Local cleaning system and method for the secondary side of a nuclear power DC steam generator

Abstract

The present invention discloses a local cleaning system and method for the secondary circuit side of a nuclear power direct current steam generator. A demineralized water inlet and a chemical dosing port are provided on the cleaning tank. A cleaning tank liquid level gauge is arranged inside the cleaning tank. A main feed water temporary blind plate is provided on the main feed water connection section of the steam generator; a main steam temporary blind plate is provided on the main steam connection section of the steam generator. The outlet of the cleaning tank is connected to the water inlet on the main feed water temporary blind plate through a cleaning pump. The water outlet on the main feed water temporary blind plate is divided into two paths. One path is connected to the inlet of the waste liquid tank through an exhaust valve, and the other path is connected to the inlet of the cleaning tank through a return water valve. The liquid level measurement port on the main feed water temporary blind plate is connected to one end of a temporary liquid level gauge, and the other end of the temporary liquid level gauge is connected to the liquid level measurement port on the main steam temporary blind plate. This system and method have the characteristics of short cleaning cycle, low consumption of chemicals and demineralized water, small equipment volume, and low cost.

Description

Technical Field

[0001] The present invention belongs to the field of chemical cleaning of nuclear power plants, and relates to a partial cleaning system and method for the secondary side of a nuclear power once-through steam generator. Background Art

[0002] Chemical cleaning technology has been widely applied to many important equipment such as the steam-water pipelines of thermal power plants, and has achieved very good economic and safety benefits. Chemical cleaning is an important means to remove various sundries remaining during the processes of manufacturing, transportation, installation, storage, etc. of the pipeline systems of power plant systems, improve the cleanliness of equipment, form a dense oxide film, and prevent corrosion damage of equipment during operation, and is an important step before the commissioning of units or during regular operation and maintenance.

[0003] At present, the feed water treatment method adopted for steam generators in nuclear power units is reductive all-volatile treatment (AVT(R)). Referring to the operating experience of once-through boilers in thermal power plants, for the water-cooled wall tubes of once-through boilers with throttle orifices at the inlet, when the feed water treatment method adopts AVT(R), blockage problems are likely to occur at the throttle orifice parts. The direct phenomenon is that the deviation of the steam generator outlet temperature increases and the differential pressure between the inlet and outlet slowly rises. To ensure the service safety of the steam generator, it is necessary to remove the scale deposits at the throttle orifice parts of the steam generator.

[0004] Considering that the comprehensive cleaning method has the following disadvantages: First, the chemical cleaning cycle is long, especially leading to an extension of the overhaul period of nuclear power plants, which has an obvious impact on the economy of nuclear power plants. Second, the consumption of chemicals and demineralized water suitable for chemical cleaning is large, the amount of wastewater generated is large, and the cost is high. Third, the equipment has a large volume and a high equipment cost, generally up to several hundred thousand yuan. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art, and provides a partial cleaning system and method for the secondary side of a nuclear power once-through steam generator, which have the characteristics of short cleaning cycle, low consumption of chemicals and demineralized water, small equipment volume and low cost.

[0006] To achieve the above purpose, the present invention discloses a partial cleaning system for the secondary side of a nuclear power once-through steam generator, including a cleaning tank, a steam generator, a cleaning pump, an exhaust valve, a waste liquid tank, a return water valve and a temporary liquid level gauge;

[0007] The cleaning tank is provided with a demineralized water inlet and a chemical dosing port, and a cleaning tank liquid level gauge is arranged inside the cleaning tank. A main feed water temporary blind plate is arranged on the main feed water connection section of the steam generator;

[0008] A main steam temporary blind plate is provided on the main steam connection section of the steam generator. The outlet of the cleaning tank is connected to the water inlet on the main feed water temporary blind plate through a cleaning pump. The water outlet on the main feed water temporary blind plate is divided into two paths. One path is connected to the inlet of the waste liquid tank through an exhaust valve, and the other path is connected to the inlet of the cleaning tank through a return water valve. The liquid level measurement port on the main feed water temporary blind plate is connected to one end of a temporary liquid level gauge, and the other end of the temporary liquid level gauge is connected to the liquid level measurement port on the main steam temporary blind plate.

