Exhaust method for boric acid recirculation pump of nuclear power plant

Abstract

The invention belongs to the technical field of nuclear power, and discloses an exhaust method for a boric acid recirculation pump of a nuclear power plant, which comprises the following steps of: filling a boric acid solution into a high-level water tank arranged on an upstream pipeline of the boric acid recirculation pump, and providing an enough inlet pressure head for the boric acid recirculation pump; a temporary pipe section is connected to the position close to the boric acid recirculation pump body; injecting a solution from the temporary pipe section to discharge gas at the upstream of the liquid injection point; injecting a solution from the temporary pipe section to discharge gas at the downstream of the liquid injection point; and starting the boric acid recirculation pump. After the exhaust method for the boric acid recirculation pump of the nuclear power plant is used, the boric acid recirculation pump is successfully started at a time, the working efficiency is improved, nuclear safety related equipment is protected, and the exhaust method is suitable for nuclear power units of the models of M310, CPR1000 and the like.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power technology, and specifically relates to a method for venting a boric acid recirculation pump in a nuclear power plant. Background Technology

[0002] In the event of an accident such as a rupture in the primary loop of a nuclear power plant reactor, the Safety Injection System (RIS) injects a high concentration of boric acid solution into the primary loop to break the chain reaction, stop the nuclear reaction, ensure that the reactor is in a subcritical state, ensure the integrity of the core fuel elements, and prevent serious accidents such as core meltdown and leakage of radioactive materials. Therefore, the Safety Injection System is a means of ensuring the safety of nuclear reactors.

[0003] In the safety injection system, the boric acid recirculation loop is used to recirculate concentrated boric acid within the system, ensuring a uniform boric acid solution, preventing boron crystallization, and thus guaranteeing the system's functionality. The boric acid recirculation pump is a fully sealed pump, and its inlet pipeline and upstream container are equipped with electric heaters, stirrers, multi-stage bends, filters, and other equipment, resulting in a complex layout.

[0004] To ensure the functionality of the boric acid recirculation pump, the equipment must be emptied and preventative maintenance performed during each major overhaul, as designed. After maintenance, the pump must be refilled with water and vented, and the parameters must be verified to meet requirements by starting it up step by step according to the pre-designed procedure. In actual production, filling and venting the boric acid recirculation pump is a challenge. The normal workflow involves filling an appropriate amount of boric acid solution into an upstream high-level water tank, allowing gravity to allow the solution to flow automatically to the downstream pump body. Due to the complexity of the equipment layout in the boric acid recirculation pump, especially with a dense filter screen connected to the outlet of the high-level water tank, this process can take a day or longer. Furthermore, this venting method generally requires multiple starts to succeed. After a failed start-up, the boric acid solution must flow downstream automatically for a period before restarting, further extending the time required. Moreover, during these multiple starts, the presence of residual gas in the pipes and pump casing introduces cavitation risk each time the water flow removes this residual gas, potentially damaging components such as the pump impeller. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the purpose of this invention is to provide a method for venting a boric acid recirculation pump in a nuclear power plant.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for venting a boric acid recirculation pump in a nuclear power plant includes the following steps:

[0008] S1. Fill the elevated water tank on the upstream pipeline of the boric acid recirculation pump with boric acid solution to provide sufficient inlet head for the boric acid recirculation pump;

[0009] S2. Connect a temporary pipe section near the boric acid recirculation pump body;

[0010] S3. Inject solution from the temporary pipe section to purge gas upstream of the injection point;

[0011] S4. Inject solution from the temporary pipe section to purge gas downstream of the injection point;

[0012] S5. Start the boric acid recirculation pump.

[0013] Furthermore, step S2, connecting a temporary pipe section near the boric acid recirculation pump body, involves: opening an injection valve on the pipe near the boric acid recirculation pump body and then connecting the temporary pipe section, or using a valve in the pipe near the boric acid recirculation pump body as an injection valve to connect the temporary pipe section.

[0014] Furthermore, the temporary pipe section can be connected at any point in the pipeline between the upstream inlet valve and the downstream drain and vent valve of the pump.

[0015] Furthermore, the valves in the pipeline near the boric acid recirculation pump body include a condensate vent valve upstream of the boric acid recirculation pump.

