Nuclear power plant main pump active shutdown sealing nitrogen tank depressurization method

Abstract

This invention discloses a method for depressurizing a nuclear power plant main pump active shutdown sealed nitrogen tank, comprising: S1, opening the containment isolation valve on the nitrogen supply pipeline of the SGN system, and installing a temporary depressurization device on a quick-connect fitting downstream of the SGN system's exhaust pipeline; S2, opening the exhaust valve on the exhaust pipeline, connecting the exhaust pipeline and the containment isolation valve, and depressurizing the main pump active shutdown sealed nitrogen tank through the containment isolation valve and the exhaust valve; S3, closing the exhaust valve when the pressure displayed by the temporary depressurization device is 0 MPa.g; S4, closing the containment isolation valve and observing the pressure change of the main pump active shutdown sealed nitrogen tank. This invention effectively reduces the pressure of the active shutdown sealed nitrogen tank, protects important nuclear safety-related equipment, and can adjust the pressure of the entire nitrogen supply pipeline to meet system requirements; it can also quickly respond to abnormal operating conditions of the active shutdown sealed nitrogen tank.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant operation control technology, and in particular to a method for depressurizing a sealed nitrogen tank for active shutdown of a nuclear power plant main pump. Background Technology

[0002] In nuclear power plants, the main pump plays a crucial role. It circulates the coolant in the primary loop, transferring heat from the reactor to the steam generator, which in turn produces steam to drive the turbine and generate electricity. It also provides sufficient pressure to the coolant, ensuring the primary loop operates under high pressure, preventing coolant boiling, and guaranteeing reactor safety. The active shutdown seal system is an important component of the main pump shaft seal system. When the pressure in the shutdown seal nitrogen tank exceeds 1.4 MPa.g, activating the shutdown seal may pose a risk of damage to the shutdown seal components. In this case, activation of the main pump shutdown seal is prohibited to prevent equipment damage. If the shutdown seal pipeline pressure continues to rise to 1.8 MPa.g, and the pressure protection function of the safety valve on the nitrogen supply main pipe fails, it may cause overpressure damage to the nitrogen tank solenoid valve, resulting in erroneous activation of the shutdown seal and potentially damaging the main pump. Due to the inherent leakage rate of the self-regulating pressure reducing valve, and given that the upstream nitrogen pressure is 4.8 MPa.g and the downstream nitrogen pressure is 1.0 MPa.g, the pressure in the nitrogen tank may continue to rise slowly. Even closing the containment isolation valves inside and outside the reactor building simultaneously cannot effectively suppress the pressure rise in the nitrogen tanks. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for depressurizing a sealed nitrogen tank for active shutdown of a nuclear power plant main pump.

[0004] The technical solution adopted by this invention to solve its technical problem is: to provide a method for depressurizing a sealed nitrogen tank for active shutdown of a nuclear power plant main pump, comprising the following steps:

[0005] S1. Open the containment isolation valve on the nitrogen supply line of the SGN system, and install a temporary pressure relief device on the quick connector downstream of the exhaust line of the SGN system.

[0006] The nitrogen supply pipeline is connected to the main pump active shutdown sealed nitrogen tank via a self-regulating pressure reducing valve; when the containment isolation valve is open, the main pump active shutdown sealed nitrogen tank downstream of the self-regulating pressure reducing valve is connected to the containment isolation valve.

[0007] S2. Open the exhaust valve on the exhaust pipeline to connect the exhaust pipeline and the containment isolation valve. The main pump active shutdown sealed nitrogen tank is depressurized through the containment isolation valve, the exhaust valve and the temporary pressure relief device.

[0008] S3. When the pressure display of the temporary pressure relief device is 0 MPa.g, close the exhaust valve;

[0009] S4. Close the containment isolation valve and observe the pressure change of the main pump's active shutdown sealed nitrogen tank.

