A numerical simulation method for critical heat flux of high burnup bubbly blanket type nuclear fuel

Abstract

The application discloses a high-burnup bubble plate type nuclear fuel critical heat flux density numerical simulation method, 1, the high-burnup bubble plate type nuclear fuel geometry model and the grid model are introduced into the ANSYS fluent of the commercial CFD software.2, set the calculation model and set the corresponding parameters.3, set the physical property parameters according to the working condition to be calculated.4, set the model boundary condition.5, open the calculation parameter monitoring.6, set the initial volume heat source heating power value in the fuel pellet to heat, improve the fluid domain wall heat flux by continuously improving the fuel pellet volume heat source, after the highest temperature of the heated wall surface and the highest void fraction reading converge, the fuel pellet power density is increased.7, repeat step 6 to continuously improve the heat source power density, when the highest temperature of the heated wall surface is monitored to have temperature runaway or the maximum void fraction of the heated wall surface is greater than 0.8, it is considered that criticality occurs at this time, and the obtained critical heat flux density is obtained.The numerical simulation method of the application has good simulation results on existing test data, and the error is within-25% to +10%.

Description

Technical Field

[0001] This invention belongs to the field of reactor safety analysis technology, specifically relating to a numerical simulation method for the critical heat flux density of high burnup bubbling plate nuclear fuel. Background Technology

[0002] Plate fuel elements are a type of nuclear fuel in which fissile material is dispersed in small particles within a non-fissile matrix of dispersed plate fuel. Unlike the rod-shaped fuels of traditional pressurized water reactors, individual plate fuels are elongated plates. Due to their advantages such as low center temperature, high safety, large heat exchange area, high specific power in the active zone, higher stiffness, high heat exchange efficiency, and compact structure, they are a relatively advanced compact reactor core and are currently widely used in research reactors and shipboard reactors. The coolant flow channels within the plate fuel assembly are narrow rectangular channels formed between the plate fuel elements, with the slit height typically ranging from 1 to 3 mm. The coolant may undergo several flow patterns from inlet to outlet, including single-phase water, two-phase flow (including subcooled boiling and saturated boiling), and single-phase steam, resulting in extremely complex flow and heat transfer conditions.

[0003] Bubbling is a unique failure mode of dispersed plate-shaped fuel elements. During long-term reactor operation, high-burnup fuel pellets develop cracks, releasing fission gases such as krypton and xenon produced during nuclear fission burnup. The increasing gas pressure due to localized accumulation triggers cladding bubbling, leading to distortion of the rectangular narrow-slot flow channel. This is a key bottleneck technology in the thermal-hydraulic design and safety analysis of dispersed fuel elements. Critical heat flux density is the heat flux density at which heat transfer deteriorates on the surface of the nuclear fuel element, resulting from a change in the two-phase boiling heat transfer mechanism. Current research on boiling criticality and thermal-hydraulic characteristics within rectangular narrow-slot flow channels is largely limited to normal rectangular narrow-slot flow channels without bubbling. Research on gas-liquid two-phase boiling heat transfer and boiling criticality in bubbled rectangular narrow-slot flow channels is relatively lacking. Furthermore, critical heat flux density, an important safety criterion, needs to be emphasized under both normal reactor operation and accident conditions.

[0004] After bubbling occurs in plate-type nuclear fuel elements, both the boiling heat transfer characteristics and the boiling criticality are affected by changes in the geometry of the coolant flow channels. Therefore, this invention uses numerical simulations to study important parameters such as the fuel element temperature distribution before boiling criticality occurs, as well as the near-wall cavitation fraction distribution of the heated wall surface at boiling criticality; it explores the impact of bubbling on the two-phase flow boiling mechanism within distorted rectangular narrow-slit channels; and it analyzes the boiling heat transfer characteristics after bubbling to provide a technical basis for formulating thermal safety criteria after bubbling. The research objectives achieved by this invention are of great significance for safety studies under various operating conditions after high burnup operation in plate-type fuel element reactor cores. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a numerical simulation method for the critical heat flux density of high burnup bubbling plate nuclear fuel. After providing a geometric model and mesh of the bubbling plate fuel element, the fluid, solid properties, and corresponding thermal-hydraulic parameters are set, and the critical heat flux density of high burnup bubbling plate nuclear fuel can be calculated.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A numerical simulation method for the critical heat flux density of high burnup bubbly plate nuclear fuel includes the following steps:

