A modeling and simulation method for the secondary condensate feed water system of a nuclear power plant

Abstract

The present invention discloses a modeling and simulation method for a secondary condensate feed water system of a nuclear power plant, which divides the secondary condensate feed water system into two systems, namely, a pipe network system and a system composed of main equipment, and models the two systems respectively based on three conservation laws; defines the connection relationship and interaction parameters between the pipe network system model and the system model composed of main equipment; solves the pipe network system model and the system model composed of main equipment respectively based on the input initial parameters; performs data exchange between the two models and updates the respective model parameters until the system is stable. The present invention simplifies the simulation of the complex secondary condensate feed water system of a nuclear power plant into the simulation of the pipe network part of the condensate feed water system and the simulation of the condensate feed water system equipment, and realizes the overall simulation between the pipe network system and the equipment module by establishing the coupling relationship between the pipe network system and the equipment. The simulation model can simulate the working conditions that are difficult or impossible to achieve in reality, thereby improving the economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear reactor systems, and in particular relates to a modeling and simulation method for a secondary loop condensate feed water system of a nuclear power plant. Background Art

[0002] In the process of the development of the secondary circuit of nuclear power plants, the modeling and simulation of the secondary circuit system of nuclear power plants is particularly important. The secondary circuit condensate feed water system of nuclear power plants is one of the most complex systems. It contains not only complex energy conversion devices, but also various complex thermodynamic cycle systems based on the Rankine cycle. In addition, it also includes a wide variety of heat exchange equipment. Therefore, establishing a simulation model for the secondary circuit condensate feed water system of nuclear power plants can achieve high economic benefits. For working conditions that are difficult or impossible to achieve in reality, they can be simulated by establishing a simulation model. From steady-state working conditions to various transient working conditions, from standard working conditions to various accident working conditions, etc., they can also be achieved through simulation.

[0003] The secondary condensate feedwater system of a nuclear power plant is composed of a complex pipe network system connected to the main heat exchange equipment, in which the pipe network system is mainly composed of pipes for transporting water, water vapor, etc. The main equipment of the system includes condensers, deaerators, feedwater heaters and other heat exchange equipment, which involve complex heat exchange and phase change processes during operation. During the operation of the condensate feedwater system, there are complex mass, energy, and momentum exchange processes. To fully describe these physical processes, it is necessary to use a refined modeling method to achieve this. Summary of the invention

[0004] In view of this, the present invention proposes a modeling and simulation method for a secondary condensate feed water system of a nuclear power plant, comprising the following steps:

[0005] S1. Divide the secondary condensate feed water system into two parts: a pipe network system and a system consisting of main equipment. Model the pipe network system based on the laws of conservation of mass, energy and momentum, and model the system consisting of main equipment based on the laws of conservation of mass and energy.

[0006] S2. Define the connection relationship and interaction parameters between the pipe network system model and the system model composed of main equipment, and input initial parameters;

[0007] S3. Based on the initial parameters, respectively solve the condensate water supply system pipe network system model and the system model composed of main equipment;

[0008] S4. Based on the connection relationship and interaction parameters between the pipe network system model and the system model composed of main equipment defined in S2, data exchange is performed between the pipe network system model of the secondary condensation water supply system and the system model composed of main equipment, and an overall model between the pipe network system and the system composed of main equipment is established;

[0009] S5. After data interaction, the pipe network system and the system composed of main equipment update their own model parameters as the initial parameters of the model, and calculate the next time step, repeating steps S3, S4 and S5 until the system is stable.

[0010] Furthermore, step S1 is specifically as follows:

[0011] S11. The pipe network system includes boundaries, nodes, and streamlines. The main equipment of the system includes deaerators, condensers, and feedwater heaters;

[0012] S12. Model the boundaries, nodes, and streamlines of the pipe network system based on the three conservation laws:

[0013] a. Mass conservation equation:

[0014]

[0015] Where V i ——The volume of internal node i, m 3 ;

[0016] ρ i ——average density of internal node i, kg / m 3 ;

[0017] X, Y, Z – the number of internal nodes, pressure boundary nodes, and flow boundary nodes;

[0018] D ij ——The association matrix between internal node i and internal node j;

[0019] DE ik ——the correlation matrix between internal node i and pressure boundary node k;

[0020] DF im ——The association matrix between internal node i and traffic boundary node m;

[0021] G ij ——Flow rate from internal node i to internal node j, kg / s;

[0022] GE ik ——Flow rate from internal node i to pressure boundary node k, kg / s;

[0023] GF im ——Flow value from internal node i to flow boundary node m, kg / s;

[0024] b. Energy conservation equation:

[0025]

[0026] Where M i ——The mass of internal node i, kg;

