A new type of nitrogen injection and oxygen control system for accident mitigation of high temperature gas cooled reactor

Abstract

The present application belongs to the technical field of nuclear power plant super design basis accident condition accident mitigation measures, and particularly relates to a new type of high temperature gas cooled reactor accident mitigation measures nitrogen injection oxygen control system. The high flow nitrogen injection system is intermediate aeration and lower exhaust. Under the super design basis accident condition, the one loop pipe break accident occurs in the reactor pressure vessel chamber and the loading and unloading main circulating chamber. After the high flow nitrogen supply system is put into operation, the initial nitrogen concentration environment of the above chambers is quickly established, and the oxygen concentration in the reactor building is reduced to a safe concentration range, preventing a large amount of oxygen from entering the reactor pressure vessel core. After the high flow nitrogen injection system creates the initial nitrogen concentration environment of the reactor building, the high flow nitrogen injection system is stopped, and then the low flow nitrogen injection system is started. The impact of the accident is effectively mitigated, secondary disasters are avoided, and large-scale release of radioactive fission products is prevented.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear power plant super-design basis accident condition accident mitigation measures, and particularly relates to a new type of high-temperature gas cooled reactor accident mitigation measures nitrogen injection oxygen control system. BACKGROUND

[0002] As a reactor type with fourth-generation nuclear power technology, the pebble bed modular high-temperature gas cooled reactor (hereinafter referred to as "high-temperature gas cooled reactor") has inherent safety characteristics. The high-temperature gas cooled reactor adopts fuel balls coated with graphite, and the core also adopts graphite as a moderator. Therefore, the high-temperature gas cooled reactor reactor pressure vessel must prevent oxygen and water vapor from entering to avoid redox reaction with graphite to generate flammable and explosive gas. Especially in the super-design basis accident condition of the unisolable break of the high-temperature gas cooled reactor primary loop system at the upper and lower two places (feed pipe and discharge pipe), the flow channel formed will cause a large amount of oxygen to enter the reactor pressure vessel, causing more serious consequences. In order to avoid the occurrence of the above accident sequence, the effective method is to quickly control the oxygen concentration in the ambient air of the pipe break area, and reduce the oxygen concentration to a safe range by rapidly injecting a large amount of nitrogen.

[0003] In order to achieve the above-mentioned goal, a set of high-temperature gas cooled reactor specific accident mitigation measures, a nitrogen making and oxygen control system, is designed. Through the continuous operation of the nitrogen making and oxygen control system after the above accident condition, the nitrogen concentration in the pipe break accident area of the primary loop system and the reactor plant is maintained in a safe concentration range, avoiding a large amount of oxygen entering the reactor pressure vessel and causing redox reaction with graphite. SUMMARY

[0004] The purpose of the present application is to provide a new type of high-temperature gas cooled reactor accident mitigation measures nitrogen injection oxygen control system, which is used when the high-temperature gas cooled reactor occurs in a super-design basis accident condition, effectively mitigates the impact of the accident, avoids secondary disasters, and causes large-scale release of radioactive fission products.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] The application discloses a new type of high temperature gas cooled reactor accident mitigation measure nitrogen injection oxygen control system, which comprises a large flow nitrogen injection system and a small flow nitrogen injection system, wherein the large flow nitrogen injection system comprises a large flow nitrogen supply system and an exhaust purification system, and the small flow nitrogen injection system comprises a nitrogen production system and a nitrogen back gas system; the large flow nitrogen injection system is used for middle air charging and lower air exhausting; in a design basis accident condition, a one loop pipe break accident occurs in a reactor pressure vessel cabin and a loading and unloading main circulating cabin; after the large flow nitrogen supply system is put into operation, an initial nitrogen concentration environment of the cabin is rapidly established, and the oxygen concentration of the reactor plant internal environment is reduced to a safe concentration range, thereby preventing a large amount of oxygen from entering the reactor pressure vessel core; the reactor plant is maintained in a relative negative pressure state through the exhaust amount of the exhaust purification system being greater than the nitrogen supply amount of the large flow nitrogen supply system, thereby preventing the release of radioactive substances to the outdoor environment; after the large flow nitrogen injection system creates the initial nitrogen concentration environment of the reactor plant, the large flow nitrogen injection system is stopped, and then the small flow nitrogen injection system is started; the small flow nitrogen injection system is used for middle air charging and lower air exhausting; the nitrogen concentration of the reactor plant internal environment is continuously improved and maintained through continuous operation of the small flow nitrogen injection system; and the reactor plant is maintained in a relative positive pressure state through the nitrogen production amount of the nitrogen production system being greater than the back gas amount of the nitrogen back gas system, thereby preventing the entry of oxygen into the indoor atmospheric environment.

