CN112652411A - Nuclear reactor pressure vessel lower end socket with high-durability composite coating structure and preparation method thereof - Google Patents
Nuclear reactor pressure vessel lower end socket with high-durability composite coating structure and preparation method thereof Download PDFInfo
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- CN112652411A CN112652411A CN201910962376.3A CN201910962376A CN112652411A CN 112652411 A CN112652411 A CN 112652411A CN 201910962376 A CN201910962376 A CN 201910962376A CN 112652411 A CN112652411 A CN 112652411A
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Images
Classifications
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C13/00—Pressure vessels; Containment vessels; Containment in general
- G21C13/02—Details
- G21C13/028—Seals, e.g. for pressure vessels or containment vessels
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C21/00—Apparatus or processes specially adapted to the manufacture of reactors or parts thereof
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Abstract
The invention discloses a nuclear reactor pressure vessel lower end enclosure and a preparation method thereof. The nuclear reactor pressure vessel lower head includes: a lower end enclosure base body; the anti-oxidation bottom layer is formed on at least part of the surface of the outer wall of the lower end socket base body; and the porous metal top layer is formed on at least part of the surface of the oxidation-resistant bottom layer far away from the outer wall of the lower end socket base body. The composite coating adopted by the lower seal head of the nuclear reactor pressure vessel can obviously improve the CHF limit value of the outer wall surface of the lower seal head, and lays a foundation for improving the effectiveness of IVR of a high-power reactor.
Description
Technical Field
The invention relates to the technical field of nuclear reactor thermal hydraulic power, in particular to a nuclear reactor pressure vessel lower end socket with a high-durability composite coating and a preparation method thereof.
Background
Melt pressure vessel entrapment (IVR) has recently been widely used in the nuclear industry as a key technology for mitigating serious accidents. Reactor pressure vessel external cooling (ERVC) is an important solution to achieving IVR. When the heat flux density of the lower end socket of the pressure container is less than the critical heat flux density (CHF) of the corresponding position of the outer surface of the pressure container, the cooling of the outer wall surface of the pressure container can be ensured, and the integrity of the pressure container is maintained. CHF therefore determines the ERVC cooling capacity limit. The greater the CHF value, the greater the safety margin of the pressure vessel and the greater the feasibility of IVR-ERVC measures. The IVR-ERVC strategy has enough safety margin on a medium-small power reactor, but the density of heat flow led out from the lower end enclosure of the high-power reactor pressure vessel is increased, and the CHF limit value needs to be increased for further improving the IVR effectiveness. Numerous studies have shown that the structural properties of the heating surfaces have a significant effect on CHF, and therefore changing the structural properties of the outer wall surfaces of the pressure vessel is a viable CHF strengthening technique. In methods for modifying surface structure to achieve enhanced CHF, it is generally contemplated to machine a special structure on the heating surface or to prepare a porous coating on the heating surface. For example, advanced processing technology is adopted to manufacture micro/nano structures, visible groove structures, mesh groove communicated array holes, convex structures and the like on the surface, or related coating preparation methods are adopted to prepare recesses and tunnels formed by porous coatings on the heating surface, so that the surface structure characteristics are changed, and the boiling heat transfer process is influenced to achieve the purposes of heat exchange enhancement and CHF enhancement.
It has been shown that preparing a porous metal coating on the outer wall of the pressure vessel with interconnected pores doubles the CHF value of the pressure vessel surface. However, a single porous metal coating may have difficulty meeting the long life requirements of nuclear reactors for pressure vessel outer wall coatings. The pressure vessel is generally made of low alloy steel with low chromium content, and the outer wall surface of the pressure vessel exposed in the air for a long time is easy to oxidize at the operating temperature (300 ℃ below zero). Because the porous coating can not isolate the contact between the outside air and the outer wall of the pressure vessel, a layer of oxide can be formed between the surface of the pressure vessel and the porous coating in the long-term operation process, and the thickening of the oxide can cause the peeling of the porous coating in a short time. Therefore, the development of a coating structure design which can significantly improve the critical heat flux density of the outer wall surface of the pressure vessel and has a long service life and a corresponding method for preparing a large-area coating are urgently needed.
