Natural circulation test system for integrated small reactor

Abstract

The application provides a natural circulation test system and test method for an integrated small reactor, wherein the test system comprises a water supply circuit, a first circuit, a second circuit, a third circuit and a discharge branch; a heating source is arranged in the first circuit only, and the second circuit, the third circuit and the discharge branch are all free of external heat sources; the water supply circuit is connected with the first circuit and the second circuit, and can supply water to the first circuit and / or the second circuit; the first circuit is arranged in the small reactor body, and the first circuit exchanges heat with the second circuit; the third circuit absorbs heat of the second circuit; the first circuit, the second circuit and the discharge branch are connected.

Description

Technical Field

[0001] This invention relates to the field of nuclear power, and more specifically to a natural circulation test system and test method for an integrated small modular reactor. Background Technology

[0002] Integrated small modular reactors (SMRs) are an advanced type of nuclear reactor developed to meet the demands for miniaturization, compactness, and high safety in nuclear power. Their core feature is that the reactor core and other primary loop equipment, such as the steam generator, are integrated within a single pressure vessel, unlike the separate layout of traditional large nuclear reactors with a "core + external steam generator." In traditional pressurized water reactors, the reactor pressure vessel only houses the core, while the primary loop equipment, such as the steam generator and main pumps, is located outside the vessel and connected via piping. In contrast, integrated SMRs integrate the core, steam generator, and main coolant pumps all within a large pressure vessel, eliminating the external piping of the primary loop. Integrated SMRs have a smaller power output, typically 50-300 MWe, lower than traditional large nuclear reactors. Furthermore, integrated SMRs generally employ passive safety technologies, relying on gravity, natural circulation, and residual heat conduction to remove residual heat in the event of an accident, without the need for active equipment such as power sources or pumps.

[0003] To verify the operating characteristics of the small modular reactor (SMR) under various conditions, including natural circulation steady-state and unsteady-state conditions, and to provide experimental verification assurance for its design to pass safety review, it is necessary to use an integrated SMR natural circulation test system and test methods for experimental verification.

[0004] In some comparative schemes, the test system often adopts a multi-heat source structure, such as adding heating devices in the secondary and tertiary loops, which leads to system complexity, high energy consumption and high operating costs.

[0005] Based on the above technical problems, this invention proposes a natural circulation test system and test method for integrated small modular reactors, which can achieve one or more effects such as simplifying the system, reducing system energy consumption, and improving operating efficiency while conducting natural circulation tests safely and reliably. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to improve the efficiency of natural circulation testing of integrated small modular reactors, and / or simplify the structure of the testing system, and / or reduce the testing energy consumption, and to provide a natural circulation testing system and testing method.

[0007] The present invention solves the above-mentioned technical problems through the following technical solution: This invention provides a natural circulation test system, comprising: a water replenishment loop, a primary loop, a secondary loop, and a tertiary loop; and a discharge branch; wherein, a heating source is provided only in the primary loop, while the secondary loop, tertiary loop, and discharge branch have no external heat source; the water replenishment loop connects to the primary loop and the secondary loop, and is capable of replenishing water to the primary loop and / or the secondary loop; the primary loop is located inside the small reactor body, and the primary loop exchanges heat with the secondary loop; the tertiary loop absorbs heat from the secondary loop; the primary loop and the secondary loop are connected to the discharge branch.

[0008] According to one or more embodiments of the present invention, the test system includes a water storage tank, a shut-off valve, a filter, a pump, a flow meter, a regulating valve, a check valve, a heater, a miniature stack body, and a heat exchanger.

[0009] According to one or more embodiments of the present invention, the water storage tank (1-1) of the water replenishment circuit is divided into two paths. One path connects to a shut-off valve (2-1), a filter (3-2), a pump (4-1), a check valve (7-1), a shut-off valve (2-3), a flow meter (5-1), and an electric heater (8) along a pipeline; the other path connects to a shut-off valve (2-2), a filter (3-1), a pump (4-2), a check valve (7-2), a shut-off valve (2-4), and a flow meter (5-2) along a pipeline. After the two paths merge, water can be replenished to the first circuit through regulating valves (6-10) and (6-3). Alternatively, water can be replenished to the second circuit through regulating valve (6-2).

[0010] According to one or more embodiments of the present invention, the pump (4-1) of the water replenishment circuit is provided with a bypass circuit and a regulating valve (6-1) for regulating the water replenishment flow rate.

