Vortex suction suppression device and method for inlet pipeline of residual heat removal system of nuclear power plant

Abstract

The invention belongs to the technical field of nuclear power plant system design, and particularly relates to a vortex inspiration suppression device and method for an inlet pipeline of a nuclear power plant waste heat removal system. Comprising a heat pipe section and filler neck fillet transition section, and the heat pipe section and filler neck fillet transition section is formed by grinding the upper edge of a heat pipe section connector and the joint of the filler neck and the heat pipe section connector into fillets. The device has the beneficial effects that the vortex suppression part is additionally arranged at the RHR system and the inlet connecting pipe of the heat pipe section, and the inlet connecting pipe adopts the modes of variable pipe diameter, inclined and smooth design entering and the like, so that the possibility of vortex suction at the inlet of the RHR connecting pipe can be effectively suppressed. The possibility of vortex generation at the inlet of the RHR connecting pipe is reduced, and the vortex suction phenomenon is avoided; the possibility of vibration noise aggravation and mechanical damage caused by vortex air suction of the RHR pump is reduced, and the running stability of the RHR is improved; the operation reliability of the RHR in the Mid-loop working condition period is improved, normal cooling of a loop is ensured, the risk of reactor core melting is reduced, and the operation safety of a unit is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power plant system design, and in particular relates to a vortex air intake suppression device and method for an inlet pipeline of a residual heat removal system of a nuclear power plant. Background Art

[0002] The residual heat removal system (RHR) is an important system used to remove the heat from the core of a nuclear power plant. During the shutdown and refueling overhaul of a nuclear power plant, the core decay heat is removed by the RHR. During the cold shutdown of a nuclear power plant, when the amount of coolant in the primary circuit drops below the top of the hot section (Mid-loop condition), due to the suction effect of the RHR pump, if the liquid level in the hot section is below a certain height, a vortex may be generated at the interface between the RHR inlet pipeline and the hot section. If the vortex is deep enough, air will enter the residual heat removal pump, causing damage to the residual heat removal pump and loss of residual heat removal capacity. Once the RHR loses its function, in the absence of other heat removal means, the coolant in the reactor may reach saturation in a short period of time, which may cause the core to be exposed, the fuel cladding to be damaged, and even cause serious consequences such as radioactivity release to the environment.

[0003] According to statistics from the Westinghouse Owners Group (WOG) and the Framatome Owners Group (FROG), there were more than 30 incidents between 1977 and 1993 where air entered the RHR pump during the mid-loop period due to vortexes generated at the interface between the RHR and the hot section, causing the nuclear power plant to lose its residual heat removal function. In 1987, the Diable Canyon Unit 2 also had an accident in which radioactive steam was released outside the containment. Therefore, preventing vortex suction from occurring during the operation of the RHR pump during the mid-loop period of a nuclear power plant is of great significance to ensure the safe operation of the power plant.

[0004] Existing studies have shown that, under the premise of certain structural parameters, the critical liquid level for generating vortex at the inlet of the RHR system depends largely on the flow velocity and flow field distribution at the suction port.

[0005] Both theoretical research and engineering operation experience show that vortex suction may occur near the inlet of the hot section of the residual exhaust pipe of a nuclear power plant during mid-loop operation. At present, the industry has carried out corresponding research on the physical mechanism of air inhalation caused by the generation of vortices. It is generally believed in engineering that there are two main reasons for the generation of vortices in the fluid at the inlet of the RHR pipe of a nuclear power plant:

[0006] First, the uneven flow field caused by the flow channel structure generates vortices in the local fluid. The vortices are continuously shed and re-formed as the flow develops, and then gather and strengthen near the inlet of the pipe, gradually developing into stronger vortices.

[0007] Secondly, the liquid level at the inlet of the pipe is low and the flow rate is fast. Under the guidance of the mainstream, the liquid surface above the inlet of the pipe continues to sink and produce a vortex.

[0008] Due to the influence of upstream liquid level, flow velocity, etc., the fluid itself has a lower pressure at the center of the vortex. At the same time, the fluid at the inlet itself has a certain flow velocity, which will also aggravate the reduction of the pressure there, causing the liquid surface near the inlet center to sag, and then air enters the fluid along with the vortex and may cause cavitation of the residual pump impeller; in addition, the residual pump blades or pump casing and other parts will also cause vibration noise and mechanical damage due to the inflow of air, which will endanger the service life and safe production of the pump. Summary of the invention

[0009] The purpose of the present invention is to provide a vortex air intake suppression device and method for the RHR inlet pipeline of a nuclear power plant. The present invention can effectively mitigate the air intake phenomenon caused by vortex when the liquid level in the hot section is constant, reduce the risk of equipment damage to the residual discharge pump due to air intake, and improve the reliability of the RHR function.

