Device and method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor

Abstract

This invention proposes a device and method for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor, belonging to the field of thermal-hydraulic experimental research on nuclear reactor engineering. The natural circulation pipeline and the forced circulation pipeline are connected in parallel, both connecting to a first water tank and an experimental heating device. A first regulating valve is located in the natural circulation pipeline, and a second regulating valve is located in the forced circulation pipeline. The outlet of the experimental heating device is connected to a second water tank. One end of the water tank connecting pipe is connected to the second water tank, and the other end is connected to the first water tank through a natural circulation valve. A cooling system is used for cooling; a pressure stabilizing system is used to balance the spatial pressure between the first and second water tanks; and a measurement and data acquisition system is used to measure the pressure and pressure difference, fluid temperature, flow rate, and liquid level of the core-pool simulation system. The focus is on studying the passive natural circulation residual heat extraction process formed between the core and the pool, verifying the rationality and effectiveness of the passive safety system design for cryogenic pool-type nuclear heating reactors.

Description

Technical Field

[0001] This invention belongs to the field of thermal-hydraulic experimental research of nuclear reactor engineering, and in particular relates to a device and method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor. Background Technology

[0002] Nuclear energy, as a clean and efficient energy source, is one of the more mature alternatives to primary energy sources. my country has conducted extensive research and investigations into nuclear heating and has begun preliminary explorations of engineering applications, achieving significant preliminary results. Studies show that utilizing nuclear heating will effectively improve my country's existing energy structure. Through comparison of existing reactor performance and summarization of operational experience, pool reactors, due to their inherent advantages such as high safety, mature technology, simple system, stable operation, small footprint, and good economic efficiency, are more suitable for use near urban residential areas and have broad application prospects in nuclear heating.

[0003] Pool reactors operate at atmospheric pressure, eliminating the need for pressure vessels and containment structures. This saves significant investment costs and eliminates the possibility of fuel rod ejection due to pressure vessel rupture, greatly enhancing the inherent safety of the reactor. Pool reactors increase the hydrostatic pressure of the coolant at the reactor outlet by increasing the depth of the pool, thereby raising the coolant's saturation temperature.

[0004] Passive systems, due to their simple structure, reduced malfunctions caused by less human intervention, inherent safety, and cost-effectiveness, are a rapidly developing trend in advanced reactor safety design, making them a popular choice for pool reactor safety systems. Natural circulation, a key application of the passive system concept, offers the advantage that heat transfer from the heat source to the heat sink occurs without the need for any other fluid machinery, relying solely on the driving force generated by the density difference caused by temperature. Therefore, passive systems based on natural circulation are simple in structure, have no active components, are less prone to failure, and exhibit high reliability.

[0005] Currently, existing nuclear heating practices both domestically and internationally mainly revolve around combined heat and power (CHP) and research reactor heating experiments, with no dedicated commercial heating reactors yet built. The "Yanlong" cryogenic pool-type nuclear heating reactor designed by CNNC has a complete passive residual heat removal system. In the event of an accident, the natural circulation valve automatically opens, and the core and pool form a natural circulation due to the coolant density difference. This natural circulation of the coolant removes heat from the core to the pool, achieving a safe reactor shutdown and avoiding the risk of core meltdown. Therefore, the performance of the natural circulation residual heat removal system of the cryogenic pool-type nuclear heating reactor directly determines the inherent safety of the "Yanlong" cryogenic pool-type nuclear heating reactor. Existing work mainly focuses on conceptual design and software calculation analysis, and relevant experimental verification is urgently needed. However, current technology lacks experimental device design and methods for studying the passive natural circulation residual heat removal process from the core to the reactor pool. Summary of the Invention

[0006] In view of this, in order to address the problem that there is no experimental device design or method in the existing technology for studying the passive natural circulation residual heat extraction process from the reactor core to the reactor water pool, this invention proposes a device and method for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor includes:

[0009] The reactor core-reactor pool simulation system includes a first water tank, a second water tank, a centrifugal pump, a test heating device, a natural circulation valve, a water tank connecting pipe, a circulation connecting pipe, a natural circulation pipe, a forced circulation pipe, a jet pipe, a first regulating valve, a second regulating valve, and a third regulating valve. One end of the natural circulation pipe is connected to the first water tank, and the other end is connected to the inlet of the test heating device through the circulation connecting pipe. One end of the forced circulation pipe is connected to the first water tank through the centrifugal pump, and the other end is connected to the inlet of the test heating device through the circulation connecting pipe. The first regulating valve is located in the natural circulation pipe, and the second regulating valve is located in the forced circulation pipe. The outlet of the test heating device is connected to the second water tank. One end of the water tank connecting pipe is connected to the second water tank, and the other end is connected to the first water tank through the natural circulation valve. One end of the jet pipe is connected to the output end of the centrifugal pump, and the jet pipe is configured such that water flowing out from its other end can control the opening and closing of the natural circulation valve. The third regulating valve is located in the jet pipe.

[0010] A cooling system is used to cool the fluids in the first water tank and the second water tank;

[0011] A pressure stabilizing system is used to balance the spatial pressure between the first water tank and the second water tank;

[0012] The measurement and data acquisition system is used to measure the pressure and differential pressure, fluid temperature, flow rate and liquid level of the reactor core-reactor pool simulation system, as well as to observe and record the fluid flow characteristics and the status of the natural circulation valve.

[0013] As a preferred embodiment of the above-mentioned device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor, the cooling system includes a circulating pump, a cooling water tank, a cooling tower, a first heat exchanger, and a second heat exchanger. The first heat exchanger and the second heat exchanger are respectively located at the top of the first water tank and the second water tank. The input end of the circulating pump is connected to the cooling water tank, and the output end of the circulating pump is connected to the inlet of the first heat exchanger and the inlet of the second heat exchanger. The outlet of the first heat exchanger and the outlet of the second heat exchanger are both connected to the cooling tower, and the cooling tower is connected to the cooling water tank.

