Method and system for simulating flow heat transfer of reactor core of pebble-bed high-temperature gas cooled reactor

Abstract

The invention discloses a pebble-bed high-temperature gas cooled reactor core flow heat transfer simulation method and system, and relates to the technical field of nuclear reactor core flow heat transfer analysis, and the method comprises the following steps: based on material parameters and contact parameters of fuel spheres, simulating a natural accumulation process of the fuel spheres through a DEM to obtain a pebble-bed high-temperature gas cooled reactor core model; structural reconstruction is conducted through the three-dimensional space coordinates of the multiple fuel spheres, a corresponding geometric model is obtained, and porosity distribution of the pebble-bed type high-temperature gas cooled reactor core is obtained based on the geometric model; porous medium parameters related to the porosity are obtained according to the porosity distribution, a porous medium equation set is constructed based on the porous medium parameters, the porous medium equation set is solved, and flow and temperature distribution in the pebble-bed high-temperature gas cooled reactor core is obtained. According to the method, the accumulation process of the fuel balls in the reactor core is simulated through the DEM, the real accumulation structure and porosity are obtained, and high-precision prediction of flow and temperature distribution in the reactor core is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of flow and heat transfer analysis in a nuclear reactor core, and in particular to a method and system for simulating flow and heat transfer in a pebble bed high-temperature gas-cooled reactor core. Background Art

[0002] The pebble bed modular high-temperature gas-cooled reactor (HTGR) nuclear power plant uses helium as the coolant, graphite as the moderator, and a graphite spherical matrix dispersed with TRISO-coated particles as the fuel elements. The robust and resilient coated particle fuel format enables the gas-cooled reactor to operate at high temperatures for extended periods. By properly selecting the coolant and structural materials, the pebble bed reactor can operate at higher temperatures than other reactors. This makes the pebble bed HTGR inherently safe, boasts high core outlet temperatures, and offers a wide range of applications.

[0003] Because the pebble-bed core is composed of a large number of fuel spheres, exhibiting a complex, irregular stacking structure, the spatial distribution of its internal fluid channels is highly uneven. This structure results in strong spatial variations in the coolant flow and heat transfer behavior within the core, significantly affecting temperature distribution, local cooling efficiency, and safety margins. Therefore, accurately modeling and predicting the flow and heat transfer characteristics in the pebble-bed core is a core aspect of the thermal safety design and operational analysis of high-temperature gas-cooled reactors.

[0004] In actual engineering analysis, to simplify the analysis, the flow and heat transfer within the sphere bed core is often equated to a non-thermal equilibrium porous media flow and heat transfer process. The influence of the stacked particles is considered by introducing models such as equivalent resistance terms and interphase heat transfer terms. This type of method is highly dependent on the selection of empirical correlations and the accuracy of the porosity. In traditional analysis, porosity is often determined by the assumptions of simple stacking, face-centered stacking, body-centered stacking, or a combination of these. These stacking methods are not the actual stacking methods of the fuel spheres in the core and therefore cannot reflect the differences in porosity in local areas. At the same time, the selected empirical formulas such as the resistance coefficient and interphase convective heat transfer coefficient do not match the actual structure, reducing the reliability and prediction accuracy of the flow and heat transfer analysis. Summary of the Invention

[0005] Based on the defects of the above-mentioned existing technologies, the present invention provides a method and system for simulating the flow and heat transfer in the core of a pebble-bed high-temperature gas-cooled reactor, which solves the problem that the existing porosity is often determined by simple stacking, face-centered stacking, body-centered stacking or several combinations. These stacking methods are not the actual stacking methods of fuel balls in the core, and thus cannot reflect the differences in porosity in local areas. At the same time, the selected empirical formulas such as the resistance coefficient and the interphase convection heat transfer coefficient do not match the actual structure, thereby reducing the reliability and prediction accuracy of the flow and heat transfer analysis.

