A method for analyzing complex two-phase discharge load under water-tight condition

Abstract

The present application belongs to the technical field of pressurized water reactor nuclear power plant accident analysis, and particularly relates to a complex two-phase discharge load analysis method under water tight condition. The present application comprises the following steps: step 1, carrying out accident analysis under the condition of water tight system to obtain the flow curve of the pressurizer safety valve, and determining the relatively severe primary cause event; step 2, carrying out thermal hydraulic analysis of the discharge process under the water tight condition through the flow curve of the pressurizer safety valve to obtain the parameters in the discharge pipeline downstream of the pressurizer safety valve; and step 3, obtaining the load time history curve of all the pipelines on the discharge pipeline according to the parameters in the discharge pipeline. The present application can evaluate the safety and the rationality of the design of the reactor system when the system appears the water tight condition caused by the misoperation of the injection pump, the misoperation of the residual heat removal pump and the like, provide the load input condition for stress analysis, and provide technical support for the optimization design of the pipeline, support, valve arrangement and the like.

Description

Technical Field

[0001] This invention belongs to the field of pressurized water reactor nuclear power plant accident analysis technology, specifically relating to a method for analyzing complex two-phase emission loads under watertight conditions. Background Technology

[0002] In the design process of pressurized water reactor nuclear power plants, calculating the impact load on downstream pipelines caused by upstream fluid in the pressurizer discharge pipeline under conditions of valve malfunction or overpressure is a crucial task. This is because it forms the basis for stress analysis and is a key aspect of ensuring the integrity of the primary circuit pressure boundary. Discharge load analysis can identify weak points in the pipeline design, thus providing guidance for support design and pipeline optimization.

[0003] Previous studies typically analyzed only the water seal discharge load. In this case, the physical process is as follows: after the valve opens, a small volume of water seal passes through the valve, followed by saturated steam from the pressurizer. The rapidly flowing steam-water mixture downstream of the valve exerts a certain impact force on downstream pipes. However, during nuclear power plant operation, if a main pump or safety injection pump malfunctions under cryogenic watertight conditions, intermittent fluid flow through the pressurizer safety valve can cause a certain impact force on the discharge pipe downstream of the valve. This is the discharge load under watertight conditions. Summary of the Invention

[0004] The technical problem solved by this invention is to provide a method for analyzing complex two-phase discharge loads under watertight conditions. This method evaluates the safety and design rationality of a reactor system when watertight conditions occur due to malfunctions of safety injection pumps, residual heat discharge pumps, etc. It provides load input conditions for stress analysis and provides technical support for the optimized design of pipelines, supports, valves, etc.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for analyzing complex two-phase emission loads under watertight conditions includes the following steps:

[0007] Step 1: Conduct an accident analysis under conditions of system watertightness, obtain the flow curve of the pressure regulator safety valve, and determine the relatively severe initial cause event;

[0008] Step 2: Using the flow curve of the pressure regulator safety valve, perform a thermal-hydraulic analysis of the discharge process under watertight conditions to obtain parameters in the downstream discharge pipeline of the pressure regulator safety valve.

[0009] Step 3: Based on the parameters in the discharge pipeline, obtain the load time history curves of all pipes in the discharge pipeline.

[0010] The aforementioned accident analysis under watertight conditions includes: conducting accident process analysis under watertight conditions using instruments such as CATHARE, ARSAC, and RELAP5, focusing on changes in pressure and water level of the pressure regulator during the accident, recording the opening and closing times of the pressure regulator's safety valve, and the flow data through the valve.

[0011] The thermal-hydraulic analysis of the discharge process under watertight conditions, based on the flow curve of the pressure regulator safety valve, specifically includes:

[0012] Define the assumptions: Assume that an infinitely large water tank is connected upstream of the pressure regulator's safety valve, the tank is filled with water at a certain temperature, and the pressure remains constant throughout the analysis.

[0013] The discharge pipeline downstream of the pressure regulator safety valve is modeled sequentially according to the flow direction, and then reasonably divided into sections to form multiple computational control volumes;

[0014] A sensitivity analysis of the water temperature in the tank was conducted to select the temperature that causes the maximum load peak.