[0010] The technical solution of the present invention is as follows: a vortex air intake suppression device for an inlet pipeline of a waste heat removal system of a nuclear power plant, comprising a hot pipe section and a fillet transition section between a hot pipe section and a pipe nozzle, wherein the hot pipe section and the fillet transition section between the hot pipe section and the pipe nozzle are grinded into fillets at the upper edge of the hot pipe section interface and the connection between the pipe nozzle and the hot pipe section.

[0011] A vortex air intake suppression device for the inlet pipeline of a residual heat removal system of a nuclear power plant comprises a large-diameter pipe nozzle connected to a hot pipe section and an inclined arrangement mode. The RHR and hot pipe section interface pipeline adopts a larger pipe diameter, that is, a larger-diameter pipe nozzle of a certain length is arranged between the RHR pump inlet pipe and the hot pipe section. The pipe nozzle is connected to the hot pipe section at a certain inclination angle, and the inclination direction is consistent with the flow direction of the upstream fluid.

[0012] A vortex air intake suppression device for an inlet pipeline of a waste heat removal system of a nuclear power plant comprises a vortex flow suppression device assembly, wherein the vortex flow suppression device assembly comprises a reducer pipe 3, guide vanes 7 and flanges at both ends of the pipe, wherein the inner edges of the guide vanes 7 intersect with each other to form a vortex suppression component 1, and the outer edges of the guide vanes 7 are welded to the inner wall surface of the reducer pipe to form a vortex suppression device assembly 5, and the vortex flow suppression device assembly 5 is connected to an upstream large-diameter pipe nozzle 2 and a downstream RHR pump inlet pipe through a flange 6.

[0013] Includes any one or more combinations of the above designs.

[0014] A method for suppressing vortex inhalation for an RHR inlet pipeline of a nuclear power plant comprises the following steps: at the interface between the RHR and the hot pipe section, the edge of the inlet hot pipe section is rounded and polished to improve the flow field stability at the interface and reduce the probability of fluid vortex generation.

[0015] A method for suppressing vortex inhalation for RHR inlet pipeline of nuclear power plant comprises the following steps: the RHR and hot pipe section interface pipeline adopts a larger pipe diameter, and the hot pipe section interface pipeline and RHR pump inlet pipeline are connected by a reducer.

[0016] A method for suppressing vortex inhalation for RHR inlet pipelines of nuclear power plants comprises the following steps: the interface pipeline between RHR and hot pipe section adopts an inclined design with a certain angle, and the inclined direction is consistent with the mainstream direction of the fluid in the main pipeline.

[0017] A method for suppressing vortex air intake in RHR inlet pipelines of nuclear power plants comprises the following steps: adding a detachable reducer connector between a hot pipe section interface pipeline and an RHR pump inlet pipeline, and installing a vortex suppressor in the connector.

[0018] The eddy current suppression member adopts a "cross blade" or other structural forms.

[0019] Use any one of the above methods or a combination of multiple methods.

[0020] The beneficial effects of the present invention are as follows: the present invention can effectively suppress the possibility of vortex suction at the inlet of the RHR pipe by adding vortex suppression parts to the inlet pipe of the RHR system and the hot pipe section, and adopting variable pipe diameter, inclined and smooth design to the inlet pipe. The possibility of vortex generation at the inlet of the RHR pipe is reduced, and the occurrence of vortex suction phenomenon is avoided; the possibility of increased vibration and noise and mechanical damage of the RHR pump due to vortex suction is reduced, and the operating stability of the RHR is improved; the operating reliability of the RHR during the Mid-loop working condition is improved, the normal cooling of the first circuit is ensured, the risk of core melting is reduced, and the safe operation of the unit is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structural design and arrangement of the vortex air intake suppression device;

[0022] Figure 2 It is a schematic diagram of the composition and application method of the vortex inhalation suppression device;

[0023] Figure 3 It is a schematic diagram of the structure of the vortex air intake suppression component;

[0024] Figure 4 for Figure 3 A top view of

[0025] Figure 5 This is a three-dimensional diagram of the structure of the vortex intake suppression component.

[0026] In the figure: 1 vortex suppression component, 2 large diameter pipe nozzle, 3 reducer pipe, 4 hot pipe section and pipe nozzle fillet transition section, 5 vortex suppression device assembly, 6 connecting flange and bolt holes, 7 guide vane. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] The present invention can effectively weaken or eliminate the vortex in the RHR suction pipeline by improving the structural design of the pipe port at the connection between the RHR system suction pipeline and the primary circuit heat pipe section, adding an eddy current suppressor and optimizing the pipe layout, thereby reducing the amount of air involved, increasing the operating safety margin of the RHR pump of the nuclear power plant during the Mid-loop operating condition, improving the reliability of the RHR, and ensuring the safe operation of the power plant.

