Method and system for analyzing thermal-hydraulic characteristics of nuclear reactor by real sea state simulation

Abstract

The application discloses a method and system for simulating and analyzing nuclear reactor thermal hydraulic characteristics of real sea conditions, and relates to the technical field of nuclear reactor thermal hydraulic characteristic analysis, and comprises the following steps: obtaining swing data for simulation calculation by processing the obtained real sea condition data; preparing real sea condition additional force programs of three coordinate directions by using the swing data, and loading the programs to a calculation model in the form of momentum sources; adding centripetal force, tangential force and Coriolis force as additional forces to each calculation node of the reactor simulation model to perform transient thermal hydraulic calculation, so as to obtain mass flow and test section pressure drop data; performing Fourier transform on the swing angle, mass flow and test section pressure drop data of the real sea condition respectively, obtaining the frequency spectrum of the three groups of data and performing normalization processing, and analyzing the reactor safety design margin according to the frequency spectrum. The method for simulating and analyzing nuclear reactor thermal hydraulic characteristics of real sea conditions can simulate the transient characteristics of the nuclear power device when sailing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear reactor thermal-hydraulic characteristic analysis, and particularly relates to a method and system for simulating and analyzing thermal-hydraulic characteristics of a nuclear reactor under real sea conditions. BACKGROUND

[0002] Under the action of marine conditions, the thermal-hydraulic characteristics of a nuclear power ship will change significantly, which poses a potential threat to the safe operation of the reactor. Simulation research is an important way to analyze the thermal-hydraulic characteristics of the reactor under marine conditions. For example, the lead-bismuth reactor is an important candidate reactor type of the fourth generation nuclear power system, which has a wide application prospect in marine nuclear power due to its inherent safety, stable operation performance, small and compact design, and long-period refueling design. However, due to its high density, high melting point and strong corrosiveness, experimental research is difficult. Therefore, it is necessary to simulate and analyze the operating characteristics of the reactor under marine conditions.

[0003] Traditional research usually sets the roll of the ship as a left-right simple harmonic oscillation, and the angular displacement, angular velocity and angular acceleration of the ship body change in a sinusoidal or cosine law, which cannot reflect the nonlinear characteristics of real sea conditions. Traditional thermal-hydraulic analysis software such as RELAP5 and CFD software usually presets a fixed acceleration, and the structure and marine model are coupled in a static way, ignoring the dynamic correlation between different frequency waves and the response of the ship reactor device, and cannot well reflect the real characteristics of the structure under the influence of sea conditions. SUMMARY

[0004] Based on the technical problems existing in the background technology, the present application provides a method and system for simulating and analyzing thermal-hydraulic characteristics of a nuclear reactor under real sea conditions, which simulates the transient characteristics of the nuclear power device during navigation.

[0005] The method for simulating and analyzing thermal-hydraulic characteristics of a nuclear reactor under real sea conditions provided by the present application comprises:

[0006] Obtaining real sea condition data and sampling the swing angle of the real sea condition, and obtaining swing data for simulation calculation after preprocessing the swing angle;

[0007] Using the program interface provided by the simulation software, using the swing data to write real sea condition additional force programs in three coordinate directions, and loading them into the calculation model of the reactor simulation model through the momentum source to simulate real sea conditions;

[0008] Adding centripetal force, tangential force and Coriolis force as additional forces to each calculation node of the reactor simulation model, and performing transient thermal-hydraulic calculation, the real sea condition additional force program will calculate the additional force at each time step and add it to the computational fluid dynamics solver for solving, and the mass flow and test section pressure drop data are obtained.

[0009] The Fourier transform is performed on the swing angle, mass flow rate and test section pressure drop data of the real sea state respectively, the frequency spectrum of the three groups of data is obtained and normalized, the loop response characteristics are analyzed, and finally the reactor safety design margin is analyzed according to the results.

