A method and system for simulating the flow and heat transfer in the core of a pebble bed high temperature gas cooled reactor

Abstract

The application discloses a kind of pebble bed type high temperature gas cooled reactor core flow heat transfer simulation method and system, it is related to nuclear reactor core internal flow heat transfer analysis technical field, including the following steps: based on the material parameters and contact parameters of fuel ball, the natural accumulation process of fuel ball is simulated by DEM, obtain pebble bed type high temperature gas cooled reactor core model;The structure reconstruction is carried out through the three-dimensional space coordinates of multiple fuel balls, obtain corresponding geometric model, obtain the porosity distribution of pebble bed type high temperature gas cooled reactor core based on geometric model;According to the porosity distribution, obtain the porous medium parameter related to porosity, construct porous medium equation set based on porous medium parameter, solve porous medium equation set, obtain the flow and temperature distribution in pebble bed type high temperature gas cooled reactor core.The application simulates the accumulation process of fuel ball in core by DEM, obtains real accumulation structure and porosity, realizes high-precision prediction to the flow and temperature distribution in core.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear reactor core flow and heat transfer analysis, in particular to a pebble bed type high temperature gas cooled reactor core flow and heat transfer simulation method and system. BACKGROUND

[0002] The pebble bed modular high temperature gas cooled reactor nuclear power plant uses helium as the coolant, graphite as the moderator, and graphite spherical matrix dispersed with TRISO coated particles as the fuel element. The solid and elastic coated particle fuel form enables the gas cooled reactor to operate at high temperature for a long time. Through appropriate selection of the coolant and structural material, the pebble bed reactor can operate at a higher temperature compared to other reactors, and therefore the pebble bed type high temperature gas cooled reactor has the characteristics of good inherent safety, high core outlet temperature, and wide application scenarios.

[0003] Since the pebble bed core is composed of a large number of fuel spheres, it presents a complex irregular packing structure, and the spatial distribution of the internal fluid channels is highly uneven. This structure leads to strong spatial variability in the flow and heat transfer behavior of the coolant inside the core, which has a significant impact on the temperature distribution, local cooling efficiency, and safety margin. Therefore, accurately modeling and predicting the flow and heat transfer characteristics in the pebble bed core is a core content of the high temperature gas cooled reactor thermal safety design and operation analysis.

[0004] In actual engineering analysis, to simplify the analysis, the flow and heat transfer in the pebble bed core is often equivalent to a non-thermal equilibrium porous medium flow and heat transfer process, and the influence of the packed particles is considered by introducing equivalent resistance terms and inter-phase heat transfer terms. This kind of method highly depends on the selection of empirical correlations and the accuracy of porosity. In traditional analysis, the porosity is often determined by simple packing, face-centered packing, body-centered packing, or a combination of several assumptions. These packing methods are not the actual packing method of the fuel spheres in the core, and therefore cannot reflect the differences in local area porosity. At the same time, the selected empirical formulas such as resistance coefficient and inter-phase convective heat transfer coefficient do not match the actual structure, which reduces the reliability and prediction accuracy of the flow and heat transfer analysis. SUMMARY

[0005] Based on the defects of the existing prior art, the present application provides a pebble bed type high temperature gas cooled reactor core flow and heat transfer simulation method and system, which solves the problem that the existing porosity is often determined by simple packing, face-centered packing, body-centered packing, or a combination of several assumptions. These packing methods are not the actual packing method of the fuel spheres in the core, and therefore cannot reflect the differences in local area porosity. At the same time, the selected empirical formulas such as resistance coefficient, inter-phase convective heat transfer coefficient, etc. do not match the actual structure, which reduces the reliability and prediction accuracy of the flow and heat transfer analysis.

[0006] The present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides a method for simulating the flow and heat transfer in a pebble bed high temperature gas cooled reactor core, comprising the following steps:

[0008] Selecting 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;

[0009] Simulating the natural accumulation process of the fuel spheres by 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; in the natural accumulation process, a cylindrical container corresponding to the actual structural size of the pebble bed high temperature gas cooled reactor core is generated, and a plurality of fuel spheres falling freely are randomly generated at 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;

[0010] Obtaining the three-dimensional spatial coordinates of the plurality of fuel spheres based on the pebble bed high temperature gas cooled reactor core model, reconstructing the structure based on the three-dimensional spatial coordinates of the plurality of fuel spheres to obtain a corresponding geometric model, and obtaining the porosity distribution of the pebble bed high temperature gas cooled reactor core based on the geometric model;

[0011] Obtaining the porous medium parameters related to the porosity based on the porosity distribution, constructing a porous medium equation set based on the porous medium parameters, and solving the porous medium equation set to obtain the flow and temperature distribution in the pebble bed high temperature gas cooled reactor core.

