Accelerator driven subcritical reactor target coupled three-dimensional thermal-hydraulic calculation method based on partition equivalence and additional source term

Abstract

This invention discloses a three-dimensional thermal-hydraulic calculation method for accelerator-driven subcritical reactors based on partitioned equivalence and additional source terms, coupled with target-state coupling. This method establishes a unified fluid-structure conjugate computational domain covering the spallation target, core, intermediate heat exchanger, main pump, coolant pool, and solid structures. It meticulously preserves the internal flow channels of the spallation target and converts the core, heat exchanger, and main pump into equivalent regions for resistance and heat generation, resistance and heat sink, and flow-driven operation, respectively. Resistance parameters are determined based on the pressure drop and velocity relationship, and core power and spatial thermal deposition in the spallation target are mapped to corresponding elements. The annular porous resistance is updated based on the flow deviation in the spallation target branches; a volumetric heat sink is generated based on the local temperature on the heat exchanger shell side, and the heat sink correction factor is updated using the outlet temperature deviation; the momentum source of the main pump is updated based on the primary loop flow deviation. Steady-state solutions, parameter extraction, and directional updates are repeated until the three types of target quantities converge jointly, outputting three-dimensional flow, temperature, and component parameters. This method reduces repetitive fine-structure meshes while preserving key three-dimensional flows in the spallation target and improving the consistency between equivalent components and target operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor thermal-hydraulic numerical calculation and multi-physical parameter equivalent modeling technology. Specifically, it relates to a reactor-target coupled three-dimensional thermal-hydraulic calculation method for a pool-type liquid metal cooling accelerator driven subcritical reactor containing a spallation target, subcritical core, intermediate heat exchanger and main pump, which implements fine region preservation, functional region equivalence, spatial source term mapping and target parameter feedback iteration in a unified fluid-structure conjugate computational domain. Background Technology

[0002] An accelerator-driven subcritical reactor consists of a high-energy proton accelerator, a spallation target, and a subcritical core. In the pool-type liquid metal cooling structure, multiple jets, recirculations, and mixtures are formed between the spallation target outlet, the outlets of each core component, the inlet of the intermediate heat exchanger, and the main pump outlet. The local temperature and velocity distribution are affected by the combined influence of the flow distribution, heat generation, and heat exchange conditions of each component. Therefore, it is necessary to obtain the three-dimensional thermal-hydraulic parameters of the entire pool.

[0003] Existing one-dimensional system calculation methods typically represent equipment as nodes and branches, providing the total loop volume, but they cannot directly analyze the flow distribution within the spallation target or the three-dimensional interaction between the target outlet jet and the core outlet jet. While full-geometric three-dimensional methods can preserve component details, they require simultaneously discretizing a large number of internal channels, heat exchange tubes, and pump structures within the core assembly, leading to a significant increase in geometry processing, mesh count, and computational cost.

[0004] Another approach treats components such as the reactor core and heat exchangers as an equivalent porous region. If the spallation target details are omitted in the full-pool model, and the spallation target is only considered a simple inlet or heat source, it becomes difficult to maintain the target flow distribution within the multi-path system and the outlet jet morphology. Furthermore, even if a spatially uniform heat sink is applied to the intermediate heat exchanger, it is impossible to update the heat transfer intensity at each location based on the local temperature on the shell side.

[0005] Therefore, a calculation method is needed that can retain the key local structure of the spallation target while controlling the scale of three-dimensional computation, and incorporate spallation target flow distribution, local heat exchange of intermediate heat exchangers and primary loop drive into the same parameter feedback closed loop. Summary of the Invention

[0006] To address the problems in existing technologies, such as the large computational scale of full-geometric 3D models, the easy loss of local flow characteristics of spallation targets in full-pool porous models, the inability of uniform heat exchanger heat sinks to respond to local shell-side temperatures, and the lack of joint operating condition calibration for parameters of multiple equivalent components, this invention aims to provide a three-dimensional thermal-hydraulic calculation method for accelerator-driven subcritical reactors based on partitioned equivalence and additional source terms coupled with target.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A three-dimensional thermal-hydraulic calculation method for accelerator-driven subcritical reactors based on partitioned equivalence and additional source terms, wherein the accelerator-driven subcritical reactor includes a spallation target, a reactor core, an intermediate heat exchanger, a main pump, a main vessel, and a liquid metal coolant contained in the main vessel. The calculation method includes the following steps: Step 1: Obtain the geometric connectivity, pressure drop versus velocity, spatial power, target flow rate, and target heat transfer parameters of each component of the accelerator-driven subcritical reactor; establish a unified fluid-structure conjugate computational domain covering the liquid metal coolant and solid structure inside the main vessel; set the internal flow channel of the spallation target as the spallation target fine computational region; set the reactor core as the reactor core equivalent computational region corresponding to its pressure drop and heat generation function; set the intermediate heat exchanger as the intermediate heat exchanger equivalent computational region corresponding to its pressure drop and heat transfer function; and set the main pump as the main pump equivalent computational region corresponding to its flow driving function. The first step adopts the above-mentioned partitioning method in order to preserve the internal structure of the spallation target that affects the jet flow and local heat transfer of the target, and to perform functional equivalence on the numerous, small-scale components that mainly undertake pressure drop, heat generation, heat exchange or driving functions, thereby overcoming the contradiction between the excessively large mesh size of the full geometric model and the loss of the local flow characteristics of the spallation target in the overall equivalent model of the whole pool.

