A calculation method for coupling the models of the core corrosion product growth and the flow heat transfer under steady and transient conditions

Abstract

The application discloses a calculation method suitable for coupling of a core corrosion product growth model and a flow heat exchange model under steady-state and transient conditions, and steps are as follows: a geometric model of a fluid domain between a fuel rod and a pressure container is constructed, and a grid is divided; a computational fluid dynamics simulation is carried out for the problem that the coolant changes from single-phase flow to subcooled boiling in a flow process, and average void fractions and average liquid temperature axial distributions are obtained; relevant information such as wall temperature, liquid temperature, coolant flow rate and void fraction obtained by calculation is introduced into a user-defined function (UDF), and deposition of dirt and a heat exchange process are calculated; and the flow heat exchange influence caused by the dirt is returned to a Fluent solver through a thermal conductivity macro function, so that a numerical simulation method capable of coupling deposition of a core corrosion product and a heat exchange process in a core under steady-state and transient conditions is formed, and the influence of the deposition layer on the flow heat exchange process can be clearly reflected.

Description

Technical Field

[0001] This invention belongs to the field of pressurized water reactor technology, specifically relating to a calculation method for coupling core corrosion product growth and flow heat transfer models under steady-state and transient conditions. Background Technology

[0002] The most widely used reactor type is the pressurized water reactor. During the long-term operation of a pressurized water reactor, the primary loop piping and equipment are subjected to corrosion, water chemical reactions, coolant scouring and other factors, resulting in a large amount of oxidation and corrosion products. Driven by supercooled boiling, a thick deposit layer (CRUD) will form on the surface of the fuel element in the supercooled boiling area. The loose and porous nature of the deposit layer not only increases the thermal resistance of the material surface, causing local overheating, but also increases the number of vaporization nuclei, resulting in heat transfer deterioration and affecting the safe operation of the reactor.

[0003] However, current research on computational methods for this problem often only sets boundary conditions for calculating fouling heat transfer, without considering different flow and heat transfer states outside the cladding. Furthermore, there is limited research on the coupling of fouling deposit growth and fouling heat transfer. To achieve a coupled study of corrosion product growth and two-phase flow heat transfer, a model coupling corrosion product growth and flow heat transfer is invented. This model can calculate the corrosion product growth and heat transfer process under both single-phase and two-phase conditions while meeting steady-state and transient requirements. This method is of great significance for studying the impact of corrosion products on cladding flow heat transfer. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a calculation method that is suitable for coupling the core corrosion product growth and flow heat transfer model under steady-state and transient conditions. This method can realize the calculation of corrosion product deposition growth and flow heat transfer of the deposition layer considering different flow regions (i.e., single-phase region and supercooled boiling region), and can meet different calculation requirements under steady-state and transient discrete conditions.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A computational method applicable to the coupling of core corrosion product growth and flow heat transfer models under steady-state and transient conditions includes the following steps: Step 1: Based on research requirements, establish a three-dimensional geometric model of the fluid domain between the pressurized water reactor fuel rods and the pressure vessel; Step 2: Divide the three-dimensional geometric model of the fluid domain established in Step 1 into a computational fluid dynamics mesh; Step 3: Based on the requirements, select the steady-state or transient time discretization algorithm, choose the corresponding time discretization method in the FLUENT solver for computational fluid dynamics, and adjust the user-defined function (UDF) according to the requirements; Step 4: Import the computational fluid dynamics mesh generated in Step 2 into the computational fluid dynamics solver, set the boundary conditions for the test run, and compile and load the user-defined function (UDF) in the computational fluid dynamics solver to calculate the corrosion product deposition layer growth model and the flow heat transfer model respectively and couple the two models. Step 5: Run the computational fluid dynamics solver and set the average liquid phase temperature and average cavitation fraction at the outlet to monitor the stability of the calculation results; Step 6: Transfer the key parameters such as temperature, velocity, and cavitation fraction obtained from the computational fluid dynamics solver to the user-defined function (UDF) attached in Step 4. In the UDF, determine the single-phase region and the subcooled boiling region. For each different flow state, use different models to perform calculation coupling of deposit layer growth and flow heat transfer to obtain the deposit layer thickness and equivalent fouling thermal resistance distribution under different flow states. Equation 1 is the relationship between thermal resistance and thermal conductivity. From this, the equivalent fouling thermal conductivity can be calculated. During the calculation process, the key parameters are stored on the corresponding grid surface using the C_UDMI function.

