Tungsten dispersion material for reactor control rod as well as manufacturing method and application of tungsten dispersion material

Abstract

A manufacturing method of the tungsten dispersion material for the reactor control rod comprises the steps that W particles and Ni powder are evenly mixed and pressed into a blank block through cold isostatic pressing treatment, sintering treatment is conducted, then hot isostatic pressing treatment and quenching treatment are conducted, and the finished tungsten dispersion material for the reactor control rod is obtained. The material has good mechanical property, heat-conducting property and corrosion resistance, and can effectively improve the safety and reliability of the reactor control rod. The invention also provides the tungsten dispersion material for the reactor control rod and the reactor control rod.

Description

Technical Field

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

[0002] The reactor control rod assembly is used to achieve reactivity control by adjusting the rod position during reactor power regulation or shutdown, and is one of the key components related to reactor safety. In the control rod assembly, the neutron absorber is used to absorb core neutrons and is the main component for achieving reactivity control. The neutron absorber material needs to have good corrosion resistance, mechanical properties, geometric stability and dimensional integrity to ensure the reliability of the control rod. At present, some technical solutions use nickel-based alloys and Ag-In-Cd alloys to jointly manufacture neutron absorbers. For example, in patent CN101369468A, nickel-based alloys such as 718 alloy are used as the first neutron absorber and placed at the bottom of the control rod, while Ag-In-Cd alloy is used as the second neutron absorber and arranged above the first neutron absorber. Due to the strong neutron absorption capacity of Ag-In-Cd alloy, this type of control rod inevitably produces the problem of uneven axial neutron absorption capacity. In other schemes, the gray rod adopts the form of arranging tungsten rods and nickel-based alloy tubes in the cladding tube. Although the nickel-based alloy can protect the tungsten rod, the form of arranging the nickel-based alloy tube in the cladding tube reduces the space utilization efficiency and limits the absorption capacity of the neutron absorber material. Therefore, providing a scheme to overcome the defects of the existing control rods is of positive significance for improving the safety and reliability of the reactor control rod assembly. Summary of the invention

[0003] The object of the present invention is to provide a method for manufacturing a tungsten dispersion material for a reactor control rod, thereby improving the reliability of a control rod core block. The present invention also provides a tungsten dispersion material for a reactor control rod and a reactor control rod.

[0004] According to an embodiment of one aspect of the present invention, a method for manufacturing a tungsten dispersion material for a reactor control rod is provided, the method comprising the following steps:

[0005] Step a): providing W particles and Ni powder, and uniformly mixing the W particles and Ni powder to obtain a mixed powder;

[0006] Step b): performing cold isostatic pressing on the mixed powder to obtain a blank block;

[0007] Step c): sintering the green block to obtain a sintered body;

[0008] Step d): performing hot isostatic pressing and quenching on the sintered body to obtain a finished tungsten dispersion material for reactor control rods.

[0009] This method can achieve uniform dispersion of W in the Ni matrix, improve the material's formability while ensuring the material's neutron absorption capacity, and can simplify the control rod structure and improve the space utilization efficiency inside the control rod when used to manufacture reactor control rod cores. W particles dispersed in the Ni matrix can improve the material's overall impact resistance, corrosion resistance, and fission product tolerance.

[0010] Furthermore, in some embodiments, in the step a), the average particle size of the W particles is 50 μm-500 μm, and the average particle size of the Ni powder is 2 μm-3 μm.

[0011] Furthermore, in some embodiments, in the step a), the volume fraction of the W particles in the mixed powder is 50%-80%.

[0012] Furthermore, in some embodiments, in the step a), the mixing is performed by ball milling, and the mixing time is 5h-15h.

[0013] Furthermore, in some embodiments, a corrosion-resistant metal coating is provided on the surface of the W particles.

[0014] Furthermore, in some embodiments, the corrosion-resistant metal coating is made of pure Ni or a nickel-based alloy, and has a thickness of 10 μm-20 μm.

[0015] Furthermore, in some embodiments, in the step b), the pressure during the cold isostatic pressing process is 120 MPa-180 MPa.

[0016] Furthermore, in some embodiments, in the step c), the sintering temperature is 1200° C.-1500° C., and the sintering time is 2 h-2.5 h.

[0017] Furthermore, in some embodiments, in the step d), the hot isostatic pressing temperature is 1000° C.-1200° C., the pressure is 180 MPa-220 MPa, and the holding time is 1 h-2 h.