[0010] In some embodiments, in step S1, the containment isolation valve is opened when the nitrogen supply isolation valve of the safety injection tank, the nitrogen supply isolation valve on the nitrogen supply pipeline of the SGN system, and the main pump shutdown sealing solenoid valve are in the closed state.

[0011] In some embodiments, during steps S1 to S4, the nitrogen pressure in the injection chamber should meet the following requirements: 4.4 MPa.g ≤ nitrogen pressure in the injection chamber ≤ 4.9 MPa.g.

[0012] In some embodiments, when the nitrogen pressure in the injection chamber is lower than 4.4 MPa.g, the injection chamber is pressurized.

[0013] Pressurizing the safety injection tank includes: opening the containment isolation valve and the nitrogen supply isolation valve on the nitrogen supply pipeline; nitrogen enters the safety injection tank through the nitrogen supply isolation valve, containment isolation valve, and nitrogen supply isolation valve; pressurization ends when the nitrogen pressure in the safety injection tank is greater than or equal to 4.4 MPa.g and less than or equal to 4.9 MPa.g; repeating steps S1 to S4 until the pressure in the upstream pipeline of the self-regulating pressure reducing valve drops to 0 MPa.g.

[0014] In some embodiments, the method for depressurizing the sealed nitrogen tank during the active shutdown of the nuclear power plant main pump further includes the following steps:

[0015] S5. When the pressure of the main pump's active shutdown sealed nitrogen tank drops to 1.0 MPa.g, pressurize the upstream pipeline of the self-regulating pressure reducing valve to the target pressure, which is 1.0 MPa.g to 1.3 MPa.g.

[0016] In some embodiments, pressurizing the upstream pipeline of the self-operated pressure reducing valve to the target pressure includes the following steps:

[0017] S5.1 Open the exhaust valve, and the temporary pressure relief device downstream of the exhaust valve is in the closed state;

[0018] S5.2 Open the nitrogen supply isolation valve on the nitrogen supply pipeline of the SGN system;

[0019] S5.3 When the pressure displayed by the temporary pressure relief device is 1.0 MPa.g to 1.3 MPa.g, close the nitrogen supply isolation valve;

[0020] S5.4 After the pressure in the downstream pipeline of the self-regulating pressure reducing valve stabilizes, the pressure in the downstream pipeline is adjusted by opening and closing the temporary pressure relief device to reach the target pressure, and then the exhaust valve is closed.

[0021] In some embodiments, the temporary pressure relief device includes a valve body with a pressure gauge and a male connector for detachable insertion into the valve body; the valve body has opposing first and second ends, the first end being for mating with the quick connector; when the male connector is inserted into the second end, the male connector communicates with an internal passage of the valve body for pressure relief; after the male connector is disengaged from the valve body, the second end of the valve body closes.

[0022] In step S5.1, the temporary pressure relief device is not equipped with the male connector, and at this time the temporary pressure relief device is in the closed state.

[0023] In some embodiments, the method for depressurizing the sealed nitrogen tank of the nuclear power plant main pump when the pressure reaches 1.4 MPa.g or above is used to depressurize the sealed nitrogen tank of the nuclear power plant main pump.

[0024] In some embodiments, the temporary pressure relief device includes a valve body with a pressure gauge and a male connector for detachable insertion into the valve body; the valve body has a first end and a second end opposite to each other, the first end being used to mate with the quick connector; when the male connector is inserted into the second end, the male connector communicates with an internal channel of the valve body for pressure relief; after the male connector is disengaged from the valve body, the second end of the valve body is closed.

[0025] In some embodiments, in step S1, the temporary pressure relief device is equipped with the male connector, at which time the temporary pressure relief device is in a pressure-relief state.