[0011] According to one or more embodiments of the present invention, after the two water replenishment circuits merge, water is sprayed into the small stack body (9) through the spray pipeline via the regulating valve (6-10), the flow meter (5-3) and the regulating valve (6-5).

[0012] According to one or more embodiments of the present invention, the primary loop is heated within the small stack body (9) by a bottom electric heating rod, and heat exchanged with the secondary loop by a heat exchanger built into the body, forming natural convection.

[0013] According to one or more embodiments of the present invention, the secondary loop includes two main paths, wherein the flow direction of the fluid in the two main paths is as follows: after being filtered by filters (3-3) / 3-4, the fluid starts from pump (4-3) / 4-4, flows through flow meters (5-5) / 5-4 and regulating valves (6-13) / 6-14, and enters the heat exchange coil of the small reactor body for heat exchange. The fluid flows out of the heat exchange coil and merges after passing through regulating valves (6-15) / 6-16.

[0014] According to one or more embodiments of the present invention, after the fluids of the two main paths of the secondary loop merge, they flow through the heat exchanger (10-2) for cooling.

[0015] According to one or more embodiments of the present invention, the heat exchanger (10-2) is provided with a bypass. After passing through the flow meter (5-10) and the regulating valve (6-17), the bypass merges with the fluid in the heat exchanger (10-2) and flows into the water storage tank (1-2).

[0016] According to one or more embodiments of the present invention, the secondary circuit is provided with a bypass for regulating the flow rate of the main circuit of the secondary circuit. The bypass is provided with flow meters (5-6) / flow meters (5-7) and regulating valves (6-11) / regulating valves (6-12) in sequence, and after merging, it merges with the main circuit fluid of the secondary circuit.

[0017] According to one or more embodiments of the present invention, the two main circuits of the two circuits are respectively equipped with voltage regulators (12-1) and voltage regulators (12-2), and the voltage regulators (12-1) and voltage regulators (12-2) are respectively equipped with shut-off valves (2-6) and shut-off valves (2-8).

[0018] According to one or more embodiments of the present invention, a dual-loop spray pipeline is provided at the outlet of pump (4-3) and pump (4-4), and flow meters (5-9), flow meters (5-8) and regulating valves (6-8) and (6-9) are respectively arranged on the spray pipeline, and are respectively connected to pressure regulator (12-1) and pressure regulator (12-2).

[0019] According to one or more embodiments of the present invention, the third loop is a cooling water branch of the plant. After the cooling water enters the heat exchanger (10-2), it absorbs the heat of the second loop.

[0020] According to one or more embodiments of the present invention, the structure in which the primary loop, the secondary loop and the downstream branch are connected is configured such that when the primary loop opens the regulating valve (6-4) and the secondary loop opens the regulating valve (6-18), the fluid enters the downstream branch, passes through the flow meter (5-12), enters the heat exchanger (10-1), and flows to the water storage tank (1-2) after cooling.

[0021] According to one or more embodiments of the present invention, the downstream branch is provided with a bypass. Before entering the heat exchanger (10-1), the bypass is provided with a flow meter (5-13) and a regulating valve (6-19). After merging with the heat exchanger (10-1), the water flows to the water storage tank (1-2).

[0022] According to one or more embodiments of the present invention, This invention provides a natural cycle test method, which uses the natural cycle test system described above to conduct natural cycle tests.

[0023] The positive and progressive effects of this invention include, but are not limited to, one or a combination of the following: 1. The system is compact and simplified. The entire test system only has an electric heating rod as a heat source in the first loop. There are no additional heat sources in the second loop, third loop and the drain branch. The structure is simpler, the operating efficiency is higher, and the energy consumption and control complexity are reduced.

[0024] 2. It realistically simulates natural circulation conditions. By heating the bottom to form natural convection, it can realistically simulate the natural circulation characteristics of integrated small reactors under steady-state and unsteady-state conditions, providing effective test data support for safety reviews.

[0025] 3. Closed-loop dual-loop design with good temperature controllability. The dual-loop adopts a closed-loop design and is equipped with a heat exchanger and two voltage regulators, which can accurately adjust the system pressure and temperature, improving the stability and repeatability of the test.

[0026] 4. Multi-loop coordination and complete functions, including water replenishment loop, primary loop, secondary loop, tertiary loop and discharge branch, covering the main processes in small reactor operation (heating, heat exchange, cooling, water replenishment and drainage, pressure relief, etc.), and has the ability to conduct overall performance tests.

