Clad failure analysis method of liquid sodium-cooled reactor metal fuel

Abstract

The invention discloses a cladding failure analysis method for metal fuel of a liquid sodium-cooled reactor, which comprises the following steps of: firstly, modeling a simulated reactor core according to structural parameters and operating parameters of the reactor, and calculating the component migration behavior of a metal fuel rod according to a one-dimensional diffusion model of a heat transport theory; by considering weakening of various chemical effects on mechanical strength of the cladding, a multi-group bubble fission gas behavior model is established to calculate fuel swelling and fission gas release amount, an improved ideal gas state equation is used to calculate fission gas cavity pressure, a fuel rod mechanical model is established to calculate mechanical behaviors of a fuel rod, and safety analysis parameters are calculated in real time. And judging whether the cladding fails or not according to a thermodynamic analysis result by adopting the cumulative life score. Compared with the prior art, the method has the advantages that various mechanism models are used, various factors influencing the cladding failure in the reactor irradiation process are considered, the stability and the calculation efficiency of a numerical algorithm are improved, and the cladding failure behavior of the metal fuel under serious accidents can be accurately and comprehensively simulated and analyzed.

Description

A method for analyzing the cladding failure of metallic fuel in liquid sodium-cooled reactors Technical Field

[0001] This invention belongs to the technical field of severe accident safety analysis in sodium-cooled fast reactors, specifically relating to a method for analyzing the failure of the cladding of metallic fuel in liquid sodium-cooled reactors. Background Technology

[0002] The early failure behavior of uranium alloy metallic fuel in severe accidents in liquid sodium-cooled reactors involves complex phenomena, including fuel component migration, fuel-cladding chemical interactions, fission gas release, fuel swelling, gas cavity pressurization, fuel axial extension, fuel-cladding mechanical interactions, and cladding corrosion. Current accident analysis software for liquid sodium-cooled reactors lacks sufficient simulation accuracy for this important physical phenomenon of metallic fuel failure; most models only provide empirical data or consider only the impact of certain phenomena on cladding failure. Current accident analysis software for liquid sodium-cooled reactors cannot clearly and comprehensively simulate this crucial phenomenon of metallic fuel cladding failure. Therefore, in-depth mechanistic research and the development of a dedicated module for liquid sodium-cooled reactor cladding failure are essential. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of the prior art by providing a failure analysis method for the cladding of liquid sodium-cooled reactor metal fuel, which solves the technical problem of failure of sodium-cooled fast reactor metal fuel cladding under the coupled effects of many factors such as heat transfer, irradiation, fuel-cladding mechanical action, fuel-cladding chemical action, and external corrosion.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a method for analyzing the cladding failure of metallic fuel in a liquid sodium-cooled reactor, comprising the following steps: S1, modeling the metallic fuel rods of the liquid sodium-cooled reactor; S2, inputting operating parameters into the metallic fuel rod model established in S1, recalculating the temperature and pressure of each node, and updating the physical property parameters of the nodes; S3, correcting the thermal conductivity of the fuel rods based on the fuel component distribution, pore distribution, and sodium permeability, and updating the temperature field of the fuel rods and coolant; S4, calculating the component migration of the metallic fuel, i.e., the migration amount of zirconium, based on the one-dimensional diffusion model of heat transport theory and the temperature field of the fuel rods and coolant in S3, and updating the fuel component distribution; S5, calculating the cladding failure. The brittle loss, eutectic and outer sodium corrosion of the cladding are analyzed to update the mechanical properties of the cladding, i.e. the mechanical properties corresponding to the effective thickness after the mechanical strength of the cladding is weakened; S6, a multi-bubble fission gas behavior model is established to obtain the fuel porosity distribution, fission gas release, fuel swelling and fission gas chamber pressure; S7, based on the fuel rod temperature field calculated in S3, the cladding mechanical properties calculated in S5 and the fuel swelling calculated in S6, the core-cladding contact stress, elastic strain and inelastic strain of the fuel rod are calculated; S8, combining the fuel rod and coolant temperature fields obtained in S3 and the core-cladding contact stress obtained in S7, the cladding lifetime fraction is calculated, and the failure criteria are used to determine whether the cladding has failed and predict the failure time and failure location of the cladding.