[0018] Furthermore, in some embodiments, in the step d), the holding temperature of the quenching treatment is 1060°C-1100°C, the holding time is 50min-70min, and the cooling rate is not less than 7°C / s.

[0019] According to another embodiment of the present invention, there is provided a tungsten dispersed material for a reactor control rod. The material comprises a Ni matrix and W dispersed particles and is manufactured using the manufacturing method of the tungsten dispersed material for a reactor control rod provided in any of the aforementioned embodiments.

[0020] According to another embodiment of the present invention, there is provided a reactor control rod, comprising a cladding and a core block, wherein the core block is made of the tungsten dispersed material for reactor control rods provided in the aforementioned embodiment.

[0021] In the core block of the control rod, the W absorber is distributed in the Ni matrix in the form of dispersed particles, so it has good impact resistance and corrosion resistance, and has better tolerance to flow-induced vibration and partial loads. Furthermore, compared with W alloy, the thermal conductivity of the material is effectively improved, and the Ni matrix can inhibit the radiation swelling of the whole material, reducing the risk of matrix cracking and reaction between the core block and the control rod cladding. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of tungsten dispersion material for reactor control rods in one embodiment.

[0023] Meaning of the reference symbols:

[0024] 1-Ni matrix;

[0025] 2-W particles.

[0026] 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. The above drawings only schematically show the structures related to the technical features of the present invention, and do not strictly draw the actual morphology of the corresponding microstructure according to the actual proportion. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0028] 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.

[0029] In the description herein, "plurality" means at least two.

[0030] The control rod assembly is the control component of the reactor. It controls the reactivity of the core by inserting and withdrawing it from the fuel assembly to compensate for the changes in core reactivity caused by changes in power, coolant temperature and boron concentration in the primary coolant during operation. At the same time, the control rod assembly also plays an important role during the reactor shutdown process. Therefore, the control rod assembly is crucial to ensure the safety of the reactor.

[0031] The control rod assembly mainly relies on neutron absorption to achieve reactivity control. The main neutron absorber in the control rod assembly plays a neutron absorption role. In order to ensure safety, the neutron absorber needs to have good corrosion resistance, mechanical properties, mechanical stability and dimensional integrity.

[0032] In some of the gray control rod assemblies that are widely used at present, the control rod cladding contains an absorber component composed of a tungsten rod and an Inconel718 alloy tube. The Inconel 718 alloy inner cladding tube provides a second layer of protection for the tungsten rod neutron absorber, so as to provide further containment for the neutron absorber and prevent the neutron absorber from contacting and reacting with the control rod cladding when it swells due to radiation, thus affecting the effectiveness of the control rod cladding. However, the Inconel 718 alloy inner cladding tube will occupy the limited space in the control rod cladding, reduce the space utilization rate, and affect the neutron absorption capacity of the control rod. Moreover, once the tungsten core block cracks and breaks due to the impact load of flow-induced vibration or radiation swelling, it will lead to uneven distribution of neutron absorption capacity in the axial direction, increasing the operating risk of the reactor.

[0033] To this end, an embodiment of the present invention provides a method for manufacturing a tungsten dispersed material for a reactor control rod, which is used to manufacture a tungsten dispersed material and effectively solve the above-mentioned problem.

[0034] The method comprises the following steps:

[0035] Step a): Provide W particles and Ni powder as raw materials, and mix the W particles and Ni powder evenly to obtain a mixed powder. In a preferred embodiment, the average particle size of the W particles is 50μm-500μm, the average particle size of the Ni powder is 2μm-3μm, and the volume fraction of the W particles is 50%-80%. The mixing process can be ball milled, and the mixing time is controlled at 5h-15h according to the raw material ratio. The W particles play a major role in neutron absorption as a neutron absorber, and the Ni powder, as a matrix, has good plasticity, corrosion resistance and thermal conductivity, and can contain and protect the W particles.

[0036] In a preferred embodiment, a corrosion-resistant metal coating is provided on the surface of the W particles to further improve the corrosion resistance and oxidation resistance of the W particles. In a further preferred embodiment, the corrosion-resistant coating can be made of pure Ni or a nickel-based alloy to improve the bonding strength between the W particles and the Ni matrix. The thickness of the pure Ni or nickel-based alloy layer is set to 10 μm-20 μm.

[0037] Step b): performing cold isostatic pressing on the mixed powder to obtain a green body.

