Element diffusion prevention brazing method for reactor core and heat pipe of heat pipe reactor

Abstract

The invention particularly relates to an element diffusion prevention brazing method for a reactor core and a heat pipe of a heat pipe reactor, a brazing sheet for brazing the reactor core and the heat pipe is of a sandwich structure formed by two layers of gold-copper alloy sheets and a tantalum sheet between the two layers of gold-copper alloy sheets, and the edge of the brazing sheet is ground. According to the method, the machining and assembling process of the brazing sheet is improved, continuous brazing of the UMo alloy fuel and the stainless steel heat pipe is achieved, and it is ensured that after brazing, the blocking layer can completely block element diffusion.

Description

Technical Field

[0001] The invention relates to the technical field of brazing of space nuclear power systems, and in particular to a method for brazing heat pipe reactor cores and heat pipes with anti-element diffusion. Background Art

[0002] Heat pipe reactors are reactor devices that use the high thermal conductivity of heat pipes to extract the heat energy generated by core fission, thereby performing thermoelectric conversion. They have the advantages of small size, small mass and high specific power, and are particularly suitable for a variety of application scenarios such as deep sea, space and other planetary surfaces. In the mid-1990s, Los Alamos National Laboratory proposed a high-potential, low-cost short-term space fission reactor system HPS (Heatpipe Power System) design, whose fuel form is UO2 / UN. The cladding and heat pipe wall of the device are mechanically connected and thermally coupled through processing methods such as brazing, electron beam welding, chemical vapor infiltration and hot isostatic pressing. In the SAFE-30 sodium heat pipe module integration demonstration experiment, the stainless steel heat pipe / three-head hoop was brazed together with nickel alloy. The HPS model using hot isostatic pressing and the SAFE-30 model heat pipe reactor using brazing have much less temperature loss in connecting the core to the heat pipe. Kilopower in the United States uses highly enriched uranium molybdenum alloy columnar fuel, with eight grooves opened on the radial outer edge of the fuel for arranging heat pipes, and multiple metal bands tightly clamp the heat pipes on the fuel in the axial direction. The use of pressure clamps to connect the core to the heat pipes will also significantly increase the temperature loss than hot isostatic pressing and brazing methods.

[0003] Therefore, how to efficiently introduce heat into the heat pipe and minimize temperature loss is one of the key points of welding UMo alloy fuel and stainless steel heat pipe. At present, brazing is used to weld UMo alloy fuel and stainless steel heat pipe. In the brazing process of UMo alloy fuel and stainless steel heat pipe, a sandwich structure brazing sheet of solder, barrier layer and solder is used. By introducing a diffusion barrier layer, direct contact between fuel elements and heat pipe elements is avoided, and the long-term stability of welding is ensured while achieving connection. However, there are still difficulties as follows: The sandwich brazing uses a tube rolling device to roll the brazing sheet into a cylinder, and the heat pipe, brazing ring and UMo fuel core are assembled and brazed after assembly. The barrier layer is discontinuous at the joint of the brazing roll, and there is a seam. After brazing, the heat pipe, brazing material and UMo are prone to element diffusion at the joint, which seriously affects the service safety and life of the core. Summary of the invention

[0004] The purpose of the present invention is to provide a method for brazing heat pipe core and heat pipe to prevent element diffusion, improve the processing and assembly process of brazing sheets, realize continuous brazing of UMo alloy fuel and stainless steel heat pipe, and ensure that the barrier layer can completely block element diffusion after brazing.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for brazing heat pipe cores and heat pipes with anti-element diffusion, wherein the brazing material sheets used for brazing the cores and heat pipes are sandwich structures formed by two layers of gold-copper alloy sheets and a tantalum sheet between the two layers of gold-copper alloy sheets, and the edges of the brazing material sheets are ground.

[0007] As one of the achievable methods, the heat pipe stack core and heat pipe anti-element diffusion brazing method specifically includes the following steps:

[0008] Step 1, preparing a core;

[0009] Step 2: Grind the heat pipe diameter;

[0010] Step 3, pretreatment of solder sheet;

[0011] Step 4: Grinding the solder sheet interface;

[0012] Step 5, preparing solder sheet coils;

[0013] Step 6, removing the oxide film on the inner wall of the core hole;

[0014] Step 7, cleaning the core, heat pipe and solder sheet;

[0015] Step 8, assembling the core, heat pipe and brazing sheet to make a brazing sample;

[0016] Step 9: Use a vacuum brazing furnace to braze the brazing sample.

