ C d <C T The overall doping oxide concentration C is in the range d causing C T is the doping oxide concentration that characterizes the composition of the ternary oxide compound formed between the matrix oxide and the doping oxide, matrix oxide structure. C d The concentration is preferably in the range of 5 to 20 mol %. In a preferred embodiment of the present invention, the doping element is Cr and the concentration of the doping oxide Cr2O3 is 5 mol %. <C d <20 mol % range, preferably 10 mol %≦C d <20 mol%. It should be emphasized that, with the exception of Nb and Sn, the doping elements listed above are characterized by a large thermal neutron absorption cross section compared to Y. With the aim of minimizing the adverse effects introduced by the coating on the neutron balance of the core, the dopant concentration should be kept as low as possible while still resulting in a composition that prevents interactions between the coating material and the reactor water. 2. Nanocrystalline or microcrystalline film structure, with the doping element preferentially distributed at the grain boundaries of the matrix-forming oxide. Overall doping oxide concentration C d 0.1 mol% or less Cd <C T In the range of C T is the doping oxide concentration that characterizes the composition of the ternary oxide compound formed between the matrix oxide and the doping oxide. In a preferred embodiment of the present invention, the doping element is Cr and the concentration of the doping oxide, Cr2O3, is as reported in item 1 above. 3. The concentration of the doping oxide is the minimum concentration C at the interface with the Zr-based substrate. m to the maximum concentration C at the coating surface M The matrix oxide structure changes with a functional gradient from C m ≧0.1 mol% and C M <CTとなる。 4. A multi-layer structure, each layer being constructed similarly to the layer described in item 1 above. Furthermore, the doping oxide concentration in each layer increases stepwise. The innermost layer is C i The outermost layer is characterized by the lowest dopant concentration of ≥ 0.1 mol % and o <C T The number of layers may be two or more.

[0034] The total thickness of the ceramic coating is between 0.1 and 10 μm, with the optimum being between 1 and 5 μm.

[0035] When multiple doping elements are present in the matrix oxide, the numerical concentrations provided above correspond to the doping element present in the highest concentration, defined herein as the "first doping element." The oxide concentrations of the other doping elements are calculated by multiplying the oxide concentration C of the first doping element by the numerical concentration C of the first doping element. d The concentration values ​​must of course be such that the sum of the concentration of the matrix oxide and the concentration of each doping oxide equals 100 mole %.

[0036] The coating is capable of withstanding the environmental conditions of an operating nuclear reactor core.

[0037] Furthermore, such coatings may be used as interdiffusion barriers in zirconium alloy / barrier layer / Cr coating systems to prevent diffusion of Cr into the Zr matrix and vice versa.

[0038] In this case, the coated component consists of a metal component acting as a support and a two-layer coating structure, including an inner layer made of the ceramic coating described above, the composition and structure of which are described in Examples 1 to 3.

[0039] An outer metal layer is applied over the inner layer and is comprised of a metal selected from the group consisting of Cr and Cr-based alloys, such as Cr. The metal layer is grown on the ceramic layer using a physical vapor deposition (PVD) method or a spray method. Examples of PVD methods include magnetron sputtering and high-power pulsed magnetron sputtering, while examples of spray methods include cold spray.

[0040] The total thickness of the ceramic coating is between 0.01 and 10 μm, with an optimum value between 0.1 and 3 μm. The outer metal cladding layer, with a thickness of 1 to 10 μm, also has the beneficial effect of improving the long-term stability of the barrier layer when exposed to the primary coolant during normal reactor operation and under LOCA accident conditions.

[0041] The layers of the materials described above are deposited on a zirconium or zirconium alloy sheet or tube by physical vapor deposition (PVD) methods, including cathodic arc evaporation, magnetron sputtering, and pulsed laser deposition (PLD). For example, they may be fabricated using a PLD system including a vacuum chamber and a laser light source. The specific PLD process used for coating deposition is performed without active heating of the substrate. In this case, the temperature of the coated surface will always be below 300°C, particularly below 100°C. As a result, the transformation of the Zr microstructure from α-Zr to β-Zr, which occurs at temperatures above 863°C, is avoided by design. Alternatively, other deposition methods involving coated surface temperatures below 300°C, such as atomic layer deposition (ALD), may be used. The ceramic and metallic material layers will have thicknesses between 1.1 and 20 μm.