[0008] Step 2: Determine the momentum drag parameters of each equivalent calculation region based on the pressure drop and velocity correspondence data; map the core space power data to the core equivalent calculation region, and map the spallation target space thermal deposition data to the spallation target fine calculation region; Step 2 determines the momentum drag based on the relationship between pressure drop and velocity, and maps the core power and spallation target thermal deposition according to spatial location, so that the calculated area after geometric equivalence still maintains the hydraulic characteristics and energy source distribution corresponding to the original components, avoiding distortion of pressure drop characteristics or heating location caused by equivalence processing.

[0009] Step 3: Based on the correspondence between the flow paths of each target and the internal flow channels of the spallation target, an annular porous resistance zone is set at the corresponding position of the double-ring guide holes, and the deviation between the calculated flow rate of each target flow path and the corresponding target flow rate is used as the basis for updating the resistance parameters of the annular porous resistance zone. Step 3 involves feeding back the flow deviation of each target flow path to the resistance parameters of the corresponding annular porous resistance zone, enabling different flow paths within the spallation target to be calibrated separately and reducing unnecessary disturbances to the target flow paths that have already met the requirements.

[0010] Step 4: Obtain the shell-side local temperature at each location in the equivalent calculation region of the intermediate heat exchanger. Calculate the single-tube heat transfer at the corresponding location based on the tube-side representative temperature, tube wall thermal resistance, and local convective heat transfer resistance. Convert the single-tube heat transfer into a volumetric heat sink in the equivalent calculation region of the intermediate heat exchanger. Use the deviation between the calculated outlet temperature of the intermediate heat exchanger and the target outlet temperature as the basis for updating the correction factor of the volumetric heat sink. Load a volumetric momentum source in the equivalent calculation region of the main pump, and use the deviation between the calculated total flow rate of the primary loop and the target total flow rate as the basis for updating the volumetric momentum source. Step four involves constructing a volumetric heat sink with spatial variations based on the local temperature on the shell side, and then using the outlet temperature of the intermediate heat exchanger and the total flow rate of the primary loop to correct the volumetric heat sink and the main pump volumetric momentum source, thereby overcoming the problem that uniform heat sinks and fixed drive sources cannot respond to local temperature distributions and target operating conditions.

[0011] Step 5: Perform steady-state iterative solution on the unified fluid-structure conjugate computational domain. Extract the calculated flow rate of each target flow path of the spallation target, the calculated outlet temperature of the intermediate heat exchanger, and the calculated total flow rate of the primary loop at the outer iteration node. When the deviation of any extracted quantity from its target value exceeds the corresponding allowable value, only update the resistance parameters of the annular porous resistance zone, the volumetric heat sink correction factor, or the main pump volumetric momentum source corresponding to the out-of-tolerance extracted quantity, and return to execute the steady-state iterative solution. When the deviation of all extracted quantities from their respective target values ​​does not exceed the corresponding allowable value, the outer iteration ends. Step 5 employs a joint judgment of three types of target quantities and a directional update method that only updates out-of-tolerance parameters. This reduces the mutual interference caused by the simultaneous adjustment of parameters of multiple equivalent components and enables the spallation target flow distribution, intermediate heat exchanger heat exchange, and primary loop drive to reach the target operating condition within the same steady-state solution closed loop.

[0012] Step 6: Output the three-dimensional velocity field, pressure field, liquid metal coolant temperature field, and solid temperature field under the joint convergence state, as well as the spallation target flow distribution, intermediate heat exchanger heat transfer parameters, and primary loop flow parameters.