[0015] Simulate the flow rate through the safety valve of the pressure regulator;

[0016] By combining flow pattern transformation to simulate the two-phase heat and mass transfer process, a thermal-hydraulic simulation of the discharge process under watertight conditions is initiated; the changes in parameters in the discharge pipeline downstream of the valve are obtained.

[0017] The length of the computational control body along the flow direction is controlled between 15cm and 25cm.

[0018] The specified temperature range is 20℃ to 180℃.

[0019] The simulation of the flow rate through the regulator's safety valve is set with a conservative margin of 1.15.

[0020] The parameters include pressure, vapor-liquid phase flow rate, cavitation fraction, and vapor-liquid phase density.

[0021] The acquisition of load time history curves for all pipes in the discharge pipeline specifically includes:

[0022] Based on the pressure, vapor-liquid phase velocity, cavitation fraction, and vapor-liquid phase density in the discharge pipeline, the pipeline load calculation process in formula (1) is realized through numerical methods to obtain the load time history curves of all pipelines on the discharge pipeline.

[0023] The formula (1) is

[0024]

[0025] In formula (1) The forces acting on the pipeline are S1 and S2, which represent the inlet and outlet sections of the pipeline, respectively. These represent the normal directions of the inlet and outlet sections, respectively. Represents the direction of gravity; These represent the liquid phase fluid velocities at the inlet and outlet cross sections, respectively. ρ represents the vapor phase fluid velocity at the inlet and outlet cross sections, respectively; l1 ρ l2 ρ represents the liquid phase fluid density at the inlet and outlet, respectively; g1 ρ g2 dV represents the vapor phase fluid density at the inlet and outlet, respectively. i Let α be the volume of the i-th control volume within the pipeline; i This represents the cavitation fraction within the i-th computed control unit in the pipeline; ρ li These represent the liquid flow velocity and liquid density within the i-th computed control volume in the pipeline, respectively. ρ gi denoted as vapor velocity and liquid density respectively within the i-th calculated control volume in the pipeline; g represents gravitational acceleration.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The present invention provides a method for analyzing complex two-phase emission loads under watertight conditions, which can be applied to the emission load analysis and design rationality evaluation of nuclear power projects. It breaks the international blockade on valve two-phase load analysis technology and fills the gap in related domestic research.

[0028] (2) The complex two-phase emission load analysis method under watertight conditions provided by this invention is an important link in the design and safety analysis of valves and emission pipelines for independent third-generation nuclear power plants.

[0029] (3) The present invention provides a method for analyzing complex two-phase discharge loads under watertight conditions. The method obtains the discharge load analysis results under watertight conditions from the selection of the initial cause event, the thermal-hydraulic analysis of the discharge process, and the load calculation, providing technical support for power plant design optimization and safety evaluation. Attached Figure Description

[0030] Figure 1 A flowchart of a method for analyzing complex two-phase emission loads under watertight conditions provided by the present invention;

[0031] Figure 2 The discharge flow rate of the pressurizer safety valve under the condition of accidental start-up of the medium-pressure safety injection pump in a domestically developed third-generation nuclear power plant under cryogenic watertight conditions;

[0032] Figure 3 The discharge flow rate of the pressurizer safety valve under the condition of accidental start-up of the main pump in a domestically developed third-generation nuclear power plant under cryogenic water tightness. Detailed Implementation

[0033] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] In the description of this invention, 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 a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] like Figure 1 As shown, the present invention provides a method for analyzing complex two-phase emission loads under watertight conditions, comprising the following steps:

[0037] Step 1: Conduct accident analysis under conditions that cause watertightness in the system.

[0038] For pressurized water reactor systems (including large pressurized water reactor nuclear power plants, modular small reactors, etc.), when the pressurizer safety valve is performing overpressure protection, if a malfunction occurs under cryogenic water tightness conditions, intermittent fluid will continuously flow through the pressurizer safety valve. The malfunctions include malfunctions of the residual heat removal system, malfunctions of the intermediate pressure safety injection system, malfunctions of the CMT (Continuous Material Handling) system, malfunctions of the chemical and volumetric system, accidental activation of the safety injection tank, and malfunctions of the main pump. The initial cause event leading to the worst emission load is determined based on the flow curve of the pressurizer safety valve under the accident conditions.

