A control method for a nuclear power steam atmosphere discharge system

Abstract

The application discloses a control method of a nuclear power steam atmosphere discharge system. The control method combines the pressure of three parallel main steam pipes, the pressure difference between the three main steam pipes and three steam generator water level parameters, preliminarily judges the fault type, and determines whether to trigger the safety injection action through a control model. The application avoids the phenomenon that the safety injection action is mistakenly triggered under the condition of the steam atmosphere discharge valve compressed air leakage fault, and improves the safety and stability of the nuclear power system.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power control technology, specifically relating to a control method for nuclear power plant steam atmospheric emission systems. This invention improves the triggering logic for safety injection actions in nuclear power units, effectively preventing erroneous triggering of safety injection actions and enhancing unit safety and stability. Background Technology

[0002] Nuclear energy, as a clean energy source, plays a vital role in ensuring energy security and reducing pollution emissions. Unlike other power generation methods, the safety of nuclear power plants is particularly critical due to the radioactivity of nuclear fuel. Following the Three Mile Island accident in 1979, the Chernobyl accident in 1986, and the Fukushima Daiichi nuclear disaster in 2011, nuclear safety has become crucial for the continued development of nuclear power. To avoid losses, accident prevention has become a focus of attention.

[0003] The safety injection system is designed to inject emergency cooling water into the reactor core coolant system in the event of a coolant loss accident in the secondary loop or a steam pipe rupture accident. This maintains the water load of the core coolant system and ensures the heat output of the reactor core. The nuclear power plant steam atmospheric venting system is a safety bypass system located after the steam generator. It is used to remove excess power from the reactor. Failure of valves in this system can lead to a loss of control of the safety system, resulting in unexpected situations such as safety valve activation or accidental triggering of the safety injection system. Summary of the Invention

[0004] This invention addresses the problems of poor safety injection control and false triggering of safety injection actions due to compressed air leakage in the steam atmospheric discharge valve. It designs a nuclear power safety injection system control method that takes into account absolute pressure over-limit signals, differential pressure over-limit signals, and steam generator water level over-limit signals, thereby improving the system's flexibility and accuracy.

[0005] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0006] A control method for a nuclear power plant steam atmospheric emission system, characterized in that: the nuclear power plant steam atmospheric emission system includes three parallel branches, each branch identically comprising a steam generator 1, a water level measuring element 2, a main steam pipe 3, a safety valve 5, a pressure measuring element 4, a steam atmospheric emission valve 6, and a steam silencer 7. The pipe-side inlet and outlet cavities of the steam generator 1 are respectively connected to both ends of the reactor and its auxiliary equipment system 9. The shell-side inlet of the steam generator 1 is connected to the outlet of the turbine and its auxiliary equipment system 8. The water level measuring element 2 is connected to the shell side of the steam generator 1. The shell-side outlet of the steam generator 1 is connected to the main steam pipe 3. The pressure measuring element 4 is connected to the main steam pipe 3. The safety valve 5 is connected to the main steam pipe 3. The outlet pipe is connected to the atmosphere. The inlet of the steam atmospheric vent valve 6 is connected to a branch of the main steam pipe 3. The outlet of the steam atmospheric vent valve 6 is connected to the bottom of the silencer 7. The top of the silencer 7 is connected to the atmosphere. The end of the main steam pipe 3 is connected to the inlet of the turbine and its auxiliary system 8. The safety injection system 10 is controlled by the control model and is connected to the reactor and its auxiliary system 9. The reactor and its auxiliary system 9 uses nuclear energy to generate heat and provides heat input to the steam generator 1 through the primary loop working fluid. The turbine and its auxiliary system 8 consumes the heat of the main steam to generate electricity and produces cooled condensate, which is sent back to the steam generator 1. The safety injection system 10 is used to cool the reactor and quickly shut it down in the event of a major unit failure, thus protecting the safety of the nuclear reactor.

