Melt and concrete multiphase heat transfer and ablation diffusion calculation method and system

Abstract

The invention discloses a melt and concrete multiphase heat transfer and ablation diffusion calculation method and system, and belongs to the technical field of pressurized water reactor serious accident analysis. The method comprises the following steps: calculating melt viscosity and diffusion radius through a fragment melt diffusion model, and determining spatial distribution; molten pool temperature and boundary heat flux density are calculated based on spatial distribution and debris decay heat; calculating heat transfer to the coolant layer through a water intrusion model and a melt eruption model; calculating an interface heat transfer coefficient by adopting a gas film or slag film model according to the decomposition state of the concrete; calculating the concrete ablation rate and distance based on the interface heat transfer coefficient; and finally, comparing the ablation distance with the safety thickness to realize the safety quantitative evaluation of the reactor pit. According to the invention, the whole interaction process of the melt and the concrete can be accurately simulated, and reliable technical support is provided for serious accident analysis.

Description

Technical Field

[0001] This invention belongs to the technical field of pressurized water reactor severe accident analysis, specifically relating to a method and system for calculating multiphase heat transfer and ablation diffusion between molten material and concrete. Background Technology

[0002] In a severe accident sequence involving core meltdown, after the reactor pressure vessel (RPV) fails, the molten material interacts with the crater concrete (Molten Corium-Concrete Interaction, MCCI). This process involves complex physicochemical phenomena such as molten material diffusion, phase change, heat and mass transfer, and concrete ablation, which directly affect the accident process and the risk of radioactive material release. It is a key aspect of severe accident analysis.

[0003] Currently, internationally widely used computational programs for the interaction between molten material and concrete, such as CORCON, still have significant shortcomings. Existing programs often assume that the molten material completely fills the bottom of the reactor crater. This assumption limits the simulation of the diffusion process after the initial molten material is poured onto the concrete base. They fail to reflect the actual physical processes during diffusion, such as the formation of a crust due to solidification, viscosity changes due to crust breakage, and flow cessation caused by shear stress equilibrium. This makes it difficult to accurately describe the spatial distribution characteristics of the molten material. Furthermore, experimental results from OECD MACE / MCCI show that water can enter the shell through a long-term cracking mechanism. After cold water invades the solid shell above the molten material, it may cause the molten material to be ejected into the cold water through cracks in the shell, forming a new debris cover layer, effectively limiting the thickness of the thermally conductive zone of the shell.

[0004] Therefore, developing a computational method that can accurately describe molten material diffusion, multi-scenario heat transfer, concrete ablation, and the coupling relationships between various processes, and making up for the deficiencies of existing technologies in physical model considerations, is of great significance for improving the accuracy of MCCI analysis in severe accidents. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method and system for calculating multiphase heat transfer and ablation diffusion between molten material and concrete. By integrating a molten material diffusion model, a water intrusion model, a melt eruption model, and a gas film and slag film model within the crater, and coupling these models, numerical simulation of the entire interaction process between molten material and concrete is achieved, and the ablation distance of the crater is evaluated. This invention addresses the technical problems of inaccurate MCCI process simulation and low reliability of crater safety assessment caused by the simplification of physical models, the absence of key phenomena, and insufficient coupling analysis capabilities in the prior art.

[0006] The present invention adopts the following technical solution: A method for calculating multiphase heat transfer and ablation diffusion between molten material and concrete includes the following steps: S1. Based on the physical property parameters of the molten fragments in the crater, the viscosity of the molten fragments is calculated using a molten fragment diffusion model, and the diffusion radius of the molten fragments on the concrete base plate is calculated based on the viscosity, thereby determining the spatial distribution of the molten fragments; S2. Based on the spatial distribution determined in step S1 and the known fragment decay heat, calculate the molten pool temperature and boundary heat flux density. S3. Based on the molten pool temperature and boundary heat flux density calculated in step S2, the coolant intrusion conditions are determined by the water intrusion model and the heat flux density of the heat conduction area is calculated. At the same time, the heat exchange of the eruption is calculated by the melt eruption model. S4. Based on the decomposition state of the concrete, select either the air film model or the slag film model, and calculate the interface heat transfer coefficient based on the calculation results of steps S2 and S3. S5. Based on the interface heat transfer coefficient calculated in step S4, calculate the ablation rate of the concrete, and calculate the ablation distance according to the ablation rate. S6. Compare the ablation distance calculated in step S5 with the design safety thickness of the crater to achieve a quantitative assessment of the structural safety of the crater.

[0007] Preferably, in step S1, the fragment melt diffusion model includes the Ramacciotti model and the Kunitz model. The corresponding model is selected to calculate the viscosity based on the solid fraction of the melt. When it is necessary to simulate the nonlinear enhancement effect of the solid fraction on the viscosity, the Ramacciotti model is selected. When it is necessary to simulate the characteristic that the viscosity tends to infinity when the solid fraction approaches 1.0, the Kunitz model is selected.

[0008] Preferably, in the Ramacciotti model, the viscosity of the melt is... for:

[0009] in, It is a constant; It is given by the molten metal layer and the molten oxide layer of the fragment; This represents the molten solids fraction.