[0010] Further, the centripetal force, tangential force and Coriolis force are added to each calculation node of the reactor simulation model as additional forces for transient thermal hydraulic calculation, the real sea state additional force program will calculate the additional force of each time step and add it to the computational fluid dynamics solver for solving, so as to obtain the mass flow rate and test section pressure drop data, specifically:

[0011] The fluid dynamics solver reads the reactor simulation model, and the solver starts to advance in time steps;

[0012] In each time step, the boundary conditions are updated, the additional force of the current time step is calculated based on the called real sea state additional force program, and the additional force is fed back to the fluid dynamics solver to solve the momentum conservation equation, while the mass conservation and energy equations are solved in parallel; the fluid dynamics solver obtains the velocity field, pressure field and temperature field of the current time step, and updates the physical quantities of all elements;

[0013] The velocity field, pressure field and temperature field of all time steps are post-processed to obtain the mass flow rate and test section pressure drop data.

[0014] Further, the swing data is used to write three coordinate direction real sea state additional force programs, wherein each real sea state additional force program is responsible for calculating the component of the total inertia force on one of the coordinate axes, and the total inertia force is the force obtained by adding the centripetal force, tangential force and Coriolis force. Further, the real sea state data is obtained and sampled to obtain the swing angle of the real sea state, and the swing data for simulation calculation is obtained after preprocessing the swing angle, specifically:

[0015] The real sea state data continuously measured and collected by the buoy is sampled, the discrete data of the swing angle is twice differentiated to obtain the discrete data of the angular velocity and angular acceleration;

[0016] The discrete data of the swing angle, angular velocity and angular acceleration are respectively interpolated to obtain the swing data for simulation calculation.

[0017] Further, the interpolation processing is specifically a third-order polynomial interpolation method.

[0018] A system for simulating and analyzing the thermal hydraulic characteristics of a nuclear reactor, comprising a data acquisition module, a program writing module, a program execution module and an analysis module;

[0019] The data acquisition module is configured to acquire real sea state data and sample swing angles of the real sea state, and to obtain swing data for simulation calculation after preprocessing the swing angles.

[0020] The program writing module is configured to use a program interface of the simulation software to write real sea state additional force programs in three coordinate directions respectively using the swing data, and to load the real sea state additional force programs into a calculation model of a reactor simulation model in a momentum source mode to simulate real sea conditions.

[0021] The program execution module is configured to add centripetal force, tangential force and Coriolis force as additional forces to each calculation node of the reactor simulation model, to perform transient thermal hydraulic calculation, and to calculate the additional forces at each time step by the real sea state additional force programs and add the additional forces to a computational fluid dynamics solver to solve the additional forces, so as to obtain mass flow rate and test section pressure drop data.

[0022] The analysis module is configured to perform Fourier transform on the swing angles of the real sea state, the mass flow rate and the test section pressure drop data respectively, to obtain frequency spectrums of the three groups of data and perform normalization processing, to analyze loop response characteristics, and to finally analyze reactor safety design margin according to the results.

[0023] Further, in the swing data for simulation calculation obtained after preprocessing the swing angles by the data acquisition module, the swing data are obtained by:

[0024] sampling real sea state data continuously measured and collected by a buoy, taking discrete data of the swing angles, and calculating two derivatives of the discrete data to obtain discrete data of angular velocity and angular acceleration respectively;

[0025] interpolating the discrete data of the swing angles, the angular velocity and the angular acceleration respectively to obtain the swing data for simulation calculation.

[0026] Further, the interpolation processing is a third-order polynomial interpolation method.

[0027] Further, the program execution module is specifically configured to:

[0028] The computational fluid dynamics solver reads the reactor simulation model, and the solver starts to advance in time steps;

[0029] In each time step, boundary conditions are updated, additional forces at the current time step are calculated based on the called real sea state additional force programs, and the additional forces are fed back to the computational fluid dynamics solver to solve the momentum conservation equation, while mass conservation and energy equations are solved in parallel; the computational fluid dynamics solver obtains velocity field, pressure field and temperature field at the current time step, and updates physical quantities of all elements;

[0030] The velocity field, pressure field and temperature field of all time steps are post-processed to obtain mass flow and test section pressure drop data.

[0031] Further, in the program writing module, each real sea state additional force program is responsible for calculating the component of the total inertial force on one of the coordinate axes, the total inertial force being the force obtained by adding the centripetal force, the tangential force and the Coriolis force.

