Cleaning agent and cleaning method for external heat exchanger of main pump of nuclear power station

Abstract

The invention provides a cleaning agent and a cleaning method for an external heat exchanger of a main pump of a nuclear power station. The cleaning agent comprises a pickling solution and a passivation solution, the pickling solution comprises a citric acid solution and a corrosion inhibitor solution; the pH value of the pickling solution is 3.5 to 3.8; the passivation solution comprises a hydrogen peroxide solution with the pH value of 9.5-10. The cleaning method is easy to operate, efficient rust removal cleaning of the external heat exchanger of the main pump of the nuclear power station is achieved, the corrosion rate of the heat exchanger is reduced, equipment disassembly is not needed, the cleaning cost is low, and the cleaning method is suitable for large-scale popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchanger rust removal, in particular to a cleaning agent and a cleaning method for an external heat exchanger of a main pump of a nuclear power plant. Background Art

[0002] The AP / CAP series nuclear power plant main pump's external heat exchanger is a shell-and-tube heat exchanger with a primary side (tube side) and a secondary side (shell side). The tube side is connected to the primary cooling water circuit and serves as the pressure boundary. After manufacturing, the AP / CAP series main pump requires extensive testing. During this testing, the heat exchanger can rust.

[0003] If rust is not dealt with in time, it will cause the following problems: 1. The rust products on the pipe side will fall off and directly enter the main pump lubrication water in the form of foreign matter. In mild cases, it will cause wear on the main pump bearings, thrust plates and other components. In severe cases, it will cause destructive damage to the main pump or even scrap it; 2. If the rust products are not dealt with in time, they will continue to corrode with the passage of storage time or operation time, causing leakage in the first circuit; and the rust products will also affect the heat exchange efficiency.

[0004] CN113881517A discloses a heat exchanger scale cleaning agent, preparation method, and use method. This heat exchanger scale cleaning agent is a calcium sulfate-specific cleaning agent and is primarily composed of a base agent, an auxiliary agent, and a pH adjuster. The base agent includes one or more of EDTA, EDTA-2Na, EDTA-4Na, and sodium glycolate; the auxiliary agent includes one or more of sodium carbonate, potassium carbonate, ammonium bicarbonate, and ammonium citrate; and the pH adjuster includes one or more of hydrochloric acid, aminosulfonic acid, and carbonic acid. The mass ratio of the base agent to the auxiliary agent is 1:1 to 5:1, and the pH of the heat exchanger scale cleaning agent is 6.5 to 7.5. The provided cleaning agent is neutral, has non-toxic ingredients, is inexpensive, can be prepared at room temperature, and is non-corrosive to equipment materials. Furthermore, the cleaning agent does not require high-temperature reaction to remove calcium sulfate. This is a specialized neutral cleaning agent for dissolving calcium sulfate, with excellent composition and performance.

[0005] CN110591829A discloses a plate heat exchanger cleaning agent and its preparation method. The cleaning agent contains, by weight, 1-5 parts sulfamic acid, 1-5 parts complexing agent, 1-5 parts dispersant, 0.1-3 parts corrosion inhibitor, and 100 parts water. It can effectively remove dirt from the surface of plate heat exchangers that have been in operation for a long time.

[0006] CN112342553A discloses a cleaning agent for plate heat exchangers, its preparation method, and application. The cleaning agent comprises sulfamic acid, phosphoric acid, a corrosion inhibitor, and water; wherein the total acid concentration is ≤20%. The cleaning agent is simple to prepare, and the components complement each other. It not only has a good scale-dissolving effect, but also reduces the corrosion of the cleaning agent to stainless steel, carbon steel, copper and copper alloys, and cast iron. Its corrosion effect is better than that of a simple 20% phosphoric acid solution, and its scale-dissolving effect is better than that of a simple 10% sulfamic acid solution. In addition, the cost of using the cleaning agent to clean plate heat exchangers is between that of a 20% phosphoric acid solution and a 10% sulfamic acid solution. It is relatively safe to prepare and has good economic and safety characteristics.