[0008] Step 1: Establish a geometric model of high burnup bubbly plate nuclear fuel and perform mesh generation. Import the geometric model and mesh file into the commercial CFD software ANSYS Fluent using ANSYS Workbench.

[0009] Step 2: In ANSYS Fluent, call the calculation model. Based on the Euler-Euler two-fluid model and the RPI wall boiling model, add the interphase interaction model, critical heat flux density model, turbulent Reynolds pressure model (RSM), and auxiliary models. The auxiliary models include the wall nucleation density model, bubble escape diameter model, bubble escape frequency model, and bubble diameter model. Set the corresponding parameters according to the pressure, temperature, and flow rate of the calculation conditions.

[0010] Step 3: Set the physical property parameters. Set the material physical property parameters according to the numerical simulation conditions. In the numerical simulation of critical heat flux density, the coolant involves a phase change process from liquid to gas. The physical property parameters of the coolant are set using a linear function relationship to characterize the property changes. The physical property parameters include the density, pressure heat capacity, thermal conductivity, viscosity and enthalpy of the fluid, and the density, specific heat and thermal conductivity of the solid.

[0011] Step 4: Set boundary conditions. Set the fluid domain inlet as a mass flow rate inlet, the outlet as a pressure outlet, the fuel pellet as a volumetric heat source, and the fluid domain-solid domain wall treatment as a standard wall function.

[0012] Step 5: Add thermal parameter monitoring during the numerical simulation process through the monitors tab of Fluent to monitor the highest temperature of the heated wall in the fluid domain and the highest cavitation fraction of the gas phase in the near-wall mesh of the heated wall, and present them as a two-dimensional curve, where the horizontal axis is the number of Fluent iteration calculation steps;

[0013] Step 6: Set the initial volumetric heat source heating power value for the fuel pellets. The initial volumetric heat source heating power value is set such that the heat flux density of the volumetric heat source on the fluid heating surface through the plate-shaped nuclear fuel cladding is 30% of the experimental value of the critical heat flux density (CHF). Observe the monitoring charts. After the readings of the highest temperature and the highest void fraction of the heated wall converge, increase the volumetric heat source power density by 5% of the experimental value. When the power density is close to the experimental value, decrease the power density increment by 1% of the experimental value.

[0014] Step 7: Repeat step 6 to continuously increase the volumetric heat source power density. When the highest temperature of the heated wall surface is detected to rise sharply or the maximum cavitation fraction of the heated wall surface is greater than 0.8, it is considered that a critical condition has occurred. The wall heat flux density of the heated wall surface in the fluid domain at this time is the critical heat flux density under this operating condition.

[0015] The high burnup bubbling plate nuclear fuel geometric model described in step 1 was modeled using SolidWorks modeling software. The fuel pellet, fuel cladding, and coolant fluid domain were established. Fission gas gaps were created inside the bubbling cladding. The thermal resistance of the internal gaps at the bubbling points was replaced by equivalent substitution. The flow rate of the fission gas gaps was ignored, and the internal gaps of the bubbling cladding were equivalent to small solid thermal resistances, simplifying the geometric model and reducing computational costs.