[0006] The present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for simulating core flow and heat transfer in a pebble bed high temperature gas-cooled reactor, comprising the following steps: The material parameters and contact parameters of the fuel spheres are selected based on the actual operating conditions of the pebble bed high temperature gas-cooled reactor core; Based on the material parameters and contact parameters of the fuel spheres, the natural accumulation process of the fuel spheres is simulated through DEM to obtain a pebble bed high-temperature gas-cooled reactor core model. During the natural accumulation process, a cylindrical container corresponding to the actual structural dimensions of the pebble bed high-temperature gas-cooled reactor core is generated, and multiple fuel spheres are randomly generated and freely fall on the top of the cylindrical container. After all the fuel spheres fall into the container, the system kinetic energy is dissipated within a set time to obtain the pebble bed high-temperature gas-cooled reactor core model. The three-dimensional spatial coordinates of multiple fuel spheres are obtained based on the core model of the pebble bed high-temperature gas-cooled reactor. The structure is reconstructed using the three-dimensional spatial coordinates of the multiple fuel spheres to obtain the corresponding geometric model. The porosity distribution of the pebble bed high-temperature gas-cooled reactor core is obtained based on the geometric model. Porosity-related porous media parameters are obtained according to the porosity distribution. A porous media equation group is constructed based on the porous media parameters. The porous media equation group is solved to obtain the flow and temperature distribution in the core of the pebble bed high-temperature gas-cooled reactor.

[0007] Preferably, in the process of simulating the natural accumulation of fuel balls by DEM, the interaction between the fuel balls is described by a contact model, and the motion behavior of the fuel balls is described by a motion model; the contact model includes a normal elastic force equation, a tangential elastic force equation and a nonlinear contact model, and the motion model is a motion equation based on Newton's second law.

[0008] Preferably, the obtaining of the porosity distribution of the pebble bed high temperature gas-cooled reactor core based on the geometric model comprises the following steps: Obtain spatial arrangement information of multiple fuel balls based on a geometric model; The geometric model is spatially divided into multiple sub-regions, and the volume fraction of the fuel spheres in each sub-region is calculated. The local porosity of the sub-region is obtained based on the volume fraction occupied by the fuel spheres.

[0009] Preferably, the porous medium parameters include resistance coefficient, interphase convection heat transfer coefficient and permeability.

[0010] Preferably, the porous medium equations are specifically as follows: ; ; ; ; Where,u For speed, is the density, t is the time variable, is the velocity vector, is the porosity, is the gradient operator, μ is the dynamic viscosity, f x for x Directional physical strength, for x The partial derivative operator in the direction, p is the fluid pressure, α is the permeability, is the drag coefficient, is the density of the fluid, c p，f is the constant pressure specific heat capacity of the fluid, T f is the fluid temperature, λ f is the thermal conductivity of the fluid, α sf is the interphase convective heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity of the solid at constant pressure, λ s is the solid thermal conductivity, Generate heat for the fuel ball.

[0011] Preferably, the fuel ball material parameters include the diameter, quantity, density, Poisson's ratio and Young's modulus of the fuel balls; the contact parameters include the normal restitution coefficient, tangential restitution coefficient, static friction coefficient and rolling friction coefficient.

[0012] In a second aspect, the present invention provides a core flow and heat transfer simulation system for a pebble bed high temperature gas-cooled reactor, comprising: A selection module is used to select the material parameters and contact parameters of the fuel spheres based on the actual operating conditions of the pebble-bed high-temperature gas-cooled reactor core; A generation module is used to simulate the natural accumulation process of fuel spheres using DEM based on the material parameters and contact parameters of the fuel spheres to obtain a pebble bed high-temperature gas-cooled reactor core model. During the natural accumulation process, a cylindrical container corresponding to the actual structural dimensions of the pebble bed high-temperature gas-cooled reactor core is generated, and multiple fuel spheres are randomly generated and freely fall on top of the cylindrical container. After all the fuel spheres fall into the container, the system kinetic energy is dissipated within a set time to obtain the pebble bed high-temperature gas-cooled reactor core model. A reconstruction module is used to obtain the three-dimensional spatial coordinates of multiple fuel spheres based on the pebble bed high-temperature gas-cooled reactor core model, perform structural reconstruction using the three-dimensional spatial coordinates of the multiple fuel spheres to obtain a corresponding geometric model, and obtain the porosity distribution of the pebble bed high-temperature gas-cooled reactor core based on the geometric model; The calculation module is used to obtain the porous medium parameters related to porosity based on the porosity distribution, construct the porous medium equation group based on the porous medium parameters, solve the porous medium equation group, and obtain the flow and temperature distribution in the core of the pebble bed high-temperature gas-cooled reactor.