[0027] h i ——specific enthalpy of internal node i, kJ / kg;

[0028] HkD k ——Specific enthalpy value of pressure boundary node k, kJ / kg;

[0029] HkD m ——Specific enthalpy value of flow boundary node m, kJ / kg;

[0030] S i ——The heat dissipation between internal node i and the environment, kJ / s;

[0031] c. Momentum conservation equation:

[0032] Momentum conservation equation for the internal streamlines:

[0033]

[0034] Momentum conservation equation for streamlines connected to a pressure boundary:

[0035]

[0036] In the formula, I ij ——Structural coefficient of the streamline between internal nodes i and j, MPa·s 2 / kg;

[0037] I ik ——Structural coefficient of the streamline connecting the internal node i and the pressure boundary node k, MPa·s 2 / kg;

[0038] PE k , P i , P j ——Pressure values ​​of pressure boundary node k, internal node i, and internal node j, MPa;

[0039] Hg ij , HEg ik ——Gravity pressure difference on the streamline between internal nodes i and j, and the streamline connecting internal node i to pressure boundary node k, MPa;

[0040] f ij ,fE ij ——Drag pressure drop from internal node i to internal node j, and from internal node i to pressure boundary node j, MPa;

[0041] Among them, fij andfE ij is the resistance of the streamline, which is proportional to the square of the flow rate:

[0042]

[0043]

[0044] In the formula, ——The maximum value of the resistance coefficient from internal node i to internal node j and from internal node i to pressure boundary node j, MPa·s 2 / kg 2 ;

[0045] S13. The modeling of deaerator, condenser and feedwater heater is mainly based on the two-phase box model.

[0046] a. Mass conservation equation of two-phase box:

[0047]

[0048]

[0049] Where: M l ,M g ——Mass of liquid and vapor phase in the two-phase box, kg;

[0050] G l,in ,G l,out ——Mass flow rate of liquid flowing into and out of the two-phase box, kg / s;

[0051] G g,in ,G g,out ——Mass flow rate of vapor phase flowing into and out of the two-phase box, kg / s;

[0052] Γ——phase variable, kg / s;

[0053] b. Energy conservation equation in two-phase box:

[0054]

[0055]

[0056] Where: h l ,h g —— enthalpy value of liquid phase and vapor phase in two-phase box, kJ / kg;

[0057] h l,in ,h l,out ——The liquid phase flows into and out of the two-phase box. Liquid phase relative enthalpy, kJ / kg;

[0058] hg,in ,h g,out ——Vapor phase relative enthalpy of vapor flowing into and out of the two-phase box, kJ / kg;

[0059] Q l ,Q g ——The heat exchange between the liquid phase and the vapor phase and the outside world, with a positive sign for heat absorption and a negative sign for heat release, kJ / kg;

[0060] Q Γ ——interphase heat transfer, kJ / kg;

[0061] c. Combine the mass conservation equation and energy conservation equation for the liquid phase and the vapor phase respectively:

[0062]

[0063]

[0064] Where: M all ——Total mass inside the two-phase box, kg;

[0065] h all ——Total average specific enthalpy value in the two-phase box, kJ / kg;

[0066] Q all ——The total heat exchange between the two-phase box and the outside world, with a positive sign for heat absorption and a negative sign for heat release, kJ / kg.

[0067] Furthermore, the connection relationship between the pipe network system and the system consisting of main equipment in step S2 includes: direct connection and indirect connection; the direct connection transports the working fluid between the pipe network system and the system consisting of main equipment, and the indirect connection transfers heat between the pipe network system and the system consisting of main equipment; the parameters of the interaction between the pipe network system and the system consisting of main equipment in step S2 include: structural parameters of the pipeline, pipeline resistance characteristic parameters, pipeline initial state parameters, deaerator equipment parameters, condenser equipment parameters, and feed water heater equipment parameters.

[0068] Furthermore, step S3 is specifically as follows:

[0069] S31, pipe network system solution;

[0070] a. Linearize the mass conservation equation, ignore the effect of enthalpy on density, and perform semi-implicit difference on the time term to obtain the linearized mass conservation equation:

[0071]

[0072] Where: P i t+Δt ——pressure of the next long internal node i, MPa;

[0073] P i t ——Pressure of internal node i at the current time, MPa;

[0074] b. Linearize the momentum conservation equation. By ignoring the non-steady-state term of the momentum conservation equation and using the semi-implicit difference method for the quadratic term of the flow, the linearized momentum conservation equation is obtained:

[0075]

[0076]

[0077] ——The flow value from the next long internal node i to the internal node j, kg / s;

[0078] ——The flow value from the next long internal node i to the pressure boundary node k, kg / s;

[0079] ——The gravity pressure difference of the streamline between the internal nodes i and j of the next step, MPa;