[0013] Step six simultaneously outputs the local three-dimensional field quantities of the entire pool and the overall parameters of the components, so that the calculation results can not only characterize the jet, recirculation and temperature distribution in the pool, but also be used for component design verification and subsequent safety analysis.

[0014] The unified fluid-structure conjugate computational domain also includes an upper chamber, a lower chamber, a descending channel, the main container wall, and in-core components; the spallation target fine computational domain is connected to the core equivalent computational domain, the intermediate heat exchanger equivalent computational domain, the main pump equivalent computational domain, and the liquid metal coolant pool through a fluid interface, and the liquid metal coolant exchanges heat with the solid structure through a conjugate heat transfer interface.

[0015] The equivalent calculation region of the reactor core is established as a hexagonal prism porous medium region according to the reactor core components. The axial viscous drag parameter and axial inertial drag parameter are determined according to the correspondence between pressure drop and velocity of various components, and the lateral drag parameter is set to be greater than the axial drag parameter. Neutron power is converted into volume heat source according to component type and axial segmentation. The component box wall adopts thin-walled thermally conductive boundary to transfer heat with the adjacent liquid metal coolant region.

[0016] The spallation target fine calculation region includes a central flow path, an inner ring flow path, and an outer ring flow path, as well as two annular porous resistance regions that control the flow distribution of the inner and outer ring flow paths; the spallation target spatial thermal deposition data is mapped to the corresponding cells of the spallation target fine calculation region through spatial interpolation.

[0017] The equivalent calculation region of the intermediate heat exchanger includes a tube bundle porous medium region, an inlet window, and an outlet window. The anisotropic momentum drag of the tube bundle porous medium region is determined according to the correspondence between axial pressure drop and axial velocity, and the correspondence between lateral pressure drop and lateral velocity. The inlet window and outlet window use surface drag to characterize the local pressure drop.

[0018] The single-tube heat exchange capacity is determined by the product of the overall heat transfer coefficient, the outer surface area of ​​a single heat exchange tube, and the difference between the tube-side representative temperature and the shell-side local temperature; the volumetric heat sink is determined by the single-tube heat exchange capacity, the number of heat exchange tubes, the equivalent calculation zone volume of the intermediate heat exchanger, and the heat sink correction factor.

[0019] The overall heat transfer coefficient is calculated in series based on the convective thermal resistance inside the tube, the thermal conductivity of the tube wall, and the convective thermal resistance outside the tube; the external convective heat transfer coefficient used to determine the external convective thermal resistance is updated based on the physical properties of the liquid metal coolant corresponding to the local temperature on the shell side and the local flow parameters.

[0020] The equivalent calculation region of the main pump includes the impeller action area, and the volumetric momentum source is loaded along the design drive direction of the main pump; when the calculated total flow rate of the primary loop does not reach the target total flow rate, the volumetric momentum source is updated according to the deviation between the two.

[0021] In the external iteration, the spallation target flow deviation, intermediate heat exchanger outlet temperature deviation, and primary loop total flow deviation are generated respectively. For target quantities that do not exceed the tolerance, their corresponding parameters remain unchanged. For target quantities that exceed the tolerance, their corresponding parameters are updated until the three deviations simultaneously meet their respective criteria or reach the preset maximum number of external iterations.

[0022] The density, viscosity, thermal conductivity, and specific heat capacity of the liquid metal coolant are updated with temperature; the liquid surface of the main container adopts an adiabatic slip boundary, the outer wall of the main container exchanges heat with the environment through an equivalent convective heat transfer boundary, and the fluid-solid interface adopts a non-slip conjugate heat transfer boundary.

[0023] Compared with the prior art, the present invention has the following advantages: 1. By meticulously preserving the internal flow channels of the spallation target within the unified full-pool computational domain and performing functional equivalence on the core assembly, intermediate heat exchanger tube bundle, and main pump impeller region, the local three-dimensional features of the spallation target flow distribution and the interaction between the outlet jet and the core jet are preserved while reducing the number of repetitive small-scale geometries and meshes.

[0024] 2. By mapping the core space power data to the core equivalent calculation region and mapping the spallation target space thermal deposition data to the spallation target fine calculation region, the space heating location corresponds to the specific calculation region, thus forming an energy transfer relationship between the core, spallation target, and liquid metal coolant.

[0025] 3. Since the heat transfer of a single tube is calculated based on the local temperature on the shell side of the intermediate heat exchanger and a volumetric heat sink with spatial variation is formed, the heat sink of the intermediate heat exchanger can respond to the temperature distribution on the shell side, thus avoiding the simplification of the heat transfer of the entire tube bundle into a uniform heat sink that is independent of the local state.