[0006] (1) in, k Equivalent fouling thermal conductivity, unit: W·m -1 ·K -1 ; The thickness of the dirt is expressed in meters (m). R Fouling thermal resistance, unit: m 2 K / W; Step 6: Mark the first layer of mesh on the fluid domain heating surface, use the surface mesh loop function of the user-defined function UDF to assign the equivalent fouling thermal conductivity calculated by the user-defined function UDF to the marked mesh, and call it in subsequent calculations through the thermal conductivity macro of the user-defined function UDF; Step 7: The equivalent fouling thermal conductivity calculated by the user-defined function (UDF) is transferred to the corresponding heating surface of Fluent through the Shell Conduction method in the Fluent wall boundary conditions. The shell temperature is then calculated, and key results such as wall temperature rise and the impact of the deposited layer on flow heat transfer can be obtained.

[0007] The present invention has the following advantages and beneficial effects: 1) Since this method can capture the changes in the cavitation fraction and perform in-depth calculations in conjunction with the UDF program, the method of this invention can realize the calculation of corrosion product deposition and growth and flow heat transfer of the deposition layer considering different flow regions (i.e., single-phase region and subcooled boiling region).

[0008] 2) Since the method of this invention uses user-defined functions (UDFs) to calculate corrosion product growth and heat transfer, it has strong universality and can analyze and calculate corrosion product deposition problems of fuel rod bundles in different pressurized water reactors.

[0009] 3) By adjusting the UDF, the model in the method of this invention can meet different computational requirements under steady-state and transient time-discrete conditions. Attached Figure Description

[0010] Figure 1 This is a flowchart of the method of the present invention.

[0011] Figure 2 This is a three-dimensional geometric model of the fluid domain used for numerical simulation, established based on experiments.

[0012] Figure 3 Mesh generation is performed on the constructed three-dimensional geometric model. Detailed Implementation

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: like Figure 1 As shown, this invention provides a calculation method for calculating the impact of core corrosion product deposition on flow heat transfer, which can meet different calculation needs under steady-state and transient conditions. The method uses computational fluid dynamics software to perform numerical simulations of Westinghouse WALT single-tube deposition experiments to obtain key parameters such as cavitation fraction, wall temperature, and near-wall fluid temperature at different locations on the fuel rod. It then uses UDF-related macros to call and calculate these parameters, obtaining the thickness and thermal resistance of the corrosion product deposition layer at different locations. Finally, it transmits the equivalent thermal conductivity of fouling at different locations to Fluent through UDF-related macro functions. Through calculation, a method for coupled calculation of corrosion product deposition and flow heat transfer models under single-phase and two-phase conditions is formed. The specific method is as follows: Step 1: Using 3D modeling software such as UG, SolidWorks, ANSYS Spaceclaim, and ANSYS DesignModeler, create a 3D geometric model of the fluid domain between the pressurized water reactor fuel rods and the pressure vessel based on the experimental geometry. Figure 2 As shown.

[0014] Step 2: Import the 3D geometric model of the fluid domain established in Step 1 into the mesh generation software ICEM. Select suitable global and local mesh sizes, generate a structured mesh, and obtain the computational fluid dynamics mesh for the coolant flow channel between the fuel rods and the pressure vessel, as shown below. Figure 3 As shown.

[0015] Step 3: Import the computational fluid dynamics (CFD) mesh file of the fluid domain between the fuel rods and the pressure vessel from Step 2 into ANSYS FLUENT, determine the steady-state or transient discretization method, modify the UDF file, add boundary conditions for the fluid domain during experimental operation, and then compile and mount the UDF.

[0016] Step 4: Set convergence conditions and solution method, select appropriate relaxation factor, run computational fluid dynamics solver to solve, and set average liquid phase temperature and average cavitation fraction at the outlet to monitor the stability of the calculation results.

[0017] Step 5: Transfer the key parameters such as temperature, velocity, and cavitation fraction obtained from the computational fluid dynamics solver to the user-defined function (UDF) attached in Step 3. In the UDF, determine the single-phase region and the subcooled boiling region. For each different flow state, adopt different models to perform the calculation coupling of deposit layer growth and flow heat transfer, and obtain the deposit layer thickness and equivalent fouling thermal resistance distribution under different flow states. Formula (1) is the relationship between thermal resistance and equivalent fouling thermal conductivity. The equivalent fouling thermal conductivity can be calculated from this. In the calculation process, the key parameters are stored on the corresponding grid surface using the C_UDMI function.