[0016] In step 2, using the Euler-Euler two-fluid model, the RPI wall boiling model, and the turbulent Reynolds pressure model (RSM), the mass, energy, and momentum equations for each phase in the gas and liquid phases during the two-phase flow boiling heat transfer process where water is heated by the wall as a nuclear fuel coolant were solved. By adding an interphase interaction model and an auxiliary model, the numerical solutions for the phase interface characteristics and the interphase mass, energy, and momentum transfer processes were achieved. The solution parameters included phase interface density, drag force, lift force, wall lubrication force, and turbulent dissipation force. The critical heat flux density model ensured the convergence of the numerical simulation calculation under the condition of near-burnout at the boiling critical point.

[0017] In step 3, the physical property parameters are set. The density, thermal conductivity, and viscosity of the fluid are characterized using a linear interpolation method with respect to temperature. The pressure heat capacity and enthalpy are achieved using a UDF-based interpolation method. The pressure heat capacity is selected by interpolating the pressure heat capacity of the inlet subcooled water and the saturated temperature water at the corresponding pressure. The enthalpy is obtained by integrating the pressure heat capacity. The density, specific heat, and thermal conductivity of the fuel pellets and fuel cladding are interpolated at the corresponding temperatures. The thermal resistance of the fission gas inside the cladding foam is characterized by temperature interpolation of density, specific heat, and thermal conductivity based on the mass fractions of krypton and xenon being 90% and 10%, respectively.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention utilizes a CFD (fluid-structure interaction) simulation method based on an Euler-Euler two-fluid model to numerically simulate the critical heat flux density of high-burnup bubbly plate nuclear fuel. This provides guidance for steady-state and accident conditions under the current long service life of this type of nuclear fuel, and also supports the design of test sections for distorted heating plates with similar geometric models. The numerical simulation method of this invention yields good simulation results based on existing experimental data, with errors ranging from -25% to +10%. Attached Figure Description

[0020] Figure 1 This is a flowchart of the numerical simulation method for the critical heat flux density of high burnup bubbly plate nuclear fuel according to the present invention.

[0021] Figure 2 This is an error analysis diagram comparing experimental data with the numerical simulation method of the critical heat flux density of high burnup bubbling plate nuclear fuel according to the present invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. For example... Figure 1 As shown, this invention is a numerical simulation method for the critical heat flux density of high burnup bubbly plate nuclear fuel, which mainly includes the following steps:

[0023] Step 1: Establish a geometric model of high-burnup bubbly plate nuclear fuel. The geometric model of the high-burnup bubbly plate nuclear fuel is created using SolidWorks 3D modeling software, distinguishing between the solid and liquid phases. Geometric parameters include the length (mm), width (mm), and height (mm) of the rectangular slit channel in the fluid domain; the fuel cladding thickness (mm) and fuel pellet thickness (mm) in the solid domain; and bubbling parameters including bubble size and specific distribution location. The geometric model is imported into Meshing in ANSYS Workbench for mesh generation using a hexahedral mesh structure. Mesh quality is controlled above 0.8, and the maximum aspect ratio is controlled below 30 to avoid convergence issues in the numerical simulation. Mesh independence analysis is performed using the same boundary conditions to verify the optimal mesh size, and a mesh file is generated. The geometric model and mesh file are then imported into ANSYS Fluent in ANSYS Workbench.

[0024] Step 2: In the ANSYS fluent models tab, call up the calculation models, including the Euler-Euler two-fluid model, the RPI wall boiling model, the turbulent Reynolds pressure model (RSM), and auxiliary models.

[0025] The Euler-Euler two-fluid model is a numerical simulation model that solves the governing equations for mass, momentum, and energy conservation for each phase separately, and then uses appropriate interphase interaction and auxiliary models to solve for the phase interface characteristics and interphase heat and mass transfer processes. The interphase energy exchange in this invention is achieved using the Ranz-Marshall equation. The heat exchange between the liquid and gas phases is Q. gl for:

[0026] Q gl =-Q lg =h l (T g -T l A i

[0027]

[0028] In the formula, Q lg —Heat exchange between the liquid and gas phases; T g —Vacuum phase temperature; R1 —Liquid phase temperature; A i —The total interfacial area (interfacial density) of the vapor and liquid phases per unit volume; d g — Bubble diameter; h l —Heat transfer coefficient / W·m -2 ·K -1 ;λ l —Liquid phase thermal conductivity / W·m -1 ·K -1 Re p —The Reynolds number with the gas phase diameter as the reference length and the interphase relative velocity as the reference velocity; Pr —The Prandtl number of the liquid phase.