[0032] The method and system for simulating and analyzing the thermal-hydraulic characteristics of a nuclear reactor under real sea conditions have the advantages that: according to real measured sea wave data, a certain sampling method and interpolation method are used to write an additional force program of real sea conditions. The program is used to analyze the instantaneous thermal-hydraulic characteristics of a reactor under real sea conditions by using simulation software. The method fills the research gap in the field of nuclear reactor thermal-hydraulic analysis, and the research results can provide more accurate reference values for the safety design margin of a nuclear reactor under sea conditions. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The figure is a structural flowchart of the present application;

[0034] Figure 2 The figure is an interpolation processing diagram of real sea state swing angle data;

[0035] Figure 3 The figure is a schematic diagram of the transient operation results of a reactor under real sea state excitation;

[0036] Figure 4 The figure is a schematic diagram of frequency spectrum results analysis. DETAILED DESCRIPTION

[0037] In the following, the technical solutions of the present application are described in detail through specific embodiments. In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be implemented in many different ways from those described herein, and those skilled in the art can make similar improvements without departing from the scope of the present application. Therefore, the present application is not limited to the specific implementations disclosed below.

[0038] As shown in the figure, the method for simulating and analyzing the thermal-hydraulic characteristics of a nuclear reactor under real sea conditions comprises: Figures 1 to 4

[0039] Step one, obtaining real sea state data and sampling real sea state swing angles, and obtaining swing data for simulation calculation after pre-processing the swing angles;

[0040] Step two, using the program interface provided by the simulation software, using the swing data to write three real sea state additional force programs in the coordinate directions, and loading the programs into the calculation model carrying the reactor simulation model in the form of momentum sources to simulate real sea conditions;​

[0041] Step three, add the centripetal force, tangential force and Coriolis force as additional force to each calculation node of the reactor simulation model, and perform transient thermal hydraulic calculation, the real sea state additional force program will calculate the additional force of each time step and add it to the computational fluid dynamics solver for solving, on the basis of which the mass flow and test section pressure drop data are obtained;

[0042] Step four, Fourier transform the real sea state swing angle, mass flow and test section pressure drop data respectively, obtain the frequency spectrum of the three groups of data and perform normalization processing, analyze the loop response characteristics, and finally analyze the reactor safety design margin according to the result.

[0043] The embodiment provides a method for simulating and studying the thermal hydraulic characteristics of a nuclear reactor under marine conditions using real sea state data, which analyzes the changes in the thermal hydraulic characteristics of the nuclear reactor by using real measured marine wave data, and truly simulates the transient characteristics of the nuclear power plant when sailing, thereby supplementing the research on the transient characteristics of the reactor based on real sea state in the field of marine nuclear power research.

[0044] It should be noted that the embodiment relates to a calculation model and a reactor simulation model;

[0045] (a1) the calculation model;

[0046] The calculation model refers to a numerical solution framework for simulating fluid dynamics and heat transfer, and generally refers to a computational fluid dynamics (CFD, Computational Fluid Dynamics) model.

[0047] The core components include a geometric model, a calculation network and control equations, specifically:

[0048] Geometric model: three-dimensional digital geometric shape of components such as reactor core, pressure vessel, piping system, etc.

[0049] Calculation network: discretize the continuous geometric space into countless small units (such as hexahedron, tetrahedron), which is the basis of all numerical calculations. Each unit is a "calculation node";

[0050] Control equation: solve the control equation in each grid unit, mainly including: mass conservation equation, momentum conservation equation and energy conservation equation.

[0051] The calculation model mainly provides a physical platform, and the real sea state additional force program (step two) will be added to the momentum conservation equation of each grid unit in the form of a momentum source, and is also the engine for transient thermal hydraulic calculation (step three).

[0052] (a2) the reactor simulation model;

[0053] The reactor simulation model refers to a model simulating the entire nuclear reactor system or key components thereof. In the present embodiment, a specific model representing the thermal hydraulic characteristics of the reactor is integrated into the computational model.

[0054] The present embodiment couples the time-varying data of the external real sea state (step one) to the reactor simulation model (step three) through a self-defined real sea state additional force program (step two) in both directions, thereby enabling high-precision simulation and analysis of the influence of real sea conditions on parameters critical to reactor safety (such as flow rate, pressure drop, and critical heat flux CHF). Finally, the main frequency of the flow fluctuation is identified through spectral analysis (step four) and compared with the frequency of ocean movement to assess the potential risks.