[0018] (1) in, k Equivalent fouling thermal conductivity, unit: W·m -1 ·K -1 ; The thickness of the dirt is expressed in meters (m). R Fouling thermal resistance, unit: m 2 K / W; Step 6: Mark the first layer of mesh on the fluid domain heating surface. Use the UDF's surface mesh loop function begin_f_loop to assign the equivalent fouling thermal conductivity calculated by the user-defined function UDF to the marked mesh. Then, use the user-defined function UDF's thermal conductivity macro DEFINE_PROPERTY to call it in subsequent calculations. Step 7: The equivalent fouling thermal conductivity calculated by the user-defined function UDF is transferred to the corresponding heating surface of Fluent through the Shell Conduction method in the Fluent wall boundary conditions to calculate the shell temperature. Key results such as wall temperature rise and the impact of the deposit layer on flow heat transfer can be obtained.

[0019] Step 8: Analyze and post-process the calculation results according to requirements.

[0020] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A computational method suitable for coupling of a core corrosion product growth and flow heat transfer model under steady state and transient conditions, characterized by: Includes the following steps: Step 1: Establish a three-dimensional geometric model of the fluid domain between the pressurized water reactor fuel rods and the pressure vessel; Step 2: Divide the three-dimensional geometric model of the fluid domain established in Step 1 into a computational fluid dynamics mesh; Step 3: Based on the requirements, select the steady-state or transient time discretization algorithm, choose the corresponding time discretization method in the computational fluid dynamics solver, and adjust the user-defined function (UDF) according to the requirements; Step 4: Import the computational fluid dynamics mesh generated in Step 2 into the computational fluid dynamics solver, set the boundary conditions for the test run, and compile and load the user-defined function (UDF) in the computational fluid dynamics solver to calculate the corrosion product deposition layer growth model and the flow heat transfer model respectively and couple the two models. Step 5: Run the computational fluid dynamics solver and set the average liquid phase temperature and average cavitation fraction at the outlet to monitor the stability of the calculation results; Step 6: Transfer the temperature, velocity, and cavitation fraction parameters obtained from the computational fluid dynamics solver to the user-defined function (UDF) attached in Step 4. In the UDF, determine the single-phase region and the subcooled boiling region. For each different flow state, use different models to perform calculation coupling of deposit layer growth and flow heat transfer to obtain the deposit layer thickness and equivalent fouling thermal resistance distribution under different flow states. Calculate the equivalent fouling thermal conductivity from this, and store the key parameters on the corresponding grid surface using the C_UDMI function during the calculation process. Step 6: Mark the first layer of mesh on the fluid domain heating surface, use the surface mesh loop function of the user-defined function UDF to assign the equivalent fouling thermal conductivity calculated by the user-defined function UDF to the marked mesh, and call it in subsequent calculations through the thermal conductivity macro of the user-defined function UDF; Step 7: The equivalent fouling thermal conductivity calculated by the user-defined function UDF is transferred to the corresponding heating surface of Fluent through the Shell Conduction method in the Fluent wall boundary conditions, and the shell temperature is calculated to obtain the results of the wall temperature rise and the impact of the deposit layer on the flow heat transfer.

2. The calculation method for coupling core corrosion product growth and flow heat transfer models under steady-state and transient conditions, as described in claim 1, is characterized in that: By coupling the corrosion product growth model and the flow heat transfer model with computational fluid dynamics methods and using user-defined functions (UDFs) for three-dimensional parameter transfer, the system can meet users' different calculation needs for steady-state and transient states. This enables the calculation of corrosion product growth and flow heat transfer, and obtains flow heat transfer information on the fuel cladding surface under corrosion product deposition conditions.

3. The calculation method according to claim 1, applicable to the coupling of core corrosion product growth and flow heat transfer models under steady-state and transient conditions, is characterized in that: The formula for calculating the equivalent fouling thermal conductivity is shown in formula (1). （1） in, k Equivalent fouling thermal conductivity, unit: W·m -1 ·K -1 ; The thickness of the dirt is expressed in meters (m). R Fouling thermal resistance, unit: m 2 ·K / W.

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