Tungsten control rod and manufacturing method thereof

Abstract

A manufacturing method of a tungsten control rod comprises the following steps that a tungsten pipe is provided, pre-electroplating treatment is conducted after cleaning and surface activating treatment, and a pre-electroplated layer is formed on the surface of the tungsten pipe; the method comprises the following steps: carrying out nickel plating treatment on an electrolyte at 85-90 DEG C, wherein the electrolyte contains 27-29 g / L of nickel sulfate, 24-26 g / L of sodium hypophosphite, 24-26 g / L of sodium citrate, 16-18 g / L of a complexing agent and 7-9 mg / L of propargyl alcohol, and the pH value of the electrolyte is 7.0-8.5, so as to obtain a nickel-plated tungsten pipe; and loading the nickel-plated tungsten tube into a cladding, welding and packaging to obtain a tungsten control rod finished product. The method can be used for manufacturing the tungsten control rod with good neutron absorptivity and reliability, and the safety of a reactor is improved. The invention also provides a tungsten control rod.

Description

Technical Field

[0001] The invention belongs to the field of nuclear power, and in particular relates to a tungsten control rod and a manufacturing method thereof. Background Art

[0002] Reactor control rod assemblies are key components related to the safety performance of nuclear power plants and are used to adjust the reactivity of the core. The neutron absorbing material in the control rod determines the overall neutron absorption capacity of the control rod. Currently, commonly used neutron absorber materials include Ag-In-Cd alloys, various B-containing materials (such as B 4 C core block, B 4 C-HfB 2 Composite core block, B 4 C-Al 2 O 3 Composite pellets, B-Al alloy, Al-B 4 C composite materials, etc.). However, Ag-In-Cd alloys will produce radioactive nuclides after neutron irradiation, and the corrosion resistance of various B-containing materials is generally insufficient.

[0003] In some schemes, a composite structure of a tungsten rod encapsulated in an Inconel 718 alloy tube is installed in the control rod cladding as a neutron absorber, and the tungsten rod absorbs neutrons, while the Inconel 718 alloy acts as a second protective layer to separate the tungsten rod from the control rod cladding. The space utilization efficiency of the double-layer cladding design in this type of scheme is low, resulting in limited neutron absorption capacity of the control rod. Therefore, providing a tungsten control rod structure with better neutron absorption capacity is of positive significance for improving the efficiency and safety of reactor control rod assemblies. Summary of the invention

[0004] The object of the present invention is to provide a method for manufacturing a tungsten control rod, so as to manufacture a tungsten control rod with good neutron absorption capability. The present invention also provides a tungsten control rod.

[0005] According to an embodiment of one aspect of the present invention, a method for manufacturing a tungsten control rod is provided, the method comprising the following steps:

[0006] Step a): providing a tungsten tube, and performing degreasing cleaning and weak acid cleaning on the tungsten tube;

[0007] Step b): performing surface activation treatment and pre-electroplating treatment on the tungsten tube to form a pre-electroplating layer;

[0008] Step c): providing an electroplating solution, wherein the electroplating solution contains 27g / L-29g / L nickel sulfate, 24g / L-26g / L sodium hypophosphite, 24g / L-26g / L sodium citrate, 16g / L-18g / L complexing agent and 7mg / L-9mg / L propargyl alcohol, and the pH value is 7.0-8.5; using the electroplating solution to nickel-plate the tungsten tube at 85°C-90°C to obtain a nickel-plated tungsten tube;

[0009] Step d): the nickel-plated tungsten tube is placed into a cladding and welded to obtain a finished tungsten control rod.

[0010] Tungsten tubes can increase the neutron absorption area of ​​tungsten as a neutron absorber and improve the neutron absorption effect of control rods; tungsten is easily oxidized when in contact with water vapor. If tungsten swells due to radiation, it is easy to come into contact with the cladding tube material and corrode. Providing a nickel plating layer on the surface of the tungsten tube can effectively improve the corrosion resistance of the tungsten tube, improve the wear resistance and chemical stability of the neutron absorber, and avoid damage caused by step loads or flow-induced vibration loads.