[0009] The outlet of the cleaning tank is connected to the water inlet on the main feed water temporary blind plate through a cleaning pump inlet valve, a cleaning pump, a cleaning pump outlet valve, a water inlet flange and a water inlet valve in sequence.

[0010] The water outlet on the main feed water temporary blind plate is divided into two paths after passing through a drain valve and a drain flange.

[0011] The liquid level measurement port on the main feed water temporary blind plate is connected to one end of the temporary liquid level gauge through an upper root valve of the temporary liquid level gauge, and the other end of the temporary liquid level gauge is connected to the liquid level measurement port on the main steam temporary blind plate through a lower root valve of the temporary liquid level gauge.

[0012] An electric heater, an ultrasonic generating device and a thermocouple are provided on the main feed water temporary blind plate.

[0013] A nitrogen charging valve is provided at the gas charging port on the main feed water temporary blind plate.

[0014] An exhaust port is provided on the main feed water temporary blind plate, and an oxygen analyzer is connected to the exhaust port.

[0015] A sampling port is provided on the main feed water temporary blind plate, and a sampling pipe is connected to the sampling port.

[0016] The present invention discloses a method for locally cleaning the secondary circuit side of a nuclear power once-through steam generator, including:

[0017] 1) Selection of cleaning chemical medium;

[0018] 2) System installation, commissioning and water flushing;

[0019] 3) System airtightness inspection;

[0020] 4) System nitrogen replacement;

[0021] 5) System filling with protective liquid;

[0022] 6) Performing citric acid cleaning and passivation;

[0023] 7) Water flushing after passivation;

[0024] 8) Overall flushing of the steam generator.

[0025] The operation process of step 6) is as follows:

[0026] 61) Start the electric heater to heat the solution in the steam generator;

[0027] 62) Open the return water valve to lower the liquid level of the solution in the steam generator below the throttling component in the steam generator, and then close the return water valve;

[0028] 63) Add cleaning agent to the cleaning tank, start the cleaning pump, and open the return water valve to balance the inlet water flow and the inlet and return water flow, and gradually add the cleaning agent to the steam generator;

[0029] 64) Take samples from the sampling port of the main feed water temporary blind plate to test the concentration of the cleaning solution. When the concentration of the cleaning solution in the steam generator reaches the process conditions, then close the return water valve and the cleaning pump;

[0030] 65) Start the electric heater to raise the temperature of the cleaning agent in the steam generator;

[0031] 66) Start the cleaning pump to make the liquid level of the solution in the steam generator higher than the position of the main feed water temporary blind plate, and then stop the cleaning pump;

[0032] 67) Every 0.5 - 1 h, open the return water valve to lower the liquid level of the solution in the steam generator below the throttling component, then close the return water valve, start the cleaning pump to make the liquid level of the solution in the steam generator higher than the position of the main feed water temporary blind plate, and then stop the cleaning pump;

[0033] 68) Repeat step 67) until the cleaning time reaches 16 h - 24 h;

[0034] 69) Every preset time, test the Fe ion concentration of the solution in the cleaning tank and the steam generator, calculate the total iron amount in the cleaning solution, and end the cleaning after the total iron concentration is balanced for 2 h - 4 h;

[0035] 610) Every preset time, start the ultrasonic generating device and close it after maintaining the preset working time;

[0036] 611) After the cleaning is completed, turn off the electric heater. After the temperature of the cleaning solution drops to the preset temperature, open the drain valve to make the cleaning waste liquid enter the waste liquid tank;

[0037] 612) Drain the waste liquid in the cleaning tank and the waste liquid tank into the transfer bucket, and then transfer it to the waste liquid storage area;

[0038] 613) Add demineralized water to the cleaning tank to the preset high liquid level, start the cleaning pump, inject the flushing solution into the steam generator. After the liquid level in the steam generator is higher than the position of the main feed water temporary blind plate, stop the cleaning pump, start the ultrasonic generating device and close it after maintaining the preset working time;