[0007] However, the above cleaning agents are not suitable for cleaning the external heat exchanger of the main pump of the nuclear power plant. The rust products may not be cleaned thoroughly or the external heat exchanger of the main pump of the nuclear power plant may be corroded. Summary of the Invention

[0008] To address the aforementioned technical issues, the present invention provides a cleaning agent and method for external heat exchangers attached to nuclear power plant main pumps. The cleaning agent utilizes a specific pickling solution for circulated cleaning of the external heat exchanger, removing rust products from the surface. Subsequently, a specific passivating solution is used for circulated passivation, forming a new, uniform passivation film on the heat exchanger's surface, thereby improving the heat exchanger's corrosion resistance. The cleaning method is simple to operate, achieves efficient rust removal and cleaning of external heat exchangers attached to nuclear power plant main pumps, and reduces corrosion rates.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a cleaning agent for an external heat exchanger of a main pump of a nuclear power plant, the cleaning agent comprising an acid cleaning solution and a passivation solution; the acid cleaning solution comprising a citric acid solution and a corrosion inhibitor solution; the pH of the acid cleaning solution is 3.5 to 3.8;

[0011] The passivation solution includes a hydrogen peroxide solution with a pH value of 9.5 to 10.

[0012] The cleaning agent for an external heat exchanger for a nuclear power plant main pump, described in the present invention, is a chemical cleaning agent. Taking into full consideration the material tolerance of the external heat exchanger for the nuclear power plant main pump and the primary circuit's requirements for halogens and sulfate ions, a citric acid solution and a corrosion inhibitor solution are used as the pickling solution, and a hydrogen peroxide solution is used as the passivation solution. This not only removes rust products but also forms a passivation film on the heat exchanger, improving corrosion resistance and preventing secondary corrosion, thereby protecting the heat exchanger and extending its service life. The cleaning agent of the present invention has a simple composition, requiring no additional surfactants or other components, and is relatively low in cost. Citric acid solution, as a key component of the pickling solution, and sodium molybdate solution, as a corrosion inhibitor in the pickling solution, effectively decompose and remove oxides and rust from metal surfaces, while forming a protective film on the metal surface to effectively prevent corrosion during the cleaning process. Furthermore, citric acid is a natural organic acid that does not pollute the environment, is harmless to the human body, and is safe and environmentally friendly.

[0013] The pH of the pickling solution described in the present invention is 3.5 to 3.8. When the pH of the pickling solution is lower than 3.5, it can damage or excessively corrode the metal surface of the external heat exchanger of the nuclear power plant's main pump. When the pH of the pickling solution is higher than 3.8, rust products cannot be completely cleaned. The passivation solution described in the present invention includes a hydrogen peroxide solution with a pH of 9.5 to 10, which maximizes the passivation reaction and forms a uniform, dense passivation film. When the pH of the passivation solution is lower than 9.5, the chemical reaction in the passivation solution is inhibited, making it difficult to form a stable passivation film, which tends to blacken and fall off easily. When the pH of the passivation solution is higher than 10, the formed passivation film is thin and uneven, resulting in poor corrosion resistance.

[0014] The pH of the pickling solution of the present invention is 3.5 to 3.8, for example, it can be 3.52, 3.55, 3.6, 3.65, 3.7, 3.75 or 3.8, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0015] The passivation solution includes a hydrogen peroxide solution with a pH of 9.5 to 10, for example, 9.5, 9.55, 9.6, 9.7, 9.8, 9.9 or 10, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0016] Preferably, the citric acid solution of the present invention is an AR grade citric acid solution.

[0017] Preferably, the concentration of the citric acid solution is 3.5% to 4.5%, for example, 3.5%, 3.6%, 3.8%, 4%, 4.2%, 4.4% or 4.5%, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0018] Preferably, the corrosion inhibitor comprises a sodium molybdate solution with a concentration of 0.3% to 1.0%, for example, 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, 0.95% or 1.0%, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0019] The preferred corrosion inhibitor of the present invention comprises an AR-grade sodium molybdate solution with a concentration of 0.3% to 1.0%, which has high purity and does not introduce additional impurities. Sodium molybdate can form a protective film on the metal surface, thereby inhibiting the occurrence of corrosion reactions.