[0007] The large flow nitrogen supply system comprises a liquid nitrogen tank group, an electric ball valve, a buffer tank, a pressure reducing valve, a check valve, a manual stop valve, a flow meter, an electric regulating valve and a nitrogen pipeline; the outlet of the liquid nitrogen tank group is connected with the inlet of the electric ball valve through the nitrogen pipeline; the outlet of the electric ball valve is connected with the inlet of the buffer tank through the nitrogen pipeline; the outlet of the buffer tank is connected with the inlet of the pressure reducing valve through the nitrogen pipeline; the outlet of the pressure reducing valve is connected with the inlet of the check valve through the nitrogen pipeline; the outlet of the check valve is connected with the inlet of the manual stop valve through the nitrogen pipeline; the outlet of the manual stop valve is connected with the inlet of the electric regulating valve through the nitrogen pipeline; the manual stop valve and the electric regulating valve are provided with the flow meter on the middle pipeline; the outlet of the electric regulating valve is connected with the nitrogen pipeline into the reactor plant; and each reactor pressure vessel cabin and loading and unloading main circulating cabin are connected to each branch pipe on the gas supply annular pipeline.

[0008] The exhaust air purification system comprises an iodine adsorber, a centrifugal fan, an electric air duct sealing valve, an air duct type regulating valve, an air duct type flow meter, and exhaust air pipes.

[0009] The nitrogen making system comprises a pressure reducing valve, a check valve, a manual stop valve, a flow meter, an electric regulating valve, a complete set of nitrogen making equipment, and nitrogen pipes.

[0010] The nitrogen gas exhaust system comprises a manual stop valve, a flow meter, an electric regulating valve, a tee joint, and nitrogen pipes.

[0011] The complete set of nitrogen making equipment comprises an air compressor unit, a wet air buffer tank, a drying and purifying unit, an activated carbon filter, a dry air buffer tank, a nitrogen making unit, a nitrogen process tank, a nitrogen storage tank, and nitrogen making equipment connecting pipes.

[0012] The present application has the following advantages:

[0013] Nitrogen injection and oxygen control system is a unique accident mitigation measure for high temperature gas cooled reactor under the condition of beyond design basis accident, which belongs to the new system. By injecting nitrogen gas into the reactor building and the accident area quickly, the oxygen concentration is reduced to the safe range, and the nitrogen concentration in the reactor building is maintained in stages to avoid the risk of explosion in the case of beyond design basis accident. Compared with the passive injection system used by pressurized water reactor, the nitrogen injection and oxygen control system has lower cost, simple system composition and convenient operation. The investment of the system will not cause any impact on the reactor core. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a process flow chart of a new type of high temperature gas cooled reactor accident mitigation measure nitrogen injection and oxygen control system;

[0015] Figure 2 It is a process layout of a complete nitrogen generating equipment;

[0016] In the figure: large flow nitrogen supply system 1; exhaust air purification system 2; liquid nitrogen tank group 3; electric ball valve 4; buffer tank 5; pressure reducing valve 6; check valve 7; manual stop valve 8; flow meter 9; electric regulating valve 10; nitrogen pipeline 11; iodine adsorber 12; centrifugal fan 13; electric air duct sealing valve 14; air duct type regulating valve 15; air duct type flow meter 16; exhaust air pipeline 17; nitrogen generating system 18; nitrogen gas return system 19; complete nitrogen generating equipment 20; three-way connector 21; air compressor unit 22; wet air buffer tank 23; drying and purification unit 24; activated carbon filter 25; dry air buffer tank 26; nitrogen generating unit 27; nitrogen process tank 28; nitrogen storage tank 29; nitrogen generating equipment connecting pipe 30. DETAILED DESCRIPTION

[0017] The application will be described in detail below in combination with the drawings and specific examples.