[0010] Preferably, in the Kunitz model, the viscosity enhancement of the melt is determined by the solid volume fraction. calculate:

[0011] in, It is given by the molten metal layer and the molten oxide layer of the fragment; This represents the molten solids fraction.

[0012] Preferably, in step S3, the criterion for judging the coolant intrusion condition of the water intrusion model is: when the heat flux at the top of the melt is less than the heat flux at the bottom. At that time, coolant is allowed to enter the solid shell; the dry heat flux The calculation formula is:

[0013] in, C dry It is a dimensionless empirical constant; h lv The latent heat of vaporization of water; ρ l The density of water; ρ v The density of water vapor; g It is the acceleration due to gravity; v v The dynamic viscosity of water vapor; N dry It is a numerical constant; k c The thermal conductivity of the solid shell; Δe sat This represents the change in specific enthalpy from the melt temperature to the saturation temperature. C p The specific heat capacity of the melt; Δe cr This represents the change in specific enthalpy from the crack temperature to the saturation temperature. α T The coefficient of thermal expansion of the melt; T cr This is the pyrolysis temperature; T sat This is the saturation temperature of the steam.

[0014] Preferably, the calculation process for the heat transfer during the eruption of the melt eruption model includes: Calculate the melt injection rate ,in, j melt The rate at which the melt is ejected; The entrainment coefficient; For gas injection rate, Calculated using the Ricou-Spalding relation: , The multiplier set for the user The density of the gas; The density of the melt; Determine if the melt meets the eruption conditions: ≥ ; Ejection heat transfer is based on the enthalpy change of the ejected material. calculate, The enthalpy difference between the temperature of the ejected material and the saturation temperature of the coolant.

[0015] Preferably, in step S4, when calculating the interfacial heat transfer coefficient using the air film model, the calculation is performed according to the air film tilt angle: When the tilt angle is <15°: the bubble model is adopted, the convective heat transfer coefficient is calculated based on the momentum balance of the Taylor unstable bubble unit, and the radiative heat transfer is calculated in combination with the Stefan-Boltzmann law. The total heat transfer coefficient is the sum of the convective heat transfer coefficient and the radiative heat transfer coefficient. When the tilt angle is >30°: According to the flow regime, the Nusselt number is used for laminar flow. , Let be the convective heat transfer coefficient of the inclined air film under laminar flow conditions. For air film thickness, Thermal conductivity at the end of the period, during turbulence , The Prandtl number of the air film. The overall heat transfer coefficient is obtained by combining the Reynolds number based on the thickness of the air film with radiative heat transfer. When 15°≤tilt angle≤30°: the distribution ratio of gas in the bubble and film is determined based on momentum balance, and the overall heat transfer coefficient is calculated by combining the bubble model and the film flow model. The interface heat transfer coefficient is the overall heat transfer coefficient of the air film model.

[0016] Preferably, in step S4, the heat transfer coefficient of the slag film model is... Calculated by the following formula:

[0017] in, The convective heat transfer coefficient represents the molten pool.

[0018] Preferably, in step S5, the ablation rate v of the concrete... ( abl ) Calculated by the following formula:

[0019] in, The heat flux density passing through the interface between the air film / slag film and the concrete; This refers to the density of concrete. The enthalpy required to decompose a unit mass of concrete.

[0020] Secondly, embodiments of the present invention provide a calculation system for multiphase heat transfer and ablation diffusion of molten material and concrete, comprising: The fragment molten material diffusion module is used to calculate the viscosity of the molten material based on the physical property parameters of the fragment molten material in the crater, and to calculate the diffusion radius of the molten material on the concrete base plate based on the viscosity, thereby determining the spatial distribution of the molten material; The thermal parameter calculation module is used to calculate the molten pool temperature and boundary heat flux density based on the spatial distribution and the known fragment decay heat. The coolant heat transfer module is used to determine the coolant intrusion conditions and calculate the heat flux density of the heat conduction area based on the molten pool temperature and the boundary heat flux density through the water intrusion model, and at the same time calculate the ejection heat transfer through the melt ejection model. The interface heat transfer module is used to select either an air film model or a slag film model based on the decomposition state of the concrete, and to calculate the interface heat transfer coefficient based on the molten pool temperature, boundary heat flux density, and ejection heat transfer. The ablation calculation module is used to calculate the ablation rate of concrete based on the interface heat transfer coefficient, and to calculate the ablation distance based on the ablation rate. The safety assessment module is used to compare the ablation distance with the designed safe thickness of the crater, thereby achieving a quantitative assessment of the structural safety of the crater.

[0021] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described calculation method for multiphase heat transfer and ablation diffusion of molten material and concrete.

[0022] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described calculation method for multiphase heat transfer and ablation diffusion between molten material and concrete.

[0023] Fifthly, a chip includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described calculation method for multiphase heat transfer and ablation diffusion of molten material and concrete.