[0029] The present invention provides a vortex suction suppression device for the RHR inlet pipeline of a nuclear power plant, which provides three design schemes for suppressing vortex suction in the RHR inlet pipe section. The layout and structural design thereof are shown in the following figure. Figure 1 , Figure 2 , Figure 3 and Figure 4 Specifically, it should include:

[0030] 1. Transition section between the hot pipe section and the fillet of the pipe nozzle: Figure 2 The rounded transition section 4 between the hot pipe section and the pipe nozzle is a rounded corner polished at the upper edge of the hot pipe section interface and the connection between the pipe nozzle and the hot pipe section. The specific polishing amount can be determined based on the hot pipe section thickness and interface size assessment to maintain the flow stability of the upstream fluid when it enters the interface and reduce the generation of local vortices.

[0031] 2. Large diameter pipe nozzles connected to the heat pipe section and inclined layout: The interface pipe between the RHR and the heat pipe section adopts a larger pipe diameter (for example, the diameter of the interface pipe can be designed to be twice the diameter of the RHR pump inlet pipe, and the specific size can be determined in combination with the actual situation of the RHR system flow, layout space, etc.), that is, a larger pipe nozzle with a certain length is set between the RHR pump inlet pipe and the heat pipe section. The specific length of the nozzle can be determined by numerical simulation or experimental verification in combination with the specific situation. The nozzle is connected to the heat pipe section at a certain inclination angle ( Figure 2 , as shown by the inclination angle θ), the inclination direction is consistent with the flow direction of the upstream fluid. The inclination angle can be determined in combination with the pipeline size and the actual layout space, and can be determined through numerical analysis or experimental verification guidance.

[0032] 3. Vortex suppression device assembly: The assembly includes a reducer pipe 3, guide vanes 7 and flanges at both ends of the pipe. The inner edges of the guide vanes 7 (4 or more) intersect to form a vortex suppression component 1. The guide vanes 7 can adopt a simple plane design or other forms of curved surface design. The outer edge of the guide vane 7 is welded to the inner wall of the reducer pipe to form an assembly 5 with a vortex suppression device, and is connected to the upstream large-diameter pipe nozzle 2 and the downstream RHR pump inlet pipe through a flange 6. The vortex suppression component and the reducer pipe design can be used alone or in combination. The specific application method can be determined according to the actual design conditions of the hot pipe section and the RHR system.

[0033] The above three design schemes can be applied individually or in combination. The specific application method can be determined based on the actual situation of the nuclear power plant.

[0034] An application of a vortex air inhalation suppression device and method for an RHR inlet pipeline of a nuclear power plant, specifically comprising the following steps:

[0035] Step 1: At the interface between the RHR and the heat pipe section, the edge of the inlet heat pipe section is rounded and polished to improve the flow field stability at the interface and reduce the probability of fluid vortex generation. According to existing studies, the sudden change of the internal structure of the flow channel is prone to vortex formation, and the vortex falls off and continuously enters the mainstream, thereby affecting the stability of the mainstream, which may increase the possibility of vortex generation in the mainstream. The use of rounded and smooth design at the interface can suppress the local vortex generation and reduce the probability of vortex generation in the fluid.

[0036] Step 2: The interface pipe between RHR and the hot pipe section adopts a larger pipe diameter, and the interface pipe between the hot pipe section and the RHR pump inlet pipeline are connected by a reducer. According to existing studies, under the same liquid level conditions, the higher the downstream fluid flow rate, the greater the possibility of generating vortices at the liquid surface. Using a larger pipe diameter design in the initial section of the interface pipe (the specific pipe diameter size can be determined based on numerical analysis or experiments) can reduce the mainstream flow rate at the inlet at the same volume flow rate, and reduce the possibility of generating obvious negative pressure in the center due to excessive mainstream flow rate, thereby generating vortices in the upstream fluid.

[0037] Step 3: The interface pipe between RHR and the hot pipe section adopts an inclined design with a certain angle. The inclination direction is consistent with the mainstream direction of the fluid in the main pipe. The specific inclination angle can be determined according to the RHR interface pipe size, flow rate and layout space. Compared with the arrangement perpendicular to the main pipe, the arrangement with a certain inclination along the flow direction can slow down the generation of vortex at the pipe connection port, thereby reducing the possibility of vortex generation in the RHR suction line.