[0018] The nitrogen-oxygen control system is divided into two subsystems: a large flow nitrogen injection system and a small flow nitrogen injection system. The large flow nitrogen injection system includes one large flow nitrogen supply system 1 and one exhaust purification system 2. The large flow nitrogen supply system includes one set of liquid nitrogen tank group 3 and its outlet electric ball valve 4, one buffer tank 5, one set of pressure reducing valve 6, one check valve 7, six manual cut-off valves 8, eleven sets of flow meters 9, seventeen electric regulating valves 10, and nitrogen pipelines 11. The exhaust purification system includes one set of iodine adsorber 12, two centrifugal fans 13, four electric air duct sealing valves 14, two air duct type regulating valves 15, one air duct type flow meter 16, and exhaust pipelines 17. The small flow nitrogen injection system includes three sets of nitrogen generation systems 18 and three sets of nitrogen back gas systems 19. Each set of nitrogen generation system includes one set of complete nitrogen generation equipment 20, one set of pressure reducing valve 6, one electric regulating valve 10, one check valve 7, one set of flow meter 9, and nitrogen pipelines 11. Each set of complete nitrogen generation equipment includes one set of air compressor unit 22, one wet air buffer tank 23, one set of drying and purification unit 24, one set of activated carbon filter 25, one dry air buffer tank 26, one set of nitrogen generation unit 27, one nitrogen process tank 28, one nitrogen storage tank 29, and nitrogen generation equipment connecting pipelines 30. Each set of nitrogen back gas system includes one electric regulating valve 10, two manual cut-off valves 8, two sets of flow meters 9, one three-way connecting piece 21, and nitrogen pipelines 11.

[0019] The large flow nitrogen injection system has the following functions: The large flow nitrogen injection system adopts an air flow design scheme of intermediate aeration and lower exhaust. Under the condition of a design reference accident, the one-loop pipe break accident occurs in the reactor pressure vessel chamber (the chamber where the feed pipe is located) and the loading and unloading main circulating chamber (the chamber where the discharge pipe is located). After the large flow nitrogen injection system is put into operation, the initial nitrogen concentration environment (the nitrogen concentration is not less than 95%) of the above-mentioned chambers can be quickly established, and at the same time, the oxygen concentration in the internal environment of the reactor building is reduced to a safe concentration range (the oxygen concentration is reduced to below 12.5%), preventing a large amount of oxygen from entering the reactor pressure vessel core. Through the difference between the exhaust capacity of the exhaust purification system and the nitrogen supply capacity of the large flow nitrogen supply system, the reactor building is maintained in a relatively negative pressure state, preventing the release of radioactive substances to the outdoor environment. After the large flow nitrogen injection system creates the initial nitrogen concentration environment of the reactor building, the large flow nitrogen injection system is stopped, and then the small flow nitrogen injection system is started.

[0020] The small flow nitrogen injection system has the following functions: The small flow nitrogen injection system adopts an air flow design scheme of intermediate aeration and lower exhaust. Through the continuous operation of the small flow nitrogen injection system, the nitrogen concentration in the internal environment of the reactor building is continuously improved and maintained, and through the difference between the nitrogen generation capacity of the nitrogen generation system and the back gas capacity of the nitrogen back gas system, the reactor building is maintained in a relatively positive pressure state, preventing the entry of oxygen into the indoor atmospheric environment. The system equipment, valves, and pipelines and their supports can withstand the safe shutdown earthquake.