[0024] In a sixth aspect, embodiments of the present invention provide an electronic device, including a computer program, which, when executed by the electronic device, implements the steps of the above-described calculation method for multiphase heat transfer and ablation diffusion between molten material and concrete.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects: A multiphase heat transfer and ablation diffusion calculation method for molten material and concrete is proposed, integrating calculation models for fragmented molten material diffusion, water intrusion, melt eruption, gas film / slag film, and ablation. This method enables numerical simulation of the entire process from molten material diffusion to crater safety assessment. The results of each step—diffusion calculation, thermal parameter solution, coolant heat transfer, interfacial heat transfer coefficient, ablation assessment, and safety judgment—are progressive and mutually supportive, overcoming the limitations of existing technologies that only assume the molten material fills the crater. This method achieves, for the first time, a full-process simulation with multi-model coupling. The step design closely reflects the physical nature of the interaction between molten material and concrete, covering core phenomena such as molten material diffusion, phase change, and heat transfer. Furthermore, it achieves quantitative safety assessment by comparing ablation distance and safe thickness. The method is logically closed-loop and highly operable, avoiding the limitations of single-model calculations. It provides a systematic and complete computational framework for severe accident analysis, significantly improving the reliability and engineering application value of the assessment results.

[0026] Furthermore, this technology overcomes the limitations of existing single-model viscosity calculations, enabling flexible model adaptation. The Ramacciotti model excels at capturing the nonlinear influence of solid fraction on viscosity, while the Kunitz model accurately simulates the physical property that viscosity tends towards infinity when the solid fraction approaches saturation. The two models complement each other, covering different operating conditions. By selectively choosing the appropriate model, the computational biases of a single model under complex conditions are avoided, significantly improving the accuracy of melt viscosity and diffusion radius calculations, and laying a reliable foundation for subsequent thermal parameter and ablation calculations.

[0027] Furthermore, the problem of ambiguous viscosity calculation parameters and poor adaptability in existing technologies has been solved. The range of values ​​for C is set in conjunction with actual working conditions to ensure the practicality of the formula; differentiated μ0 calculation logic is designed for the different characteristics of metal and oxide melts, avoiding the adaptability defects of a unified formula. The calculation results are stable and reliable, accurately reflecting the enhancing effect of solid fraction on viscosity, providing key technical support for the accurate simulation of melt diffusion processes.

[0028] Furthermore, the viscosity tends to infinity when the solid fraction is close to 1.0, which is consistent with physical reality; at the same time, the maximum value of Φ is set to 0.9 to avoid calculation singularities and ensure the stability of numerical calculation.

[0029] Furthermore, a scientific mechanism for judging coolant intrusion conditions was established, which comprehensively considers thermal-hydraulic parameters, material properties, and temperature conditions. It can accurately predict the timing and conditions for water to enter the solid shell, providing a basis for subsequent heat transfer calculations.

[0030] Furthermore, this method addresses the shortcoming of existing technologies that do not consider the heat transfer effect of melt ejection, and fully simulates the logical chain of ejection rate → ejection judgment → heat transfer calculation. The calculations of ejection rate and ejection conditions are based on classical fluid dynamics relationships, providing solid theoretical support; the heat transfer calculation incorporates the temperature changes of the ejected material, closely reflecting the actual heat transfer process. The model is coupled with the water intrusion model through drying heat flux, achieving multi-model coupling, supplementing the impact of the ejection process on overall heat transfer, making the coolant layer heat transfer calculation more comprehensive, and improving the accuracy of molten pool temperature updates.

[0031] Furthermore, the interfacial heat transfer coefficient is calculated based on the tilt angle of the air film. Different calculation models are used for different tilt angles, including bubble model, film flow model, and conversion model, comprehensively covering various possible operating conditions; at the same time, the influence of radiative heat transfer is considered, improving the accuracy of the interfacial heat transfer coefficient calculation.

[0032] Furthermore, the overall heat transfer coefficient was calculated using parallel thermal resistance, and a value of 1000 W / m was set. 2 The lower limit of K ensures both the physical rationality of the calculation and the numerical stability, and is applicable to actual working conditions where concrete and debris are in intermittent contact.

[0033] Furthermore, a direct correlation between interfacial heat flux density and ablation rate was established. By decomposing the enthalpy required per unit mass of concrete, the heat transfer process was transformed into an ablation process, providing key parameters for the final safety assessment.

[0034] It is understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0035] In summary, this invention achieves accurate simulation of the entire interaction process between molten material and concrete through multi-model coupling and systematic design, breaks through the simplification assumptions of traditional methods, improves the accuracy and reliability of severe accident analysis, and provides an effective technical means for nuclear safety assessment.

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0037] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram of the molten pool layering. Figure 3 The results are the simulation results of the CCI-1 experiment, where (a) is the final state of concrete ablation in the CCI-2 experiment, and (b) is the final state of concrete ablation in the simulation calculation. Figure 4A schematic diagram of a computer device provided in an embodiment of the present invention; Figure 5 This is a block diagram of a chip provided according to an embodiment of the present invention.