In the technical scheme disclosed in patent CN103903658A, a machining manner is adopted, a groove structure, a mesh groove communicated array holes, a protrusion structure and the like are machined on the heating surface, and the surface structure characteristics are changed, so that the CHF value of the heating surface is improved by more than 50%. If the technology is popularized to the actual engineering, the safety margin of the passive cooling technology of the nuclear power station can be greatly improved. However, in engineering applications, the process difficulty of processing a special surface structure on the surface of the lower head of the reactor pressure vessel, especially the surface of the lower head of an in-service reactor, is high, and the mechanical properties of the surface treated by the special structure need to be further evaluated. On the other hand, the outer wall surface of the pressure vessel exposed to air for a long time is very likely to be oxidized at an operating temperature, and holes and grooves formed in the outer wall surface of the pressure vessel may be corroded and disappeared.
In the technical scheme disclosed in patent CN102303117A, Ti powder, Al powder and Nb powder are mixed and dried, and then deposited on a metal substrate at one time, and vacuum sintering is performed by a three-stage sintering process, so as to obtain a TiAl-based alloy porous coating on a metal substrate. The TiAl-based porous coating prepared by the technology has uniform thickness and pores, is firm and not easy to fall off, and is suitable for plate-type or tube-type heat exchangers in the fields of chemical industry, petroleum, metallurgy, seawater desalination, high-temperature heat exchange and the like. The method for preparing the porous coating by adopting powder high-temperature sintering or electro-deposition is more suitable for equipment with smaller size, and does not have the capability of preparing the coating on the outer wall surface of the lower end enclosure of the large-size reactor pressure vessel. On the other hand, the problem that the surface of the low carbon steel base is easily oxidized is not mentioned and considered in the technology.
In summary, the existing nuclear reactor pressure vessel bottom head and the surface strengthening technology thereof still need to be improved.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. To this end, an object of the present invention is to propose a nuclear reactor pressure vessel lower head with a high-durability composite coating and a preparation method thereof. The composite coating adopted by the lower seal head of the nuclear reactor pressure vessel can obviously improve the CHF limit value of the outer wall surface of the lower seal head, and lays a foundation for improving the effectiveness of IVR of a high-power reactor.
In one aspect of the invention, a nuclear reactor pressure vessel lower head is provided. According to an embodiment of the invention, the nuclear reactor pressure vessel bottom head comprises: a lower end enclosure base body; the anti-oxidation bottom layer is formed on at least part of the surface of the outer wall of the lower end socket base body; and the porous metal top layer is formed on at least part of the surface of the oxidation-resistant bottom layer far away from the outer wall of the lower end socket base body.
According to the lower seal head of the pressure vessel of the nuclear reactor, the outer wall surface of the lower seal head is provided with the composite coating structure comprising the anti-oxidation bottom layer and the porous metal top layer, wherein the anti-oxidation bottom layer has excellent anti-oxidation performance and can isolate the contact between the external air and the surface of the lower seal head of the pressure vessel after passing through the porous metal top layer, so that the peeling of the coating caused by the excessive growth of an interface oxide is prevented, the reduction of the porosity of the porous metal top layer due to the oxidation in the composite coating is avoided in the use process of the lower seal head, and the durability of the coating is enhanced; the porous metal top layer can obviously increase the contact area between the outer wall surface of the lower end enclosure of the pressure vessel and cooling water, and the mutually communicated pores are favorable for the escape of generated water vapor, so that the obstruction of a vapor film on the heat transfer between the cooling water and the surface of the pressure vessel is avoided, thereby enhancing the boiling heat exchange of the outer wall surface of the lower end enclosure of the pressure vessel and improving the critical heat flux density. Therefore, the composite coating adopted by the lower seal head of the nuclear reactor pressure vessel can obviously improve the CHF limit value of the outer wall surface of the lower seal head, and lays a foundation for improving the effectiveness of IVR of a high-power reactor.
In addition, the lower head of the nuclear reactor pressure vessel according to the embodiment of the invention can also have the following additional technical characteristics:
in some embodiments of the invention, the bottom head base is formed from at least one selected from SA508 steel, SA533 steel.
In some embodiments of the invention, the oxidation resistant underlayer is formed of an oxidation resistant alloy material.
In some embodiments of the present invention, the oxidation resistant alloy material comprises at least one selected from the group consisting of a FeCr-based stainless steel material, a NiCr-based alloy, and a CoNiCr-based alloy.
In some embodiments of the invention, the porous metal top layer is formed from at least one selected from the group consisting of 304 stainless steel, 310 stainless steel, 316 stainless steel.