[0055] In one embodiment, step one involves obtaining real sea state data and sampling the roll angle of the real sea state. After preprocessing the roll angle, the roll data for simulation calculation is obtained, specifically as follows:

[0056] (b1) Obtain real sea state data and sample the roll angle of the real sea state;

[0057] Since the real sea state data continuously measured and collected by the buoy can be very high (e.g., 10 times per second), long-term recording will generate a large number of data points (several million or even hundreds of millions). Directly using such a large data set will bring a huge storage and computing burden, and even make the calculation impossible. Therefore, by sampling (e.g., from 10 Hz to 1 Hz), the present embodiment can greatly reduce the data volume while retaining the main features of the original signal. This makes subsequent data processing and simulation calculation feasible and efficient.

[0058] (b2) Take the second derivative of the discrete data of the roll angle to obtain the discrete data of the angular velocity and angular acceleration;

[0059] The buoy usually directly measures the roll angle. However, according to Newton's second law, the size of the inertial force depends not only on the position (angle), but also on the acceleration. Therefore, the present embodiment takes the derivative of the roll angle to numerically derive the discrete sequences of the angular velocity and angular acceleration. In this way, all three dynamic parameters (roll angle, angular velocity, and angular acceleration) required to describe the roll motion are completely reconstructed from a single angle information, providing indispensable input for the subsequent accurate calculation of the three inertial forces and ensuring the integrity of the physical model.

[0060] (b3) Perform third-order polynomial interpolation on the discrete data of the roll angle, angular velocity, and angular acceleration to obtain the roll data for simulation calculation.

[0061] The fluid dynamics solver is advanced step by step with tiny time steps. It needs to acquire the current sea state parameters (roll angle, angular velocity, and angular acceleration) at any time point. However, the original data is still discrete time point data. Thus, this embodiment uses a third-order polynomial interpolation to construct smooth and continuous functions for the discrete roll angle, angular velocity, and angular acceleration data, respectively.

[0062] The above processing method has the advantages of arbitrary time point value and smoothness, namely:

[0063] Arbitrary time point value: the fluid dynamics solver can instantly calculate the required sea state parameter value at the exact time of each time step through the interpolation function, realizing the conversion from discrete data to continuous input;

[0064] Smoothness: the third-order polynomial has continuous first-order derivatives, which means that the curve constructed by it is smooth and has no sharp corners or abrupt changes. This is very important because the motion of the physical world (such as ship rolling) is continuous, and acceleration will not change abruptly. Smooth input can avoid introducing non-physical high-frequency oscillations in subsequent calculations, ensuring the stability of numerical calculations.

[0065] It should be noted that this embodiment considers the balance between accuracy, smoothness, and computational efficiency in selecting the interpolation method. (1) Low-order interpolation (such as linear interpolation) has poor accuracy, and the constructed curve is composed of broken line segments, which is not smooth. At the break point, the first-order derivative (angular velocity) is discontinuous, and the second-order derivative (angular acceleration) is infinite, which will introduce non-physical impact loads and cause calculation instability. (2) High-order interpolation (such as five or more) is smoother, but the computational load is larger, and it may have overfitting phenomenon (Runge's phenomenon), producing unnecessary oscillations between data points, which deviates from the true physical process.

[0066] Finally, this embodiment selects the third-order polynomial interpolation method, which can balance accuracy, smoothness, and computational efficiency. It can ensure that the first and second derivatives of the curve are continuous, thus accurately restoring the continuous change process of the angle, angular velocity, and angular acceleration, while not bringing excessive computational burden and overfitting risk.

[0067] Thus, the data processing process of (b1) to (b3) in this embodiment is a crucial bridge connecting "real sea measurement" and "high-fidelity numerical simulation", with the following advantages:

[0068] 1. Cost reduction and efficiency improvement: by sampling to reduce data volume, large-scale simulation becomes possible.

[0069] 2. Physical completeness: By derivation, the angular velocity and angular acceleration required for calculating the added mass force are completely extracted from the roll angle, ensuring the correctness of the physical model.