[0038] Among them, 60. Computer equipment; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic device; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0041] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0042] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0043] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0044] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0045] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0046] This invention provides a calculation method for multiphase heat transfer and ablation diffusion between molten material and concrete. It integrates a molten material diffusion model, a water intrusion model, a melt eruption model, and a gas film / slag film model within the crater to numerically simulate the entire interaction process between molten material and concrete in a severe accident. First, based on the physical properties of the molten material fragments, the viscosity and diffusion radius of the molten material are calculated using the Ramacciotti or Kunitz model to determine the spatial distribution of the molten material on the concrete substrate. Then, combining the calculated melt temperature, decay heat, and boundary heat flux density, the heat transfer with the coolant and the heat transfer during eruption are determined based on the water intrusion and melt eruption models. Next, depending on the concrete decomposition state, a gas film or slag film model is used to calculate the interfacial heat transfer coefficient and assess the ablation rate of the concrete. Finally, the calculated ablation depth is compared with the designed safe thickness of the crater to complete a quantitative assessment of the structural integrity and safety status of the crater.

[0047] Please see Figure 2 The physical system considered in this invention includes an axisymmetric concrete cavity, a multi-layered debris pool, and a coolant layer located on top of the debris. In numerical modeling, the debris bed within the crater is divided into three layers based on debris density: a light debris layer, an intermediate debris layer, and a heavy debris layer. The distribution and geometric relationships of each layer are as follows: Figure 2As shown, heat transfer between layers occurs through conduction and phase change, and the heat transfer conditions of each layer are simultaneously affected by the heat exchange of the coolant and the heat transfer between the upper and lower layers. To simulate the concrete ablation process, the boundary of the crater is discretized into several nodes, the ablation distance is calculated at each node, and the temperature field and heat transfer state of each layer are dynamically updated in conjunction with the interlayer heat flow distribution.

[0048] Please see Figure 1 This invention provides a method for calculating multiphase heat transfer and ablation diffusion between molten material and concrete, comprising the following steps: S1, a model for the diffusion of molten debris within a crater; Suppose that the crater physics system consists of an axisymmetric concrete cavity containing one or more layers of molten material fragments ejected from the failure rupture of the lower head of the reactor pressure vessel (RPV), or whose initial physical state is set by the user.

[0049] Previous calculation methods for molten material and concrete assumed that the molten pool consisted of core fragments, coolant, ablation products of concrete, and surrounding ablation material, completely filling the bottom of the reactor pit. This assumption cannot simulate the transient process of core fragments initially being dumped onto the concrete base plate, followed by the diffusion of molten fragments on the base plate.

[0050] The spreading of a viscous liquid on a solid surface is a complex physical process. This process becomes even more complicated if the liquid begins to solidify during flow. If a crust begins to form on the surface of the spreading liquid, the crust may remain stable or break down and become incorporated into the liquid. In the latter case, the resulting slurry has high viscosity and high surface tension. Eventually, the shear stress required to maintain flow exceeds the stress driving the flow, and the flow ceases. The molten material continues to solidify in place and may erode the substrate. A crater-based debris melt diffusion model allows for the formalization of debris diffusion using melt properties, thus enabling a more realistic model of debris diffusion.

[0051] One advantage of using a melt diffusion model is that it calculates the viscosity of molten fragments as a function of the melt solid fraction. Two models are used to calculate the viscosity enhancement caused by the solid / liquid phase: the Ramacciotti model and the Kunitz model.

[0052] S101, Ramacciotti model of two-phase viscosity Viscosity of molten pool fragments μ It is given by the following formula: (1) in, C It is a constant, ranging from 4 to 8, depending on the calculation conditions; μ 0 is given by the molten metal layer and the molten oxide layer of the fragment; This represents the molten solids fraction.

[0053] For molten metal: (2) in, T It is the temperature of the molten layer; M user It is the multiplier set by the user.

[0054] For oxides, μ 0 is calculated using a complex function defined by the Kendell-Moroe or Shaw relation. This method uses the maximum value of the two relations. However, if the calculated viscosity is not greater than zero, the Basalt viscosity formula is used: (3) in, T It is the temperature of the molten layer; M user It is a multiplier set by the user.

[0055] S102, Kunitz model of two-phase viscosity The Kunitz model describes the viscosity increase caused by solids suspended in a melt. The predicted viscosity increase is a function of the solid volume fraction, which is 1 when the solid fraction is negligible and approaches infinity as the solid fraction approaches 1.0.

[0056] (4) in, It is calculated based on temperature: (5) in, T liq It is the liquidus temperature. T sol It is the solidus temperature. T ave The average liquid temperature is given by the following formula: (6) in, T Z It is the axial average liquid temperature. T R It is the radial average liquid temperature. Z and R These are measurements of melt thickness and radius, respectively. Note that... The maximum value is set to 0.9. Figure 3The viscosity multipliers of Kunitz and Ramacciotti were plotted. M user Follow The relationship between the changes is shown in the figure. The Ramacciotti relation is plotted in this figure. C Several possible values.

[0057] The analysis of the melt diffusion model assumes a radius of R Height is H Volume is V=πR 2 H Density is ρ Viscosity is μ The fragments are straight cylindrical shapes. Assuming the fragment diffusion process is driven by gravity, hindered by viscous forces, and the flow is laminar, the force balance is represented by pressure: (7) in, g The acceleration due to gravity is m / s². 2 ; v(dR / dt) The characteristic velocity of the flow.