[0080] ——The gravity pressure difference on the streamline connecting the next long internal node i to the pressure boundary node k, MPa;

[0081] ——The pressure value of the next long pressure boundary node k, MPa;

[0082] ——The resistance coefficient from the next internal node i to the internal node j, MPa·s 2 / kg 2 ;

[0083] ——The resistance coefficient from the next long internal node i to the pressure boundary node k, MPa·s 2 / kg 2 ;

[0084] ——The flow value from internal node i to pressure boundary node k at the current time, kg / s;

[0085] c. Establish the pressure matrix of the pipe network system by combining the linearized mass conservation equation and momentum conservation equation and arranging the equation into a matrix form:

[0086] A.P. t+Δt =B (14)

[0087] A and B are the coefficient matrix of the pressure equation group and the right vector of the pressure equation group after sorting, respectively, where:

[0088]

[0089]

[0090]

[0091] ——The flow value from the next long internal node i to the flow boundary node m, kg / s;

[0092] By solving the pressure matrix as above, the pressure distribution of the pipe network system is obtained;

[0093] d. Solve the streamline flow value. After solving the pressure matrix to obtain the pressure distribution of the pipe network system, substitute the pressure value into the linearized momentum conservation equation to obtain the streamline flow value;

[0094] e. Solve the mass value of the internal node by using the implicit Euler method for the mass conservation equation:

[0095]

[0096] Where: ——The mass of the next long internal node i, kg;

[0097] ——The mass of internal node i at the current time, kg;

[0098] Substitute the calculated flow value into the linearized mass conservation equation and solve for the mass of the internal node;

[0099] f. Linearize the energy conservation equation. The energy conservation equation (2) is written on the left side as:

[0100]

[0101] The implicit Euler method is used for equation (16) to obtain:

[0102]

[0103] g. Establish the energy matrix of the pipe network system

[0104] M.h t+Δt =N (18)

[0105] Where M is the enthalpy matrix, h t+Δt It represents the enthalpy value of the long pipe network system in the next step, and N is the right vector of the enthalpy equation group:

[0106]

[0107]

[0108]

[0109] Where m ii , m ij , n i is the corresponding matrix M or the N parameter of the matrix;

[0110] ——Specific enthalpy value of internal node i at the current time, kJ / kg;

[0111] ——The specific enthalpy value of the next long pressure boundary node k, kJ / kg;

[0112] ——Specific enthalpy value of the next long flow boundary node m, kJ / kg;

[0113] ——The heat dissipated between the next long internal node i and the environment, kJ / s;

[0114] ——The work done by the next internal node i, kW;

[0115] By solving the enthalpy matrix, the enthalpy distribution of the pipe network system is obtained;

[0116] S32, system solution of main equipment components;

[0117] The phase change side is in a state of thermodynamic equilibrium, and the average specific enthalpy and specific volume inside the two-phase box are:

[0118] h all =(1-x)h l +xh g (19)

[0119] v all =(1-x)v l +xv g (20)

[0120] Where: v all ——Total average specific volume in the two-phase box, m 3 / kg;

[0121] x——steam dryness;

[0122] v l ,v g ——Specific volume of liquid phase and vapor phase in the two-phase box, m 3 / kg;

[0123] The specific enthalpy and specific volume of the liquid phase and the vapor phase are functions of pressure. The pressure solution function of the two-phase box model is established:

[0124]

[0125] Using Newton's iteration method, solve for the pressure:

[0126]

[0127] Where: P t+Δt ——Pressure of the next long box, MPa;

[0128] P t ——Pressure of the box at the current time, MPa;

[0129] f′(P t ) represents the derivative of f(P).

[0130] Further, step S4 is specifically as follows:

[0131] The condenser and feed water heater are calculated as separate modules, and data is exchanged with the pipe network system through pressure boundary nodes or flow boundary nodes to achieve joint solution; the pressure value of the system composed of main equipment is assigned to the pipe network system, and at the same time, the temperature, pressure and flow of the pipe network system are assigned to the system interface composed of main equipment to realize data interaction between the pipe network system and the system composed of main equipment.