[0039] 614) Open the drain valve to allow the cleaning waste liquid in the steam generator to enter the waste liquid tank, drain the waste liquid in the waste liquid tank into the transfer bucket, and then transfer it to the waste liquid storage area;

[0040] 615) Repeat step 613) and step 614) to rinse the steam generator again;

[0041] 616) Fill water into the steam generator and test the Fe ion concentration of the solution in the steam generator. When the Fe ion concentration of the solution in the steam generator is less than 50 mg / L, proceed to step 617); otherwise, repeat step 613) and step 614);

[0042] 617) Start the cleaning pump and the return water valve to establish a circulation between the cleaning tank and the steam generator, and add EDTA and ammonia water with a concentration of 0.3%-0.5% to the cleaning liquid;

[0043] 618) Stop the cleaning pump, close the return water valve, start the electric heater to heat the solution, and after stabilizing for 2-4 hours, the passivation is completed.

[0044] The present invention has the following beneficial effects:

[0045] When the local cleaning system and method for the secondary side of a nuclear power once-through steam generator described in the present invention are specifically operated, the main feed water connection section and the main steam connection section are covered with temporary blind plates. The chemical agents are injected into the secondary side of the steam generator through the temporary blind plate of the main feed water by using the cleaning tank and the pump to soak and clean the throttle components. The electric heater is used to raise the temperature of the chemical cleaning liquid, the ultrasonic generating device is regularly used to disturb the cleaning liquid, and the chemical cleaning liquid is regularly filled and drained to enhance the cleaning effect. It should be noted that the present invention can significantly shorten the time of chemical cleaning, reduce the consumption of chemical cleaning drugs and demineralized water, reduce the generated wastewater, has a small equipment volume, and a low investment cost, generally several tens of thousands of yuan, and the economic benefits are obvious. Description of the Drawings

[0046] Figure 1 is the structural diagram of the present invention;

[0047] Figure 2 is the structural diagram of the temporary blind plate of the main feed water connecting pipe in the present invention.

[0048] Among them, 1 is a steam generator, 2 is a throttling component, 3 is a main feed water connection section, 4 is a main feed water temporary blind plate, 5 is a main steam connection section, 6 is a main steam temporary blind plate, 7 is an upper root valve of a temporary liquid level gauge, 8 is a temporary liquid level gauge, 9 is a cleaning tank, 10 is a cleaning tank liquid level gauge, 11 is a demineralized water inlet, 12 is a chemical dosing port, 13 is a cleaning pump inlet valve, 14 is a cleaning pump, 15 is a cleaning pump outlet valve, 16 is a return water valve, 17 is a vent valve, 18 is a waste liquid tank, 19 is a power supply box, 401 is a bolt hole, 402 is a water inlet flange, 403 is a water inlet valve, 404 is an electric heater, 405 is an ultrasonic generating device, 406 is a nitrogen charging valve, 407 is a thermocouple, 408 is a lower root valve of a temporary liquid level gauge, 409 is a drain flange, 410 is a drain valve. Detailed implementation manners

[0049] In order to enable those skilled in the art of the present technology to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and are not intended to limit the scope of the present invention disclosure. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessarily confusing the concepts disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0050] The structural schematic diagrams according to the disclosed embodiments of the present invention are shown in the drawings. These figures are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are only exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0051] Embodiment 1

[0052] Reference Figure 1 and Figure 2, the local cleaning system for the secondary side of the nuclear power once-through steam generator described in the present invention includes a steam generator 1, a throttling assembly 2, a main feed water connection section 3, a main feed water temporary blind plate 4, a main steam connection section 5, a main steam temporary blind plate 6, an upper root valve 7 of a temporary liquid level gauge, a temporary liquid level gauge 8, a cleaning tank 9, a cleaning tank liquid level gauge 10, a demineralized water inlet 11, a chemical dosing port 12, a cleaning pump inlet valve 13, a cleaning pump 14, a cleaning pump outlet valve 15, a return water valve 16, a drain valve 17, a waste liquid tank 18, a power supply box 19, bolt holes 401, an inlet flange 402, an inlet valve 403, an electric heater 404, an ultrasonic generating device 405, a nitrogen filling valve 406, a thermocouple 407, a lower root valve 408 of a temporary liquid level gauge, a drain flange 409 and a drain valve 410;

[0053] The cleaning tank 9 is provided with a demineralized water inlet 11 and a chemical dosing port 12, the cleaning tank 9 is internally provided with a cleaning tank liquid level gauge 10, and the main feed water connection section 3 is provided with a main feed water temporary blind plate 4.