[0070] 3. Continuity and stability: By using a third-order polynomial interpolation, smooth and continuous sea state input at any time is provided for the fluid dynamics solver, ensuring the accuracy and numerical stability of the calculation.

[0071] In one embodiment, step two uses the program interface provided by the simulation software to write three coordinate direction real sea state added mass force programs using the roll data, which are loaded into the calculation model of the reactor simulation model through momentum source to simulate real sea conditions, specifically:

[0072] (c1) Real sea state added mass force programs for three coordinate directions;

[0073] Firstly, it is necessary to understand the setting of the coordinate system, which is usually considered as a non-inertial system (i.e. a reference system that is rotating and translating itself). In order to use Newton's second law directly in this moving reference frame, a series of inertial forces must be introduced, which are due to the acceleration of the reference frame itself.

[0074] It should be noted that the three coordinate direction roll added mass force programs are independent, and each coordinate direction roll added mass force program calculates the component of the momentum source in its coordinate direction. The core physical formula of the three coordinate direction roll added mass force programs is the same, which is the total inertial force .

[0075] The total inertial force received by any calculation node in the reactor simulation model in the non-inertial system is:

[0076] ;

[0077] where, is the density of the fluid at the calculation node, is the total acceleration, is the roll angular velocity, is the roll angular acceleration, is the roll radius, is the tangential acceleration; is the centripetal acceleration; is the Coriolis acceleration.

[0078] That is, represents the tangential force, represents the centrifugal force, which is the reaction force of the centripetal force, represents the Coriolis force.

[0079] ​That is, the sway additional force program of three coordinate directions is to calculate the components of inertial forces (centripetal force, tangential force and Coriolis force) in the non-inertial system in three directions.

[0080] (c2) Writing of the real sea state additional force program;

[0081] Using the program interface of the simulation software, the embodiment usually uses the user-defined function (UDF) interface or field function interface of the computational fluid dynamics software to realize.

[0082] After the real sea state additional force programs of three coordinate directions are written by using the sway data, they are assigned to the current calculation node as momentum sources, and the subsequent fluid dynamics solver considers this additional force into the solution of the momentum conservation equation.

[0083] The writing process of the real sea state additional force program is transient and carried out at each time step and each calculation node, ensuring the authenticity and accuracy of the simulation. At the same time, combined with the transient thermal hydraulic calculation of step three, the velocity field, pressure field and temperature field at each time step are obtained, and the mass flow and test section pressure drop data are obtained after post-processing.

[0084] In one embodiment, the centripetal force, tangential force and Coriolis force are added as additional forces to each calculation node of the reactor simulation model, and the transient thermal hydraulic calculation is carried out. The real sea state additional force program will calculate the additional force at each time step and add it to the computational fluid dynamics solver for solving, and the mass flow and test section pressure drop data are obtained; specifically:

[0085] (d1) The fluid dynamics solver reads the reactor simulation model (including grid, material, boundary condition, initial flow field, etc.), and the solver starts to advance by time step (i.e. loop by time step);

[0086] (d2) In each time step, update the boundary condition, calculate the additional force of the current time step based on the called real sea state additional force program, and feed the additional force back to the fluid dynamics solver to solve the momentum conservation equation, while solving the mass conservation equation and energy conservation equation in parallel; The fluid dynamics solver obtains the velocity field, pressure field and temperature field at the current time step, and updates the physical quantities of all elements;

[0087] Among them, the updated boundary conditions are: according to the preset, update the inlet flow, temperature, wall heat power, etc. (which are the inputs of the reactor simulation model).

[0088] That is, in each time step, after updating the boundary conditions, the fluid dynamics solver automatically calls the real sea state added force program through the UDF interface, the real sea state added force program adds the calculated momentum source of the current time step to the fluid dynamics solver, the fluid dynamics solver integrates the momentum source with other terms such as pressure gradient, viscous force, etc. to the momentum conservation equation for solving, while solving the mass conservation equation and the energy conservation equation in parallel. The fluid dynamics solver obtains the new velocity field, pressure field and temperature field corresponding to the current time step, and updates the physical quantities of all calculation nodes. Then, repeat all time steps to obtain the velocity field, pressure field and temperature field of each time step.