[0007] Using the measured values ​​of pressure measuring element 4 in main steam pipeline 3 and water level measuring element 2 in steam generator 1 as input signals for the control model, the control model for triggering the safety injection system 10 in the nuclear power plant steam atmospheric emission system is as follows:

[0008] 1) When the pressure over-limit signal of main steam pipeline 3, the pressure difference over-limit signal between the three branch main steam pipelines 3, and the water level over-limit signal of steam generator 1 are simultaneously satisfied, the control model controls the safety injection system 10 to trigger the safety injection action. The control model is as follows:

[0009] F safety-injection =f bool (F P +F P-diff +F SG-level ≥3) (1)

[0010] In the formula: F safety-injection The safety injection action is triggered by a Boolean signal; a value of 0 indicates no safety injection action is triggered, while a value of 1 indicates a safety injection action is triggered; F P This is a Boolean signal for judging the pressure over-limit of main steam pipeline 3. A value of 0 indicates that the pressure of main steam pipeline 3 is not over-limit, and a value of 1 indicates that the pressure of main steam pipeline 3 is over-limit; F P-diffThis is a Boolean signal indicating that the pressure difference between the three main steam pipelines on the three branch lines exceeds the limit. A value of 0 indicates that the pressure difference between the three main steam pipelines on the three branch lines does not exceed the limit, while a value of 1 indicates that the pressure difference between the three main steam pipelines on the three branch lines exceeds the limit. (F) SG-level This is a Boolean signal for judging whether the water level of steam generator 1 exceeds the limit. A value of 0 indicates that the water level of steam generator 1 is not exceeded, and a value of 1 indicates that the water level of steam generator 1 exceeds the limit.

[0011] 2) In the control model for triggering safety injection actions in the nuclear power plant steam atmospheric emission system, there are three input variables: the Boolean signal F for judging pressure over-limit in the main steam pipeline 3. P Three main steam pipelines on three branch lines exceeded the pressure difference limit, triggering a Boolean signal F. P-diff Boolean signal F for judging water level exceeding limit in steam generator 1 SG-level ;

[0012] The control method for the nuclear power plant steam atmospheric emission system is as follows:

[0013] If the pressure in any of the three main steam pipes 3 exceeds the upper limit signal value, the pressure in the main steam pipe 3 is determined to be out of limit.

[0014]

[0015] In the formula: P1(t), P2(t), and P3(t) are the pressure measurements of the main steam pipeline 3 on the three branches at time t, respectively, in MPa; t is the time axis, in seconds; P max The upper pressure limit signal value for main steam pipeline 3, in MPa;

[0016] If the pressure difference between any two main steam pipes 3 on the three branch lines exceeds the upper limit signal value, it is determined that the pressure difference between the main steam pipes 3 is excessive.

[0017]

[0018] Where: ΔP is the upper limit signal value of the differential pressure in the main steam pipeline 3, in MPa;

[0019] If the water level in any of the three steam generators 1 exceeds the upper or lower limit of the water level limit, the water level of steam generator 1 is determined to be out of limit.

[0020]

[0021] In the formula: L1(t), L2(t), and L3(t) are the water levels of the three steam generators 1 at time t, respectively, in meters; H max The upper limit signal value of the water level for steam generator 1, in meters (m); H min The lower limit signal value of the water level for steam generator 1 is in meters (m).

[0022] The following points are involved in the judgment process:

[0023] I. Based on calculations and empirical judgment, the default value of ΔP in the judgment of excessive pressure difference between the three main steam pipelines is 0.7.

[0024] II. The upper limit and lower limit values ​​of the water level in the water level over-limit signal of steam generator 1 are the upper limit and lower limit of the height of the steam-water separator in steam generator 1.

[0025] Third, this control method identifies the characteristics of compressed air leakage faults in steam atmospheric discharge valve 6 and suppresses the accidental triggering of safety injection actions caused by such faults. Specifically, the compressed air leakage fault in steam atmospheric discharge valve 6 causes pressure fluctuations in the main steam pipeline measured by pressure measuring element 4. When the peak value of the fluctuation reaches the upper limit of the pressure of safety valve 5, the safety valve opens to release pressure. Under the large pressure drop, the triggering logic of the safety injection action is intervened to avoid accidental triggering of the safety injection action under the compressed air leakage fault of steam atmospheric discharge valve 6.