[0012] Preferably, in the natural accumulation process of the fuel spheres simulated by DEM, the interaction between the fuel spheres is described by a contact model, and the motion behavior of the fuel spheres is described by a motion model; the contact model comprises 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.

[0013] Preferably, the porosity distribution of the pebble bed high temperature gas cooled reactor core is obtained based on the geometric model, comprising the following steps:

[0014] Obtaining the spatial arrangement information of the plurality of fuel spheres based on the geometric model;

[0015] Dividing the geometric model in space to obtain a plurality of sub-regions, and counting the volume fraction of the fuel spheres in each sub-region;

[0016] Obtaining the local porosity of the sub-region based on the volume fraction of the fuel spheres.

[0017] Preferably, the porous medium parameters comprise a drag coefficient, an interfacial heat transfer coefficient and a permeability.

[0018] Preferably, the porous medium equation set is specifically as follows:

[0019] ;

[0020] ;

[0021] ;

[0022] ;

[0023] wherein, u is the velocity, 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 is the x body force term in the x-direction, is the x partial derivative operator in the x-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 specific heat capacity at constant pressure of the fluid, T f is the fluid temperature, λ f is the thermal conductivity of the fluid, α sf is the interfacial heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity at constant pressure of the solid, λ s is the thermal conductivity of the solid, is the fuel pellet heat generation rate.

[0024] Preferably, the fuel pellet material parameters include diameter, number, density, Poisson's ratio and Young's modulus of the fuel pellet; and the contact parameters include normal restitution coefficient, tangential restitution coefficient, static friction coefficient and rolling friction coefficient.

[0025] In a second aspect, the present application provides a simulation system for core flow and heat transfer of a pebble bed high temperature gas cooled reactor, comprising:

[0026] a selection module configured to select material parameters and contact parameters of the fuel pellets based on actual operation conditions of the core of the pebble bed high temperature gas cooled reactor;

[0027] The generating module is used for simulating a natural accumulation process of the fuel balls based on the material parameters and the contact parameters of the fuel balls through DEM to obtain a pebble bed high temperature gas cooled reactor core model; in the natural accumulation process, a cylindrical container corresponding to an actual structure size of the pebble bed high temperature gas cooled reactor core is generated, and a plurality of fuel balls in free falling are randomly generated on the top of the cylindrical container; after all the fuel balls fall into the container, kinetic energy dissipation of the system is performed within a set time to obtain the pebble bed high temperature gas cooled reactor core model;

[0028] The reconstructing module is used for obtaining three-dimensional space coordinates of the plurality of fuel balls based on the pebble bed high temperature gas cooled reactor core model, reconstructing a structure based on the three-dimensional space coordinates of the plurality of fuel balls to obtain a corresponding geometric model, and obtaining a porosity distribution of the pebble bed high temperature gas cooled reactor core based on the geometric model.

[0029] The calculating module is used for obtaining a plurality of porous medium parameters related to the porosity according to the porosity distribution, constructing a porous medium equation group based on the porous medium parameters, and solving the porous medium equation group to obtain flow and temperature distribution in the pebble bed high temperature gas cooled reactor core.

[0030] Compared with the prior art, the above at least one technical solution of the present application can achieve the following beneficial effects:

[0031] The present application firstly selects the material parameters and the contact parameters of the fuel balls based on the actual operation condition of the pebble bed high temperature gas cooled reactor core, and simulates the natural accumulation process of the fuel balls based on the material parameters and the contact parameters of the fuel balls. In the natural accumulation process, a cylindrical container corresponding to the actual structure size of the pebble bed high temperature gas cooled reactor core is generated, and a plurality of fuel balls in free falling are randomly generated on the top of the cylindrical container, which accurately simulates the process of the fuel balls in free falling under the action of gravity, and finally kinetic energy dissipation of the system is performed within a set time to obtain a stable pebble bed high temperature gas cooled reactor core model. The present application simulates the accumulation process of the fuel balls in the core through the discrete element method to obtain a real accumulation structure and a spatial distribution porosity. In combination with the porosity variation of the modeling region, the empirical correlations of the resistance coefficient, the interfacial heat transfer coefficient and the permeability rate and the like which are matched with the porosity variation are selected to construct a porous medium flow and heat transfer calculation model, and high-precision prediction of the flow and temperature distribution in the core is realized. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, brief descriptions will be given to the drawings needed to be used in the embodiments or prior art descriptions. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0033] Figure 1 A flow chart of a ball bed type high temperature gas cooled reactor core flow heat transfer simulation method of the present application;

[0034] Figure 2 A schematic diagram of the overall composition structure of a ball bed type high temperature gas cooled reactor core flow heat transfer simulation method of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0036] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other manners different from those described herein, and a person of ordinary skill in the art can make similar generalizations without departing from the concept of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0037] Secondly, the "one embodiment" or "embodiment" referred to herein means that a specific feature, structure or characteristic can be included in at least one implementation of the present application. The "in one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an independent or selective embodiment that excludes other embodiments.

[0038] The present application is described in detail in combination with the schematic diagram, and when the embodiments of the present application are described, the cross-sectional view of the device structure will be partially enlarged without the general proportion for the convenience of description, and the schematic diagram is only an example, which should not limit the protection scope of the present application herein. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in actual manufacturing.

[0039] Meanwhile, in the description of the present application, it should be noted that the positions or relationships indicated by the terms "up, down, inside and outside" are based on the positions or relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present application. In addition, the terms "first, second or third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0040] Unless otherwise defined, the terms "mounting, connecting, associating" in the present application should be interpreted broadly, for example: it can be fixed connection, detachable connection or integral connection; it can also be mechanical connection, electrical connection or direct connection, it can also be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0041] Embodiment 1

[0042] In order to more truly reflect the influence of the core structure on the flow and heat transfer behavior, a more reasonable method is needed to obtain the spatial distribution of the porosity inside the core.

[0043] The discrete element method (DEM) is a numerical method for simulating the motion of a large number of discrete particles, which can simulate the real accumulation and stabilization process of fuel balls in the core under the consideration of contact mechanics. Through DEM simulation, the arrangement of fuel balls and the local porosity distribution at each position inside the core can be obtained, which can be used as input to select the flow resistance and heat transfer correlation that matches the porosity, thereby improving the accuracy of the flow and heat transfer modeling in the pebble bed reactor core.

[0044] The present application provides a kind of pebble bed high temperature gas cooled reactor core flow and heat transfer simulation method, specifically relates to a kind of pebble bed high temperature gas cooled reactor core flow and heat transfer simulation method based on discrete element method-porous medium model, the method is simulated by discrete element method The accumulation process of fuel balls in the core, the real accumulation structure and spatial distribution of porosity are obtained;Combined with the porosity variation of the modeling area, the resistance coefficient, the interfacial heat transfer coefficient and the permeability of the empirical correlation matched with it are selected, and then the porous medium flow and heat transfer calculation model is constructed, the high-precision prediction of the flow and temperature distribution inside the core is realized. Figure 1 , comprising the following steps:

[0045] S1: selecting 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.

[0046] Specifically, the related parameters of the pebble bed high temperature gas cooled reactor core model can be divided into two categories: fuel ball material parameters and contact parameters. The fuel ball material parameters include the diameter, number, density, Poisson's ratio and Young's modulus of the fuel ball; the contact parameters include the normal restitution coefficient, the tangential restitution coefficient, the static friction coefficient and the rolling friction coefficient, etc. The above parameters should be reasonably selected and set according to the specific design requirements and operating conditions of the core, so as to ensure that the results obtained in the simulation process have good physical reality and engineering applicability.

[0047] S2: Based on the material parameters and contact parameters of the fuel spheres, the natural accumulation process of the fuel spheres is simulated by DEM to obtain a pebble bed high temperature gas cooled reactor core model.