[0021] The nitrogen-oxygen control system is divided into two subsystems: a large flow nitrogen injection system and a small flow nitrogen injection system. The large flow nitrogen injection system adopts a gas flow design scheme of middle aeration and lower exhaust. Under the super design reference accident condition, the one-loop pipe break accident occurs in the reactor pressure vessel chamber (the chamber where the feed pipe is located) and the main circulating chamber for loading and unloading (the chamber where the discharge pipe is located). After the large flow nitrogen injection system is put into operation, the initial nitrogen concentration environment (the nitrogen concentration is not less than 95%) of the above-mentioned chambers can be quickly established, and at the same time, the oxygen concentration in the internal environment of the reactor building is reduced to a safe concentration range (the oxygen concentration is reduced to below 12.5%), preventing a large amount of oxygen from entering the reactor pressure vessel core. Through the exhaust amount of the exhaust purification system being greater than the nitrogen supply amount of the large flow nitrogen supply system, the reactor building is maintained in a relatively negative pressure state to prevent the release of radioactive substances to the outdoor environment. After the large flow nitrogen injection system creates the initial nitrogen concentration environment of the reactor building, the large flow nitrogen injection system is stopped, and then the small flow nitrogen injection system is started. The small flow nitrogen injection system adopts a gas flow design scheme of middle aeration and lower exhaust. Through the continuous operation of the small flow nitrogen injection system, the nitrogen concentration in the internal environment of the reactor building is continuously improved and maintained, and through the nitrogen production amount of the nitrogen production system being greater than the nitrogen return amount of the nitrogen return system, the reactor building is maintained in a relatively positive pressure state to prevent the entry of oxygen into the indoor atmospheric environment.

[0022] The large flow nitrogen supply system operation scheme: when the above-mentioned super design basis accident condition occurs, the downstream electric ball valve (normally closed) of the liquid nitrogen tank is opened in turn, the liquid nitrogen is expanded and gasified after pressure reduction, enters the buffer tank, is reduced in pressure by a group of pressure reducing valves (reduced to 1 MPa), and the nitrogen enters the reactor building through the nitrogen main pipe. A hand-operated stop valve (for flow adjustment during commissioning), a check valve (to prevent backflow of nitrogen), a group of flow meters (for monitoring the amount of nitrogen supply), and an electric regulating valve (opened during system operation, normally closed, set outside the boundary of the reactor building to ensure the integrity of the pressure boundary of the reactor building) are also provided on the main pipe. After entering the reactor building, the nitrogen enters the nitrogen loop which is symmetrically arranged relative to the C-shaped building layout of the reactor building. The nitrogen loop is provided with 13 branches, of which 3 branches supply nitrogen to the reactor building, with an angle of 120° between them, and a normally open hand-operated stop valve (for flow adjustment during commissioning) is provided at the end of each branch; 10 branches are connected to 10 reactor pressure vessel compartments and loading and unloading main circulating compartments, respectively, and an electric regulating valve (normally closed, opened when power is lost, which can also be used for remote adjustment of nitrogen flow during system operation) and a group of flow meters are provided outside each compartment, and the downstream of the group of flow meters is divided into two sub-branches to introduce nitrogen into the two compartments. Nitrogen enters the reactor building, the reactor pressure vessel compartment and the loading and unloading main circulating compartment where the pipe break accident occurs through the above-mentioned nitrogen loop, branch and sub-branch. In view of the single failure criterion requirement, it is considered that only one reactor pressure vessel compartment and loading and unloading main circulating compartment have a one-loop system up and down pipe break accident. The electric regulating valve outside the compartment where the pipe break accident occurs is remotely opened, and the electric regulating valve outside the other compartments where no pipe break accident occurs remains closed.

