Heat pipe micro-lattice matrix test piece and method of manufacturing the same

Abstract

The application discloses a heat pipe micro-lattice base test piece and a manufacturing method thereof, and belongs to the field of nuclear power. The manufacturing method of the heat pipe micro-lattice base test piece comprises the following steps: machining a thermocouple mounting groove on a lattice base blank; installing a thermocouple at the bottom of the thermocouple mounting groove; welding the thermocouple mounting groove by using laser welding, so that the base metal of the two sidewalls melts and covers the thermocouple, and the laser spot diameter is not less than the width of the thermocouple mounting groove; providing inert gas protection to the welding area after welding, and then accelerating cooling by using compressed air to obtain a heat pipe micro-lattice base test piece finished product. The method can effectively improve the welding quality of the heat pipe micro-lattice base test piece and improve the reliability of the test piece in a long-term test process.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power, specifically relating to a heat pipe microreactor grid substrate test piece and its manufacturing method. Background Technology

[0002] During the design phase, heat pipe microreactor fuel assemblies require a series of verification tests using prototypes. The fuel assembly grid substrate prototype needs grooves on its surface to accommodate thermocouples, followed by sealing welds. Damage to the thermocouples must be avoided during welding, and a high degree of surface smoothness is required for the weld. Existing processes typically employ filler wire tungsten inert gas (TIG) welding, but this method suffers from difficulties in penetrating narrow gaps, arc interference from sidewall short circuits, challenges in molten pool control, and poor heat dissipation in narrow gaps, which can induce post-weld cracks and other defects. These issues affect the molding quality of the fuel grid substrate prototype, hindering the efficiency and reliability of verification tests. Therefore, providing a manufacturing method for heat pipe microreactor grid substrate prototypes with higher weld quality has significant practical value. Summary of the Invention

[0003] The purpose of this invention is to provide a method for manufacturing a heat pipe micropile grid substrate test piece, thereby improving the molding quality of the thermocouple embedding area. This invention also provides a heat pipe micropile grid substrate test piece.

[0004] According to one aspect of the present invention, a method for manufacturing a heat pipe micro-pile grid substrate test specimen is provided, the method comprising the following steps: Step a): Provide a grid substrate blank, the grid substrate blank being made of stainless steel; provide a thermocouple mounting groove on the surface of the grid substrate blank by machining, the thermocouple mounting groove extending along the axial direction of the grid substrate blank, the width of the thermocouple mounting groove not exceeding 2mm, and the depth being 2.5mm-3mm; Step b): Place the thermocouple at the bottom of the thermocouple mounting slot; Step c): Laser welding is performed on the thermocouple mounting groove to melt the base material of the two side walls of the thermocouple mounting groove and cover the thermocouple. The diameter of the laser spot is not less than the width of the thermocouple mounting groove, the welding power is 3kW-6kW, the welding speed is 0.1m / min-1m / min, and the positive defocusing amount is 4mm-8mm. Step d): After welding, the welding area is protected with inert gas and cooled by compressed air to obtain the finished heat pipe micro-stacking grid substrate test piece.

[0005] This method utilizes the self-fusion of the base material to fill the weld, effectively avoiding damage to the thermocouple. Laser welding technology helps improve the surface quality of the weld and enhances the long-term reliability and stability of the finished test piece.

[0006] Furthermore, in some embodiments, in step a), the distance between the centerline of the thermocouple mounting groove and the edge of the grid substrate blank is 9mm-10mm.

[0007] Furthermore, in some embodiments, in step b), when the thermocouple is placed at the bottom of the thermocouple mounting groove, the thermocouple is fixed using high-temperature adhesive.

[0008] Furthermore, in some embodiments, in step c), laser welding is protected with argon or a helium-argon mixture.

[0009] Furthermore, in some embodiments, in step c), the protective gas is sprayed at an angle using a double-layer concentric nozzle, with the inner layer gas flow rate being 10L / min-25L / min and the outer layer gas flow rate not exceeding 10L / min, and the spray range covering the weld pool at least 20mm before and after the welding direction.

[0010] Furthermore, in some embodiments, in step c), the laser pulse frequency is 50Hz-200Hz and the duty cycle is 30%-70%.

[0011] Furthermore, in some embodiments, in step d), the inert gas protection of the welded area after welding lasts for 10-15 seconds.

[0012] Furthermore, in some embodiments, in step d), after inert gas protection is completed, the weld is cooled to below 100°C by supplying compressed air to the heat-affected zone of the weld.

[0013] According to another aspect of the present invention, a heat pipe micropile grid substrate test specimen is provided, the test specimen comprising a grid substrate and a plurality of thermocouples, and manufactured using the heat pipe micropile grid substrate test specimen manufacturing method provided in any of the foregoing embodiments. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the cross-sectional structure of the thermocouple mounting groove in one embodiment; Figure 2 This is a schematic diagram of the cross-sectional structure of a heat pipe micropile grid substrate test specimen in one embodiment; Figure 3 for Figure 2 Enlarged schematic diagram of region A in the middle.