[0005] Specifically, in step S1, based on the structural parameters of the liquid sodium-cooled reactor metallic fuel, the computational domain is discretized into radial and axial nodes. A single fuel rod entity is represented by an independent flow channel, encompassing the fuel pellet, cladding structure, coolant corresponding to the channel, and the pipe walls of local components. A one-dimensional unidirectional flow is set within the flow channel, and the temperature fields of the fuel pellet, cladding, coolant, and support structure are distributed using a radial-axial two-dimensional spatial distribution model. The axial scale of the flow channel covers the entire length of the component (from the coolant inlet to the outlet), where the fuel region represents the fuel rod portion, including the fuel pellet, the upper and lower transition zones, and the gas chamber; other regions represent the upper and lower reflector layers of the fuel rod.

[0006] Specifically, in step S3, the correction for the fuel thermal conductivity is as follows: Where k0 is the thermal conductivity of the pre-fabricated fuel; P c This is the porosity correction factor for sodium permeation; p is the fuel porosity; k fThis is the corrected fuel thermal conductivity; W Zr W represents the mass fraction of zirconium. Pu P represents the mass fraction of plutonium. Na Sodium permeability; K Na ρ is the thermal conductivity of sodium; T is the fuel temperature.

[0007] Specifically, in step S4, the flux equation for Zr element migration is: in It is the Zr element migration flux. It refers to the elemental concentration of the fuel rods. It represents the percentage of Zr element concentration. It is the percentage of Pu element concentration. It is the diffusion coefficient of Zr element. It is heat transfer in a local phase. It is the universal gas constant.

[0008] Specifically, in step S5, it is assumed that the brittle loss layer, eutectic layer, and outer sodium corrosion layer cannot withstand mechanical stress, and the effective thickness of the cladding after the mechanical strength is weakened is: w eff It is the effective thickness of the casing, w wast w represents the brittle loss thickness of the cladding. eut w represents the eutectic thickness of the cladding. Na The thickness of sodium corrosion on the outer side of the cladding.

[0009] Specifically, in step S6, the amount of fission gas released is: Where C gr It is the amount of fission gas released; J gi ab is the gas diffusion rate of bubble i; ij It is the diffusion transfer rate from bubble i to bubble j; gab ij This is the transfer rate from bubble i to bubble j caused by the radial growth of bubble i.

[0010] Specifically, in step S6, in the multi-bubble fission gas behavior model, the fission gas is released in two ways: (1) closed bubbles grow into open pores; (2) when the swelling caused by closed bubbles reaches the swelling threshold of 10% of the fuel volume, it is assumed that 1% of the closed bubbles will instantly transform into open pores.

[0011] Specifically, in step S6, fuel swelling S t for: Where V1 is the volume of small bubbles, V2 is the total volume of medium bubbles, V3 is the total volume of large bubbles, V4 is the total volume of open pores, and Bu is the percentage fuel consumption.

[0012] Specifically, in step S7, the strain of both the fuel and the cladding is divided into elastic strain and inelastic strain. The elastic strain depends on the contact stress between the fuel and the cladding, while the inelastic strain includes thermal expansion, swelling, and creep. Metallic fuels exhibit a significant radially preferential anisotropic expansion characteristic during swelling. To address this issue, an anisotropic swelling factor is used to correct the swelling strain of the fuel as follows: in It is the axial component of the swelling strain. It is the radial component of the swelling strain. It is the circumferential component of the swelling strain. It is an anisotropy correction factor. It is the swelling of the total volume of fuel.

[0013] Specifically, in step S8, the failure criterion is the cumulative damage score. When the cumulative damage score reaches 1, the casing is considered to have failed. The failure time is calculated as follows: Where CDF is the cumulative lifetime fraction of the cladding, t r It is the expiration time, t f It is the final runtime, σ θ It is circumferential stress, T c It is the cladding temperature.

