Flow operation control method for intermediate loop of sodium-cooled fast reactor accident residual heat removal system

Abstract

The invention particularly relates to an intermediate loop flow operation control method for a sodium-cooled fast reactor accident waste heat removal system. The method comprises the following steps that 101, the state of the accident waste heat removal system is verified; 102, in the reactor power increasing process, the flow of an intermediate loop of the accident waste heat removal system is controlled to operate stably; and step 103, in the reactor power reduction process, controlling the flow of the intermediate loop of the accident residual heat removal system to operate stably. According to the flow operation control method for the intermediate loop of the sodium-cooled fast reactor accident waste heat removal system, the opening degree of an inlet and outlet air door of a sodium-air heat exchanger is adjusted and controlled and the electric heating temperature of a cold and hot section pipeline of the intermediate loop of the accident waste heat removal system is increased according to the change of the end difference of the cold and hot sections of the intermediate loop of the accident waste heat removal system; and it is ensured that the intermediate loop of the accident waste heat removal system can establish stable natural circulation flow.

Description

Technical Field

[0001] The invention relates to the technical field of sodium-cooled fast reactor reactors, and in particular to an intermediate loop flow rate operation control method for a sodium-cooled fast reactor accident residual heat removal system. Background Art

[0002] The accident residual heat removal system is a dedicated safety facility for sodium-cooled fast reactors. Its function is to remove residual heat when the reactor is shut down due to an expected operating event or a design basis accident, and the residual heat cannot be removed through the main heat transfer system. The accident residual heat removal system reduces the temperature of the core and reactor coolant at a certain rate to ensure that the fuel rods, reactor internals and reactor vessels are within an acceptable temperature limit range, ensuring that the reactor is in a safe state.

[0003] When the sodium-cooled fast reactor reactor is in power operation, power increase or decrease, shutdown and refueling conditions, the intermediate loop of the accident waste heat removal system needs to maintain a certain flow rate to ensure that a stable natural circulation capacity can be established. When the sodium-cooled fast reactor reactor is in power operation, shutdown and refueling conditions, the temperature inside the reactor is relatively stable, and the end difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is relatively stable, so the flow rate of the intermediate loop also tends to be stable. However, when the sodium-cooled fast reactor reactor is in the process of power increase or decrease, the temperature inside the reactor changes, resulting in a change in the end difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system, so the flow rate of the intermediate loop will also change, and it is necessary to pay close attention to the natural circulation capacity of the intermediate loop. Summary of the invention

[0004] The object of the present invention is to provide a flow operation control method for an intermediate loop of a sodium-cooled fast reactor accident waste heat removal system. According to the change of the terminal difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system, the opening of the inlet and outlet dampers of the sodium-air heat exchanger is adjusted and controlled, and the electric heating temperature of the cold and hot section pipelines of the intermediate loop of the accident waste heat removal system is increased, so as to ensure that the intermediate loop of the accident waste heat removal system can establish a stable natural circulation flow.

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

[0006] A method for controlling the flow rate of an intermediate loop of a sodium-cooled fast reactor accident residual heat removal system comprises the following steps:

[0007] Step 101, verifying the status of the accident waste heat removal system;

[0008] Step 102: During the reactor power increase process, the flow rate of the intermediate loop of the accident residual heat removal system is controlled to operate stably;

[0009] Step 103: During the reactor power reduction process, the flow rate of the intermediate loop of the accident residual heat removal system is controlled to operate stably.

[0010] As one of the feasible methods, step 101 needs to verify the following conditions of the accident waste heat removal system: the liquid level of the sodium buffer tank is between (1280 and 2870) mm; the blocking temperature of the accident waste heat removal system is lower than 180°C; the covering gas pressure of the accident waste heat removal system is between (0.05 and 0.35) MPa; the accident waste heat removal system is in hot standby condition, and the intermediate loop flow rate is greater than 5 kg / s; the inlet and outlet dampers of the sodium-air heat exchanger are available, and the initial state is fully closed; the electric heating temperature setting value of the intermediate loop pipeline of the accident waste heat removal system is (200°C to 250)°C.

[0011] As one of the feasible ways, in step 102, during the reactor power increase process, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is reduced by increasing the electric heating temperature of the cold section pipeline of the intermediate loop of the accident waste heat removal system, and the flow rate of the intermediate loop of the accident waste heat removal system is stabilized.