[0026] The beneficial effects of this invention are: it effectively reduces the pressure of the active shutdown sealed nitrogen tank, protects important nuclear safety-related equipment, and can adjust the pressure of the entire nitrogen supply pipeline to meet system requirements; using this method, abnormal operating conditions of the active shutdown sealed nitrogen tank can be responded to quickly, and the response can be completed outside the reactor building, avoiding the need for personnel to enter the reactor building to remove gauges and relieve pressure, thus avoiding unnecessary radiation doses and reducing the collective dose to the power plant. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0028] Figure 1 This is a schematic diagram of the nuclear power system connection used in the nuclear power main pump active shutdown sealed nitrogen tank depressurization method according to an embodiment of the present invention;

[0029] Figure 2This is a schematic diagram of a temporary pressure relief device according to an embodiment of the present invention. Detailed Implementation

[0030] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0031] The nuclear power plant main pump active shutdown sealing nitrogen tank depressurization method of the present invention involves a nuclear power system including a RIS system (safety injection system), a SGN system (nitrogen distribution system), and an RCP system (reactor coolant system). The SGN system (nitrogen distribution system) is used to supply nitrogen to at least the RIS system (safety injection system) and the RCP system (reactor coolant system).

[0032] like Figure 1 As shown, the main pump's active shutdown sealed nitrogen tank 100 is subordinate to the RCP system. The SGN system is connected to the RIS system and the RCP system respectively via a nitrogen supply line 10. The nitrogen supply line 10 includes a nitrogen supply isolation valve 11, a containment isolation valve 12, and a self-regulating pressure reducing valve 13; the nitrogen supply isolation valve 11 is located outside the containment. Figure 1 The device has two nitrogen supply isolation valves 11 and two containment isolation valves 12. The nitrogen supply line 10 is also connected to an exhaust line 14, which is equipped with an exhaust valve 15. Downstream of the exhaust valve 15, there is a quick connector 16 for connecting various required pipelines or tools. Downstream of the self-operated pressure reducing valve 13, it is connected to the main pump active shutdown sealed nitrogen tank 100 via a check valve 20 and a pipeline. The main pump active shutdown sealed nitrogen tank 100, the check valve 20, and the pipeline thereon also form the downstream pipeline of the self-operated pressure reducing valve 13. The nitrogen supply line 10 and the containment isolation valves 12 upstream of the self-operated pressure reducing valve 13 form the upstream pipeline of the self-operated pressure reducing valve 13.

[0033] The main pump's active shutdown sealing nitrogen tank 100 is connected to the main pump shaft seal via the main pump shutdown sealing solenoid valve 21. Figure 1 In the embodiment shown, the RCP system has three main pump active shutdown sealing nitrogen tanks 100. The three main pump active shutdown sealing nitrogen tanks 100 are respectively connected to the No. 1 main pump shaft seal, the No. 2 main pump shaft seal, and the No. 3 main pump shaft seal through their respective main pump shutdown sealing solenoid valves 21.

[0034] The RIS system (Safety Injection System) includes an injection tank 200, an injection line 30 connected between the injection tank 200 and the nitrogen supply line 10, a check valve 31 and a nitrogen supply isolation valve 32 installed on the injection line 30; the injection line 30 is connected to the nitrogen supply line 10 between the self-regulating pressure reducing valve 13 and the containment isolation valve 12. Figure 1In the embodiment shown, the RIS system includes three injection tanks 200, which are connected upstream of the self-regulating pressure reducing valve 13 via their respective nitrogen supply isolation valves 32 and check valves 31.

[0035] The self-operated pressure reducing valve 13 is used to reduce the medium-pressure nitrogen gas from 4.8 MPa.g to 1.0 MPa.g for use by the downstream main pump's actively shut-off sealed nitrogen tank 100. The self-operated pressure reducing valve 13 relies on the spring force setting to determine the outlet pressure, ensuring downstream pressure stability. When the upstream pipeline of the self-operated pressure reducing valve 13 is depressurized in the reverse direction, due to the certain leakage rate of the self-operated pressure reducing valve 13, the downstream pressure gradually leaks upstream. When the downstream pressure drops below the set value, the self-operated pressure reducing valve 13 opens to replenish pressure under the action of the spring force, which is actually depressurization, thus completing the depressurization operation.