In some embodiments of the present invention, the thickness of the bottom oxidation resistant layer is 80 to 150 μm.
In some embodiments of the present invention, the porous metal top layer has a thickness of 250 to 350 μm.
In another aspect of the invention, the invention provides a method for preparing the lower head of the nuclear reactor pressure vessel of the embodiment. According to an embodiment of the invention, the method comprises: (1) pretreating the outer wall of the lower end socket base body; (2) spraying an anti-oxidation alloy material on at least part of the surface of the outer wall of the lower end socket substrate to form an anti-oxidation bottom layer; (3) mixing a metal pore-forming agent with a top layer alloy material, and spraying the obtained mixture on at least part of the surface of the oxidation-resistant bottom layer far away from the outer wall of the lower end socket substrate to form a metal top layer; and (4) removing the metal pore-forming agent in the metal top layer to form a porous metal top layer, thereby obtaining the lower end enclosure of the nuclear reactor pressure vessel. Therefore, the method can prepare the composite coating structure comprising the antioxidant bottom layer and the porous metal top layer on the outer wall surface of the lower seal head of the nuclear reactor in a large area, and the thermal influence on the base material can not be generated in the preparation process, so that the mechanical property of the base material can not be degraded. In addition, the method also has the advantages of low production cost and high production efficiency.
In addition, the method for preparing the lower head of the nuclear reactor pressure vessel according to the embodiment of the invention can also have the following additional technical characteristics:
in some embodiments of the invention, the oxidation resistant underlayer is formed by a kerosene fuel supersonic flame spray treatment, the process parameters of the kerosene fuel supersonic flame spray treatment comprising: the flow rate of kerosene is 20-25L/h, the flow rate of oxygen is 1800-1900 slm, the powder feeding speed is 60-70 g/min, the scanning speed of a spray gun is 900-1100 mm/s, and the number of spraying times is 4-8.
In some embodiments of the invention, the mass ratio of the metal pore-forming agent to the top layer alloy material is (3-5): 5-7.
In some embodiments of the invention, the average grain size of the anti-oxidation alloy material is 15-45 μm.
In some embodiments of the present invention, the top alloy material has an average grain size of 30 to 50 μm.
In some embodiments of the present invention, the metal pore former comprises at least one selected from the group consisting of aluminum, aluminum alloys, magnesium, and magnesium alloys.
In some embodiments of the present invention, the metal pore former has an average particle size of 30 to 60 μm.
In some embodiments of the invention, the metal top layer is formed by a cold spray process, and the process parameters of the cold spray process include: the gas temperature is 450-550 ℃, the main gas pressure is 3.0-4.0 MPa, the powder feeding speed is 45-55 g/min, the moving speed of the spray gun is 150-250 mm/s, and the spraying distance is 15-25 mm.
In some embodiments of the invention, a corrosive medium is contacted with the metal top layer to remove the metal pore former.
In some embodiments of the invention, the etching medium is at least one selected from the group consisting of aqueous sodium hydroxide, hydrochloric acid, and acetic acid.
In some embodiments of the invention, the contacting is performed at 25-35 ℃ for 45-75 min.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic flow diagram of a method for preparing a nuclear reactor pressure vessel bottom head according to one embodiment of the present disclosure;
FIG. 2 is a sectional structure diagram of the composite coating on the outer wall surface of the lower head of the nuclear reactor pressure vessel prepared in example 1;
FIG. 3 is a cross-sectional view of a pore structure in a porous metal top layer in a composite coating on the outer wall surface of a lower head of a nuclear reactor pressure vessel prepared in example 1.
Detailed Description
The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In one aspect of the invention, a nuclear reactor pressure vessel lower head is provided. According to an embodiment of the invention, the nuclear reactor pressure vessel bottom head comprises: a lower end enclosure base body; the anti-oxidation bottom layer is formed on at least part of the surface of the outer wall of the lower end socket base body; and the porous metal top layer is formed on at least part of the surface of the oxidation-resistant bottom layer far away from the outer wall of the lower end socket base body.