[0020] Preferably, the concentration of the hydrogen peroxide solution is 0.3% to 1.0%, for example, 0.3%, 0.5%, 0.6%, 0.8%, 0.9%, 0.95% or 1.0%, etc., but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0021] In a second aspect, the present invention further provides a method for cleaning an external heat exchanger of a main pump of a nuclear power plant, the method being performed using the cleaning agent for an external heat exchanger of a main pump of a nuclear power plant described in the first aspect; the method comprising the following steps:

[0022] (1) Fill the main pump external heat exchanger with water and exhaust it to form a circulation loop between the main pump external heat exchanger and the cleaning water tank;

[0023] (2) Add pickling solution to the cleaning water tank and control the temperature of the solution in the circulation loop to 50-60°C, and start circulating cleaning;

[0024] (3) After the cycle cleaning is completed, empty the main pump external heat exchanger and cleaning water tank;

[0025] (4) After the main pump external heat exchanger and the cleaning water tank are rinsed with water for the first time, the passivation solution is added to the cleaning water tank and the temperature of the solution in the circulation loop is controlled to 50-60°C for circulatory passivation;

[0026] (5) After the second water flushing of the main pump external heat exchanger and the cleaning water tank, drain the water from the main pump external heat exchanger and the cleaning water tank and dry them.

[0027] The cleaning method for the external heat exchanger of the main pump of a nuclear power plant described in the present invention is simple to operate. A circulation loop is formed between the external heat exchanger of the main pump and a cleaning water tank, and an acid cleaning solution and a passivation solution are sequentially added to the cleaning water tank. Circulating cleaning and rust removal are performed at a temperature of 50 to 60° C., thereby effectively removing rust products in the external heat exchanger of the main pump and forming a passivation film, thereby improving the corrosion resistance of the heat exchanger.

[0028] The present invention adopts pickling solution cleaning and passivation solution cleaning both at 50-60°C. When the cleaning temperature is low, the reaction speed is slow and the cleaning time is long. When the cleaning temperature is high, although the cleaning time can be shortened, the effective ingredients in the cleaning agent may be decomposed, the rust removal ability is lost, and the corrosion of the heat exchanger may be aggravated.

[0029] The present invention adds pickling solution to the cleaning water tank and controls the temperature of the solution in the circulation loop to be 50-60°C, for example, it can be 50°C, 52°C, 54°C, 55°C, 57°C, 58°C or 60°C, etc., but is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0030] Add passivation liquid to the cleaning water tank and control the temperature of the solution in the circulation loop to 50-60°C, for example, it can be 50°C, 52°C, 54°C, 55°C, 57°C, 58°C or 60°C, etc., but it is not limited to the listed values. Other unlisted values within this numerical range are also applicable.

[0031] Before the step (1) of the present invention, the rusted part is examined by endoscopy and photographed for preservation. After the step (5) is dried, the rusted part is also examined by endoscopy and photographed for comparison and evaluation of the cleaning effect of the rusted part.

[0032] The present invention uses a wash water pump to fill the main pump's external heat exchanger with water and exhaust it. The wash water pump then creates a circulation loop between the main pump's external heat exchanger and the wash water tank. Conventional heating devices, such as electric heating rods, are used to control the water temperature in the wash water tank. Conventional pH testing methods, such as pH test paper or a pH meter, are used to test the solution's pH.

[0033] Preferably, the step of adding pickling solution in step (2) includes first adding corrosion inhibitor particles to the water in the cleaning water tank, adding citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjusting the pH.

[0034] Since the corrosion inhibitor sodium molybdate used in this invention is typically in the form of solid particles, for cleaning purposes, the corrosion inhibitor particles are added to the water used to clean the tank and dissolved to form the desired corrosion inhibitor solution. The corrosion inhibitor particles are completely dissolved, forming a protective film on the metal surface of the external heat exchanger of the nuclear power plant's main pump, thereby inhibiting corrosion caused by the subsequent addition of the citric acid solution.

[0035] Preferably, during the cyclic cleaning process, the pH value of the solution in the cleaning water tank is detected every 20 to 30 minutes, for example, it can be 20 minutes, 22 minutes, 24 minutes, 25 minutes, 27 minutes, 29 minutes or 30 minutes, etc., but it is not limited to the listed values. Other values not listed within this numerical range are also applicable; at the same time, the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, ammonia water is added to adjust it to 3.8.

[0036] The present invention preferably uses AR grade ammonia water to adjust the pH, as the ammonia water has high purity and will not introduce additional impurities.

[0037] Preferably, the criterion for judging the end of the cyclic cleaning in step (3) is that all the rust products on the monitoring piece are cleaned.

[0038] Preferably, the first water flushing in step (4) is performed with deionized water, the drain valve of the cleaning water tank is opened during the first water flushing process, and the drain valve is closed after the cleaning is completed.