[0029] The interphase exchange added in this invention is the evaporation of the liquid phase. Condensation of the phase and gas phase In two-phase flow heat transfer, this is represented as follows:

[0030]

[0031] Where, q e ——Evaporation heat flux density / W·m -2 Extracted from the RPI wall boiling model, F / V is the ratio of the wall area to the volume of the near-wall mesh, expressed as F / V in m². 2 ·m -3 Its function is to convert the surface heat flux density into a volumetric heat source for the first layer of the grid; h g —Gas phase enthalpy / J·kg -1 h l ——Liquid phase enthalpy / J·kg -1 .

[0032] The phase interaction model added in this invention includes drag, lift, turbulent dissipation force, and wall lubrication force.

[0033] Drag force refers to the force exerted on a bubble in a continuous fluid, opposite to the direction of relative motion, due to viscosity, when the bubble is dispersed in the fluid and there is relative motion between them. The drag force acting on a single bubble can be expressed as:

[0034]

[0035] In the formula: where C d —The drag coefficient is calculated using the Schiller-Naumann recommended formula:

[0036]

[0037] In the formula, Re p —The Reynolds number with the gas phase diameter as the reference length and the interphase relative velocity as the reference velocity; ρ l —Liquid phase density; —Liquid phase velocity; —Gas phase velocity.

[0038] Lift is caused by the non-uniformity of the flow field; an unavoidable velocity gradient exists in the liquid phase perpendicular to the flow direction. When dispersed vapor bubbles move in a liquid-phase shear flow field, they will experience lift. The direction of lift is perpendicular to the relative velocity direction of the vapor and liquid phases, and can be expressed as the expression for the relative velocity of the two phases and the curl of the liquid phase velocity, i.e.:

[0039]

[0040] In the formula: C L —Lift coefficient; ρ l —Liquid phase density; α g —Vacuum bubble share; —Liquid phase velocity; —Gas phase velocity.

[0041] This invention selects the Moraga model to calculate interphase lift, and its lift coefficient calculation model is as follows:

[0042]

[0043] In the formula: φ—the product of the bubble Reynolds number and the vorticity Reynolds number, derived from the bubble diameter d g Calculate using the following formula:

[0044]

[0045]

[0046] In the formula: ρ l —Liquid phase density; —Liquid phase velocity; —Gas phase velocity; μ l Viscosity;

[0047] In the Euler-Euler two-fluid model, the ensemble averaging of turbulent fluctuations in the eddy viscosity turbulence model eliminates the additional force of the fluctuations on the discrete phase, thus requiring the addition of turbulent dissipation force. Turbulent dissipation force itself is a model-generated force, primarily dependent on the magnitude of the vapor phase cavitation fraction gradient within the flow field. This invention uses the calculation model based on interphase drag force proposed by Burns et al. through mass averaging, expressed as follows:

[0048]

[0049] In the formula: —Turbulent dissipation force; C TD —Turbulent dissipation force coefficient, with a value of 1.0; σ lg —Constant, 0.9; C d —Drag coefficient; μ t,l — Turbulent liquid viscosity / Pa·s; μ l — Liquid phase molecular viscosity / Pa·s; other symbols have the same meaning as above.

