阅读说明：本技术 核电厂严重事故的应对安全系统及其控制方法 (Coping safety system for severe accident of nuclear power plant and control method thereof ) 是由 展德奎 赵鑫海 夏少雄 陈鹏 符卉 吴梓杰 于 2020-01-07 设计创作，主要内容包括：一种核电厂严重事故的应对安全系统及其控制方法,应对安全系统包括至少一用于向反应堆压力容器(1)内注水的堆内注水系统(10)；堆内注水系统(10)包括多阶段安注箱(11)、连接一回路系统(3)冷管段(301)的第一注水管线(12)；多阶段安注箱(11)的内部空间包括自上而下分布的气相空间(101)、第一阶段注水空间(102)以及第二阶段注水空间(103)；多阶段安注箱(11)上设有第一流量管线(111)和管径小于第一流量管线(111)的第二流量管线(112),第一流量管线(111)连通第一阶段注水空间(102)和第一注水管线(12),第二流量管线(112)连通第二阶段注水空间(103)和第一注水管线(12)。该核电厂严重事故的应对安全系统以堆内注水系统(10)配合堆外冷却注水系统(20)进行堆内、堆外冷却,实现严重事故后维持反应堆压力容器(1)的完整性。(A safety system for dealing with serious accidents of a nuclear power plant and a control method thereof are provided, wherein the safety system for dealing with serious accidents of the nuclear power plant comprises at least one in-reactor water injection system (10) for injecting water into a reactor pressure vessel (1); the in-pile water injection system (10) comprises a multi-stage safety injection box (11) and a first water injection pipeline (12) connected with a cold pipe section (301) of the loop system (3); the internal space of the multi-stage safety injection box (11) comprises a gas phase space (101), a first-stage water injection space (102) and a second-stage water injection space (103) which are distributed from top to bottom; the multi-stage safety injection box (11) is provided with a first flow pipeline (111) and a second flow pipeline (112) with the pipe diameter smaller than that of the first flow pipeline (111), the first flow pipeline (111) is communicated with the first-stage water injection space (102) and the first water injection pipeline (12), and the second flow pipeline (112) is communicated with the second-stage water injection space (103) and the first water injection pipeline (12). According to the safety system for dealing with the severe accident of the nuclear power plant, the in-reactor water injection system (10) is matched with the out-reactor cooling water injection system (20) to carry out in-reactor and out-reactor cooling, so that the integrity of the reactor pressure vessel (1) is maintained after the severe accident.)

A safety system for dealing with serious accidents of a nuclear power plant is characterized by comprising at least one in-reactor water injection system for injecting water into a reactor pressure vessel;

the in-pile water injection system comprises a multi-stage safety injection box and a first water injection pipeline connected with a cold pipe section of the primary loop system; the internal space of the multi-stage safety injection box comprises a gas phase space, a first-stage water injection space and a second-stage water injection space which are distributed from top to bottom; the multi-stage safety injection box is provided with a first flow pipeline and a second flow pipeline, the pipe diameter of the second flow pipeline is smaller than that of the first flow pipeline, the first flow pipeline is communicated with the first-stage water injection space and the first water injection pipeline, and the second flow pipeline is communicated with the second-stage water injection space and the first water injection pipeline.

A safety system for handling severe accidents in nuclear power plants according to claim 1, characterized in that the first flow line has a pipe diameter of 100mm or more; the pipe diameter of the second flow pipeline is 40mm-80mm, and the water injection flow is 20m³/h -60m ³/h。

A safety system for handling severe accidents in nuclear power plants according to claim 1, characterized in that the pressure of the gas phase space is 4.0-5.0 MPa;

the pressure of a loop system of the nuclear power plant corresponding to the first-stage water injection space when starting water injection is 4.0-5.0 MPa;

and the pressure of a loop system of the nuclear power plant corresponding to the second stage water injection space when starting water injection is 0.4-1.0 MPa.

A safety system for handling a severe accident in a nuclear power plant according to claim 1, wherein the in-core water injection system further comprises a first check valve provided on the first water injection line, a first power valve provided on the first flow line, and a second power valve provided on the second flow line.