[0013] Compared with the prior art, the at least one technical solution adopted by the present invention can achieve the following beneficial effects: The present invention first selects the material parameters and contact parameters of the fuel balls based on the actual operating conditions of the pebble bed type high temperature gas-cooled reactor core, and based on the material parameters and contact parameters of the fuel balls, simulates the natural stacking process of the fuel balls through DEM. During the natural stacking process, a cylindrical container corresponding to the actual structural dimensions of the pebble bed type high temperature gas-cooled reactor core is generated, and a plurality of fuel balls that fall freely are randomly generated on the top of the cylindrical container, accurately simulating the free fall process of the fuel balls under the action of gravity. Finally, the system kinetic energy is dissipated within a set time to obtain a stable pebble bed type high temperature gas-cooled reactor core model. The present invention simulates the stacking process of the fuel balls in the core by the discrete element method to obtain the real stacking structure and spatial distribution of porosity. Combined with the porosity changes in the modeling area, the matching empirical correlations such as the resistance coefficient, interphase convection heat transfer coefficient and permeability are selected, and then a porous medium flow heat transfer calculation model is constructed to achieve high-precision prediction of the flow and temperature distribution inside the core. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 This is a flow chart of a method for simulating core flow and heat transfer in a pebble bed high-temperature gas-cooled reactor according to the present invention; Figure 2 The figure is a schematic diagram of the overall composition structure of a pebble bed high temperature gas-cooled reactor core flow and heat transfer simulation method of the present invention. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0018] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0019] The present invention is described in detail with reference to schematic diagrams. For ease of illustration, cross-sectional views of device structures may be partially enlarged and not to scale when describing embodiments of the present invention. Furthermore, the schematic diagrams are merely illustrative and should not limit the scope of the present invention. Furthermore, in actual production, the three-dimensional dimensions of length, width, and depth should be included.

[0020] In the description of the present invention, it should be noted that the terms "upper, lower, inner, and outer" and other references to orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first, second, or third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] In this disclosure, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they may refer to fixed, removable, or integral connections. They may also refer to mechanical, electrical, or direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this disclosure.

[0022] Example 1 In order to more realistically reflect the influence of core structure on flow and heat transfer behavior, a more reasonable method is needed to obtain the spatial distribution of porosity inside the core.

[0023] The Discrete Element Method (DEM) is a numerical technique for simulating the motion of large numbers of discrete particles. It can simulate the actual accumulation and stabilization of fuel spheres in the reactor core while accounting for contact mechanics. DEM simulations reveal the distribution of fuel spheres at various locations within the core and the local porosity distribution. These insights serve as input for selecting a flow resistance and heat transfer correlation that matches the porosity, thereby improving the accuracy of flow and heat transfer modeling within the pebble bed core.

[0024] The present invention provides a method for simulating the flow and heat transfer in the core of a pebble-bed high-temperature gas-cooled reactor, specifically a method for simulating the flow and heat transfer in the core of a pebble-bed high-temperature gas-cooled reactor based on a discrete element method-porous medium model. This method simulates the stacking process of fuel balls in the core using the discrete element method to obtain a true stacking structure and spatially distributed porosity. Combined with the porosity changes in the modeling area, empirical correlations such as the resistance coefficient, interphase convection heat transfer coefficient, and permeability that match the modeling area are selected to construct a porous medium flow and heat transfer calculation model, thereby achieving high-precision prediction of the flow and temperature distribution inside the core. Figure 1 , including the following steps: S1: The material parameters and contact parameters of the fuel spheres are selected based on the actual operating conditions of the pebble bed high temperature gas-cooled reactor core.

[0025] Specifically, the relevant parameters of the pebble-bed high-temperature gas-cooled reactor core model can be divided into two categories: fuel sphere material parameters and contact parameters. Fuel sphere material parameters include the diameter, number, density, Poisson's ratio, and Young's modulus of the fuel spheres; contact parameters include the normal restitution coefficient, tangential restitution coefficient, static friction coefficient, and rolling friction coefficient. These parameters should be appropriately selected and set based on the specific core design requirements and operating conditions to ensure that the simulation results have good physical realism and engineering applicability.

[0026] S2: Based on the material parameters and contact parameters of the fuel balls, the natural accumulation process of the fuel balls is simulated by DEM to obtain the core model of the pebble bed high-temperature gas-cooled reactor.