[0039] Preferably, the first water flushing is performed until the drainage conductivity is less than 30 us / cm, for example, it can be 29.9 us / cm, 29 us / cm, 28 us / cm, 25 us / cm, 23 us / cm or 20 us / cm, etc., but is not limited to the listed values. Other values not listed in the numerical range are also applicable, and the flushing is terminated;

[0040] Preferably, during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 0.5 to 1 hour, for example, it can be 0.5h, 0.55h, 0.6h, 0.7h, 0.9h or 1h, etc., but it is not limited to the listed values. Other unlisted values within the numerical range are also applicable; if the pH is lower than 9.5, ammonia water is added to adjust it to 10, and the cyclic passivation is ended after 6 to 7 hours.

[0041] Preferably, the second water rinse in step (5) is performed using deionized water.

[0042] Preferably, the second water is flushed until the drainage conductivity is less than 30us / cm, for example, it can be 29.9us / cm, 29us / cm, 28us / cm, 25us / cm, 23us / cm or 20us / cm, etc., but it is not limited to the listed values. Other unlisted values within the numerical range are also applicable, and the flushing is completed.

[0043] Preferably, the drying comprises hot air drying.

[0044] As a preferred technical solution of the present invention, the cleaning method comprises the following steps:

[0045] (1) Use the cleaning water pump to fill the main pump external heat exchanger with water and exhaust it, so that a circulation loop is formed between the main pump external heat exchanger and the cleaning water tank;

[0046] (2) First add the corrosion inhibitor particles to the water in the cleaning water tank, and then add the citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjust the pH; at the same time, control the temperature of the solution in the circulation loop to 50-60°C, and start the circulation cleaning; during the circulation cleaning process, the pH value of the solution in the cleaning water tank is detected every 20-30 minutes, and the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, add ammonia water to adjust it to 3.8;

[0047] (3) After all the rust products on the monitoring plate are cleaned, the cycle cleaning is completed; the main pump external heat exchanger and the cleaning water tank are emptied;

[0048] (4) Use deionized water to perform a first water flush on the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; add passivation liquid to the cleaning water tank and control the temperature of the solution in the circulation loop to 50-60°C for cyclic passivation; during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 0.5-1h; if the pH is lower than 9.5, add ammonia water to adjust it to 10, and the cyclic passivation is completed after 6-7h;

[0049] (5) Use deionized water to perform a second water flush on the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; drain the water from the main pump external heat exchanger and the cleaning water tank, and dry them with hot air.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects:

[0051] The cleaning agent provided by the present invention for the external heat exchanger of the main pump of a nuclear power plant has simple ingredients, meets the material tolerance of the external heat exchanger of the main pump of the nuclear power plant and the requirements of the primary circuit for halogen and sulfate ions, can effectively clean the external heat exchanger of the main pump of the nuclear power plant without the need for equipment disassembly, has low cleaning costs, and is suitable for large-scale promotion. DETAILED DESCRIPTION

[0052] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0053] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0054] The following are typical but non-limiting examples of the present invention:

[0055] Example 1

[0056] This embodiment provides a cleaning agent for an external heat exchanger of a nuclear power plant main pump, the cleaning agent comprising an acid cleaning solution and a passivation solution; the acid cleaning solution comprising a citric acid solution and a corrosion inhibitor solution; the pH of the acid cleaning solution is 3.6; and the concentration of the citric acid solution is 4%.

[0057] The corrosion inhibitor includes a sodium molybdate solution with a concentration of 0.5%.

[0058] The passivation solution includes a hydrogen peroxide solution with a pH of 9.8; the concentration of the hydrogen peroxide solution is 0.5%.

[0059] Example 2

[0060] This embodiment provides a cleaning agent for an external heat exchanger of a nuclear power plant main pump, the cleaning agent comprising an acid cleaning solution and a passivation solution; the acid cleaning solution comprising a citric acid solution and a corrosion inhibitor solution; the pH of the acid cleaning solution is 3.5; and the concentration of the citric acid solution is 4.5%.

[0061] The corrosion inhibitor includes a sodium molybdate solution with a concentration of 1.0%.

[0062] The passivation solution includes a hydrogen peroxide solution with a pH of 9.5; the concentration of the hydrogen peroxide solution is 0.3%.

