Shielded cooling water system maintenance method

Abstract

The invention provides a maintenance method for a shielding cooling water system, and relates to the field of nuclear power plant equipment maintenance. The maintenance method for the shielded cooling water system is applied to the high-temperature gas cooled reactor, the shielded cooling water system comprises a dosing tank and a circulating pump, and the maintenance method comprises the following steps: S1, dosing: adding demineralized water and an ammonia water stock solution into the dosing tank, and mixing to prepare a maintenance solution with the pH value of 10.0-10.5; s2, injecting liquid and exhausting gas; s3, circulating operation and sampling analysis; s4, maintenance: adjusting the pressure of the system to stabilize the pressure of the maintenance liquid in the shielding cooling water system in a range of 0.3 MPa-0. 5 MPa, closing the circulating pump, and entering a long-term maintenance state; and S5, regular monitoring: regularly detecting the pH value of the preservative solution in the shielded cooling water system. According to the maintenance method, oxygen corrosion and acid corrosion are effectively prevented, and therefore the service life of key components of the shielding cooling water system is greatly prolonged.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant equipment maintenance, and more specifically, to a method for maintaining a shielded cooling water system. Background Technology

[0002] The shielded cooling water system is a crucial auxiliary system for high-temperature gas-cooled reactors (HTGRs), primarily used for radiation shielding and cooling of the reactor core pressure vessel's outer wall and other critical equipment. In existing technologies, the main body of the piping and equipment in HTGR shielded cooling water systems is generally made of high-quality carbon steel, a material with advantages such as moderate cost and mature processing technology. However, in actual operating environments, carbon steel undergoes oxidation-reduction reactions when in prolonged contact with oxygen-containing water media. This electrochemical corrosion process is significantly accelerated, especially during system shutdowns when residual water films within the pipes come into contact with air.

[0003] Currently, two conventional methods are mainly used for corrosion prevention in this system: one is to periodically flush the system, removing loose corrosion products through short-term, high-flow-rate rinsing. However, this method cannot change the electrochemical activity of the metal substrate, and the exposed fresh metal surface after flushing may actually accelerate subsequent corrosion. The second method is to apply anti-corrosion coatings such as epoxy resin to the outer surface of the equipment. However, due to process limitations, this coating technology cannot be applied to the protection of complex flow channel structures such as the inner walls of pipes and heat exchangers. Neither of these methods fundamentally solves the problem of continuous corrosion in the parts of the system that come into contact with the water medium, and they are insufficient to meet the long-term corrosion prevention requirements of the high-temperature gas-cooled reactor's design life. Summary of the Invention

[0004] This invention provides a maintenance method for a shielded cooling water system. By injecting an alkaline maintenance solution with a pH value of 10.0 to 10.5 into the shielded cooling water system and stabilizing the system pressure between 0.3 MPa and 0.5 MPa during the maintenance phase, the occurrence of oxygen corrosion and acid corrosion is effectively prevented, thereby significantly extending the service life of key components of the shielded cooling water system.

[0005] This maintenance method for the shielded cooling water system is applied to high-temperature gas-cooled reactors. The shielded cooling water system includes a dosing tank and a circulating pump. The maintenance method includes the following steps: S1, Preparation: Add deionized water and ammonia solution to the dosing tank and mix to prepare a maintenance solution with a pH of 10.0 to 10.5; S2, Fluid Injection and Air Exhaust: Inject maintenance fluid into the shielded cooling water system and expel any residual air from the shielded cooling water system; S3, Circulation and Sampling Analysis: Start the circulation pump, and after the maintenance solution has circulated for a preset time, take a sample to test the pH value of the maintenance solution; If the test results meet the maintenance criteria of 10.0 to 10.5, then proceed to the pressure holding stage; If the pH value is not met, replenish or replace with freshly prepared maintenance solution. The maintenance solution will continue to circulate and be sampled and tested until the pH value meets the standard. S4, Maintenance: Adjust the system pressure to stabilize the pressure of the maintenance fluid in the shielded cooling water system within the range of 0.3MPa to 0.5MPa, turn off the circulation pump, and enter the long-term maintenance state; S5, Regular monitoring: Regularly test the pH value of the maintenance solution in the shielded cooling water system. If the pH value is within the range of 10.0 to 10.5, extend the sampling interval. If the pH value is not within the range of 10.0 to 10.5, terminate the current maintenance process, return to step S1 to re-prepare the solution and perform subsequent operations.