[0027] 5. It has a safety protection mechanism, with spray pipelines and regulating valves, which can spray to reduce pressure when the small reactor body or pressurizer is overpressurized, thereby improving the safety of the test bench.

[0028] 6. Adjustable flow rate and accurate measurement: Multiple flow meters and regulating valves are installed to achieve precise control and real-time monitoring of flow in each branch, which is beneficial for data analysis and operating condition adjustment.

[0029] 7. Supports bypass adjustment, highly flexible, with a bypass system in the secondary loop and heat exchanger, which can be used to adjust the main flow rate and temperature to adapt to different test requirements and enhance system adaptability. Attached Figure Description

[0030] The above and other features, properties and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of a natural circulation test system for an integrated small modular reactor according to an embodiment of the present invention; Figure 2 This is a schematic flowchart of a natural circulation test method for an integrated small reactor according to an embodiment of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments and accompanying drawings. More details are set forth in the following description in order to provide a full understanding of the present invention. However, the present invention can obviously be implemented in many other ways different from those described herein. Those skilled in the art can make similar extensions and derivations based on actual application situations without departing from the spirit of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0033] In natural circulation test systems and methods for integrated small modular reactors, traditional test systems often employ a multi-heat source structure, such as adding heating devices to the secondary and tertiary loops, resulting in complex systems, high energy consumption, and high operating costs.

[0034] Based on this, please refer to Figure 1 This application proposes a natural circulation test system for an integrated small modular reactor (SMR), comprising: a water tank 1, a shut-off valve 2, a filter 3, a pump 4, a flow meter 5, a regulating valve 6, a check valve 7, an electric heater 8, a SMR body 9, a heat exchanger 10, a safety valve 11, and a pressure regulator 12.

[0035] The above components constitute the test system, which includes a water replenishment circuit, a primary circuit, a secondary circuit, a tertiary circuit, and a discharge branch. A heating source is only provided in the primary circuit; the secondary circuit, tertiary circuit, and discharge branch have no external heat sources. The water replenishment circuit connects to the primary and secondary circuits, enabling water replenishment to the primary and / or secondary circuits. The primary circuit is located inside the small reactor body and exchanges heat with the secondary circuit. The tertiary circuit absorbs heat from the secondary circuit. The primary and secondary circuits are connected to the discharge branch.

[0036] The meanings of the water supply circuit, primary circuit, secondary circuit, tertiary circuit, and downstream branch circuit are similar to their usual meanings in this field.

[0037] The primary loop is the core cooling loop on the nuclear side and the core verification object of the natural circulation test. It is necessary to measure parameters such as its circulation flow rate, core inlet and outlet temperature difference, pressure loss, and flow stability to verify the cooling capacity of the "passive drive".

[0038] The secondary loop is a non-nuclear side thermal circulation loop. In the experiment, it simulates the real thermal load. By adjusting the steam flow rate and pressure of the secondary loop, the heat output demand of the primary loop can be changed, and the natural circulation stability of the primary loop under different heat loads, such as the flow response when the transient load changes, can be verified.

[0039] The third loop is the final cooling loop. In the experiment, the cooling capacity of the second loop condenser was kept stable to ensure that the heat load boundary conditions of the second loop were controllable. For example, by adjusting the flow rate of the third loop, the vacuum degree of the condenser was controlled, which indirectly affected the heat exchange efficiency of the first loop and verified the adaptability of natural circulation under different heat exchange conditions.

[0040] The makeup water circuit is an auxiliary circuit, either primary, secondary, or tertiary, that replenishes the media lost due to leakage, evaporation, or sewage discharge, maintaining stable system liquid level, pressure, and water quality. It is divided into "nuclear-side makeup water" and "non-nuclear-side makeup water." It provides stable initial liquid level and pressure conditions for natural circulation tests and verifies the synergistic capability of the makeup water system with natural circulation in transient / accident condition simulations, such as whether passive makeup water meets the media requirements for long-term waste heat discharge.

[0041] The downstream branch, which enables controlled sewage discharge and achieves pressure regulation, water purification, and sampling monitoring of the primary and / or secondary circuits in the experiment, is classified as a "safety and auxiliary branch".

[0042] The following details the specific structure of the water supply circuit, primary circuit, secondary circuit, tertiary circuit, and discharge circuit.