[0014] Compared with existing technologies, this invention has at least the following beneficial effects: This invention provides a method for analyzing the cladding failure of metallic fuel in liquid sodium-cooled reactors, coupling multiple physical processes such as component migration, cladding loss, eutectic melting, fission gas release, and fuel swelling. This enables a more effective simulation of the evolution of fuel element cladding failure under severe accident conditions. Based on this, a quantitative analysis of the failure probability is conducted, thereby assessing the mechanism by which the damage behavior affects reactor safety and reliability. Such assessment results can support the formulation of emergency measures and safety strategies in severe accident response, thereby reducing potential risks and enhancing reactor safety performance.

[0015] Furthermore, in the modeling, each channel corresponds to a single fuel element, requiring axial and radial meshing of the fuel element structure. Simultaneously, the coolant flow is set as one-dimensional, while the temperature and pressure fields are distributed in two dimensions; this approach simplifies the problem and facilitates the analysis process.

[0016] Furthermore, the effects of component migration, fuel porosity caused by fission gases, and sodium permeation on the thermal conductivity of metallic fuels were considered. The thermal conductivity of the fuel was corrected in real time at each time step to provide a more accurate fuel rod temperature distribution.

[0017] Furthermore, considering various factors affecting the mechanical properties of the cladding, such as inner cladding losses, eutectic melting, and sodium corrosion on the outer cladding, the prediction accuracy of thermodynamic failure of the cladding is improved.

[0018] Furthermore, the contact stress, elastic deformation, and inelastic deformation of the fuel and cladding are calculated. Considering the high plasticity of metallic fuels, it is assumed that there is no stress gradient inside the fuel when calculating fuel stress. Simultaneously, taking into account the anisotropic expansion characteristics of metallic fuels, corrections are made for the axial and radial expansion of the fuel based on EBR-II experimental data.

[0019] Furthermore, the cumulative damage function model is used to assess the thermodynamic failure risk of the metal fuel cladding and predict the failure time and location.

[0020] In summary, this invention considers various irradiation and chemical factors that may lead to thermodynamic failure of metallic fuels during the operation of liquid sodium cold reactors. It features detailed core modeling of liquid sodium cold reactors and improves the stability and computational efficiency of numerical algorithms. It can more accurately and efficiently simulate and verify the core behavior of liquid sodium cold reactors under accident conditions and predict the risk of cladding failure. Attached Figure Description

[0021] Figure 1 is a flowchart of the analytical method of the present invention; Figure 2 is a pseudo-binary phase diagram of metallic fuels. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a method for analyzing the failure of cladding metal fuel in liquid sodium-cooled reactors. It explores the failure mechanism of cladding metal fuel in liquid sodium-cooled reactors and develops a preliminary validated cladding failure model. A series of cladding failure models are developed, including those for component migration, fission gas release, fuel swelling, cladding loss, eutectic melting, sodium corrosion on the outer cladding surface, cladding creep, cladding failure criteria, and material properties. Numerical calculations are performed on liquid sodium-cooled reactors under severe accidents. Referring to Figure 1, a method for analyzing the failure of cladding metal fuel in liquid sodium-cooled reactors includes the following steps: S1, Modeling the liquid sodium-cooled reactor metal fuel rods; Based on the structural parameters of the liquid sodium-cooled reactor metal fuel, the computational domain is discretized into radial and axial nodes; Independent flow channels are used to represent individual fuel rod entities, encompassing the fuel pellet, cladding structure, coolant corresponding to the channels, and the pipe walls of local components. A one-dimensional unidirectional flow is set within the flow channels, and the temperature fields of the fuel pellet, cladding, coolant, and support structure adopt a radial-axial two-dimensional spatial distribution model. The axial dimension of the flow channel covers the entire length of the assembly (from coolant inlet to outlet), where the fuel region represents the fuel rod portion, including the fuel pellet, upper and lower conversion zones, and gas chamber, while the other regions represent the upper and lower reflector layers of the fuel rod.