[0023] The exhaust air purification system operation scheme: the system is operated simultaneously with the large flow nitrogen supply system to purify and discharge radioactive substances, and the relative negative pressure state of the reactor building is maintained by setting the difference between the supply and exhaust air flow rates to prevent the release of radioactive substances to the outdoor environment. Two exhaust air branches are provided at the bottom of the reactor building, symmetrically arranged on both sides of the C-shaped port of the reactor building, and the leaked one-loop helium and other gases in the internal environment of the reactor building are discharged from the reactor building through the two exhaust air branches, then enter the exhaust air main pipe, and then enter the iodine adsorber for deiodination purification treatment, and then are discharged to the chimney by the exhaust fan (1 for use and 1 as a backup), and then are discharged to the outdoor atmosphere through the chimney. An electric air duct sealing valve (opened during system operation, normally closed, set outside the boundary of the reactor building to ensure the integrity of the pressure boundary of the reactor building) is provided in each exhaust branch. An electric air duct sealing valve (opened during system operation, normally closed, to ensure that the system is isolated from other systems when it is shut down) and an air duct type regulating valve (for air flow balance during commissioning) are provided at the outlet and inlet of the exhaust fan, respectively. A group of air duct type flow meters (for monitoring the exhaust air flow rate) are provided downstream of the exhaust fan.

[0024] The operation scheme of the nitrogen production system: The complete nitrogen production equipment of the nitrogen production system adopts centralized control. When the nitrogen concentration in the reactor building reaches 87.5%, the complete nitrogen production equipment is started by one button. The fresh air is pressurized by the air compressor unit, enters the wet air buffer tank, then enters the drying and purification unit for treatment, enters the activated carbon filter, is purified again, enters the dry air buffer tank, and then enters the nitrogen production unit to produce nitrogen. The downstream of the nitrogen production unit is provided with a nitrogen process tank and a nitrogen storage tank. The produced nitrogen is depressurized by the pressure reducing valve group, and then enters the reactor building through the low-flow nitrogen supply pipeline. A manual stop valve (for flow adjustment during debugging), a check valve (to prevent nitrogen backflow), a flow meter (for nitrogen supply amount monitoring), and an electric regulating valve (opened during system operation for flow adjustment during operation, normally closed, arranged outside the pressure boundary of the reactor building to ensure the integrity of the pressure boundary of the reactor building) are arranged on the dry road of the nitrogen production system. The system is provided with three sets of complete nitrogen production equipment, and the nitrogen supply pipelines are independently arranged and arranged in three directions of the reactor building to maintain the uniformity of the nitrogen concentration. Each set of nitrogen production equipment provides 500 Nm 3 / h of nitrogen, and three sets of equipment provide 1500 Nm 3 / h of nitrogen.

[0025] The operation scheme of the nitrogen back gas system: The nitrogen back gas system relies on the negative pressure provided by the air compressor unit to extract gas from the reactor building into the air compressor unit, so that the internal gas of the reactor building circulates and flows, continuously discharges oxygen, and gradually increases the concentration of nitrogen in the reactor building. The system is provided with an electric regulating valve (opened during system operation for flow adjustment during operation, normally closed, arranged outside the pressure boundary of the reactor building to ensure the integrity of the pressure boundary of the reactor building) outside the reactor building. A three-way connector for the convergence of back air and fresh air is arranged at the air inlet of the air compressor unit. A manual stop valve and a flow meter are arranged on the back air and fresh air branches for adjusting and monitoring the flow of back air and fresh air, keeping the back air flow of each system at 300 Nm 3 / h, and the fresh air flow at 200 Nm 3 / h.

[0026] The large flow nitrogen supply system 1 comprises: a liquid nitrogen tank group 3, an electric ball valve 4, a buffer tank 5, a pressure reducing valve 6, a check valve 7, a manual stop valve 8, a flow meter 9, an electric regulating valve 10, and a nitrogen pipeline 11. The outlet of the liquid nitrogen tank group 3 is connected to the inlet of the electric ball valve 4 through the nitrogen pipeline 11, the outlet of the electric ball valve 4 is connected to the inlet of the buffer tank 5 through the nitrogen pipeline 11, the outlet of the buffer tank 5 is connected to the inlet of the pressure reducing valve 6 through the nitrogen pipeline 11, the outlet of the pressure reducing valve 6 is connected to the inlet of the check valve 7 through the nitrogen pipeline 11, the outlet of the check valve 7 is connected to the inlet of the manual stop valve 8 through the nitrogen pipeline 11, the outlet of the manual stop valve 8 is connected to the inlet of the electric regulating valve 10 through the nitrogen pipeline 11, the flow meter 9 is arranged on the pipeline between the manual stop valve 8 and the electric regulating valve 10, and the outlet of the electric regulating valve 10 is connected to the nitrogen pipeline 11 into the reactor building through a gas supply annular pipeline and connected to each reactor pressure vessel chamber and loading and unloading main circulating chamber through each branch pipeline.