[0016] Further, step S3 is as follows: close the outlet valve of the boric acid recirculation pump, open the injection valve and the inlet valve of the boric acid recirculation pump, inject the solution into the temporary pipe section described in step S2 until the boric acid solution in the high-level water tank no longer produces bubbles and the liquid level begins to rise, then close the injection valve and the inlet valve of the boric acid recirculation pump.

[0017] Or / and, step S4 is: opening the injection valve and the outlet valve of the boric acid recirculation system, injecting the solution into the temporary pipe section described in step S2 until the condensate vent valve downstream of the boric acid recirculation pump starts to discharge water, and then closing the injection valve.

[0018] Furthermore, the amount of boric acid solution added in step S1 satisfies the following condition: the level of boric acid solution in the high-level water tank is 0-2 cm higher than the low-level alarm line.

[0019] Furthermore, the temporary pipe section mentioned in step S2 includes one of braided silicone pipe and plastic pipe.

[0020] Furthermore, the solutions described in steps S3 and S4 independently include at least one of demineralized water and boric acid solution.

[0021] Furthermore, the concentrations of the boric acid solutions described in steps S1, S3, and S4 independently conform to the unit's control range for boric acid concentration, which is 2400-15000 ppm.

[0022] Furthermore, the injection rates of the injected solution in steps S3 and S4 independently satisfy the condition that the injected solution is propelled forward while the pipe is fully filled.

[0023] Furthermore, in step S3, the pressure injected into the solution is greater than the sum of the resistance generated by the pipeline and equipment along the path from the injection point to the high-level water tank and the gravity caused by the height difference between the injection point and the high-level water tank.

[0024] Furthermore, the pressure injected into the injection solution in step S3 is 1-8 bar.

[0025] Furthermore, in step S4, the pressure injected into the injection solution is greater than the opening pressure of the outlet check valve.

[0026] Furthermore, the pressure injected into the injection solution in step S4 is 1-8 bar.

[0027] Furthermore, before or after step S5, the following steps are included: removing the temporary pipe section and sealing the connection.

[0028] Furthermore, in step S5, if the boric acid recirculation pump fails to start, steps S3-S5 are repeated until the boric acid recirculation pump is successfully started.

[0029] The implementation of this invention has the following beneficial effects:

[0030] The venting method for boric acid recirculation pumps in nuclear power plants of the present invention solves the problems of difficult venting, long time consumption, and equipment damage caused by boric acid recirculation pumps in nuclear power plants. After using the venting method for boric acid recirculation pumps in nuclear power plants of the present invention, the boric acid recirculation pump can be successfully started on the first attempt, improving working efficiency and protecting nuclear safety-related equipment. It is applicable to nuclear power units of models such as M310 and CPR1000. Attached Figure Description

[0031] Figure 1 This is a flowchart of the venting method for the boric acid recirculation pump in a nuclear power plant according to the present invention.

[0032] Figure 2 This is a schematic diagram of the valve positions in the venting method of the boric acid recirculation pump in a nuclear power plant according to the present invention. Detailed Implementation

[0033] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the invention will now be described in detail with reference to the accompanying drawings. In the following description, it should be understood that the orientations or positional relationships indicated by terms such as "front," "rear," "upper," "lower," "left," "right," "longitudinal," "horizontal," "vertical," "horizontal," "top," "bottom," "inner," "outer," "head," and "tail" are based on the orientations or positional relationships shown in the accompanying drawings, and are constructed and operated in a specific orientation. They are only for the convenience of describing the present invention and do not indicate that the device or element referred to must have a specific orientation; therefore, they should not be construed as limitations on the present invention.

[0034] It should also be noted that, unless otherwise explicitly specified and limited, terms such as "installation," "connection," "linking," "fixing," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. When an component is referred to as being "on" or "below" another component, the component can be located "directly" or "indirectly" on the other component, or there may be one or more intermediary components. The terms "first," "second," "third," etc., are used only for the convenience of describing the present invention and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. For those skilled in the art, the specific meaning of the above terms in the present invention can be understood according to the specific circumstances.