[0017] As one possible implementation method, step 1, preparing a core, includes the following steps:

[0018] Step 11, first use a drill to drill a hole in the middle of the cylindrical uranium-molybdenum alloy fuel block, and then use a boring tool to perform size finishing on the cylindrical uranium-molybdenum alloy block;

[0019] Step 12: Process a groove on the inner edge of the upper end surface of the uranium-molybdenum alloy fuel block to form a core; the groove is used to assemble the annular brazing material for brazing the core and the heat pipe.

[0020] As one of the feasible ways, in step 11, the dimensional accuracy of the cylindrical uranium-molybdenum alloy block is controlled within ±5um; in step 12, a groove with a length of 3mm and a chamfer angle of 45° is processed on the inner edge of the upper end surface of the uranium-molybdenum alloy fuel block.

[0021] As one of the feasible methods, in step 2, the heat pipe diameter accuracy is controlled within ±5um; the heat pipe diameter needs to satisfy the following formula:

[0022] Dd-2l≤2L

[0023] Wherein, D is the inner diameter of the core; d is the inner diameter of the heat pipe; l is the thickness of the brazing sheet; and L is the assembly clearance between the core and the heat pipe, which is equal to the inner diameter of the core minus the outer diameter of the heat pipe divided by 2.

[0024] As one possible implementation method, step 3, pre-treatment of the solder sheet, includes the following steps:

[0025] Step 31, calculating the length of the brazing sheet required for brazing the core and the heat pipe according to the core inner diameter and the heat pipe outer diameter;

[0026] Step 32, cut the solder sheet of the required length for brazing the core and the heat pipe, place the solder sheet on the vacuum chuck, extract the gas inside the vacuum chuck to form a vacuum state, so that a pressure difference is formed between the inside and outside of the solder sheet, and finally the solder sheet is successfully adsorbed on the vacuum chuck.

[0027] As one of the achievable methods, step 4, solder sheet interface grinding treatment, includes the following steps:

[0028] Step 41, grinding the edge of the solder sheet using a grinding disc;

[0029] Step 42, after the vacuum is released from the solder sheet, the solder sheet is turned over 180 degrees, and the opposite edges of the solder sheet are further ground so that the interface of the curled solder sheet is a trapezoidal shape.

[0030] As one of the feasible methods, the thickness of the solder sheet is 200 μm; in step 41, a grinding wheel is used to grind the 1 mm width of the edge of the solder sheet, and the grinding depth is (90-110) μm; in step 42, after the vacuum of the solder sheet is vented, the solder sheet is flipped 180°, and the 1 mm width of the opposite edge of the solder sheet is further ground, and the grinding depth is (100-120) μm, so that the interface of the curled solder sheet is trapezoidal.

[0031] As one of the feasible ways, step 5, preparation of solder sheet coiling, comprises the following steps: coiling the solder sheet for 70 to 90 times, and rolling the solder sheet into a cylindrical shape.

[0032] As one possible implementation method, step 6, removing the oxide film on the inner wall of the core hole, includes the following steps:

[0033] Step 61, rubbing the inner wall of the core hole with 2400-grit sandpaper (30-60 times);

[0034] Step 62: Use a cotton swab dipped in nitric acid aqueous solution to wipe the inner wall of the core to remove the oxide film on the inner wall of the core.

[0035] As one achievable method, in step 62, the mass percentage of the nitric acid aqueous solution is (5-10)%.

[0036] As one possible implementation method, step 7, cleaning the core, heat pipes and solder sheets, includes the following steps:

[0037] Step 71, place the core, heat pipe and solder sheet in a beaker, pour alcohol into it, and completely immerse the core, heat pipe and solder sheet;

[0038] Step 72: Use an ultrasonic cleaner to clean the core, heat pipe and solder sheet for (3 to 5) minutes.

[0039] As one of the feasible methods, step 8, assembling the core, heat pipe and solder sheet to make a brazing sample, includes the following steps: placing the core 1 vertically, wrapping the heat pipe 3 with the solder sheet 2, and inserting the solder sheet 2 and the heat pipe 3 into the inner hole of the core 1 at the same time to make a brazing sample; during the assembly process of the core, heat pipe and solder sheet, pouring alcohol to lubricate them.