[0014] As a preferred embodiment of the above-mentioned device for simulating the natural circulation waste heat removal of a cryogenic pool-type nuclear heating reactor, the pressure stabilization system includes a nitrogen cylinder, a first on / off valve, a second on / off valve, a safety valve, and a pressure control valve. The two ends of the first on / off valve are respectively connected to the nitrogen cylinder and the first water tank. The two ends of the second on / off valve are respectively connected to the first water tank and the second water tank. The safety valve and the pressure control valve are both connected to the second water tank at one end and to the atmosphere at the other end.

[0015] As a preferred embodiment of the above-mentioned device for simulating the natural circulation waste heat extraction of a low-temperature pool-type nuclear heating reactor, there are multiple water tank connecting pipes, which are spaced apart in a vertical direction. One end of each of the multiple water tank connecting pipes is connected to the second water tank, and the other end of one of the multiple water tank connecting pipes is connected to the first water tank through the natural circulation valve.

[0016] As a preferred embodiment of the aforementioned device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor, the measurement and data acquisition system includes a data acquisition machine and a high-speed camera connected to the data acquisition machine, a weighing water tank, a thermocouple assembly, a pressure differential transmitter assembly, an electromagnetic flowmeter assembly, a float level gauge assembly, and an angle sensor. The high-speed camera is used to capture the fluid flow characteristics in the first water tank and the opening and closing status of the natural circulation valve. The weighing water tank is connected to the water tank connection pipe through a leakage test pipeline, and the weighing water tank can weigh the fluid leaking from the natural circulation valve. The thermocouple assembly is used to measure the fluid temperature inside the first water tank, the fluid temperature at the inlet and outlet of the experimental heating device, and the temperature of the second... The pressure differential transmitter group measures the pressure of the jet pipeline, the pressure at the inlet of the test heating device, the pressure of the fluid at the bottom of the first water tank, the pressure of the gas space at the top of the first and second water tanks, the pressure difference between the inlet of the test heating device and the fluid at the bottom of the first water tank, the pressure difference between the inlet and outlet of the test heating device, and the pressure difference between the two ends of the water tank connecting pipe; the electromagnetic flowmeter group measures the flow rate of the jet pipeline, the natural circulation pipeline, and the leakage test pipeline; the float level gauge group measures the liquid level of the first and second water tanks; and the angle sensor measures the opening angle of the natural circulation valve.

[0017] As a preferred embodiment of the above-mentioned device for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor, the test heating device includes an electric heating structure and a core fuel rod bundle simulation structure. The core fuel rod bundle simulation structure includes an outer shell and multiple heating elements. The multiple heating elements are spaced apart and all are located inside the outer shell. The inlet of the outer shell is connected to the circulation connection pipeline, and the outlet of the outer shell is connected to the second water tank. The electric heating structure can heat the heating elements.

[0018] As a preferred embodiment of the above-mentioned device for simulating the natural circulation waste heat extraction of a low-temperature pool-type nuclear heating reactor, the outer shell includes a collector box and a heating cylinder. The inlet of the collector box is connected to the circulation connection pipeline, the outlet of the collector box is connected to the inlet of the heating cylinder, and the outlet of the heating cylinder is connected to the second water tank.

[0019] As a preferred embodiment of the above-mentioned device for simulating the natural circulation waste heat extraction of a low-temperature pool-type nuclear heating reactor, the heating element includes a stainless steel heating rod, a first copper rod, a second copper rod, and a flexible connecting copper wire. The flexible connecting copper wire, the first copper rod, the stainless steel heating rod, and the second copper rod are connected in sequence. The flexible connecting copper wire and the second copper rod are both connected to the electric heating structure. The flexible connecting copper wire and the first copper rod are located in the current collector box, and the stainless steel heating rod and the second copper rod are located in the heating cylinder.

[0020] As a preferred embodiment of the above-mentioned device for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor, the reactor core fuel rod bundle simulation structure further includes a polytetrafluoroethylene (PTFE) plate layer disposed on the inner wall of the heating cylinder.

[0021] The present invention also provides a method for simulating the natural circulation waste heat removal of a cryogenic pool-type nuclear heating reactor, using the above-mentioned apparatus for simulating the natural circulation waste heat removal of a cryogenic pool-type nuclear heating reactor, comprising:

[0022] S1: Fill the device for simulating the residual heat extraction of a low-temperature pool-type nuclear heating reactor with water until the liquid level in the first water tank reaches the first set liquid level and the liquid level in the second water tank reaches the second set liquid level.

[0023] S2: Close the first regulating valve and the third regulating valve, open the second regulating valve, and start the centrifugal pump to achieve forced circulation of fluid;

[0024] S3: Start the pressure stabilizing system and adjust the pressure stabilizing system to ensure that the pressure in the upper gas space of the first water tank and the second water tank reaches the set pressure;

[0025] S4: Start the test heating device to heat the fluid undergoing forced circulation until the fluid temperature inside the first water tank, the fluid temperature at the inlet and outlet of the test heating device, and the fluid temperature inside the second water tank all reach the set temperature value.

[0026] S5: Close the centrifugal pump and the second regulating valve, open the first regulating valve, the test heating device increases the heating power in steps, and at the same time start the cooling system to maintain the temperature in the first water tank and the second water tank constant. Observe the establishment of the test loop natural circulation through the measurement and data acquisition system, and record the test data of the passive natural circulation waste heat extraction characteristics.

[0027] S6: The test heating device gradually reduces the heating power until it is zero. The cooling system reduces the fluid temperature inside the first water tank, the fluid temperature at the inlet and outlet of the test heating device, and the fluid temperature inside the second water tank to below 50°C. The pressure stabilizing system is then turned off, and the overall pressure is reduced to atmospheric pressure.