[0063] Example 3

[0064] This embodiment provides a cleaning agent for an external heat exchanger of a nuclear power plant main pump, the cleaning agent comprising an acid cleaning solution and a passivation solution; the acid cleaning solution comprising a citric acid solution and a corrosion inhibitor solution; the pH of the acid cleaning solution is 3.8; and the concentration of the citric acid solution is 3.5%.

[0065] The corrosion inhibitor includes a sodium molybdate solution with a concentration of 0.3%.

[0066] The passivation solution includes a hydrogen peroxide solution with a pH of 9.5; the concentration of the hydrogen peroxide solution is 1.0%.

[0067] Comparative Example 1

[0068] This comparative example provides a cleaning agent for an external heat exchanger of a main pump of a nuclear power plant. The cleaning agent is the same as that of Example 1 except that the pH value of the pickling solution is 3.

[0069] Comparative Example 2

[0070] This comparative example provides a cleaning agent for an external heat exchanger of a main pump of a nuclear power plant. The cleaning agent is the same as that of Example 1 except that the pH value of the pickling solution is 4.

[0071] Comparative Example 3

[0072] This comparative example provides a cleaning agent for an external heat exchanger of a main pump of a nuclear power plant. The cleaning agent is the same as that of Example 1 except that the passivation solution is a hydrogen peroxide solution with a pH of 9.

[0073] Comparative Example 4

[0074] This comparative example provides a cleaning agent for an external heat exchanger of a main pump of a nuclear power plant. The cleaning agent is the same as that of Example 1 except that the passivation solution is a hydrogen peroxide solution with a pH of 10.5.

[0075] Application Example 1

[0076] This application example provides a method for cleaning an external heat exchanger of a main pump of a nuclear power plant. The cleaning method is performed using the cleaning agent for an external heat exchanger of a main pump of a nuclear power plant described in Example 1. The cleaning method comprises the following steps:

[0077] (1) Use the cleaning water pump to fill the main pump external heat exchanger with water and exhaust it, so that a circulation loop is formed between the main pump external heat exchanger and the cleaning water tank;

[0078] (2) First add the corrosion inhibitor particles to the water in the cleaning water tank, and then add the citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjust the pH; at the same time, control the temperature of the solution in the circulation loop to 55°C, and start the circulation cleaning; during the circulation cleaning process, the pH value of the solution in the cleaning water tank is detected every 25 minutes, and the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, add ammonia water to adjust it to 3.8;

[0079] (3) After all the rust products on the monitoring plate are cleaned, the cycle cleaning is completed; the main pump external heat exchanger and the cleaning water tank are emptied;

[0080] (4) Use deionized water to rinse the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; add passivation solution to the cleaning water tank and control the temperature of the solution in the circulation loop to 55°C to perform cyclic passivation; during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 0.7h; if the pH is lower than 9.5, add ammonia water to adjust it to 10, and the cyclic passivation is completed after 6.7h;

[0081] (5) Use deionized water to perform a second water flush on the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; drain the water from the main pump external heat exchanger and the cleaning water tank, and dry them with hot air.

[0082] Application Example 2

[0083] This application example provides a method for cleaning an external heat exchanger of a main pump of a nuclear power plant. The cleaning method is performed using the cleaning agent for an external heat exchanger of a main pump of a nuclear power plant described in Example 2. The cleaning method comprises the following steps:

[0084] (1) Use the cleaning water pump to fill the main pump external heat exchanger with water and exhaust it, so that a circulation loop is formed between the main pump external heat exchanger and the cleaning water tank;

[0085] (2) First add the corrosion inhibitor particles to the water in the cleaning water tank, and then add the citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjust the pH; at the same time, control the temperature of the solution in the circulation loop to 50°C, and start the circulation cleaning; during the circulation cleaning process, the pH value of the solution in the cleaning water tank is detected every 30 minutes, and the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, add ammonia water to adjust it to 3.8;

[0086] (3) After all the rust products on the monitoring plate are cleaned, the cycle cleaning is completed; the main pump external heat exchanger and the cleaning water tank are emptied;

[0087] (4) Use deionized water to rinse the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; add passivation liquid to the cleaning water tank and control the temperature of the solution in the circulation loop to 60°C to perform cyclic passivation; during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 1 hour; if the pH is lower than 9.5, add ammonia water to adjust it to 10, and the cyclic passivation is completed after 6 hours;

[0088] (5) Use deionized water to perform a second water flush on the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; drain the water from the main pump external heat exchanger and the cleaning water tank, and dry them with hot air.

