A test device for simulating high temperature heat transfer in a narrow annular gap channel of a pressurized water reactor fuel rod

Abstract

The application discloses a kind of test devices of simulating high-temperature heat transfer of annular narrow air gap channel in pressurized water reactor fuel rod, belong to the field of reactor thermal hydraulic research.The device includes coaxially arranged heating pipe, inner sleeve and outer sleeve, annular air gap channel is formed between heating pipe and inner sleeve, annular cooling water channel is formed between inner sleeve and outer sleeve.Heating pipe is connected with electrode at both ends, expansion joint is arranged at upper end to absorb axial thermal expansion of heating pipe, and composite insulation sealing structure is arranged at upper and lower ends.The device is also equipped with cooling water circulation system, test gas supply and exhaust system, electric heating simulation system and data acquisition system.The application simulates and explores that heat generated inside fuel rod is conducted to coolant outside through annular air gap between cladding and fuel pellet under high-temperature condition, and the influence of size deviation caused by thermal expansion under high temperature on heat transfer and temperature, and various parameters required to be collected during experiment can be comprehensively obtained and real-time monitored.

Description

Technical Field

[0001] This invention belongs to the field of reactor thermal-hydraulic research technology, specifically relating to an experimental device for simulating high-temperature heat transfer in an annular narrow air gap channel inside a pressurized water reactor fuel rod. Background Technology

[0002] In a pressurized water reactor, the fuel rods are one of the core components. The heat generated inside them is conducted outward to the coolant through the annular air gap between the cladding and the fuel pellets. Along this heat transfer path, the material properties and structural dimensions have a decisive influence on the heat transfer capacity. When the air gap is filled with helium, parameters such as high-temperature thermal expansion, dimensional deviations, and high-temperature radiation all significantly affect the heat transfer process.

[0003] Currently, academic research on the high-temperature heat transfer process of fuel rods mainly focuses on two aspects: direct calculation of the heat transfer process and simulation calculation of the effect of geometric structure and physical properties on the heat transfer coefficient along the heat transfer path. However, during the actual operation of fuel rods, the thermal expansion caused by high temperatures affects the air gap size and physical properties, and the changes in the air gap, in turn, alter the heat transfer path. Existing research on this thermo-mechanical coupling process is relatively lacking.

[0004] Therefore, it is urgent to design an experimental device that can simulate heat transfer under high-temperature conditions in annular narrow air gap channels within the reactor, and to investigate the heat transfer performance of reactor fuel rods under high-temperature conditions through experimental methods. Summary of the Invention

[0005] The purpose of this invention is to provide an experimental device for simulating high-temperature heat transfer in the annular narrow air gap channel inside the fuel rod of a pressurized water reactor, so as to investigate the influence of thermal deformation of the annular narrow air gap of the fuel rod on the heat transfer capacity under high temperature conditions.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An experimental apparatus for simulating high-temperature heat transfer in an annular narrow air gap channel within a pressurized water reactor fuel rod includes:

[0008] The simulated test specimen, wherein a heating tube, an inner sleeve, and an outer sleeve are coaxially arranged from the inside out.

[0009] An annular air gap channel is formed between the heating tube and the inner sleeve, and an annular cooling water channel is formed between the inner sleeve and the outer sleeve;

[0010] Electrodes are coaxially connected to both ends of the heating tube;

[0011] A cooling water circulation system, connected to the annular cooling water channel, is used to supply circulating cooling water to the annular cooling water channel;

[0012] An electrothermal simulation system, electrically connected to electrodes, is used to provide electric heating power to the heating tube;

[0013] The data acquisition system is connected to the temperature measuring element, pressure measuring element, and flow measuring element respectively installed on the simulated test piece, and is used to collect and record test parameters;

[0014] The upper end of the simulation test piece is provided with an expansion joint, which is arranged around the heating tube. One end of the expansion joint is connected to the upper flange structure of the simulation test piece, and the other end is connected to the heating tube through a fastening sleeve. It is used to generate axial expansion and contraction deformation when the heating tube is heated and expands axially to absorb the thermal expansion.

[0015] The test gas supply and exhaust system is connected to the expansion joint, the annular air gap channel, the gas chamber, and the gas outlet pipeline through a gas inlet pipeline, and is used to fill the annular air gap channel with test gas and adjust its pressure.