[0011] Furthermore, in some embodiments, the outer diameter of the tungsten tube in step a) is 7 mm-9 mm, and the inner diameter is 5.5 mm-6.5 mm.

[0012] Furthermore, in some embodiments, in the step b), the pre-electroplating layer is configured as a pure nickel layer and / or a W—Ni alloy transition layer.

[0013] Since tungsten is prone to surface oxidation, resulting in low metal deposition efficiency during the plating process, setting a pre-electroplating layer can effectively improve the bonding strength between the tungsten tube and the nickel plating layer, improve the adhesion and stability of the nickel plating layer under high-temperature irradiation conditions, and avoid coating peeling.

[0014] Furthermore, in some embodiments, in the step b), the W—Ni alloy transition layer is configured as a 95W-3Ni alloy layer.

[0015] Furthermore, in some embodiments, in the step b), the thickness of the pre-electroplating layer is 5 μm-10 μm.

[0016] Furthermore, in some embodiments, in the step c), nickel plating is performed on both the inner surface and the outer surface of the tungsten tube.

[0017] Nickel plating of both the inner and outer layers of the tungsten tube can further improve the reliability of the tungsten tube as a neutron absorber and prevent oxidation corrosion on the inner side of the tungsten tube.

[0018] Furthermore, in some embodiments, in the step c), the nickel coating obtained by the nickel plating process has a purity of not less than 99.5% by weight.

[0019] Furthermore, in some embodiments, in the step c), the nickel plating layer obtained by the nickel plating treatment has a thickness of 2 μm-200 μm.

[0020] Furthermore, in some embodiments, in the step d), the control rod cladding is made of zirconium alloy, nickel-based alloy or stainless steel, and is sealed by laser welding.

[0021] According to an embodiment of another aspect of the present invention, there is provided a tungsten control rod, comprising a cladding and a neutron absorber, wherein the neutron absorber is configured as a nickel-plated tungsten tube, and the tungsten control rod is manufactured using the manufacturing method of the tungsten control rod provided in any of the aforementioned embodiments.

[0022] The tungsten control rod provided in the above embodiment has the advantages of high neutron absorption efficiency, light weight, simple structure and good reliability; since a nickel plating layer is provided on the surface of the tungsten tube, the whole has good water corrosion resistance and wear resistance, which improves reliability while reducing manufacturing and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the cross-sectional structure of a tungsten control rod in one embodiment.

[0024] Meaning of the reference symbols:

[0025] 1- cladding tube;

[0026] 2- Gap;

[0027] 3-Nickel plating;

[0028] 4- Pre-plating;

[0029] 5- Tungsten tube.

[0030] The purpose of the above drawings is to explain the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. For the sake of simplicity, the above drawings only schematically illustrate the structures related to the technical features of the present invention, and do not strictly follow the actual proportions to draw the complete structure and all details. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0033] In the description of this document, terms indicating orientation or positional relationships, such as "up", "down", "left", "right", "horizontal", "vertical", "height", "length", and "width", are intended to accurately describe the embodiments and simplify the description, but are not intended to limit the parts or structures involved to have a specific orientation, be installed or operate in a specific orientation, and should not be construed as a limitation on the embodiments in this document.

[0034] In the description of this article, the terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating relative importance or limiting the quantity, specific order or primary and secondary relationship of the described technical features. In the description of this article, the meaning of "plurality" is at least two.

[0035] Reactor control rod assemblies are key components for controlling the reactivity of nuclear power plant cores and are vital to the overall safety of nuclear power plants. Therefore, the neutron absorber materials in reactor control rod assemblies have always been highly valued in the industry.

[0036] At present, a variety of technical solutions have been formed for the neutron absorber core block materials in reactor control rods. For example, patent CN115679145A discloses a neutron absorber material, the matrix of which is an Ag-In-Cd alloy, and dispersed yttrium oxide particles are distributed in the matrix. Ag-In-Cd alloy has a strong neutron absorption ability, but after being irradiated by neutrons, Ag-In-Cd alloy will produce a relatively strong induced radioactivity, which will lead to an increase in the pressure of radioactive waste disposal.