[0043] Water supply circuit

[0044] In some embodiments, the water storage tank 1-1 of the water replenishment circuit is divided into two paths, one of which is connected to the shut-off valve 2-1, filter 3-2, pump 4-1, check valve 7-1, shut-off valve 2-3, flow meter 5-1 and electric heater 8 along the pipeline.

[0045] The other path connects to shut-off valve 2-2, filter 3-1, pump 4-2, check valve 7-2, shut-off valve 2-4, and flow meter 5-2 along the pipeline. After the two paths merge, water can be supplied to the first loop through regulating valves 6-10 and 6-3, or water can be supplied to the second loop through regulating valve 6-2.

[0046] In some embodiments, the pump 4-1 of the water replenishment circuit is equipped with a bypass circuit and a regulating valve 6-1 for regulating the water filling flow rate. (Continue to refer to...) Figure 1 As shown, after the two water supply circuits merge, water is sprayed into the test body through the spray pipeline via regulating valve 6-10, flow meter 5-3 and regulating valve 6-5.

[0047] First circuit

[0048] Continue to refer to Figure 1 The primary loop is located within the small reactor body 9 and is heated by bottom electric heating rods and heat exchanged with the secondary loop via a built-in heat exchanger, forming natural convection.

[0049] Two-circuit

[0050] The secondary loop comprises two main paths, with the fluid flow direction configured as follows: after being filtered by filter 3-3 / filter 3-4, the fluid originates from pump 4-3 / pump 4-4, flows through flow meter 5-5 / flow meter 5-4 and regulating valve 6-13 / regulating valve 6-14, and enters the heat exchange coil of the small reactor body for heat exchange. The fluid then flows out of the heat exchange coil, passes through regulating valve 6-15 / regulating valve 6-16, and merges with the flow source.

[0051] Continue to refer to Figure 1 After the fluids from the two loops merge, they flow through heat exchanger 10-2 for cooling.

[0052] The heat exchanger 10-2 is equipped with a bypass. After passing through the flow meter 5-10 and the regulating valve 6-17, the bypass flows into the water storage tank 1-2 after merging with the fluid in the heat exchanger 10-2.

[0053] In some embodiments, continue to refer to Figure 1 The secondary circuit is equipped with a bypass for regulating the flow rate of the main circuit of the secondary circuit. The bypass is equipped with flow meters 5-6 / 5-7 and regulating valves 6-11 / 6-12 in sequence, which merge with the main circuit fluid of the secondary circuit.

[0054] In some embodiments, the two main circuits of the dual circuit are respectively equipped with voltage regulator 12-1 and voltage regulator 12-2, and voltage regulator 12-1 and voltage regulator 12-2 are respectively equipped with shut-off valve 2-6 and shut-off valve 2-8.

[0055] Continue to refer to Figure 1 As shown, pump 4-3 and pump 4-4 outlets are equipped with dual-loop spray pipelines. Flow meters 5-9 and 5-8, and regulating valves 6-8 and 6-9 are respectively arranged on the spray pipelines and are connected to voltage stabilizer 12-1 and voltage stabilizer 12-2 respectively.

[0056] Three-circuit

[0057] In some embodiments, the third loop is a branch of the plant cooling water. After the cooling water enters the heat exchanger 10-2, it absorbs the heat from the second loop.

[0058] Downstream branch

[0059] The structure connecting the primary loop, the secondary loop, and the downstream branch is configured such that when the primary loop opens the regulating valve 6-4 and the secondary loop opens the regulating valve 6-18, the fluid enters the downstream branch, first passes through the flow meter 5-12, enters the heat exchanger 10-1, and after cooling, flows to the water storage tank 1-2.

[0060] In some embodiments, the drain branch is provided with a bypass. Before entering the heat exchanger 10-1, the bypass is equipped with a flow meter 5-13 and a regulating valve 6-19. After merging with the heat exchanger 10-1, the water flows to the water storage tank 1-2.

[0061] The following flowchart illustrates the operations performed according to the manufacturing method of the panel parts. It should be understood that, depending on the actual situation, the preceding or following operations may not be performed precisely in sequence. Other operations may be added to these processes, or one or more operations may be removed from them.

[0062] As described above, this invention also provides a natural circulation test method for integrated small modular reactors, employing the natural circulation test system described above, such as... Figure 2 As shown, the cyclic testing method may include the following steps: S100. Water is replenished through the water replenishment circuit. When replenishing water through the water replenishment circuit, open regulating valves 6-10 and 6-2, and start pump 4-1 to replenish water to the primary and secondary circuits.