[0039] Specifically, accident process analysis under watertight conditions was conducted using instruments such as CATHARE, ARSAC, and RELAP5. The analysis focused on changes in the pressure regulator's water level and pressure during the accident, recording the opening and closing times of the pressure regulator's safety valves, as well as the flow data through the valves. Figure 2 and Figure 3 As shown, Figure 2 The valves in the medium pressure system have a larger peak flow rate and a higher frequency of opening and closing, so it can be preliminarily determined that the malfunction of the medium pressure safety injection system is a relatively serious initial cause event.

[0040] Step 2: Thermal-hydraulic analysis of the discharge process under watertight conditions

[0041] Using the pressure regulator safety valve flow curve obtained in step 1 as input, an analysis program capable of simulating complex two-phase discharge processes is selected to perform a thermal-hydraulic analysis of the discharge process under watertight conditions. The specific steps include the following:

[0042] Step 2.1: Select either ARSAC or RELAP5 to simulate the emission process;

[0043] Step 2.2: Assume that an infinitely large water tank is connected upstream of the pressure regulator safety valve. The water tank is filled with water at a certain temperature, generally within the range of 20℃ to 180℃, and the pressure remains constant throughout the analysis. Model the downstream discharge pipeline of the pressure regulator safety valve sequentially according to the flow direction, and reasonably divide it into segments to form multiple computational control volumes. Each pipeline consists of multiple computational control volumes, and the length of each computational control volume along the flow direction is controlled between 15cm and 25cm.

[0044] Step 2.3: Perform a sensitivity analysis on the temperature of the water in the tank and select the temperature that causes the maximum load peak.

[0045] Step 2.4: Simulate the flow rate through the safety valve while considering a certain conservative margin. For example, for the autonomous third-generation nuclear power plant we are studying, the flow rate should be selected as follows: Figure 2 The flow rate curve in the figure is used as the input value to input intermittent flow rate to the valve, and a conservative margin of 1.15 times is considered on this basis;

[0046] Step 2.5: Since the pressure in the downstream discharge pipeline of the pressure regulator safety valve is generally low, the liquid upstream of the valve will vaporize during the flow process, forming various flow patterns downstream of the valve, including: bubbly flow, slug flow, annular flow, and diffuse flow. The two-phase heat and mass transfer process should be simulated in conjunction with the flow pattern transformation during the simulation process.

[0047] Step 2.6: Set the calculation time step to 1.0 × 10⁻⁶. -4The process begins with a thermal-hydraulic simulation of the discharge process under watertight conditions, and changes in parameters such as pressure, vapor-liquid phase velocity, cavitation fraction, and vapor-liquid phase density are obtained in the downstream discharge pipeline of the valve.

[0048] Step 3: Calculation of discharge load under watertight conditions

[0049] Based on the parameters such as pressure, vapor-liquid phase velocity, cavitation fraction, and vapor-liquid phase density obtained in step 2, a reasonable numerical method is selected to realize the pipeline load calculation process in formula (1), thereby obtaining the load time history curves of all pipelines on the discharge pipeline.

[0050]

[0051] In formula (1) The forces acting on the pipeline are S1 and S2, which represent the inlet and outlet sections of the pipeline, respectively. These represent the normal directions of the inlet and outlet sections, respectively. Represents the direction of gravity; These represent the liquid phase fluid velocities at the inlet and outlet cross sections, respectively. ρ represents the vapor phase fluid velocity at the inlet and outlet cross sections, respectively; l1 ρ l2 ρ represents the liquid phase fluid density at the inlet and outlet, respectively; g1 ρ g2 dV represents the vapor phase fluid density at the inlet and outlet, respectively. i Let α be the volume of the i-th control volume within the pipeline; i This represents the cavitation fraction within the i-th computed control unit in the pipeline; ρ li These represent the liquid flow velocity and liquid density within the i-th computed control volume in the pipeline, respectively. ρ gi denoted as vapor velocity and liquid density respectively within the i-th calculated control volume in the pipeline; g represents gravitational acceleration.