[0028] Compared with existing technologies, the beneficial effects of the device and method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor provided by this invention are:

[0029] 1. This invention provides a device and method for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor. Compared with other passive heat extraction devices or natural circulation cooling systems, this device is applicable to the Yanlong-type cryogenic heating reactor or other low-pressure pool-type heating reactors proposed by CNNC, rather than shell-type reactors. The target reactor type is clearly defined, and the focus is on studying the passive natural circulation residual heat extraction process formed between the reactor core and the reactor water pool, verifying the rationality and effectiveness of the passive safety system design of the cryogenic pool-type heating reactor.

[0030] 2. This invention provides a device and method for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor. This device can also conduct a series of mechanistic experiments on the simulated core rod bundle flow heat transfer characteristics, system natural circulation flow instability, and flow-induced vibration characteristics of key components within the reactor under cryogenic and low-pressure conditions. The experimental data will effectively support the model verification and development of reactor system design and safety analysis software. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0032] Figure 1 This is an overall structural diagram of the device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor provided in a specific embodiment of the present invention.

[0033] Figure 2 This is a structural diagram of the simulated fuel rod bundle structure of the device for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor provided in a specific embodiment of the present invention.

[0034] Figure 3 This is a cross-sectional schematic diagram of the simulated structure of the fuel rod bundle in the core of the device for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor provided in a specific embodiment of the present invention.

[0035] Figure 4This is a schematic diagram of the upper conductive copper electrode plate of the core fuel rod bundle simulation structure of the device for simulating the natural circulation residual heat extraction of a low-temperature pool-type nuclear heating reactor provided in a specific embodiment of the present invention.

[0036] Figure 5 This is a schematic diagram of the conductive copper clamp at the bottom of the core fuel rod bundle simulation structure of the device for simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor provided in a specific embodiment of the present invention, viewed from a first perspective.

[0037] Figure 6 This is a schematic diagram of the conductive copper clamp at the bottom of the core fuel rod bundle simulation structure of the device for simulating the residual heat extraction of natural circulation in a cryogenic pool-type nuclear heating reactor, provided in a specific embodiment of the present invention, from a second perspective.

[0038] In the picture:

[0039] 11. First water tank; 12. Second water tank; 121. Water tank; 122. Ascending cylinder; 13. Centrifugal pump; 14. Test heating device; 141. DC power supply; 142. Conductive copper busbar; 143. Outer shell; 1431. Current collector; 1432. Heating cylinder; 144. Heating element; 1441. Stainless steel heating rod; 1442. First copper rod; 1443. Flexible connecting copper wire; 1444. Second copper rod; 145. Conductive copper clamp; 146. Packing; 147. Positioning grid; 148. Conductive copper electrode plate; 149. Pressure tapping pipe; 1410. PTFE plate layer; 15. Natural circulation valve; 16. Water tank connection pipe; 17. Circulation connection pipe; 18. Natural circulation pipe; 19. Forced circulation pipe; 110. Jet pipe; 111. First regulating valve; 112. Second regulating valve; 113. Third regulating valve;

[0040] 21. Cooling water tank; 22. Circulating pump; 23. First heat exchanger; 24. Second heat exchanger; 25. Cooling tower; 26. Fourth regulating valve; 27. Fifth regulating valve;

[0041] 31. Nitrogen cylinder; 32. First opening / closing valve; 33. Second opening / closing valve; 34. Safety valve; 35. Pressure control valve;

[0042] 41. Data acquisition unit; 42. High-speed camera; 431. First thermocouple; 432. Second thermocouple; 433. Third thermocouple; 434. Fourth thermocouple; 435. Fifth thermocouple; 436. Sixth thermocouple; 437. Seventh thermocouple; 438. Eighth thermocouple; 439. Ninth thermocouple; 4310. Tenth thermocouple; 441. First pressure transmitter; 442. Second pressure transmitter; 443. 444. Third pressure transmitter; 445. Fourth pressure transmitter; 446. First differential pressure transmitter; 447. Second differential pressure transmitter; 458. Pressure of the third differential pressure transmitter; 459. First electromagnetic flowmeter; 450. Second electromagnetic flowmeter; 451. Third electromagnetic flowmeter; 462. Second float level gauge; 463. First float level gauge; 47. Angle sensor; 48. Leakage test pipeline; 49. Weighing water tank. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0044] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0046] In the description of this embodiment, the terms "upper," "lower," "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0047] See Figure 1-6 This invention provides a device and method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor. The device includes: a core-reservoir simulation system, a cooling system, a pressure stabilization system, and a measurement and data acquisition system. The core-reservoir simulation system includes a first water tank 11, a second water tank 12, a centrifugal pump 13, a test heating device 14, a natural circulation valve 15, a water tank connecting pipe 16, a circulation connecting pipe 17, a natural circulation pipe 18, a forced circulation pipe 19, a jet pipe 110, a first regulating valve 111, a second regulating valve 112, and a third regulating valve 113. One end of the natural circulation pipe 18 is connected to the first water tank 11, and the other end is connected to the inlet of the test heating device 14 through the circulation connecting pipe 17. One end of the forced circulation pipe 19 is connected to the first water tank 11 through the centrifugal pump 13, and the other end is connected to the test heating device 14 through the circulation connecting pipe 17. The inlet of the reactor core is connected to the reactor water tank 12. The first regulating valve 111 is located in the natural circulation pipeline 18, and the second regulating valve 112 is located in the forced circulation pipeline 19. The outlet of the test heating device 14 is connected to the second water tank 12. One end of the water tank connecting pipe 16 is connected to the second water tank 12, and the other end is connected to the first water tank 11 through the natural circulation valve 15. One end of the jet pipeline 110 is connected to the output end of the centrifugal pump 13. The jet pipeline 110 is configured such that the water flowing out from its other end can control the opening and closing of the natural circulation valve 15. The third regulating valve 113 is located in the jet pipeline 110. The cooling system is used to cool the fluid in the first water tank 11 and the second water tank 12. The pressure stabilizing system is used to balance the spatial pressure of the first water tank 11 and the second water tank 12. The measurement and data acquisition system is used to measure the pressure and pressure difference, fluid temperature, flow rate and liquid level of the reactor core-reactor pool simulation system, as well as to observe and record the fluid flow characteristics and the status of the natural circulation valve 15.