The safety system for handling severe accidents in nuclear power plants according to claim 4, wherein the in-pile water injection system further comprises a level gauge provided on the multi-stage safety tank corresponding to the first-stage water injection space;

when the liquid level in the multi-stage safety injection tank drops to a preset value, triggering a signal for closing the first power valve, and disconnecting the first flow pipeline from the first-stage water injection space; the preset value is higher than the connecting position of the first flow pipeline on the multistage safety injection box.

A safety system for handling severe accidents at nuclear power plants according to claim 1, wherein the in-stack water injection system further comprises a pressure test meter and a high pressure gas source connected to the gas phase space; a third power valve is arranged on a connecting pipeline between the high-pressure air source and the gas phase space; and when the gas pressure of the multi-stage safety injection box is less than 2.0MPa, triggering a signal for starting the third power valve, wherein the third power valve is opened, and the high-pressure gas source supplies gas to the multi-stage safety injection box.

A safety system for handling severe accidents at nuclear power plants according to claim 1, wherein the internal space of the multi-stage safety injection tank further comprises at least one third stage water injection space located below the second stage water injection space; the multi-stage safety injection box is also provided with at least one third flow pipeline, and the third flow pipeline is communicated with the third-stage water injection space and has a pipe diameter smaller than that of the first flow pipeline.

A safety-countermeasure system for a severe accident in a nuclear power plant according to any one of claims 1 to 7, further comprising at least one overboard cooling water injection system for injecting water into the pit;

the out-of-pile cooling water injection system comprises a high-level water injection water tank and a second water injection pipeline, wherein the high-level water injection water tank is arranged at a position higher than that of the reactor pressure vessel, and the second water injection pipeline is connected between the high-level water injection water tank and the pile pit.

A safety system for handling severe accidents at a nuclear power plant according to claim 8, wherein the off-core cooling water injection system further comprises a third flow line connected between the high level water injection tank and the second water injection line; the pipe diameter of the third flow pipeline is smaller than that of the second water injection pipeline, and the third flow pipeline is located at a connecting position on the high-position water injection water tank, which is lower than that of the second water injection pipeline.

A safety system for handling a severe accident of a nuclear power plant according to claim 9, wherein the off-core cooling water injection system further comprises a fourth power valve and a second check valve provided on the second water injection line in sequence in a direction from the high level water injection tank to the pit, a fifth power valve provided on the third flow line;

the connection location of the third flow line on the second water injection line is between the fourth power valve and the second check valve.

A safety system for handling a severe accident of a nuclear power plant according to claim 8, further comprising a pit water injection circulation cooling system provided between the reactor pressure vessel and the pit; the reactor pressure vessel is suspended in the reactor pit and a heat-insulating flow-guiding layer is arranged on the periphery of the reactor pressure vessel;

the reactor pit water injection circulating cooling system comprises a cooling water flow channel formed between a reactor pressure container and a heat preservation flow guide layer, a reactor pit water injection space formed between the heat preservation flow guide layer and the inner wall surface of a reactor pit, an annular reservoir arranged on the periphery of the upper end of the reactor pressure container, and a water return flow channel arranged in the pit wall and communicated with the annular reservoir and the reactor pit water injection space; the second water injection pipeline is communicated with the annular reservoir or the pit water injection space;

the bottom of the heat-preservation flow-guiding layer is provided with a water inlet communicated with the cooling water flow channel and the pile pit water injection space, so that cooling water in the pile pit water injection space enters the cooling water flow channel through the water inlet; the upper end on heat preservation water conservancy diversion layer is equipped with the steam drain, the steam drain intercommunication cooling water runner and annular cistern.

The safety system for handling the severe accident of the nuclear power plant as claimed in claim 11, wherein a buoyancy opening member is provided on a water outlet of the water return channel communicating with the pit water injection space;

under the normal operation condition of the reactor, the water outlet is kept normally closed; under the working condition of a serious accident of the reactor, the buoyancy opening piece is automatically opened after the reactor pit is filled with water.

A safety system for handling severe accidents at nuclear power plants according to claim 12, characterized in that the passive opening and closing element is a buoyant sphere or a buoyant cover plate.

A safety system for handling severe accidents at a nuclear power plant according to claim 11, wherein the water inlet of the thermal insulation diversion layer is kept normally closed under normal operation conditions of the reactor; and under the condition of a serious accident of the reactor, the water inlet is opened.