[0027] The exhaust air purification system 2 comprises: an iodine adsorber 12, a centrifugal fan 13, an electric air duct sealing valve 14, an air duct type regulating valve 15, an air duct type flow meter 16, and an exhaust air pipeline 17. Two exhaust air pipelines 17 are connected to the inlets of the electric air duct sealing valves 14 after leaving the reactor building, the outlets of the electric air duct sealing valves 14 are connected to the inlets of the iodine adsorber 12 through the exhaust air pipelines 17, the outlet of the iodine adsorber 12 is divided into two parts through the exhaust air pipelines 17 and connected to the inlets of the air duct type regulating valves 15 of each branch, the outlets of the air duct type regulating valves 15 are connected to the inlets of the centrifugal fan 13 through the exhaust air pipelines 17, the outlet of the centrifugal fan 13 is connected to the inlet of the electric air duct sealing valve 14 through the exhaust air pipeline 17, and the outlet of the electric air duct sealing valve 14 is connected to a chimney through the exhaust air pipeline 17, and the air duct type flow meter 16 is arranged on the upstream exhaust air pipeline 17 of the chimney.

[0028] The nitrogen making system 18 comprises: a pressure reducing valve 6, a check valve 7, a manual stop valve 8, a flow meter 9, an electric regulating valve 10, a complete set of nitrogen making equipment 20, and a nitrogen pipeline 11. The outlet of the complete set of nitrogen making equipment 20 is connected to the inlet of the pressure reducing valve 6 through the nitrogen pipeline 11, the outlet of the pressure reducing valve 6 is connected to the inlet of the check valve 7 through the nitrogen pipeline 11, the outlet of the check valve 7 is connected to the inlet of the manual stop valve 8 through the nitrogen pipeline 11, the flow meter 9 is arranged on the pipeline between the check valve 7 and the manual stop valve 8, the outlet of the manual stop valve 8 is connected to the inlet of the electric regulating valve 10 through the nitrogen pipeline 11, and the outlet of the electric regulating valve 10 is connected to the nitrogen pipeline 11 into the reactor building.

[0029] The nitrogen back gas system 19 comprises a manual stop valve 8, a flow meter 9, an electric regulating valve 10, a three-way connector 21 and a nitrogen pipeline 11. The nitrogen pipeline 11 is connected to the inlet of the electric regulating valve 10 outside the reactor building, the outlet of the electric regulating valve 10 is connected to the inlet of the manual stop valve 8 through the nitrogen pipeline 11, the flow meter 9 is arranged on the pipeline between the electric regulating valve 10 and the manual stop valve 8, the outlet of the manual stop valve 8 is connected to one end of the three-way connector 21 through the nitrogen pipeline 11, the other end of the three-way connector 21 is connected to the outlet of the manual stop valve 8, the inlet of the manual stop valve 8 is connected to a pipeline for indoor air intake, and the flow meter 9 is arranged on the pipeline.