[0027] Specifically, in the pebble bed high temperature gas-cooled reactor core model used for discrete element method simulation, a cylindrical container corresponding to the actual structural size of the core is first generated. Fuel balls are randomly generated on the top of the container, and the fuel balls fall freely under the action of gravity with an initial velocity of zero. After all the fuel balls fall into the container, the simulation continues for 20 seconds of physical time to dissipate the kinetic energy of the system, and finally a stable pebble bed stacking structure is formed. DEM is constructed based on Euler's law and Newton's second law, and is used to simulate the stacking behavior of fuel balls in the core. The method includes a contact model that describes the interaction between fuel balls and a motion model that describes the motion behavior of fuel balls. Among them, the contact model of the interaction between fuel balls decomposes the contact force into two components: normal elastic force and tangential elastic force, and solves them separately. The normal elastic force is calculated using Hertz theory, and the normal elastic force equation is: (1); Where, F n is the normal elastic force, is the equivalent elastic modulus, is the equivalent contact radius between fuel balls, is the normal overlap.

[0028] The tangential elastic force is calculated using the Mindlin method, and the tangential elastic force equation is: (2); Where, F t is the tangential elastic force, is the equivalent shear modulus, is the tangential overlap.

[0029] The energy dissipation during the contact process is described using the nonlinear damping model proposed by Tsuji. This model comprehensively considers the normal nonlinear contact and tangential friction and slip behavior between particles and is suitable for describing the dynamic behavior of multi-particle systems. Based on this, a nonlinear contact model (Hertz-Mindlin model) is formed. In the motion model describing the motion of the fuel spheres, each fuel sphere is regarded as a rigid discrete unit, and its motion behavior follows Newton's second law. The motion equation is: (3); (4); in: m is the mass of the fuel ball, v is the translational speed, w is the angular velocity, is the contact force, is gravity, I is the moment of inertia, T is the torque.

[0030] S3: Based on the core model of the pebble bed high-temperature gas-cooled reactor, the three-dimensional spatial coordinates of multiple fuel spheres are obtained, and the structure is reconstructed using the three-dimensional spatial coordinates of the multiple fuel spheres.

[0031] Specifically, the spatial distribution of fuel spheres within the reactor core, as simulated using the DEM method, is imported into 3D modeling software (such as SpaceClaim) to reconstruct the pebble bed structure. Specifically, the DEM method is used to obtain the 3D coordinate data of each fuel sphere in the HTGR pebble bed. The pebble bed geometry model is then automatically reconstructed using the scripting function of the 3D modeling software SpaceClaim.

[0032] S4: Obtain the porosity distribution of the pebble bed high-temperature gas-cooled reactor core based on the geometric model.

[0033] Obtaining the porosity distribution in the core means that after completing the three-dimensional structure reconstruction, the core model is rationally divided into spaces based on the spatial arrangement information of the spheres, and the volume fraction of the fuel spheres in each sub-region is counted. The local porosity is then calculated (local porosity = 1 - local volume fraction of the fuel spheres), thereby realizing the extraction of the spatial distribution of the porosity inside the core.

[0034] S5: Obtaining porous media parameters based on porosity distribution.

[0035] Specifically, the resistance coefficient is determined according to the porosity distribution in the core, and an empirical model of the resistance coefficient considering the wall effect is adopted. The calculation formula is: (5); (6); (7); in, is the drag coefficient, Represents porosity, Re p represents the Reynolds number based on the ball diameter. The empirical formula is applicable to , .

[0036] Interphase convection heat transfer coefficient α sf The calculation is based on the porosity distribution in the core, and the interphase convective heat transfer coefficient is calculated by the specific surface area. and unit convection heat transfer coefficient Determine by multiplying: (8); in: λ f is the thermal conductivity of the fluid, d p is the diameter of the fuel ball,S is the porosity function, used to correct the specific surface area, Nu p is the Nusselt number based on the fuel sphere diameter.

[0037] The specific surface area is calculated using the modified fitting formula: (9); (10); The fitting formula is applicable to , .

[0038] The permeability is obtained based on the porosity distribution in the core, according to the empirical formula , A =160 is obtained.

[0039] S6: Construction of porous media model for flow and heat transfer calculation in the core.