[0089] Application Example 3

[0090] This application example provides a method for cleaning an external heat exchanger of a main pump of a nuclear power plant. The cleaning method is performed using the cleaning agent for an external heat exchanger of a main pump of a nuclear power plant described in Example 2. The cleaning method comprises the following steps:

[0091] (1) Use the cleaning water pump to fill the main pump external heat exchanger with water and exhaust it, so that a circulation loop is formed between the main pump external heat exchanger and the cleaning water tank;

[0092] (2) First add the corrosion inhibitor particles to the water in the cleaning water tank, and then add the citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjust the pH; at the same time, control the temperature of the solution in the circulation loop to 60°C, and start the circulation cleaning; during the circulation cleaning process, the pH value of the solution in the cleaning water tank is detected every 30 minutes, and the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, add ammonia water to adjust it to 3.8;

[0093] (3) After all the rust products on the monitoring plate are cleaned, the cycle cleaning is completed; the main pump external heat exchanger and the cleaning water tank are emptied;

[0094] (4) Use deionized water to rinse the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; add passivation solution to the cleaning water tank and control the temperature of the solution in the circulation loop to 50°C to perform cyclic passivation; during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 0.5h; if the pH is lower than 9.5, add ammonia water to adjust it to 10, and the cyclic passivation is completed after 7h;

[0095] (5) Use deionized water to perform a second water flush on the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; drain the water from the main pump external heat exchanger and the cleaning water tank, and dry them with hot air.

[0096] It can be seen from the comprehensive application examples 1 to 3 that the cleaning method for the external heat exchanger of the main pump of the nuclear power plant provided by the present invention is simple to operate, and the specific pickling solution and the specific passivation solution can effectively clean and remove the rust products in the external heat exchanger of the main pump of the nuclear power plant, and there is no need to disassemble the equipment, so the cleaning cost is low.

[0097] Comparative Application Example 1

[0098] This application example provides a method for cleaning an external heat exchanger of a nuclear power plant main pump. The cleaning method is performed using the cleaning agent for an external heat exchanger of a nuclear power plant main pump described in Comparative Example 1. The cleaning method is the same as that in Application Example 1.

[0099] Application Comparative Example 2

[0100] This application example provides a method for cleaning an external heat exchanger of a nuclear power plant main pump. The cleaning method is performed using the cleaning agent for an external heat exchanger of a nuclear power plant main pump described in Comparative Example 2. The cleaning method is the same as that in Application Example 1.

[0101] From the comprehensive application example 1 and the application comparative examples 1 to 2, it can be seen that in the application comparative example 1, the cleaning agent in comparative example 1 is used, wherein the pH of the pickling solution is low, which will cause the pickling solution to damage or excessively corrode the metal surface of the external heat exchanger of the main pump of the nuclear power plant; in the application comparative example 2, the cleaning agent in comparative example 2 is used, wherein the pH of the pickling solution is high, and the rust products are not cleaned cleanly.

[0102] Application Comparative Example 3

[0103] This application example provides a method for cleaning an external heat exchanger of a nuclear power plant main pump. The cleaning method is performed using the cleaning agent for an external heat exchanger of a nuclear power plant main pump described in Comparative Example 3. The cleaning method is the same as that in Application Example 1.

[0104] Comparative Application Example 4

[0105] This application example provides a method for cleaning an external heat exchanger of a nuclear power plant main pump. The cleaning method is performed using the cleaning agent for an external heat exchanger of a nuclear power plant main pump described in Comparative Example 4. The cleaning method is the same as that of Application Example 1.

[0106] From the comprehensive application example 1 and the application comparative examples 3 to 4, it can be seen that the cleaning agent in comparative example 3 is used in the application comparative example 3, wherein the pH of the passivation solution is relatively low, resulting in the chemical reaction in the passivation solution being inhibited, making it difficult to form a stable passivation film, and the passivation film is prone to blackening and falling off; the cleaning agent in comparative example 4 is used in the application comparative example 4, wherein the pH of the passivation solution is relatively high, resulting in the formed passivation film being thin and uneven, and the corrosion resistance effect is poor.

[0107] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A cleaning agent for an external heat exchanger of a nuclear power plant main pump, characterized in that: The cleaning agent includes a pickling solution and a passivation solution; the pickling solution includes a citric acid solution and a corrosion inhibitor solution; the pH of the pickling solution is 3.5 to 3.8; The passivation solution includes a hydrogen peroxide solution with a pH value of 9.5 to 10.