[0040] As one of the feasible methods, in step 9, a vacuum brazing furnace is used to braze the brazing sample, and the vacuum degree is 10 -3 Below pa, the brazing temperature is (920-980)℃, the holding time is (3-15)min, the heating rate is 10℃ / min, the brazing sample is cooled in a vacuum environment with the vacuum brazing furnace, and the brazing of the core and the heat pipe is completed.

[0041] As one possible approach, the core is made of uranium-molybdenum alloy fuel.

[0042] As one possible implementation, the heat pipe is made of stainless steel.

[0043] As one possible implementation, the gold-copper alloy sheet constituting the solder sheet is made of a gold-copper alloy composed of 80 wt % of gold and 20 wt % of copper.

[0044] Beneficial technical effects of the present invention:

[0045] The method for preventing element diffusion of heat pipe stack core and heat pipe of the present invention comprises a brazing sheet having a sandwich structure formed by two layers of gold-copper alloy sheets and a tantalum sheet between the two layers of gold-copper alloy sheets, and the edge of the brazing sheet is ground to minimize the assembly gap between the core and the heat pipe, and to make up for the discontinuity of the barrier layer of the unground brazing sheet at the weld, thereby effectively improving the mutual diffusion of elements between the core and the heat pipe, and finally meeting the service requirements of the core, and preventing the premature failure of the brazing between the core and the heat pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic structural diagram of an embodiment of a brazing sample;

[0047] Figure 2A top view of an embodiment of a solder sheet interface after grinding.

[0048] In the figure, 1, core; 2, solder sheet; 3, heat pipe. DETAILED DESCRIPTION

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0050] 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 application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0051] The technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0052] The present embodiment provides a method for brazing heat pipe core and heat pipes to prevent element diffusion. The brazing sheet used for brazing the core and the heat pipe is a sandwich structure formed by two layers of gold-copper alloy sheets and a tantalum sheet between the two layers of gold-copper alloy sheets. The edges of the brazing sheet are ground to minimize the assembly gap between the core and the heat pipe, and to compensate for the discontinuity of the barrier layer of the unground brazing sheet at the weld, thereby effectively improving the mutual diffusion of elements between the core and the heat pipe, ultimately meeting the service requirements of the core and preventing premature failure of the brazing of the core and the heat pipe.

[0053] In this embodiment, as one of the achievable methods, the method for brazing the heat pipe stack core and the heat pipe with anti-element diffusion specifically includes the following steps:

[0054] Step 1, preparing a core;

[0055] Step 2: Grind the heat pipe diameter;

[0056] Step 3, pretreatment of solder sheet;

[0057] Step 4: Grinding the solder sheet interface;

[0058] Step 5, preparing solder sheet coils;

[0059] Step 6, removing the oxide film on the inner wall of the core hole;

[0060] Step 7, cleaning the core, heat pipe and solder sheet;

[0061] Step 8, assembling the core, heat pipe and brazing sheet to make a brazing sample;

[0062] Step 9: Use a vacuum brazing furnace to braze the brazing sample.

[0063] In this embodiment, as one of the achievable methods, step 1, preparing a core, includes the following steps:

[0064] Step 11, first use a drill to drill a hole in the middle of the cylindrical uranium-molybdenum alloy fuel block, and then use a boring tool to perform size finishing on the cylindrical uranium-molybdenum alloy block;

[0065] Step 12: Process a groove on the inner edge of the upper end surface of the uranium-molybdenum alloy fuel block to form a core; the groove is used to assemble the annular brazing material for brazing the core and the heat pipe, the purpose of which is to fill the assembly gap during the brazing process of the core and the heat pipe to ensure that there is no cavity in the welding of the core and the heat pipe.

[0066] In this embodiment, as one of the feasible methods, in step 11, the dimensional accuracy of the cylindrical uranium-molybdenum alloy block is controlled within ±5um; in step 12, a groove with a length of 3mm and a chamfer angle of 45° is processed on the inner edge of the upper end surface of the uranium-molybdenum alloy fuel block.

[0067] In this embodiment, as one of the feasible methods, in step 2, the heat pipe diameter accuracy is controlled within ±5um; the heat pipe diameter needs to satisfy the following formula:

[0068] Ed-2l≤2L

[0069] Wherein, D is the inner diameter of the core; d is the inner diameter of the heat pipe; l is the thickness of the brazing sheet; and L is the assembly clearance between the core and the heat pipe, which is equal to the inner diameter of the core minus the outer diameter of the heat pipe divided by 2.