[0048] In this device simulating the natural circulation residual heat extraction of a cryogenic pool-type nuclear heating reactor, the geometric and thermal-hydraulic parameters of the reactor core-reactor pool simulation system are selected based on similarity analysis. The first water tank 11 is the simulation body of the reactor pool, and the second water tank 12 is the simulation body of the top space of the reactor core. The switching between forced circulation and natural circulation in the main loop is achieved by controlling the opening and closing of the first regulating valve 111 and the second regulating valve 112. When the second regulating valve 112 is opened and the first regulating valve 111 and the third regulating valve 113 are closed, the centrifugal pump 13 is started, and the main loop undergoes forced circulation. Under forced circulation conditions, the entire water flow loop is as follows: water flows out of the first water tank 11, sequentially through the centrifugal pump 13, the second regulating valve 112, the experimental heating device 14, the water tank connecting pipe 16, and the natural circulation valve 15, finally returning to the first water tank 11. With the second regulating valve 112 and the third regulating valve 113 closed, and the first regulating valve 111 opened, the main circuit undergoes natural circulation. Under natural circulation conditions, the entire water flow loop is as follows: water flows out of the first water tank 11, passes sequentially through the first regulating valve 111, the test heating device 14, the water tank connecting pipe 16, and the natural circulation valve 15, and finally returns to the first water tank 11. The third regulating valve 113 plays a role in studying the opening and closing behavior of the natural circulation valve 15. After the third regulating valve 113 is opened, the jet water in the jet pipe 110 acts on the valve disc of the natural circulation valve 15, pushing the valve disc to close, and the natural circulation valve 15 closes. When the third regulating valve 113 is closed or the flow rate is low, the force of the jet water in the jet pipe 110 acting on the valve disc of the natural circulation valve 15 decreases, which is insufficient to push the valve disc to close, and the natural circulation valve 15 opens. The cooling system is used to cool the fluids in the first water tank 11 and the second water tank 12, thereby cooling the fluids throughout the entire device during fluid flow. The pressure stabilization system is used to balance the spatial pressure of the first water tank 11 and the second water tank 12, that is, to balance the pressure of the gas space above the first water tank 11 and the second water tank 12, and the pressure stabilization system can simulate the working pressure of a deep-pool heating reactor. The measurement and data acquisition system is used to measure the pressure and pressure difference, fluid temperature, flow rate and liquid level of the core-pool simulation system, as well as to observe and record the fluid flow characteristics and the status of the natural circulation valve 15.

[0049] This device, simulating the natural circulation residual heat removal of a cryogenic pool-type nuclear heating reactor, is suitable for the Yanlong-type cryogenic heating reactor or other low-pressure pool-type heating reactors proposed by CNNC, rather than shell-type reactors, given its clearly defined target reactor type. The focus is on studying the passive natural circulation residual heat removal process between the reactor core and the reactor water pool, verifying the rationality and effectiveness of the passive safety system design for cryogenic pool-type heating reactors. Furthermore, it can conduct a series of mechanistic experiments simulating the flow heat transfer characteristics of the reactor core rod bundles under cryogenic and low-pressure conditions, the instability of the system's natural circulation flow, and the flow-induced vibration characteristics of key in-reactor components. The experimental data will effectively support the model verification and development of reactor system design and safety analysis software.

[0050] Optionally, the cooling system includes a circulating pump 22, a cooling water tank 21, a cooling tower 25, a first heat exchanger 23, and a second heat exchanger 24. The first heat exchanger 23 and the second heat exchanger 24 are respectively disposed at the top of the first water tank 11 and the second water tank 12. The input end of the circulating pump 22 is connected to the cooling water tank 21, and the output end of the circulating pump 22 is connected to the inlet of the first heat exchanger 23 and the inlet of the second heat exchanger 24. The outlets of the first heat exchanger 23 and the second heat exchanger 24 are both connected to the cooling tower 25, and the cooling tower 25 is connected to the cooling water tank 21. Both the first heat exchanger 23 and the second heat exchanger 24 are spiral tube heat exchangers. The first heat exchanger 23 and the second heat exchanger 24 are respectively disposed on the top side wall of the first water tank 11 and the second water tank 12. Cooling water is pumped by circulating pump 22 into the first heat exchanger 23 and the second heat exchanger 24, where it undergoes sufficient heat exchange with the fluids inside the first water tank 11 and the second water tank 12 before flowing out to the cooling tower 25. There, it is sprayed to cool down before flowing back to the cooling water tank 21, completing one cooling cycle. Optionally, a fourth regulating valve 26 is installed between circulating pump 22 and the first heat exchanger 23 to control the on / off state of the pipeline between them. A fifth regulating valve 27 is installed between circulating pump 22 and the second heat exchanger 24 to control the on / off state of the pipeline between them.

[0051] Optionally, the pressure stabilizing system includes a nitrogen cylinder 31, a first on / off valve 32, a second on / off valve 33, a safety valve 34, and a pressure control valve 35. The first on / off valve 32 is connected to the nitrogen cylinder 31 and the first water tank 11 at both ends. The second on / off valve 33 is connected to the first water tank 11 and the second water tank 12 at both ends. Both the safety valve 34 and the pressure control valve 35 are connected to the second water tank 12 at one end and to the atmosphere at the other end. Opening the second on / off valve 33 maintains pressure balance in the gas space above the first water tank 11 and the second water tank 12. The safety valve 34 provides overpressure protection for the first water tank 11 and the second water tank 12. The pressure control valve 35 can be opened manually or electrically to regulate the internal pressure of the first water tank 11 and the second water tank 12.