[0058] Equation (7) can be rewritten as follows: (8) Assuming the volume of the fragment is approximately constant, it can be expressed as volume. V To rewrite equation (8) to eliminate height H : (9) in, C 1 is a proportionality constant. The solution to equation (9) is as follows: (10) Where R(t0) is the radius of the melt set at the initial time, in meters; C The recommended value for 1 is 0.136.

[0059] Diffusion is calculated only if liquid remains in the molten layer. Therefore, the liquid portion of each layer in the fragment needs to be summarized.

[0060] The volume of each molten layer (including both liquid and solid components) is calculated as follows: (11) in, V m is the volume of the molten layer. 3 ; m The mass of the molten layer is expressed in kg. ρ The density of the molten layer is kg / m³ 3Once the volume and floor height are calculated... H lay Represented as: (12) in, R This is the previously calculated fragment radius. Liquid height per layer. H lay，liq Calculate as follows: (13) in, δ This refers to the solid shell at the top and bottom of the molten layer. Similarly, the liquid radius of each layer... R lay,liq The calculation is as follows: (14) in, δ It is a radially formed solid shell. Based on the radius and height of each liquid layer, assuming it is a straight cylinder, the volume of liquid in each layer is calculated. Once this volume is calculated, the liquid volume fraction can be determined. (15) The total liquid volume is calculated by dividing the average density by the total liquid mass of the fragments. Average properties such as viscosity and density are then calculated. The diffusion within the time step is then estimated using the total liquid volume, average viscosity, and density in equation (9). Equation (10) is then integrated using numerical Euler integration: y n+1 =y n +y' n ·Δt.

[0061] S2, Water Intrusion Model; The model posits that the heat flux at the top is less than the heat flux during the dry period. q'' dry In this case, water is allowed to enter the solid shell. This criterion applies to the top of the shell's conductive region. The expression for the drying heat flux is: (16) in, q'' dry For the dry heat flux, W / m 2 ; C dry It is a dimensionless empirical constant; h lv The latent heat of vaporization of water is expressed in J / kg. ρ l The density of water is kg / m³. 3 Here we take 960 kg / m 3 ; ρ vLet be the density of water vapor, which is taken as 0.59 kg / m³. 3 ; g The acceleration due to gravity is 9.8 m / s². 2 ; v v Let m be the dynamic viscosity of water vapor. 2 / s, here we take 1.29×10 -5 m 2 / s; N dry Let be a numerical constant, taken as 0.1 K·m. 1 / 2 ; k c ν is the thermal conductivity of the solid shell, W / (m·K); Δe sat The specific enthalpy change from melt temperature to saturation temperature is expressed in J / kg. C p is the specific heat capacity of the melt, J / (kg·K); Δe cr The specific enthalpy change from the crack temperature to the saturation temperature is expressed in J / kg. α T The coefficient of thermal expansion of the melt is 1 / K; T cr The pyrolysis temperature is K; T sat Let K be the saturation temperature of the steam.

[0062] The pyrolysis temperature was evaluated using the Lister formula: (17) in, σtens Let be the tensile strength of the shell, in Pa, which is taken here as 6.77 × 10⁻⁶. 7 Pa; E Let be the Young's modulus of the shell, in Pa, which is taken as 1.25 × 10⁻⁶ here. 11 Pa.

[0063] Based on the obtained dry heat flux, the thickness of the heat-conducting region σ cond The estimate is: (18) Epstein's final solution is: (19) in, α The thermal diffusivity of the solid shell; ρ Density of the solid shell, kg / m³ 3 ; q'' B The curing surface temperature, in K; hfs The latent heat of the molten material during two-phase transformation, J / kg. T mp The curing temperature of the molten layer is 1425K; T sat The saturation temperature of water is 373K.

[0064] Based on the thickness of the conductive region σ cond The thermal conductivity and heat flux density of the region can be calculated using Fourier's law, thereby determining the heat transfer and related thermal parameters between the fragment bed and the overlying coolant.

[0065] S3, Melt eruption model; Melt ejection is the process of transferring mass from the molten layer to a fragmented layer on top of the molten layer. The melt ejection rate is directly proportional to the gas ejection rate. (20) in, j melt ρ is the velocity of melt injection, in m / s; K ent The entrainment coefficient; j gas denoted as gas injection rate, in m / s.

[0066] Entrainment coefficient K ent Calculate using the Ricou-Spalding relation: (twenty one) in, E ent The multiplier set by the user defaults to 0.06; ρ gas The density of the gas is kg / m³. 3 ; ρ melt The density is the melt density, kg / m³. 3 .

[0067] There is also a condition for determining whether the melt has erupted, which is based on the minimum gas flow rate and shell permeability, and is expressed as follows: (twenty two) in, j min Minimum gas flow rate, m / s; m is the shell permeability. 2 ; ρ c The density of the shell is kg / m³. 3 ; μ gLet be the viscosity of the gas, Pa·s.

[0068] This equation applies to the assumption of a solid shell floating on the melt, and is therefore a term representing the difference between the density of the solid shell and the density of the melt.

[0069] For shell permeability Drying heat flux in the water intrusion model constructed based on step S2 q'' dry calculate: (twenty three) in, μ v Let be the viscosity of the vapor, Pa·s.