According to the lower seal head of the pressure vessel of the nuclear reactor, the outer wall surface of the lower seal head is provided with the composite coating structure comprising the anti-oxidation bottom layer and the porous metal top layer, wherein the anti-oxidation bottom layer has excellent anti-oxidation performance and can isolate the contact between the external air and the surface of the lower seal head of the pressure vessel after passing through the porous metal top layer, so that the peeling of the coating caused by the excessive growth of an interface oxide is prevented, the reduction of the porosity of the porous metal top layer due to the oxidation in the composite coating is avoided in the use process of the lower seal head, and the durability of the coating is enhanced; the porous metal top layer can obviously increase the contact area between the outer wall surface of the lower end enclosure of the pressure vessel and cooling water, and the mutually communicated pores are favorable for the escape of generated water vapor, so that the obstruction of a vapor film on the heat transfer between the cooling water and the surface of the pressure vessel is avoided, thereby enhancing the boiling heat exchange of the outer wall surface of the lower end enclosure of the pressure vessel and improving the critical heat flux density. Therefore, the composite coating adopted by the lower seal head of the nuclear reactor pressure vessel can obviously improve the CHF limit value of the outer wall surface of the lower seal head, and lays a foundation for improving the effectiveness of IVR of a high-power reactor.
The nuclear reactor pressure vessel lower head according to the embodiment of the invention is further described in detail below.
According to an embodiment of the present invention, the specific material of the bottom head base is not particularly limited, and may be a bottom head base commonly used in the art, and may be formed of at least one selected from low carbon steels for pressure vessels such as SA508 steel and SA533 steel, for example. That is, the composite coating provided by the invention has no particular limitation on the specific material of the lower head substrate, and can be used for reinforcing the lower head substrate of the conventional nuclear reactor pressure vessel so as to improve the critical heat flux density and the durability of the lower head substrate.
According to an embodiment of the present invention, the oxidation resistant underlayer is formed of an oxidation resistant alloy material. Specifically, the oxidation resistant alloy material includes at least one material that may be selected from a FeCr-based stainless steel material (e.g., 304 stainless steel, 310 stainless steel, 316 stainless steel, etc.), a NiCr-based alloy (e.g., NiCr20CuMo, NiCr20TiAl, etc.), a CoNiCr-based alloy (e.g., NiCoCrAlY, CoNiCrA1WBSi, etc.). The alloy material has excellent oxidation resistance under the atmospheric condition of 200-350 ℃, can effectively isolate the contact of external air with the surface of the lower end enclosure of the pressure vessel after passing through the porous metal top layer, prevents the peeling of a coating caused by excessive growth of an interface oxide, further can ensure that the porosity of the porous metal top layer is not reduced due to the internal oxidation of a composite coating when the lower end enclosure is used, and enhances the durability of the coating.
According to an embodiment of the present invention, the above porous metal top layer may be formed of at least one selected from 304 stainless steel, 310 stainless steel, 316 stainless steel, and the like. The contact area between the outer wall surface of the lower end enclosure of the pressure container and cooling water can be obviously increased by the porous metal top layer formed by the metal material, the mutually communicated pores are favorable for the generated steam to escape, and the obstruction of the steam film on the heat transfer between the cooling water and the surface of the pressure container is avoided, so that the boiling heat exchange of the outer wall surface of the lower end enclosure of the pressure container is enhanced, and the critical heat flux density is improved.
According to an embodiment of the present invention, the thickness of the bottom oxidation resistant layer may be 80 to 150 μm, such as 80 μm, 100 μm, 120 μm, 150 μm, and the like. By controlling the thickness of the anti-oxidation bottom layer within the range, the capability of the anti-oxidation bottom layer for sensing the outside air can be further improved, so that the integral durability of the composite coating is further improved.
According to an embodiment of the present invention, the thickness of the porous metal top layer may be 250 to 350 μm, such as 250 μm, 270 μm, 300 μm, 320 μm, 350 μm, and the like. By controlling the thickness of the porous metal top layer within the above range, the contact area of the porous metal top layer and the cooling water can be further increased, thereby further increasing the critical heat flux density of the material.
In another aspect of the invention, the invention provides a method for preparing the lower head of the nuclear reactor pressure vessel of the embodiment. According to an embodiment of the invention, the method comprises: (1) pretreating the outer wall of the lower end socket base body; (2) spraying an anti-oxidation alloy material on at least part of the surface of the outer wall of the lower end socket substrate to form an anti-oxidation bottom layer; (3) mixing a metal pore-forming agent with a top layer alloy material, and spraying the obtained mixture on at least part of the surface of the oxidation-resistant bottom layer far away from the outer wall of the lower end socket substrate to form a metal top layer; and (4) removing the metal pore-forming agent in the metal top layer to form a porous metal top layer, thereby obtaining the lower end enclosure of the nuclear reactor pressure vessel. Therefore, the method can prepare the composite coating structure comprising the antioxidant bottom layer and the porous metal top layer on the outer wall surface of the lower seal head of the nuclear reactor in a large area, and the thermal influence on the base material can not be generated in the preparation process, so that the mechanical property of the base material can not be degraded. In addition, the method also has the advantages of low production cost and high production efficiency.