[0052] Optionally, there are multiple water tank connecting pipes 16, which are arranged vertically at intervals. One end of each water tank connecting pipe 16 is connected to the second water tank 12, and the other end of one of the water tank connecting pipes 16 is connected to the first water tank 11 through a natural circulation valve 15. To study the influence of different installation heights of the natural circulation valve 15 on the natural circulation waste heat removal process, multiple water tank connecting pipes 16 are arranged vertically at intervals, and one water tank connecting pipe 16 is selected to be connected to the natural circulation valve 15.

[0053] Optionally, the measurement and data acquisition system includes a data acquisition unit 41 and a high-speed camera 42 connected to the data acquisition unit 41, a weighing water tank 49, a thermocouple assembly, a pressure differential transmitter assembly, an electromagnetic flowmeter assembly, a float level gauge assembly, and an angle sensor 47. The high-speed camera 42 is used to capture the fluid flow characteristics in the first water tank 11 and the opening and closing status of the natural circulation valve 15. The weighing water tank 49 is connected to the water tank connecting pipe 16 through a leakage test pipeline 48, and the weighing water tank 49 can weigh the fluid leaking from the natural circulation valve 15. The thermocouple assembly is used to measure the fluid temperature inside the first water tank 11, the fluid temperature at the inlet and outlet of the test heating device 14, and the fluid temperature inside the second water tank 12. Temperature; pressure differential transmitter group is used to measure the pressure of jet pipeline 110, pressure at the inlet of test heating device 14, pressure of fluid in the lower part of first water tank 11, pressure of gas space in the upper part of first water tank 11 and second water tank 12, pressure difference between the inlet of test heating device 14 and the fluid in the lower part of first water tank 11, pressure difference between the inlet and outlet of test heating device 14, and pressure difference between the two ends of water tank connecting pipe 16; electromagnetic flow meter group is used to measure the flow rate of jet pipeline 110, natural circulation pipeline 18 and leakage test pipeline 48; float level gauge group is used to measure the liquid level of first water tank 11 and second water tank 12; angle sensor 47 is used to measure the opening angle of natural circulation valve 15.

[0054] The second water tank 12 includes an ascending cylinder 122 and a water tank 121, which are connected. The water tank 121 is located above the ascending cylinder 122.

[0055] The device for simulating the natural circulation waste heat extraction of a low-temperature pool-type nuclear heating reactor is made of stainless steel. The fluid is ionized water. Quartz glass observation windows can be opened at corresponding positions of components such as the riser 122 and the first water tank 11 as needed to facilitate the observation of the internal fluid flow characteristics and the behavior of internal components.

[0056] The natural circulation valve 15 is a simulation designed based on the design dimensions of the prototype deep-pool heating reactor using a reasonable similarity analysis method. An angle sensor 47 is installed on it to indicate the opening angle. At the same time, a high-speed camera 42 is used for auxiliary shooting to obtain visual image data of the opening behavior of the natural circulation valve 15. The high-speed camera 42 can be placed outside the first water tank 11 and take pictures through the quartz glass observation window opened on the first water tank 11, or it can be placed inside the first water tank 11 after waterproofing to take close-up pictures. Its advantage is that the shooting position can be flexibly adjusted according to the experimental needs. The specific installation method can be determined according to the actual experimental requirements.

[0057] The weighing tank 49 is connected to the tank connecting pipe 16 via the leakage test pipe 48. The weighing tank 49 can weigh the fluid leaking from the natural circulation valve 15. An on / off valve is installed between the connection point of the leakage test pipe 48 and the tank connecting pipe 16 and the second tank 12. When investigating the leakage problem of the natural circulation valve 15, this on / off valve should be closed. If the natural circulation valve 15 leaks, fluid will flow from the first tank 11 through the natural circulation valve 15, through the tank connecting pipe 16 and the leakage test pipe 48, and into the weighing tank 49. The weighing tank 49 can weigh the leakage flow rate of the natural circulation valve 15. When not investigating the leakage problem of the natural circulation valve 15, the on / off valve should be opened.

[0058] The thermocouple assembly includes a first thermocouple 431, a second thermocouple 432, a third thermocouple 433, a fourth thermocouple 434, a fifth thermocouple 435, a sixth thermocouple 436, a seventh thermocouple 437, an eighth thermocouple 438, a ninth thermocouple 439, and a tenth thermocouple 4310. The first thermocouple 431, the second thermocouple 432, the third thermocouple 433, and the fourth thermocouple 434 are arranged vertically at intervals in the first water tank 11 for measuring the temperature of the fluid inside the first water tank 11. The fifth thermocouple 435 and the sixth thermocouple 436 are respectively installed at the inlet and outlet of the test heating device 14 to measure the fluid temperature at the inlet and outlet of the test heating device 14. The seventh thermocouple 437, the eighth thermocouple 438, the ninth thermocouple 439 and the tenth thermocouple 4310 are arranged vertically at intervals in the second water tank 12 to measure the fluid temperature inside the second water tank 12. Among them, the seventh thermocouple 437, the eighth thermocouple 438 and the ninth thermocouple 439 are used to measure the fluid temperature inside the riser 122, and the tenth thermocouple 4310 is used to measure the fluid temperature inside the water tank.

[0059] The pressure differential transmitter group includes a first pressure transmitter 441, a second pressure transmitter 442, a third pressure transmitter 443, a fourth pressure transmitter 444, a first differential pressure transmitter 445, a second differential pressure transmitter 446, and a third differential pressure transmitter. The first pressure transmitter 441 is used to measure the pressure at the bottom of the first water tank 11. The second pressure transmitter 442 is used to measure the pressure at the inlet of the test heating device 14. The third pressure transmitter 443 is used to measure the pressure in the upper air space of the first water tank 11 and the second water tank 12. The fourth pressure transmitter 444 is used to measure the pressure in the jet pipe 110. The first differential pressure transmitter 445 is used to measure the pressure difference between the inlet of the test heating device 14 and the bottom of the first water tank 11. The second differential pressure transmitter 446 is used to measure the pressure difference of the fluid at the inlet and outlet of the test heating device 14. The third differential pressure transmitter is used to measure the pressure difference between the two ends of the water tank connecting pipe 16.