[0006] Optionally, the shielded cooling water system also includes a stirring device installed in the dosing tank, and the dosing step S1 specifically includes: Inject demineralized water into the dosing tank to the preset level; Turn on the stirring device; During the stirring process, ammonia water is injected into the demineralized water, and the pH value of the solution in the dosing tank is monitored in real time. Once the pH of the solution stabilizes within the range of 10.0 to 10.5, stop injecting ammonia water to complete the preparation of the maintenance solution.

[0007] Optionally, in the drug preparation step S1, the pH value is detected using multi-point sampling, and the specific detection steps include: Using a pH meter, three sampling points were selected at different locations in the dosing tank to collect samples of the maintenance solution. The pH value of each sample was measured separately; If the pH value at all three sampling points is within the range of 10.0 to 10.5, the maintenance solution is deemed qualified and can proceed to the next step. If the pH value at any sampling point exceeds the range, ammonia or demineralized water needs to be added to adjust the pH value. After adding the ammonia or demineralized water, samples should be taken again at the three sampling points and the pH value should be monitored until the maintenance solution is qualified.

[0008] Optionally, the shielded cooling water system also includes an air vent valve, and the liquid injection and air venting steps S2 specifically include: Open the exhaust valve; Inject maintenance fluid into the shielded cooling water system; Once the vent valve starts to continuously release maintenance fluid, close the vent valve.

[0009] Optionally, the shielded cooling water system also includes a metering pump, a manifold assembly, and a regulating valve. The manifold assembly includes an upper manifold and a lower manifold, which are connected to form a closed loop via external piping. The metering pump and regulating valve are installed in a closed loop, with the metering pump located on the connecting pipe between the dosing tank and the loop.

[0010] Optionally, after opening the vent valve, the injection and venting step S2 further includes the following steps: Start the metering pump. The maintenance fluid is injected into the shielded cooling water system via a metering pump.

[0011] Optionally, the periodic monitoring step S5 specifically includes: During the first 7 days after entering the maintenance state, samples of the maintenance solution were collected daily and their pH values ​​were measured. If the pH value measured for 7 consecutive days is within the range of 10.0 to 10.5, the monitoring frequency will be adjusted to once every 3 days starting from the 8th day. If any measured pH value exceeds the range of 10.0 to 10.5, terminate the current maintenance process, return to step S1 to re-prepare the medication, and perform subsequent operations.

[0012] Optionally, terminating the current maintenance procedure may specifically include: draining the maintenance fluid from the shielded cooling water system.

[0013] Optionally, the demineralized water has a conductivity ≤0.5 μS / cm and a hardness ≤2 μmol / L.

[0014] Optionally, the ammonia solution is industrial-grade ammonia solution with a concentration of 32%.

[0015] The beneficial effects of the shielded cooling water system maintenance method of this invention include: By preparing an alkaline maintenance solution with a pH of 10.0–10.5 (composed of a mixture of demineralized water and ammonia concentrate), a stable passivation protective layer is formed on the metal surface of the pipes, significantly reducing the electrochemical corrosion rate of carbon steel, stainless steel, and other pipelines and equipment inner walls. This is particularly effective in preventing oxygen and acid corrosion, thereby significantly extending the service life of key components in the shielded cooling water system. During the maintenance phase, maintaining the system pressure stably between 0.3 MPa and 0.5 MPa effectively prevents the infiltration of external air, carbon dioxide, and impurities, avoiding problems such as increased ammonia volatilization and carbonate deposition due to pH drops caused by CO2 dissolution. This maintains the system's sealing and chemical stability, further preventing electrochemical corrosion and achieving effective maintenance of the shielded cooling water system. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of the maintenance method for the shielded cooling water system provided in this embodiment; Figure 2 This is a schematic diagram of the shielded cooling water system provided in this embodiment; Figure 3 This is a flowchart illustrating the drug preparation step S1 provided in this embodiment; Figure 4 This is a schematic diagram of the injection and venting step S2 provided in this embodiment.