A method of preparing a nuclear reactor pressure vessel according to an embodiment of the present invention is described in further detail below. Referring to fig. 1, according to an embodiment of the invention, the method comprises:
s100: substrate pretreatment
In the step, the outer wall of the lower end socket base body is pretreated. According to a specific example of the invention, the metal substrate on the outer wall of the lower end socket base body can be subjected to surface roughening by adopting a sand blasting method, and then the surface of the substrate is cleaned by adopting compressed air. Therefore, the roughness of the metal substrate on the outer wall of the lower end socket base body can be effectively improved, and the binding force between the metal substrate and the anti-oxidation bottom layer material is effectively improved.
S200: forming an oxidation resistant underlayer
In the step, an antioxidant alloy material is sprayed on at least part of the surface of the outer wall of the lower end socket substrate to form an antioxidant bottom layer. According to the embodiment of the invention, the anti-oxidation alloy material can be provided in the form of powder and is formed on at least part of the surface of the outer wall of the lower end socket base body by a cold spraying or hot spraying (preferably thermal spraying) method, and the cold spraying or hot spraying method is suitable for preparing an anti-oxidation bottom layer in a large area and has strong operability.
According to an embodiment of the present invention, the particle size of the antioxidant alloy material may be 15 to 45 μm, for example, 15 μm, 20 μm, 30 μm, 35 μm, 45 μm, or the like. Therefore, the compactness of the coating formed by the anti-oxygen alloy material can be further improved.
According to an embodiment of the present invention, the above-mentioned oxidation resistant underlayer is formed by a kerosene fuel high velocity flame spraying (HVOF) process, the process parameters of which include: the flow rate of kerosene is 20-25L/h (for example, 20L/h, 22L/h, 24L/h, 25L/h, etc.), the flow rate of oxygen is 1800-1900 slm (for example, 1800slm, 1850slm, 1900slm, etc.), the powder feeding rate is 60-70 g/min (for example, 60g/min, 65g/min, 70g/min, etc.), the scanning speed of the spray gun is 900-1100 mm/s (for example, 900mm/s, 1000mm/s, 1100mm/s, etc.), and the number of spraying passes is 4-8 (for example, 4 passes, 5 passes, 6 passes, 8 passes, etc.). The oxidation-resistant bottom layer formed by spraying under the conditions has high density and porosity not higher than 0.5%.
S300: forming a metal top layer
In the step, a metal pore-forming agent is mixed with a top alloy material, and the obtained mixture is sprayed on at least part of the surface of the oxidation-resistant bottom layer, which is far away from the outer wall of the lower end socket substrate, to form a metal top layer. According to the embodiment of the invention, the metal pore-forming agent and the alloy material can be provided in the form of powder and formed on at least part of the surface of the oxidation-resistant bottom layer by a cold spraying or thermal spraying (preferably cold spraying) method, and the cold spraying or thermal spraying method is suitable for preparing the metal top layer in a large area and has strong operability.
According to an embodiment of the present invention, the specific type of the metal pore-forming agent is not particularly limited, and a corrodible metal pore-forming material commonly used in the art, such as pure aluminum, aluminum alloy, pure magnesium, magnesium alloy, etc., may be used. The average particle diameter of the metal pore-forming agent may be 30 to 60 μm, for example, 30 μm, 35 μm, 50 μm, 60 μm, or the like. Thus, a porous metal top layer of suitable porosity can be obtained by removing the metal pore former after the metal top layer is formed.
According to an embodiment of the present invention, the average grain size of the top layer alloy material is 30 to 50 μm, such as 30 μm, 35 μm, 40 μm, 50 μm, etc. Therefore, the mixing effect between the top layer alloy material and the metal pore-forming agent can be further improved, and the porous metal top layer with proper porosity can be further obtained.