[0052] Since the above physical quantities change in real time during the transient process, the emission load time history curve can be obtained through formula (1).

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0054] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for analyzing complex two-phase emission loads under watertight conditions, characterized in that, Includes the following steps: Step (1): Conduct accident analysis under the condition of system water tightness, obtain the flow curve of the pressure regulator safety valve, and determine the relatively serious initial cause event; Step (2): Using the flow curve of the pressure regulator safety valve, perform a thermal-hydraulic analysis of the discharge process under watertight conditions to obtain parameters in the downstream discharge pipeline of the pressure regulator safety valve. Step (3): Based on the parameters in the discharge pipeline, obtain the load time history curves of all pipelines on the discharge pipeline; The aforementioned accident analysis under watertight conditions includes: conducting accident process analysis under watertight conditions using CATHARE, ARSAC, and RELAP5, focusing on changes in pressure and water level of the pressure regulator during the accident, recording the opening and closing times of the pressure regulator safety valve, and the flow data through the valve. The thermal-hydraulic analysis of the discharge process under watertight conditions, based on the flow curve of the pressure regulator safety valve, specifically includes: Define the assumptions: Assume that an infinitely large water tank is connected upstream of the pressure regulator's safety valve, the tank is filled with water at a certain temperature, and the pressure remains constant throughout the analysis. The discharge pipeline downstream of the pressure regulator safety valve is modeled sequentially according to the flow direction, and then reasonably divided into sections to form multiple computational control volumes; A sensitivity analysis of the water temperature in the tank was conducted to select the temperature that causes the maximum load peak. Simulate the flow rate through the regulator's safety valve; By combining flow pattern conversion to simulate the two-phase heat and mass transfer process, a thermal-hydraulic simulation of the discharge process under watertight conditions is initiated; the changes in parameters in the discharge pipeline downstream of the valve are obtained. The parameters include pressure, vapor-liquid phase flow rate, cavitation fraction, and vapor-liquid phase density.

2. The method for analyzing complex two-phase emission loads under watertight conditions according to claim 1, characterized in that, The length of the computational control body along the flow direction is controlled between 15cm and 25cm.

3. The method for analyzing complex two-phase emission loads under watertight conditions according to claim 1, characterized in that, The specified temperature is within the range of 20℃ to 180℃.

4. The method for analyzing complex two-phase emission loads under watertight conditions according to claim 1, characterized in that, The simulation of the flow rate through the regulator's safety valve is set with a conservative margin of 1.

15.

5. The method for analyzing complex two-phase emission loads under watertight conditions according to claim 1, characterized in that, The acquisition of load time history curves for all pipes in the discharge pipeline specifically includes: Based on the pressure, vapor-liquid phase velocity, cavitation fraction, and vapor-liquid phase density within the discharge pipeline, the pipeline load calculation process is implemented using numerical methods to obtain the load time history curves for all pipelines on the discharge pipeline.

6. The method for analyzing complex two-phase emission loads under watertight conditions according to claim 5, characterized in that, The calculation formula is （1） In formula (1) The force exerted on the pipe, , These represent the inlet and outlet sections of the pipeline, respectively. , These represent the normal directions of the inlet and outlet sections, respectively. Represents the direction of gravity; , These represent the liquid phase fluid velocities at the inlet and outlet cross sections, respectively. , These represent the vapor phase fluid velocities at the inlet and outlet sections, respectively. , These represent the liquid phase fluid densities at the inlet and outlet, respectively. , These represent the vapor phase fluid densities at the inlet and outlet, respectively. Let be the volume of the i-th control volume within the pipeline; This represents the cavitation fraction within the i-th computed control unit in the pipeline; , These represent the liquid flow velocity and liquid density within the i-th computed control volume in the pipeline, respectively. , denoted as vapor velocity and liquid density respectively within the i-th calculated control volume in the pipeline; g represents gravitational acceleration.

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