[0060] The electromagnetic flowmeter group includes a first electromagnetic flowmeter 451, a second electromagnetic flowmeter 452, and a third electromagnetic flowmeter 453. The first electromagnetic flowmeter 451 is used to measure the flow rate of the jet pipe 110, the second electromagnetic flowmeter 452 is used to measure the flow rate of the natural circulation pipe 18, and the third electromagnetic flowmeter 453 is used to measure the flow rate of the leakage test pipe 48.

[0061] The float level gauge assembly includes a first float level gauge 462 and a second float level gauge 461. The first float level gauge 462 is used to measure the liquid level of the first water tank 11, and the second float level gauge 461 is used to measure the liquid level of the second water tank 12.

[0062] Optionally, the test heating device 14 includes an electric heating structure and a core fuel rod bundle simulation structure. The core fuel rod bundle simulation structure includes a shell 143 and multiple heating elements 144. The multiple heating elements 144 are spaced apart and all located inside the shell 143. The inlet of the shell 143 is connected to the circulation connection pipe 17, and the outlet of the shell 143 is connected to the second water tank 12. The electric heating structure can heat the heating elements 144. The electric heating structure heats the heating elements 144, and the heating elements 144 heat the fluid entering the shell 143. After the fluid in the first water tank 11 is heated by the core fuel rod bundle simulation structure, it enters the second water tank 12.

[0063] Optionally, the outer casing 143 includes a manifold 1431 and a heating cylinder 1432. The inlet of the manifold 1431 is connected to the circulation connection pipe 17, and the outlet of the manifold 1431 is connected to the inlet of the heating cylinder 1432. The outlet of the heating cylinder 1432 is connected to the second water tank 12. The manifold 1431 is located at the lower part of the heating cylinder 1432. The water flows into the manifold 1431 first and then into the heating cylinder 1432. The manifold 1431 can buffer and equalize the flow of the test fluid.

[0064] Optionally, the heating element 144 includes a stainless steel heating rod 1441, a first copper rod 1442, a second copper rod 1444, and a flexible connecting copper wire 1443. The flexible connecting copper wire 1443, the first copper rod 1442, the stainless steel heating rod 1441, and the second copper rod 1444 are connected in sequence. Both the flexible connecting copper wire 1443 and the second copper rod 1444 are connected to the electric heating structure. The flexible connecting copper wire 1443 and the first copper rod 1442 are located in the collector box 1431, and the stainless steel heating rod 1441 and the second copper rod 1444 are located in the heating cylinder 1432.

[0065] The electric heating structure includes a DC power supply 141 and two conductive copper busbars 142. Both conductive copper busbars 142 are connected to the DC power supply 141. One conductive copper busbar 142 is connected to a flexible connecting copper wire 1443 via a conductive copper clamp 145 and packing 146. The other conductive copper busbar 142 is connected to a second copper rod 1444 via a conductive copper electrode plate 148. A stainless steel heating rod 1441 serves as the main heating element, and its front and rear ends are brazed to the first copper rod 1442 and the second copper rod 1444, respectively. The front end of the first copper rod 1442 is connected to the flexible connecting copper wire 1443 to accommodate the thermal expansion of the stainless steel heating rod 1441. Two pressure-sensing tubes 149 are also provided on the outer casing 143. Multiple spaced positioning grids 147 are also provided inside the outer casing 143 for fixing the stainless steel heating rod 1441.

[0066] The two conductive copper busbars 142 are bolted and tightened to the lower conductive copper clamp 145 and the upper conductive copper electrode plate 148 respectively through bolt holes and flanges. Before bolting, the surfaces to be connected need to be cleaned with fine sandpaper to remove the oxide layer, thereby reducing contact resistance and preventing local overload heating.

[0067] The conductive copper electrode plate 148 has circular holes with the same diameter and number as the second copper rod 1444, and the conductive copper electrode plate 148 is connected to the second copper rod 1444 by brazing. At the same time, the conductive copper electrode plate 148 is also provided with several water flow holes as needed to ensure that the fluid does not need to change its flow direction after absorbing heat in the heating cylinder 1432 and flows out directly.

[0068] Optionally, the simulated fuel rod bundle structure in the reactor core also includes a polytetrafluoroethylene (PTFE) plate 1410, which is disposed on the inner wall of the heating cylinder 1432. The heating cylinder 1432 is made of stainless steel, and the PTFE plate 1410 fits tightly against the inner side of the heating cylinder 1432, preventing short circuits caused by the stainless steel heating rod 1441 deforming and overlapping with the stainless steel heating cylinder 1432, thus providing electrical insulation and isolation.

[0069] This invention also provides a method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor. The method employs the aforementioned device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor. The design and construction of this device are based on similarity analysis of prototype reactor parameters to obtain similarity criterion numbers, thereby obtaining a scale for geometric and thermal parameters, ensuring the similarity of key physical phenomena and processes in the system. Based on this device, experimental research on the passive natural circulation waste heat extraction characteristics of cryogenic pool-type nuclear heating reactors and performance testing of key equipment can be conducted, providing reliable experimental data for the design and improvement of passive natural circulation waste heat extraction systems in actual reactors. The method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor provided by this invention includes:

[0070] S1: Fill the device for simulating the residual heat extraction of a cryogenic pool-type nuclear heating reactor with water until the liquid level in the first water tank 11 reaches the first set liquid level and the liquid level in the second water tank 12 reaches the second set liquid level.