[0016] The upper and lower ends of the simulated test piece are respectively provided with composite insulation sealing structures. The composite insulation sealing structures are disposed between the heating tube and the inner sleeve, and are used to electrically isolate the charged heating tube from the inner sleeve and the outer sleeve.

[0017] Furthermore, the heating tube has a through central gas passage along its axis, and the electrode has a thermocouple insertion hole and a side gas passage, the central gas passage being connected to the thermocouple insertion hole and the side gas passage.

[0018] Furthermore, the middle heating section of the heating tube is made of hollow molybdenum tube, and the electrode is made of solid molybdenum electrode. The resistance of the hollow molybdenum tube is greater than the resistance of the solid molybdenum electrode, so that the heating section is concentrated in the middle heating section.

[0019] Furthermore, the composite insulating sealing structure includes insulating ceramic and insulating mica, with the insulating ceramic sleeved outside the heating tube and the insulating mica sleeved outside the insulating ceramic.

[0020] Furthermore, the two ends of the heating tube pass through the upper flange structure and the lower flange structure of the simulated test piece, respectively. The two composite insulating sealing structures are connected to the upper flange structure and the lower flange structure, respectively. The composite insulating sealing structure located at the upper part is connected to the expansion joint, and the composite insulating sealing structure located at the lower part is connected to the gas chamber.

[0021] Furthermore, the cooling water circulation system includes a cooling water tank, a cooling water pump, a pressurized gas cylinder, a heating coil, and a cooling coil. The inlet of the cooling water pump is connected to the cooling water tank, the outlet of the cooling water pump is connected to the inlet of the annular cooling water channel, and the outlet of the annular cooling water channel is connected to the cooling water tank through a return water pipe, forming a closed circulation loop.

[0022] Both the heating coil and the cooling coil are installed inside the cooling water tank to regulate the water temperature inside the cooling water tank;

[0023] The pressurized gas cylinder is connected to the gas phase space above the cooling water tank through a pressurized pipe, which is used to provide basic pressure for the cooling water circulation loop and prevent the cooling water from boiling at high temperatures.

[0024] Furthermore, the test gas supply and exhaust system includes a test gas cylinder and an exhaust valve. The test gas cylinder is connected to the gas inlet pipe located at the upper end of the simulated test piece via a gas supply pipe. A control valve is provided on the outlet pipe of the test gas cylinder. The exhaust valve is located at the end of the exhaust pipe of the gas outlet pipe located at the lower end of the simulated test piece. A vacuum pump is also connected to the end of the exhaust pipe for evacuating the annular air gap channel.

[0025] Furthermore, the temperature measuring element includes:

[0026] The first thermocouple and the second thermocouple are disposed on the inner wall surface of the heating tube and are used to measure the inner wall temperature of the heating tube. The first thermocouple and the second thermocouple are two different types of thermocouples used for mutual calibration under high temperature conditions.

[0027] The third thermocouple is disposed on the outer wall surface of the inner sleeve and is used to measure the temperature of the outer wall of the inner sleeve;

[0028] The fourth and fifth thermocouples are respectively installed at the inlet and outlet of the annular cooling water channel, the gas inlet pipe, and the gas outlet pipe, and are used to measure the inlet and outlet temperatures of the cooling water and the test gas.

[0029] The pressure measuring element includes a differential pressure sensor arranged between the inlet and outlet of the annular cooling water channel and a pressure gauge installed on the cooling water inlet pipe;

[0030] The flow measurement element is a turbine flow meter installed on the cooling water pipeline.

[0031] Furthermore, the thermocouple insertion hole adopts an eccentric design and is offset towards the edge of the electrode. The first thermocouple and the second thermocouple extend into the interior of the heating tube through the thermocouple insertion hole, and the temperature measuring end is close to the inner wall of the heating tube.

[0032] Furthermore, the electrothermal simulation system includes a DC power supply cabinet, which is connected to the two electrodes via cables. The DC power supply cabinet, the upper electrode, the heating tube, and the lower electrode together form an electric heating circuit.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention ensures sealing during thermal deformation. Considering that the heating tube expands significantly axially when heated, it is prone to deformation and leakage. Therefore, an expansion joint is set in the test device. When the heating tube expands, the expansion joint is moved outward in coordination to reduce the expansion and ensure sealing.