[0026] 4. Since the deviation of the spallation target flow rate, the deviation of the intermediate heat exchanger outlet temperature, and the deviation of the primary loop total flow rate are fed back to the annular porous resistance parameter, the volumetric heat sink correction factor, and the main pump volumetric momentum source, respectively, each out-of-tolerance target has a clear parameter update direction, and the parameters that have met the target can remain unchanged.

[0027] 5. By adopting a joint convergence criterion for three types of objective quantities, it is possible to simultaneously constrain the target flow distribution, intermediate heat exchanger heat removal, and loop flow drive in the same steady-state calculation closed loop, and output local three-dimensional distribution parameters in the pool that cannot be directly provided by one-dimensional methods. Attached Figure Description

[0028] Figure 1 This is a flowchart of the overall method of the present invention, which shows the sequential relationship between input acquisition, unified computational domain partitioning, resistance and heat source mapping, steady-state solution, extraction of three types of target quantities, directional parameter update, joint judgment and output.

[0029] Figure 2 This diagram illustrates the relationship between the fine calculation region and the equivalent calculation region, expressing the spatial connectivity and energy and momentum exchange relationships between the fine calculation region of the spallation target, the equivalent calculation region of the core assembly, the equivalent calculation region of the intermediate heat exchanger, the equivalent calculation region of the main pump, and the liquid metal coolant pool. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1 As shown, the present invention provides a three-dimensional thermo-hydraulic calculation method for accelerator-driven subcritical reactors based on partitioned equivalence and additional source terms, which includes the following steps: Step 1: Input to obtain and calculate the domain partition.

[0032] Obtain the geometric dimensions and connectivity of the main vessel, spallation target, core assembly, intermediate heat exchanger, main pump, and in-core components; obtain the pressure drop versus velocity data for each equivalent component, core space power, spallation target space heat deposition, target mass flow rate of each flow path in the spallation target, target outlet temperature of the intermediate heat exchanger, and target total flow rate of the primary loop. Establish a unified fluid-structure conjugate computational domain covering the liquid metal coolant and solid structure within the main vessel. Following the principle of preserving structures affecting the jet flow and local heat transfer in the target and functionally equivalent to repeating small flow channels, the internal flow channels of the spallation target are designated as the spallation target fine computational region; the core assembly is designated as the core equivalent computational region with both drag and heat generation functions; the intermediate heat exchanger is designated as the intermediate heat exchanger equivalent computational region with both anisotropic drag and local heat sink functions; and the main pump impeller action area is designated as the main pump equivalent computational region with a loaded volume momentum source. Step one outputs the topological relationships of each region and the region identifiers required for subsequent mapping. Figure 2 As shown, the fine calculation region of the spallation target is located at the center of the reactor core, the equivalent calculation region of the reactor core assembly is arranged around the spallation target, and the equivalent calculation regions of the intermediate heat exchanger and the main pump are arranged on the periphery of the reactor core. The above calculation regions are interconnected through the upper chamber, lower chamber, descending channel and liquid metal coolant pool, and exchange mass, momentum and energy in a unified fluid-solid conjugate calculation domain.

[0033] Step 2: Determining momentum drag and mapping space heat sources.

[0034] For the equivalent calculation region of the core assembly and intermediate heat exchanger tube bundle, momentum drag parameters are fitted based on the corresponding pressure drop and velocity data. In the direction... i The momentum source of the porous medium is: In the formula, S M,i for i Momentum source per unit volume of porous medium in a directional direction, with units of N / m³; μ This is the dynamic viscosity, measured in Pa·s. α i for i Directional permeability, in m²; u i for i Directional velocity, in m / s; ρ Density, in kg / m³; C 2,i for i Directional inertial drag coefficient, in meters - ¹; |u| The velocity modulus is obtained from the fitting. αi and C 2,i They are respectively transferred to the corresponding equivalent computation regions.

[0035] The neutron power given by the core assembly and axial position is converted into the volumetric heat source of the corresponding core unit. The spallation target thermal deposition field provided by the Monte Carlo calculation is mapped to spatial coordinates as follows: In the formula, S E,target The volumetric heat source for the spallation target unit is expressed in W / m³. q MC Data for Monte Carlo thermal deposition, in W / m³; I b This is a spatial interpolation operator for transforming the thermal deposition data coordinate system to the three-dimensional computational domain coordinate system. The mapped volumetric heat source is used in the energy equation of step five.

[0036] Step 3: Equivalent and feedback interface for spallation target flow distribution.