[0036] The check valve 20 at the front end of the main pump's active-operated shut-off sealed nitrogen tank 100 is a lift-type check valve with a hard-seal structure, which has a certain leakage rate and therefore can depressurize in the reverse direction.

[0037] refer to Figure 1 An embodiment of the present invention provides a method for depressurizing a nuclear power plant main pump active shutdown sealed nitrogen tank 100 when the pressure reaches 1.4 MPa.g or higher. The depressurization method may include the following steps:

[0038] S1. With the nitrogen supply isolation valve 32 of the safety injection tank 200, the nitrogen supply isolation valve 11 on the nitrogen supply line 10 of the SGN system, and the main pump shutdown sealing solenoid valve 21 in the closed state, open the containment isolation valve 12 on the nitrogen supply line 10 of the SGN system; install a temporary pressure relief device 40 on the quick connector 16 downstream of the exhaust line 14 of the SGN system.

[0039] The nitrogen supply pipeline 10 is connected to the main pump's active shutdown sealed nitrogen tank 100 via a self-regulating pressure reducing valve 13.

[0040] After step S1 is executed, with the containment isolation valve 12 open, the main pump active shutdown sealed nitrogen tank 100, which is downstream of the self-operated pressure reducing valve 13, is connected to the containment isolation valve 12.

[0041] Among them, such as Figure 2As shown, the temporary pressure relief device 40 includes a valve body 42 with a pressure gauge 41 and a male connector 43 for detachable insertion into the valve body 42. The valve body 42 has a first end 421 and a second end 422 opposite to each other. The first end 421 is used to mate with a quick connector 16. When the male connector 43 is inserted into the second end 422, the male connector 43 communicates with the internal passage of the valve body 42 for pressure relief. After the male connector 43 is disengaged from the valve body 42, the second end 422 of the valve body 42 closes. In step S1, the temporary pressure relief device 40 has the male connector 43, and at this time, the temporary pressure relief device 40 is in a pressure-relief state.

[0042] S2. Open the exhaust valve 15 on the exhaust line 14 to connect the exhaust line 14 and the containment isolation valve 12. The main pump active shutdown sealed nitrogen tank 100 is depressurized through the containment isolation valve 12 and the exhaust valve 15. That is, the nitrogen in the main pump active shutdown sealed nitrogen tank 100 is discharged in sequence through the check valve 20, the self-regulating pressure reducing valve 13, the containment isolation valve 12, the exhaust valve 15 and the temporary pressure relief device 40.

[0043] Since check valve 20 is a lift-type check valve with a hard seal structure, it has a certain leakage rate and can release pressure in the reverse direction.

[0044] Control the opening of the exhaust valve 15 to release pressure at an appropriate degree. Excessive valve opening will cause excessive pipe vibration and a sharp, piercing sound. A reasonable opening degree prevents pipe breakage due to high vibration and ensures the safety of on-site personnel.

[0045] During the depressurization process, the pressure of the three main pumps in the automatically shut-off sealed nitrogen tank 100 must be closely monitored. If any abnormality is detected, the depressurization process must be stopped immediately.

[0046] S3. When the pressure display of the temporary pressure relief device 40 is 0 MPa.g, close the exhaust valve 15.

[0047] S4. Close the containment isolation valve 12 and observe the pressure change of the main pump active shutdown sealed nitrogen tank 100.

[0048] During steps S1 to S4 above, the nitrogen pressure inside the injection tank 200 should meet the following requirements: 4.4 MPa.g ≤ nitrogen pressure inside injection tank 200 ≤ 4.9 MPa.g. If the nitrogen pressure inside injection tank 200 is lower than 4.4 MPa.g, the injection tank 200 should be pressurized.