[0071] Fill the entire device circuit with water until the liquid level in the first water tank 11 reaches the first set liquid level and the liquid level in the second water tank 12 reaches the second set liquid level, that is, until the upper air space height of the first water tank 11 and the second water tank 12 is about one meter. Ensure that the circuit is well sealed.

[0072] S2: Close the first regulating valve 111 and the third regulating valve 113, open the second regulating valve 112, and start the centrifugal pump 13 to achieve forced circulation of fluid.

[0073] At this time, the main circuit is forced to circulate. The water flows out of the first water tank 11, passes through the centrifugal pump 13, the second regulating valve 112, the test heating device 14, the water tank connecting pipe 16 and the natural circulation valve 15 in sequence, and finally returns to the first water tank 11.

[0074] S3: Start the pressure stabilization system and adjust it to ensure that the pressure in the upper gas space of the first water tank 11 and the second water tank 12 reaches the set pressure. The third differential pressure transmitter is used to measure the pressure in the upper gas space of the first water tank 11 and the second water tank 12. Adjust the pressure stabilization system until the reading of the third differential pressure transmitter reaches the set pressure.

[0075] S4: Start the test heating device 14 to heat the fluid undergoing forced circulation until the fluid temperature inside the first water tank 11, the fluid temperature at the inlet and outlet of the test heating device 14, and the fluid temperature inside the second water tank 12 all reach the set temperature value. That is, start the electric heating structure and rely on forced circulation to raise the circuit temperature until the readings of the first thermocouple 431, the second thermocouple 432, the third thermocouple 433, the fourth thermocouple 434, the fifth thermocouple 435, the sixth thermocouple 436, the seventh thermocouple 437, the eighth thermocouple 438, the ninth thermocouple 439, and the tenth thermocouple 4310 all reach the set value.

[0076] S5: Turn off the centrifugal pump 13 and the second regulating valve 112, open the first regulating valve 111, the test heating device 14 increases the heating power in steps, and at the same time start the cooling system to maintain the temperature in the first water tank 11 and the second water tank 12 constant. Observe the establishment of the test loop natural circulation through the measurement and data acquisition system, and record the test data of the passive natural circulation residual heat extraction characteristics.

[0077] Close the second regulating valve 112 and the third regulating valve 113, open the first regulating valve 111, and the main circuit will circulate naturally. The water flows out of the first water tank 11, passes through the first regulating valve 111, the test heating device 14, the water tank connecting pipe 16 and the natural circulation valve 15 in sequence, and finally returns to the first water tank 11.

[0078] S6: The test heating device 14 gradually reduces the heating power to zero, and relies on the cooling system to reduce the fluid temperature inside the first water tank 11, the fluid temperature at the inlet and outlet of the test heating device 14, and the fluid temperature inside the second water tank 12 to below 50°C, shuts off the pressure stabilizing system, and reduces the overall pressure to atmospheric pressure.

[0079] The cooling system reduces the readings of the first thermocouple 431, second thermocouple 432, third thermocouple 433, fourth thermocouple 434, fifth thermocouple 435, sixth thermocouple 436, seventh thermocouple 437, eighth thermocouple 438, ninth thermocouple 439, and tenth thermocouple 4310 to below 50°C. The system pressure is then reduced to atmospheric pressure by opening the pressure control valve 35.

[0080] Obviously, the above-disclosed embodiments of the present invention are merely illustrative of the invention. The embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. It is neither necessary nor possible to exhaustively list all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor, characterized in that, include: The reactor core-reactor pool simulation system includes a first water tank (11), a second water tank (12), a centrifugal pump (13), a test heating device (14), a natural circulation valve (15), a water tank connecting pipe (16), a circulation connecting pipe (17), a natural circulation pipe (18), a forced circulation pipe (19), a jet pipe (110), a first regulating valve (111), a second regulating valve (112), and a third regulating valve (113). One end of the natural circulation pipe (18) is connected to the first water tank (11), and the other end is connected to the inlet of the test heating device (14) through the circulation connecting pipe (17). One end of the forced circulation pipe (19) is connected to the first water tank (11) through the centrifugal pump (13), and the other end is connected to the inlet of the test heating device (14) through the circulation connecting pipe (17). The connecting pipe (17) is connected to the inlet of the test heating device (14), the first regulating valve (111) is located in the natural circulation pipe (18), the second regulating valve (112) is located in the forced circulation pipe (19), the outlet of the test heating device (14) is connected to the second water tank (12), one end of the water tank connecting pipe (16) is connected to the second water tank (12), and the other end is connected to the first water tank (11) through the natural circulation valve (15). One end of the jet pipe (110) is connected to the output end of the centrifugal pump (13), and the jet pipe (110) is configured such that the water flowing out from its other end can control the opening and closing of the natural circulation valve (15). The third regulating valve (113) is located in the jet pipe (110). A cooling system is used to cool the fluids in the first water tank (11) and the second water tank (12); A pressure stabilizing system is used to balance the spatial pressure between the first water tank (11) and the second water tank (12); The measurement and data acquisition system is used to measure the pressure and differential pressure, fluid temperature, flow rate and liquid level of the reactor core-reactor pool simulation system, as well as to observe and record the fluid flow characteristics and the status of the natural circulation valve (15).

2. The device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 1, characterized in that, The cooling system includes a circulating pump (22), a cooling water tank (21), a cooling tower (25), a first heat exchanger (23), and a second heat exchanger (24). The first heat exchanger (23) and the second heat exchanger (24) are respectively located at the top of the first water tank (11) and the second water tank (12). The input end of the circulating pump (22) is connected to the cooling water tank (21), and the output end of the circulating pump (22) is connected to the inlet of the first heat exchanger (23) and the inlet of the second heat exchanger (24). The outlet of the first heat exchanger (23) and the outlet of the second heat exchanger (24) are both connected to the cooling tower (25), and the cooling tower (25) is connected to the cooling water tank (21).