[0132] The beneficial effects brought by the technical solution provided by the present invention are:

[0133] The present invention provides a modeling and simulation method for a secondary condensate feed water system of a nuclear power plant, which simplifies the simulation of a complex secondary condensate feed water system of a nuclear power plant into a simulation of a pipe network part of the condensate feed water system and a simulation of the condensate feed water system equipment, and realizes an overall simulation between the pipe network system and the equipment module by establishing a coupling relationship between the pipe network system and the equipment. The simulation model can simulate working conditions that are difficult or impossible to achieve in reality, thereby improving economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0134] Figure 1 A flowchart of a modeling and simulation method for a secondary condensate feed water system of a nuclear power plant according to the present invention;

[0135] Figure 2 is a schematic diagram of a pipe network system according to an embodiment of the present invention;

[0136] Figure 3 This is a modeling diagram of a deaerator according to an embodiment of the present invention;

[0137] Figure 4 This is a modeling diagram of a condenser according to an embodiment of the present invention;

[0138] Figure 5 It is a modeling diagram of a feedwater heater according to an embodiment of the present invention. DETAILED DESCRIPTION

[0139] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0140] refer to Figure 1 , Figure 1 The flowchart of a modeling and simulation method for a secondary condensate feed water system of a nuclear power plant according to the present invention is as follows:

[0141] S1. Model the secondary condensate water supply system. Divide the secondary condensate water supply system into two parts: the pipe network system and the system composed of main equipment. Model the pipe network system based on the laws of conservation of mass, energy and momentum, and model the system composed of main equipment based on the laws of conservation of mass and energy.

[0142] S11. The pipe network system includes boundaries, nodes, and streamlines. The main equipment of the system includes deaerators, condensers, and feedwater heaters. Figure 2 As shown, Figure 2 It is a schematic diagram of a pipe network system according to an embodiment of the present invention.

[0143] S12. Model the boundaries, nodes, and streamlines of the pipe network system based on the three conservation laws, such as Figure 3 , 4, 5 as shown, Figure 3 This is a modeling diagram of a deaerator according to an embodiment of the present invention. Figure 4 This is a modeling diagram of a condenser according to an embodiment of the present invention. Figure 5 It is a modeling diagram of a feedwater heater according to an embodiment of the present invention.

[0144] a. Mass conservation equation:

[0145]

[0146] Where V i ——The volume of internal node i, m 3 ;

[0147] ρ i ——average density of internal node i, kg / m 3 ;

[0148] X, Y, Z – the number of internal nodes, pressure boundary nodes, and flow boundary nodes;

[0149] D ij ——The association matrix between internal node i and internal node j;

[0150] DE ik ——the correlation matrix between internal node i and pressure boundary node k;

[0151] DF im ——The association matrix between internal node i and traffic boundary node m;

[0152] G ij ——Flow rate from internal node i to internal node j, kg / s;

[0153] GE ik ——Flow rate from internal node i to pressure boundary node k, kg / s;

[0154] GF im ——Flow value from internal node i to flow boundary node m, kg / s;

[0155] When the flow value is a positive number, it means that the fluid flow direction is the same as the direction specified by the footmark; when the flow value is a negative number, it means that the fluid flow direction is opposite to the direction specified by the footmark.

[0156] b. Energy conservation equation:

[0157]

[0158] Where M i ——The mass of internal node i, kg;

[0159] h i ——specific enthalpy of internal node i, kJ / kg;

[0160] HkD k ——Specific enthalpy value of pressure boundary node k, kJ / kg;

[0161] HkD m ——Specific enthalpy value of flow boundary node m, kJ / kg;

[0162] S i ——The heat dissipation between internal node i and the environment, kJ / s;

[0163] c. Momentum conservation equation:

[0164] Momentum conservation equation for the internal streamlines:

[0165]

[0166] Momentum conservation equation for streamlines connected to a pressure boundary:

[0167]

[0168] In the formula, I ij ——Structural coefficient of the streamline between internal nodes i and j, MPa·s 2 / kg;

[0169] I ik ——Structural coefficient of the streamline connecting the internal node i and the pressure boundary node k, MPa·s 2 / kg;

[0170] PE k , P i , P j ——Pressure values ​​of pressure boundary node k, internal node i, and internal node j, MPa;

[0171] Hg ij , HEg ik ——Gravity pressure difference on the streamline between internal nodes i and j, and the streamline connecting internal node i to pressure boundary node k, MPa;

[0172] f ij ,fE ij ——Drag pressure drop from internal node i to internal node j, and from internal node i to pressure boundary node j, MPa;

[0173] Among them, f ij andfE ij is the resistance of the streamline, which is proportional to the square of the flow rate:

[0174]

[0175]

[0176] In the formula, ——The maximum value of the resistance coefficient from internal node i to internal node j and from internal node i to pressure boundary node j, MPa·s 2 / kg 2 ;

[0177] S13. The modeling of deaerator, condenser and feedwater heater is mainly based on the two-phase box model.

[0178] a. Mass conservation equation of two-phase box:

[0179]

[0180]

[0181] Where: M l ,M g ——Mass of liquid and vapor phase in the two-phase box, kg;

[0182] Gl,in ,G l,out ——Mass flow rate of liquid flowing into and out of the two-phase box, kg / s;

[0183] G g,in ,G g,out ——Mass flow rate of vapor phase flowing into and out of the two-phase box, kg / s;

[0184] Γ——phase variable, kg / s.