[0037] Two annular porous resistance zones are set at the corresponding positions of the double-ring guide holes on the spalling target, so that the central flow path, inner ring flow path, and outer ring flow path each form an identifiable flow statistics section. Using the target mass flow rate of each flow path of the spalling target input in step one as a benchmark, the corresponding calculated flow rate is read and a deviation is generated at each outer iteration node. If the deviation of a certain flow path exceeds its allowable value, only the resistance parameters of the annular porous resistance zone controlling that flow path are updated; the parameters of flow paths that meet the criteria remain unchanged. Step three transmits the current annular porous resistance zone resistance parameters to step five.

[0038] Step 4: Construction of local heat sink in heat exchanger and volume momentum source of main pump.

[0039] Read the position from the equivalent calculation area of ​​the intermediate heat exchanger. x The local temperature on the shell side is calculated, and the heat transfer of a single tube is calculated based on the representative temperature on the tube side: In the formula, Φ(x) This refers to the heat exchange of a single tube, measured in W. k(x) The overall heat transfer coefficient is expressed in W / (m²·K). A out The outer surface area of ​​a single heat exchange tube is expressed in m². T t and T s (x) These represent the tube-side representative temperature and the shell-side local temperature, respectively, in Kelvin (K). The overall heat transfer coefficient is determined by the series connection of convection inside the tube, heat conduction through the tube wall, and convection resistance outside the tube. In the formula, h in and h out ( x ) are the heat transfer coefficients on the inside and outside of the tube, respectively, in W / (m²·K); r in and r out These are the inner and outer radii of the pipe, respectively, in meters. λ w The value is the thermal conductivity of the pipe wall, expressed in W / (m·K). h out ( x The calculations are performed using the physical properties and flow parameters corresponding to the local temperature on the shell side. The heat transfer of a single tube is converted into the volumetric heat sink of the equivalent calculation region of the intermediate heat exchanger. In the formula, S E,IHX ( x (This refers to the location of the intermediate heat exchanger) x The volumetric heat sink at that location, expressed in W / m³. N This refers to the number of heat exchange tubes; V IHX The volume of the equivalent calculation zone of the intermediate heat exchanger is in m³. F IHX For heat sink correction factors. The current volumetric heat sink is passed back to the intermediate heat exchanger unit in step five; each outer iteration node extracts the intermediate heat exchanger outlet temperature and updates it when it exceeds the tolerance. F IHX The main pump volumetric momentum source is loaded in the main pump impeller operating region along the designed drive direction. Each external iteration node extracts the total flow rate of a loop; when it exceeds the tolerance, the main pump volumetric momentum source is updated.

[0040] Step 5: Unified solution, joint judgment and targeted update.

[0041] The resistance output from step two, along with the space heat source, the spallation target annular resistance output from step three, and the heat exchanger volumetric heat sink and main pump volumetric momentum source output from step four, are loaded into a unified fluid-structure conjugate computational domain to solve the mass, momentum, energy, and solid thermal conductivity equations. At the current outer iteration node, the calculated flow rates of each flow path of the spallation target, the calculated outlet temperature of the intermediate heat exchanger, and the calculated total flow rate of the primary loop are extracted and compared with the target values.

[0042] When the deviations of the three target quantities do not exceed their corresponding allowable values, and the flow field residuals and mass and energy imbalances meet the convergence thresholds, joint convergence is determined. When there is an out-of-range target quantity, the parameters that have met the criteria are kept unchanged, only the parameters corresponding to the out-of-range target are updated, and then steady-state solution continues. When joint convergence is not achieved after reaching the maximum number of external iterations, a non-convergence status flag and out-of-range parameters are output, and the current calculation is stopped. This process is a steady-state external iteration and does not include transient time steps or system program data exchange.

[0043] Step 6: Output.

[0044] After joint convergence, the system outputs the three-dimensional velocity field, pressure field, liquid metal coolant temperature field, and solid temperature field of the entire pool; it also outputs the flow rates of each flow path of the spallation target and each component of the core, the heat exchange heat and outlet temperature of the intermediate heat exchanger, the total flow rate of the primary loop, as well as the resistance parameters of the final annular porous resistance zone, the volumetric heat sink correction factor, and the volumetric momentum source of the main pump, for design verification or subsequent safety analysis.

[0045] Example The following examples are used to illustrate how the method can be implemented and do not constitute a limitation on reactor type, number of components, software, physical model, number of grids, and parameter values.