[0048] Specifically, in the pebble bed high temperature gas cooled reactor core model for discrete element method simulation, a cylindrical container corresponding to the actual structure size of the core is first generated. Fuel spheres are randomly generated at the top of the container, and the fuel spheres freely fall under the action of gravity under the condition that the initial velocity is zero. After all the fuel spheres 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 accumulation structure is formed. DEM is based on Euler's law and Newton's second law, and is used to simulate the accumulation behavior of the fuel spheres in the core. The method includes a contact model describing the interaction between the fuel spheres and a motion model describing the motion behavior of the fuel spheres. Among them, the contact model between the fuel spheres is divided into two components, i.e. normal elastic force and tangential elastic force, which are solved respectively. The normal elastic force is calculated by Hertz theory, and the normal elastic force equation is:

[0049] (1);

[0050] In the formula, F n is the normal elastic force, is the equivalent elastic modulus, is the equivalent contact radius between the fuel spheres, is the normal overlap.

[0051] The tangential elastic force is calculated by Mindlin method, and the tangential elastic force equation is:

[0052] (2);

[0053] In the formula, F t is the tangential elastic force, is the equivalent shear modulus, is the tangential overlap.

[0054] The energy dissipation in the contact process is described by the nonlinear damping model proposed by Tsuji, which takes into account the normal nonlinear contact and tangential friction slip behavior between particles, and is suitable for describing the dynamic behavior of a multi-particle system. Accordingly, 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 element, and its motion behavior follows Newton's second law, and the motion equation is:

[0055] (3);

[0056] (4);

[0057] wherein: m is the mass of the fuel sphere, v is the translational velocity, w is the angular velocity, is the contact force, is the gravity, I is the moment of inertia, T is the torque.

[0058] S3: Obtain three-dimensional spatial coordinates of a plurality of fuel spheres based on a pebble bed type high temperature gas cooled reactor core model, and reconstruct a structure based on the three-dimensional spatial coordinates of the plurality of fuel spheres.

[0059] Specifically, the spatial distribution of the fuel spheres in the core obtained by the DEM method is imported into a three-dimensional modeling software (for example, SpaceClaim) for reconstruction of the pebble bed structure. Specifically, three-dimensional spatial coordinate data of each fuel sphere in the pebble bed of the high temperature gas cooled reactor is obtained by the DEM method, and the script function of the three-dimensional modeling software SpaceClaim is used to realize automatic reconstruction of the pebble bed geometric model.

[0060] S4: Obtain the porosity distribution of the pebble bed type high temperature gas cooled reactor core based on the geometric model.

[0061] The obtaining of the porosity distribution in the core refers to, after the three-dimensional structure reconstruction is completed, based on the spatial arrangement information of the spheres, reasonably dividing the core model in space, and statistically calculating the volume fraction of the fuel spheres in each sub-region, and then calculating the local porosity, local porosity = 1 - local volume fraction of fuel spheres, to realize the extraction of the spatial distribution of the porosity in the core.

[0062] S5: Obtain the porous medium parameters based on the porosity distribution.

[0063] Specifically, the drag coefficient is determined according to the porosity distribution in the core, and an empirical model of the drag coefficient considering the wall effect is used, and the calculation formula is:

[0064] (5);

[0065] (6);

[0066] (7);

[0067] wherein, is the drag coefficient, represents the porosity, Re p represents the Reynolds number based on the sphere diameter, and the empirical formula is applicable to , .

[0068] Interfacial convective heat transfer coefficient α sf The calculation is based on the porosity distribution in the core, and the interfacial convective heat transfer coefficient is determined by the product of the specific surface area and the unit convective heat transfer coefficient :

[0069] (8);

[0070] Wherein: λ f is the thermal conductivity of the fluid, d p is the diameter of the fuel sphere, S is the porosity function used to correct the specific surface area, Nu p is the Nusselt number based on the diameter of the fuel sphere.

[0071] The calculation of the specific surface area uses a modified fitting formula:

[0072] (9);

[0073] (10);

[0074] This fitting formula is applicable to , .

[0075] According to the permeability obtained from the porosity distribution in the core, the permeability is obtained according to the empirical formula , A =160.

[0076] S6: Construction of porous medium model for flow and heat transfer calculation in the core.