A safety control method for coping with a severe accident of a nuclear power plant, characterized in that the safety system for coping with a severe accident of a nuclear power plant according to any one of claims 1 to 14 is adopted; the safety control method for handling the serious accident of the nuclear power plant comprises the following steps:

before the working condition of a serious accident of the reactor, when the pressure of a primary loop system of the reactor is lower than a first set value, quickly injecting water into a reactor pressure vessel by an in-reactor water injection system through a first flow pipeline, a first water injection pipeline and a cold pipe section to submerge a reactor core; when the pressure of the primary loop system is lower than a second set value, the in-reactor water injection system injects water into the reactor pressure vessel through the second flow pipeline, the first water injection pipeline and the cold pipe section to submerge the reactor core again; the first set value is higher than the second set value.

The safety method for handling a severe accident of a nuclear power plant according to claim 15, further comprising: and when the reactor is in a serious accident condition, the cooling water injection system outside the reactor injects water into the reactor pit through the second water injection pipeline.

The safety method for handling the severe accident of the nuclear power plant according to claim 16, wherein in the severe accident condition of the reactor, after the water injection system injects water into the reactor pit to the target liquid level, water is continuously supplemented into the reactor pit through a third flow pipeline; the water supplement flow is 30m³/h-70m ³/h。

The safety method for dealing with the serious accident of the nuclear power plant according to claim 16, wherein when the reactor is in a serious accident condition, the cooling water injected into the water injection space of the pile pit enters the cooling water flow channel through the water inlet of the heat preservation flow guide layer, the cooling water is heated outside the reactor pressure vessel to form a steam-water two-phase flow, the steam-water two-phase flow flows upwards along the cooling water flow channel, the steam and the water are separated after passing through the steam outlet, and the liquid water falls into the annular reservoir; and cooling water in the annular reservoir returns to the water injection space of the pile pit through the return water flow channel so as to circulate.

Technical Field

The invention relates to the technical field of nuclear power, in particular to a coping safety system for severe accidents of a nuclear power plant and a control method thereof.

Background

After a serious accident of the nuclear power plant occurs, the reactor core is exposed and finally melted due to the loss of water of a primary loop system of the nuclear power plant, and the molten reactor core finally collapses into an RPV (reactor pressure vessel) lower seal head. If the molten core cannot be cooled in time, the molten core will finally melt through the wall surface of the RPV lower end enclosure due to the decay heat of the core, so that the molten core falls into the pit and possibly melts through the bottom plate of the containment, and finally a large amount of radioactive materials are leaked.

At present, most domestic and external pressurized water reactor nuclear power plants adopt a reactor pit water injection system to realize reactor pit water injection, and form forced or natural circulation cooling on the outer wall surface of a reactor pressure vessel to take away decay heat, so that a lower seal head is prevented from being melted through. However, under the severe working conditions that large and medium breaches are the starting events, the reactor pressure vessel has a high water loss rate due to the large area of the primary loop boundary breaches, and the possibility that the reactor core melt penetrates through the RPV still exists by simply adopting the cooling mode of the outer wall surface of the reactor pressure vessel due to the uncertainty of the reactor core melting process, the delay of the personnel starting time and other factors.

The existing pressurized water reactor nuclear power plants are all designed with 2 or more than 2 rows of safety injection tanks, and the safety injection tanks are divided into gas spaces (about 25 m)³) And boric acid water (about 35 m)³) When the pressure of a primary loop of the nuclear power plant is lower than a certain specific value, the electric valve is automatically opened, generally 4.0-5.0MPa, and the boric acid water is rapidly injected into a Reactor Pressure Vessel (RPV) through a cold pipe section at one time. However, in other cases, no water will be available in the safety injection tank, and therefore an accident of core melting may occur.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a schematic structural diagram of a safety system for handling a severe accident in a nuclear power plant according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of the in-pile water injection system of the corresponding safety system shown in FIG. 1;

fig. 3 is a schematic structural diagram of a pit water injection circulation cooling system in the counter safety system shown in fig. 1.