[0038] Step 4: Add a removable reducer between the hot pipe section interface pipe and the RHR pump inlet pipeline, and install a vortex suppressor in the connector. The vortex suppressor can be a "cross blade" or other structural form. The size of the vortex suppressor is determined according to the diameter, flow rate and other relevant parameters of the RHR inlet pipe section of the specific nuclear power plant. The distance between the vortex suppressor and the pipe port can be determined based on numerical analysis or experiments. When the vortex enters the suppressor position, it is blocked by the vortex suppressor blades, thereby destroying the vortex shape and guiding the fluid into the downstream pipeline along the flow channel formed between the blades. In this process, the air that may be carried in the vortex will be retained upstream, further reducing the possibility of air entering the downstream, thereby maximizing the prevention of the impact of air inhalation on the stability of RHR operation.

[0039] The innovatively designed vortex inhalation suppression method proposed in the present invention comprises four steps, which can be implemented separately or in combination according to the actual situation of a nuclear power plant.

[0040] The vortex suction suppression device and method proposed in the present invention can effectively suppress the generation of vortex at the RHR inlet pipe section under Mid-loop conditions, reduce the possibility of vortex suction entering the RHR pump, thereby ensuring the normal operation of the RHR pump and improving the reliability of the RHR system. It is suitable for nuclear power plants whose RHR systems need to operate under Mid-loop conditions.

Claims

1. A vortex air intake suppression device for an inlet pipeline of a waste heat removal system of a nuclear power plant, characterized in that: It includes a heat pipe section and a fillet transition section, wherein the heat pipe section and the fillet transition section are the upper edge of the heat pipe section interface and the connection between the fillet and the heat pipe section, which are polished into fillets.

2. A vortex air intake suppression device for an inlet pipeline of a waste heat removal system of a nuclear power plant, characterized in that: Including a large-diameter pipe nozzle connected to the hot pipe section and an inclined arrangement method, the interface pipe between the RHR and the hot pipe section adopts a larger pipe diameter, that is, a larger-diameter pipe nozzle of a certain length is set between the RHR pump inlet pipe and the hot pipe section, and the pipe nozzle is connected to the hot pipe section at a certain inclination angle, and the inclination direction is consistent with the flow direction of the upstream fluid.

3. A vortex air intake suppression device for an inlet pipeline of a waste heat removal system of a nuclear power plant, characterized in that: It includes a vortex flow suppression device assembly, which includes a reducer pipe 3, guide vanes 7 and flanges at both ends of the pipe. The inner edges of the guide vanes 7 are crossed with each other to form a vortex suppression part 1. The outer edges of the guide vanes 7 are welded to the inner wall of the reducer pipe to form a vortex suppression device assembly 5, and are connected to the upstream large-diameter pipe nozzle 2 and the downstream RHR pump inlet pipe through flanges 6.

4. A vortex air intake suppression device for an inlet pipeline of a waste heat removal system of a nuclear power plant, characterized in that: The invention comprises any one or more device combinations according to claims 1 to 3.

5. A method for suppressing vortex inhalation in the RHR inlet pipeline of a nuclear power plant, characterized in that: The following steps are involved: At the interface between RHR and the heat pipe section, the edge of the inlet heat pipe section is rounded and polished to improve the flow field stability at the interface and reduce the probability of fluid vortex generation.

6. A method for suppressing vortex inhalation in the RHR inlet pipeline of a nuclear power plant, characterized in that: The following steps are involved: The interface pipe between RHR and the hot pipe section adopts a larger pipe diameter, and the hot pipe section interface pipe and the RHR pump inlet pipeline are connected by a reducer.

7. A method for suppressing vortex inhalation in the RHR inlet pipeline of a nuclear power plant, characterized in that: The following steps are involved: The interface pipe between the RHR and the heat pipe section adopts an inclined design with a certain angle, and the inclination direction is consistent with the mainstream direction of the fluid in the main pipe.

8. A method for suppressing vortex inhalation in the RHR inlet pipeline of a nuclear power plant, characterized in that: The following steps are involved: A detachable reducer is added between the hot pipe section interface pipeline and the RHR pump inlet pipeline, and an eddy current suppressor is installed in the connector.

9. A method for suppressing vortex inhalation in a RHR inlet pipeline of a nuclear power plant according to claim 8, characterized in that: The eddy current suppression member adopts a "cross blade" or other structural form.

10. A method for suppressing vortex inhalation in the RHR inlet pipeline of a nuclear power plant, characterized in that: The following steps are involved: Adopt any one method or a combination of multiple methods as described in claims 5-8.

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