[0077] Specifically, a porous medium model for flow and heat transfer calculation in the core region is constructed, and the flow and heat transfer behavior of the coolant in the reactor core region is modeled and described in the form of volume-averaged control equation. Based on the volume-averaged theory, the model assumes that the flow of the porous medium in the calculation domain is incompressible laminar flow, and the model equations include:

[0078] (11);

[0079] (12);

[0080] (13);

[0081] (14);

[0082] Wherein, u is the velocity, 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 is x is the body force term in the direction, is x is 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 specific heat capacity at constant pressure of the fluid, T f is the fluid temperature, λ f is the thermal conductivity of the fluid, α sf is the interfacial heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity at constant pressure of the solid, λ s is the thermal conductivity of the solid, is the heat generation rate of the fuel sphere.

[0083] By solving the porous medium equation set, the flow and temperature distribution in the core of the pebble bed high temperature gas cooled reactor can be obtained.

[0084] Example 2

[0085] The application provides a pebble bed high temperature gas cooled reactor core flow and heat transfer simulation system based on a discrete element method-porous medium model, which comprises a selection module, a generation module, a reconstruction module and a calculation module.

[0086] The selection module is used for selecting material parameters and contact parameters of fuel spheres based on actual operation conditions of the pebble bed high temperature gas cooled reactor core.

[0087] The generation module is used for simulating a natural accumulation process of the fuel spheres by DEM based on the material parameters and the contact parameters of the fuel spheres, so as to obtain a pebble bed high temperature gas cooled reactor core model; in the natural accumulation process, a cylindrical container corresponding to an actual structure size of the pebble bed high temperature gas cooled reactor core is generated, and a plurality of fuel spheres falling freely are randomly generated on the top of the cylindrical container; after all the fuel spheres fall into the container, system kinetic energy dissipation is performed within a set time, so as to obtain the pebble bed high temperature gas cooled reactor core model.

[0088] The reconstruction module is configured to obtain three-dimensional spatial coordinates of a plurality of fuel spheres based on a pebble bed high-temperature gas-cooled reactor core model, reconstruct a structure based on the three-dimensional spatial coordinates of the plurality of fuel spheres, and obtain a corresponding geometric model, and obtain a porosity distribution of the pebble bed high-temperature gas-cooled reactor core based on the geometric model.

[0089] The calculation module is configured to obtain a plurality of porous medium parameters related to the porosity based on the porosity distribution, construct a plurality of porous medium equations based on the plurality of porous medium parameters, and solve the plurality of porous medium equations to obtain a flow and temperature distribution in the pebble bed high-temperature gas-cooled reactor core.

[0090] With reference to Figure 2 The system further includes a pebble bed high-temperature gas-cooled reactor core parameter input module, 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.

[0091] The pebble bed high-temperature gas-cooled reactor core parameter input module is configured to select material parameters and contact model parameters of the fuel spheres as input bases for simulating pebble bed accumulation behavior by the discrete element method, according to core structure design and operating conditions. The DEM modeling and pebble bed structure generation module is configured to simulate a free accumulation process of the fuel spheres under the action of gravity based on the discrete element method, and generate a stable pebble bed structure. The pebble bed structure reconstruction and porosity distribution extraction module is configured to import the accumulation results into a three-dimensional modeling software, reconstruct the pebble bed geometric structure, divide the space, and calculate the porosity of each region. The multi-physical parameter calculation module is configured to calculate parameters such as drag coefficient, interfacial heat transfer coefficient, and permeability, according to the extracted porosity spatial distribution, using an empirical model. The porous medium modeling module for flow and heat transfer in the core is configured to construct a N-S equation set (Navier-Stokes equations) in the form of a porous medium, simulate the flow and heat transfer process in the core, and obtain the temperature field and flow field distribution.

[0092] Further, the pebble bed high-temperature gas-cooled reactor core parameter input module is configured to determine the physical and contact parameters related to the fuel spheres before simulating the generation of the pebble bed structure of the high-temperature gas-cooled reactor core, in combination with the core structure design requirements and actual operating conditions. The material parameters of the fuel spheres include the diameter, number, density, Poisson's ratio, and Young's modulus of the fuel spheres, and the contact model parameters include the normal restitution coefficient, the tangential restitution coefficient, the static friction coefficient, and the rolling friction coefficient.