[0070] In this embodiment, as one of the achievable methods, step 3, pre-treatment of the solder sheet, includes the following steps:

[0071] Step 31, calculating the length of the brazing sheet required for brazing the core and the heat pipe according to the core inner diameter and the heat pipe outer diameter;

[0072] Step 32, cut the solder sheet of the required length for brazing the core and the heat pipe, place the solder sheet on the vacuum chuck, extract the gas inside the vacuum chuck to form a vacuum state, so that a pressure difference is formed between the inside and outside of the solder sheet, and finally the solder sheet is successfully adsorbed on the vacuum chuck.

[0073] In this embodiment, as one of the achievable methods, step 4, solder sheet interface grinding treatment, includes the following steps:

[0074] Step 41, grinding the edge of the solder sheet using a grinding disc;

[0075] Step 42, after the vacuum is released from the solder sheet, the solder sheet is turned over 180 degrees, and the opposite edges of the solder sheet are further ground so that the interface of the curled solder sheet is a trapezoidal shape.

[0076] In this embodiment, as one of the feasible methods, the thickness of the solder sheet is 200 μm; in step 41, a grinding wheel is used to grind the 1 mm width of the edge of the solder sheet, and the grinding depth is (90-110) μm; in step 42, after the vacuum of the solder sheet is vented, the solder sheet is flipped 180°, and the 1 mm width of the opposite edge of the solder sheet is continued to be ground, and the grinding depth is (100-120) μm, so that the interface of the curled solder sheet is trapezoidal.

[0077] In this embodiment, as one of the feasible methods, step 5, preparation of solder sheet coiling, includes the following steps: coiling the solder sheet for 70 to 90 times, and rolling the solder sheet into a cylindrical shape.

[0078] In this embodiment, as one of the achievable methods, step 6, removing the oxide film on the inner wall of the core hole, includes the following steps:

[0079] Step 61, rub the inner wall of the core hole with 2400 grit sandpaper (30 to 60 times) to make the inner wall as smooth as possible;

[0080] Step 62: Use a cotton swab dipped in nitric acid aqueous solution to wipe the inner wall of the core to remove the oxide film on the inner wall of the core.

[0081] In this embodiment, as one of the feasible ways, in step 62, the mass percentage of the nitric acid aqueous solution is (5-10)%.

[0082] In this embodiment, as one of the achievable methods, step 7, cleaning the core, heat pipes and solder sheets, includes the following steps:

[0083] Step 71, place the core, heat pipe and solder sheet in a beaker, pour alcohol into it, and completely immerse the core, heat pipe and solder sheet;

[0084] Step 72: Use an ultrasonic cleaner to clean the core, heat pipe and solder sheet for (3 to 5) minutes.

[0085] In this embodiment, as one of the achievable methods, step 8, assembling the core, the heat pipe and the brazing sheet to make a brazing sample, includes the following steps: placing the core 1 vertically, wrapping the heat pipe 3 with the brazing sheet 2, and simultaneously inserting the brazing sheet 2 and the heat pipe 3 into the inner hole of the core 1 to make a Figure 1The brazing sample shown; during the assembly process of the core, heat pipe and brazing sheet, alcohol is poured to lubricate them.

[0086] In this embodiment, as one of the achievable methods, in step 9, a vacuum brazing furnace is used to braze the brazing sample, and the vacuum degree is 10 -3 Below pa, the brazing temperature is (920-980)℃, the holding time is (3-15)min, the heating rate is 10℃ / min, the brazing sample is cooled in a vacuum environment with the vacuum brazing furnace, and the brazing of the core and the heat pipe is completed.

[0087] In this embodiment, as one of the feasible ways, the core is made of uranium-molybdenum alloy fuel.

[0088] In this embodiment, as one of the feasible ways, the heat pipe is made of stainless steel.

[0089] In this embodiment, as one possible implementation, the gold-copper alloy sheet constituting the solder sheet is made of a gold-copper alloy consisting of 80 wt % gold and 20 wt % copper.

[0090] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for brazing heat pipe core and heat pipe to prevent element diffusion, characterized in that: The brazing sheet used for brazing the core and the heat pipe is a sandwich structure formed by two layers of gold-copper alloy sheets and a tantalum sheet between the two layers of gold-copper alloy sheets, and the edge of the brazing sheet is ground.