[0054] The main steam connection section 5 of the steam generator 1 is provided with a main steam temporary blind plate 6. The outlet of the cleaning tank 9 is successively connected to the water inlet on the main feed water temporary blind plate 4 through a cleaning pump inlet valve 13, a cleaning pump 14, a cleaning pump outlet valve 15, an inlet flange 402 and an inlet valve 403. The water outlet on the main feed water temporary blind plate 4 is divided into two paths after passing through a drain valve 410 and a drain flange 409. One path is connected to the inlet of the waste liquid tank 18 through a drain valve 17, and the other path is connected to the inlet of the cleaning tank 9 through a return water valve 16. The liquid level measurement port on the main feed water temporary blind plate 4 is connected to one end of the temporary liquid level gauge 8 through an upper root valve 7 of the temporary liquid level gauge, and the other end of the temporary liquid level gauge 8 is connected to the liquid level measurement port on the main steam temporary blind plate 6 through a lower root valve 408 of the temporary liquid level gauge.

[0055] In this embodiment, the main feed water temporary blind plate 4 is provided with an electric heater 404, an ultrasonic generating device 405 and a thermocouple 407.

[0056] In this embodiment, a nitrogen filling valve 406 is provided at the gas charging port on the main feed water temporary blind plate 4.

[0057] In this embodiment, it further includes a power supply box 19 for providing electric energy.

[0058] In this embodiment, the main feed water temporary blind plate 4 is provided with bolt holes 401, and bolts pass through the bolt holes 401 and are inserted into the main feed water connection section 3 to connect the main feed water temporary blind plate 4 and the main feed water connection section 3.

[0059] In this embodiment, the main feed water temporary blind plate 4 is provided with an exhaust port, and the exhaust port is connected to an oxygen analyzer.

[0060] In this embodiment, a sampling port is provided on the main feed water temporary blind plate 4, and a sampling pipe is connected to the sampling port.

[0061] The method for local cleaning of the secondary side of a nuclear power once-through steam generator applicable to the present invention includes the following steps:

[0062] 1) Selection of cleaning chemical medium;

[0063] The present invention selects 4.0%-6.0% citric acid + 0.5%-1.0% co-solvent + reducing agent + corrosion inhibitor, with a pH value of 3.8-4.0 and a temperature of 80-85 °C.

[0064] 2) System installation, commissioning and water flushing;

[0065] After the reactor is shut down and cooled, the main feed water pipe and the main steam pipe are removed. A main feed water temporary blind plate 4 is installed on the main feed water connection section 3, and a main steam temporary blind plate 6 is installed on the main steam connection section 5 to establish a temporary system. The electric heater 404, the ultrasonic generator 405 and the cleaning pump 14 are commissioned with water to ensure that the equipment is available, and the temporary system is flushed with water until the drained water is visually clear.

[0066] 3) System airtightness inspection;

[0067] The temporary system is filled with nitrogen and pressurized to test the system tightness. Nitrogen enters from the nitrogen filling valve 406, and after pressurizing to 0.1 MPa - 0.2 MPa, it is kept under pressure. If the pressure does not drop within 10 minutes, it is qualified.

[0068] 4) System nitrogen replacement;

[0069] The pressure in the system is reduced to atmospheric pressure, and nitrogen is filled into the steam generator 1 through the nitrogen filling valve 406 by a nitrogen cylinder for deoxidation. The oxygen content of the discharged gas is measured by an oxygen analyzer at the exhaust port of the main feed water temporary blind plate 4 to make the oxygen content of the discharged gas less than 5%.

