Three-dimensional lead-based cold micro reactor integrated thermal hydraulic calculation method based on UDF development

Abstract

The invention belongs to the technical field of nuclear thermal hydraulic power, and particularly relates to a three-dimensional lead-based cold micro reactor integrated thermal hydraulic calculation method based on UDF development. Comprising the following steps: developing thermophysical property modules of density, constant pressure specific heat capacity, heat conductivity and viscosity of coolant lead / lead bismuth; determining a numerical value of a turbulence Prandtt number Prt in the turbulence model; obtaining a viscous resistance coefficient and an inertial resistance coefficient of the porous medium model of the single-box fuel assembly; acquiring a viscous resistance coefficient and an inertial resistance coefficient of the porous medium model of the main heat exchanger; cFD numerical simulation calculation is carried out; the lead-based cold micro reactor is subjected to integrated modeling, and a reactor core, a pump channel, a main heat exchanger and a coolant flow channel are simplified. The method has the beneficial effects that by developing and calling the UDF of the physical property module and the turbulent flow Prandtt number calculation module, the physical property parameters of the liquid metal lead in the flowing process and the change of the turbulent flow heat conductivity in the turbulent flow model can be more accurately simulated.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear thermal hydraulic technology, and in particular relates to a three-dimensional lead-based cooled micro-reactor integrated thermal hydraulic calculation method developed based on UDF. Background Art

[0002] Fast reactor is a nuclear reactor that does not require a moderator and directly uses high-energy fast neutrons to maintain a chain reaction. Compared with thermal neutron reactors, fast reactors have higher neutron economy, which gives them unique advantages in fuel proliferation, resource utilization and nuclear waste treatment. Lead-based cold fast reactor is a type of fast reactor that uses lead or lead-bismuth alloy as coolant. It has the advantages of high temperature resistance, corrosion resistance and high density, and is suitable for the design concept of long life and closed operation. It is one of the representatives of the fourth generation of nuclear reactor technology in the future. However, due to the high density and high specific heat capacity of lead / lead-bismuth as coolant, the fluid dynamics and heat transfer characteristics are relatively complex, especially in the compact structure of micro-reactors, and the internal structure of lead-based cold micro-reactors is relatively complex. Taking the design scheme of megawatt-class compact lead-cooled fast reactors as an example, the small and micro lead-cooled fast reactors adopt an integrated layout, the steam generator, the main pump, etc. are all arranged in the pressure vessel, the core is arranged at the bottom of the reactor pressure vessel, the main pump is arranged at the center just above the core, and 6 main heat exchangers of spiral tube structure are evenly arranged around. When the liquid lead coolant flows through the core, it absorbs the heat generated by the fission of the nuclear fuel, and the temperature rises in the process. The coolant then flows upward into the main pump, and after being pressurized by the main pump, it flows into the main heat exchanger. In the main heat exchanger cavity, the coolant flows from top to bottom, and in this process, heat is transferred with the secondary cold fluid in the tube, and the temperature is reduced. After leaving the main heat exchanger cavity, the coolant continues to flow upward, then flows into the descending channel through the hole in the pressure vessel wall, and finally returns to the core to complete a cycle. In more complex geometric structures (such as narrow channels and small fuel assemblies), fine mesh division is required, which greatly increases the computational cost. Therefore, it is very challenging to directly carry out three-dimensional full-core integrated numerical simulation calculations for lead-based cold micro-reactors.