Modes for carrying out the invention

For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in fig. 1, the safety system for dealing with a severe accident of a nuclear power plant according to an embodiment of the present invention is disposed in a containment, and includes at least one in-core water injection system 10 for injecting water into a reactor pressure vessel 1, and at least one out-of-core cooling water injection system 20 for injecting water into a pit 2.

With reference to fig. 1 and 2, the in-stack water injection system 10 includes a multistage safety injection tank 11 and a first water injection line 12 connected to the cold pipe section 301 of the primary circuit system 3. The internal space of the multi-stage safety injection box 11 comprises a gas phase space 101, a first stage water injection space 102 and a second stage water injection space 103 which are distributed from top to bottom. The gas phase space 101 is used as a nitrogen gas space and the pressure is 4.0MPa-5.0 MPa. The first-stage water injection space 102 and the second-stage water injection space 103 are liquid-phase spaces for storing cooling water (water containing boron such as boric acid water) as medium-pressure-stage water injection and low-pressure-stage water injection, respectively. When the first-stage water injection space 102 starts water injection, the pressure of the nuclear power plant primary loop system corresponding to the first-stage water injection space is 4.0-5.0MPa, namely when the pressure of the nuclear power plant primary loop system is 4.0-5.0MPa, the first-stage water injection space 102 starts to inject water. When the second-stage water injection space 103 starts water injection, the pressure of the primary loop system of the nuclear power plant is 0.4MPa-1.0MPa, namely when the pressure of the primary loop system of the nuclear power plant is 0.4MPa-1.0MPa, the second-stage water injection space 103 starts to inject water. The multistage safety injection box 11 is provided with a first flow line 111 and a second flow line 112, the first flow line 111 communicates with the first stage water injection space 102 and the first water injection line 12, and the second flow line 112 communicates with the second stage water injection space 10 and the first water injection line 12. In comparison, the pipe diameter of the first flow pipe 111 is larger than that of the second flow pipe 112, so that the first flow pipe 111 is a large flow pipe, and the cooling water in the first-stage flooding space 102 can be rapidly injected into the core of the reactor, and the second flow pipe 112 is a small flow pipe, so that the core is flooded by the loop system 3 in a low-pressure state.

Alternatively, the first flow pipeline 111 has a pipe diameter of 100mm or more and a flow rate of 300m or more³H; the pipe diameter of the second flow pipeline 112 is 40mm-80mm, and the water injection flow is 20m³/h -60m ³H is used as the reference value. The first flow line 111 may be the same as the first water injection line 12.

The first flow line 111 may correspond to a lower end of the first stage water injection space 102, and has one end connected to the multistage safety injection tank 11 and communicated with the first stage water injection space 102 and the other end connected to and communicated with the first water injection line 12. The second flow line 112 may correspond to the second stage water injection space 103, and one end is connected to the lower end or bottom of the multistage safety injection tank 11 and the other end is connected to and communicated with the first water injection line 12.

Further, the in-stack water injection system 10 further includes a first check valve 13 disposed on the first water injection line 12, a first power valve 14 disposed on the first flow line 111, and a second power valve 15 disposed on the second flow line 112. A first check valve 13 is provided on the first water injection line 12 to prevent the cooling water from flowing backward. The first power valve 14 is used to control the opening and closing of the first flow line 111, and the second power valve 15 is used to control the opening and closing of the second flow line 112.

Alternatively, the first power valve 14 and the second power valve 15 are electrically operated valves and connected with an instrument control system of the nuclear power plant, and the instrument control system controls the opening and closing of the first power valve 14 or the second power valve 15 through automatic signals to realize the automatic injection of cooling water into the reactor. When the nuclear power plant is in power failure, the first power valve 14 or the second power valve 15 can be manually opened to realize water injection.

The in-pile water injection system 10 further comprises a liquid level meter 16 arranged on the multi-stage safety injection tank 11 corresponding to the first-stage water injection space 102 and used for monitoring the liquid level of the first-stage water injection space 102. When the liquid level of the first-stage water injection space 102 in the multi-stage safety injection box 11 falls to a preset value, a liquid level alarm is triggered, a signal for closing the first power valve 14 is triggered, the first power valve 14 is automatically closed, the communication between the first-stage water injection space 102 and the first flow pipeline 111 is cut off, and therefore the situation that gas in the multi-stage safety injection box 11 leaks to cause insufficient back pressure during starting in the second stage and enters a reactor through the first flow pipeline 11 can be prevented. The preset value of the liquid level is located at a position higher than the connection position of the first flow line 111 on the multistage safety injection box 11, so that the gas in the multistage safety injection box 11 is ensured not to leak.