[0070] 5) System filling with protective liquid;

[0071] Make up water to the cleaning tank 9 through the demineralized water inlet 11, add ammonia water to the cleaning tank 9 through the chemical dosing port 12 to make the pH value of the solution above 10.5, start the cleaning pump 14, inject water into the steam generator 1, calibrate the temporary liquid level gauge 8, and make the liquid level of the solution in the steam generator 1 reach about 2 m above the main feed water temporary blind plate 4, and then stop the cleaning pump 14.

[0072] 6) Perform citric acid cleaning and passivation;

[0073] 61) Start the electric heater 404 to raise the temperature of the solution in the steam generator 1 to 60 °C, and the temperature of the solution is detected by the thermocouple 407;

[0074] 62) Open the return water valve 16 to lower the liquid level of the solution in the steam generator 1 below the throttling component 2 in the steam generator 1, and then close the return water valve 16;

[0075] 63) Add cleaning agent to the cleaning tank 9, start the cleaning pump 14, and open the return water valve 16 to balance the inlet water flow and the inlet and return water flow, and gradually add the cleaning agent to the steam generator 1;

[0076] 64) Take a sample from the sampling port of the main feed water temporary blind plate 4 to test the concentration of the cleaning solution. When the concentration of the cleaning solution in the steam generator 1 reaches the process conditions, close the return water valve 16 and the cleaning pump 14. At this time, the liquid level should still be below the throttling component 2;

[0077] 65) Start the electric heater 404 to raise the temperature of the cleaning agent in the steam generator 1 to 85°C - 90°C;

[0078] 66) Start the cleaning pump 14. After the liquid level of the solution in the steam generator 1 is 2 m higher than the position of the main feed water temporary blind plate 4, stop the cleaning pump 14;

[0079] 67) Every 0.5 - 1 h, open the return water valve 16 to lower the liquid level of the solution in the steam generator 1 below the throttling component 2, then close the return water valve 16, start the cleaning pump 14. After the liquid level of the solution in the steam generator 1 is 2 m higher than the position of the main feed water temporary blind plate 4, stop the cleaning pump 14;

[0080] 68) Repeat step 67) until the cleaning time reaches 16 h - 24 h;

[0081] 69) Every 1 h, test the Fe ion concentration of the solution in the cleaning tank 9 and the steam generator 1, calculate the total iron amount in the cleaning solution, and end the cleaning after the total iron concentration is balanced for 2 h - 4 h;

[0082] 610) Every 1 h, start the ultrasonic generating device 405 and keep it on for 10 minutes and then turn it off;

[0083] 611) After the cleaning is completed, turn off the electric heater 404. After the temperature of the cleaning solution drops to 60°C, open the drain valve 410 to allow the cleaning waste liquid to enter the waste liquid tank 18;

[0084] 612) Drain the waste liquid in the cleaning tank 9 and the waste liquid tank 18 into the transfer bucket, and then transfer it to the waste liquid storage area;

[0085] 613) Add demineralized water to the cleaning tank 9 to the preset high liquid level, start the cleaning pump 14, inject the flushing solution into the steam generator 1, and after the liquid level in the steam generator 1 is 2 m higher than the position of the main feed water temporary blind plate 4, stop the cleaning pump 14, start the ultrasonic generating device 405, and close it after maintaining for 10 min;

[0086] 614) Open the drain valve 410 to allow the cleaning waste liquid in the steam generator 1 to enter the waste liquid tank 18, drain the waste liquid in the waste liquid tank 18 into the transfer bucket, and then transfer it to the waste liquid storage area;

[0087] 615) Repeat steps 613) and 614) to rinse the steam generator 1 again;

[0088] 616) Make up water into the steam generator 1, test the Fe ion concentration of the solution in the steam generator 1. When the Fe ion concentration of the solution in the steam generator 1 is less than 50 mg / L, proceed to step 617); otherwise, repeat steps 613) and 614);

[0089] 617) Start the cleaning pump 14 and the return water valve 16 to establish a circulation between the cleaning tank 9 and the steam generator 1, and add EDTA and ammonia water with a concentration of 0.3% - 0.5% to the cleaning liquid;

[0090] 618) Stop the cleaning pump 14, close the return water valve 16, start the electric heater 404 to make the temperature of the solution reach 85 °C, and after stabilizing for 2 - 4 h, the passivation is completed.