[0035] During the implementation of the boric acid recirculation pump exhaust method for nuclear power plants in this invention, the downstream injection valve is always kept closed.

[0036] like Figure 1 As shown, this invention provides a method for venting a boric acid recirculation pump in a nuclear power plant, comprising the following steps, wherein the positions of each valve are as follows: Figure 2 As shown:

[0037] S1. Fill the elevated water tank on the upstream pipeline of the boric acid recirculation pump with boric acid solution to provide sufficient inlet head for the boric acid recirculation pump.

[0038] Specifically, the amount of boric acid solution added should meet the following requirements: the level of boric acid solution in the high-level water tank should be 0-2 cm higher than the low-level alarm line. The level can be any value within this range. This level provides sufficient inlet head for the downstream boric acid recirculation pump and a certain buffer margin for the pipeline network, preventing cavitation caused by insufficient inlet pressure in unexpected situations. Preferably, the level should be 0 cm, 1 cm, or 2 cm higher than the low-level alarm line. If the level is too low, it may cause damage to the pump due to insufficient inlet head. If the level is too high, it may affect subsequent water filling operations, leading to overflow during the filling process.

[0039] Specifically, the concentration of the boric acid solution conforms to the unit's control range for boric acid concentration; further, the concentration of the boric acid solution is 2400-15000 ppm. The concentration of the boric acid solution can be any value within this range, preferably 2400 ppm, 8000 ppm, or 15000 ppm.

[0040] S2. Connect a temporary pipe section near the boric acid recirculation pump body.

[0041] Specifically, a liquid injection valve is installed on the pipeline near the boric acid recirculation pump body, and a temporary pipeline section is then connected. Alternatively, a valve in the pipeline near the boric acid recirculation pump body can be used as a liquid injection valve to connect the temporary pipeline section. Further, the temporary pipeline section can be connected at any point in the pipeline between the upstream inlet valve and the downstream drain and vent valve. When the temporary pipeline section is connected to the upstream pipeline of the boric acid recirculation pump, step S3 vents the gas in the upstream pipeline, and step S4 vents the gas in the downstream pipeline and inside the pump. When the temporary pipeline section is connected to the downstream pipeline of the boric acid recirculation pump, step S3 vents the gas in the upstream pipeline and inside the pump, and step S4 vents the gas in the downstream pipeline. In short, after steps S3 and S4, the gas inside the boric acid recirculation pump and in the upstream and downstream pipelines is vented. The valve in the pipeline near the boric acid recirculation pump body includes the upstream drain and vent valve of the boric acid recirculation pump.

[0042] When the temporary pipeline is connected near the boric acid recirculation pump body, filling the point with water ensures that the water flows smoothly through the upstream pipeline of the pump into the high-level water tank; and maximizes the function of water injection and air release; furthermore, the injection point does not contain equipment such as check valves, which would prevent the solution from being injected.

[0043] Specifically, the temporary pipe sections include either braided silicone tubing or plastic tubing. The material of this type of temporary pipe section will not introduce other ionic impurities, ensuring the safety of the upstream water source and preventing the introduction of other ions.

[0044] S3. Inject solution from temporary pipeline to expel gas upstream of injection point: Close the outlet valve of boric acid recirculation pump, open the injection valve and the inlet valve of boric acid recirculation pump, inject solution into the temporary pipeline in step S2 until the boric acid solution in the high-level water tank no longer produces bubbles and the liquid level begins to rise, then close the injection valve and the inlet valve of boric acid recirculation pump.

[0045] Specifically, the solution includes at least one of demineralized water and boric acid solution. When the injected solution is boric acid solution, since boric acid solution is generally stored in atmospheric pressure containers, and the injection process requires a certain pressure, an external component is needed to provide pressure during the injection process. When the injected solution is demineralized water, since the demineralized water system is a fundamental system in the design of the nuclear power plant, and this system provides the corresponding pressure when outputting demineralized water, directly using the existing demineralized water system as the water source can fully meet the requirements for flow rate, water pressure, and water quality. Furthermore, for the type of injected solution, any water source that meets the requirements of subsequent operations and will not affect the boric acid recirculation system is acceptable. The concentration of the boric acid solution complies with the unit's control range for boric acid concentration; furthermore, the concentration of the boric acid solution is 2400-15000 ppm. The concentration of the boric acid solution can be selected from any value within this range, preferably 2400 ppm, 8000 ppm, or 15000 ppm.