When the pressure of a primary loop system 3 of the reactor is lower than a first set value (such as 4.0MPa-5.0 MPa), an instrument control system of the nuclear power plant starts a first power valve 14 through an automatic signal, and fast water is injected into a Reactor Pressure Vessel (RPV) through a first flow pipeline 111 and a cold pipe section 301, so that reactor core re-submergence under accident conditions is realized; when the liquid level in the multi-stage safety injection tank 11 is lower than a preset value, a liquid level alarm is triggered, a signal for closing the first power valve 14 is triggered, and the first power valve 14 is automatically closed; when the pressure of the loop system 3 continuously drops to be lower than a second set value (0.4 MPa-1 MPa), a signal for starting the second power valve 15 is triggered, the second power valve 15 is automatically started, water is injected into the reactor pressure vessel through the second flow pipeline 112, and the re-submerging of the loop system 3 in a low-pressure state is implemented.

The internal space of the multistage safety injection tank 11 may further include at least one third-stage water injection space (not shown) located below the second-stage water injection space 103 as a subsequent-stage water injection space, as necessary. Correspondingly, the multistage safety injection tank 11 is further provided with at least one third flow pipeline (not shown), and the third flow pipeline is communicated with the third stage water injection space and has a pipe diameter smaller than that of the first flow pipeline 111. The third flow line may have the same diameter and flow rate as the second flow line 112. Similarly, a power valve is also arranged on the third flow pipeline to control the on-off of the third flow pipeline. And the pressure of a primary loop system of the nuclear power plant corresponding to the water injection space starting water injection in the third stage is smaller than the pressure of the primary loop system of the nuclear power plant corresponding to the water injection space starting water injection in the second stage.

Further, the in-stack water injection system 10 further includes a pressure measuring meter (not shown) connected to the gas phase space 101 and a high-pressure gas source 17 (e.g., a high-pressure gas tank); the third power valve 18 is provided on the connecting line 171 of the high-pressure gas source 17 and the gas phase space 101. The third power valve 18 can adopt an electric valve, the pressure test meter and the third power valve 18 are connected with an instrument control system of the nuclear power plant, and the instrument control system controls the opening and closing of the third power valve 18 through a pressure signal to charge and boost the gas phase space 101. When the gas pressure of the multi-stage safety injection box 11 is less than 2.0MPa, a signal for starting the third power valve 18 is triggered, the third power valve 18 is opened, and the high-pressure gas source 17 supplies gas to the multi-stage safety injection box 11.

The in-pile water injection system 10 can be two or more, and is respectively connected with each cold pipe section 301.

As shown in fig. 2, the overboard cooling water injection system 20 includes a high level water injection tank 21 disposed at a position higher than the reactor pressure vessel 1, and a second water injection line 22 connected between the high level water injection tank 21 and the pit 2. The high-level water injection tank 21 is used for storing cooling water (boron-containing water), and can inject water into the pile pit 2 under the action of gravity without a power pump.

The second water injection pipeline 22 is a pipeline with the pipe diameter being more than or equal to 100mm, and can quickly fill the pile pit 2 with cooling water.

In the present invention, the off-stack cooling water injection system 20 further includes a third flow line 23 connected between the high-level water injection tank 21 and the second water injection line 22.

The pipe diameter of the third flow line 23 is smaller than that of the second water injection line 22, and the connection position of the third flow line 23 on the high level water injection tank 21 is lower than that of the second water injection line 22 on the high level water injection tank 21. For example, the second water injection line 22 may be connected to the middle portion 21 or the lower end position of the high level water injection tank 21, and the cooling water is injected into the pit 2 through the second water injection line 22, and may be stopped until the liquid level drops below the water inlet end of the second water injection line 22. The third flow pipeline 23 is connected with the bottom of the high-level water injection water tank 21, the subsequent cooling water can be continuously supplemented for the pit 2 through the third flow pipeline 23 at a relatively small flow, and the flow of the third flow pipeline 23 can be 30m³/h-70m ³/h。