[0026] Advantages of the present invention

[0027] (1) The present invention can optimize the control logic of nuclear power safety injection signals and improve the safety of the unit.

[0028] (2) In the application of this invention, the control method can be added as a new safety injection control signal and the control parameters can be set to improve the control of the safety injection system. Attached Figure Description

[0029] Figure 1 This is a model diagram of a nuclear power plant's steam atmospheric emission system.

[0030] Figure 2 This is the control logic diagram for triggering safety injection actions in the nuclear power plant's steam atmospheric emission system. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and examples.

[0032] In a nuclear power unit's nuclear power steam atmosphere venting system, a failure of steam atmosphere venting valve 6 caused a leak in compressed air, resulting in severe pressure fluctuations in the main steam pipeline 3. The water hammer effect in the condensate drain pipe caused the pressure difference between the three main steam pipelines to reach 0.7 MPa, triggering the safety injection system. This fault was classified as a minor fault, and the triggering of the safety injection system was a false triggering.

[0033] Steam atmospheric vent valve 6 is a steam-opening pneumatic control valve. When a compressed air leak occurs, the valve opening decreases, opening becomes slower, and closing becomes faster. Simulation and actual machine data show that after the fault occurs, the pressure in the main steam pipeline 3 fluctuates, and the liquid flow rate in the condensate pipeline fluctuates slightly accordingly.

[0034] Fluctuations in liquid water flow triggered water hammer in the condensate drain pipe. A significant pressure change in the main steam pipe 3 caused a pressure differential of 0.7 MPa, triggering safety valve 5. This pressure relief in the main steam pipe 3 then activated the safety injection system. The reason for this accidental activation of the safety injection system was its overly simplistic triggering logic. Therefore, a new condition was added to the original logic that only triggered the safety injection system based on pressure differential to prevent similar malfunctions from causing accidental activation.