[0030] The complete nitrogen generating equipment comprises an air compressor unit 22, a wet air buffer tank 23, a drying and purifying unit 24, an activated carbon filter 25, a dry air buffer tank 26, a nitrogen generating unit 27, a nitrogen process tank 28, a nitrogen storage tank 29 and a nitrogen generating equipment connecting pipeline 30. The outlet of the air compressor unit 22 is connected to the inlet of the wet air buffer tank 23 through the nitrogen generating equipment connecting pipeline 30, the outlet of the wet air buffer tank 23 is connected to the inlet of the drying and purifying unit 24 through the nitrogen generating equipment connecting pipeline 30, the outlet of the drying and purifying unit 24 is connected to the inlet of the activated carbon filter 25 through the nitrogen generating equipment connecting pipeline 30, the outlet of the activated carbon filter 25 is connected to the inlet of the dry air buffer tank 26 through the nitrogen generating equipment connecting pipeline 30, the outlet of the dry air buffer tank 26 is connected to the inlet of the nitrogen generating unit 27 through the nitrogen generating equipment connecting pipeline 30, the outlet of the nitrogen generating unit 27 is connected to the inlet of the nitrogen process tank 28 through the nitrogen generating equipment connecting pipeline 30, the outlet of the nitrogen process tank 28 is connected to the inlet of the nitrogen storage tank 29 through the nitrogen generating equipment connecting pipeline 30, and the outlet of the nitrogen storage tank 29 is connected to the main pipeline of the nitrogen generating system.

Claims

1. A novel Nitrogen injection Oxygen control system for accident mitigation measures of a High Temperature Gas-cooled Reactor characterized in that: The system comprises a large-flow nitrogen injection system and a small-flow nitrogen injection system, the large-flow nitrogen injection system comprises a large-flow nitrogen supply system and an exhaust purification system, and the small-flow nitrogen injection system comprises a nitrogen generation system and a nitrogen back gas system; the large-flow nitrogen injection system is used for middle charging and lower exhausting, and under a super design reference accident condition, a one-loop pipe break accident occurs in a reactor pressure vessel cabin and a loading and unloading main circulating cabin, after the large-flow nitrogen supply system is put into operation, an initial nitrogen concentration environment of the cabins is rapidly established, and the oxygen concentration in the reactor building is reduced to a safe concentration range, thereby preventing a large amount of oxygen from entering the reactor pressure vessel core; the exhaust amount of the exhaust purification system is greater than the nitrogen supply amount of the large-flow nitrogen supply system, so that the reactor building is maintained in a relatively negative pressure state, thereby preventing the release of radioactive substances to the outdoor environment; after the large-flow nitrogen injection system creates the initial nitrogen concentration environment of the reactor building, the large-flow nitrogen injection system is stopped, and then the small-flow nitrogen injection system is started; the small-flow nitrogen injection system is used for middle charging and lower exhausting, the nitrogen concentration in the reactor building is continuously increased and maintained through continuous operation of the small-flow nitrogen injection system, and the nitrogen generation amount of the nitrogen generation system is greater than the back gas amount of the nitrogen back gas system, so that the reactor building is maintained in a relatively positive pressure state, thereby preventing the entry of oxygen into the indoor atmospheric environment.

2. The novel high temperature gas-cooled reactor accident mitigation measures nitrogen injection oxygen control system according to claim 1, characterized in that: The large-flow nitrogen supply system comprises a liquid nitrogen tank group, an electric ball valve, a buffer tank, a pressure reducing valve, a check valve, a manual stop valve, a flowmeter, an electric regulating valve and a nitrogen pipeline, the outlet of the liquid nitrogen tank group is connected with the inlet of the electric ball valve through the nitrogen pipeline, the outlets of the electric ball valve are connected with the inlet of the buffer tank through the nitrogen pipeline, the outlet of the buffer tank is connected with the inlet of the pressure reducing valve through the nitrogen pipeline, the outlet of the pressure reducing valve is connected with the inlet of the check valve through the nitrogen pipeline, the outlet of the check valve is connected with the inlet of the manual stop valve through the nitrogen pipeline, the outlet of the manual stop valve is connected with the inlet of the electric regulating valve through the nitrogen pipeline, the flowmeter is arranged on the pipeline between the manual stop valve and the electric regulating valve, the outlet of the electric regulating valve is connected with the nitrogen pipeline which enters the reactor building, and each reactor pressure vessel cabin and the loading and unloading main circulating cabin are connected to each branch pipe on the gas supply annular pipeline.