[0024] S2. Input the operating parameters into the metal fuel rod model established in S1, recalculate the temperature and pressure of each node, and update the physical property parameters of the nodes; S3. Correct the thermal conductivity of the fuel rod based on the fuel component distribution, pore distribution, and sodium permeability, and update the temperature field of the fuel rod and coolant; Fuel rod thermal conductivity k f The specific corrections are as follows: Where k0 is the thermal conductivity of the pre-fabricated fuel; P c This is the porosity correction factor for sodium permeation; p is the fuel porosity; k f This is the corrected fuel thermal conductivity; W Zr W represents the mass fraction of zirconium. Pu P represents the mass fraction of plutonium. Na Sodium permeability; K Na ρ is the thermal conductivity of sodium; T is the fuel temperature.

[0025] S4. Based on the one-dimensional diffusion model of thermal transport theory and the temperature field of S3, the component migration of metallic fuel, i.e., the migration amount of Zr element, is calculated to update the fuel component distribution. During irradiation operation, component migration occurs in metallic fuels, causing changes in the fuel's structure and composition, thus affecting the fuel's thermal conductivity. This invention uses a one-dimensional diffusion model based on thermal transport theory to predict the redistribution of fuel components. Based on experimental phenomena, it is assumed that U and Zr atoms exchange positions, Pu atoms remain stationary, the enthalpy of the solution is negligible, and the kinetic reaction stops when the solubility limit is reached.

[0026] The flux equation for Zr element migration in the single-phase region is: The flux equation for Zr element migration in the two-phase region is as follows (taking the γ phase and β phase as examples): in It is the Zr element migration flux. It refers to the elemental concentration of the fuel rods. It represents the percentage of Zr element concentration. It is the percentage of Pu element concentration. It is the diffusion coefficient of Zr element. It is heat transfer in a local phase. It is the enthalpy of phase transition. It is the phase weight score. It is the universal gas constant. It's the fuel temperature. Phase transition temperature, It is a solubility curve. It is the solubility at the phase transition temperature.

[0027] For the specific pseudo-binary phase diagram, please refer to Figure 2, and for the phase diagram parameters, please refer to Table 1.

[0028] Table 1 Phase Diagram Coefficients Using the finite volume method and applying the divergence theorem to the above equations, we obtain the atomic fractional discrete equations for Zr: Where C is the concentration of Zr, s is the yield of Zr, S5, calculate the brittle loss of the cladding, eutectic and outer sodium corrosion, update the mechanical properties of the cladding, i.e. the mechanical properties corresponding to the effective thickness after the mechanical strength of the cladding is weakened; the brittle loss rate of the cladding is: The eutectic velocity is: The outer sodium corrosion thickness is: It is the rate of brittle loss of the shell. It's a percentage of fuel consumption. It is activation energy. Empirical fit coefficients It is the eutectic velocity. It depends on the empirical proportionality factor of the Pu content. , The lowest rapid eutectic formation temperature, The highest rapid eutectic formation temperature. The temperature at which the peak eutectic formation rate is reached. It is the sodium corrosion rate on the outer side of the cladding.

[0029] It is assumed that the brittle loss layer, eutectic layer, and outer sodium corrosion layer cannot withstand mechanical stress, and the effective thickness of the cladding after the mechanical strength is weakened is: w eff It is the effective thickness of the casing, w wast w represents the brittle loss thickness of the cladding. eut w represents the eutectic thickness of the cladding. Na The thickness of sodium corrosion on the outer side of the cladding.