[0049] Pressurizing the safety injection tank 200 includes: opening the containment isolation valve 12 and the nitrogen supply isolation valve 11 on the nitrogen supply line 10; nitrogen enters the safety injection tank 200 through the nitrogen supply isolation valve 11, the containment isolation valve 12, and the nitrogen supply isolation valve 32; pressurization ends when the nitrogen pressure inside the safety injection tank 200 is greater than or equal to 4.4 MPa.g and less than or equal to 4.9 MPa.g. Steps S1 to S4 are repeated until the pressure in the upstream pipeline of the self-regulating pressure reducing valve 13 drops to 0 MPa.g.

[0050] In some embodiments, the method for depressurizing the sealed nitrogen tank during the active shutdown of the main pump in a nuclear power plant further includes the following steps:

[0051] S5. When the pressure of the main pump active shutdown sealed nitrogen tank 100 drops to 1.0 MPa.g, pressurize the upstream pipeline of the self-operated pressure reducing valve 13 to the target pressure, which is 1.0 MPa.g to 1.3 MPa.g.

[0052] In step S5, the pressure change of the main pump's active shutdown sealed nitrogen tank 100 is continuously observed until its pressure drops to 1.0 MPa.g. This observation period generally needs to last for several days.

[0053] Furthermore, pressurizing the upstream pipeline of the self-operated pressure reducing valve 13 to the target pressure includes the following steps:

[0054] S5.1 Open the exhaust valve 15, and the temporary pressure relief device 40 downstream of the exhaust valve 15 is in the closed state;

[0055] In step S5.1, the temporary pressure relief device 40 is not equipped with the male connector 43, and at this time the temporary pressure relief device 40 is in the closed state (cannot relieve pressure).

[0056] S5.2. Open the nitrogen supply isolation valve 11 on the nitrogen supply line 10 of the SGN system.

[0057] The nitrogen supply isolation valve 11 is pressurized with a small opening. If the valve opening is too large, it will cause large vibrations in the pipeline and a sharp, piercing sound.

[0058] Nitrogen enters the main pump's active shutdown sealed nitrogen tank 100 through the nitrogen supply isolation valve 11, the containment isolation valve 12, the nitrogen supply line 10, and the self-regulating pressure reducing valve 13. At the same time, nitrogen also enters the exhaust line 14 and reaches the temporary pressure relief device 40 through the exhaust valve 15.

[0059] S5.3 When the pressure reading of the temporary pressure relief device 40 is 1.0 MPa.g to 1.3 MPa.g, close the nitrogen supply isolation valve 11.

[0060] S5.4 Continuously observe until the pressure in the downstream pipeline (including the main pump active shutdown sealed nitrogen tank 100) of the self-regulating pressure reducing valve 13 stabilizes. After adjusting the downstream pipeline pressure to the target pressure by opening and closing the temporary pressure relief device 40, close the exhaust valve 15.

[0061] The downstream pipeline pressure of the self-operated pressure reducing valve 13 requires 30 minutes or more to stabilize.

[0062] The opening and closing adjustment of the temporary pressure relief device 40 is the operation of inserting and removing the male connector 43; when the downstream pipeline pressure is higher than the target pressure, the male connector 43 is inserted to relieve pressure.

[0063] After the above is completed, disassembly and restoration work can be carried out, including: removing the temporary pressure relief device 40 on the quick connector 16, closing the containment isolation valve 12, and opening the nitrogen supply isolation valve 11.