[0038] The mixed powder is loaded into a mold and subjected to cold isostatic pressing at 120MPa-180MPa, so that the Ni powder and the W particles are connected together by mechanical deformation, and the mixed powder is pressed into a formed billet block for subsequent processing.

[0039] Step c): sintering the green block to obtain a sintered body.

[0040] In a preferred embodiment, the sintering temperature is set at 1200°C-1500°C, and the sintering time is 2h-2.5h. During the sintering process, the Ni powders are interconnected to form a whole. If the sintering temperature is too low, it may lead to uneven and insufficient sintering, and there may be unsintered powders; if the sintering temperature is too high, there is a risk of causing Ni to melt and produce a liquid phase. The sintering process is carried out under argon protection to avoid oxidation of W particles, while improving the sintering activity of Ni and preventing Ni from generating NiO under high temperature conditions.

[0041] Step d): performing hot isostatic pressing and quenching on the sintered body to obtain a finished tungsten dispersion material for reactor control rods.

[0042] In a preferred embodiment, the parameters of the hot isostatic pressing treatment are: a holding temperature of 1000°C-1200°C, a pressure of 180MPa-220MPa, and a holding time of 1h-2h. The hot isostatic pressing treatment can eliminate defects such as holes remaining in the sintering process through high temperature and high pressure, promote the full recrystallization of the Ni matrix, and improve the material density and organizational uniformity.

[0043] In a preferred embodiment, the holding temperature of the quenching treatment is 1060°C-1100°C, the holding time is 50min-70min, and the cooling rate during quenching is not less than 7°C / s.

[0044] Through the above steps, the Figure 1 The tungsten dispersion material for reactor control rods shown in the figure has a uniform Ni matrix 1 in which dispersed W particles 2 are distributed. The material can be used to manufacture pellets for reactor control rods.

[0045] Among them, Ni as a matrix can effectively improve the thermal conductivity of the core block, and the good plasticity of the Ni matrix 1 can reduce the risk of cracking and damage of the core block due to radiation swelling or vibration load, and avoid uneven distribution of neutron absorption capacity in the axial direction of the control rod after the neutron absorber is crushed; W particles 2 are dispersed in the Ni matrix 1, which effectively improves the impact resistance of the core block. At the same time, due to the coating of the Ni matrix 1, the risk of corrosion or oxidation caused by contact between W and the cladding tube is reduced.

[0046] In a preferred embodiment, a manufacturing process of a reactor control rod core block is as follows:

[0047] First, W particles with an average particle size of 50 μm and Ni powder of 2 μm-3 μm are provided, wherein the volume fraction of the W particles is 50%, and the powders are mixed uniformly by ball milling for 5 h-15 h.

[0048] Next, the mixed powder is pressed into a green block by cold isostatic pressing at 120MPa-180MPa.

[0049] Next, under the protection of argon, the green block is sintered at a temperature of 1200° C. to 1500° C. for 2 h to 2.5 h to sinter the green block into a sintered body.

[0050] Next, the sintered body is placed in a can and hot isostatic pressing is performed at 1000-1200°C and 200MPa for 2h-2.5h to fully recrystallize the material matrix and eliminate defects such as holes left during the sintering process. After hot isostatic pressing, the can is removed and heated to 1080°C in a vacuum quenching furnace for 1h, and quenched at a cooling rate of 7°C / s.

[0051] Finally, the material out of the furnace is machined and polished to form the shape and size required by the control rod design to obtain the finished core block.

[0052] The finished pellets are filled into the stainless steel control rod cladding and welded to obtain the finished control rod. Since the inner tube of the cladding is not required, the control rod has a simple structure and a larger effective volume of the neutron absorber. At the same time, since the pellets have better plasticity, thermal conductivity and corrosion resistance, the risk of neutron absorber breakage during the service of the control rod can be reduced, and uneven axial neutron absorption capacity can be avoided; at the same time, the risk of cladding corrosion and damage caused by radiation swelling can be reduced, effectively improving the safety and reliability of the control rod.

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

[0054] First, W particles with an average particle size of 250 μm and Ni powder of 2 μm-3 μm are provided, wherein the volume fraction of W particles is 80%, and a W-Ni alloy coating with a thickness of 10 μm is provided on the surface, and the coating can be formed by chemical vapor deposition or physical vapor deposition, or by ion sputtering and other processes. The powders are mixed evenly by ball milling for 5h-15h.