2. The method for brazing heat pipe stack core and heat pipe to prevent element diffusion according to claim 1, characterized in that: The specific steps include: Step 1, preparing a core; Step 2: Grind the heat pipe diameter; Step 3, pretreatment of solder sheet; Step 4: Grinding the solder sheet interface; Step 5, preparing solder sheet coils; Step 6, removing the oxide film on the inner wall of the core hole; Step 7, cleaning the core, heat pipe and solder sheet; Step 8, assembling the core, heat pipe and brazing sheet to make a brazing sample; Step 9: Use a vacuum brazing furnace to braze the brazing sample.

3. The method for brazing heat pipe core and heat pipe to prevent element diffusion according to claim 2, characterized in that: Step 1, preparing the core, includes the following steps: Step 11, first use a drill to drill a hole in the middle of the cylindrical uranium-molybdenum alloy fuel block, and then use a boring tool to perform size finishing on the cylindrical uranium-molybdenum alloy block; Step 12: Process a groove on the inner edge of the upper end surface of the uranium-molybdenum alloy fuel block to form a core; the groove is used to assemble the annular brazing material for brazing the core and the heat pipe.

4. The method for brazing heat pipe stack core and heat pipe to prevent element diffusion according to claim 3, characterized in that: In step 11, the dimensional accuracy of the cylindrical uranium-molybdenum alloy block is controlled within ±5um; in step 12, a groove with a length of 3mm and a chamfer angle of 45° is processed on the inner edge of the upper end surface of the uranium-molybdenum alloy fuel block.

5. The method for brazing heat pipe core and heat pipe to prevent element diffusion according to claim 2, characterized in that: Step 2: The heat pipe diameter accuracy is controlled within ±5um; the heat pipe diameter needs to satisfy the following formula: Dd-2l≤2L Wherein, D is the inner diameter of the core; d is the inner diameter of the heat pipe; l is the thickness of the brazing sheet; and L is the assembly clearance between the core and the heat pipe, which is equal to the inner diameter of the core minus the outer diameter of the heat pipe divided by 2.

6. The method for brazing heat pipe stack core and heat pipe to prevent element diffusion according to claim 2, characterized in that: Step 3, solder sheet pretreatment, includes the following steps: Step 31, calculating the length of the brazing sheet required for brazing the core and the heat pipe according to the core inner diameter and the heat pipe outer diameter; Step 32, cut the solder sheet of the required length for brazing the core and the heat pipe, place the solder sheet on the vacuum chuck, extract the gas inside the vacuum chuck to form a vacuum state, so that a pressure difference is formed between the inside and outside of the solder sheet, and finally the solder sheet is successfully adsorbed on the vacuum chuck.

7. The method for brazing heat pipe core and heat pipe to prevent element diffusion according to claim 2, characterized in that: Step 4, grinding the solder sheet interface, includes the following steps: Step 41, grinding the edge of the solder sheet using a grinding disc; Step 42, after the vacuum is released from the solder sheet, the solder sheet is turned over 180 degrees, and the opposite edges of the solder sheet are further ground so that the interface of the curled solder sheet is a trapezoidal shape.

8. The method for brazing heat pipe core and heat pipe to prevent element diffusion according to claim 7, characterized in that: The thickness of the solder sheet is 200 μm; in step 41, a grinding wheel is used to grind the 1 mm width of the edge of the solder sheet, and the grinding depth is (90-110) μm; in step 42, after the vacuum of the solder sheet is vented, the solder sheet is turned 180°, and the 1 mm width of the opposite edge of the solder sheet is further ground, and the grinding depth is (100-120) μm, so that the interface of the curled solder sheet is trapezoidal.

9. The method for brazing heat pipe core and heat pipe to prevent element diffusion according to claim 2, characterized in that: Step 8, assembling the core, heat pipe and solder sheet to make a brazing sample, includes the following steps: placing the core 1 vertically, wrapping the heat pipe 3 with the solder sheet 2, inserting the solder sheet 2 and the heat pipe 3 into the inner hole of the core 1 at the same time to make a brazing sample; during the assembly process of the core, heat pipe and solder sheet, pouring alcohol to lubricate them.

10. The method for brazing heat pipe core and heat pipe to prevent element diffusion according to claim 2, characterized in that: Step 9: During the brazing process of the brazing sample using a vacuum brazing furnace, the vacuum degree is 10 -3 Below pa, the brazing temperature is (920-980)℃, the holding time is (3-15)min, the heating rate is 10℃ / min, the brazing sample is cooled in a vacuum environment with the vacuum brazing furnace, and the brazing of the core and the heat pipe is completed.

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