[0015] Meaning of the reference numerals in the attached figures: 1-Thermocouple mounting slot; 2-Thermocouple; 3-Clad layer; 4-Grid substrate.

[0016] The purpose of the above-described drawings is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and is not intended to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the present invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0017] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0018] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places 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 will understand that the embodiments herein can be combined with other embodiments without causing structural conflicts.

[0019] In this description, terms such as "upper," "lower," "left," "right," "lateral," "longitudinal," "height," "length," and "width," which indicate orientation or positional relationships, are intended to accurately describe the embodiments and simplify the description, rather than limiting the parts or structures involved to have a specific orientation, or to be installed or operated in a specific orientation, and should not be construed as limiting the embodiments in this document.

[0020] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0021] Heat pipe microreactors are novel all-solid-state reactors that eliminate the complex primary loop of pressurized water reactors. They employ an all-solid-state core structure, directly transferring heat generated by the fuel rods through the solid core, which is then output via heat pipes. Heat pipe microreactors offer advantages such as small size, simple structure, and inherent safety, and are considered to have promising application prospects. The grid substrate of the solid core in a heat pipe microreactor provides support for the fuel rods and heat pipes and is also a crucial heat conduction path, significantly impacting reactor safety. The design and manufacturing process of heat pipe microreactors requires extensive verification tests on the grid substrate to validate the temperature distribution on its surface under different operating conditions. The grid substrate is made of stainless steel and is currently typically manufactured using a method of slotting the grid surface, installing thermocouples, and then performing filler wire tungsten inert gas welding. However, the gaps where thermocouples are installed are generally narrow, making it difficult for the electric arc and filler wire to enter the narrow gaps, and the welding torch nozzle cannot penetrate deeply. During welding, the electric arc may be interfered with by short circuits on the bevel sidewalls. Controlling the molten pool during welding is difficult, and the molten metal easily adheres to the sidewalls under surface tension, forming discontinuous weld beads that can easily damage the embedded thermocouples. Furthermore, narrow gaps have weak heat dissipation capacity, leading to rapid local heat accumulation during welding and easily causing defects such as crystallization cracks. These factors collectively result in poor thermocouple embedding quality in current grid-based test specimens, leading to insufficient reliability during long-term testing.

[0022] To overcome the aforementioned problems of the prior art, one embodiment of the present invention provides a method for manufacturing a heat pipe micro-stacking grid substrate test piece, the method comprising the following steps: Step a): Provide a grid substrate blank, which is hexagonal in shape and has mounting holes along the axial direction for mounting fuel rods and heat pipes. For example... Figure 2 As shown, a thermocouple mounting groove 1 is machined onto the surface of the grid substrate 4. The thermocouple mounting groove 1 extends along the axial direction of the grid substrate 4 and is combined with... Figure 3 Its width D does not exceed 2mm, its depth H is 2.5mm-3mm, and its length is approximately 700mm. In a preferred embodiment, the distance L between the thermocouple mounting groove 1 and the edge of the grid substrate 4 is 9mm-10mm.

[0023] Step b): Combining Figure 1 The thermocouple 2 is placed at the bottom of the thermocouple mounting groove 1. In a preferred embodiment, the thermocouple 2 can be bonded to the bottom of the thermocouple mounting groove 1 using high-temperature adhesive.

[0024] Step c): Laser welding is performed on the thermocouple mounting slot 1. Specifically, the laser spot diameter is set to be no less than the width of the thermocouple mounting slot 1. The laser beam and welding direction are in the same vertical plane and form an angle of 80°-90°. The spot is directly facing the center of the thermocouple mounting slot 1. The welding power is set to 3kW-6kW, the welding speed to 0.1m / min-1m / min, and the positive defocusing amount to 4mm-8mm. Argon or a helium-argon mixture with a purity of 99.99% or higher is used as the shielding gas. In a preferred embodiment, the shielding gas is sprayed at an angle using a double-layer concentric nozzle. The inner layer gas flow rate is 10L / min-25L / min, and the outer layer gas flow rate does not exceed 10L / min. The spray range covers the weld pool at least 20mm forward and backward along the welding direction. Laser welding melts the base material on both sides of the thermocouple mounting slot 1 and flows onto the thermocouple 2, forming a cladding layer 3. Because the cladding layer 3 is formed by the self-melting of the base material, it has good fluidity and can effectively fill the weld, making it less prone to forming discontinuous welds.

[0025] Step d): After welding, the welded area is protected with an inert gas and cooled rapidly using compressed air to prevent σ-phase precipitation. In a preferred embodiment, the inert gas protection of the welded area lasts for 10-15 seconds after welding. After the inert gas protection is completed, the weld is cooled rapidly to below 100°C by supplying compressed air to the heat-affected zone of the weld (avoiding direct blowing onto the weld). After completing the above steps, the finished heat pipe micro-stacking grid substrate test piece is obtained.