[0093] DEM modeling and pebble bed structure generation module is to simulate the process of fuel pebble free accumulation in the gravitational field by discrete element method, and generate stable core pebble bed structure. The module takes the fuel pebble material parameters and contact parameters provided by the key parameter selection module as input, establishes the interaction mechanics model between the pebbles and the container wall, adopts Hertz-Mindlin nonlinear contact model, that is, Hertz theory to calculate normal elastic force, Mindlin method to calculate tangential elastic force, and Tsuji's nonlinear damping term to calculate energy dissipation. In the simulation process, the fuel pebble is randomly distributed at the top of the core cylinder with initial speed of zero, and falls freely under the action of gravity. After multiple contacts with other fuel pebbles and wall, its kinetic energy is gradually attenuated through contact dissipation, and finally forms a stable accumulation state. Through this module, the stable position coordinates of each fuel pebble in three-dimensional space can be obtained, providing high-precision input data for subsequent geometric structure reconstruction and porosity distribution extraction.

[0094] Pebble bed structure reconstruction and porosity distribution extraction module is based on the three-dimensional coordinate data of fuel pebble obtained by discrete element simulation, and realizes the automatic reconstruction of pebble bed geometric structure by the script function of three-dimensional modeling software SpaceClaim. The module imports each fuel pebble as an independent geometric entity into the modeling environment, and reconstructs the three-dimensional model of the pebble bed consistent with the actual structure of the core. After completing the geometric structure reconstruction, the entire model is divided into multiple sub-regions, and the ratio of the volume occupied by the pebble to the total volume is calculated in each sub-region, thereby obtaining the local porosity of the region.

[0095] Multi-physical parameter calculation module is used to calculate the key transfer parameters in the porous medium region related to porosity based on the local porosity distribution of the core obtained by the pebble bed structure reconstruction and porosity distribution extraction module, including resistance coefficient, interfacial heat transfer coefficient and permeability, etc.

[0096] Porous medium modeling module for core flow and heat transfer calculation is used to construct the porous medium model in the core region of high temperature gas cooled reactor based on the porosity distribution and its corresponding local transfer parameters, and realize the coupled simulation of flow and heat transfer process. The module adopts volume average theory to construct control equations, and establishes a control system including mass conservation equation, momentum conservation equation and energy conservation equation, and the model equation is:

[0097] ;

[0098] ;

[0099] ;

[0100] ;

[0101] where, u is the velocity; ρ is the fluid density; p is the fluid pressure; c p is the fluid specific heat at constant pressure; T s is the solid temperature; T f is the fluid temperature; λ s is the solid thermal conductivity; is the fuel sphere heat generation rate; μ is the dynamic viscosity; is the drag coefficient; α is the permeability. By solving the above set of equations in this module, the flow and temperature distribution within the core pebble bed are obtained. The first is the mass conservation equation, the second is the momentum conservation equation, and the third and fourth are the energy conservation equations.

[0102] The present application accurately captures the fuel sphere packing behavior by the DEM method, improves the physical authenticity of porosity extraction; combines geometric modeling and empirical parameter model, realizes effective mapping of structure parameters to thermal model; by constructing the porous medium model of flow and heat transfer simulation, can efficiently and reliably predict the flow and temperature distribution inside the core of gas cooled reactor.

[0103] While the preferred embodiments of the application have been described, additional modifications and changes can occur to those skilled in the art once they learn of the basic creative principles disclosed herein. Therefore, the present application is to be interpreted in the broadest sense and is intended to cover all modifications and changes that fall within the scope of the present application.

[0104] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the present application. Thus, it is intended that the present application encompass all such modifications and changes as fall within the scope of the appended claims and their equivalents.

Claims

1. A method of simulation of flow and heat transfer in a pebble bed high temperature gas cooled reactor core, characterized in that, The method comprises the following steps: material parameters and contact parameters of the fuel spheres are selected based on the actual operation condition of the pebble bed high-temperature gas-cooled reactor core; a natural accumulation process of the fuel spheres is simulated by DEM based on the material parameters and the contact parameters of the fuel spheres, to obtain a pebble bed high-temperature gas-cooled reactor core model; in the natural accumulation process, a cylindrical container corresponding to the actual structural size of the pebble bed high-temperature gas-cooled reactor core is generated, and a plurality of fuel spheres in free falling are randomly generated on the top of the cylindrical container; after all the fuel spheres fall into the container, system kinetic energy dissipation is performed within a set time, to obtain the pebble bed high-temperature gas-cooled reactor core model; three-dimensional spatial coordinates of the plurality of fuel spheres are obtained based on the pebble bed high-temperature gas-cooled reactor core model, a corresponding geometric model is obtained by structure reconstruction based on the three-dimensional spatial coordinates of the plurality of fuel spheres, and a porosity distribution of the pebble bed 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, and the porous medium equation set is solved, to obtain the flow and temperature distribution of fluid in the pebble bed high-temperature gas-cooled reactor core; the porous medium equation set is specifically as follows: ； ； ； ； where u is the velocity, 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 is the x body force term in the direction, is the x partial derivative in the direction, p is the fluid pressure, α is the permeability, is the resistance coefficient, is the density of the fluid, c p，f is the specific heat capacity at constant pressure of the fluid, T f is the fluid temperature, λ f is the thermal conductivity of the fluid, α sf is the interfacial heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity at constant pressure of the solid, λ s is the thermal conductivity of the solid, is the fuel pellet heat generation rate.