[0018] Icons: 1-Shielded cooling water system; 10-Dosing tank; 20-Circulating pump; 30-Metering pump; 40-Manifold assembly; 41-Upper manifold; 42-Lower manifold; 50-Regulating valve; 60-External piping. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this invention, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0023] Furthermore, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. Also, in the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0024] It should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections, electrical connections, or connections that allow for communication; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] It should also be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0026] As described in the background section, existing methods for addressing the problem of electrochemical corrosion of pipelines during the shutdown of shielded cooling water systems have failed to fundamentally solve the problem of continuous corrosion in the parts of the system that come into contact with the water medium, making it difficult to meet the long-term corrosion protection requirements of the high-temperature gas-cooled reactor design life.

[0027] Please refer to Figure 1 and Figure 2 This application provides a maintenance method for a shielded cooling water system 1, which can solve the above-mentioned technical problems.

[0028] This maintenance method for the shielded cooling water system 1 is applied to a high-temperature gas-cooled reactor. The shielded cooling water system 1 includes a chemical dosing tank 10 and a circulating pump 20. The maintenance method includes the following steps: S1, Preparation: Add deionized water and ammonia solution to the dosing tank 10 and mix to prepare a maintenance solution with a pH of 10.0 to 10.5; S2, Injection and Exhaust: Inject the maintenance fluid into the shielded cooling water system 1 and expel any residual air in the shielded cooling water system 1; S3, Circulation and Sampling Analysis: Start the circulation pump 20. After the maintenance solution has circulated for a preset time, take a sample to test the pH value of the maintenance solution. If the test results meet the maintenance criteria of 10.0 to 10.5, then proceed to the pressure holding stage; If the pH value is not met, replenish or replace with freshly prepared maintenance solution. The maintenance solution will continue to circulate and be sampled and tested until the pH value meets the standard. S4, Maintenance: Adjust the system pressure to stabilize the pressure of the maintenance fluid in the shielded cooling water system 1 within the range of 0.3MPa to 0.5MPa, turn off the circulation pump 20, and enter the long-term maintenance state; S5, Regular monitoring: Regularly test the pH value of the maintenance solution in the shielded cooling water system 1. If the pH value is within the range of 10.0 to 10.5, extend the sampling interval; if the pH value is not within the range of 10.0 to 10.5, terminate the current maintenance process, return to step S1 to re-prepare the solution and perform subsequent operations.

[0029] By preparing an alkaline maintenance solution with a pH of 10.0–10.5 (composed of a mixture of demineralized water and ammonia concentrate), a stable passivation protective layer is formed on the metal surface of the pipes, significantly reducing the electrochemical corrosion rate of the inner walls of carbon steel, stainless steel, and other pipelines and equipment. In particular, it effectively prevents oxygen corrosion and acid corrosion, thereby significantly extending the service life of key components in the shielded cooling water system 1. During the maintenance phase, maintaining the system pressure stably between 0.3 MPa and 0.5 MPa effectively prevents the infiltration of external air, carbon dioxide, and impurities, avoiding the problems of increased ammonia volatilization and carbonate deposition caused by pH drop due to CO2 dissolution. This maintains the system's sealing and chemical stability, further preventing electrochemical corrosion and achieving effective maintenance of the shielded cooling water system 1.

[0030] Further, please refer to Figure 3 The shielded cooling water system 1 also includes a stirring device installed in the dosing tank 10. The dosing step S1 specifically includes: Inject demineralized water into the dosing tank 10 to the preset level; Turn on the stirring device; During the stirring process, ammonia water is injected into the demineralized water, and the pH value of the solution in the dosing tank 10 is monitored in real time. Once the pH of the solution stabilizes within the range of 10.0 to 10.5, stop injecting ammonia water to complete the preparation of the maintenance solution.

[0031] By combining a stirring device with real-time monitoring, the need for re-preparation of chemicals due to substandard pH levels is reduced, thus decreasing material waste and labor costs while improving work efficiency. Furthermore, the stirring device ensures more uniform mixing of ammonia and demineralized water, avoiding potential safety hazards such as ammonia gas escape from areas of high ammonia concentration, thereby enhancing operational safety.

[0032] Furthermore, to ensure improved accuracy and reliability of drug preparation, the pH value detection in drug preparation step S1 employs multi-point sampling. Specific detection steps include: Using a pH meter, three sampling points were selected at different locations in the dosing tank 10 to collect samples of the maintenance solution. The pH value of each sample was measured separately; If the pH value at all three sampling points is within the range of 10.0 to 10.5, the maintenance solution is deemed qualified and can proceed to the next step. If the pH value at any sampling point exceeds the range, ammonia or demineralized water needs to be added to adjust the pH value. After adding the ammonia or demineralized water, samples should be taken again at the three sampling points and the pH value should be monitored until the maintenance solution is qualified.