[0070] Data from reactor material fragment cooling tests show that the ejected molten fragments rapidly cool into a fragment layer, gradually accumulating on the hard shell. Considering this rapid cooling process, the increase in overlying hydrothermal flux due to the molten ejection can be calculated using the following equation: (twenty four) in, Δh m,sat The enthalpy change of the ejected material as it cools completely from the molten pool temperature to the coolant saturation temperature, expressed in J / kg.

[0071] S4, gas film model and slag film model.

[0072] Early MCCI calculation programs used a heat transfer model where the molten pool was in direct contact with the concrete, failing to consider the potential presence of an air film generated by concrete decomposition or a slag film formed by intermittent contact between the concrete and debris, thus neglecting this important heat transfer effect. This invention introduces possible air film and slag film models respectively.

[0073] S401, air-supported membrane model; The gases released during concrete decomposition are sufficient to form a stable gas film between the concrete and the core molten pool. On horizontal and near-horizontal surfaces, Taylor instability causes bubbles to form and enter the melt, while on steeper, sloping surfaces, the gases form a flowing gas film.

[0074] Specifically, for stable air films, two heat transfer models are used: one for nearly horizontal air films, where there is almost no airflow parallel to the concrete surface; and the other for inclined air films, where there is airflow parallel to the concrete surface. If the inclination of the air film is less than 15 degrees, it is classified as "nearly horizontal".

[0075] For a stable gas film on a near-horizontal surface, also known as a bubble model, the heat transfer process is calculated using a mechanistic model based on the momentum balance principle in Taylor's unstable bubble unit.

[0076] The results can be presented in the form of a Nusselt number based on film thickness: (25) in, h B The convective heat transfer coefficient of the air film is W / (m²). 2 ·K); δ B The thickness of the air film is in meters (m). k g Thermal conductivity at the end of the period, W / (m·K).

[0077] The thickness of the air film is given by the following formula: (26) in, L Material properties; Re B Reynolds number. Material properties. L It is given by the following formula: (27) Where g is the acceleration due to gravity, m / s² 2 ; ρ l , ρ g These are the density of the molten pool and the density of the gas film, respectively, in kg / m³. 3 ; μ g ρ is the viscosity of the gas film, Pa·s.

[0078] Reynolds number Re B It is given by the following formula: (28) in, j g The apparent velocity of the gas entering the friction is m / s; a The Laplace characteristic length is given by the following formula: (29) in, σ t The surface tension of the molten layer is N / m.

[0079] Substituting the above formula into equation (25), the convective heat transfer coefficient of the near-horizontal membrane can be obtained, and then the heat transfer from the air film to the concrete can be obtained.

[0080] This bubble model is suitable for tilt angles less than 15 degrees. For tilt angles greater than 30 degrees, a membrane flow model is used, considering both laminar and turbulent membranes. The Nusselt number for turbulent conditions is... Nu LF for: (30) For laminar flow, the Nusselt number Nu TF for: (31) in, Pr It is the Prandtl number of the air film. The Reynolds number is based on the thickness of the gas film and is determined by the following formula: (32) in, u denoted as the average velocity of the air film, in m / s.

[0081] The thickness of the air film satisfies the following formula: (33) (34) in, θ The angle of inclination of the air film relative to the horizontal plane.

[0082] The above formula can be used to calculate the convective heat transfer coefficient when the air film tilt angle is above 30 degrees, and then the heat transfer from the air film to the concrete can be obtained.

[0083] Here, a conversion model between the bubble model and the membrane flow model needs to be added, with the angle between the gas film and the horizontal between 15° and 30°. A mechanism model based on momentum balance is introduced, in which part of the injected gas enters the bubble, and the remainder is used to form a thin film. The result is: (35) (36) Where f is the proportion that enters the bubble during the gas generation process.

[0084] Because the temperature of the air film is relatively high, radiative heat transfer on the air film must also be considered. Radiative heat transfer is calculated by the following formula: (37) in, T A The temperature of the gas film on the molten pool side, in K; T W The temperature of the ablation surface of the concrete, in K; ε P Emissivity of the gas film on the molten pool side; ε W Emissivity of the ablated concrete surface; σ B The Stefan-Boltzmann constant is 5.67 × 10⁻⁶. -8 W / (m 2 ·K 4 ).

[0085] S402, slag film model; In most real-world accident conditions, the stable gas film assumption is incorrect. Instead, the amount of gas released is typically far less than required to form a stable gas film, resulting in intermittent contact between the concrete and the debris. This intermittent contact leads to the periodic growth and shedding of slag at the interface, and, depending on the temperature of the molten debris, may also cause the periodic growth and shedding of the debris shell. Users can choose between a slag model or a gas film model at the start of the calculation.

[0086] The heat transfer coefficient of the slag film is given by the following formula: (38) in, h p The convective heat transfer coefficient of the molten pool, W / m 2 K; h s The convective heat transfer coefficient of the slag film, W / m 2 K. It is recommended to set one here. h s Lower limit: 1000W / m 2 K, this value simulates the heat conduction on a 1 mm slag film layer.

[0087] Heat transfer through a gas film or slag film is calculated based on its surface temperature. On the molten pool side, the temperature T is indirectly determined by the requirement of heat flux continuity. In summary, the total heat transfer through the molten pool film is: (39) in, h f This is the heat transfer coefficient of the gas film / slag film; when using the slag film model for calculation, the radiation heat transfer term is ignored.