[0037] Patent CN85105559A discloses a control rod in which neutron absorbing materials (B 4 C) Pellets and inert pellets (ZrO 2 ). Element B also has good neutron absorption properties. 4 C and its composite materials composed of various ceramic materials or metal materials have also been widely used as control rod neutron absorbers. 4 B-containing compounds such as C have insufficient corrosion resistance under high-temperature neutron irradiation conditions. During the long-term operation of the reactor, the neutron absorber material in the control rod is prone to irradiation swelling and creep after absorbing neutrons. Under the combined influence of flow-induced vibration and step load in the primary circuit of the reactor, the control rod cladding is at risk of wear and rupture. Once the neutron absorber in the cladding is corroded by the primary circuit coolant, it will seriously threaten the safety of the reactor operation.

[0038] Some other technical solutions use tungsten rods as neutron absorbers, but the tungsten rods themselves are prone to oxidation. In order to further improve the corrosion resistance of the tungsten rods, the tungsten rods are placed in inner cladding tubes made of Inconel718 alloy, thereby forming a double layer of protection for the tungsten rods together with the control rod cladding. However, gaps need to be reserved between the inner cladding tube and the control rod cladding, as well as between the inner cladding tube and the tungsten rods. Such a setting will reduce the efficiency of space utilization in the control rods and affect the overall neutron absorption performance of the control rods.

[0039] In order to overcome the above problems, an embodiment of one aspect of the present invention provides a method for manufacturing a tungsten control rod, which is used to manufacture a tungsten control rod with high neutron absorption efficiency and good reliability. The method comprises the following steps:

[0040] First, a tungsten tube is provided as the base of the neutron absorber. The tungsten tube is degreased and cleaned with weak acid to remove surface contamination and oxide layer. Using tubular tungsten material as a neutron absorber can effectively increase the effective neutron absorption area, reduce the weight of the control rod, and thus reduce the overall load of the control rod assembly. The tungsten tube does not have an inner cladding or support tube structure, which can simplify the structure of the control rod and improve the reliability of the device.

[0041] Next, the tungsten tube is subjected to substrate coarsening, sensitization and surface activation treatments, and pre-plating treatment is performed to form a pre-plating layer on the surface of the tungsten tube. In a preferred embodiment, the pre-plating layer can be set as a pure nickel plating layer or a W-Ni alloy layer, such as a 95W-3Ni alloy layer. In a preferred embodiment, the thickness of the pre-plating layer is set to 5μm-10μm. The pre-plating layer can be prepared by a conventional electroplating process, or it can be formed by ion plating or the like.

[0042] Next, the tungsten tube is nickel-plated in the electroplating solution to obtain a nickel-plated tungsten tube. Due to the presence of the pre-electroplating layer, the bonding strength between the tungsten substrate and the nickel plating layer is effectively improved, so that the nickel plating layer is not easy to crack or peel off under long-term high-temperature neutron irradiation conditions; and the nickel plating layer has good high-temperature oxidation resistance and high hardness and wear resistance, which can effectively improve the corrosion resistance of the tungsten tube and effectively prevent the tungsten tube from being damaged under the action of step loads and flow-induced vibration loads.

[0043] Specifically, the electroplating solution contains: 27g / L-29g / L nickel sulfate, 24g / L-26g / L sodium hypophosphite, 24g / L-26g / L sodium citrate, 16g / L-18g / L complexing agent and 7mg / L-9mg / L propargyl alcohol, the pH value of the electroplating solution is adjusted to 7.0-8.5, and the temperature of the electroplating treatment is 85°C-90°C. After the electroplating treatment, a nickel plating layer with a thickness of 2μm-200μm is formed on the surface of the tungsten tube, and in a preferred embodiment, the purity of Ni in the nickel plating layer is not less than 99.5% by weight.

[0044] In a preferred embodiment, both the inner and outer surfaces of the tungsten tube are electroplated, so that nickel plating is formed on both the inner and outer surfaces of the tungsten tube.