[0035] During the experiment of this invention, only the heating tube and electrode parts are energized. Insulating ceramics and insulating mica are used to isolate the heating tube from the inner and outer sleeves. Furthermore, all interfaces are connected with insulating materials to improve the electrical insulation performance of the ends.

[0036] The present invention maintains a constant temperature for the cooling water. The cooling water tank is equipped with an electric heating element, a cooling coil, and a temperature sensor. When the water temperature deviates, it can be adjusted at any time to keep it constant, thus avoiding the impact of continuous heating of the cooling water temperature on the test.

[0037] The cooling water circuit of this invention has a pressurized gas cylinder, which can pressurize the cooling water to simulate the high pressure in a pressurized water reactor.

[0038] This invention provides comprehensive data acquisition and monitoring. Temperature and pressure sensors are installed at the cooling water inlet and outlet, and the gas chamber inlet and outlet pipes. Two thermocouples are arranged in the middle section of the inner side of the heating tube, and thermocouples are evenly arranged on both sides of the inner sleeve. This allows for the comprehensive acquisition of various parameters required for the experiment and real-time monitoring.

[0039] The present invention can calculate the degree of radial thermal deformation of the heating tube by reverse calculation of the final temperature measured by the thermocouple. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the experimental device of the present invention;

[0041] Figure 2 This is a schematic diagram of the structure of the simulated test piece of the present invention.

[0042] Figure 1The components are as follows: 1. Data acquisition computer; 2. DC power supply cabinet; 3. Data acquisition system; 4. Wires; 5. Gas cylinder pressure gauge; 6. Test gas cylinder; 7. Gas outlet valve; 8. Pressurized gas cylinder; 9. Cooling water pump; 10. Heating coil; 11. Water tank thermometer; 12. Cooling water tank; 13. Cooling coil; 14. Electrode; 15. Central gas passage of heating tube; 16. Fastening sleeve; 17. Inlet and outlet gas pipelines; 18. Expansion joint; 19. Insulating ceramic; 20. Insulating mica; 21. Inner sleeve; 22. Inlet and outlet water pipelines; 23. Outer sleeve; 24. Helium gas passage; 25. Heating tube; 26. Gas chamber; 27. Gas outlet pipeline; 28. Thermocouple insertion hole; 29. ​​Side gas passage. Detailed Implementation

[0043] The present invention will now be further described with reference to the accompanying drawings.

[0044] Example 1:

[0045] Figure 1 and Figure 2 As shown, this invention provides an experimental apparatus for simulating high-temperature heat transfer in a narrow annular air gap channel within a pressurized water reactor fuel rod. The apparatus includes a simulated test piece, a cooling water circulation system, a test gas supply and exhaust system, an electrothermal simulation system, and a data acquisition system. The simulated test piece is vertically arranged in the center of the apparatus. The cooling water circulation system is connected to the cooling water channel of the simulated test piece. The test gas supply and exhaust system is connected to the annular air gap channel 24 inside the simulated test piece. The electrothermal simulation system is connected to the heating tube 25 in the simulated test piece. The data acquisition system is connected to temperature, pressure, and flow measurement elements within the apparatus, thereby enabling the heating, cooling, gas supply and exhaust of the test piece, as well as the acquisition of test parameters.

[0046] like Figure 2 As shown, the simulated test piece adopts a coaxial multi-layer cylindrical structure, with a heating tube 25, an inner sleeve 21, and an outer sleeve 23 arranged radially from the inside out. The heating tube 25 is located at the center of the test piece, the inner sleeve 21 is coaxially fitted outside the heating tube 25, and the outer sleeve 23 is coaxially fitted outside the inner sleeve 21. An annular air gap channel 24 is formed between the heating tube 25 and the inner sleeve 21, and the channel is filled with test gas; an annular cooling water channel is formed between the inner sleeve 21 and the outer sleeve 23, through which cooling water flows and carries away the heat transferred outward by the heating tube 25.

[0047] A central gas passage 15, extending axially through the center of the heating tube 25, is provided, extending upwards and downwards to both ends of the heating tube 25. The upper and lower ends of the heating tube 25 are connected to electrodes 14, which are coaxially arranged with the heating tube 25. Electrodes 14 serve two purposes: firstly, to transmit the current output from the DC power supply cabinet 2 to the heating tube 25; and secondly, to support and position the two ends of the heating tube 25. When the heating tube 25 is energized, current enters the heating tube 25 through one electrode 14, flows through the middle heating section, and exits through the other electrode 14, causing Joule heating in the middle portion of the heating tube 25.