3. The device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 1, characterized in that, The pressure stabilizing system includes a nitrogen cylinder (31), a first on / off valve (32), a second on / off valve (33), a safety valve (34), and a pressure control valve (35). The two ends of the first on / off valve (32) are connected to the nitrogen cylinder (31) and the first water tank (11), respectively. The two ends of the second on / off valve (33) are connected to the first water tank (11) and the second water tank (12), respectively. The safety valve (34) and the pressure control valve (35) are both connected to the second water tank (12) at one end and connected to the atmosphere at the other end.

4. The device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 1, characterized in that, The number of water tank connecting pipes (16) is multiple, and the multiple water tank connecting pipes (16) are arranged at intervals in the vertical direction. One end of each of the multiple water tank connecting pipes (16) is connected to the second water tank (12), and the other end of one of the multiple water tank connecting pipes (16) is connected to the first water tank (11) through the natural circulation valve (15).

5. The device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 1, characterized in that, The measurement and data acquisition system includes a data acquisition unit (41) and a high-speed camera (42), a weighing water tank (49), a thermocouple assembly, a pressure differential transmitter assembly, an electromagnetic flowmeter assembly, a float level gauge assembly, and an angle sensor (47) connected to the data acquisition unit (41). The high-speed camera (42) is used to capture the fluid flow characteristics in the first water tank (11) and the opening and closing status of the natural circulation valve (15). The weighing water tank (49) is connected to the water tank connecting pipe (16) through a leakage test pipeline (48), and the weighing water tank (49) can weigh the fluid leaking from the natural circulation valve (15). The thermocouple assembly is used to measure the fluid temperature inside the first water tank (11), the fluid temperature at the inlet and outlet of the test heating device (14), and the fluid temperature inside the second water tank (12). The pressure differential transmitter assembly... The instrument group is used to measure the pressure of the jet pipeline (110), the pressure at the inlet of the test heating device (14), the pressure of the fluid at the bottom of the first water tank (11), the pressure of the gas space at the top of the first water tank (11) and the second water tank (12), the pressure difference between the inlet of the test heating device (14) and the fluid at the bottom of the first water tank (11), the pressure difference between the inlet and outlet of the test heating device (14), and the pressure difference between the two ends of the water tank connecting pipe (16); the electromagnetic flowmeter group is used to measure the flow rate of the jet pipeline (110), the natural circulation pipeline (18), and the leakage test pipeline (48); the float level gauge group is used to measure the liquid level of the first water tank (11) and the second water tank (12); and the angle sensor (47) is used to measure the opening angle of the natural circulation valve (15).

6. The device for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 1, characterized in that, The test heating device (14) includes an electric heating structure and a core fuel rod bundle simulation structure. The core fuel rod bundle simulation structure includes an outer shell (143) and multiple heating elements (144). The multiple heating elements (144) are spaced apart and are all located inside the outer shell (143). The inlet of the outer shell (143) is connected to the circulation connection pipe (17), and the outlet of the outer shell (143) is connected to the second water tank (12). The electric heating structure can heat the heating elements (144).

7. The apparatus for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 6, characterized in that, The outer casing (143) includes a manifold (1431) and a heating cylinder (1432). The inlet of the manifold (1431) is connected to the circulation connection pipe (17), the outlet of the manifold (1431) is connected to the inlet of the heating cylinder (1432), and the outlet of the heating cylinder (1432) is connected to the second water tank (12).

8. The apparatus for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 7, characterized in that, The heating element (144) includes a stainless steel heating rod (1441), a first copper rod (1442), a second copper rod (1444), and a flexible connecting copper wire (1443). The flexible connecting copper wire (1443), the first copper rod (1442), the stainless steel heating rod (1441), and the second copper rod (1444) are connected in sequence. The flexible connecting copper wire (1443) and the second copper rod (1444) are both connected to the electric heating structure. The flexible connecting copper wire (1443) and the first copper rod (1442) are located inside the current collector (1431), and the stainless steel heating rod (1441) and the second copper rod (1444) are located inside the heating cylinder (1432).

9. The apparatus for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor according to claim 7, characterized in that, The simulated core fuel rod bundle structure also includes a polytetrafluoroethylene (PTFE) plate (1410), which is disposed on the inner wall of the heating cylinder (1432).

10. A method for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor, characterized in that, The apparatus for simulating the natural circulation waste heat extraction of a cryogenic pool-type nuclear heating reactor as described in any one of claims 1-9 comprises: S1: Fill the device for simulating the residual heat of a low-temperature pool-type nuclear heating reactor with water until the liquid level in the first water tank (11) reaches the first set liquid level and the liquid level in the second water tank (12) reaches the second set liquid level. S2: Close the first regulating valve (111) and the third regulating valve (113), open the second regulating valve (112), and start the centrifugal pump (13) to achieve forced circulation of fluid; S3: Start the pressure stabilization system and adjust the pressure stabilization system to ensure that the pressure in the upper gas space of the first water tank (11) and the second water tank (12) reaches the set pressure; S4: Start the test heating device (14) to heat the fluid undergoing forced circulation until the fluid temperature inside the first water tank (11), the fluid temperature at the inlet and outlet of the test heating device (14), and the fluid temperature inside the second water tank (12) all reach the set temperature value. S5: Turn off the centrifugal pump (13) and the second regulating valve (112), open the first regulating valve (111), the test heating device (14) increases the heating power step by step, and at the same time start the cooling system to maintain the temperature in the first water tank (11) and the second water tank (12) constant. Observe the establishment of the test loop natural circulation through the measurement and data acquisition system, and record the test data of the passive natural circulation residual heat extraction characteristics. S6: The test heating device (14) gradually reduces the heating power to zero, and relies on the cooling system to reduce the fluid temperature inside the first water tank (11), the fluid temperature at the inlet and outlet of the test heating device (14), and the fluid temperature inside the second water tank (12) to below 50°C, shuts off the pressure stabilizing system, and reduces the overall pressure to normal pressure.

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