[0088] S5, ablation of concrete; Heat transfer between the air film / slag film and the concrete controls the ablation of the concrete. The heat flux density across the interface between the air film / slag film and the concrete is... q p From equation (39), the ablation rate on the concrete boundary is calculated as follows: (40) in, The density of concrete, kg / m³ 3 ; The enthalpy required to decompose a unit mass of concrete, in J / kg.

[0089] The ablation distance can then be calculated: (41) in, δ abl Let be the distance of concrete ablation within time t, in meters.

[0090] By comparing the calculated ablation distance of the concrete with the designed safe thickness of the crater, a quantitative assessment can be made as to whether the crater has burned through. When the ablation distance reaches or exceeds the actual thickness of the crater, it can be determined that the crater has burned through; if the ablation distance is less than the thickness of the crater, it indicates that the crater still maintains its structural integrity. This assessment result can provide a direct basis for judging the safety status of the reactor crater, formulating emergency protection measures, and designing subsequent structural repair plans.

[0091] In another embodiment of the present invention, a multiphase heat transfer and ablation diffusion calculation system for molten material and concrete is provided. This system can be used to implement the above-mentioned multiphase heat transfer and ablation diffusion calculation method for molten material and concrete. Specifically, the multiphase heat transfer and ablation diffusion calculation system for molten material and concrete includes a fragment molten material diffusion module, a thermal parameter calculation module, a coolant heat transfer module, an interface heat transfer module, an ablation calculation module, and a safety assessment module.

[0092] Among them, the fragment melt diffusion module is used to calculate the viscosity of the melt based on the physical property parameters of the fragment melt in the pile pit, and calculate the diffusion radius of the melt on the concrete base plate according to the viscosity, thereby determining the spatial distribution of the melt; The thermal parameter calculation module is used to calculate the molten pool temperature and boundary heat flux density based on the spatial distribution and the known fragment decay heat. The coolant heat transfer module is used to determine the coolant intrusion conditions and calculate the heat flux density of the heat conduction area based on the molten pool temperature and the boundary heat flux density through the water intrusion model, and at the same time calculate the ejection heat transfer through the melt ejection model. The interface heat transfer module is used to select either an air film model or a slag film model based on the decomposition state of the concrete, and to calculate the interface heat transfer coefficient based on the molten pool temperature, boundary heat flux density, and ejection heat transfer. The ablation calculation module is used to calculate the ablation rate of concrete based on the interface heat transfer coefficient, and to calculate the ablation distance based on the ablation rate. The safety assessment module is used to compare the ablation distance with the designed safe thickness of the crater, thereby achieving a quantitative assessment of the structural safety of the crater.

[0093] This invention provides a terminal device comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or corresponding function. The processor described in this embodiment can be used for the operation of a calculation method for multiphase heat transfer and ablation diffusion of molten material and concrete, including: Based on the physical properties of the molten fragments within the crater, the viscosity of the molten fragments is calculated using a fragment diffusion model, and the diffusion radius of the molten fragments on the concrete base is calculated based on the viscosity, thereby determining the spatial distribution of the molten fragments. Based on the determined spatial distribution and the known fragment decay heat, the molten pool temperature and boundary heat flux density are calculated. Based on the calculated molten pool temperature and boundary heat flux density, the coolant intrusion conditions are determined using a water intrusion model, and the heat flux density of the heat conduction zone is calculated. Simultaneously, the ejection heat transfer is calculated using a melt ejection model. Depending on the decomposition state of the concrete, either a gas film model or a slag film model is selected, and the interface heat transfer coefficient is calculated based on the calculation results. Based on the calculated interface heat transfer coefficient, the ablation rate of the concrete is calculated, and the ablation distance is calculated based on the ablation rate. The calculated ablation distance is compared with the designed safe thickness of the crater to achieve a quantitative assessment of the structural safety of the crater.

[0094] Please see Figure 4The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the multiphase heat transfer and ablation diffusion calculation method between the molten material and concrete in this embodiment. To avoid repetition, these details are not elaborated here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the multiphase heat transfer and ablation diffusion calculation system between the molten material and concrete in this embodiment. To avoid repetition, these details are not elaborated here.

[0095] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 4 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0096] The processor 61 may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0097] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or RAM of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., provided on the computer device 60.

[0098] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0099] Please see Figure 5 The terminal device is an electronic device 600, which is manifested in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0100] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 1 The steps are shown in the figure.

[0101] Storage unit 620 may include a readable medium in the form of a volatile storage unit, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include a read-only memory (ROM) 6203.

[0102] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0103] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0104] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem). This communication can be performed via input / output interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network, wide area network, and / or public network, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0105] Example 4 This invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). More specific examples of the computer-readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, random access memory, read-only memory, erasable programmable read-only memory, optical fiber, portable compact disk read-only memory, optical storage device, magnetic storage device, or any suitable combination thereof.

[0106] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, radio frequency, etc., or any suitable combination thereof.