[0003] At present, the widely used thermal hydraulic programs for the thermal hydraulic calculation of the internal cold and hot hydraulics of lead-based cold fast reactors at home and abroad include system programs and computational fluid dynamics (CFD) programs. The core model in the system program is mostly a single or multiple flow channels, which can only be used to provide the average value of some thermal hydraulic parameters in the reactor. It can only be used as a part of the integrated thermal hydraulic calculation, and cannot achieve the accurate calculation requirements of the three-dimensional lead-based cold micro reactor. Although the common CFD method can accurately simulate the thermal hydraulic parameters of each component in the reactor, when calculating the integrated or more complex model, the number of grids is large, and the computer has a high demand for computing power. At present, when performing thermal hydraulic calculations of lead-based cold fast reactors, only the fuel assembly, heat exchanger and other components are calculated separately. For example, Chai et al. used CFD software to simulate the three-dimensional flow and temperature distribution of LBE for the wire-wound 19 rod bundle, and evaluated the temperature change of the fuel element surface due to mass flow. Yang Yupeng et al. numerically simulated the detailed modeling of the primary and secondary sides of the small lead reactor heat exchanger based on FLUENT software and analyzed its flow and heat transfer properties, verifying the correctness of the numerical simulation method. In view of the coupling calculation of the primary coolant system of the lead-cooled fast reactor, Zhao Pengcheng established a system program suitable for the steady-state thermal-hydraulic analysis of the primary coolant system of the small natural circulation lead-cooled fast reactor, and developed a steady-state fuel rod heat transfer model and auxiliary models such as shell-and-tube heat exchangers to obtain the analysis results of the steady-state natural circulation flow distribution characteristics of the whole core, and the transient thermal safety characteristics analysis was carried out using the system safety analysis program ATHLET. At present, there is a lack of integrated thermal-hydraulic calculations for the full-core and detailed three-dimensional numerical simulation of lead-based cooled micro-reactors at home and abroad. Summary of the invention

[0004] The purpose of the present invention is to provide a three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method based on UDF development. This method develops a temperature-dependent physical property module of lead / lead-bismuth and a turbulent Prandtl number model suitable for liquid metal coolants based on UDF. The complex fuel assembly structure and spiral tube heat exchanger are simplified through a porous medium model. In addition, in order to solve the problem of a large number of grids and a large computational load in integrated modeling, different components of the primary circuit are simplified and partitioned into grids, and connected and coupled through interfaces to achieve fluid and heat exchange between partitions. Through this method, the numerical simulation calculation of the core, spiral tube heat exchanger, pump channel, core flow distribution and full core integration can be efficiently and accurately realized, so as to reduce the workload of model modification and numerical calculation.

[0005] The technical solution of the present invention is as follows: A three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method developed based on UDF comprises the following steps:

[0006] Step 1: Develop a thermophysical property module for the density, constant pressure specific heat capacity, thermal conductivity and viscosity of the coolant lead / lead-bismuth;

[0007] Step 2: Determine the value of a turbulent Prandtl number Prt in the turbulence model;

[0008] Step 3: Carry out CFD numerical simulation calculation of a 1:1 model for a single-box fuel assembly to obtain the flow rate and pressure drop parameters. By fitting the fv relationship, perform pressure drop coupling of the core fuel assembly to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the single-box fuel assembly.

[0009] Step 4: Obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the main heat exchanger;

[0010] Step 5: Carry out CFD numerical simulation calculation for the flow distribution in the core area of ​​the lead-based cooled micro reactor;

[0011] Step 6: Perform integrated modeling for the lead-based cooled micro-reactor and simplify the core, pump channel, main heat exchanger and coolant flow channel.

[0012] The empirical formula for determining Prt in step 2 is:

[0013]

[0014] The step 3 is to carry out CFD numerical simulation calculation of a 1:1 model for a single-box fuel assembly based on Fluent software, obtain the flow rate and pressure drop parameters, and couple the pressure drop of the core fuel assembly by fitting the fv relationship to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the single-box fuel assembly; according to the formula Calculate the Reynolds number range, switch the flow model through the functions DEFINE_EXECUTE_AT_END(calculate_Re_and_switch_model), RP_Set_String("models / viscous","laminar"), and RP_Set_String("models / viscous","k-epsilon"), and realize the simultaneous calculation method of "inter-box flow + intra-box flow" in the core.

[0015] The step 4 is based on the Fluent software to carry out CFD numerical simulation calculation of the 1:1 model for the spiral tube heat exchanger, obtain the flow rate and pressure drop parameters, and carry out the pressure drop coupling of the main heat exchanger by fitting the fv relationship to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the main heat exchanger.