[0050] Wall lubrication force refers to the additional force exerted on the bubble near the wall due to the high near-wall liquid phase velocity gradient caused by the large difference in velocity distribution around the bubble. Because there is no slip condition, the continuous phase flow rate between the bubble and the wall decreases while the flow rate on the other side of the bubble increases. This force pushes the bubble away from the wall. Wall lubrication force is calculated using the following formula:

[0051]

[0052] In the formula: —The unit vector normal to the wall; α g —Vacuum bubble share; —Liquid phase velocity; —Gas phase velocity; C W —The wall lubrication coefficient is calculated using the Antal model:

[0053]

[0054] In the formula: C1, C2—dimensionless constants, respectively -0.01 and 0.05; y w —Distance from the wall / m. Wall lubrication only acts in regions where the liquid phase velocity has a gradient, i.e., the fluid domain near the wall, when the distance from the wall satisfies this condition: The wall lubrication force is 0, indicating that the location is in the fully developed turbulent region, the radial velocity gradient of the liquid phase is very small, and the wall lubrication force can be ignored.

[0055] The RPI wall boiling model is currently the most widely used wall boiling model. It divides the heat transfer process into three modes: single-phase convective heat flow, evaporative heat flow, and quenching heat flow, the sum of which is the total wall heat flow. For the turbulence model, the Reynolds pressure model (RSM) is selected. This model is the best performing RANS turbulence model for simulating flows in complex geometries among the Reynolds time-averaged method models. Although the solution cost is higher, its simulation results for complex flows are superior to other simpler RANS turbulence models, such as the standard k-ε model.

[0056] Finally, in order to close the equations and achieve numerical solutions for the flow boiling, some auxiliary models need to be introduced, including the heating surface nucleation density model, the bubble escape diameter model, the bubble escape frequency model, and the bubble diameter model.

[0057] The bubble detachment diameter model is the diameter of a bubble as it detaches from the heated wall surface. Its size depends on the force balance during the bubble's growth. The bubble detachment model can be obtained through force analysis of the bubble or by summarizing experimental observation data. This invention uses an empirical model proposed by Tolubinsky et al. based on experimental observations to calculate the bubble detachment diameter:

[0058]

[0059] Where: ΔT sub —Near-wall fluid undercooling / K; d ref =0.6mm; ΔT ref =45K; d max =1.4mm.

[0060] The wall nucleation density model is the number of vaporization nuclei per unit area of ​​heated wall surface, typically expressed in N. w This invention uses the empirical formula proposed by Lemmert-Chawla to calculate the nucleation density on the heated surface. In this model, the nucleation density is only related to the wall superheat, i.e.:

[0061] N w =C n ΔT sup n

[0062] In the formula: C = 210; n = 1.805; ΔT sup —Wall superheat / K, ΔT sup =T w -T sat .

[0063] The bubble detachment frequency is a measure of the detachment velocity of bubbles on a heated wall surface and is an important parameter in bubble dynamics. For a given nucleation point, assume the bubble waiting time is t. wt The bubble growth time is t. ct The bubble detachment frequency can then be expressed as:

[0064]

[0065] Cole et al. recommend using the following formula for calculation.

[0066]

[0067] In the formula: C f —Drag factor for bubble detachment from wall, default value is 1; g —Acceleration due to gravity; ρ l —Liquid phase density; ρ g —Gas phase density, d w —The bubble detachment diameter is calculated based on this model in this invention.

[0068] The bubble diameter model adopts an improved version of the bubble diameter model proposed by Anglat et al. This model sets upper and lower limits for the bubble diameter, assuming that when the fluid subcooling is higher than ΔT0, the bubble diameter in the mainstream is d0, and when the fluid subcooling is less than ΔT1, the bubble diameter is d1, as shown in the following formula:

[0069]

[0070] In the formula: d g —77 Bubble diameter; d0=0.0001m; d1=0.0015m; ΔT0=13.5K; ΔT1=0K; ΔT sup —Wall superheat / K.

[0071] All of the above models can be selected from the Fluent model library.