Claims

1. A control method for a nuclear power plant steam atmospheric emission system, characterized in that: The nuclear power plant's steam atmospheric emission system includes three parallel branches. All three branches are identical, each including a steam generator (1), a water level measuring element (2), a main steam pipe (3), a safety valve (5), a pressure measuring element (4), a steam atmospheric emission valve (6), and a steam silencer (7). The pipe-side inlet and outlet of the steam generator (1) are connected to both ends of the reactor and its auxiliary systems (9). The shell-side inlet of the steam generator (1) is connected to the outlet of the turbine and its auxiliary systems (8). The water level measuring element (2) is connected to the shell side of the steam generator (1). The shell-side outlet of the steam generator (1) is connected to the main steam pipe (3). The pressure measuring element (4) is connected to the main steam pipe (3). The safety valve (5) is connected to the main steam pipe (3). The outlet pipe of the safety valve (5) is connected to the main steam pipe. The steam atmospheric discharge valve (6) is connected to the inlet of the main steam pipeline (3) and the outlet of the steam atmospheric discharge valve (6) is connected to the bottom of the silencer (7). The top of the silencer (7) is connected to the atmosphere. The end of the main steam pipeline (3) is connected to the inlet of the turbine and its auxiliary system (8). The safety injection system (10) is controlled by the control model and connected to the reactor and its auxiliary system (9). The reactor and its auxiliary system (9) uses nuclear energy to generate heat and provides heat input to the steam generator (1) through the primary loop working fluid. The turbine and its auxiliary system (8) consumes the heat of the main steam to generate electricity and produces cooled condensate that is sent back to the steam generator (1). The safety injection system (10) is used to cool the reactor and shut it down quickly in the event of a major unit failure, thus protecting the safety of the nuclear reactor. Using the measured values ​​of the pressure measuring element (4) in the main steam pipeline (3) and the water level measuring element (2) in the steam generator (1) as the input signals for the control model, the control model for triggering the safety injection system (10) of the nuclear power plant steam atmospheric emission system is as follows: 1) When the pressure over-limit signal of the main steam pipeline (3), the pressure difference over-limit signal between the main steam pipelines (3) on the three branches and the water level over-limit signal of the steam generator (1) are simultaneously satisfied, the control model controls the safety injection system (10) to trigger the safety injection action. The control model is as follows: F safety-injection =f bool (F P +F P-diff +F SG-level ≥3) (1) In the formula: F safety-injection The safety injection action is triggered by a Boolean signal; a value of 0 indicates no safety injection action is triggered, while a value of 1 indicates a safety injection action is triggered; F P The Boolean signal for judging the pressure over-limit of the main steam pipeline (3) is 0. A value of 0 indicates that the pressure of the main steam pipeline (3) is not over-limit, and a value of 1 indicates that the pressure of the main steam pipeline (3) is over-limit; F P-diff This is a Boolean signal indicating that the pressure difference between the main steam pipes (3) on the three branch lines exceeds the limit. A value of 0 indicates that the pressure difference between the three main steam pipes (3) does not exceed the limit, while a value of 1 indicates that the pressure difference between the main steam pipes (3) on the three branch lines exceeds the limit. SG-level The Boolean signal is used to determine if the water level of the steam generator (1) exceeds the limit. A value of 0 indicates that the water level of the steam generator (1) is not exceeded, and a value of 1 indicates that the water level of the steam generator (1) exceeds the limit. 2) In the control model for triggering safety injection actions in the nuclear power plant steam atmospheric emission system, there are three input variables, namely the main steam pipeline (3) pressure over-limit judgment Boolean signal F P The pressure difference between the main steam pipes (3) on the three branch lines exceeds the limit, triggering a Boolean signal F. P-diff And steam generator (1) water level over-limit judgment Boolean signal F SG-level ; The control method for the nuclear power plant steam atmospheric emission system is as follows: If the pressure in any of the three main steam pipes (3) exceeds the upper limit signal value, the pressure in the main steam pipe (3) is determined to be out of limit. In the formula: P1(t), P2(t) and P3(t) are the pressure measurements of the main steam pipeline (3) on the three branches at time t, respectively, in MPa; t represents the time axis, in seconds; P max The upper limit signal value of the pressure of the main steam pipeline (3), MPa; If the pressure difference between any two main steam pipes (3) on the three branch lines exceeds the upper limit signal value, it is determined that the pressure difference between the main steam pipes (3) exceeds the limit. Where: ΔP is the upper limit signal value of the differential pressure in the main steam pipeline (3), MPa; If the water level of any one of the three steam generators (1) exceeds the upper or lower limit of the water level limit, the water level of steam generator (1) is determined to be out of limit: In the formula: L1(t), L2(t), and L3(t) are the water levels of the three steam generators (1) at time t, respectively, in meters; H max The upper limit signal value of the water level of the steam generator (1), m; H min The lower limit signal value of the water level of the steam generator (1) is m.

2. The control method for a nuclear power plant steam atmospheric emission system according to claim 1, characterized in that: Based on calculations and empirical judgment, the default value of ΔP in the judgment of excessive pressure difference between the main steam pipeline (3) is 0.

7.

3. The control method for a nuclear power plant steam atmospheric emission system according to claim 1, characterized in that: The upper limit signal value and the lower limit signal value of the water level in the water level over-limit signal of the steam generator (1) are the upper limit and lower limit of the height of the steam-water separator in the steam generator (1), respectively.

4. The control method for a nuclear power plant steam atmospheric emission system according to claim 1, characterized in that: The control method identifies the characteristics of the compressed air leakage fault of the steam atmospheric discharge valve (6) and suppresses the accidental activation of the safety injection system (10) caused by such fault. Specifically, the compressed air leakage fault of the steam atmospheric discharge valve (6) causes the pressure of the main steam pipeline measured by the pressure measuring element (4) to fluctuate. When the peak value of the fluctuation reaches the upper limit of the pressure of the safety valve (5), the safety valve starts to release pressure. Under the large pressure drop, the triggering logic of the safety injection action is intervened to avoid the accidental activation of the safety injection action under the compressed air leakage fault of the steam atmospheric discharge valve (6).

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