System and control method for passive waste heat export of steam generator

Abstract

The invention belongs to the field of nuclear power station operation and automatic control, and particularly relates to a system for passive waste heat export of a steam generator and a control method.The system comprises the steam generator, a heat exchanger, an emergency heat extraction box, a small starting valve and a large starting valve, and the heat exchanger is arranged in the emergency heat extraction box; one side of the steam generator is connected with one side of the heat exchanger through a pipeline, the other side of the steam generator is connected with the large starting valve through a pipeline, and the large starting valve is connected with the other side of the heat exchanger through a pipeline. One side of the small starting valve is connected with a pipeline between the large starting valve and the steam generator through a pipeline, and the other side of the small starting valve is connected with a pipeline between the large starting valve and the heat exchanger through a pipeline. According to the system, the small starting valve and the large starting valve are respectively opened according to different accident types of a nuclear power plant, waste heat in a reactor is cooled by cooling water stored in the emergency heat removal water tank, a reactor core is prevented from being dried, and the temperature of a fuel element does not exceed a nominal value.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power plant operation and automatic control, specifically relating to a system and control method for passive waste heat extraction from steam generators. Background Technology

[0002] During the operation of a pressurized water reactor nuclear power plant reactor, the primary coolant carries the heat released from the nuclear fuel out of the reactor and into the steam generator. Through thousands of heat transfer tubes, the heat is transferred to the secondary coolant outside the tubes, causing the water to boil and produce steam. After flowing through the steam generator, the primary coolant is then pumped back into the reactor by the main pump. Through this circulation, the heat in the reactor is continuously carried out and converted into steam.

[0003] Currently, in the event of an accident, the reactor uses a residual heat removal system to transfer the core heat to the final heat sink. However, the existing technology lacks a backup system in case the active residual heat removal system fails or cannot be put into operation, and there is a lack of control methods for controlling the use of the backup system for different accident conditions. Summary of the Invention

[0004] This invention provides a system and control method for passive waste heat extraction from a steam generator, addressing the lack of a backup system and control method in the prior art when the active waste heat extraction system fails or cannot be put into operation.

[0005] The technical solution of the present invention is as follows:

[0006] This method proposes a system for passive waste heat extraction from a steam generator. The system includes a steam generator, a heat exchanger, an emergency heat exhaust box, a small start valve, and a large start valve. The heat exchanger is installed inside the emergency heat exhaust box. One side of the steam generator is connected to one side of the heat exchanger via a pipe, and the other side of the steam generator is connected to the large start valve via a pipe. The large start valve is connected to the other side of the heat exchanger via a pipe. One side of the small start valve is connected to the pipe between the large start valve and the steam generator via a pipe, and the other side of the small start valve is connected to the pipe between the large start valve and the heat exchanger via a pipe. The height of the emergency heat exhaust box and the heat exchanger is higher than that of the steam generator.

[0007] In some embodiments, a manual controller A is installed on the pipeline where the small start valve is located, and a manual controller B is installed on the pipeline where the large start valve is located. The water tank of the emergency heat dissipation box has a water space of 600m³. 3 The normal liquid level is 5.8m. The cooling rate of the reactor primary circuit when starting with the large start valve should not exceed 60℃ / h, and the cooling rate of the reactor primary circuit when starting with the small start valve should not exceed 30℃ / h.

[0008] In some embodiments, the pipeline connecting the steam generator to the heat exchanger is provided with containment isolation valve A and containment isolation valve B, and the pipeline connecting the large start valve to the heat exchanger is provided with containment isolation valve C and containment isolation valve D. The pipeline between the large start valve and containment isolation valve D is connected to a safety valve via a pipeline.

[0009] In some embodiments, when the system is operating at normal reactor power, containment isolation valves A, B, C, and D are open, the large start valve and small start valve are closed, manual controllers A and B are 80% open, the safety valves are closed, the emergency heat exhaust box is at the normal liquid level, the heat exchanger is in standby mode, and the steam generator is operating normally.

[0010] This invention proposes a control method for passive waste heat extraction from a steam generator, the method comprising:

[0011] When a Class A accident occurs in the reactor, the system opens the small start-up valve to transfer the heat from the steam generator to the emergency heat exhaust box via the heat exchanger.

[0012] When a Type B accident occurs in the reactor, the system opens the large start valve and transfers the heat from the steam generator to the emergency heat exhaust box via the heat exchanger.

[0013] When the reactor is operating at normal power, the system is tested periodically.

[0014] In some embodiments, a Class A accident specifically includes: a low-pressure safety injection start signal at the primary loop rupture of the reactor, and a malfunction of the atmospheric release valve of the main steam system; a secondary loop rupture of the reactor, and the pump outlet flow rate is below 11 kg / s after the emergency feedwater pump is started; a primary loop temperature greater than 150°C and a steam generator pressure greater than 8 MPa; a primary loop temperature greater than 150°C and a steam generator liquid level 0.875 m below the normal liquid level; a non-isolated rupture in the secondary loop of the reactor and a high-pressure safety injection system flow rate below 11 kg / s; and a complete power outage of the nuclear power plant.