[0016] In step 6, the core fuel assembly and the spiral tube main heat exchanger are simplified using a porous medium model, and the grid is divided into zones. The coolant thermophysical properties and turbulent Prandtl number UDF are compiled, and the thermal simulation calculation results of the single-box fuel assembly and the main heat exchanger are coupled to realize the integrated thermal calculation of the core, the main heat exchanger and other coolant flow channels.

[0017] The beneficial effects of the present invention are as follows: Taking a small and micro lead-cooled fast reactor as an example, the present invention can more accurately simulate the changes in the physical property parameters of liquid metal lead during the flow process and the turbulent thermal conductivity in the turbulent model through the UDF development and calling of the physical property module and the turbulent Prandtl number calculation module. By carrying out 1:1 numerical simulation calculations on single-box fuel assemblies and spiral tube heat exchangers, the porous medium model parameters of the corresponding areas are obtained, thereby simplifying the complex structure of the fuel assembly and the spiral tube heat exchanger, greatly reducing the calculation cost. In addition, in order to solve the problem of a large number of integrated grid divisions, grid division is performed on different components of the first circuit, and each component is coupled and connected through an interface, thereby realizing the core flow distribution of the lead-based cold micro reactor and the thermal-hydraulic numerical simulation calculation of the integrated model. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a circuit diagram;

[0019] Figure 2 A flow chart of the integrated thermal-hydraulic calculation method for a three-dimensional lead-based cold micro-reactor developed based on UDF provided by the present invention;

[0020] Figure 3 A simplified integrated model for a small micro lead-cooled fast reactor. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] The present invention provides a three-dimensional integrated thermal-hydraulic calculation method for lead-based cooled micro-reactors based on UDF (User Defined Function), which aims to solve the problems of large structural size differences and difficult grid division in complex superimposed spaces when performing three-dimensional thermal-hydraulic calculations on lead-based cooled micro-reactors. This method can be used to simplify the complex structure in the reactor, and through the UDF technology, the calculation structures of various components are coupled to achieve three-dimensional integrated thermal-hydraulic calculations of the entire core.

[0023] like Figure 2 As shown in the figure, the three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method developed based on UDF includes the following steps:

[0024] Step 1: Develop a thermophysical property module for coolant lead / lead-bismuth, which includes the functional form of thermophysical properties such as density, specific heat capacity at constant pressure, thermal conductivity and dynamic viscosity of liquid lead / lead-bismuth as they change with temperature. In order to make the numerical simulation results more accurate, considering the influence of temperature rise on parameters such as thermal conductivity, specific heat capacity at constant pressure and density during heat exchange, the physical property parameters of coolant liquid lead are expressed as functions of temperature in the calculation, as shown in Table 1 below. The dynamic change of physical properties with temperature is realized by writing UDF program;

[0025] Table 1

[0026]

[0027] Among them, λ, c p , ρ, and η are the thermal conductivity, specific heat capacity at constant pressure, density, and dynamic viscosity of liquid lead, respectively.

[0028] Step 2: When carrying out numerical simulation calculations, the quality of the numerical simulation depends to a certain extent on the selected turbulence model. It is very important to choose the right turbulence model. For one of the turbulence models, the Prandtl number Pr t The value of conventional fluid Pr t = 0.85 is no longer applicable to liquid metal, so it is necessary to develop a UDF program to correct the turbulence model applicable to liquid metal. The corrected empirical formula is:

[0029]

[0030] Among them, Pe is the Berkeley number, which represents the relative size of convection and diffusion.

[0031] Step 3: Based on the Fluent commercial software, a 1:1 model CFD numerical simulation calculation is carried out for a single-box fuel assembly. The key thermal parameters such as flow velocity and pressure drop in the fuel assembly are extracted through post-processing. The pressure drop coupling of the core fuel assembly is performed by fitting the fv relationship. According to the Ergun equation:

[0032]

[0033] Where D p is the average particle diameter, μ is the fluid viscosity, ΔP is the pressure drop, L is the porous medium thickness, and v is the flow velocity.