[0046] I. Calculation Objects and Region Composition A pool-type lead-bismuth cooled accelerator-driven subcritical reactor was selected as the implementation object. This object includes a spallation target located at the core center, a subcritical core composed of different types of hexagonal prism assemblies, intermediate heat exchangers and main pumps located around the core, a main vessel, and liquid metal coolant in the pool.

[0047] The unified computational domain includes the liquid metal coolant flow channels and solid target body inside the spallation target, the equivalent computational domain of the core assembly and its box walls, the equivalent computational domain of the intermediate heat exchanger, the main pump flow channels and impeller action area, the upper chamber, the lower chamber, the descending channel, the main vessel wall, and the liquid metal coolant pool. Structures inside the spallation target that affect the distribution of multiple flow streams and the outlet jet are preserved; details of the rod bundles inside the core, the numerous heat exchange tubes of the intermediate heat exchanger, and the main pump impeller are equivalent according to their primary functions.

[0048] II. Core Equivalent and Space Power Loading Each core assembly has an independent hexagonal prism porous region. Pressure drop versus velocity data were obtained for the fuel assembly, transmutation assembly, and reflector assembly, respectively, and a quadratic relationship was fitted to equation (1) in the direction... i Parameters when taking the axial direction α i and C 2,iTo suppress lateral through-flow that does not conform to the characteristics of the component channel, the lateral resistance can be 10³ times the axial resistance; this multiple is set in this embodiment and does not constitute the only limitation.

[0049] The power calculated by neutrons is allocated as volumetric heat sources according to component type and axial segmentation, and written into the corresponding core unit based on the region identifier. The component box wall can adopt a thin-walled thermally conductive boundary of equivalent thickness to form a heat transfer relationship between adjacent liquid metal coolant and the box wall.

[0050] III. Fine-scale modeling and thermal deposition mapping of spallation targets The spallation target retains the central flow path, inner ring flow path, outer ring flow path, and double-ring guide holes. Two annular porous resistance zones are established at the height of the double-ring guide holes, and branch flow statistics sections are set in each zone.

[0051] The space thermal deposition generated by the interaction between the proton beam and the target was obtained by Monte Carlo calculation. The intersection of the spallation target axis and the initial axial section of the thermal deposition data was selected as the origin of the coordinate system, and the positive axial direction was taken as the direction in which the axial coordinates of the thermal deposition data increased; for coordinates in the three-dimensional computational domain ( x , y , z The spallation target element, based on its radial distance to the spallation target axis. r and axial coordinates z Bilinear interpolation is performed on the Monte Carlo radial-axial thermal deposition data, and the interpolation results are expanded circumferentially and written into the corresponding cells. For cells outside the coverage of the Monte Carlo data, the volumetric heat source is set to zero. After mapping, the thermal deposition in the three-dimensional computational domain is integrated by volume, and the volumetric heat source of each cell is uniformly corrected according to the ratio of the total deposition power given by the Monte Carlo data to the integrated power after mapping, so that the total deposition power before and after mapping remains consistent.

[0052] After the initial solution, integrate the mass flow rates of the three flow path statistical sections. If the flow rate deviation of a certain flow path exceeds the tolerance, adjust the resistance parameters of the annular porous resistance zone controlling that flow path and continue solving.

[0053] IV. Equivalent and Local Heat Sink of Intermediate Heat Exchanger The intermediate heat exchanger tube bundle region uses a porous medium. The axial resistance and lateral resistance are fitted by the correspondence between axial pressure drop and axial velocity, and the correspondence between lateral pressure drop and lateral velocity, respectively. The local pressure drop of the inlet window and outlet window is represented by surface resistance. The heat exchange does not use a uniform constant heat sink throughout the region. Instead, the local shell-side temperature of each intermediate heat exchanger unit is read, and the heat exchange of a single tube is calculated according to equations (3) and (4).

[0054] The convective heat transfer coefficients inside and outside the tube can be calculated using the corresponding liquid metal heat transfer correlations. The tube-side representative temperature is taken as a constant value; the convective heat transfer coefficient outside the tube is updated based on the local shell-side temperature and local flow state. The heat transfer of a single tube is converted into a volumetric heat sink according to equation (5), and the average mixing temperature is statistically calculated at the outlet of the intermediate heat exchanger. The heat sink correction factor is calibrated using the target outlet temperature.

[0055] V. Main Pump Drive, Boundaries, and Physical Properties A volumetric momentum source is applied along the design flow direction in the main pump impeller operating region, and the total mass flow rate is obtained at the loop statistical section. The main pump volumetric momentum source is adjusted when the calculated value exceeds the tolerance.