[0040] Specifically, a porous media model for flow and heat transfer calculations in the core region is constructed, and the flow and heat transfer behavior of the coolant in the reactor core region are modeled and described in the form of volume-averaged governing equations. This model is based on volume-averaged theory and assumes that the porous media flow in the computational domain is incompressible laminar flow. The model equations include: (11); (12); (13); (14); in, u For speed, is the density, t is the time variable, is the velocity vector, is the porosity, is the gradient operator, μ is the dynamic viscosity, f x for x Directional physical strength, for x The partial derivative operator in the direction, p is the fluid pressure, α is the permeability, is the drag coefficient, is the density of the fluid, c p，f is the constant pressure specific heat capacity of the fluid, T f is the fluid temperature, λf is the thermal conductivity of the fluid, α sf is the interphase convective heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity of the solid at constant pressure, λ s is the solid thermal conductivity, Generate heat for the fuel ball.

[0041] By solving the porous media equations, the flow and temperature distribution inside the core pebble bed can be obtained.

[0042] Example 2 The present invention provides a pebble bed type high temperature gas-cooled reactor core flow and heat transfer simulation system based on a discrete element method-porous medium model, comprising a selection module, a generation module, a reconstruction module and a calculation module.

[0043] The selection module is used to select the material parameters and contact parameters of the fuel balls based on the actual operating conditions of the pebble bed high temperature gas-cooled reactor core.

[0044] The generation module is used to simulate the natural accumulation process of fuel spheres using DEM based on the material parameters and contact parameters of the fuel spheres to obtain a pebble-bed high-temperature gas-cooled reactor core model. During the natural accumulation process, a cylindrical container corresponding to the actual structural dimensions of the pebble-bed high-temperature gas-cooled reactor core is generated, and multiple fuel spheres are randomly generated and freely fall on top of the cylindrical container. After all the fuel spheres fall into the container, the system kinetic energy is dissipated within a set time to obtain the pebble-bed high-temperature gas-cooled reactor core model. The reconstruction module is used to obtain the three-dimensional spatial coordinates of multiple fuel balls based on the pebble bed high-temperature gas-cooled reactor core model, perform structural reconstruction through the three-dimensional spatial coordinates of multiple fuel balls, obtain the corresponding geometric model, and obtain the porosity distribution of the pebble bed high-temperature gas-cooled reactor core based on the geometric model.

[0045] The calculation module is used to obtain the porous media parameters related to porosity according to the porosity distribution, construct the porous media equations based on the porous media parameters, solve the porous media equations, and obtain the flow and temperature distribution in the core of the pebble bed high-temperature gas-cooled reactor.

[0046] Reference Figure 2 The system also includes a core parameter input module for a pebble-bed high-temperature gas-cooled reactor, a DEM modeling and pebble-bed structure generation module, a pebble-bed structure reconstruction and porosity distribution extraction module, a multi-physical parameter calculation module, and a porous medium modeling module for flow and heat transfer in the core.

[0047] The core parameter input module for the pebble-bed high-temperature gas-cooled reactor selects the material and contact model parameters of the fuel spheres based on the core structural design and operating conditions, serving as the input for discrete element method simulations of pebble bed stacking behavior. The DEM modeling and pebble bed structure generation module simulates the free stacking of fuel spheres under gravity using the discrete element method to generate a stable pebble bed structure. The pebble bed structure reconstruction and porosity distribution extraction module imports the stacking results into 3D modeling software, reconstructs the pebble bed geometry, performs spatial partitioning, and calculates the porosity of each region. The multi-physics parameter calculation module uses empirical models to calculate parameters such as the resistance coefficient, interphase convective heat transfer coefficient, and permeability based on the extracted spatial distribution of porosity. The porous medium modeling module for in-core flow and heat transfer constructs the Navier-Stokes equations (NS) in the form of porous media to simulate the flow and heat transfer processes in the core and obtain the temperature and flow field distribution.

[0048] Furthermore, the core parameter input module for the pebble-bed high-temperature gas-cooled reactor is used to determine the physical and contact parameters related to the fuel spheres before generating the pebble bed structure in the simulated high-temperature gas-cooled reactor core, combining core structural design requirements with actual operating conditions. Fuel sphere material parameters include diameter, number, density, Poisson's ratio, and Young's modulus. Contact model parameters include normal restitution coefficient, tangential restitution coefficient, static friction coefficient, and rolling friction coefficient.