[0091] 7) Flush with water after passivation;

[0092] 71) Start the cleaning pump 14, open the return water valve 16 to establish a circulation between the cleaning tank 9 and the steam generator 1;

[0093] 72) Open the drain valve 410 to discharge the waste water into the nuclear island waste water sump, add demineralized water and ammonia water to the cleaning tank 9, maintain the pH value (≥10.0) and liquid level of the flushing water, continuously take samples of the steam generator 1, test the Fe ion concentration of the solution in the steam generator 1, and end the water flushing when the Fe ion concentration of the solution in the steam generator 1 is less than 10 mg / L.

[0094] 8) Overall flushing of the steam generator 1;

[0095] Continuously supplement demineralized water to the cleaning tank 9, adjust the pH to above 10 with ammonia, then start the cleaning pump 14 to make up water into the secondary side of the steam generator 1, and drain it after the steam generator 1 is filled.

[0096] 9) System restoration and maintenance after cleaning;

[0097] 91) Remove the temporary system, drain the water in the system memory, remove the temporary system for restoration work, and check the cleaning effect of the throttling component 2.

[0098] 92) Perform maintenance according to the maintenance procedure of the steam generator 1.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific embodiments of the present invention or make equivalent replacements, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A local cleaning system applicable to the secondary circuit side of a nuclear power once-through steam generator, characterized in that It includes a cleaning tank (9), a steam generator (1), a cleaning pump (14), an evacuation valve (17), a waste liquid tank (18), a return water valve (16) and a temporary liquid level gauge (8); The cleaning tank (9) is provided with a demineralized water inlet (11) and a chemical dosing port (12). A cleaning tank liquid level gauge (10) is arranged inside the cleaning tank (9). A main feed water temporary blind plate (4) is arranged on the main feed water connection section (3) of the steam generator (1); A main steam temporary blind plate (6) is arranged on the main steam connection section (5) of the steam generator (1). The outlet of the cleaning tank (9) is connected to the water inlet on the main feed water temporary blind plate (4) via the cleaning pump (14). The water outlet on the main feed water temporary blind plate (4) is divided into two paths. One path is connected to the inlet of the waste liquid tank (18) via the evacuation valve (17), and the other path is connected to the inlet of the cleaning tank (9) via the return water valve (16). The liquid level measurement port on the main feed water temporary blind plate (4) is connected to one end of the temporary liquid level gauge (8), and the other end of the temporary liquid level gauge (8) is connected to the liquid level measurement port on the main steam temporary blind plate (6); The liquid level measurement port on the main feed water temporary blind plate (4) is connected to one end of the temporary liquid level gauge (8) via the upper root valve (7) of the temporary liquid level gauge, and the other end of the temporary liquid level gauge (8) is connected to the liquid level measurement port on the main steam temporary blind plate (6) via the lower root valve (408) of the temporary liquid level gauge; An electric heater (404), an ultrasonic generating device (405) and a thermocouple (407) are arranged on the main feed water temporary blind plate (4); A nitrogen filling valve (406) is arranged at the gas filling port on the main feed water temporary blind plate (4); An exhaust port is arranged on the main feed water temporary blind plate (4), and an oxygen analyzer is connected to the exhaust port; A sampling port is arranged on the main feed water temporary blind plate (4), and a sampling tube is connected to the sampling port.

2. The local cleaning system for the secondary side of a nuclear power once-through steam generator according to claim 1, wherein The outlet of the cleaning tank (9) is connected to the water inlet on the main feed water temporary blind plate (4) via the cleaning pump inlet valve (13), the cleaning pump (14), the cleaning pump outlet valve (15), the inlet flange (402) and the inlet valve (403) in sequence.