[0089] (d3) Post-processing the velocity field, pressure field and temperature field of all time steps to obtain mass flow rate and test section pressure drop data.

[0090] The mass flow rate and test section pressure drop data are extracted from the post-processing of the velocity field, pressure field and temperature field, for example, the test section pressure drop data is the difference between the average pressures of the inlet and outlet cross sections; the mass flow rate is obtained by integrating the velocity of the inlet cross section.

[0091] For example, a strong centrifugal force (generated by rotation around the X axis) will significantly change the transverse (Y and Z direction) velocity distribution and pressure distribution of the coolant in the core. The fluid dynamics solver naturally obtains the flow rate and pressure drop results under this new force state by solving the momentum conservation equation containing the added centripetal force.

[0092] It can be understood that the fluid dynamics solver is equivalent to a main program, and the real sea state added force program is equivalent to a dynamic link library or a plug-in. The main program calls the plug-in when needed (every time step, every calculation node), the plug-in returns a value (added force), and the main program uses the value in the calculation.

[0093] In one embodiment, step four, Fourier transform the real sea state swing angle, mass flow rate and test section pressure drop data respectively, obtain the frequency spectrum of the three groups of data and normalize the processing, analyze the loop response characteristics, and finally analyze the reactor safety design margin according to the results, specifically:

[0094] The reactor safety design margin refers to the buffer space or safety margin between the key parameters of the reactor under the design condition and the predicted operating event and the limit value that may cause fuel failure or radioactive release.

[0095] The Fourier transform is performed on the real sea state swing angle, mass flow rate and test section pressure drop data, and normalized, to analyze how the safety margin changes and why it changes, and to assess the risk.

[0096] The simulation results of this embodiment are shown in Figure 3 . The mass flow rate has a high similarity with the swing angle of the real sea state, and the change trend at the same time is basically the same. However, the mass flow rate and the pressure drop waveform are out of sync, and the pressure drop appears irregular fluctuations. Fourier transform is performed on the real sea state swing angle, mass flow rate and test section pressure drop data as shown in Figure 4 . It is found that the mass flow rate has a linear response to the real sea state excitation in the medium frequency band. However, the pressure has a stronger high-frequency response to the swing, and the nonlinearity is strong in a larger frequency range. Simple swing research with sinusoidal excitation cannot accurately reflect the pressure fluctuation in the real sea state, and has limitations.

[0097] Specifically, as shown in Figure 4 , the main spectrum peak of the swing angle of this real sea state is located at 0.3 Hz, and there are several small peak values at 0.61 Hz, 0.03 Hz and lower frequencies. By comparing the mass flow rate spectrum with the test section pressure drop data spectrum, it is found that there is a significant resonance phenomenon between the two.

[0098] 0.3 Hz, and there are several secondary peaks at 0.61 Hz, 0.03 Hz and lower frequencies. By comparing the frequency spectrum characteristics of the mass flow rate and the test section pressure drop calculation results, the response characteristics of the swing angle to the wave in the real sea state can be reflected. The response of the mass flow rate to the swing angle is poor in the low frequency range below 0.04 Hz, indicating that very slow swing angle has little effect on the lead bismuth ring. At the main peak value 0.3 Hz and the secondary peak value 0.61 Hz of the swing angle spectrum of the real sea state, the mass flow rate response is relatively linear, and the frequency spectrum trend of the mass flow rate is similar to that of the swing angle. However, the high frequency response deteriorates again. The test section pressure drop response is linear in the low frequency range below 0.1 Hz, but the response ability increases with the increase of frequency. The main peak intensity of 0.3 Hz in the swing angle spectrum of the real sea state is 610% of the secondary peak of 0.61 Hz, while the peak intensity of 0.3 Hz in the test section pressure drop spectrum is 76.7% of the peak of 0.61 Hz. The pressure response has a high frequency characteristic, and its intensity increases with the increase of frequency.