[0012] As one of the feasible ways, step 102, during the reactor power increase process, when the temperature of the cold section of the intermediate loop of the accident waste heat removal system is lower than 300°C, the electric heating temperature of the cold section pipeline of the intermediate loop of the accident waste heat removal system is increased at a rate not exceeding 0.5°C / min, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

[0013] As one of the feasible ways, in step 103, during the reactor power reduction process, by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger and increasing the electric heating temperature of the hot section of the intermediate loop of the accident waste heat discharge system, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat discharge system is increased, and the flow rate of the intermediate loop of the accident waste heat discharge system is stabilized.

[0014] As one of the achievable methods, in step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is ≥300°C or the temperature of the hot section of the intermediate loop of the accident waste heat removal system is <250°C, by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s;

[0015] When the temperature of the hot section of the intermediate loop of the accident waste heat removal system is 250℃≤<300℃, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is made greater than 2℃ by increasing the electric heating temperature of the hot section pipeline of the intermediate loop of the accident waste heat removal system, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

[0016] As one of the achievable methods, in step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is ≥300°C, by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s, including the following steps:

[0017] Adjust the inlet and outlet damper openings of the sodium-air heat exchanger to (1-10)%, and the inlet damper opening of the sodium-air heat exchanger to (0-100)%, so that the wall temperature of the lower heat exchange tube of the sodium-air heat exchanger slowly decreases and is not lower than 180°C, and the wall temperature of the upper heat exchange tube of the sodium-air heat exchanger is stable, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat discharge system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat discharge system is stable and greater than 5kg / s.

[0018] As one of the feasible ways, in step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is less than 250°C, the sodium temperature at the outlet of the sodium-air heat exchanger is made to be (205-250)°C by adjusting the inlet and outlet damper openings of the sodium-air heat exchanger to (0-5)%, the temperature difference between the hot and cold sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

[0019] As one of the feasible ways, the accident waste heat removal system includes an independent heat exchanger, a sodium buffer tank, a sodium-air heat exchanger and an extraction chimney; wherein, the tube side outlet of the independent heat exchanger is connected to the sodium buffer tank and the tube side inlet of the sodium-air heat exchanger in sequence through pipelines, forming a hot section of the intermediate loop of the accident waste heat removal system; the tube side outlet of the sodium-air heat exchanger is connected to the tube side inlet of the independent heat exchanger, forming a cold section of the intermediate loop in the accident waste heat removal system; the shell side inlet of the sodium-air heat exchanger is connected to the air through the inlet damper, and the shell side outlet of the sodium-air heat exchanger is connected to the extraction chimney through the outlet damper; the shell side inlet and outlet of the independent heat exchanger are both connected to the sodium of the first loop of the reactor.

[0020] Beneficial technical effects of the present invention:

[0021] The sodium-cooled fast reactor accident waste heat removal system intermediate loop flow operation control method of the present invention has been verified in the debugging and operation stages, and has achieved stable operation of the accident waste heat removal system intermediate loop flow during the reactor power increase or decrease process and reduced heat loss in the reactor; and has avoided the accident waste heat removal system intermediate loop flow interruption and loss of natural circulation during the reactor power increase or decrease process, and the sodium-air heat exchanger heat exchanger tube blockage.

[0022] The sodium-cooled fast reactor accident waste heat removal system intermediate loop flow operation control method of the present invention reduces the temperature difference between the cold and hot sections of the accident waste heat removal system intermediate loop by increasing the electric heating temperature of the cold section pipeline of the accident waste heat removal system intermediate loop during the reactor power increase process, thereby stabilizing the flow of the accident waste heat removal system intermediate loop and reducing heat loss in the reactor.

[0023] The sodium-cooled fast reactor accident waste heat removal system intermediate loop flow operation control method of the present invention reduces the temperature difference between the cold and hot sections of the accident waste heat removal system intermediate loop flow and stabilizes the accident waste heat removal system intermediate loop flow during the reactor power reduction process by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger and increasing the electric heating temperature of the hot section pipeline of the accident waste heat system.