[0063] S200. Pressurize the primary and secondary circuits. After water replenishment is completed, start pump 4-1 to pressurize the primary and secondary circuits.

[0064] S300. Heating the Small Reactor. Heating begins at the bottom core and top pressurizer of the Small Reactor Body 9. Simultaneously, pumps 4-3 and 4-4 are activated, and regulating valves 6-11, 6-12, 6-13, 6-14, 6-15, 6-16, 6-17, and 6-21 are set to ensure the secondary loop meets appropriate flow and heat requirements. The heating power of pressurizers 12-1 and 12-2 in the secondary loop is adjusted to achieve the required pressure. As the temperature and pressure of the primary loop increase, the secondary loop continuously matches the temperature, pressure, and flow rate of the fluid entering the heat exchanger within the Small Reactor Body 9.

[0065] During the experiment, flow meter 5 can be used to monitor the flow rate of each loop, and regulating valve 6 can be used to regulate the flow rate of each loop.

[0066] If overpressure occurs in the small reactor body 9 during the test, pump 4-1 will be started and regulating valves 6-10 and 6-5 will be opened to spray the built-in pressure regulator on the top of the small reactor body 9.

[0067] If overpressure occurs in voltage regulators 12-1 and 12-2 during the test, control valves 6-8 and 6-9 will be opened to spray voltage regulators 12-1 and 12-2.

[0068] S400. Cooling and depressurization. During cooling of the primary and secondary loops, the bottom core heating rods of the small reactor body 9 are shut off. Heat is transferred from the primary loop to the secondary loop, and then from the secondary loop to the tertiary loop. After cooling is complete, control valves 6-4 and 6-18 are opened to reduce the pressure of the primary and secondary loops.

[0069] In summary, the beneficial effects of the natural cycle test system and test method described in the above embodiments include, but are not limited to, one or a combination of the following: 1. The system is compact and simplified. The entire test system only has an electric heating rod as a heat source in the first loop. There are no additional heat sources in the second loop, third loop and the drain branch. The structure is simpler, the operating efficiency is higher, and the energy consumption and control complexity are reduced.

[0070] 2. It realistically simulates natural circulation conditions. By heating the bottom to form natural convection, it can realistically simulate the natural circulation characteristics of integrated small reactors under steady-state and unsteady-state conditions, providing effective test data support for safety reviews.

[0071] 3. Closed-loop dual-loop design with good temperature controllability. The dual-loop adopts a closed-loop design and is equipped with a heat exchanger and two voltage regulators, which can accurately adjust the system pressure and temperature, improving the stability and repeatability of the test.

[0072] 4. Multi-loop coordination and complete functions, including water replenishment loop, primary loop, secondary loop, tertiary loop and discharge branch, covering the main processes in small reactor operation (heating, heat exchange, cooling, water replenishment and drainage, pressure relief, etc.), and has the ability to conduct overall performance tests.

[0073] 5. It has a safety protection mechanism, with spray pipelines and regulating valves, which can spray to reduce pressure when the small reactor body or pressurizer is overpressurized, thereby improving the safety of the test bench.

[0074] 6. Adjustable flow rate and accurate measurement: Multiple flow meters and regulating valves are installed to achieve precise control and real-time monitoring of flow in each branch, which is beneficial for data analysis and operating condition adjustment.

[0075] 7. Supports bypass adjustment, highly flexible, with a bypass system in the secondary loop and heat exchanger, which can be used to adjust the main flow rate and temperature to adapt to different test requirements and enhance system adaptability.

[0076] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation", "connection", "joining", and "fixing" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can also refer to mechanical connections. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0077] This application uses specific terms to describe embodiments of the application. Terms such as "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of the application. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0078] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any variations and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the invention, fall within the protection scope defined by the claims of the present invention.