[0045] Finally, the nickel-plated tungsten tube is installed into the control rod cladding, the end plug is installed and welded to obtain the finished tungsten control rod. In different embodiments, the control rod cladding can be made of zirconium alloy, nickel-based alloy stainless steel and other materials, and laser welding is used to seal. In other embodiments, the control rod can also be made of composite materials such as SiC.

[0046] The structure of the tungsten control rod produced by this method is as follows: Figure 1 As shown, it includes a cladding tube 1 and a tungsten tube 5 enclosed in the cladding tube 1, the inner and outer surfaces of the tungsten tube 5 are provided with a pre-plating layer 4, and a nickel plating layer 2 is further formed on the pre-plating layer; a gap 2 is reserved between the tungsten tube 5 and the cladding tube 1 to accommodate the fission gas generated after neutron irradiation and to reserve a certain space for possible radiation swelling and creep.

[0047] The control rod is simple, light and has high neutron absorption value. Due to the protection of the nickel plating, the neutron absorber has good water corrosion resistance, high hardness and wear resistance. It can effectively prevent the tungsten matrix from reacting with water vapor at a temperature not exceeding 1200°C and has good safety performance.

[0048] In a preferred embodiment, a tungsten control rod manufacturing process is as follows:

[0049] Provide tungsten tubes with an outer diameter of Φ8mm and an inner diameter of Φ6mm. First, degrease and clean the tungsten tubes to remove surface oil stains, and then use weak acid cleaning to remove the oxide layer.

[0050] Next, the tungsten tube is subjected to substrate roughening, sensitization and surface activation, followed by pre-electroplating to form a pure nickel pre-plating layer with a thickness of 2 μm.

[0051] Subsequently, an electroplating solution is prepared, the components of which are: 28 g / L nickel sulfate, 25 g / L sodium hypophosphite, 25 g / L sodium citrate, 17 g / L complexing agent, 8 mg / L stabilizer, and 8 mg / L propargyl alcohol; the pH value is adjusted to 7.0-8.5. Electroplating is performed in an electroplating solution at 88° C. to form a nickel coating with a thickness not exceeding 20 μm, and the purity of the nickel coating by weight is not less than 99.5%, thereby obtaining a nickel-plated tungsten tube.

[0052] In the tungsten control rod, the tungsten neutron absorber is tubular, has a large neutron absorption area, high neutron absorption value and is relatively light in weight. Under the protection of the nickel plating, the neutron absorber has a high tolerance to flow-induced vibration and step loads. In the event of damage to the control rod cladding, it has good tolerance to water corrosion and can serve stably for a long time.

[0053] In another preferred embodiment, a manufacturing process of a tungsten control rod is as follows:

[0054] Provide tungsten tubes with an outer diameter of Φ8mm and an inner diameter of Φ6mm. First, degrease and clean the tungsten tubes to remove surface oil stains, and then use weak acid cleaning to remove the oxide layer.

[0055] Next, the tungsten tube is subjected to substrate roughening, sensitization and surface activation, followed by pre-electroplating treatment to form a 95W-3Ni metal pre-plating layer with a thickness of 5 μm-10 μm.

[0056] Subsequently, an electroplating solution is prepared, the components of which are: 28 g / L nickel sulfate, 25 g / L sodium hypophosphite, 25 g / L sodium citrate, 17 g / L complexing agent, 8 mg / L stabilizer, and 8 mg / L propargyl alcohol; the pH value is adjusted to 7.0-8.5. Electroplating is performed in an electroplating solution at 88° C. to form a nickel plating layer with a thickness of 200 μm, and the purity of the nickel plating layer is not less than 99.5% by weight, thereby obtaining a nickel-plated tungsten tube.

[0057] In the tungsten control rod, the tungsten neutron absorber is tubular, has a large neutron absorption area, high neutron absorption value and is relatively light in weight; under the protection of the nickel plating, the neutron absorber has a high tolerance to flow-induced vibration and step loads; in the event of damage to the control rod cladding, it has good tolerance to water corrosion and can serve stably for a long time; due to the provision of a W-Ni pre-plating layer, the nickel plating layer and the tungsten substrate have better bonding strength, which can further improve the mechanical properties of the nickel-plated tungsten tube and reduce the risk of plating cracking.