3. The novel high temperature gas cooled reactor accident mitigation measures nitrogen injection oxygen control system according to claim 1, characterized in that: The exhaust purification system comprises an iodine adsorber, a centrifugal fan, an electric air duct sealing valve, an air duct type regulating valve, an air duct type flowmeter and an exhaust pipeline, two exhaust pipelines are connected with the inlets of the electric air duct sealing valves after exiting the reactor building, the outlets of the electric air duct sealing valves are connected with the inlet of the iodine adsorber through the exhaust pipeline, the outlet of the iodine adsorber is divided into branches and connected with the inlets of the air duct type regulating valves, the outlets of the air duct type regulating valves are connected with the inlet of the centrifugal fan through the exhaust pipeline, the outlet of the centrifugal fan is connected with the inlet of the electric air duct sealing valve on the branch through the exhaust pipeline, the outlets of the electric air duct sealing valves are connected with a chimney through the exhaust pipeline after being converged, and the air duct type flowmeter is arranged on the exhaust pipeline upstream of the chimney.

4. The novel high temperature gas-cooled reactor accident mitigation measures nitrogen injection oxygen control system according to claim 1, characterized in that: The nitrogen system comprises a pressure reducing valve, a check valve, a manual stop valve, a flow meter, an electric regulating valve, a complete nitrogen generating device, and a nitrogen pipeline, the outlet of the complete nitrogen generating device is connected to the inlet of the pressure reducing valve through the nitrogen pipeline, the outlet of the pressure reducing valve is connected to the inlet of the check valve through the nitrogen pipeline, the outlet of the check valve is connected to the inlet of the manual stop valve through the nitrogen pipeline, the flow meter is arranged on the pipeline between the check valve and the manual stop valve, the outlet of the manual stop valve is connected to the inlet of the electric regulating valve through the nitrogen pipeline, and the outlet of the electric regulating valve is connected to the nitrogen pipeline entering the reactor building.

5. The novel high temperature gas-cooled reactor accident mitigation measures nitrogen injection and oxygen control system according to claim 1, characterized in that: The nitrogen back-gas system comprises a manual stop valve, a flow meter, an electric regulating valve, a tee connector, and a nitrogen pipeline, the outlet of the reactor building is connected to the inlet of the electric regulating valve, the outlet of the electric regulating valve is connected to the inlet of the manual stop valve through the nitrogen pipeline, the flow meter is arranged on the pipeline between the electric regulating valve and the manual stop valve, the outlet of the manual stop valve is connected to one end of the inlet of the tee connector through the nitrogen pipeline, the other end of the inlet of the tee connector is connected to the outlet of the manual stop valve, and the inlet of the manual stop valve is connected to a pipeline for indoor air intake, and the flow meter is arranged on the pipeline.

6. The novel high temperature gas-cooled reactor accident mitigation measures nitrogen injection oxygen control system according to claim 4, characterized in that: The complete nitrogen generating device comprises an air compressor unit, a wet air buffer tank, a drying and purifying unit, an activated carbon filter, a dry air buffer tank, a nitrogen generating unit, a nitrogen process tank, a nitrogen storage tank, and a nitrogen generating device connecting pipeline, the outlet of the air compressor unit is connected to the inlet of the wet air buffer tank through the nitrogen generating device connecting pipeline, the outlet of the wet air buffer tank is connected to the inlet of the drying and purifying unit through the nitrogen generating device connecting pipeline, the outlet of the drying and purifying unit is connected to the inlet of the activated carbon filter through the nitrogen generating device connecting pipeline, the outlet of the activated carbon filter is connected to the inlet of the dry air buffer tank through the nitrogen generating device connecting pipeline, the outlet of the dry air buffer tank is connected to the inlet of the nitrogen generating unit through the nitrogen generating device connecting pipeline, the outlet of the nitrogen generating unit is connected to the inlet of the nitrogen process tank through the nitrogen generating device connecting pipeline, the outlet of the nitrogen process tank is connected to the inlet of the nitrogen storage tank through the nitrogen generating device connecting pipeline, and the outlet of the nitrogen storage tank is connected to the main pipeline of the nitrogen system.

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