[0046] Specifically, the injection rate of the solution must meet the following condition: the solution must be kept filling the pipe before it can be pushed forward. This includes the following steps: slowly increase the opening of the injection valve at the temporary pipe connection until the sound of fluid flow can be heard, and maintain this opening. This is the injection rate that meets the above condition. If the solution injection rate is too fast, laminar flow will occur, causing the water to jet and resulting in insufficient venting; if it is too slow, the injection will take a long time to complete, reducing work efficiency.

[0047] Specifically, the pressure injected into the solution is greater than the sum of the resistance generated by the pipeline and equipment along the path from the injection point to the high-level water tank and the gravity caused by the height difference between the injection point and the high-level water tank. The equipment along the path includes valves, filters, etc. Furthermore, the pressure injected into the solution is 1-8 bar, and any value can be selected within this range, preferably 1 bar, 5 bar or 8 bar.

[0048] S4. Inject solution from temporary pipe section to expel gas downstream of injection point: Open injection valve and outlet valve of boric acid recirculation system, inject solution into temporary pipe section of step S2 until water starts to flow from condensate vent valve downstream of boric acid recirculation pump, then close injection valve.

[0049] Specifically, similar to step S3, the solution includes at least one of demineralized water and boric acid solution. The concentration of the boric acid solution conforms to the unit's control range for boric acid concentration; further, the concentration of the boric acid solution is 2400-15000 ppm. The concentration of the boric acid solution can be selected from any value within this range, preferably 2400 ppm, 8000 ppm, or 15000 ppm.

[0050] Specifically, similar to step S3, the injection rate of the solution into the injection solution satisfies the following condition: the injected solution is pushed forward while the pipe is fully filled.

[0051] Specifically, the pressure injected into the injection solution is greater than the opening pressure of the outlet check valve; further, the pressure injected into the injection solution is 1-8 bar, and any value can be selected within this range, preferably 1 bar, 5 bar or 8 bar.

[0052] S5. Start the boric acid recirculation pump. Starting the pump once can completely remove the trace amounts of residual gas remaining in the system that do not affect the pump's operation, making the venting process more perfect.

[0053] Specifically, before step S5, the relevant equipment is set to a state that allows the pump to start according to the unit requirements, including: opening the inlet valve and outlet valve of the boric acid recirculation pump, opening the recirculation valve of the boric acid recirculation pump, closing the downstream injection valve, powering on the pump, powering on the heater, reconfirming that the liquid level in the high-level water tank is between the high and low liquid level alarm lines, and reinstalling the pump and pipeline insulation.

[0054] Specifically, if startup fails, repeat steps S3-S5 until the boric acid recirculation pump starts successfully. During the startup of the boric acid recirculation pump, the venting is judged by whether the pump can establish an outlet pressure head. If an outlet pressure head cannot be established, it is considered that the venting is not sufficient, and the previous venting steps can be repeated once. If an outlet pressure head can be established, it proves that the venting work is completed.

[0055] Example 1

[0056] S1. Fill the high-level water tank set on the upstream pipeline of the boric acid recirculation pump with 2400ppm boric acid solution until the liquid level is 1cm higher than the low liquid alarm line, that is, the low liquid level alarm will not be triggered.

[0057] S2. Connect the hydrophobic vent valve upstream of the boric acid recirculation pump to a braided silicone tube;

[0058] S3. Inject solution from the braided silicone tubing to expel gas upstream of the injection point (upstream of the boric acid recirculation pump): Connect the other end of the braided silicone tubing to the demineralized water system. Close the outlet valve of the boric acid recirculation pump, open the condensate vent valve and the inlet valve of the boric acid recirculation pump, and inject demineralized water from the demineralized water system into the braided silicone tubing. Slowly increase the opening of the condensate vent valve until you hear the choking sound caused by the fluid flowing through it. The injected demineralized water will then move forward while the pipe is full. Continue injecting demineralized water at this opening until the boric acid solution in the high-level tank no longer produces bubbles and the liquid level rises. Close the condensate vent valve and the inlet valve of the boric acid recirculation pump. The pressure of the demineralized water injected into the demineralized water system is 8 bar.