[0026] The above method can effectively improve the surface quality of the weld, completely covering the thermocouple 2 below the cladding layer 3, thereby improving the reliability of the thermocouple 2 and the accuracy of the measurement results during long-term testing. Due to the use of laser welding technology, the cladding layer 3 has excellent surface quality, preventing damage to the thermocouple 2 from the electric arc during welding, and ensuring stable weld quality.

[0027] In a preferred embodiment, the fabrication process of the heat pipe micropile grid substrate prototype is as follows: First, a grid substrate blank made of 316Ti stainless steel is provided. A thermocouple mounting groove 1 is opened on the surface of the grid substrate blank. The thermocouple mounting groove 1 is a rectangular groove with a center distance L of 9.5mm from the edge of the grid substrate. The width D of the thermocouple mounting groove 1 is 1mm, the depth is 2.5mm, and the length along the axis of the grid substrate is 700mm.

[0028] Next, install thermocouple 2 at the bottom of thermocouple mounting slot 1.

[0029] Next, set the laser welding parameters: laser spot diameter 1.5mm-2mm, positive defocusing amount 4mm-8mm, welding speed 0.4m / min-1m / min, welding power 3kW-6kW, laser pulse frequency 50Hz-200Hz, and duty cycle 30%-70%. For welding, use argon gas with a purity of 99.99% or higher as the shielding gas, and employ a double-layer concentric nozzle. The inner layer has a gas flow rate of 25L / min, and the outer layer has a gas flow rate of 10L / min. The shielding gas covers a 20mm area before and after the weld along the weld direction. Specifically, use a nozzle with a 30° tilt angle to side-blow argon gas, allowing the shielding gas to cover the weld at an angle.

[0030] After welding is completed, inert gas is used for delayed protection, and argon gas is continued to be supplied for 10-15 seconds to prevent high-temperature oxidation of the weld. After the inert gas protection ends, compressed air is supplied to the heat-affected zone of the weld to accelerate the cooling of the weld structure until the weld cools to below 100°C to prevent the formation of harmful σ phase.

[0031] Finally, the welds were visually inspected, subjected to penetrant testing, and X-ray inspection to ensure that the weld surface was smooth, well-formed, and free of internal porosity or lack of fusion. After inspection, the heat pipe micro-stacking grid substrate test specimen was obtained.

[0032] The purpose of the above embodiments is to provide a further detailed description of the present invention 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, optimization or equivalent substitution of the technical features involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a heat pipe micro-pile grid substrate test specimen, characterized in that, Includes the following steps: Step a): Provide a grid substrate blank, the grid substrate blank being made of stainless steel; provide a thermocouple mounting groove on the surface of the grid substrate blank by machining, the thermocouple mounting groove extending along the axial direction of the grid substrate blank, the width of the thermocouple mounting groove not exceeding 2mm and the depth of 2.5mm-3mm; Step b): Place the thermocouple at the bottom of the thermocouple mounting slot; Step c): Laser welding is performed on the thermocouple mounting groove to melt the base material of the two side walls of the thermocouple mounting groove and cover the thermocouple. The diameter of the laser spot is not less than the width of the thermocouple mounting groove, the welding power is 3kW-6kW, the welding speed is 0.1m / min-1m / min, and the positive defocusing amount is 4mm-8mm. Step d): After welding, the welding area is protected with inert gas and cooled by compressed air to obtain the finished heat pipe micro-stacking grid substrate test piece.

2. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 1, characterized in that, In step a), the distance between the centerline of the thermocouple mounting groove and the edge of the grid substrate blank is 9mm-10mm.

3. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 1, characterized in that, In step b), when the thermocouple is placed at the bottom of the thermocouple mounting groove, the thermocouple is fixed with high-temperature adhesive.

4. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 1, characterized in that, In step c), laser welding is protected with argon or a helium-argon mixture.

5. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 4, characterized in that, In step c), the protective gas is sprayed at an angle using a double-layer concentric nozzle. The inner layer gas flow rate is 10L / min-25L / min, and the outer layer gas flow rate does not exceed 10L / min. The spray range covers the weld pool at least 20mm before and after the welding direction.

6. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 1, characterized in that, In step c), the laser pulse frequency is 50Hz-200Hz and the duty cycle is 30%-70%.

7. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 1, 4, or 5, characterized in that, In step d), the inert gas protection of the welded area lasts for 10-15 seconds after welding.

8. The method for manufacturing a heat pipe micro-pile grid substrate test specimen according to claim 7, characterized in that, In step d), after inert gas protection is completed, the weld is cooled to below 100°C by supplying compressed air to the heat-affected zone of the weld.

9. A heat pipe micro-pile grid substrate test specimen, characterized in that, The heat pipe micropile grid substrate test specimen includes a grid substrate and multiple thermocouples, and the heat pipe micropile grid substrate test specimen is manufactured using the heat pipe micropile grid substrate test specimen manufacturing method as described in any one of claims 1 to 8.

10. The heat pipe micro-pile grid substrate test specimen according to claim 9, characterized in that, The grid substrate is made of 316Ti stainless steel.

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