[0034] Obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of a single-box fuel assembly; by writing a UDF program, according to the formula Calculate the Reynolds number range. When the Re number is less than 2300, the fluid flow is laminar, and when the Re number is greater than 2300, the fluid flow is turbulent. Different flow models need to be selected according to different flow states. Therefore, the flow model is switched through the functions DEFINE_EXECUTE_AT_END(calculate_Re_and_switch_model), RP_Set_String("models / viscous","laminar"), and RP_Set_String("models / viscous","k-epsilon"); realize the core "inter-box flow + intra-box flow" joint calculation method;

[0035] Step 4: Based on the Fluent commercial software, a 1:1 model CFD numerical simulation calculation is carried out for the spiral tube heat exchanger. The key thermal parameters such as flow rate and pressure drop are extracted through post-processing. The pressure drop coupling of the main heat exchanger is performed by fitting the fv relationship to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the main heat exchanger. The calculation formula is the Ergun equation:

[0036]

[0037] Where D p is the average particle diameter, μ is the fluid viscosity, P is the pressure drop, L is the porous medium thickness, and v is the flow velocity.

[0038] Step 5: Carry out CFD numerical simulation calculation for the flow distribution in the core area of ​​the lead-based cooled micro reactor to extract the mass flow rate Q at the inlet of each fuel assembly i , calculate the average mass flow rate of the core fuel assembly In order to quantitatively and intuitively determine the uniformity of flow distribution at the reactor core inlet, the normalized flow distribution factor q is defined as i is the flow rate Q at the inlet of a fuel assembly i The average flow rate at the core inlet Ratio of:

[0039]

[0040] Where n is the number of fuel assembly boxes.

[0041] By normalizing the flow distribution factor q i The deviation can reflect the core flow distribution effect, and can be used as a basis to optimize and improve the flow distribution device, thereby improving the uniformity of fuel assembly mass flow distribution.

[0042] Step 6: Carry out integrated 3D modeling for the lead-based cooled micro-reactor, and reasonably simplify the core, pump channel, main heat exchanger, coolant flow channel and other parts. The core fuel assembly and spiral tube main heat exchanger are simplified using porous media models, and the detailed modeling of the above parts is omitted in the 3D model. When meshing, the overall model is divided into different areas such as the core fuel assembly, the lower chamber, the upper space of the core, and the descending channel between the inner and outer containers, and different mesh sizes are set for meshing. The number of meshes can be greatly reduced by partitioning the mesh, and when the model is changed, only specific areas need to be replaced and re-meshed, which greatly reduces the workload of meshing.

[0043] Step 7: In the Fluent numerical simulation calculation, compile the coolant thermophysical properties and turbulent Prandtl number UDF; determine the key boundary condition settings: set the mass flow rate and temperature of the inlet, set the main heat exchanger as a body cold source, set the fuel assembly as a body heat source, and set the outlet as a pressure outlet boundary condition, etc.; couple the thermal simulation calculation results of the single-box fuel assembly and the main heat exchanger, that is, the porous medium parameters; set the mesh interface of different regions as the interface surface to realize the transmission of data in each region. Through the above operations, the integrated thermal calculation of the core, main heat exchanger and other coolant flow channels is realized.

[0044] The present invention can realize three-dimensional full-core integrated numerical simulation calculation, and is suitable for small and micro lead-based cold fast reactors with complex in-core structures. Through the UDF development and calling of the physical property module and the turbulent Prandtl number calculation module, the changes in the physical property parameters of liquid metal lead during the flow process and the turbulent thermal conductivity in the turbulence model can be simulated more accurately. When performing three-dimensional geometric modeling, the fuel assemblies with narrow channels, the spiral tube heat exchangers with more tube bundles, and the main pump channels can be simplified, and their internal structures can be replaced by the porous medium model obtained by 1:1 calculation. Calculation, greatly reducing the workload of modeling and the computational cost of meshing. At the same time, the model structure of the partitioned mesh can be coupled through the interface to achieve the purpose of reducing the workload of model modification and numerical calculation.