[0042] In the specific case of coatings made by PLD, these will have an amorphous structure, without any porosity, and with a density exceeding 85% of the theoretical density of conventional crystalline materials obtained from PLD targets. These combined features can improve barrier efficiency, since there are no short-circuit paths created by grain boundaries, porosity, or defects that, if present, would allow oxidizing species or hydrogen to penetrate the coating. The composition of the material, in the presence of appropriate dopants, can provide the following basic characteristics: - Stability with Zr at the coating / cladding interface or anti-diffusion barrier / cladding interface. This feature can be imparted by Y2O3, whose lower standard free energy of formation than ZrO2 will prevent oxidation of the Zr cladding and reduction of the Y2O3-based coating. Chemical compatibility with the primary coolant of the PWR core: the composition of the coating is designed to avoid the rapid formation of hydroxides or water-soluble species that could compromise the integrity of the coating itself. Low neutron absorption cross section. Zirconium has a thermal neutron absorption cross section of approximately 0.18 b, while currently used zirconium alloys have a thermal neutron absorption cross section of 0.2 b. An ideal coating layer should have a cross section equal to or less than this cross section to minimize adverse effects on the neutron balance of the core. However, current candidate materials have cross sections in the range of 2-4 b. With this invention, it is possible to obtain materials with cross sections between 0.5-2 b.

[0043] The above-described products are versatile and can be used as both interdiffusion and corrosion barrier layers. Their dense structure, combined with a lower density and smaller thermal neutron absorption cross section than Cr, would significantly reduce the adverse impact on neutron balance introduced by Cr coatings. For interdiffusion barriers, the total required Cr thickness can be reduced from the order of 0.1 μm to values ​​in the range of 5-10 μm, since no reaction with Zr is expected to wear the coating under LOCA conditions. Substituting Cr as an outer layer would reduce the cross section from approximately 3.16 μm to less than 2 μm. Thus, a smaller increase in fuel enrichment, consistent with current performance, would result in a smaller increase in fuel cost compared to conventional Cr coatings.

[0044] Furthermore, since the Zr matrix remains unaltered by oxidation and interdiffusion mechanisms, the mechanical properties of the coated cladding are preserved during normal operation and in the event of a LOCA until the emergency cooling system of the core is activated.

[0045] The compatibility of Y2O3 with the primary coolant of a pressurized water reactor (PWR) was investigated by exposing PLD-coated Zr samples to a simulated PWR coolant environment in a static autoclave.

[0046] The effect of single-element doping using Cr2O3 is shown in Figure 2. SEM top-view analysis revealed severe delamination and cracking of the coating in the pure Y2O3-coated sample, resulting in exposure of the Zr substrate. Adding the doping oxide at a concentration of 5 mol% improved the overall coating stability but did not prevent delamination. Finally, when the dopant concentration was increased to 10 mol%, the film became stable and protective.

[0047] A demonstration of the effectiveness of YO as a diffusion barrier in the Zr / YO / Cr system is shown in Figure 2. A cross-sectional image of a Zircaloy-4 tube coated with a bilayer structure of YO / Cr deposited by PLD and magnetron sputtering, respectively, after annealing at 1200 °C for 1 hour in flowing argon, observed using a backscattered electron detector to enhance compositional contrast, demonstrates that the presence of the 1 μm YO layer deposited by PLD effectively prevents out-diffusion of Zr from the cladding and in-diffusion of Cr from the cladding.

[0048] More generally, the coatings described above may be applied as protective coatings to metallic components for use in aqueous environments at various temperatures, including both liquid and gas phases, which can be readily demonstrated with an Ellingham diagram. As is well known, this diagram shows the temperature dependence of the stability of some compounds, such as oxides. In this regard, the Ellingham diagram reports the change in Gibbs free energy (ΔG) for each oxidation reaction as a function of temperature. A more negative ΔG value indicates a more thermodynamically favorable reaction.

[0049] When a pure substance and an oxide are in contact, the oxide is stable only if its ΔG is more negative than the ΔG of the oxide of the pure substance it is in contact with. Otherwise, the oxide is reduced to the corresponding pure substance while an oxide is formed from the other originally pure substance. As can be seen from the Ellingham diagrams in Figures 3 and 4, the Zr-ZrO2 line has a more negative ΔG than the oxygen compounds of most other elements on the periodic table, with the exception of the rare earth elements and a few others.

[0050] This, in turn, causes the reduction of any oxides that come into contact with Zr when the temperature is increased and the kinetic limitations are overcome: even oxides considered to be the most stable, such as Al2O3 and MgO, are reduced to Al and Mg upon interaction with Zr.