[0015] In some embodiments, a Class B accident specifically includes: a rupture in the reactor primary loop and a high-pressure safety injection start signal, and the high-pressure safety injection system has a low flow rate; a steam generator heat transfer tube rupture accident occurs in the reactor, a signal is sent to open an intact steam generator atmospheric release valve, and the steam generator atmospheric release valve malfunctions; a rupture occurs in the reactor primary loop and the high-pressure safety injection system issues a start-up failure signal.

[0016] In some embodiments, the method of periodically testing the system specifically includes:

[0017] Step 1: Check that the reactor primary loop is hot and the system is in standby mode;

[0018] Step 2: Open the small start-up valve, check that the reactor primary loop cooling rate does not exceed 30℃ / h, and close the small start-up valve after it has been open for no more than 5 seconds;

[0019] Step 3: Check that the reactor primary loop has been restored to a hot state;

[0020] Step 4: Open the main start valve, check that the reactor primary loop cooling rate does not exceed 60℃ / h, and close the main start valve after it has been open for no more than 9 seconds;

[0021] Step 5: Restore the primary circuit to a hot state.

[0022] In some embodiments, the system is in standby mode as follows: containment isolation valves A, B, C, and D are open; the large start valve and small start valve are closed; manual controllers A and B are 80% open; the safety valve is closed; the emergency heat exhaust box is at the normal liquid level; the heat exchanger is in standby mode; and the steam generator is operating normally.

[0023] The implementation of this invention has the following beneficial effects:

[0024] 1. This invention relates to a system for passive waste heat removal from a steam generator. Based on the passive principle, upon receiving protection and interlock signals, the system automatically removes heat from the reactor to the emergency heat removal box by opening a small start valve or a large open valve, utilizing the height difference between the emergency heat removal box and the reactor. The heat from the emergency heat removal box is then discharged to the final heat sink through water evaporation in the water tank. The system is designed to provide at least 24 hours of fully autonomous operation without an operator. During the 24–72 hour period, system operation can be ensured through on-site mobile equipment and stored water.

[0025] 2. This invention proposes a control method for passive residual heat removal from a steam generator. This method opens a small start valve and a large start valve respectively for different accident types in nuclear power plants. The residual heat in the reactor is cooled by cooling water stored in the emergency wastewater tank to prevent the reactor core from drying out and to ensure that the fuel element temperature does not exceed the nominal value. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a system for passive waste heat extraction from a steam generator, as proposed in an embodiment of the present invention.

[0027] Figure descriptions: 1. Steam generator; 2. Containment isolation valve A; 3. Containment isolation valve B; 4. Heat exchanger; 5. Emergency heat exhaust box; 6. Containment isolation valve C; 7. Safety valve; 8. Containment isolation valve D; 9. Small start valve; 10. Manual controller A; 11. Large start valve; 12. Manual controller B. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown, this invention proposes a system for passive waste heat extraction from a steam generator. The system includes a steam generator 1, a heat exchanger 4, an emergency heat exhaust box 5, a small start valve 9, a large start valve 11, a manual controller A10, and a manual controller B12. The emergency heat exhaust box 5 has a water tank with a water volume of 600 m³. 3 The normal liquid level is 5.8m. The large start valve 11 starts the reactor primary circuit cooling rate at a rate not exceeding 60℃ / h, and the small start valve 9 starts the reactor primary circuit cooling rate at a rate not exceeding 30℃ / h.

[0030] The emergency heat exhaust box 5 houses a heat exchanger 4. One side of the steam generator 1 is connected to the other side of the heat exchanger 4 via a pipe. This pipe is equipped with containment isolation valves A2 and B3. The emergency heat exhaust box 5 and the heat exchanger 4 are higher than the steam generator 1. The other side of the steam generator 1 is connected to a manual controller B12 via a pipe. The manual controller B12 is connected to a large start valve 11 via a pipe. The large start valve 11 is connected to the other side of the heat exchanger 4 via a pipe. The pipe connecting the large start valve 11 and the heat exchanger 4 is equipped with containment isolation valves C6 and D8. The pipe between the large start valve 11 and the containment isolation valve D8 is connected to a safety valve 7, which is used to prevent overpressure in the pipeline.

[0031] One side of the small start valve 9 is connected to the pipe between the large start valve 11 and the steam generator 1 via a pipeline. A manual controller A10 is installed on this pipeline. The other side of the small start valve 9 is connected to the pipe between the large start valve 11 and the heat exchanger 4 via a pipeline. The manual controller is used to limit the condensate flow rate of the emergency heat exhaust box to ensure that the power characteristics of the passive waste heat exhaust system of the steam generator are at the level required after the start valve is opened.