[0045] Example:

[0046] A three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method developed based on UDF includes:

[0047] Step 1: Select UDF function

[0048] Through the porous media formula Ergun equation:

[0049]

[0050] Turbulent Prandtl number formula: 1000<Pe≤6000,

[0051] Physical property formula (such as liquid lead metal)

[0052] C P Pb=176.2-4.923·10 -2 ·T+1.544·10 -5 ·T 2 -1.524·T -2 J / (Kg·K),

[0053] ρ Pb =11441-1.2795·T Kg / m 3 ,

[0054] λ Pb =9.2+0.11·TW / (m·K),

[0055]

[0056] And the Reynolds number formula: Select the corresponding code.

[0057] (2) Develop a thermophysical property module for the density, specific heat at constant pressure, thermal conductivity and viscosity of the coolant lead / lead-bismuth. In order to accurately simulate the effect of temperature changes on the thermophysical properties of the material during the heat exchange process, it is necessary to consider the dynamic effect of temperature increase on the thermal conductivity, specific heat at constant pressure, density and other parameters of the liquid lead or lead-bismuth coolant. Based on this, by referring to the "Lead-Bismuth Thermophysical Property Manual", the physical property parameters of liquid lead / lead-bismuth are expressed as a function of temperature, and the UDF program is written based on this.

[0058] Through this UDF module, Fluent can call the function expressions of various physical property parameters during the solution process, and update the physical property parameters such as thermal conductivity, specific heat capacity and density of the coolant in real time according to the temperature of the current calculation unit, thereby improving the calculation accuracy and simulation reliability.

[0059] (3) Develop a turbulent Prandtl number calculation module. For the value of the turbulent Prandtl number Prt in the turbulence model, the conventional fluid Prt = 0.85 is no longer applicable to liquid metal. In the existing turbulence models, only the turbulent viscosity, that is, the model of turbulent momentum diffusivity is usually established, and the turbulent thermal conductivity is not directly defined. In order to model the turbulent thermal conductivity, Prt is defined as the ratio of turbulent momentum diffusivity to turbulent thermal conductivity, and a UDF program is written. Through this UDF module, Fluent can automatically call the relevant turbulent Prandtl number function, thereby achieving more accurate thermal fluid simulation.

[0060] (4) A 1:1 CFD numerical simulation calculation of a single-box fuel assembly is carried out. During the simulation process, a fine grid division strategy is adopted to obtain key thermal parameters such as the core coolant inlet and outlet temperatures, coolant flow rate, and resistance characteristics such as pressure drop, which can meet the design requirements of lead-based reactor oxide layer corrosion and fuel rod bundle melting point. By fitting the fv relationship, the pressure drop coupling of the core fuel assembly is carried out to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the single-box fuel assembly. In subsequent calculations, the core fuel assembly can be simplified through the porous medium model to improve the calculation efficiency.

[0061] The UDF program is written to implement the joint calculation method of "inter-box flow + intra-box flow" in the core. In this step, the UDF needs to implement the following two functions: ① Extract the key thermal parameters of the 1:1 simulation calculation of the single box component; ② Calculate the Re number through the extracted thermal parameters and determine whether to use the laminar flow model or the turbulent flow model. This UDF can realize the joint calculation of the inter-box flow and the intra-box flow under different flow conditions.

[0062] (5) A full-scale CFD numerical simulation of the spiral tube heat exchanger with a 1:1 model was performed. During the simulation, a fine meshing strategy was also used. The obtained temperature distribution and flow pressure drop data can be further used to derive the viscous resistance coefficient and inertial resistance coefficient of the porous medium model applicable to the main heat exchanger area. The spiral tube heat exchanger area can be simplified by the porous medium model to effectively reduce the computational complexity in the integrated simulation.

[0063] (6) Calculations are performed on the flow distribution of the lead-based cooled micro-reactor to obtain the flow distribution characteristics in the pool and the normalized flow distribution factor, so as to evaluate the flow distribution effect of the core. Based on the calculation results of the flow distribution, an optimization scheme for the core flow distribution can be proposed to achieve a more uniform flow distribution, improve the uniformity of the coolant flow in each area of ​​the core, avoid local overheating, and improve the overall safety and operational stability of the micro-reactor.