[0048] In this embodiment, the electrode 14 is provided with a thermocouple insertion hole 28 and a side gas passage 29, and the central gas passage 15 is connected to the thermocouple insertion hole and the side gas passage 29.

[0049] Preferably, the middle heating section of the heating tube 25 is made of a hollow molybdenum tube, and the electrode 14 is made of a solid molybdenum electrode. The resistance of the hollow molybdenum tube is greater than the resistance of the solid molybdenum electrode, so that the heating section is concentrated in the middle heating section.

[0050] The fastening sleeve 16 is positioned at the connection point between the electrode 14 and the end of the test piece. It is used to fix the electrode 14 and the heating tube 25, restrict the radial movement of the heating tube 25, and maintain the coaxiality between the heating tube 25, the inner sleeve 21, and the outer sleeve 23. The heating tube 25 passes through the flange structure at the upper and lower ends of the test piece at both ends. The fastening sleeve 16 clamps the protruding part to prevent the heating tube 25 from deviating from its central position due to vibration, thermal expansion, or fluid action during the test.

[0051] The expansion joint 18 is disposed at the upper end of the simulated test piece and connected to the insulating mica 20. The expansion joint 18 is arranged around the heating tube 25, with one end connected to the insulating mica 20 by bolts and the other end welded to the heating tube 25 by a fastening sleeve. When the heating tube 25 expands axially due to heat, the expansion joint 18 can generate corresponding axial expansion and contraction deformation, thereby absorbing the thermal expansion of the heating tube 25, reducing the thermal stress at the end connection position, and avoiding bending of the heating tube 25, end seal failure, or test gas leakage due to rigid constraints.

[0052] Insulating ceramic 19 and insulating mica 20 are installed at the flange connection positions at the upper and lower ends of the simulated test specimen. Insulating ceramic 19 is located near the heating tube 25 and electrode 14, serving to separate the energized heating tube 25 and electrode 14 from the inner sleeve 21, outer sleeve 23, and metal flange, while also providing high-temperature insulation and radial positioning for the heating tube 25. Insulating mica 20 is located around or adjacent to insulating ceramic 19, further improving the electrical insulation performance at the ends and providing auxiliary sealing for the gap between insulating ceramic 19 and the metal flange. Insulating ceramic 19 and insulating mica 20 together constitute a composite insulating and sealing structure at the ends of the test specimen.

[0053] Gas inlet pipe 17 and gas outlet pipe 27 are respectively located at the upper and lower ends of the test piece and are welded to the end structures near the expansion joint 18 and gas chamber 26. Gas inlet pipe 17 is connected to the expansion joint 18, the annular air gap channel 24, the gas chamber 26, and gas outlet pipe 27. Specifically, gas inlet pipe 17 is connected to the expansion joint 18 as the test gas inlet, and gas outlet pipe 27 is connected to the gas chamber 26 as the test gas outlet. After the test gas enters the annular air gap channel 24 through gas inlet pipe 17, it flows axially along the heating pipe 25 and is discharged through gas outlet pipe 27 at the other end. Through this connection method, the annular air gap channel can be pumped, filled, pressure stabilized, and vented, and the pressure and composition of the test gas in the air gap can be changed.

[0054] Furthermore, the cooling water circulation system is connected to the annular cooling water channel of the simulated test piece through inlet and outlet water pipes 22 to maintain the flow and circulation of cooling water within the simulated test piece.

[0055] like Figure 1 As shown, the cooling water circulation system mainly consists of a pressurized gas cylinder 8, a cooling water tank 12, a heating coil 10, a cooling coil 13, a cooling water pump 9, a flow meter, and a regulating valve. Its main function is to provide the test piece with high-pressure circulating cooling water with controllable temperature and constant flow rate.

[0056] The cooling water tank 12 is connected to the cooling water pump 9 via a circulation pipe. The outlet of the cooling water pump 9 is connected to the inlet and outlet water pipes 22 on the inlet side of the simulated test piece via a pipe, a flow measuring element, and a regulating valve. The inlet and outlet water pipes 22 on the outlet side of the simulated test piece are connected to the cooling water tank 12 via a return water pipe, thus forming a closed cooling water circulation loop. The cooling water in the cooling water tank 12 flows into the simulated test piece under the drive of the cooling water pump 9, flows through the annular cooling water channel, returns to the cooling water tank 12, and is then pumped back into the simulated test piece by the cooling water pump 9.