[0051] On the other hand, Y2O3 is more stable than ZrO2 at all temperatures, ensuring its own stability as a high-temperature barrier layer.

[0052] Therefore, an oxide barrier that is stable on Zr is naturally or thermodynamically stable on any other industrial metallic material (Fe and steel, Cu, Ti, Mo, W, Ta, Al, Mg, etc.) at any temperature.

Claims

1. 1. A metallic component for an aqueous environment, comprising a metallic body and a protective coating applied to an outer surface of the metallic body, the metallic body being intended to come into contact with an aqueous working fluid in use, the metallic component comprising: The protective coating comprises at least one oxide layer, the oxide layer comprising a matrix oxide and at least one doping oxide dispersed in the matrix oxide, the matrix oxide comprising Y ２ O ３ , La ２ O ３ , Sc ２ O ３ , Yb ２ O ３ , CaO, MgO, Mg ２ Al ２ O ４ or a combination thereof, wherein the at least one doping oxide is selected from the group consisting of oxides of Ti, V, Cr, Fe, Ni, Cu, Zr, Nb, Sn, Ta, and P; The at least one doping oxide is A single doped oxide, wherein the oxidized element of the single doped oxide can form a ternary compound with the matrix oxide, and the concentration C of the single doped oxide ｄ is 0.1 mol% or less C ｄ <C Ｔ So, C Ｔ is a single doped oxide, where t is the maximum concentration defined as the single doped oxide concentration in the ternary compound associated with the highest matrix oxide concentration in the matrix oxide-single doped oxide phase diagram, or a first doping oxide and at least one second doping oxide, wherein an oxidized element of the first doping oxide can form a ternary compound with the matrix oxide, and the concentration C of the first doping oxide is ｄ is 0.1 mol% or less C ｄ <C Ｔ So, C Ｔ is a maximum concentration defined as the first doping oxide concentration in the ternary compound associated with the highest matrix oxide concentration in a matrix oxide-first doping oxide phase diagram; Including, The concentration of each second doping oxide is C ｄ The following metal components for aqueous environments:

2. the concentration C of the doping oxide or the first doping oxide ｄ is 5 mol%<C ｄ <C Ｔ The metal member according to claim 1 ,

3. the concentration C of the doping oxide or the first doping oxide ｄ has a gradient along the thickness direction of the oxide layer, and has a minimum value C at the interface between the oxide layer and the metallic material body. ｍ and the maximum value C at the outermost surface of the oxide layer Ｍ and C Ｍ >C ｍ The metal member according to claim 1 or 2, wherein

4. The at least one oxide layer includes an innermost layer and an outermost layer, and the concentration C of the doping oxide or the first doping oxide in the innermost layer ｄ is the minimum value C ｉ and the concentration C of the doping oxide or the first doping oxide in the outermost layer ｄ is the maximum value C ｏ and C ｏ >C ｉ The metal member according to claim 1 or 2, wherein

5. The metal component according to any one of claims 1 to 4, wherein the at least one oxide is uniformly dispersed in the oxide layer.

6. 3. The metallic component according to claim 1 or 2, wherein the matrix oxide is in microcrystalline or nanocrystalline form and the at least one doping oxide is dispersed in the grain boundaries of the matrix oxide.

7. The matrix oxide is Y ２ O ３ The metal member according to any one of claims 1 to 6,

8. The metal member according to claim 7 , wherein the doping oxide or the first doping oxide is a Cr oxide.

9. 9. The metallic component of claim 1, wherein the protective coating further comprises an outer metallic layer applied to the at least one oxide layer, the outer metallic layer being comprised of a metal selected from the group consisting of Cr and Cr alloys.

10. The metal member according to any one of claims 1 to 9, wherein the metal member is a nuclear fuel cladding tube for a water-cooled reactor.

11. The metal member according to any one of claims 1 to 10, wherein the metal material is a zirconium alloy.

12. The method for producing a metal component according to any one of claims 1 to 11, comprising a step of depositing the at least one oxide layer on the metal material body by physical vapor deposition or cold spraying while maintaining the metal material body at a deposition temperature of less than 300°C, preferably less than 100°C.

13. 13. The method of claim 12, wherein the physical vapor deposition is selected from the group consisting of cathodic arc evaporation, magnetron sputtering, atomic layer deposition, and pulsed laser deposition.

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