[0049] The DEM Modeling and Pebble Bed Structure Generation module uses the discrete element method to simulate the free accumulation of fuel spheres in a gravity field, generating a stable core pebble bed structure. This module uses the fuel sphere material and contact parameters provided by the Key Parameter Selection module as input to establish a mechanical model for the interactions between the spheres and between the spheres and the container walls. It employs the Hertz-Mindlin nonlinear contact model, which calculates the normal elastic force using Hertz theory, the tangential elastic force using the Mindlin method, and the energy dissipation using the nonlinear damping term proposed by Tsuji. During the simulation, fuel spheres are initially randomly distributed at the top of the core cylinder and fall freely under gravity with an initial velocity of zero. After multiple contacts with other fuel spheres and the wall, their kinetic energy gradually decays through contact dissipation, ultimately forming a stable accumulation state. This module obtains the stable position coordinates of each fuel sphere in three-dimensional space, providing high-precision input data for subsequent geometry reconstruction and porosity distribution extraction.

[0050] The pebble bed structure reconstruction and porosity distribution extraction module uses the scripting capabilities of the 3D modeling software SpaceClaim to automatically reconstruct the pebble bed geometry based on the 3D spatial coordinate data of the fuel spheres obtained through discrete element simulation. This module imports each fuel sphere into the modeling environment as an independent geometric entity, reconstructing a 3D pebble bed model consistent with the actual core structure. After completing the geometric reconstruction, the entire model is divided into multiple subregions. Within each subregion, the ratio of the volume occupied by the spheres to the total volume is calculated to determine the local porosity of that region.

[0051] The multi-physics parameter calculation module is used to calculate the local porosity distribution of the core based on the pebble bed structure reconstruction and porosity distribution extraction modules. It uses multiple empirical correlation models to calculate key transfer parameters in the porous media area related to porosity, including resistance coefficient, interphase convective heat transfer coefficient, and permeability.

[0052] The porous media modeling module for in-core flow and heat transfer calculations is used to construct a porous media model within the core region of a high-temperature gas-cooled reactor based on the porosity distribution and its corresponding local transfer parameters, enabling coupled simulation of the flow and heat transfer processes. This module uses volume-averaged theory to construct the control equations, establishing a control system including the mass conservation equation, momentum conservation equation, and energy conservation equation. The model equations are: ; ; ; ; in, u for speed; ρ is the fluid density; p is the fluid pressure; c p is the specific heat capacity of the fluid at constant pressure; T s is the solid temperature; T f is the fluid temperature; λ s is the thermal conductivity of the solid; Generate heat for the fuel ball; μ is the dynamic viscosity; is the drag coefficient; α is the permeability. By solving the above equations in this module, we can obtain the flow and temperature distribution within the core pebble bed. The first equation is the mass conservation equation, the second is the momentum conservation equation, and the third and fourth are the energy conservation equations.

[0053] The present invention uses the DEM method to accurately capture the stacking behavior of fuel balls and improve the physical reality of porosity extraction; combines geometric modeling with empirical parameter models to achieve effective mapping of structural parameters to thermal models; and constructs a porous medium model for flow and heat transfer simulation to efficiently and reliably predict the flow and temperature distribution inside the core of a gas-cooled reactor.

[0054] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0055] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A method for simulating core flow and heat transfer in a pebble bed high temperature gas-cooled reactor, characterized in that: The following steps are involved: The material parameters and contact parameters of the fuel spheres are selected based on the actual operating conditions of the pebble bed high temperature gas-cooled reactor core; Based on the material parameters and contact parameters of the fuel spheres, the natural accumulation process of the fuel spheres is simulated through DEM to obtain a pebble bed high-temperature gas-cooled reactor core model. During the natural accumulation process, a cylindrical container corresponding to the actual structural dimensions of the pebble bed high-temperature gas-cooled reactor core is generated, and multiple fuel spheres are randomly generated and freely fall on the top of the cylindrical container. After all the fuel spheres fall into the container, the system kinetic energy is dissipated within a set time to obtain the pebble bed high-temperature gas-cooled reactor core model. The three-dimensional spatial coordinates of multiple fuel spheres are obtained based on the core model of the pebble bed high-temperature gas-cooled reactor. The structure is reconstructed using the three-dimensional spatial coordinates of the multiple fuel spheres to obtain the corresponding geometric model. The porosity distribution of the pebble bed high-temperature gas-cooled reactor core is obtained based on the geometric model. Porosity-related porous media parameters are obtained according to the porosity distribution. A porous media equation group is constructed based on the porous media parameters. The porous media equation group is solved to obtain the flow and temperature distribution in the core of the pebble bed high-temperature gas-cooled reactor.