[0057] To prevent a continuous rise in the inlet water temperature, a heating coil 10 and a cooling coil 13 are installed inside the cooling water tank 12. The heating coil 10 heats the cooling water in the tank when the temperature is lower than the test set value, while the cooling coil 13 removes excess heat when the cooling water absorbs heat from the test specimen and the temperature exceeds the set value. A water tank thermometer 11 is installed inside the cooling water tank 12 to measure the water temperature in the tank 12 in real time. The operating status of the heating coil 10 and the cooling coil 13 is adjusted according to the measurement results of the water tank thermometer 11 to keep the cooling water temperature entering the simulated test specimen stable.

[0058] The pressurized gas cylinder 8 is connected to the upper gas phase space of the cooling water tank 12 via a pressurized pipeline. A pressure gauge and control valve are installed on the pressurized pipeline. After opening the control valve of the pressurized gas cylinder 8, high-pressure gas enters the upper part of the cooling water tank 12, acting on the cooling water surface through gas pressure to provide the base pressure for the entire cooling water circulation loop. By adjusting the outlet pressure of the pressurized gas cylinder 8, the working pressure in the cooling water tank 12 and the cooling water channel of the simulated test piece can be changed to prevent the cooling water from boiling or vaporizing under high-temperature conditions. Simultaneously, regulating valves and bypass lines are arranged in the pipeline to regulate the cooling water flow rate.

[0059] In this embodiment, the test gas supply and exhaust system is connected to the annular air gap channel 24 within the simulated test specimen. For example... Figure 1 As shown, the test gas supply and exhaust system mainly consists of test gas cylinder 6, regulating valve, pressure gauge 5, vacuum pump, etc. Its main function is to fill and exhaust the annular air gap channel 24 in the simulated test piece.

[0060] The test gas cylinder 6 is connected to the gas inlet pipe 17 at the top of the simulated test piece via a gas supply pipe. A control valve and a cylinder pressure gauge 5 are sequentially installed on the outlet pipe of the test gas cylinder 6. The cylinder pressure gauge 5 is used to monitor the gas pressure at the outlet of the test gas cylinder 6 and in the gas supply pipe, while the control valve is used to regulate the charging rate and supply volume of pure helium. The test gas flows out of the test gas cylinder 6, passes through the pipe section containing the control valve and cylinder pressure gauge 5, and then enters the inlet / outlet gas pipe 17, subsequently entering the annular air gap channel 24 between the heating tube 25 and the inner sleeve 21.

[0061] The gas inlet pipe 17 at the upper end of the simulated test piece is connected to the air intake pipe, and the gas outlet pipe 27 at the lower end of the simulated test piece is connected to the exhaust pipe. An outlet valve 7 is installed at the end of the exhaust pipe, and the exhaust pipe connects to the external environment. After opening the outlet valve 7, the existing gas in the annular air gap channel 24 can be discharged through the gas outlet pipe 27. After closing the outlet valve 7 and opening the gas supply valve of the test gas cylinder 6, test gas can be introduced into the annular air gap channel 24. By coordinating and adjusting the outlet valve of the test gas cylinder 6 and the outlet valve 7, the replacement, filling, exhaust, and pressure regulation of the annular air gap channel 24 can be achieved.

[0062] Preferably, the test gas cylinder 6 is a helium cylinder, and the test gas is helium. The helium used in the test has a lower density than air. A vacuum pump is used to evacuate the gas in the outlet section. Valves are installed in the inlet section, outlet section and cylinder 6. The gas pressure in the gas gap can be controlled by adjusting the opening and closing of the gas path through the valves.

[0063] Furthermore, the electrothermal simulation system is the main source of heat for the entire experimental setup. For example... Figure 1 and Figure 2 As shown, the electrothermal simulation system mainly consists of a DC power supply cabinet 2, a heating tube 25, an electrode 14, and corresponding cables and copper busbars.