[0024] The present invention provides a method for controlling the flow rate of an intermediate loop of an accident waste heat removal system of a sodium-cooled fast reactor. When the inlet and outlet dampers of a sodium-air heat exchanger are closed, there is a certain amount of air leakage. During the reactor power reduction process, it is found and verified through practice that the temperature of the heat exchange tube wall of the sodium-air heat exchanger can more quickly characterize the temperature change of the hot and cold sections of the intermediate loop of the accident waste heat removal system when the inlet and outlet dampers are opened at a small degree. This can better achieve the precise control of the opening degree of the inlet and outlet dampers of the sodium-air heat exchanger, thereby ensuring the stability of the natural circulation of the flow rate of the intermediate loop of the accident waste heat removal system during the reactor power increase and decrease process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a structural schematic diagram of an embodiment of a sodium-cooled fast reactor accident residual heat removal system.

[0026] In the figure, 1. Reactor; 2. Independent heat exchanger; 3. Sodium buffer tank; 4. Sodium-air heat exchanger; 5. Inlet damper; 6. Outlet damper; 7. Extraction chimney. DETAILED DESCRIPTION

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0028] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0029] The technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0030] refer to Figure 1 , showing a schematic structural diagram of an embodiment of a sodium-cooled fast reactor accident waste heat removal system, the accident waste heat removal system comprises an independent heat exchanger 2, a sodium buffer tank 3, a sodium-air heat exchanger 4 and an extraction chimney 7; wherein, the tube side outlet of the independent heat exchanger 2 is connected to the sodium buffer tank 3 and the tube side inlet of the sodium-air heat exchanger 4 in sequence through pipelines, forming a hot section of the intermediate loop of the accident waste heat removal system; the tube side outlet of the sodium-air heat exchanger 4 is connected to the tube side inlet of the independent heat exchanger 2, forming a cold section of the intermediate loop in the accident waste heat removal system; the shell side inlet of the sodium-air heat exchanger 4 is connected to the air through the inlet damper 5, and the shell side outlet of the sodium-air heat exchanger 4 is connected to the extraction chimney 7 through the outlet damper 6; the shell side inlet and outlet of the independent heat exchanger 2 are both connected to the sodium of the first loop of the reactor 1.

[0031] This embodiment provides a method for controlling the flow rate of an intermediate loop of a sodium-cooled fast reactor accident residual heat removal system, comprising the following steps:

[0032] Step 101, verifying the status of the accident waste heat removal system;

[0033] Step 102: During the reactor power increase process, the flow rate of the intermediate loop of the accident residual heat removal system is controlled to operate stably;

[0034] Step 103: During the reactor power reduction process, the flow rate of the intermediate loop of the accident residual heat removal system is controlled to operate stably.

[0035] In this embodiment, as one of the feasible methods, step 101 needs to verify the following states of the accident waste heat removal system: the liquid level of the sodium buffer tank 3 is at (1280~2870) mm; the blocking temperature of the accident waste heat removal system is lower than 180°C; the covering gas pressure of the accident waste heat removal system is at (0.05~0.35) MPa; the accident waste heat removal system is in hot standby condition, and the intermediate loop flow rate is greater than 5kg / s; the inlet and outlet dampers of the sodium-air heat exchanger 4 are available, and the initial state is fully closed; the electric heating temperature setting value of the intermediate loop pipeline of the accident waste heat removal system is (200℃~250)℃.

[0036] In this embodiment, as one of the feasible methods, in step 102, during the reactor power increase process, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is reduced by increasing the electric heating temperature of the cold section pipeline of the intermediate loop of the accident waste heat removal system, and the flow rate of the intermediate loop of the accident waste heat removal system is stabilized.

[0037] In this embodiment, as one of the feasible methods, step 102, during the reactor power increase process, when the temperature of the cold section of the intermediate loop of the accident waste heat removal system is lower than 300°C, the electric heating temperature of the cold section pipeline of the intermediate loop of the accident waste heat removal system is increased at a rate not exceeding 0.5°C / min, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

[0038] During the process of increasing the reactor power of the sodium-cooled fast reactor, the sodium temperature in the reactor 1 continues to rise, and the independent heat exchanger 2 transfers the sodium temperature in the reactor 1 to the hot section of the intermediate loop of the accident waste heat removal system, causing the temperature of the hot section of the intermediate loop of the accident waste heat removal system to rise; after the hot section of the intermediate loop of the accident waste heat removal system passes through the sodium-air heat exchanger 4, part of the heat is taken away by the air.