[0064] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for depressurizing a nitrogen tank for active parking seal of a nuclear power primary pump, characterized in that, The method comprises the following steps: S1, opening the containment isolation valve on the nitrogen supply pipeline of the SGN system, and installing a temporary pressure relief device on the quick connector downstream of the exhaust pipeline of the SGN system; Wherein, the nitrogen supply pipeline is connected with the main pump active parking sealing nitrogen tank through the self-operated pressure reducing valve; in the open state of the containment isolation valve, the main pump active parking sealing nitrogen tank downstream of the self-operated pressure reducing valve is communicated with the containment isolation valve; The temporary pressure relief device comprises a valve body with a pressure gauge, a male head for detachably inserting into the valve body; the valve body has opposite first and second ends, the first end is used for mating connection with the quick connector; when the male head is inserted into the second end, the male head is communicated with the internal passage of the valve body for pressure relief; after the male head is separated from the valve body, the second end of the valve body is closed; S2, opening the exhaust valve on the exhaust pipeline, and communicating the exhaust pipeline and the containment isolation valve, the main pump active parking sealing nitrogen tank is relieved through the containment isolation valve, the exhaust valve and the temporary pressure relief device; S3, when the pressure display of the temporary pressure relief device is 0 MPa.g, closing the exhaust valve; S4, closing the containment isolation valve, and observing the pressure change of the main pump active parking sealing nitrogen tank; S5, when the pressure of the main pump active parking sealing nitrogen tank drops to 1.0 MPa.g, pressurizing the pipeline upstream of the self-operated pressure reducing valve to a target pressure, and the target pressure is 1.0 MPa.g-1.3 MPa.g; Pressurizing the pipeline upstream of the self-operated pressure reducing valve to the target pressure comprises the following steps: S5.1, opening the exhaust valve, and the temporary pressure relief device downstream of the exhaust valve is in a closed state; the temporary pressure relief device does not have the male head, at this time, the temporary pressure relief device is in a closed state; S5.2, opening the nitrogen supply isolation valve on the nitrogen supply pipeline of the SGN system; S5.3, when the pressure display of the temporary pressure relief device is 1.0 MPa.g-1.3 MPa.g, closing the nitrogen supply isolation valve; S5.4, after the pressure of the pipeline downstream of the self-operated pressure reducing valve is stabilized, the downstream pipeline pressure is adjusted to the target pressure by opening and closing the temporary pressure relief device, and then the exhaust valve is closed.

2. The method of claim 1, wherein the pressure relief is performed by opening a valve of the nitrogen tank. In step S1, the containment isolation valve is opened under the condition that the nitrogen supply isolation valve on the injection box, the nitrogen supply isolation valve on the nitrogen supply pipeline of the SGN system and the main pump parking sealing electromagnetic valve are in a closed state.

3. The method of claim 1, wherein the method further comprises, During steps S1 to S4, the nitrogen pressure in the injection box should satisfy: 4.4 MPa.g≤ nitrogen pressure in the injection box≤4.9 MPa.g.

4. The method of claim 3, wherein the pressure relief is performed by opening a valve of the nitrogen tank. When the nitrogen pressure in the injection box is lower than 4.4 MPa.g, the injection box is pressurized; The pressure compensation of the injection tank comprises: opening the containment isolation valve and the nitrogen supply isolation valve on the nitrogen supply pipeline, nitrogen enters the injection tank through the nitrogen supply isolation valve, the containment isolation valve and the nitrogen supply isolation valve, and the pressure compensation ends when the nitrogen pressure in the injection tank is greater than or equal to 4.4 MPa.g and less than or equal to 4.9 MPa.g; steps S1 to S4 are re-executed until the pressure of the pipeline upstream of the self-operated pressure reducing valve is reduced to 0 MPa.g.

5. The method of claim 1-4, wherein the method further comprises, The method for depressurizing the active parking sealing nitrogen tank of the nuclear power main pump can be used for depressurizing the active parking sealing nitrogen tank of the nuclear power main pump when the pressure of the active parking sealing nitrogen tank reaches 1.4 MPa.g or above.

6. The method of claim 1-4, wherein the method further comprises, In step S1, the temporary pressure relief device is provided with the male head, and at this time, the temporary pressure relief device is in a pressure relief state.

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