[0064] The DC power supply cabinet 2 is connected to the electrodes 14 at both ends of the simulated test piece via large-section cables or copper busbars, and the electrodes 14 transmit current to the heating tube 25. The DC power supply cabinet 2, the upper electrode 14, the heating tube 25, and the lower electrode 14 together form an electric heating circuit. By adjusting the output current and output voltage of the DC power supply cabinet 2, the electric heating power of the heating tube 25 can be changed, thereby simulating the heating process under different heat load conditions.

[0065] To reduce heat generation in other parts, the electrothermal simulation system uses large-diameter cables and copper busbars for all components except the heating section, which uses a hollow molybdenum tube 25. Larger diameter solid electrodes 14 are connected to the copper busbars at both ends of the heating tube 25 to reduce the resistance of the electrodes 14, decrease the voltage drop, and thus reduce heat generation. During the experiment, the heating power is adjusted by regulating the current of the DC power supply cabinet 2.

[0066] Furthermore, the data acquisition system 3 is connected to the temperature measuring element, pressure measuring element, and flow measuring element respectively installed on the simulated test piece, for recording and acquiring parameters such as temperature, pressure, and flow rate during the test. During the test, thermocouples are used to measure the inlet and outlet temperatures of the cooling water, the inlet and outlet temperatures of the helium gas, and the outer wall surface temperature. To measure the inner wall temperature of the heating section, holes are made on the electrodes 14 at both ends. The holes are positioned eccentrically, offset towards the edge of the electrodes 14. The thermocouples at both ends are inserted into the heating tube 25 through the holes, with the thermocouple measuring ends close to the inner wall of the heating section. Two different types of thermocouples are used simultaneously in the test to achieve temperature calibration under high-temperature conditions.

[0067] The data acquisition system 3 is connected to the thermocouples, pressure sensors, differential pressure sensors, and cooling water flow meters on the simulated test piece via wires 4. Measuring elements arranged near the heating tube 25, electrode 14, inner sleeve 21, outer sleeve 23, inlet / outlet gas pipe 17, and inlet / outlet water pipe 22 transmit temperature, pressure, differential pressure, and flow signals to the data acquisition system 3 via wires 4. The data acquisition system 3 samples, conditions, and converts different types of measurement signals, and then transmits the processed data to the data acquisition computer 1.

[0068] The pressure drop of the cooling water flow in the simulated test piece was measured by a differential pressure sensor arranged between the cooling water inlet and outlet pipes 22, while a pressure gauge was used to monitor the pressure of the inlet cooling water; the flow rate of the cooling water was measured using a turbine flow meter.

[0069] The data acquisition computer 1 is communicatively connected to the data acquisition system 3, and is used to display, record, and save the changes of various measured parameters over time during the experiment. The data acquisition computer 1 can simultaneously obtain parameters such as the temperature of the heating tube 25, the wall temperatures of the inner sleeve 21 and the outer sleeve 23, the inlet and outlet temperatures of the cooling water, the inlet and outlet temperatures of the test gas, the cooling water pressure, the test gas pressure, the cooling water flow rate, and the pressure drop of the test piece, so as to analyze the heat transfer characteristics, temperature distribution, and operating status of the device.

[0070] Specifically, the temperature measuring element includes:

[0071] The first thermocouple and the second thermocouple are disposed on the inner wall surface of the heating tube 25 for measuring the inner wall temperature of the heating tube. The first thermocouple and the second thermocouple are two different types of thermocouples used for mutual calibration under high temperature conditions.

[0072] The third thermocouple is disposed on the outer wall surface of the inner sleeve 21 and is used to measure the temperature of the outer wall of the inner sleeve.

[0073] The fourth and fifth thermocouples are respectively installed at the inlet and outlet of the annular cooling water channel, the gas inlet pipe 17, and the port of the gas outlet pipe 27, and are used to measure the inlet and outlet temperatures of the cooling water and the test gas.

[0074] The pressure measuring element includes a differential pressure sensor arranged between the inlet and outlet of the annular cooling water channel and a pressure gauge installed on the cooling water inlet pipe;

[0075] The flow measurement element is a turbine flow meter installed on the cooling water pipeline.