According to the embodiment of the invention, the mass ratio of the metal pore-forming agent to the top layer alloy material is (3-5): 5-7. Specifically, the metal pore-forming agent may be 3, 4, 5, etc. parts by weight, and the top layer alloy material may be 5, 6, 7, etc. parts by weight. Thereby, it is possible to further contribute to obtaining a porous metal top layer of suitable porosity.
According to an embodiment of the present invention, the metal top layer may be formed by a cold spraying process, and process parameters of the cold spraying process include: the gas temperature is 450-550 ℃ (for example 450 ℃, 500 ℃, 550 ℃ and the like), the main gas pressure is 3.0-4.0 MPa (for example 3.0MPa, 3.5MPa, 4.0MPa and the like), the powder feeding rate is 45-55 g/min (for example 45g/min, 50g/min, 55g/min and the like), the spray gun moving speed is 150-250 mm/s (for example 150mm/s, 200mm/s, 250mm/s and the like), and the spraying distance is 15-25 mm (for example 15mm, 20mm, 25mm and the like). The metal top layer formed by spraying under the conditions has proper porosity, is beneficial to the escape of water vapor generated in use, strengthens the boiling heat exchange of the outer wall surface of the lower end enclosure of the pressure vessel and improves the critical heat flux density.
S400: removing metal pore-forming agent
In the step, removing the metal pore-forming agent in the metal top layer to form a porous metal top layer, and obtaining a lower end socket product of the nuclear reactor pressure vessel.
According to an embodiment of the present invention, a porous metal top layer may be obtained by contacting an etching medium with the metal top layer to remove the metal pore former.
According to the embodiment of the present invention, the specific type of the etching medium is not particularly limited as long as the metal pore former in the metal top layer can be removed without affecting other materials, and for example, an alkaline solution or an acidic solution may be used. According to a specific example of the present invention, the alkaline solution may be, for example, a1 to 5mol/L NaOH aqueous solution, and the acidic solution may be, for example, hydrochloric acid, acetic acid, or the like.
According to the embodiment of the invention, the contact can be carried out at 25-35 ℃ for 45-75 min. Specifically, the contact temperature may be 25 ℃, 30 ℃, 35 ℃ and the like, and the contact time may be 45min, 60min, 75min and the like. Therefore, the metal pore-forming agent in the metal top layer can be effectively removed, and the porous metal top layer is obtained. In addition, electrochemical acceleration (namely, applying voltage by taking the metal top layer as an anode) can be assisted in the contact process so as to accelerate the speed of removing the metal pore-forming agent.
In addition, it should be noted that all the features and advantages described above for the "lower head of a nuclear reactor pressure vessel" are also applicable to the "method for preparing a lower head of a nuclear reactor pressure vessel", and are not described in detail herein.
In addition, the invention also provides a method for forming the bottom oxidation resistant layer and the porous metal top layer on the surface of the metal substrate. The metal substrate, the oxidation-resistant bottom layer, the porous metal top layer and the forming method thereof are all as described above, and are not described in detail herein.
The invention will now be described with reference to specific examples, which are intended to be illustrative only and not to be limiting in any way.
Example 1
The method comprises the steps of adopting a nuclear reactor pressure vessel lower head base body made of SA508 steel, taking SA508 steel as a base material, firstly adopting a sand blasting method to roughen the surface of the SA508 steel base material, and then adopting compressed air to clean the surface of the base material.
NiCoCrAlY powder with the particle size of 15-45 mu m is used as a bottom coating material, and a kerosene fuel supersonic flame spraying (HVOF) technology is adopted to prepare a high-density antioxidant bottom layer on the surface of SA508 steel. The specific process parameters are as follows: the kerosene flow is 22.4L/h, the oxygen flow is 1831slm, the powder feeding rate is 65g/min, the spray gun scanning speed is 1000mm/s, and the spraying times are 6 times. The obtained coating had a porosity of only 0.5% and a thickness of 120 μm.
Pure aluminum powder with the particle size of 30-60 mu m is used as pore-forming agent powder, and 304 stainless steel powder with the particle size of 30-50 mu m is used as a top coating material. And fully and mechanically mixing the two powders according to the volume ratio of 4:6, and preparing the metal top layer by using the mixed powder as a spraying raw material and adopting cold spraying. The specific process parameters are as follows: the gas temperature is 500 ℃, the main gas pressure is 3.5MPa, the powder feeding speed is 50g/min, the moving speed of the spray gun is 200mm/s, and the spraying distance is 20 mm. The deposition yielded a two-component top coat of pure aluminum and 304 stainless steel with a thickness of about 300 microns.