Claims

1. A testing system, characterized in that, include: Water supply circuit, primary circuit, secondary circuit, tertiary circuit, and downstream branch circuit; In this circuit, a heating source is provided only in the first circuit, while the second circuit, the third circuit, and the drain branch have no external heat source. The water replenishment circuit connects the first circuit and the second circuit, and the water replenishment circuit is used to replenish water to the first circuit and the second circuit; The first loop is located inside the small reactor body and is heated by the bottom electric heating rod. It exchanges heat with the second loop through the heat exchange structure built into the small reactor body (9) to form natural convection. The third loop absorbs the heat from the second loop. Both the first circuit and the second circuit are connected to the downstream branch; The water storage tank (1) of the water replenishment circuit is divided into two paths. One path is connected to the first shut-off valve (2-1), the second filter (3-2), the high-pressure water replenishment pump (4-1), the first check valve (7-1), the third shut-off valve (2-3), the first flow meter (5-1), and the electric heater (8) along the pipeline. Another route connects the second shut-off valve (2-2), the first filter (3-1), the low-pressure water supply pump (4-2), the second check valve (7-2), the fourth shut-off valve (2-4), and the second flow meter (5-2) along the pipeline. After the two water replenishment circuits merge, water is replenished to the first circuit through the eighth regulating valve (6-10) and the third regulating valve (6-3); water is replenished to the second circuit through the second regulating valve (6-2). After the two water replenishment circuits merge, the water also flows through the eighth regulating valve (6-10), the third flow meter (5-3), and the fifth regulating valve (6-5), and the water is sprayed into the small reactor body (9) through the spray pipeline.

2. The testing system as described in claim 1, characterized in that, The high-pressure water pump (4-1) of the water replenishment circuit is equipped with a bypass circuit and a first regulating valve (6-1) for adjusting the water filling flow rate of the high-pressure water pump (4-1) to the first circuit and / or the second circuit.

3. The testing system as described in claim 2, characterized in that, The secondary loop includes two main paths, and the flow direction of the fluid in the two main paths is as follows: after being filtered by the third filter (3-3), the fluid starts from the third pump (4-3), flows through the fifth flow meter (5-5) and the eleventh regulating valve (6-13), and enters the heat exchange coil of the small reactor body (9) for heat exchange; or, After being filtered by the fourth filter (3-4), the fluid starts from the fourth pump (4-4), flows through the fourth flow meter (5-4) and the twelfth regulating valve (6-14), and enters the heat exchange coil of the small stack body (9) for heat exchange; The water flows out from the heat exchange coil and merges after passing through the thirteenth regulating valve (6-15) or the fourteenth regulating valve (6-16).

4. The testing system as described in claim 3, characterized in that, After the fluids from the two main paths of the secondary loop merge, they flow through the second heat exchanger (10-2) for cooling.

5. The testing system as described in claim 4, characterized in that, The second heat exchanger (10-2) is provided with a bypass. After passing through the tenth flow meter (5-10) and the fifteenth regulating valve (6-17), the bypass merges with the fluid of the second heat exchanger (10-2) and flows into the water storage tank.

6. The testing system as described in claim 3, characterized in that, The secondary loop is provided with two bypasses, which are used to regulate the flow of the two main lines of the secondary loop respectively. One bypass is equipped with a sixth flow meter (5-6) and a ninth regulating valve (6-11) in sequence, and the other bypass is equipped with a seventh flow meter (5-7) and a tenth regulating valve (6-12). After the two bypasses merge, they are combined with the main line fluid of the secondary loop.

7. The testing system as described in claim 3, characterized in that, The two main circuits of the two circuits are respectively equipped with a first voltage regulator (12-1) and a second voltage regulator (12-2). The first voltage regulator (12-1) and the second voltage regulator (12-2) are respectively equipped with a fifth shut-off valve (2-6) and a sixth shut-off valve (2-8).

8. The testing system as described in claim 4, characterized in that, The three-loop circuit is a branch circuit for the plant cooling water. After the cooling water enters the second heat exchanger (10-2), it absorbs the heat from the second loop.

9. The testing system as described in claim 1, characterized in that, The structure connecting the primary circuit, the secondary circuit, and the downstream branch is configured such that when the primary circuit opens the fourth regulating valve (6-4) and the secondary circuit opens the sixteenth regulating valve (6-18), the fluid enters the downstream branch, passes through the eleventh flow meter (5-12), enters the first heat exchanger (10-1), and flows to the water storage tank after cooling.

10. The testing system as described in claim 9, characterized in that, The downstream branch is equipped with a bypass. Before entering the first heat exchanger (10-1), the bypass is equipped with a twelfth flow meter (5-13) and a seventeenth regulating valve (6-19). After merging with the first heat exchanger (10-1), the water flows to the storage tank.

11. A natural circulation test method for integrated small modular reactors, characterized in that, The test system described in any one of claims 1-10 is used.

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