[0056] The density, specific heat capacity, dynamic viscosity, and thermal conductivity of the liquid metal coolant update with temperature. In this example, the gas-liquid interface of the main vessel uses an adiabatic slip boundary, and the heat dissipation from the reactor body to the environment is characterized by ambient temperature and convective heat transfer coefficient on the outer wall of the main vessel. All fluid-solid interfaces use no-slip conjugate heat transfer conditions. The boundary values ​​are for illustrative purposes only, and there are no restrictions on using other boundary inputs consistent with actual facilities.

[0057] VI. Mesh, Physical Model, and Steady-State External Iteration Local mesh refinement is applied to the spallation target flow channel, component outlet, and jet mixing zone, while coarser meshes are used for large-scale pool regions and regular equivalent regions. The mesh type and quantity are selected based on geometric and computational resources. The fluid region can employ RANS methods and turbulent closure suitable for liquid metal flow; this is not the core of the invention.

[0058] Initialize the resistance of each region, the space heat source, the intermediate heat exchanger heat sink correction factor, and the main pump volumetric momentum source, and perform a steady-state solution. After reaching an external iteration node, extract the target quantities and calculate the deviations in the order of the flow rates of the three flow paths of the spallation target, the outlet temperature of the intermediate heat exchanger, and the total flow rate of the primary loop. Update the annular porous resistance, volumetric heat sink correction factor, and main pump volumetric momentum source for out-of-tolerance targets. Continue solving after parameter updates until all three target quantities meet the criteria and the flow field residuals, mass, and energy imbalances meet the thresholds.

[0059] VII. Complete Implementation Process and Verification The complete implementation process is as follows: import geometric and operating condition data; generate region identifiers and meshes; fit and load anisotropic drag; map core power and target thermal deposition; load local heat sinks in intermediate heat exchangers and volume momentum sources in main pumps; perform steady-state iterations; extract three types of target quantities; update in a directional manner according to deviation conditions; and output three-dimensional field quantities and component statistics after joint convergence.

[0060] The method of the present invention can verify the pressure drop data of a single component against the resistance of a porous structure, verify the design data of a single tube or intermediate heat exchanger against the heat sink, verify the mapped power by the energy integration of the target area, and verify the closure by the overall mass and energy balance.

Claims

1. A three-dimensional thermal-hydraulic calculation method for accelerator-driven subcritical reactors based on partitioned equivalence and additional source terms, wherein the accelerator-driven subcritical reactor includes a spallation target, a reactor core, an intermediate heat exchanger, a main pump, a main vessel, and a liquid metal coolant contained within the main vessel, characterized in that, The calculation method includes the following steps: Step 1: Obtain the geometric connectivity, pressure drop versus velocity, spatial power, target flow rate, and target heat transfer parameters of each component of the accelerator-driven subcritical reactor; establish a unified fluid-structure conjugate computational domain covering the liquid metal coolant and solid structure inside the main vessel; set the internal flow channel of the spallation target as the spallation target fine computational region; set the reactor core as the reactor core equivalent computational region corresponding to its pressure drop and heat generation function; set the intermediate heat exchanger as the intermediate heat exchanger equivalent computational region corresponding to its pressure drop and heat transfer function; and set the main pump as the main pump equivalent computational region corresponding to its flow driving function. Step 2: Determine the momentum drag parameters of each equivalent calculation region based on the pressure drop and velocity correspondence data; map the core space power data to the core equivalent calculation region, and map the spallation target space thermal deposition data to the spallation target fine calculation region; Step 3: Based on the correspondence between the flow paths of each target and the internal flow channels of the spallation target, an annular porous resistance zone is set at the corresponding position of the double-ring guide holes, and the deviation between the calculated flow rate of each target flow path and the corresponding target flow rate is used as the basis for updating the resistance parameters of the annular porous resistance zone. Step 4: Obtain the shell-side local temperature at each location in the equivalent calculation region of the intermediate heat exchanger. Calculate the single-tube heat transfer at the corresponding location based on the tube-side representative temperature, tube wall thermal resistance, and local convective heat transfer resistance. Convert the single-tube heat transfer into a volumetric heat sink in the equivalent calculation region of the intermediate heat exchanger. Use the deviation between the calculated outlet temperature of the intermediate heat exchanger and the target outlet temperature as the basis for updating the correction factor of the volumetric heat sink. Load a volumetric momentum source in the equivalent calculation region of the main pump, and use the deviation between the calculated total flow rate of the primary loop and the target total flow rate as the basis for updating the volumetric momentum source. Step 5: Perform steady-state iterative solution on the unified fluid-structure conjugate computational domain. Extract the calculated flow rate of each target flow path of the spallation target, the calculated outlet temperature of the intermediate heat exchanger, and the calculated total flow rate of the primary loop at the outer iteration node. When the deviation of any extracted quantity from its target value exceeds the corresponding allowable value, only update the resistance parameters of the annular porous resistance zone, the volumetric heat sink correction factor, or the main pump volumetric momentum source corresponding to the out-of-tolerance extracted quantity, and return to execute the steady-state iterative solution. When the deviation of all extracted quantities from their respective target values ​​does not exceed the corresponding allowable value, the outer iteration ends. Step 6: Output the three-dimensional velocity field, pressure field, liquid metal coolant temperature field, and solid temperature field under the joint convergence state, as well as the spallation target flow distribution, intermediate heat exchanger heat transfer parameters, and primary loop flow parameters.