[0072] Step 3: Set material properties. Configure the property parameters according to the required calculation conditions. In the "Cell Zone Condition" tab, set the system pressure in the fluid domain, such as 13.8 MPa for the example calculation condition. The saturation temperature of the coolant at this pressure is 608.68 K. In the "Materials" tab, express the changes in property parameters with temperature using linear interpolation. The pressure, heat capacity, and enthalpy of the gas and liquid phases are expressed through UDF compilation. Density, thermal conductivity, and viscosity are interpolated between the inlet subcooled fluid temperature and the saturation temperature using the piece linear method. In the solid domain, the density, specific heat, and thermal conductivity of fuel pellets and cladding are interpolated with respect to temperature. Specific materials include water, steam, aluminum alloys, and U10Mo alloys.

[0073] Step 4: Set the model boundary conditions, using mass flow rate at the inlet and pressure at the outlet. Add a source term as a volumetric heat source to the entire solid domain of the fuel pellet using Fluent to achieve fluid-structure interaction heat transfer calculations within the fuel pellet-fuel cladding-fluid domain. Standard wall functions are used for wall treatment. Input the initial conditions calculated for the corresponding operating conditions, such as inlet temperature, fluid velocity, turbulent kinetic energy, turbulent dissipation rate, and saturation temperature, in the initialization interface.

[0074] Step 5: Using the report plots function in the monitors tab of Fluent, add thermal parameter monitoring during the numerical simulation calculation. Select the solid-fluid heating boundary surface as the monitoring surface. Add the maximum wall temperature and the maximum gas phase cavitation fraction to the monitoring parameters through the facet-maximum option. This enables the monitoring of the maximum temperature of the heated wall surface in the fluid domain and the maximum gas phase cavitation fraction of the near-wall mesh of the heated wall surface, and presents it as a two-dimensional curve. The horizontal axis of the curve image is the number of Fluent iteration calculation steps.

[0075] Step 6: Set the initial volumetric heat source heating power value for the fuel pellets. In the source term of the solid domain of the fuel pellets, set the initial volumetric heat source heating power value to 30% of the experimental value of the critical heat flux density (CHF) on the fluid heating surface through the plate-shaped nuclear fuel cladding. Start the simulation calculation until convergence. Observe the monitoring charts during the calculation. After the highest temperature and highest void fraction readings of the heated wall converge, increase the volumetric heat source power density by 5% of the experimental value. When the power density is close to the experimental value, decrease the power density increment by 1% of the experimental value.

[0076] Step 7: Repeat step 6 to continuously increase the volumetric heat source power density of the fuel pellets. When the highest temperature of the heated wall surface is detected to rise rapidly or the maximum cavitation fraction of the heated wall surface is greater than 0.8, it is considered that a critical condition has occurred. The wall heat flux density of the heated wall surface in the fluid domain at this time is the critical heat flux density under this operating condition. Figure 2 The numerical simulation method for the critical heat flux density of high burnup bubbling plate nuclear fuel of this invention simulates the critical heat flux density in a rectangular narrow slit channel under normal non-bubbling conditions. Compared with the error of the critical heat flux density experimental data of the rectangular narrow slit channel with double heating surface in Westinghouse's Bettis laboratory, the simulation error of the critical heat flux density in the normal rectangular narrow slit channel is -24.92% to 9.39%, and the overall simulation results are good.