[0185] b. Energy conservation equation in two-phase box:

[0186]

[0187]

[0188] Where: h l ,h g —— enthalpy value of liquid phase and vapor phase in two-phase box, kJ / kg;

[0189] h l,in ,h l,out ——The liquid phase flows into and out of the two-phase box. Liquid phase relative enthalpy, kJ / kg;

[0190] h g,in ,h g,out ——Vapor phase relative enthalpy of vapor flowing into and out of the two-phase box, kJ / kg;

[0191] Q l ,Q g ——The heat exchange between the liquid phase and the vapor phase and the outside world, with a positive sign for heat absorption and a negative sign for heat release, kJ / kg;

[0192] Q Γ ——Interphase heat transfer, kJ / kg.

[0193] c. Combine the mass conservation equation and energy conservation equation for the liquid phase and the vapor phase respectively:

[0194]

[0195]

[0196] Where: M all ——Total mass inside the two-phase box, kg;

[0197] h all ——Total average specific enthalpy value in the two-phase box, kJ / kg;

[0198] Q all ——The total heat exchange between the two-phase box and the outside world, with a positive sign for heat absorption and a negative sign for heat release, kJ / kg.

[0199] S2. Define the connection relationship and interaction parameters between the pipe network system model and the system model composed of main equipment, and input initial parameters.

[0200] There are two main types of connection relationships between the pipe network system and the equipment. One is direct connection, where the pipe network system is directly connected to the deaerator or condenser, or the shell side of the feedwater heater, and the working fluid is transported to these devices for mixing; the other is indirect connection, where the pipe network system is connected to the condenser or the tube side of the feedwater heater, and acts as a cold source to exchange heat with the shell side. When directly connected, the equipment can be used as the boundary of the pipe network system. After the equipment solution is completed, the boundary parameters of the pipe network system are updated synchronously; when indirectly connected, the equipment can be used as part of the pipe network and participate in the pipe network solution.

[0201] The model parameters include the structural parameters of the pipeline (pipeline diameter, pipeline length, pipe wall thickness, etc.), pipeline resistance characteristic parameters (relative roughness, shape correction factor, etc.), pipeline initial state parameters (pressure, flow, temperature, etc.), deaerator equipment parameters (initial water level, volume, etc.), condenser equipment parameters (condenser heat exchange tube constant pressure specific heat, density, inner diameter, outer diameter, number of heat exchange tubes, heat exchange area, heat exchange tube layout, number of tube rows, etc.), feed water heater equipment parameters (feed water heater heat exchange tube constant pressure specific heat, density, inner diameter, outer diameter, number of heat exchange tubes, heat exchange area, heat exchange tube layout, number of tube rows, etc.).

[0202] S3. Based on the initial parameters, solve the condensate water supply system pipe network system model and the system model composed of main equipment respectively.

[0203] S31, pipe network system solution;

[0204] a. Linearize the mass conservation equation, ignore the effect of enthalpy on density, and perform semi-implicit difference on the time term to obtain the linearized mass conservation equation:

[0205]

[0206] Where: P i t+Δt ——pressure of the next long internal node i, MPa;

[0207] P i t ——Pressure of internal node i at the current time, MPa.

[0208] b. Linearize the momentum conservation equation. By ignoring the non-steady-state term of the momentum conservation equation and using the semi-implicit difference method for the quadratic term of the flow, the linearized momentum conservation equation is obtained:

[0209]

[0210]

[0211] in, ——The flow value from the next long internal node i to the internal node j, kg / s;

[0212] ——The flow value from the next long internal node i to the pressure boundary node k, kg / s;

[0213] ——The gravity pressure difference of the streamline between the internal nodes i and j of the next step, MPa;

[0214] ——The gravity pressure difference on the streamline connecting the next long internal node i to the pressure boundary node k, MPa;

[0215] ——The pressure value of the next long pressure boundary node k, MPa;

[0216] ——The resistance coefficient from the next internal node i to the internal node j, MPa·s 2 / kg 2 ;

[0217] ——The resistance coefficient from the next long internal node i to the pressure boundary node k, MPa·s 2 / kg 2 ;

[0218] ——The flow value from internal node i to pressure boundary node k at the current time, kg / s.