[0059] S4. Inject solution from the braided silicone tubing to expel gas downstream of the injection point (borate recirculation pump and downstream): Open the condensate vent valve and the outlet valve of the borate recirculation system. Inject demineralized water into the braided silicone tubing from the demineralized water system. Slowly increase the opening of the condensate vent valve until you hear the choking sound caused by the fluid flowing through. The injected demineralized water will then advance forward while the pipe is full. Continue injecting demineralized water at this opening until the condensate vent valve downstream of the borate recirculation pump starts to discharge water. Close the condensate vent valve that you just observed starting to discharge water. Close the condensate vent valve connected to the silicone tubing for filling with water. The pressure of the demineralized water injected into the demineralized water system is 8 bar.

[0060] S5. Start the boric acid recirculation pump. The pump starts successfully on the first attempt.

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 is that the pressure of the demineralized water injected into the demineralized water system in steps S3 and S4 is 1 bar, and the pump is successfully started on the first attempt.

[0063] Example 3

[0064] The difference between this embodiment and embodiment 1 is that the pressure of the demineralized water injected into the demineralized water system in steps S3 and S4 is 5 bar, and the pump is successfully started on the first attempt.

[0065] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A method for venting a boric acid recirculation pump in a nuclear power plant, characterized in that, Includes the following steps: S1. Fill the elevated water tank on the upstream pipeline of the boric acid recirculation pump with boric acid solution to provide sufficient inlet head for the boric acid recirculation pump; S2. Connect a temporary pipe section near the boric acid recirculation pump body; S3. Inject solution from the temporary pipe section to purge gas upstream of the injection point; S4. Inject solution from the temporary pipe section to purge gas downstream of the injection point; S5. Start the boric acid recirculation pump.

2. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 1, characterized in that: Step S2, connecting a temporary pipe section near the boric acid recirculation pump body, involves: opening an injection valve on the pipe near the boric acid recirculation pump body and then connecting the temporary pipe section, or using a valve in the pipe near the boric acid recirculation pump body as an injection valve to connect the temporary pipe section.

3. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 2, characterized in that: Step S3 is as follows: close the outlet valve of the boric acid recirculation pump, open the injection valve and the inlet valve of the boric acid recirculation pump, inject the solution into the temporary pipeline section described in step S2, until the boric acid solution in the high-level water tank no longer produces bubbles and the liquid level begins to rise, then close the injection valve and the inlet valve of the boric acid recirculation pump. Or / and, step S4 is: opening the injection valve and the outlet valve of the boric acid recirculation system, injecting the solution into the temporary pipe section described in step S2 until the condensate vent valve downstream of the boric acid recirculation pump starts to discharge water, and then closing the injection valve.

4. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 1, characterized in that, The amount of boric acid solution added in step S1 shall meet the following requirement: the level of boric acid solution in the high-level water tank shall be 0-2 cm higher than the low-level alarm line.

5. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 1, characterized in that: The solutions described in steps S3 and S4 independently include at least one of demineralized water and boric acid solution; Or / and the injection rate of the injection solution in steps S3 and S4 independently satisfies the following: the injected solution is kept in a state of filling the pipe and moving forward.

6. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 1, characterized in that: The pressure injected into the solution in step S3 is greater than the sum of the resistance generated by the pipeline and equipment along the path from the injection point to the high-level water tank and the gravity caused by the height difference between the injection point and the high-level water tank.

7. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 6, characterized in that: The pressure injected into the solution in step S3 is 1-8 bar.

8. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 1, characterized in that: In step S4, the pressure injected into the solution is greater than the opening pressure of the outlet check valve.

9. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 8, characterized in that: The pressure injected into the injection solution in step S4 is 1-8 bar.

10. The method for venting the boric acid recirculation pump in a nuclear power plant according to claim 1, characterized in that: If the start-up of the boric acid recirculation pump fails in step S5, repeat steps S3-S5 until the boric acid recirculation pump is started successfully.

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