[0058] The manufacturing method of the tungsten control rod provided in the above embodiment can be used to manufacture a control rod with good neutron absorption performance and reliability, using tungsten as the neutron absorber. The control rod has the following technical effects:

[0059] 1. Under normal operating conditions, even if the control rod cladding is worn and cracked, the nickel coating can still effectively protect the tungsten tube, preventing the tungsten tube, which serves as a neutron absorber, from being corroded and losing its neutron absorption capacity;

[0060] 2. The nickel coating has good hardness, plasticity and wear resistance, which effectively reduces the risk of the tungsten tube falling off or slag falling after neutron irradiation, and enhances the geometric stability of the tungsten tube;

[0061] 3. The nickel coating can effectively protect the tungsten tube after the cladding tube is damaged under accident conditions, avoiding steam corrosion and loss of neutron absorber materials, and improving the accident tolerance of the control rod;

[0062] 4. The bonding strength between the tungsten substrate and the nickel coating is further improved by setting a pre-plating layer;

[0063] 5. The inner cladding tube is replaced by nickel plating, which effectively simplifies the internal structure of the control rod, improves the space utilization efficiency of the control rod, improves the neutron absorption capacity of the control rod, and improves the reliability of the control rod assembly.

[0064] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, the optimization or equivalent replacement of the method steps involved, and the combination of the implementation methods in different embodiments without conflict of structure and principle, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a tungsten control rod, characterized in that: The following steps are involved: Step a): providing a tungsten tube, and performing degreasing cleaning and weak acid cleaning on the tungsten tube; Step b): performing surface activation treatment and pre-electroplating treatment on the tungsten tube to form a pre-electroplating layer; Step c): providing an electroplating solution, wherein the electroplating solution contains 27g / L-29g / L nickel sulfate, 24g / L-26g / L sodium hypophosphite, 24g / L-26g / L sodium citrate, 16g / L-18g / L complexing agent and 7mg / L-9mg / L propargyl alcohol, and the pH value is 7.0-8.5; using the electroplating solution to nickel-plate the tungsten tube at 85°C-90°C to obtain a nickel-plated tungsten tube; Step d): the nickel-plated tungsten tube is placed into a cladding and welded to obtain a finished tungsten control rod.

2. The method for manufacturing a tungsten control rod according to claim 1, characterized in that: The outer diameter of the tungsten tube in step a) is 7 mm to 9 mm, and the inner diameter is 5.5 mm to 6.5 mm.

3. The method for manufacturing a tungsten control rod according to claim 1, characterized in that: In the step b), the pre-electroplating layer is configured as a pure nickel layer and / or a W—Ni alloy transition layer.

4. The method for manufacturing a tungsten control rod according to claim 3, characterized in that: In the step b), the W-Ni alloy transition layer is configured as a 95W-3Ni alloy layer.

5. The method for manufacturing a tungsten control rod according to claim 1, 3 or 4, characterized in that: In the step b), the thickness of the pre-electroplating layer is 5 μm-10 μm.

6. The method for manufacturing a tungsten control rod according to claim 1, characterized in that: In the step c), both the inner surface and the outer surface of the tungsten tube are nickel plated.

7. The method for manufacturing a tungsten control rod according to claim 6, characterized in that: In the step c), the nickel coating obtained by the nickel plating treatment has a purity of not less than 99.5% by weight.

8. The method for manufacturing a tungsten control rod according to claim 6 or 7, characterized in that: In the step c), the nickel plating layer obtained by the nickel plating treatment has a thickness of 2 μm-200 μm.

9. The method for manufacturing a tungsten control rod according to claim 1, characterized in that: In the step d), the control rod cladding is made of zirconium alloy, nickel-based alloy or stainless steel and is sealed by laser welding.

10. A tungsten control rod, comprising a cladding and a neutron absorber, characterized in that: The neutron absorber is configured as a nickel-plated tungsten tube, and the tungsten control rod is manufactured by the manufacturing method of a tungsten control rod according to any one of claims 1 to 9.

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