2. The method for simulating core flow and heat transfer of a pebble bed high temperature gas-cooled reactor according to claim 1, wherein: In the process of simulating the natural accumulation of fuel balls by DEM, the interaction between the fuel balls is described by the contact model, and the motion behavior of the fuel balls is described by the motion model; the contact model includes the normal elastic force equation, the tangential elastic force equation and the nonlinear contact model, and the motion model is a motion equation based on Newton's second law.

3. The method for simulating core flow and heat transfer of a pebble bed high temperature gas-cooled reactor according to claim 1, wherein: The method of obtaining the porosity distribution of the core of a pebble bed high temperature gas-cooled reactor based on a geometric model comprises the following steps: Obtain spatial arrangement information of multiple fuel balls based on a geometric model; The geometric model is spatially divided into multiple sub-regions, and the volume fraction of the fuel spheres in each sub-region is calculated. The local porosity of the sub-region is obtained based on the volume fraction occupied by the fuel spheres.

4. The method for simulating core flow and heat transfer of a pebble bed high temperature gas-cooled reactor according to claim 1, wherein: The porous medium parameters include resistance coefficient, interphase convection heat transfer coefficient and permeability.

5. The method for simulating core flow and heat transfer of a pebble bed high temperature gas-cooled reactor according to claim 1, wherein: The porous media equations are specifically as follows: ； ； ； ； Where, u For speed, is the density, t is the time variable, is the velocity vector, is the porosity, is the gradient operator, μ is the dynamic viscosity, f x for x Directional physical strength, for x The partial derivative operator in the direction, p is the fluid pressure, α is the permeability, is the drag coefficient, is the density of the fluid, c p，f is the constant pressure specific heat capacity of the fluid, T f is the fluid temperature, λ f is the thermal conductivity of the fluid, α sf is the interphase convective heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity of the solid at constant pressure, λ s is the solid thermal conductivity, Generate heat for the fuel ball.

6. The method for simulating core flow and heat transfer of a pebble bed high temperature gas-cooled reactor according to claim 1, wherein: The fuel ball material parameters include the diameter, quantity, density, Poisson's ratio and Young's modulus of the fuel balls; the contact parameters include the normal restitution coefficient, tangential restitution coefficient, static friction coefficient and rolling friction coefficient.

7. A core flow and heat transfer simulation system for a pebble bed high temperature gas-cooled reactor, characterized in that: include: A selection module is used to select the material parameters and contact parameters of the fuel spheres based on the actual operating conditions of the pebble-bed high-temperature gas-cooled reactor core; A generation module is used to simulate the natural accumulation process of fuel spheres using DEM based on the material parameters and contact parameters of the fuel spheres to obtain a pebble bed high-temperature gas-cooled reactor core model. During the natural accumulation process, a cylindrical container corresponding to the actual structural dimensions of the pebble bed high-temperature gas-cooled reactor core is generated, and multiple fuel spheres are randomly generated and freely fall on top of the cylindrical container. After all the fuel spheres fall into the container, the system kinetic energy is dissipated within a set time to obtain the pebble bed high-temperature gas-cooled reactor core model. A reconstruction module is used to obtain the three-dimensional spatial coordinates of multiple fuel spheres based on the pebble bed high-temperature gas-cooled reactor core model, perform structural reconstruction using the three-dimensional spatial coordinates of the multiple fuel spheres to obtain a corresponding geometric model, and obtain the porosity distribution of the pebble bed high-temperature gas-cooled reactor core based on the geometric model; The calculation module is used to obtain the porous medium parameters related to porosity based on the porosity distribution, construct the porous medium equation group based on the porous medium parameters, solve the porous medium equation group, and obtain the flow and temperature distribution in the core of the pebble bed high-temperature gas-cooled reactor.

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