[0033] Further, please refer to Figure 4 In order to effectively expel air from the shielded cooling water system 1 and fill the pipes with maintenance fluid, the shielded cooling water system 1 also includes an air vent valve. The fluid injection and air venting steps S2 specifically include: Open the exhaust valve; Inject maintenance fluid into the shielded cooling water system 1; Once the vent valve starts to continuously release maintenance fluid, close the vent valve.

[0034] Furthermore, please combine again Figure 2 The shielded cooling water system 1 also includes a metering pump 30, a manifold assembly 40, and a regulating valve 50. The manifold assembly 40 includes an upper manifold 41 and a lower manifold 42. The upper manifold 41 and the lower manifold 42 are connected to form a closed loop through an external pipe 60. The metering pump 30 and the regulating valve 50 are installed on the closed loop. The metering pump 30 is installed on the connecting pipe between the dosing tank 10 and the loop.

[0035] The maintenance method described in this application fully utilizes the existing equipment in the original shielded cooling water system 1, including the dosing tank 10, metering pump 30, circulation pump 20, and regulating valve 50, without adding any new equipment, thus achieving effective system maintenance. This method not only fully utilizes the potential of the original system and saves on modification costs, but is also simple to operate, easy to implement, and has good practicality and scalability.

[0036] Furthermore, the injection and venting steps of S2 are performed by injecting maintenance fluid through the metering pump 30 in the shielded cooling water system 1. After opening the venting valve, the injection and venting steps of S2 also include the following steps: Start metering pump 30, The maintenance fluid is injected into the shielded cooling water system 1 via metering pump 30.

[0037] Furthermore, the regular monitoring step S5 specifically includes: During the first 7 days after entering the maintenance state, samples of the maintenance solution were collected daily and their pH values ​​were measured. If the pH value measured for 7 consecutive days is within the range of 10.0 to 10.5, the monitoring frequency will be adjusted to once every 3 days starting from the 8th day. If any measured pH value exceeds the range of 10.0 to 10.5, terminate the current maintenance process, return to step S1 to re-prepare the medication, and perform subsequent operations.

[0038] By conducting daily monitoring during the initial maintenance phase, problems can be detected and addressed promptly when they first appear, preventing minor issues from escalating into major malfunctions. Once the system stabilizes, the monitoring frequency can be reduced, decreasing the investment of manpower and resources and improving work efficiency.

[0039] Furthermore, in this embodiment, terminating the current maintenance process specifically includes: draining the maintenance fluid from the shielded cooling water system 1.

[0040] In some other implementations, terminating the current maintenance process does not require first draining the maintenance fluid from the shielded cooling water system 1. Instead, the process returns directly to step S1, and once the newly prepared maintenance fluid meets the requirements, it is injected directly into the system through the metering valve. At the same time, the old, substandard maintenance fluid is discharged from the system through the outlet.

[0041] Furthermore, the demineralized water meets the following requirements: conductivity ≤ 0.5 μS / cm, hardness ≤ 2 μmol / L.

[0042] Low conductivity and low hardness demineralized water reduces the ion content in the water, effectively lowering the risk of corrosion to equipment and pipelines and extending the system's service life. Furthermore, the low hardness of the water reduces the deposition of calcium and magnesium ions, preventing scaling and maintaining the system's efficient operation.

[0043] Furthermore, in order to reduce raw material costs, the ammonia solution is industrial-grade ammonia solution with a concentration of 32%.

[0044] In summary, the maintenance method for a shielded cooling water system 1 provided in this embodiment effectively prevents oxygen corrosion and acid corrosion by injecting an alkaline maintenance solution with a pH value of 10.0 to 10.5 into the shielded cooling water system 1 and stabilizing the system pressure between 0.3 MPa and 0.5 MPa during the maintenance phase. This significantly extends the service life of key components of the shielded cooling water system 1. More importantly, the maintenance method fully utilizes existing devices in the original shielded cooling water system 1, including the dosing tank 10, metering pump 30, circulation pump 20, and regulating valve 50, without adding any new equipment, thus achieving effective system maintenance and demonstrating good practicality and scalability.

[0045] The specific implementation methods described herein are not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed herein should be included within the protection scope of this invention.