Claims

1. A numerical simulation method of critical heat flux density of high burnup bubbled plate type nuclear fuel, characterized by: The method comprises the following steps: Step 1: a high-burnup blister plate-type nuclear fuel geometric model is established, and mesh division is carried out, and the geometric model and the mesh file are imported into ANSYS fluent of a commercial CFD software through ANSYS workbench; Step 2: a calculation model is called in ANSYS fluent, on the basis of an Euler-Euler two-fluid model and an RPI wall boiling model, an interphase interaction model, a critical heat flux density model, a turbulent Reynolds pressure model RSM and auxiliary models are added, the auxiliary models comprise a wall nucleation density model, a bubble detachment diameter model, a bubble detachment frequency model and a bubble diameter model, and corresponding parameters are set according to pressure, temperature and flow velocity of a calculation condition; Step 3: material property parameters are set, material property parameters are set according to a numerical simulation condition, in a numerical simulation process of the critical heat flux density, a phase change process from a liquid state to a gas state is involved for the coolant, a linear function relationship is adopted to represent property changes of the coolant, the property changes comprise density, pressure heat capacity, thermal conductivity, viscosity and enthalpy of the fluid, and density, specific heat and thermal conductivity of the solid; Step 4: boundary conditions are set, the fluid domain inlet is set as a mass flow rate inlet, the outlet is set as a pressure outlet, the fuel pellet is set as a volume heat source, and the fluid domain-solid domain wall surface is processed by using a standard wall surface function; Step 5: thermal parameters in a numerical simulation process are monitored by adding a monitors tab of fluent, the highest temperature of the fluid domain heating wall surface, the highest void fraction of the heating wall surface near-wall surface mesh in the gas phase are monitored and presented in a two-dimensional curve, and the abscissa is the iteration calculation step number of fluent; Step 6: the initial volume heat source heating power value is set in the fuel pellet for heating, the initial volume heat source heating power value is set as 30% of the critical heat flux density CHF experimental value of the heat flux density of the plate-type nuclear fuel cladding to the fluid heating surface, the simulation calculation is started, the monitoring chart is observed, after the highest temperature of the heating wall surface and the highest void fraction reading converge, the volume heat source power density is increased, the power density increment is 5% of the experimental value, and when the power density approaches the experimental value, the power density increment is reduced to 1% of the experimental value; Step 7: step 6 is repeated to continuously increase the volume heat source power density, when it is monitored that the highest temperature of the heating wall surface rises sharply or the maximum void fraction of the heating wall surface is greater than 0.8, it is considered that the critical condition occurs at this time, and the wall surface heat flux density of the fluid domain heating wall surface at this time is the critical heat flux density under the condition; The high-burnup blister plate-type nuclear fuel geometric model in step 1 is modeled by using a SolidWorks modeling software, a fuel pellet, a fuel cladding and a coolant fluid domain are established, a fissile gas gap is established in a blister of the cladding, an internal gap thermal resistance of the blister is equivalently replaced, the flowability of the fissile gas gap is ignored, the gap in the blister is equivalently replaced by a small solid thermal resistance, the geometric model is simplified, and the calculation cost is reduced. In step 2, the mass, energy and momentum equations of the gas and liquid phases in the two-phase flow boiling heat transfer process of water as nuclear fuel coolant under the wall heating are solved respectively by using the Euler-Euler two-fluid model, the RPI wall boiling model and the turbulent Reynolds pressure model RSM; the numerical solution of the phase interface characteristics and the numerical solution of the mass, energy and momentum transfer process between the phases are realized by adding the interphase action model and the auxiliary model, and the solving parameters include the phase interface density, drag force, lift force, wall lubrication force and turbulent dissipation force; The critical heat flux density model ensures the convergence of the numerical simulation calculation under the condition of boiling critical approximation burnout; In step 3, the physical property parameters are set, the density, thermal conductivity and viscosity of the fluid are characterized by using the linear interpolation method with respect to temperature, the pressure heat capacity and enthalpy value are realized by the interpolation method based on UDF, the pressure heat capacity is temperature-interpolated by selecting the pressure heat capacity of the inlet subcooled water and the saturated temperature water under the corresponding pressure, the enthalpy value is obtained by pressure heat capacity integration, the density, specific heat and thermal conductivity of the fuel pellet and fuel cladding are temperature-interpolated, and the fission gas thermal resistance in the cladding bubble is characterized by temperature-interpolated density, specific heat and thermal conductivity according to the mass fraction of krypton and xenon being 90% and 10% respectively.

Images