[0039] Because the accident waste heat removal system takes time to transfer heat, the temperature rise of the cold section of the intermediate loop of the accident waste heat removal system lags behind the temperature of the hot section, resulting in an increase in the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system, an increase in the flow rate of the intermediate loop of the accident waste heat removal system, and an increase in the natural circulation capacity of the flow rate of the intermediate loop of the accident waste heat removal system, while the heat dissipation increases.

[0040] Therefore, when the temperature of the cold section of the intermediate loop of the accident waste heat removal system is lower than 300°C, the electric heating temperature of the cold section of the pipeline of the intermediate loop of the accident waste heat removal system is increased at a rate not exceeding 0.5°C / min, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s, while reducing the heat dissipation of the reactor. The temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, which can ensure that there is no risk of flow interruption in the intermediate loop of the accident waste heat removal system.

[0041] In this embodiment, as one of the feasible ways, in step 103, during the reactor power reduction process, by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger 4 and increasing the electric heating temperature of the hot section of the intermediate loop of the accident waste heat discharge system, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat discharge system is increased, and the flow rate of the intermediate loop of the accident waste heat discharge system is stabilized.

[0042] In this embodiment, as one of the achievable methods, in step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is ≥300°C or the temperature of the hot section of the intermediate loop of the accident waste heat removal system is <250°C, by adjusting the inlet and outlet damper openings of the sodium-air heat exchanger 4, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s;

[0043] When the temperature of the hot section of the intermediate loop of the accident waste heat removal system is 250℃≤<300℃, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is made greater than 2℃ by increasing the electric heating temperature of the hot section pipeline of the intermediate loop of the accident waste heat removal system, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

[0044] During the power reduction process of the sodium-cooled fast reactor, the sodium temperature in the reactor continues to decrease, and the independent heat exchanger 2 transfers the sodium temperature in the reactor 1 to the hot section of the intermediate loop of the accident waste heat removal system, causing the temperature of the hot section of the intermediate loop of the accident waste heat removal system to decrease; after the temperature of the hot section of the intermediate loop of the accident waste heat removal system passes through the sodium-air heat exchanger 4, part of the heat is provided by the air.

[0045] Since the accident waste heat removal system takes time to transfer heat, the temperature of the hot section of the intermediate loop of the accident waste heat removal system drops faster than the temperature of the cold section, resulting in a decrease in the temperature difference between the hot and cold sections of the intermediate loop of the accident waste heat removal system, a decrease in the flow rate of the intermediate loop of the accident waste heat removal system, and a weakening of the natural circulation capacity of the flow rate of the intermediate loop of the accident waste heat removal system.

[0046] If the reactor power drops rapidly, the heat transfer in the accident waste heat removal system takes time, resulting in a continuous decrease in the temperature difference between the hot and cold sections of the intermediate loop of the accident waste heat removal system, and a continuous decrease or even interruption of the flow rate in the intermediate loop of the accident waste heat removal system.

[0047] In this embodiment, as one of the achievable methods, in step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is ≥300°C, by adjusting the inlet and outlet damper openings of the sodium-air heat exchanger 4, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s, including the following steps:

[0048] The inlet and outlet damper openings of the sodium-air heat exchanger 4 are adjusted to (1-10)%, and the inlet damper opening of the sodium-air heat exchanger 4 is adjusted to (0-100)%, so that the wall temperature of the lower heat exchange tube of the sodium-air heat exchanger 4 slowly decreases and is not lower than 180°C, and the wall temperature of the upper heat exchange tube of the sodium-air heat exchanger 4 is stable, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat discharge system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat discharge system is stable and greater than 5kg / s.

[0049] In this embodiment, as one of the feasible ways, in step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is less than 250°C, by adjusting the inlet and outlet damper opening of the sodium-air heat exchanger 4 to (0-5)%, the sodium temperature at the outlet of the sodium-air heat exchanger 4 is made to be (205-250)°C, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

[0050] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for controlling the flow rate of an intermediate loop of a sodium-cooled fast reactor accident residual heat removal system, characterized in that: The following steps are involved: Step 101, verifying the status of the accident waste heat removal system; Step 102: During the reactor power increase process, the flow rate of the intermediate loop of the accident residual heat removal system is controlled to operate stably; Step 103: During the reactor power reduction process, the flow rate of the intermediate loop of the accident residual heat removal system is controlled to operate stably.

2. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 1, characterized in that: Step 101, it is necessary to verify the following states of the accident waste heat removal system: the liquid level of the sodium buffer tank (3) is (1280~2870) mm; the blocking temperature of the accident waste heat removal system is lower than 180°C; the covering gas pressure of the accident waste heat removal system is (0.05~0.35) MPa; the accident waste heat removal system is in hot standby condition, and the intermediate loop flow is greater than 5kg / s; the inlet and outlet dampers of the sodium-air heat exchanger (4) are available, and the initial state is fully closed; the electric heating temperature setting value of the intermediate loop pipeline of the accident waste heat removal system is (200℃~250)℃.

3. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 1, characterized in that: Step 102, during the reactor power increase process, the temperature of the cold section pipeline of the intermediate loop of the accident waste heat removal system is increased by electrically heating the temperature, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is reduced, and the flow rate of the intermediate loop of the accident waste heat removal system is stabilized.

4. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 3 is characterized in that: Step 102, during the reactor power increase process, when the temperature of the cold section of the intermediate loop of the accident waste heat removal system is lower than 300°C, the electric heating temperature of the cold section pipeline of the intermediate loop of the accident waste heat removal system is increased at a rate not exceeding 0.5°C / min, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

5. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 1, characterized in that: Step 103, during the reactor power reduction process, by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger (4) and increasing the electric heating temperature of the hot section of the intermediate loop of the accident waste heat removal system, the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is increased, and the flow rate of the intermediate loop of the accident waste heat removal system is stabilized.

6. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 5, characterized in that: Step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is ≥300°C or the temperature of the hot section of the intermediate loop of the accident waste heat removal system is <250°C, by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger (4), the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2°C, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

7. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 5, characterized in that: Step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is 250℃≤<300℃, the electric heating temperature of the hot section pipeline of the intermediate loop of the accident waste heat removal system is increased, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2℃, and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5kg / s.

8. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 6, characterized in that: In step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is ≥300° C., by adjusting the opening of the inlet and outlet dampers of the sodium-air heat exchanger (4), the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2° C., and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5 kg / s, comprising the following steps: The inlet and outlet damper openings of the sodium-air heat exchanger (4) are adjusted to (1-10)%, and the inlet damper opening of the sodium-air heat exchanger (4) is adjusted to (0-100)%, so that the wall temperature of the heat exchange tube at the lower part of the sodium-air heat exchanger (4) shows a slow downward trend and is not lower than 180° C., and the wall temperature of the heat exchange tube at the upper part of the sodium-air heat exchanger (4) is stable, so that the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat discharge system is greater than 2° C., and the flow rate of the intermediate loop of the accident waste heat discharge system is stable and greater than 5 kg / s.

9. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to claim 6, characterized in that: In step 103, during the reactor power reduction process, when the temperature of the hot section of the intermediate loop of the accident waste heat removal system is less than 250° C., the sodium temperature at the outlet of the sodium-air heat exchanger (4) is adjusted to (0-5)% by adjusting the inlet and outlet damper openings of the sodium-air heat exchanger (4) to (205-250)° C., the temperature difference between the cold and hot sections of the intermediate loop of the accident waste heat removal system is greater than 2° C., and the flow rate of the intermediate loop of the accident waste heat removal system is stable and greater than 5 kg / s.

10. The method for controlling the flow rate of the intermediate loop of the sodium-cooled fast reactor accident residual heat removal system according to any one of claims 1 to 9, characterized in that: The accident waste heat removal system comprises an independent heat exchanger (2), a sodium buffer tank (3), a sodium-air heat exchanger (4) and an extraction chimney (7); wherein the tube side outlet of the independent heat exchanger (2) is connected to the sodium buffer tank (3) and the tube side inlet of the sodium-air heat exchanger (4) in sequence through pipelines, forming a hot section of an intermediate loop of the accident waste heat removal system; the tube side outlet of the sodium-air heat exchanger (4) is connected to the tube side inlet of the independent heat exchanger (2), forming a cold section of the intermediate loop of the accident waste heat removal system; the shell side inlet of the sodium-air heat exchanger (4) is connected to the air through an inlet damper (5), and the shell side outlet of the sodium-air heat exchanger (4) is connected to the extraction chimney (7) through an outlet damper (6); and the shell side inlet and outlet of the independent heat exchanger (2) are both connected to the sodium of the primary loop of the reactor (1).

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