2. A pebble bed high temperature gas cooled reactor core flow heat transfer simulation method as claimed in claim 1, characterized in that, in the natural accumulation process of the fuel spheres simulated by DEM, a contact model is used to describe the interaction between the fuel spheres, and a motion model is used to describe the motion behavior of the fuel spheres; the contact model comprises 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.

3. A pebble bed high temperature gas cooled reactor core flow and heat transfer simulation method as claimed in claim 1, characterized in that, the porosity distribution of the pebble bed high-temperature gas-cooled reactor core is obtained based on the geometric model, comprising the following steps: spatial arrangement information of the plurality of fuel spheres is obtained based on the geometric model; the geometric model is spatially divided to obtain a plurality of sub-regions, and the volume fraction of the fuel spheres in each sub-region is counted; the local porosity of the sub-region is obtained based on the volume fraction of the fuel spheres.

4. A pebble bed high temperature gas cooled reactor core flow and heat transfer simulation method as set forth in Claim 1, characterized in that, the porous medium parameters comprise a drag coefficient, an interfacial heat transfer coefficient and a permeability.

5. A pebble bed high temperature gas cooled reactor core flow heat transfer simulation method as defined in claim 1 wherein, the material parameters of the fuel spheres comprise the diameter, the number, the density, the Poisson's ratio and the Young's modulus of the fuel spheres; and the contact parameters comprise a normal restitution coefficient, a tangential restitution coefficient, a static friction coefficient and a rolling friction coefficient.

6. A pebble bed high temperature gas cooled reactor core flow heat transfer simulation system characterized by, comprise: a selection module configured to select material parameters and contact parameters of the fuel spheres based on the actual operation condition of the pebble bed high-temperature gas-cooled reactor core; a generation module configured to simulate a natural accumulation process of the fuel spheres by DEM based on the material parameters and the contact parameters of the fuel spheres, to obtain a pebble bed high-temperature gas-cooled reactor core model; in the natural accumulation process, a cylindrical container corresponding to the actual structural size of the pebble bed high-temperature gas-cooled reactor core is generated, and a plurality of fuel spheres in free falling are randomly generated on the top of the cylindrical container; after all the fuel spheres fall into the container, system kinetic energy dissipation is performed within a set time, to obtain the pebble bed high-temperature gas-cooled reactor core model; The reconstruction module is configured to obtain three-dimensional spatial coordinates of a plurality of fuel spheres based on a pebble bed high-temperature gas cooled reactor core model, reconstruct a structure based on the three-dimensional spatial coordinates of the plurality of fuel spheres, and obtain a corresponding geometric model, and obtain a porosity distribution of the pebble bed high-temperature gas cooled reactor core based on the geometric model. The calculation module is configured to obtain a plurality of porous medium parameters related to the porosity based on the porosity distribution, construct a plurality of porous medium equations based on the porous medium parameters, and solve the plurality of porous medium equations to obtain flow and temperature distribution of a fluid in the pebble bed high-temperature gas cooled reactor core. The plurality of porous medium equations are specifically as follows: ； ； ； ； where u is the velocity, 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 is the x body force term in the direction, is the x partial derivative 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 specific heat capacity at constant pressure of the fluid, T f is the fluid temperature, λ f is the thermal conductivity of the fluid, α sf is the interfacial heat transfer coefficient, T s is the solid temperature, is the density of the solid, c p，s is the specific heat capacity at constant pressure of the solid, λ s is the thermal conductivity of the solid, is the fuel pellet heat generation rate.

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