[0219] c. Establish the pressure matrix of the pipe network system by combining the linearized mass conservation equation (11) and momentum conservation equations (12) and (13) and arranging the equations into matrix form:

[0220] A.P. t+Δt =B (14)

[0221] A and B are the coefficient matrix of the pressure equation group and the right vector of the pressure equation group after sorting, respectively, where:

[0222]

[0223]

[0224]

[0225] By solving the pressure matrix as above, the pressure distribution of the pipe network system is obtained;

[0226] d. Solve the streamline flow value. After solving the pressure matrix to obtain the pressure distribution of the pipe network system, substitute the pressure value into the linearized momentum conservation equations (12) and (13) to obtain the streamline flow value.

[0227] e. Solve the mass value of the internal node by using the implicit Euler method for the mass conservation equation:

[0228]

[0229] Where: ——The mass of the next long internal node i, kg;

[0230] ——The mass of internal node i at the current time, kg;

[0231] Substitute the calculated flow value into the linearized mass conservation equation (11) and solve for the mass of the internal node;

[0232] f. Linearize the energy conservation equation. The left side of the energy conservation equation is written as:

[0233]

[0234] The implicit Euler method is used for equation (16) to obtain:

[0235]

[0236] g. Establish the energy matrix of the pipe network system

[0237] M.h t+Δt =N (18)

[0238] Where M is the enthalpy matrix, h t+Δt It represents the enthalpy value of the long pipe network system in the next step, and N is the right vector of the enthalpy equation group:

[0239]

[0240]

[0241]

[0242] Where m ii , m ij , n i is the corresponding matrix M or the N parameter of the matrix;

[0243] ——Specific enthalpy value of internal node i at the current time, kJ / kg;

[0244] ——The specific enthalpy value of the next long pressure boundary node k, kJ / kg;

[0245] ——Specific enthalpy value of the next long flow boundary node m, kJ / kg;

[0246] ——The heat dissipated between the next long internal node i and the environment, kJ / s;

[0247] ——The work done by the next internal node i, kW;

[0248] By solving the enthalpy matrix, the enthalpy distribution of the pipe network system is obtained;

[0249] S32, system solution of main equipment components;

[0250] The phase change side is in a state of thermodynamic equilibrium, and the average specific enthalpy and specific volume inside the two-phase box are:

[0251] h all =(1-x)h l +xh g (19)

[0252] v all =(1-x)v l +xv g (20)

[0253] Where: v all ——Total average specific volume in the two-phase box, m 3 / kg;

[0254] x——steam dryness;

[0255] v l ,v g ——Specific volume of liquid phase and vapor phase in the two-phase box, m 3 / kg.

[0256] The specific enthalpy and specific volume of the liquid phase and the vapor phase are functions of pressure. The pressure solution function of the two-phase box model is established:

[0257]

[0258] Using Newton's iteration method, solve for the pressure:

[0259]

[0260] Where: P t+Δt ——Pressure of the next long box, MPa;

[0261] P t——Pressure of the box at the current time, MPa;

[0262] f′(P t ) represents the derivative of f(P).

[0263] S4. Based on the connection relationship and interaction parameters between the pipe network system model and the system model consisting of main equipment defined in S2, data exchange is carried out between the pipe network system model of the secondary condensate water supply system and the system model consisting of main equipment, and an overall model between the pipe network system and the system consisting of main equipment is established.

[0264] For heat exchange equipment such as condensers and feedwater heaters that have multiple inlets and outlets and produce complex phase changes during the heat exchange process, they can be calculated as separate modules, and data can be exchanged with the pipe network system through pressure boundary nodes or flow boundary nodes to achieve joint solution.

[0265] In the secondary condensate feed water system of a nuclear power plant, the shell side of the condenser, the shell side of the feed water heater and the deaerator are essentially hybrid heat exchangers. The deaerator has only one heat exchange side and is a pure hybrid heat exchanger, while the condenser, feed water heater and other equipment have two heat exchange sides, the shell side and the tube side. The tube side heat exchange forms of these heat exchange equipment are the same, but the shell side heat exchange environment is different. For the condenser and feed water heater, the shell side is a single condensation heat exchange.

[0266] The pressure value of the system composed of main equipment is assigned to the pipe network system. At the same time, the temperature, pressure and flow of the pipe network system are assigned to the system interface composed of main equipment to realize data interaction between the pipe network system and the system composed of main equipment.

[0267] S5. After data interaction, the pipe network system and the system composed of main equipment update their own model parameters as the initial parameters of the model, and calculate the next time step, repeating steps S3, S4 and S5 until the system is stable.