[0030] S6. Establish a multi-bubble fission gas behavior model to obtain fuel pore distribution, fission gas release, fuel swelling, and fission gas chamber pressure. The fission bubble movement mechanism of the multi-bubble fission gas behavior model can be described as follows: the fission gas produced by the fission reaction is first uniformly dispersed into the metallic fuel matrix. The fission gas in the fuel matrix becomes bubble 1 through nucleation. Bubble 1 forms bubble 2 through diffusion and growth and collision with each other. Bubble 2 can form bubble 3 through collision with each other, or it can merge into bubble 3 or bubble 4 through collision. When bubble 2 expands with bubble 1, it absorbs bubble 1. Bubble 3 is the largest closed bubble. Collisions between them will not form larger bubbles. When bubble 3 collides with bubble 1 or bubble 2, it will absorb them. When it collides with open bubbles, it will become part of the open bubbles. Open bubbles can be divided into bubble 41, bubble 42, and bubble 43 according to their source. The fission gas is released in two ways: (1) closed bubbles grow into open pores; (2) when the swelling caused by the closed bubbles reaches the swelling threshold of 10% of the fuel volume, it is assumed that 1% of the closed bubbles will be instantaneously converted into open pores.

[0031] Atomic density of fission gases in metallic fuel matrix: Density of closed bubbles: Open bubble density: fission gas release: Among them, C g It is the concentration of gas atoms in the fuel matrix; C gbi It is the concentration of gas atoms present as gas bubbles i in the fuel matrix; C gr Y is the amount of fission gas released; Y is the fission yield of gas atoms, set to 0.25; F is the fission density relative to the manufacturing volume; J gi J is the gas diffusion rate of bubble i; b1,nucl This is the nucleation rate of bubble 1; ab ij It is the diffusion transfer rate from bubble i to bubble j; gab ij This is due to the radial growth of bubble i, causing the transfer rate from bubble i to bubble j; f i,i+1 It is the probability that bubble i transforms into bubble i+1 due to a collision; It is the sintering rate of the pores.

[0032] The relationship between bubble density and total gas atomic density is as follows: Where, ρ gi N is the density of gas atoms in bubble i; bi It is the density of closed bubbles i in the fuel matrix.

[0033] Volume V of fission bubble i for: Total fuel swelling is: Where V1 is the volume of small bubbles, V2 is the total volume of medium bubbles, V3 is the total volume of large bubbles, V4 is the total volume of open pores, and Bu is the percentage fuel consumption.

[0034] S7 calculates the core-cladding contact stress, elastic strain, and inelastic strain of the fuel rod based on the fuel rod temperature field calculated in S3, the cladding mechanical properties calculated in S5, and the fuel swelling calculated in S6. In the mechanical calculations, considering the high plasticity of metallic fuels, it is assumed that there is no stress gradient inside the fuel when calculating fuel stress. Simultaneously, considering the anisotropic expansion characteristics of metallic fuels, corrections are made for the axial and radial expansion of the fuel based on EBR-II experimental data.

[0035] The strain of both fuel and cladding is divided into elastic strain and inelastic strain. Elastic strain depends on the contact stress between fuel and cladding, while inelastic strain includes thermal expansion, swelling, and creep.

[0036] When metallic fuels swell, they exhibit a clear radial preference tendency. To address this issue, an anisotropic swelling factor is used to correct the swelling strain of the fuel. in It is the axial component of the swelling strain. It is the radial component of the swelling strain. It is the circumferential component of the swelling strain. It is the anisotropy correction factor (0.75 based on EBR-II experimental data). It is the swelling of the total volume of fuel.

[0037] S8. Combining the temperature field obtained from S3 and the stress obtained from S7, the lifetime fraction of the cladding is calculated. The cumulative damage function model is used to assess the thermodynamic failure risk of the metal fuel cladding and predict the failure time and failure location.

[0038] The failure criterion is the cumulative damage score. When the cumulative damage score reaches 1, the casing is considered to have failed. The failure time is calculated as follows: Where CDF is the cumulative lifetime fraction of the cladding, t r It is the expiration time, t f It is the final runtime, σ θ It is circumferential stress, T c It is the cladding temperature.