[0099] The 0.3 Hz peak value in the pressure drop spectrum of the test section was only 76.7% of the 0.61 Hz peak value. The high-frequency response of the pressure drop to the rolling angle was stronger, and it showed significant nonlinearity in a wider frequency band, which may be related to pressure chaos. The mass flow rate showed a relatively linear response in the medium frequency band, which included the main frequency spectrum peak value of the real sea condition rolling angle. The real sea condition rolling angle had a certain dominant frequency. Therefore, the sine rolling excitation condition has a certain reliability when simulating the real sea condition, because this method is widely used in many ocean condition studies. On the other hand, however, the real sea condition has a more complex effect on the pressure, and a simple sine excitation may not accurately reflect the pressure fluctuations under real sea conditions, thus having limitations.

[0100] As an embodiment;

[0101] As shown in Figure 2 The real sea condition data obtained by interpolation is taken as an example. The real sea condition additional force program is written using the obtained data and is added to the simulation software for transient calculation, and the specific implementation steps are as follows:

[0102] S1: Obtain rolling data for simulation calculation;

[0103] The data of the buoy continuously measures the ocean wave data, and the angle change data measured by the buoy is used in the embodiment. The sampling rate of the buoy data is 4 Hz, and the discrete data of the angle is twice differentiated to obtain the discrete data of the angular velocity and the angular acceleration. The discrete data of the angle, the angular velocity and the angular acceleration are respectively interpolated by a third-order polynomial to obtain the data for simulation calculation. A 100s angle change data is selected for simulation calculation, Figure 2 The interpolation results of the angle and the second integral value of the interpolation results of the angular acceleration are compared, and the interpolation method has good accuracy.

[0104] S2: Use the program interface provided by the simulation software to write the rolling additional force program in three coordinate directions respectively;

[0105] The additional force formula is as follows:

[0106] ;

[0107] The centripetal force, tangential force and Coriolis force of each time step are loaded into the reactor simulation model as additional forces through the momentum source to simulate the real sea condition.

[0108] S3: The simulation reliability of the reactor loop is verified by comparing the key thermal-hydraulic parameters of the simulation and the experiment to verify the reliability of the calculation model. The real sea condition additional force program written based on the data is imported into the simulation software for transient calculation, and the specific operation process is as shown in Figure 1 .

[0109] S4: Fourier transform the real sea state swing angle, mass flow and test section pressure drop data respectively, get the frequency spectrum of the three groups of data and normalize, as shown in Figure 4 illustrated, to analyze the reactor safety design margin.

[0110] This embodiment uses a certain sampling method and interpolation method to write an additional force program of real sea state according to the real measured ocean wave data. It is used for analyzing the instantaneous thermal hydraulic characteristics of the reactor under real sea state by using simulation software. It fills the research gap of lack of real sea state in the field of nuclear reactor thermal hydraulics analysis. The research results can provide more accurate reference value for the safety design margin of nuclear reactor under sea conditions.

[0111] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art, according to the technical solution and the inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method of simulating the thermal-hydraulic behavior of a nuclear reactor core using realistic sea state conditions, characterized in that, The method comprises the following steps: Real sea state data is acquired and sampled to obtain the rolling angle of the real sea state, and the rolling angle is preprocessed to obtain rolling data for simulation calculation; Using the program interface of the simulation software, real sea state additional force programs in three coordinate directions are written using the rolling data, and the programs are loaded into the calculation model of the reactor simulation model in the form of momentum sources to simulate real sea conditions; Centripetal force, tangential force and Coriolis force are added to each calculation node of the reactor simulation model as additional forces, and transient thermal-hydraulic calculation is performed, the real sea state additional force program calculates the additional force at each time step and adds it to the computational fluid dynamics solver for solving, and mass flow rate and test section pressure drop data are obtained; Fourier transform is performed on the rolling angle, mass flow rate and test section pressure drop data of the real sea state respectively, the frequency spectrum of the three groups of data is obtained and normalized, the loop response characteristics are analyzed, and finally the reactor safety design margin is analyzed according to the results.