And (3) using NaOH aqueous solution with the concentration of 3mol/L as a corrosion medium, and removing pore-forming aluminum particles in the two-component top coating under the parameter conditions that the temperature is 30 ℃ and the time is 60 min. Finally, the composite coating with a double-layer structure is obtained, wherein the porosity of the top porous metal layer is 38%, the porosity of the bottom NiCoCrAlY layer is only 0.5% (shown in figure 2), and the pore size is about 10-35 μm (shown in figure 3). The bonding strength of the coating is tested according to the ASTM C633 standard, and the test result shows that the bonding strength of the coating reaches 35 MPa. The related thermal test results show that the coating can improve CHF of the surface of the base material by more than 50%.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A nuclear reactor pressure vessel bottom head, comprising:
a lower end enclosure base body;
the anti-oxidation bottom layer is formed on at least part of the surface of the outer wall of the lower end socket base body;
the porous metal top layer is formed on at least part of the surface of the oxidation-resistant bottom layer, which is far away from the outer wall of the lower end socket base body.
2. A nuclear reactor pressure vessel bottom head as claimed in claim 1, wherein the bottom head substrate is formed from at least one selected from SA508 steel, SA533 steel.
3. The nuclear reactor pressure vessel bottom head of claim 1, wherein the oxidation resistant bottom layer is formed from an oxidation resistant alloy material;
optionally, the anti-oxidant alloy material is formed of at least one selected from the group consisting of FeCr-based stainless steel material, NiCr-based alloy, and CoNiCr-based alloy.
4. The nuclear reactor pressure vessel bottom head of claim 1, wherein the porous metal top layer is formed from at least one selected from the group consisting of 304 stainless steel, 310 stainless steel, 316 stainless steel.
5. The lower head of the nuclear reactor pressure vessel of claim 1, wherein the thickness of the bottom oxidation-resistant layer is 80-150 μm;
optionally, the thickness of the porous metal top layer is 250-350 μm.
6. A method for preparing a nuclear reactor pressure vessel lower head of any one of claims 1 to 5, comprising:
(1) pretreating the outer wall of the lower end socket base body;
(2) spraying an anti-oxidation alloy material on at least part of the surface of the outer wall of the lower end socket substrate to form an anti-oxidation bottom layer;
(3) mixing a metal pore-forming agent with a top layer alloy material, and spraying the obtained mixture on at least part of the surface of the oxidation-resistant bottom layer far away from the outer wall of the lower end socket substrate to form a metal top layer;
(4) and removing the metal pore-forming agent in the metal top layer to form a porous metal top layer, thereby obtaining the lower end enclosure of the nuclear reactor pressure vessel.
7. The method of claim 6, wherein the oxidation resistant underlayer is formed by a kerosene fuel supersonic flame spray process, the process parameters of the kerosene fuel supersonic flame spray process comprising: the flow rate of kerosene is 20-25L/h, the flow rate of oxygen is 1800-1900 slm, the powder feeding speed is 60-70 g/min, the scanning speed of a spray gun is 900-1100 mm/s, and the number of spraying times is 4-8.
8. The method of claim 6, wherein the mass ratio of the metal pore former to the top alloy material is (3-5): (5-7);
optionally, the average grain size of the anti-oxidation alloy material is 15-45 μm;
optionally, the average grain diameter of the top layer alloy material is 30-50 μm;
optionally, the metal pore former comprises at least one selected from the group consisting of aluminum, aluminum alloys, magnesium, and magnesium alloys;
optionally, the average particle size of the metal pore former is 30-60 μm.
9. The method of claim 6, wherein the metal top layer is formed by a cold spray process, the process parameters of the cold spray process comprising: the gas temperature is 450-550 ℃, the main gas pressure is 3.0-4.0 MPa, the powder feeding speed is 45-55 g/min, the moving speed of the spray gun is 150-250 mm/s, and the spraying distance is 15-25 mm.
10. The method of claim 6 wherein a corrosive medium is contacted with the metal top layer to remove the metal pore former;
optionally, the etching medium is at least one selected from the group consisting of aqueous sodium hydroxide solution, hydrochloric acid, and acetic acid;
optionally, the contacting is done at 25-35 ℃ for 45-75 min.
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