[0032] In normal reactor power operation, the passive heat transfer system of steam generator 1 is in standby mode. Containment isolation valves A2, B3, C6, and D8 are open. Large start valve 11 and small start valve 9 are closed. Manual controllers A10 and B12 are at a certain opening degree (80%). Safety valve 7 is closed. Emergency heat exhaust box 5 is at the normal liquid level, which is 5.8m, with an allowable liquid level range of 5.8-6.1m. Heat exchanger 4 is in standby mode, and steam generator 1 is operating normally.

[0033] This invention relates to a system and control method for passive waste heat extraction from a steam generator. Because the system operates on a passive principle, upon receiving protection and interlock signals, it automatically exhausts heat from the reactor to the emergency heat extraction box by opening a small start-up valve or a large pneumatic valve, utilizing the height difference between the emergency heat extraction box and the reactor. The heat from the emergency heat extraction box is then discharged to the final heat sink through water evaporation in the water tank. The system is designed to provide at least 24 hours of fully autonomous operation without an operator. During the 24–72 hour period, operation can be ensured by using on-site mobile equipment and stored water.

[0034] This invention proposes a control method for passive waste heat extraction from a steam generator, the method comprising:

[0035] When the reactor experiences the following accident, the system opens the small start valve 9. Based on the passive principle, the heat from the steam generator 1 is transferred to the emergency heat exhaust box 5 through the heat exchanger 4, so that the primary circuit cooling rate of the reactor does not exceed 30°C / h.

[0036] 1. A low-pressure safety injection start signal was present at the reactor primary loop rupture, and the atmospheric release valve of the main steam system was malfunctioning;

[0037] 2. The reactor secondary loop is breached, and the pump outlet flow rate is less than 11 kg / s after the emergency feedwater pump is started;

[0038] 3. The primary loop temperature of the reactor is greater than 150℃, and the pressure of all steam generators is greater than 8MPa;

[0039] 4. The primary circuit temperature of the reactor is greater than 150℃, and the liquid level of all steam generators is 0.875m lower than the normal liquid level.

[0040] 5. A non-isolated breach occurs in the secondary loop of the reactor and the flow rate of the high-pressure safety injection system is below 11 kg / s;

[0041] 6. The entire nuclear power plant lost power.

[0042] When the reactor experiences the following accident, the system opens the large start valve 11. Based on the passive principle, the heat from the steam generator 1 is transferred to the emergency heat exhaust box 5 through the heat exchanger 4, so that the primary circuit cooling rate of the reactor does not exceed 60°C / h.

[0043] 1. A breach has occurred in the reactor's primary loop, and a high-pressure safety injection activation signal is present, with the high-pressure safety injection system experiencing low flow.

[0044] 2. A heat transfer tube rupture accident occurred in the reactor steam generator 1. The reactor had a signal to open the atmospheric release valve of the intact steam generator 1, but the atmospheric release valve of steam generator 1 was faulty.

[0045] 3. A primary circuit rupture occurs in the reactor and the high-pressure injection system issues a startup failure signal.

[0046] To ensure the availability of the passive heat transfer system of steam generator 1 and to meet the requirements of the nuclear safety oversight program, the system needs to be tested periodically, once per refueling cycle. The testing method includes the following steps:

[0047] Step 1: Check that the reactor primary loop is hot, the system is in standby mode, containment isolation valves A2, B3, C6, and D8 are open, large start valve 11 and small start valve 9 are closed, manual controllers A10 and B12 are at a certain opening degree (80% opening), safety valve 7 is closed, emergency heat exhaust box 5 is at the normal liquid level, heat exchanger 4 is in standby mode, and steam generator 1 is operating normally.

[0048] Step 2: Open the small start-up valve 9, check that the reactor primary loop cooling rate does not exceed 30℃ / h, and close the small start-up valve 9 after it has been open for no more than 5 seconds;

[0049] Step 3: Check that the reactor primary loop has been restored to a hot state;

[0050] Step 4: Open the large start valve 11, check that the reactor primary loop cooling rate does not exceed 60℃ / h, and close the large start valve 11 after the opening time does not exceed 9 seconds;

[0051] Step 5: Restore the primary circuit to a hot state.

[0052] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A system for passive waste heat extraction from a steam generator, characterized in that, The system includes a steam generator (1), a heat exchanger (4), an emergency heat exhaust box (5), a small start valve (9), and a large start valve (11). The emergency heat exhaust box (5) is equipped with a heat exchanger (4). One side of the steam generator (1) is connected to one side of the heat exchanger (4) through a pipe, and the other side of the steam generator (1) is connected to the large start valve (11) through a pipe. The large start valve (11) is connected to the other side of the heat exchanger (4) through a pipe. One side of the small start valve (9) is connected to the pipe between the large start valve (11) and the steam generator (1) through a pipe, and the other side of the small start valve (9) is connected to the pipe between the large start valve (11) and the heat exchanger (4) through a pipe. The height of the emergency heat exhaust box (5) and the heat exchanger (4) is higher than that of the steam generator (1).