2. The method of nuclear reactor thermal-hydraulic characteristics according to claim 1, characterized in that, The centripetal force, tangential force and Coriolis force are added to each calculation node of the reactor simulation model as additional forces, and transient thermal-hydraulic calculation is performed, the real sea state additional force program calculates the additional force at each time step and adds it to the computational fluid dynamics solver for solving, and mass flow rate and test section pressure drop data are obtained, specifically: The fluid dynamics solver reads the reactor simulation model, and the solver starts to advance in time steps; In each time step, the boundary conditions are updated, the additional force at the current time step is calculated based on the called real sea state additional force program, and the additional force is fed back to the fluid dynamics solver to solve the momentum conservation equation, while the mass conservation equation and the energy conservation equation are solved in parallel; The fluid dynamics solver obtains the velocity field, pressure field and temperature field at the current time step, and updates the physical quantities of all calculation nodes; The velocity field, pressure field and temperature field at all time steps are post-processed to obtain mass flow rate and test section pressure drop data.

3. The method of nuclear reactor thermal-hydraulic characteristics according to claim 1, wherein, The rolling data for simulation calculation is obtained by preprocessing the rolling angle of the real sea state, specifically:

4. The method of nuclear reactor thermal-hydraulic characteristics according to claim 1, wherein, The real sea state data continuously measured by the buoy is sampled, and the discrete data of the rolling angle is twice differentiated to obtain the discrete data of the angular velocity and the angular acceleration; The discrete data of the rolling angle, the angular velocity and the angular acceleration are respectively interpolated to obtain the rolling data for simulation calculation. The interpolation processing is a three-order polynomial interpolation method.

5. The method of nuclear reactor thermal-hydraulic characteristics according to claim 4, wherein, The method comprises a data acquisition module, a program writing module, a program execution module and an analysis module; 6. A system for analyzing thermal-hydraulic characteristics of a nuclear reactor core using realistic sea state simulation, characterized by, The data acquisition module is used to acquire real sea state data and sample the rolling angle of the real sea state, and the rolling angle is preprocessed to obtain rolling data for simulation calculation; ​ The program writing module is configured to use a program interface of the simulation software to write three real sea condition additional force programs in three coordinate directions respectively by using the rolling data, and load the programs into a calculation model of a reactor simulation model in a momentum source mode to simulate real sea conditions. The program execution module is configured to add the centripetal force, the tangential force and the Coriolis force as additional forces to each calculation node of the reactor simulation model, and perform transient thermal hydraulic calculation, the real sea condition additional force program calculates the additional force of each time step and adds the additional force to a computational fluid dynamics solver to solve, so as to obtain mass flow rate and test section pressure drop data. The analysis module is configured to perform Fourier transform on the rolling angle, the mass flow rate and the test section pressure drop data of the real sea condition respectively, obtain frequency spectra of the three groups of data and perform normalization processing, analyze loop response characteristics, and finally analyze a reactor safety design margin according to a result.

7. The nuclear reactor thermal-hydraulic characteristics system of claim 6, wherein, The data acquisition module obtains rolling data for simulation calculation after preprocessing of the rolling angle, and specifically includes the following steps. Sampling real sea condition data continuously measured and collected by a buoy, taking discrete data of the rolling angle to obtain two derivatives, and obtaining discrete data of angular velocity and angular acceleration respectively. Performing interpolation processing on the discrete data of the rolling angle, the angular velocity and the angular acceleration to obtain the rolling data for simulation calculation.

8. The nuclear reactor thermal-hydraulic characteristics system of claim 7, wherein, The interpolation processing is a third-order polynomial interpolation method.

9. The nuclear reactor thermal-hydraulic characteristics system of claim 6, wherein, The program execution module is specifically configured to: A fluid dynamics solver reads the reactor simulation model, and the solver starts to advance in time steps. In each time step, a boundary condition is updated, the real sea condition additional force program calculates the additional force of each time step, and the additional force is fed back to the computational fluid dynamics solver to solve a momentum conservation equation, while mass conservation and energy equations are solved in parallel; the fluid dynamics solver obtains a velocity field, a pressure field and a temperature field of the current time step, and updates physical quantities of all elements. The velocity field, the pressure field and the temperature field of all time steps are post-processed to obtain mass flow rate and test section pressure drop data.

10. The nuclear reactor thermal-hydraulic characteristics system of claim 6, wherein, In the program writing module, each real sea condition additional force program is responsible for calculating a component of total inertia force on one of the coordinate axes, the total inertia force being a force obtained by adding the centripetal force, the tangential force and the Coriolis force.

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