[0055] Next, the mixed powder is pressed into a green block by cold isostatic pressing at 120MPa-180MPa.

[0056] Next, under the protection of argon, the green block is sintered at a temperature of 1200° C. to 1500° C. for 2 h to 2.5 h to sinter the green block into a sintered body.

[0057] Next, the sintered body is placed in a can and hot isostatic pressing is performed at 1000-1200°C and 200MPa for 2h-2.5h to fully recrystallize the material matrix and eliminate defects such as holes left during the sintering process. After hot isostatic pressing, the can is removed and heated to 1080°C in a vacuum quenching furnace for 1h, and quenched at a cooling rate of 7°C / s.

[0058] Finally, the material out of the furnace is machined and polished to form the shape and size required by the control rod design to obtain the finished core block.

[0059] In the finished pellet, the W-Ni alloy coating on the surface of the W particles can, on the one hand, provide the bonding strength between the W particles and the Ni matrix, reducing the risk of cracks initiating near the W particles when the pellet is subjected to impact or uneven stress under high temperature and irradiation conditions; on the other hand, it can further protect the W particles. When the Ni matrix cracks, the coating can form an oxide layer to prevent the W particles from oxidizing; when W particles are distributed on the surface of the finished pellet, the coating can also prevent the W particles from direct contact with the control rod cladding, reducing the risk of corrosion.

[0060] The finished core blocks are filled into the stainless steel control rod cladding and welded closed to obtain the finished control rods.

[0061] The manufacturing method of tungsten dispersion material for reactor control rods provided in the embodiment of the present invention protects W particles by micro-sealing to form a dispersion composite material, which can effectively improve the corrosion resistance and impact resistance of the material under high-temperature neutron irradiation conditions, and at the same time effectively improve the overall thermal conductivity of the material, reduce the risk of cracking due to radiation swelling and the risk of contact corrosion between the neutron absorber and the control rod cladding.

[0062] 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 components or method steps involved, and the combination of 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 dispersion material for a reactor control rod, characterized in that: The following steps are involved: Step a): providing W particles and Ni powder, and uniformly mixing the W particles and Ni powder to obtain a mixed powder; Step b): performing cold isostatic pressing on the mixed powder to obtain a blank block; Step c): sintering the green block to obtain a sintered body; Step d): performing hot isostatic pressing and quenching on the sintered body to obtain a finished tungsten dispersion material for reactor control rods.

2. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1, characterized in that: In the step a), the average particle size of the W particles is 50 μm-500 μm, and the average particle size of the Ni powder is 2 μm-3 μm.

3. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1 or 2, characterized in that: In the step a), the volume fraction of the W particles in the mixed powder is 50%-80%.

4. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1 or 2, characterized in that: In the step a), the mixing is performed by ball milling, and the mixing time is 5h-15h.

5. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1 or 2, characterized in that: The surface of the W particles is provided with a corrosion-resistant metal coating.

6. The method for manufacturing tungsten dispersed material for reactor control rods according to claim 5, characterized in that: The corrosion-resistant metal coating is made of pure Ni or a nickel-based alloy and has a thickness of 10 μm to 20 μm.

7. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1, characterized in that: In the step b), the pressure during the cold isostatic pressing process is 120 MPa-180 MPa.

8. The method for manufacturing tungsten dispersion material for reactor control rods according to claim 1, characterized in that: In the step c), the sintering temperature is 1200° C.-1500° C., and the sintering time is 2 h-2.5 h.

9. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1, characterized in that: In the step d), the hot isostatic pressing temperature is 1000° C.-1200° C., the pressure is 180 MPa-220 MPa, and the holding time is 1 h-2 h.

10. The method for manufacturing a tungsten dispersion material for a reactor control rod according to claim 1 or 9, characterized in that: In the step d), the holding temperature of the quenching treatment is 1060° C.-1100° C., the holding time is 50 min-70 min, and the cooling rate is not less than 7° C. / s.

11. A tungsten dispersion material for reactor control rods, characterized in that: The invention comprises a Ni matrix and W dispersed particles, and is manufactured by the manufacturing method of a tungsten dispersed material for a reactor control rod according to any one of claims 1 to 10.

12. A reactor control rod, comprising a cladding and a pellet, characterized in that: The core block is made of the tungsten dispersion material for reactor control rods as claimed in claim 11.

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