The off-pile cooling water injection system 20 further includes a fourth power valve 24 and a second check valve 26 provided on the second water injection line 22, and a fifth power valve 25 provided on the third flow line 23 in this order in the direction from the high-level water injection tank 21 to the pile pit 2; the connection location of the third flow line 23 on the second water injection line 22 is between the fourth power valve 24 and the second check valve 26. A second check valve 26 is provided on the second water filling line 22 for preventing the cooling water from flowing backward. The fourth power valve 24 is used for controlling the on-off of one end of the second water injection pipeline 22 connected with the high-level water injection water tank 21, and the fifth power valve 25 is used for controlling the on-off of the third flow pipeline 23.

Alternatively, the fourth power valve 24 and the fifth power valve 25 are electrically operated valves and are connected with an instrument control system of the nuclear power plant, and the instrument control system controls the opening and closing of the fourth power valve 24 or the fifth power valve 25 through automatic signals to realize the automatic injection of the cooling water into the pit 2. When the nuclear power plant is in power failure, the fourth power valve 24 and the fifth power valve 25 can be manually opened to realize water injection.

Further, the safety system for dealing with a severe accident of a nuclear power plant of the present invention further includes a pit water injection circulation cooling system 30 disposed between the reactor pressure vessel 1 and the pit 2. The reactor pressure vessel 1 is arranged in the reactor pit 2 in a suspended manner, and the periphery of the reactor pressure vessel 1 is provided with a heat-preservation flow-guiding layer 4; the pile pit 2 is formed by the enclosure of shielding walls.

As shown in fig. 1 and 3, the pit filling water circulation cooling system 30 includes a cooling water flow path 31 formed between the reactor pressure vessel 1 and the heat-insulating flow-guiding layer 4, a pit filling water space 32 formed between the heat-insulating flow-guiding layer 4 and the inner wall surface of the pit 2, an annular reservoir 33 provided at the periphery of the upper end of the reactor pressure vessel 1, and a return water flow path 34 provided in the pit wall (shielding wall) and communicating the annular reservoir 33 and the pit filling water space 32.

Wherein, the bottom of the heat preservation diversion layer 4 is provided with a water inlet 41 communicating the cooling water channel 31 and the pit water injection space 32, so that the cooling water in the pit water injection space 32 enters the cooling water channel 32 through the water inlet 41. The water inlet 41 of the heat-preservation flow-guiding layer 4 keeps normally closed under the normal operation condition of the reactor; in a severe reactor accident condition, the water inlet 41 is opened. The upper end of the heat preservation diversion layer 4 is provided with a steam outlet (not shown), and the steam outlet is communicated with the cooling water flow passage 31 and the annular reservoir 32. The steam outlet is always positioned above the liquid level of the annular water storage tank 32, and the distance between the center distance of the steam outlet and the liquid level can be 0.1-0.8 m.

Specifically, the heat-insulating flow-guiding layer 4 comprises a flow-guiding plate and a heat-insulating layer which are sequentially arranged outside the reactor pressure vessel 1.

The second water injection pipeline 22 of the off-stack cooling water injection system 20 is connected and communicated with the annular reservoir 33 or the pit water injection space 32, and the cooling water is filled in the pit 2 to fill the cooling water flow passage 31, the pit water injection space 32 and the annular reservoir 33.

A buoyancy opening piece 341 is arranged on a water outlet of the water return channel 34 communicated with the pit water injection space 32; the reactor is kept normally closed under the normal operation condition of the reactor, and the bypass of a ventilation system is reduced; under the severe accident condition of the reactor, the buoyancy opening piece 341 can be automatically opened after the reactor pit is filled with water. The buoyancy opening member 341 may be a buoyancy ball or a buoyancy cover plate, and the buoyancy ball floats upwards to open the water outlet after the cooling water is injected into the pit filling water space 32. The water inlet 41 of the heat preservation and flow guide layer 4 is also provided with a passive opening and closing piece, such as a buoyancy cover plate and the like, and the water inlet 41 is opened by floating upwards under the condition of water and closed under the condition of no water.