[0039] In another embodiment of the present invention, a terminal device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment can be used in the operation of a cladding failure analysis method for liquid sodium cold reactor metal fuel, including: establishing a heat transfer and mechanical model of liquid sodium cold reactor metal fuel rods; inputting operating parameters into the established metal fuel rod model, calculating the temperature and pressure of each node, updating the physical property parameters of the nodes, and completing steady-state calculation initialization; according to... The thermal conductivity of the fuel rod is corrected and the temperature field of the fuel rod and coolant is updated based on the fuel component distribution, porosity distribution, and sodium permeability. The fuel component distribution is updated by calculating the component migration of metallic fuel based on the temperature field using a one-dimensional diffusion model of heat transport theory. The brittle loss, eutectic reaction, and external sodium corrosion of the cladding are calculated, updating the mechanical properties of the cladding. A multi-bubble fission gas behavior model is established to obtain the fuel porosity distribution, fission gas release, fuel swelling, and fission gas cavity pressure. The fuel swelling is calculated using a fuel rod mechanical model, and the core-cladding contact stress, elastic strain, and inelastic strain of the fuel rod are calculated. The calculations for each time step are completed sequentially, and the failure criteria are used to determine whether the cladding has failed.

[0040] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium (Memory). This computer-readable storage medium is a memory device in a terminal device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the terminal device and extended storage media supported by the terminal device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device.

[0041] One or more instructions stored in the computer-readable storage medium can be loaded and executed by the processor to implement the corresponding steps of the cladding failure analysis method for liquid sodium cold reactor metallic fuel in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps: establishing a heat transfer and mechanical model of liquid sodium cold reactor metallic fuel rods; inputting operating parameters into the established metallic fuel rod model, calculating the temperature and pressure of each node, updating the physical property parameters of the nodes, and completing steady-state calculation initialization; and adjusting the thermal conductivity of the fuel rods according to the fuel component distribution, pore distribution, and sodium permeability. The temperature fields of the fuel rods and coolant are corrected and updated; the component migration of metallic fuel is calculated based on the temperature field using a one-dimensional diffusion model of heat transport theory, and the fuel component distribution is updated; the brittle loss, eutectic and outer sodium corrosion of the cladding are calculated, and the mechanical properties of the cladding are updated; a multi-bubble fission gas behavior model is established to obtain the fuel porosity distribution, fission gas release, fuel swelling and fission gas cavity pressure; the fuel swelling is calculated using a fuel rod mechanical model, and the core-cladding contact stress, elastic strain and inelastic strain of the fuel rod are calculated; the calculations for each time step are completed sequentially, and the failure criteria are used to determine whether the cladding has failed.

[0042] In summary, this invention provides a cladding failure analysis method for liquid sodium-cooled reactor metallic fuel. It calculates the component migration behavior of metallic fuel rods based on a one-dimensional diffusion model of thermal transport theory, considers the weakening effect of various chemical reactions on the mechanical strength of the cladding, establishes a multi-bubble fission gas behavior model to calculate fuel swelling and fission gas release rate, calculates fission chamber pressure using an improved ideal gas equation of state, establishes a fuel rod mechanical model to calculate stress and strain, calculates safety analysis parameters in real time, uses cumulative lifetime fractions, and determines whether cladding failure has occurred based on the thermodynamic analysis results.

[0043] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0044] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0045] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0046] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0047] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0048] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0049] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, or a read-only memory (ROM). Computer-readable media may include only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content of the computer-readable media may be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media may not include electrical carrier signals and telecommunication signals.