[0064] (7) Integrated three-dimensional modeling of the lead-based cooled micro-reactor was carried out. The lead-based cooled micro-reactor had the problem of large differences in structural dimensions in the complex overlapping space and difficulty in meshing. Therefore, the core, pump channel, main heat exchanger and coolant flow channel were reasonably simplified. The core fuel assembly and spiral tube main heat exchanger were simplified using porous media models. The detailed modeling of the above parts was omitted in the three-dimensional model, and the overall model was divided into different areas such as the core fuel assembly, the lower chamber, the upper space of the core and the descending channel between the inner and outer containers, and different mesh sizes were set for meshing.

[0065] (8) In the integrated numerical calculation, the grids of each area are connected by defining the wall boundary as the interface to realize the fluid and heat exchange between the partitions, ensure the smooth transmission of the calculation results between the areas, compile the coolant thermophysical properties and turbulent Prandtl number UDF, determine the key boundary condition settings: set the mass flow rate and temperature at the inlet, set the main heat exchanger as the body cold source, set the fuel assembly as the body heat source, set the outlet as the pressure outlet boundary condition, etc., couple the thermal calculation results of the single-box fuel assembly and the main heat exchanger, simplify the above components through the porous medium parameters, and realize the integrated thermal calculation of the core, main heat exchanger and other coolant flow channels.

Claims

1. A three-dimensional lead-based cold micro-reactor integrated thermal-hydraulic calculation method developed based on UDF, characterized in that: The steps include: Step 1: Develop a thermophysical property module for the density, constant pressure specific heat capacity, thermal conductivity and viscosity of the coolant lead / lead-bismuth; Step 2: Determine the value of a turbulent Prandtl number Prt in the turbulence model; Step 3: Carry out CFD numerical simulation calculation of a 1:1 model for a single-box fuel assembly to obtain the flow rate and pressure drop parameters. By fitting the fv relationship, perform pressure drop coupling of the core fuel assembly to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the single-box fuel assembly. Step 4: Obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the main heat exchanger; Step 5: Carry out CFD numerical simulation calculation for the flow distribution in the core area of ​​the lead-based cooled micro reactor; Step 6: Perform integrated modeling for the lead-based cooled micro-reactor and simplify the core, pump channel, main heat exchanger and coolant flow channel.

2. The three-dimensional lead-based cold micro-reactor integrated thermal-hydraulic calculation method based on UDF development as claimed in claim 1 is characterized by: In the step 1, the physical property parameters of the coolant liquid lead / lead-bismuth are expressed as a function of temperature in the calculation, as shown in the following table:

3. The three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method based on UDF development as claimed in claim 1 is characterized by: The empirical formula for determining Prt in step 2 is:

4. The three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method based on UDF development as claimed in claim 1 is characterized by: The step 3 is to carry out CFD numerical simulation calculation of a 1:1 model for a single-box fuel assembly based on Fluent software, obtain the flow rate and pressure drop parameters, and couple the pressure drop of the core fuel assembly by fitting the fv relationship to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the single-box fuel assembly; according to the formula Calculate the Reynolds number range, switch the flow model through the functions DEFINE_EXECUTE_AT_END(calculate_Re_and_switch_model), RP_Set_String("models / viscous","laminar"), and RP_Set_String("models / viscous","k-epsilon"), and realize the simultaneous calculation method of "inter-box flow + intra-box flow" in the core.

5. The three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method based on UDF development as claimed in claim 1 is characterized by: The step 4 is based on the Fluent software to carry out CFD numerical simulation calculation of the 1:1 model for the spiral tube heat exchanger, obtain the flow rate and pressure drop parameters, and carry out the pressure drop coupling of the main heat exchanger by fitting the fv relationship to obtain the viscous resistance coefficient and inertial resistance coefficient of the porous medium model of the main heat exchanger.

6. The three-dimensional lead-based cold micro-reactor integrated thermal hydraulic calculation method based on UDF development as claimed in claim 1 is characterized by: In step 6, the core fuel assembly and the spiral tube main heat exchanger are simplified using a porous medium model, and the grid is divided into zones. The coolant thermophysical properties and turbulent Prandtl number UDF are compiled, and the thermal simulation calculation results of the single-box fuel assembly and the main heat exchanger are coupled to realize the integrated thermal calculation of the core, the main heat exchanger and other coolant flow channels.

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