2. A system for passive waste heat extraction from a steam generator according to claim 1, characterized in that, The small start valve (9) is connected to a manual controller A (10) on its pipeline, and the large start valve (11) is connected to a manual controller B (12) on its pipeline; the emergency heat dissipation box (5) has a water tank with a water volume of 600 m³. 3 The normal liquid level is 5.8m. The large start valve (11) starts the reactor primary circuit cooling rate at a rate not exceeding 60℃ / h, and the small start valve (9) starts the reactor primary circuit cooling rate at a rate not exceeding 30℃ / h.

3. A system for passive waste heat extraction from a steam generator according to claim 2, characterized in that, The steam generator (1) is connected to the heat exchanger (4) via a pipe equipped with a containment isolation valve A (2) and a containment isolation valve B (3). The large start valve (11) is connected to the heat exchanger (4) via a pipe equipped with a containment isolation valve C (6) and a containment isolation valve D (8). The pipe between the large start valve (11) and the containment isolation valve D (8) is connected to a safety valve (7).

4. A system for passive waste heat extraction from a steam generator according to claim 3, characterized in that, When the system is operating at normal reactor power, containment isolation valves A (2), B (3), C (6), and D (8) are open, the large start valve (11) and small start valve (9) are closed, manual controllers A (10) and B (12) are 80% open, the safety valve (7) is closed, the emergency heat exhaust box (5) is at the normal liquid level, the heat exchanger (4) is in standby mode, and the steam generator (1) is operating normally.

5. A control method for passive waste heat extraction from a steam generator according to any one of claims 1-4, characterized in that, The method includes: When a Class A accident occurs in the reactor, the system opens the small start valve (9) to export the heat from the steam generator (1) to the emergency heat exhaust box (5) through the heat exchanger (4); When a Class B accident occurs in the reactor, the system opens the large start valve (11) and discharges the heat from the steam generator (1) to the emergency heat exhaust box (5) through the heat exchanger (4). When the reactor is operating at normal power, the system is subjected to periodic tests.

6. The control method for passive waste heat extraction from a steam generator according to claim 5, characterized in that, The Class A accidents specifically include: a low-pressure safety injection start signal at the primary loop rupture of the reactor and a malfunction of the atmospheric release valve of the main steam system; a rupture at the secondary loop of the reactor and a pump outlet flow rate of less than 11 kg / s after the emergency feedwater pump is started; a primary loop temperature greater than 150°C and a steam generator (1) pressure greater than 8 MPa; a primary loop temperature greater than 150°C and a steam generator (1) liquid level 0.875 m lower than the normal liquid level; a non-isolated rupture at the secondary loop of the reactor and a high-pressure safety injection system flow rate of less than 11 kg / s; and a complete power outage at the nuclear power plant.

7. The control method for passive waste heat extraction from a steam generator according to claim 6, characterized in that, The Class B accidents specifically include: a rupture in the reactor primary loop and a high-pressure safety injection start signal, and the high-pressure safety injection system has a low flow rate; a rupture accident in the heat transfer tube of the steam generator (1) of the reactor, a signal to open the atmospheric release valve of the intact steam generator (1) of the reactor, and a malfunction of the atmospheric release valve of the steam generator (1); a rupture in the reactor primary loop and a start-up failure signal issued by the high-pressure safety injection system.

8. The control method for passive waste heat extraction from a steam generator according to claim 7, characterized in that, The method for periodically testing the system specifically includes: Step 1: Check that the reactor primary loop is hot and the system is in standby mode; Step 2: Open the small start-up valve (9), check that the cooling rate of the reactor primary loop does not exceed 30℃ / h, and close the small start-up valve (9) after the opening time does not exceed 5 seconds; Step 3: Check that the reactor primary loop has been restored to a hot state; Step 4: Open the large start-up valve (11), check that the cooling rate of the reactor primary loop does not exceed 60℃ / h, and close the large start-up valve (11) after the opening time does not exceed 9 seconds; Step 5: Restore the primary circuit to a hot state.

9. A control method for passive waste heat extraction from a steam generator according to claim 8, characterized in that, The system is in standby mode as follows: containment isolation valves A (2), B (3), C (6), and D (8) are open; large start valve (11) and small start valve (9) are closed; manual controllers A (10) and B (12) are 80% open; safety valve (7) is closed; emergency heat exhaust box (5) is at normal liquid level; heat exchanger (4) is in standby mode; and steam generator (1) is operating normally.

Images