2. The method according to claim 1, characterized in that, The unified fluid-structure conjugate computational domain also includes an upper chamber, a lower chamber, a descending channel, the main container wall, and in-core components; the spallation target fine computational domain is connected to the core equivalent computational domain, the intermediate heat exchanger equivalent computational domain, the main pump equivalent computational domain, and the liquid metal coolant pool through a fluid interface, and the liquid metal coolant exchanges heat with the solid structure through a conjugate heat transfer interface.

3. The method according to claim 1, characterized in that, The equivalent calculation region of the reactor core is established as a hexagonal prism porous medium region according to the reactor core components. The axial viscous drag parameter and axial inertial drag parameter are determined according to the correspondence between pressure drop and velocity of various components, and the lateral drag parameter is set to be greater than the axial drag parameter. Neutron power is converted into volume heat source according to component type and axial segmentation. The component box wall adopts thin-walled thermally conductive boundary to transfer heat with the adjacent liquid metal coolant region.

4. The method according to claim 1, characterized in that, The spallation target fine calculation region includes a central flow path, an inner ring flow path, and an outer ring flow path, as well as two annular porous resistance regions that control the flow distribution of the inner and outer ring flow paths; the spallation target spatial thermal deposition data is mapped to the corresponding cells of the spallation target fine calculation region through spatial interpolation.

5. The method according to claim 1, characterized in that, The equivalent calculation region of the intermediate heat exchanger includes a tube bundle porous medium region, an inlet window, and an outlet window. The anisotropic momentum drag of the tube bundle porous medium region is determined according to the correspondence between axial pressure drop and axial velocity, and the correspondence between lateral pressure drop and lateral velocity. The inlet window and outlet window use surface drag to characterize the local pressure drop.

6. The method according to claim 1, characterized in that, The single-tube heat exchange capacity is determined by the product of the overall heat transfer coefficient, the outer surface area of ​​a single heat exchange tube, and the difference between the tube-side representative temperature and the shell-side local temperature; the volumetric heat sink is determined by the single-tube heat exchange capacity, the number of heat exchange tubes, the equivalent calculation zone volume of the intermediate heat exchanger, and the heat sink correction factor.

7. The method according to claim 6, characterized in that, The overall heat transfer coefficient is calculated in series based on the convective thermal resistance inside the tube, the thermal conductivity of the tube wall, and the convective thermal resistance outside the tube; the external convective heat transfer coefficient used to determine the external convective thermal resistance is updated based on the physical properties of the liquid metal coolant corresponding to the local temperature on the shell side and the local flow parameters.

8. The method according to claim 1, characterized in that, The equivalent calculation region of the main pump includes the impeller action area, and the volumetric momentum source is loaded along the design drive direction of the main pump; when the calculated total flow rate of the primary loop does not reach the target total flow rate, the volumetric momentum source is updated according to the deviation between the two.

9. The method according to claim 1, characterized in that, In the external iteration, the spallation target flow deviation, intermediate heat exchanger outlet temperature deviation, and primary loop total flow deviation are generated respectively. For target quantities that do not exceed the tolerance, their corresponding parameters remain unchanged. For target quantities that exceed the tolerance, their corresponding parameters are updated until the three deviations simultaneously meet their respective criteria or reach the preset maximum number of external iterations.

10. The method according to claim 1, characterized in that, The density, viscosity, thermal conductivity, and specific heat capacity of the liquid metal coolant are updated with temperature; the liquid surface of the main container adopts an adiabatic slip boundary, the outer wall of the main container exchanges heat with the environment through an equivalent convective heat transfer boundary, and the fluid-solid interface adopts a non-slip conjugate heat transfer boundary.

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