Claims

1. A method for maintaining a shield cooling water system applied to a high temperature gas cooled reactor, characterized in that, The shielding cooling water system comprises a dosing tank and a circulating pump, and the maintenance method comprises the following steps: S1, dosing: adding desalted water and ammonia water stock solution into the dosing tank to prepare a maintenance solution with pH value of 10.0-10.5; S2, liquid injection and air exhaust: injecting the maintenance solution into the shielding cooling water system and exhausting the residual air in the shielding cooling water system; S3, circulating operation and sampling analysis: starting the circulating pump, sampling and detecting the pH value of the maintenance solution after the maintenance solution is circulated for a preset time; if the detection result meets the maintenance index of 10.0-10.5, entering the pressure maintaining stage; if not, supplementing or replacing the newly prepared maintenance solution, continuing the circulation of the maintenance solution and sampling and detecting, until the pH value meets the standard; S4, maintenance maintaining: adjusting the system pressure to stabilize the pressure of the maintenance solution in the shielding cooling water system in the range of 0.3-0.5 MPa, closing the circulating pump and entering the long-term maintenance state; S5, regular monitoring: regularly detecting the pH value of the maintenance solution in the shielding cooling water system, if the pH value is in the range of 10.0-10.5, extending the sampling interval, if the pH value is not in the range of 10.0-10.5, terminating the current maintenance process and returning to step S1 to re-dose and perform subsequent operations.

2. The method of claim 1, wherein The shielding cooling water system further comprises a stirring device arranged in the dosing tank, and the dosing step S1 specifically comprises: injecting desalted water into the dosing tank to a preset liquid level; starting the stirring device; in the stirring process, injecting ammonia water into the desalted water and monitoring the pH value of the solution in the dosing tank in real time; when the pH value of the solution is stabilized in the range of 10.0-10.5, stopping the injection of ammonia water and completing the preparation of the maintenance solution.

3. The method of claim 1, wherein the method further comprises: In the dosing step S1, the detection of the pH value adopts multi-point sampling detection, and the specific detection steps comprise: using a pH meter to collect the maintenance solution samples at three sampling points selected at different positions of the dosing tank; respectively measuring the pH value of each sample; if the pH value of any sampling point exceeds the range, ammonia water or desalted water needs to be added to adjust the pH value; after supplementing, the samples are taken again at the three sampling points and the pH value is monitored until the maintenance solution is qualified. The shielding cooling water system further comprises an air exhaust valve, and the liquid injection and air exhaust step S2 specifically comprises:

4. The method of claim 1, wherein opening the air exhaust valve; injecting the maintenance solution into the shielding cooling water system; when the air exhaust valve starts to continuously flow out the maintenance solution, closing the air exhaust valve. The shielding cooling water system further comprises a metering pump, a header assembly and a regulating valve, the header assembly comprises an upper header and a lower header, and the upper header and the lower header are connected into a closed loop through external pipelines, 5. The method of claim 4, wherein the step of applying the protective coating is performed after the step of applying the shielding layer. the metering pump and the regulating valve are arranged on the closed loop, and the metering pump is arranged on the connecting pipeline between the dosing tank and the closed loop. After opening the air exhaust valve, the liquid injection and air exhaust step S2 further comprises the following steps:

6. The method of claim 5, wherein the step of applying the protective coating is performed after the step of applying the shielding layer. ​ starting the metering pump, injecting the maintenance liquid into the shielded cooling water system through the metering pump.

7. The method of claim 1, wherein the method further comprises: The periodic monitoring step S5 specifically comprises: collecting the maintenance liquid sample and measuring the pH value every day within the first 7 days after entering the maintenance state; if the pH value measured continuously for 7 days is within the range of 10.0-10.5, then the monitoring frequency is adjusted to once every 3 days from the 8th day; if the pH value measured at any time exceeds the range of 10.0-10.5, then the current maintenance process is terminated, and the subsequent operation is returned to step S1 to re-dispense the medicine.

8. The method of claim 1, wherein the method further comprises: The step of terminating the current maintenance process specifically comprises: emptying the maintenance liquid in the shielded cooling water system.

9. The method of claim 1, wherein The desalted water satisfies the conductivity ≤0.5 μS / cm, and the hardness ≤2 μmol / L.

10. The method of claim 1, wherein The ammonia water stock solution is an industrial-grade ammonia water with a concentration of 32%.

Images