Under the working condition of a serious accident of the reactor, cooling water is heated outside the reactor pressure vessel 1 to form steam-water two-phase flow, the steam-water two-phase flow flows upwards along the cooling water flow channel 31 and is separated from steam after passing through a steam discharge port, and liquid water falls into the annular reservoir 33; the cooling water in the annular reservoir 33 flows back to the pit filling space 32 through the return water channel 34, thereby forming a natural circulation loop. The plurality of return water flow channels 34 are arranged in the pit wall (shielding wall) of the pile pit 2 at intervals along the circumferential direction of the reactor pressure vessel 1, so that the space of the pile pit is not occupied, and meanwhile, the influence of deformation or leakage of the heat-preservation flow guide layer 4 or installation clearance on the establishment of natural circulation of the pile pit is avoided.

In the pit water injection circulation cooling system 30, natural circulation is formed by utilizing the density difference of water in the pit 2 and the return water channel 34, and the natural circulation flow can reach the natural circulation flow3000m ³Over h, the cooling capacity of the outer wall surface of the reactor pressure vessel 1 is improved; meanwhile, the steam-water two-phase flow discharged from the steam discharge hole realizes the automatic steam-water separation above the annular reservoir 33, and the steam is discharged to a large space in the containment vessel through a hole between a main pipeline at the upper end of the reactor pressure vessel 1 and a pit shielding wall.

The safety control method for coping with the serious accident of the nuclear power plant adopts the safety system for coping with the serious accident of the nuclear power plant. With reference to fig. 1 to 3, the safety control method for handling a severe accident in a nuclear power plant may include:

before the working condition of a serious accident of the reactor, when the pressure of a primary loop system 3 of the reactor is lower than a first set value (such as 4.0MPa-5.0 MPa), a reactor water injection system 10 quickly injects water into a reactor pressure vessel 1 through a first flow pipeline 111, a first water injection pipeline 12 and a cold pipe section 301 to submerge the reactor core; when the pressure of the primary loop system 3 is lower than a second set value (e.g., 0.4MPa to 1.0 MPa), the in-reactor water injection system 10 injects water into the reactor pressure vessel 1 through the second flow line 112, the first water injection line 12, and the cold leg 301 to submerge the reactor core. The first set point is higher than the second set point.

In the severe accident condition of the reactor, the reactor external cooling water injection system 20 injects water into the reactor pit 2 through the second water injection pipeline 22.

When the reactor is in a serious accident condition, the reactor external cooling water injection system 20 injects water into the reactor pit 2 to a target liquid level, and then continuously supplies water to the reactor pit 2 through the third flow pipeline 23; the water supplement flow is 30m³/h-70m ³/h。

Specifically, when the reactor is in a serious accident condition, cooling water injected into a pit water injection space 32 of a pit 3 enters a cooling water flow channel 31 through a water inlet of a heat preservation flow guide layer 4, the outside of the reactor pressure vessel 1 is heated to form a steam-water two-phase flow, the steam-water two-phase flow flows upwards along the cooling water flow channel 31, the steam and the water are separated after passing through a steam outlet, and liquid water falls into an annular reservoir 33; the cooling water in the annular reservoir 33 is returned to the pit filling space 32 through the return water flow passage 34 to be circulated.

In the invention, the in-pile water injection system is matched with the out-pile cooling water injection system to carry out in-pile and out-pile cooling, before a serious accident of the reactor occurs, the in-pile water injection system is used for cooling the reactor, and meanwhile, the starting time of the out-pile cooling water injection system can be prolonged.

For example, if the volume of the multistage safety injection tank 11 is increased by 60m³The water injection starting time of the out-of-pile cooling water injection system can be prolonged to more than 3.5 hours after an accident occurs, and the corresponding out-of-pile water injection flow can be between 180m³/h-360 m ³And h, the starting time and the flow rate of the water injected outside the reactor are mutually coupled. Free volume for pit of 180m³If the flow rate of the water injected outside the pile is larger, the filling time is shorter, the filling time is 30min at present, and the corresponding flow rate is 360 m³The starting time can be 4 hours after the accident; if the flow of the water injected outside the reactor is 180m³If the fill time is 1 hour, the start time is 3.5 hours. Obviously, compared with the condition of no water injection in the pile for 20-30 min, the starting time is greatly prolonged, and very abundant time is provided for judgment and operation of field accident handling personnel.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.