2. The cleaning agent according to claim 1, characterized in that The concentration of the citric acid solution is 3.5% to 4.5%.

3. The cleaning agent according to claim 1 or 2, characterized in that The corrosion inhibitor comprises a sodium molybdate solution with a concentration of 0.3% to 1.0%.

4. The cleaning agent according to any one of claims 1 to 3, characterized in that The concentration of the hydrogen peroxide solution is 0.3% to 1.0%.

5. A method for cleaning an external heat exchanger of a nuclear power plant main pump, characterized in that: The cleaning method is performed using the cleaning agent for the external heat exchanger of the main pump of a nuclear power plant according to any one of claims 1 to 4; the cleaning method comprises the following steps: (1) Fill the main pump external heat exchanger with water and exhaust it to form a circulation loop between the main pump external heat exchanger and the cleaning water tank; (2) Add pickling solution to the cleaning water tank and control the temperature of the solution in the circulation loop to 50-60°C, and start circulating cleaning; (3) After the cycle cleaning is completed, empty the main pump external heat exchanger and cleaning water tank; (4) After the main pump external heat exchanger and the cleaning water tank are rinsed with water for the first time, the passivation solution is added to the cleaning water tank and the temperature of the solution in the circulation loop is controlled to 50-60°C for circulatory passivation; (5) After the second water flushing of the main pump external heat exchanger and the cleaning water tank, drain the water from the main pump external heat exchanger and the cleaning water tank and dry them.

6. The cleaning method according to claim 5, characterized in that The step of adding the pickling solution in step (2) comprises first adding the corrosion inhibitor particles to the water in the cleaning water tank, adding the citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjusting the pH; Preferably, during the cyclic cleaning process, the pH value of the solution in the cleaning water tank is detected every 20 to 30 minutes, and the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, ammonia water is added to adjust it to 3.

8.

7. The cleaning method according to claim 5 or 6, characterized in that: The judgment standard for the end of the cyclic cleaning in step (3) is that all the rust products on the monitoring piece are cleaned.

8. The cleaning method according to any one of claims 5 to 7, characterized in that: The first water rinse in step (4) is performed using deionized water; Preferably, the first water flushing is completed until the drainage conductivity is less than 30us / cm; Preferably, during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 0.5 to 1 hour; if the pH is lower than 9.5, ammonia water is added to adjust the pH to 10, and the cyclic passivation is terminated after 6 to 7 hours.

9. The cleaning method according to any one of claims 5 to 8, characterized in that: The second water rinse in step (5) is performed using deionized water; Preferably, the second water flushing is completed until the drainage conductivity is less than 30us / cm; Preferably, the drying comprises hot air drying.

10. The cleaning method according to any one of claims 5 to 9, characterized in that: The cleaning method comprises the following steps: (1) Fill the main pump external heat exchanger with water and exhaust it to form a circulation loop between the main pump external heat exchanger and the cleaning water tank; (2) First add the corrosion inhibitor particles to the water in the cleaning water tank, and then add the citric acid solution after the corrosion inhibitor particles are completely dissolved, and adjust the pH; at the same time, control the temperature of the solution in the circulation loop to 50-60°C, and start the circulation cleaning; during the circulation cleaning process, the pH value of the solution in the cleaning water tank is detected every 20-30 minutes, and the cleaning monitoring piece is taken out to observe the cleaning effect. If the pH is lower than 3.5, add ammonia water to adjust it to 3.8; (3) After all the rust products on the monitoring plate are cleaned, the cycle cleaning is completed; the main pump external heat exchanger and the cleaning water tank are emptied; (4) Use deionized water to rinse the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; add passivation solution to the cleaning water tank and control the temperature of the solution in the circulation loop to 50-60°C for cyclic passivation; during the cyclic passivation process, the pH value of the solution in the cleaning water tank is detected every 0.5-1h; if the pH is lower than 9.5, add ammonia water to adjust it to 10, and the cyclic passivation is completed after 6-7h; (5) Use deionized water to perform a second water flush on the main pump external heat exchanger and the cleaning water tank until the drainage conductivity is less than 30us / cm, and the flushing is completed; drain the water from the main pump external heat exchanger and the cleaning water tank, and dry them with hot air.