[0050] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

[0051] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0052] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0053] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for analyzing the cladding failure of metallic fuel in a liquid sodium-cooled reactor, characterized by comprising the following steps: S1. Modeling the metal fuel rods of a liquid sodium cold reactor; S2. Input the operating parameters into the metal fuel rod model established in S1, recalculate the temperature and pressure of each node, and update the physical property parameters of the node; S3. Correct the fuel thermal conductivity based on the fuel component distribution, pore distribution and sodium permeability, and update the temperature field of the fuel rod and coolant. S4. Calculate the component migration of metallic fuel, i.e., the migration amount of Zr element, based on the one-dimensional diffusion model of heat transport theory and the temperature field of fuel rods and coolant in S3, and update the fuel component distribution. S5. Calculate the brittle loss, eutectic, and outer sodium corrosion of the cladding, and update the mechanical properties of the cladding, i.e., the mechanical properties corresponding to the effective thickness after the reduction of the cladding's mechanical strength. S6. Establish a multi-bubble fission gas behavior model to obtain the fuel porosity distribution, fission gas release, fuel swelling, and fission gas cavity pressure. S7. Calculate the core-cladding contact stress, elastic strain, and inelastic strain of the fuel rod based on the fuel rod temperature field calculated in S3, the cladding mechanical properties calculated in S5, and the fuel swelling calculated in S6. S8. Combine the fuel rod and coolant temperature field obtained in S3 and the core-cladding contact stress obtained in S7 to calculate the cladding lifetime fraction, determine whether the cladding has failed using failure criteria, and predict the cladding failure time and location.

2. The method for analyzing cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S1, the computational domain is discretized into nodes radially and axially based on the structural parameters of the liquid sodium cold reactor metallic fuel. A single fuel rod entity is represented by an independent flow channel, covering the fuel pellet, cladding structure, coolant corresponding to the channel, and the pipe wall of local components. A one-dimensional unidirectional axial flow is set in the flow channel, and the temperature field of the fuel pellet, cladding, coolant, and support structure adopts a radial-axial two-dimensional spatial distribution model.

3. The method for analyzing cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S3, the correction for the fuel thermal conductivity is as follows: Where k0 is the thermal conductivity of the pre-fabricated fuel; P c This is the porosity correction factor for sodium permeation; p is the fuel porosity; k f This is the corrected fuel thermal conductivity; W Zr W represents the mass fraction of zirconium. Pu P represents the mass fraction of plutonium. Na Sodium permeability; K Na ρ is the thermal conductivity of sodium; T is the fuel temperature.

4. The method for analyzing cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S5, the effective thickness w after the mechanical strength of the shell is weakened eff for: Among them, w c w represents the initial thickness of the casing. wast w represents the brittle loss thickness of the cladding. eut w represents the eutectic thickness of the cladding. Na The thickness of sodium corrosion on the outer side of the cladding.

5. The method for analyzing the cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S6, the amount of fission gas released is: Where C gr It is the amount of fission gas released; J gi ab is the gas diffusion rate of bubble i; ij It is the diffusion transfer rate from bubble i to bubble j; gab ij This is the transfer rate from bubble i to bubble j caused by the radial growth of bubble i.

6. The method for analyzing cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S6, in the multi-bubble fission gas behavior model, the fission gas is released in two ways: (1) closed bubbles grow into open pores; (2) when the swelling caused by closed bubbles reaches the swelling threshold of 10% of the fuel volume, it is assumed that 1% of the closed bubbles will be instantly transformed into open pores.

7. The method for analyzing the cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S6, the fuel swells S t for: Where V1 is the volume of small bubbles, V2 is the total volume of medium bubbles, V3 is the total volume of large bubbles, V4 is the total volume of open pores, and Bu is the percentage fuel consumption.

8. The method for analyzing the cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S7, the strain of both the fuel and the cladding is divided into elastic strain and inelastic strain. The elastic strain depends on the contact stress between the fuel and the cladding, while the inelastic strain includes thermal expansion, swelling, and creep. Metallic fuels exhibit a significant radially preferential anisotropic expansion characteristic during swelling. To address this issue, an anisotropic swelling factor is used to correct the swelling strain of the fuel as follows: in It is the axial component of the swelling strain. It is the radial component of the swelling strain. It is the circumferential component of the swelling strain. It is an anisotropy correction factor. It is the swelling of the total volume of fuel.

9. The method for analyzing cladding failure of liquid sodium-cooled reactor metallic fuel according to claim 1, characterized in that, In step S8, the cumulative lifetime fraction is used as the failure judgment criterion, and the failure time t r The calculation is as follows: Where CDF is the cumulative lifetime fraction of the cladding, t f It is the final runtime, σ θ It is circumferential stress, T c It is the cladding temperature.

Images