[0268] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A modeling and simulation method for a secondary condensate feed water system of a nuclear power plant, characterized in that: The following steps are involved: S1. Divide the secondary condensate feed water system into two parts: a pipe network system and a system consisting of main equipment. Model the pipe network system based on the laws of conservation of mass, energy and momentum, and model the system consisting of main equipment based on the laws of conservation of mass and energy. S2. Define the connection relationship and interaction parameters between the pipe network system model and the system model composed of main equipment, and input initial parameters; S3. Based on the initial parameters, respectively solve the condensate water supply system pipe network system model and the system model composed of main equipment; S4. Based on the connection relationship and interaction parameters between the pipe network system model and the system model composed of main equipment defined in S2, data exchange is performed between the pipe network system model of the secondary condensation water supply system and the system model composed of main equipment, and an overall model between the pipe network system and the system composed of main equipment is established; S5. After data interaction, the pipe network system and the system composed of the main equipment update their own model parameters as the initial parameters of the model, and calculate the next step length, and repeat steps S3, S4 and S5 until the system is stable; Step S1 is specifically as follows: S11. The pipe network system includes boundaries, nodes, and streamlines. The main equipment of the system includes deaerators, condensers, and feedwater heaters; S12. Model the boundaries, nodes, and streamlines of the pipe network system based on the three conservation laws: a. Mass conservation equation: Where V i ——The volume of internal node i, m 3 ; ρ i ——average density of internal node i, kg / m 3 ; X, Y, Z – the number of internal nodes, pressure boundary nodes, and flow boundary nodes; D ij ——The association matrix between internal node i and internal node j; DE ik ——the correlation matrix between internal node i and pressure boundary node k; DF im ——The association matrix between internal node i and traffic boundary node m; G ij ——Flow rate from internal node i to internal node j, kg / s; GE ik ——Flow rate from internal node i to pressure boundary node k, kg / s; GF im ——Flow value from internal node i to flow boundary node m, kg / s; b. Energy conservation equation: Where M i ——The mass of internal node i, kg; h i ——specific enthalpy of internal node i, kJ / kg; HkD k ——Specific enthalpy value of pressure boundary node k, kJ / kg; HkD m ——Specific enthalpy value of flow boundary node m, kJ / kg; S i ——The heat dissipation between internal node i and the environment, kJ / s; c. Momentum conservation equation: Momentum conservation equation for the internal streamlines: Momentum conservation equation for streamlines connected to a pressure boundary: In the formula, I ij ——Structural coefficient of the streamline between internal nodes i and j, MPa·s 2 / kg; I ik ——Structural coefficient of the streamline connecting the internal node i and the pressure boundary node k, MPa·s 2 / kg; PE k , P i , P j ——Pressure values ​​of pressure boundary node k, internal node i, and internal node j, MPa; Hg ij ,HEg ik ——Gravity pressure difference on the streamline between internal nodes i and j, and the streamline connecting internal node i to pressure boundary node k, MPa; f ij ,fE ij ——Drag pressure drop from internal node i to internal node j, and from internal node i to pressure boundary node j, MPa; Among them, f ij andfE ij is the resistance of the streamline, which is proportional to the square of the flow rate: In the formula, ——The maximum value of the resistance coefficient from internal node i to internal node j and from internal node i to pressure boundary node j, MPa·s 2 / kg 2 ; S13. Modeling of deaerator, condenser and feedwater heater is based on two-phase box model. a. Mass conservation equation of two-phase box: Where: M l ,M g ——Mass of liquid and vapor phase in the two-phase box, kg; G l,in ,G l,out ——Mass flow rate of liquid flowing into and out of the two-phase box, kg / s; G g,in ,G g,out ——Mass flow rate of vapor phase flowing into and out of the two-phase box, kg / s; Γ——phase variable, kg / s; b. Energy conservation equation in two-phase box: Where: h l ,h g —— enthalpy value of liquid phase and vapor phase in two-phase box, kJ / kg; h l,in ,h l,out ——The liquid phase flows into and out of the two-phase box. Liquid phase relative enthalpy, kJ / kg; h g,in ,h g,out ——Vapor phase relative enthalpy of vapor flowing into and out of the two-phase box, kJ / kg; Q l ,Q g ——The heat exchange between the liquid phase and the vapor phase and the outside world, with a positive sign for heat absorption and a negative sign for heat release, kJ / kg; Q Γ ——interphase heat transfer, kJ / kg; c. Combine the mass conservation equation and energy conservation equation for the liquid phase and the vapor phase respectively: Where: M all ——Total mass inside the two-phase box, kg; h all ——Total average specific enthalpy value in the two-phase box, kJ / kg; Q all ——The total heat exchange between the two-phase box and the outside world, with a positive sign for heat absorption and a negative sign for heat release, kJ / kg.

2. A modeling and simulation method for a secondary condensate feed water system of a nuclear power plant according to claim 1, characterized in that: The connection relationship between the pipe network system and the system consisting of main equipment in step S2 includes: direct connection and indirect connection; the direct connection transports the working fluid between the pipe network system and the system consisting of main equipment, and the indirect connection transfers heat between the pipe network system and the system consisting of main equipment; the parameters of the interaction between the pipe network system and the system consisting of main equipment in step S2 include: structural parameters of the pipeline, pipeline resistance characteristic parameters, pipeline initial state parameters, deaerator equipment parameters, condenser equipment parameters, and feed water heater equipment parameters.