3. The local cleaning system for the secondary side of a nuclear power DC steam generator according to claim 2, characterized in that, The water outlet on the main feed water temporary blind plate (4) is divided into two paths after passing through the drain valve (410) and the drain flange (409).

4. A local cleaning method for the secondary side of a nuclear power DC steam generator, characterized in that, The local cleaning system for the secondary circuit side of a nuclear power once-through steam generator according to claim 1 includes: 1) Selection of cleaning chemical medium; 2) System installation, commissioning and water flushing; 3) System airtightness inspection; 4) System nitrogen replacement; 5) System filling with protective liquid; 6) Performing citric acid cleaning and passivation; 7) Water flushing after passivation; 8) Overall flushing of the steam generator (1).

5. The method for local cleaning of the secondary side of a nuclear power once-through steam generator according to claim 4, wherein, The operation process of step 6) is as follows: 61) Start the electric heater (404) to heat the solution in the steam generator (1); 62) Open the return water valve (16) to lower the liquid level of the solution in the steam generator (1) below the throttling component (2) in the steam generator (1), and then close the return water valve (16); 63) Add cleaning agent into the cleaning tank (9), start the cleaning pump (14), and open the return water valve (16) to balance the inlet water flow and the inlet and return water flow, and gradually add the cleaning agent into the steam generator (1); 64) Take samples from the sampling port of the main feed water temporary blind plate (4) to test the concentration of the cleaning solution. When the concentration of the cleaning solution in the steam generator (1) reaches the process conditions, then close the return water valve (16) and the cleaning pump (14); 65) Start the electric heater (404) to raise the temperature of the cleaning agent in the steam generator (1); 66) Start the cleaning pump (14) to make the liquid level of the solution in the steam generator (1) higher than the position of the main feed water temporary blind plate (4), and then stop the cleaning pump (14); 67) Every 0.5 - 1 h, open the return water valve (16) to make the liquid level of the solution in the steam generator (1) drop below the throttling component (2), then close the return water valve (16), start the cleaning pump (14) to make the liquid level of the solution in the steam generator (1) higher than the position of the main feed water temporary blanking plate (4), and then stop the cleaning pump (14); 68) Repeat step 67) until the cleaning time reaches 16 h - 24 h; 69) Every preset time, test the Fe ion concentration of the solution in the cleaning tank (9) and the steam generator (1), calculate the total iron amount in the cleaning solution, and end the cleaning after the total iron concentration is balanced for 2 h - 4 h; 610) Every preset time, start the ultrasonic generating device (405) and close it after maintaining the preset working time; 611) After the cleaning is over, close the electric heater (404). After the temperature of the cleaning solution drops to the preset temperature, open the drain valve (410) to make the cleaning waste liquid enter the waste liquid tank (18); 612) Drain the waste liquid in the cleaning tank (9) and the waste liquid tank (18) into the transfer bucket and then transfer it to the waste liquid storage area; 613) Add demineralized water into the cleaning tank (9) to the preset high liquid level, then start the cleaning pump (14) to inject the flushing solution into the steam generator (1). After the liquid level in the steam generator (1) is higher than the position of the main feed water temporary blind plate (4), stop the cleaning pump (14), start the ultrasonic generating device (405) and close it after maintaining the preset working time; 614) Open the drain valve (410) to make the cleaning waste liquid in the steam generator (1) enter the waste liquid tank (18); 615) Repeat step 613) and step 614) to rinse the steam generator (1) again; 616) Supply water to the steam generator (1) and test the Fe ion concentration of the solution in the steam generator (1). When the Fe ion concentration of the solution in the steam generator (1) is less than 50 mg / L, then go to step 617), otherwise, repeat step 613) and step 614); 617) Start the cleaning pump (14) and the return water valve (16) to establish a circulation between the cleaning tank (9) and the steam generator (1), and add EDTA and ammonia water with a concentration of 0.3% - 0.5% to the cleaning solution; Shut down the cleaning pump (14), close the return water valve (16), start the electric heater (404) to heat the solution, and after stabilizing for another 2 - 4 hours, the passivation is completed.

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