[0076] Example 2:

[0077] The operating procedure for conducting high-temperature heat transfer tests in annular narrow air gap channels is as follows:

[0078] Step 1: Sealing check:

[0079] Check if the data acquisition system 3 is functioning correctly. After adding sufficient cooling water to the cooling water tank 12, turn on the cooling water pump 9 to circulate the cooling water in the cooling water circuit. Check for leaks and ensure the water layer of the device is well-sealed. Connect the gas inlet pipe 17 to the test gas cylinder 6. Open the valves at the inlet and outlet of the gas inlet and continuously flush the air gap of the test section with helium for a period of time to expel all the air from the simulated test piece. Then close the outlet valve. Once the pressure gauge at the inlet pipe of the annular air gap channel 24 shows that the absolute pressure has reached the required pressure, close the inlet valve, let the test piece stand still, and monitor the pressure gauge data to check for leaks. If the pressure reading in the narrow air gap channel does not decrease within a certain period of time, it indicates that the test piece is well-sealed.

[0080] Step 2: Cooling water circuit debugging:

[0081] Pressurize the cooling water circuit using pressurized gas cylinder 8 to reach the required test pressure. Maintain the test gas in the annular air gap channel 24, turn on the cooling water pump 9, and adjust the flow rate through the inlet and return valves, observing the electromagnetic flowmeter reading until the flow rate reaches the set value. Adjust the temperature inside the cooling water tank 12, using heating coil 10 and cooling coil 13 to maintain the water temperature within room temperature range, ensuring the cooling water temperature at the inlet of the annular narrow air gap channel test piece remains at room temperature.

[0082] Step 3: Power Boost Test

[0083] Turn on the power to DC power cabinet 2 to heat the simulated test piece. Calculate the thermal power of the electric heating simulator using the current and voltage readings on the display. Gradually increase the power of the electric heating simulator to begin the power increase test. Maintain this power constant until all temperature measurement points stabilize. Record the changes in test parameters, including the temperature of the electric heating simulator, the outer wall temperature of the inner sleeve, the air gap pressure, the cooling water outlet temperature, and the electric heating power of the test section. Repeat the above process after each increase in power until the outer surface temperature of the electric heating simulator reaches the required test temperature.

[0084] Step 4: Power reduction test:

[0085] When the outer surface temperature of the simulated test piece reaches the required test temperature, the power reduction test begins. The linear power is gradually reduced while maintaining this power constant until the data from all temperature measurement points stabilizes, at which point the test data is recorded. This process is repeated after each power reduction until the power returns to its initial value. After all power increases and decreases and the experimental data recording are completed, the DC power supply cabinet 2 switch is turned off to stop heating the electric heating element. However, the cooling water circuit must remain flowing to continuously cool the test section. The cooling water valve is closed once the heating element temperature has cooled to room temperature.

[0086] Step 5: Replace the test piece:

[0087] After completing the entire set of high-temperature heat transfer tests in the annular narrow air gap channel, test pieces with different air gap thicknesses can be used to conduct another high-temperature heat transfer test on the simulated test piece. Once all the test conditions are completed, the operating characteristics of the annular narrow air gap channel high-temperature heat transfer test piece with different air gap layer thicknesses can be obtained.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A test apparatus for simulating high-temperature heat transfer in an annular narrow air gap channel within a pressurized water reactor fuel rod, characterized in that, include: The simulated test piece is provided with a heating tube (25), an inner sleeve (21) and an outer sleeve (23) arranged coaxially from the inside to the outside. An annular air gap channel (24) is formed between the heating tube (25) and the inner sleeve (21), and an annular cooling water channel is formed between the inner sleeve (21) and the outer sleeve (23). The heating tube (25) is coaxially connected to electrodes (14) at both ends. A cooling water circulation system, connected to the annular cooling water channel, is used to supply circulating cooling water to the annular cooling water channel; An electrothermal simulation system, electrically connected to the electrode (14), is used to provide electric heating power to the heating tube (25); The data acquisition system (3) is connected to the temperature measuring element, pressure measuring element and flow measuring element respectively set on the simulated test piece, and is used to collect and record test parameters; The upper end of the simulation test piece is provided with an expansion joint (18), which is arranged around the heating tube (25). One end of the expansion joint (18) is connected to the upper flange structure of the simulation test piece, and the other end is connected to the heating tube (25) through a fastening sleeve (16). It is used to generate axial expansion and contraction deformation when the heating tube (25) is heated and expands axially to absorb the thermal expansion. The test gas supply and exhaust system is connected to the expansion joint (18), the annular air gap channel (24), the gas chamber (26), and the gas outlet pipeline (27) through the gas inlet pipeline (17), and is used to fill the annular air gap channel (24) with test gas and adjust its pressure; The upper and lower ends of the simulated test piece are respectively provided with composite insulation sealing structures. The composite insulation sealing structures are set between the heating tube (25) and the inner sleeve (21) to electrically isolate the charged heating tube (25) from the inner sleeve (21) and the outer sleeve (23).

2. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The heating tube (25) has a through central gas passage (15) along its axis. The electrode (14) has a thermocouple insertion hole (28) and a side gas passage (29). The central gas passage (15) is connected to the thermocouple insertion hole and the side gas passage (29).

3. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The heating tube (25) has a hollow molybdenum tube in the middle heating section and a solid molybdenum electrode (14). The resistance of the hollow molybdenum tube is greater than that of the solid molybdenum electrode, so that the heating section is concentrated in the middle heating section.

4. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The composite insulating sealing structure includes an insulating ceramic (19) and an insulating mica (20). The insulating ceramic (19) is sleeved on the outside of the heating tube (25), and the insulating mica (20) is sleeved on the outside of the insulating ceramic (19).

5. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The two ends of the heating tube (25) pass through the upper flange structure and the lower flange structure of the simulated test piece, respectively. The two composite insulation sealing structures are connected to the upper flange structure and the lower flange structure, respectively. The composite insulation sealing structure located at the upper part is connected to the expansion joint (18), and the composite insulation sealing structure located at the lower part is connected to the gas chamber (26).

6. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The cooling water circulation system includes a cooling water tank (12), a cooling water pump (9), a pressurized gas cylinder (8), a heating coil (10), and a cooling coil (13). The inlet of the cooling water pump (9) is connected to the cooling water tank (12), the outlet of the cooling water pump (9) is connected to the inlet of the annular cooling water channel, and the outlet of the annular cooling water channel is connected to the cooling water tank (12) through a return water pipe, forming a closed circulation loop. The heating coil (10) and the cooling coil (13) are both located inside the cooling water tank (12) and are used to regulate the water temperature inside the cooling water tank (12); The pressurized gas cylinder (8) is connected to the gas phase space above the cooling water tank (12) through a pressurized pipe, which is used to provide basic pressure for the cooling water circulation loop and prevent the cooling water from boiling at high temperature.

7. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The test gas supply and exhaust system includes a test gas cylinder (6) and an exhaust valve (7). The test gas cylinder (6) is connected to the gas inlet pipe (17) located at the upper end of the simulated test piece through a gas supply pipe. A control valve is provided on the outlet pipe of the test gas cylinder (6). The exhaust valve (7) is located at the end of the exhaust pipe of the gas outlet pipe (27) located at the lower end of the simulated test piece. A vacuum pump is also connected to the end of the exhaust pipe for evacuating the annular air gap channel (24).

8. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The temperature measuring element includes: The first thermocouple and the second thermocouple are disposed on the inner wall surface of the heating tube (25) for measuring the inner wall temperature of the heating tube. The first thermocouple and the second thermocouple are two different types of thermocouples used for mutual calibration under high temperature conditions. The third thermocouple is disposed on the outer wall surface of the inner sleeve (21) and is used to measure the temperature of the outer wall of the inner sleeve; The fourth thermocouple and the fifth thermocouple are respectively installed at the inlet and outlet of the annular cooling water channel, at the port of the gas inlet pipe (17), and at the port of the gas outlet pipe (27) to measure the inlet and outlet temperatures of the cooling water and the test gas; The pressure measuring element includes a differential pressure sensor arranged between the inlet and outlet of the annular cooling water channel and a pressure gauge installed on the cooling water inlet pipe; The flow measurement element is a turbine flow meter installed on the cooling water pipeline.

9. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 2, characterized in that, The thermocouple insertion hole is designed to be eccentric and biased toward the edge of the electrode (14). The first thermocouple and the second thermocouple extend into the interior of the heating tube (25) through the thermocouple insertion hole, and the temperature measuring end is close to the inner wall of the heating tube (25).

10. The experimental apparatus for simulating high-temperature heat transfer in the annular narrow air gap channel within a pressurized water reactor fuel rod according to claim 1, characterized in that, The electrothermal simulation system includes a DC power supply cabinet (2), which is connected to two electrodes (14) via cables. The DC power supply cabinet (2), the upper electrode (14), the heating tube (25), and the lower electrode (14) together form an electric heating circuit.

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