3. A modeling and simulation method for a secondary condensate feed water system of a nuclear power plant according to claim 2, characterized in that: Step S3 is specifically as follows: S31, pipe network system solution; a. Linearize the mass conservation equation, ignore the effect of enthalpy on density, and perform semi-implicit difference on the time term to obtain the linearized mass conservation equation: Where: P i t+Δt ——pressure of the next long internal node i, MPa; P i t ——Pressure of internal node i at the current time, MPa; b. Linearize the momentum conservation equation. By ignoring the non-steady-state term of the momentum conservation equation and using the semi-implicit difference method for the quadratic term of the flow, the linearized momentum conservation equation is obtained: ——The flow value from the next long internal node i to the internal node j, kg / s; ——The flow value from the next long internal node i to the pressure boundary node k, kg / s; ——The gravity pressure difference of the streamline between the internal nodes i and j of the next step, MPa; ——The gravity pressure difference on the streamline connecting the next long internal node i to the pressure boundary node k, MPa; ——The pressure value of the next long pressure boundary node k, MPa; ——The resistance coefficient from the next internal node i to the internal node j, MPa·s 2 / kg 2 ; ——The resistance coefficient from the next long internal node i to the pressure boundary node k, MPa·s 2 / kg 2 ; ——The flow value from internal node i to pressure boundary node k at the current time, kg / s; c. Establish the pressure matrix of the pipe network system by combining the linearized mass conservation equation and momentum conservation equation and arranging the equation into a matrix form: A·P t+Δt =B (14) A and B are the coefficient matrix of the pressure equation group and the right vector of the pressure equation group after sorting, respectively, where: ——The flow value from the next long internal node i to the flow boundary node m, kg / s; By solving the pressure matrix as above, the pressure distribution of the pipe network system is obtained; d. Solve the streamline flow value. After solving the pressure matrix to obtain the pressure distribution of the pipe network system, substitute the pressure value into the linearized momentum conservation equation to obtain the streamline flow value; e. Solve the mass value of the internal node by using the implicit Euler method for the mass conservation equation: Where: ——The mass of the next long internal node i, kg; ——The mass of internal node i at the current time, kg; Substitute the calculated flow value into the linearized mass conservation equation and solve for the mass of the internal node; f. Linearize the energy conservation equation. The energy conservation equation (2) is written on the left side as: The implicit Euler method is used for equation (16) to obtain: g. Establish the energy matrix of the pipe network system M·h t+Δt =N (18) Where M is the enthalpy matrix, h t+Δt It represents the enthalpy value of the long pipe network system in the next step, and N is the right vector of the enthalpy equation group: Where m ii , m ij , n i is the corresponding matrix M or the N parameter of the matrix; ——Specific enthalpy value of internal node i at the current time, kJ / kg; ——Specific enthalpy value of the next long pressure boundary node k, kJ / kg; ——The specific enthalpy value of the next long flow boundary node m, kJ / kg; ——The heat dissipated between the next long internal node i and the environment, kJ / s; W i t+Δt ——The work done by the next internal node i, kW; By solving the enthalpy matrix, the enthalpy distribution of the pipe network system is obtained; S32, system solution of main equipment components; The phase change side is in a state of thermodynamic equilibrium, and the average specific enthalpy and specific volume inside the two-phase box are: h all =(1-x)h l +xh g (19) v all =(1-x)v l +xv g (20) Where: v all ——Total average specific volume in the two-phase box, m 3 / kg; x——steam dryness; v l ,v g ——Specific volume of liquid phase and vapor phase in the two-phase box, m 3 / kg; The specific enthalpy and specific volume of the liquid phase and the vapor phase are functions of pressure. The pressure solution function of the two-phase box model is established: Using Newton's iteration method, solve for the pressure: Where: P t+Δt ——Pressure of the next long box, MPa; P t ——Pressure of the box at the current time, MPa; f′(P t ) represents the derivative of f(P).

4. A modeling and simulation method for a secondary condensate feed water system of a nuclear power plant according to claim 3, characterized in that: Step S4 is specifically as follows: The condenser and feed water heater are calculated as separate modules, and data is exchanged with the pipe network system through pressure boundary nodes or flow boundary nodes to achieve joint solution; the pressure value of the system composed of main equipment is assigned to the pipe network system, and at the same time, the temperature, pressure and flow of the pipe network system are assigned to the system interface composed of main equipment to realize data interaction between the pipe network system and the system composed of main equipment.

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