[0107] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0108] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the calculation method for multiphase heat transfer and ablation diffusion between molten material and concrete in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor in the following steps: Based on the physical properties of the molten fragments within the crater, the viscosity of the molten fragments is calculated using a fragment diffusion model, and the diffusion radius of the molten fragments on the concrete base is calculated based on the viscosity, thereby determining the spatial distribution of the molten fragments. Based on the determined spatial distribution and the known fragment decay heat, the molten pool temperature and boundary heat flux density are calculated. Based on the calculated molten pool temperature and boundary heat flux density, the coolant intrusion conditions are determined using a water intrusion model, and the heat flux density of the heat conduction zone is calculated. Simultaneously, the ejection heat transfer is calculated using a melt ejection model. Depending on the decomposition state of the concrete, either a gas film model or a slag film model is selected, and the interface heat transfer coefficient is calculated based on the calculation results. Based on the calculated interface heat transfer coefficient, the ablation rate of the concrete is calculated, and the ablation distance is calculated based on the ablation rate. The calculated ablation distance is compared with the designed safe thickness of the crater to achieve a quantitative assessment of the structural safety of the crater.

[0109] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0110] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0111] To verify the correctness and effectiveness of the calculation method for multiphase heat transfer and ablation diffusion between melt and concrete based on melt stratification, a melt cooling and concrete interaction (CCI) experiment conducted by the Organization for Economic Co-operation and Development (OECD) was used for verification.

[0112] The purpose of the CCI experiment was to provide validation data on the interaction between the reactor core molten material and the concrete base under severe accident conditions, including the rates of lateral and axial erosion of the concrete, the generation of gases / aerosols, the formation and strength of the top shell, and the cooling properties of the molten material ejected from the top surface. The CCI-2 experiment, conducted within this framework, aimed to study concrete erosion. The experimental setup consisted of a test section, the lower part of which contained concrete / magnesia walls and a bottom, a device for submerging the molten material, a permeation lance for testing the shell strength, and piping for condensation / steam collection. The internal gas was initially helium; no analysis was attempted on the escaping gases / aerosols, which were filtered out at the drill outlet. The initial molten material was formed by the combustion of thermite, and power input was maintained using a direct electric heater, keeping the molten material temperature at approximately 1880°C. The concrete chamber bottom dimensions were 50cm × 50cm, the initial molten material height was 25cm, the total mass was approximately 400kg, and the average bulk density was 2900kg / m³. 3The average porosity of the entire charge was approximately 48%. The chamber walls were made of MgO, with the bottom and sides constructed of silica concrete. The maximum permissible lateral / axial ablation depth was 35 cm. The experimental procedure is as follows: 1) First, after an initial heating stage, the thermite is completely burned, and the initial melting temperature is 2000°C; 2) Concrete ablation begins approximately 0.1-0.38 minutes into the experiment; 3) The electric heater reached its maximum power at approximately 1.56 minutes into the experiment; 4) When the experiment had been going on for about 300.79 minutes, water began to be added. 5) At approximately 312.6 minutes into the experiment, the power supply to the electric heater was switched to constant voltage, and the power decreased. 6) Data acquisition was terminated at approximately 423.1 minutes into the experiment.

[0113] Table 1 Comparison of simulation results and experimental results

[0114] The crater geometry, melt mass, and material properties from the CCI-2 experiment were input as boundary conditions into the model. The calculated results were compared with the experimental results, and the corresponding simulation results are as follows: Figure 3 As shown in the figure. The comparison results of simulation and experiment show that the calculation method model developed in this invention based on melt layering and multiphase heat transfer and ablation diffusion between molten material and concrete can effectively predict the sidewall ablation distance, the base ablation distance, and the corresponding ablation rate of the crater.

[0115] In summary, this invention provides a method and system for calculating multiphase heat transfer and ablation diffusion between molten material and concrete. Based on multi-physics model coupling, it integrates a fragment molten material diffusion model, a water intrusion model, a melt eruption model, and a gas film / slag film model to numerically simulate the entire interaction process between molten material and concrete under severe nuclear power plant accidents. First, the viscosity and diffusion radius of the molten material are calculated. Then, the coolant intrusion conditions and eruption heat transfer effects are determined by combining the heat transfer calculation results. Subsequently, either a gas film model or a slag film model is selected to accurately calculate the interfacial heat transfer coefficient and the concrete ablation rate. Through the above analysis and calculation, the obtained concrete ablation depth is compared with the designed safe thickness of the crater, quantitatively assessing the safety status of the crater structure and providing a scientific basis for safety judgment and emergency decision-making under severe accidents.

[0116] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0117] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0118] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0119] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0120] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0121] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0122] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random-access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electrical carrier signals and telecommunication signals.

[0123] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus, and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0124] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0125] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0126] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for multiphase heat transfer and ablation diffusion of a melt with concrete, characterized in that, The method comprises the following steps: S1, based on the physical parameters of the debris melt in the pit, the viscosity of the melt is calculated by a debris melt diffusion model, and the diffusion radius of the melt on the concrete bottom plate is calculated according to the viscosity, so as to determine the spatial distribution of the melt; S2, based on the spatial distribution determined in step S1 and the known decay heat of the debris, the pool temperature and the boundary heat flux are calculated; S3, based on the pool temperature and the boundary heat flux calculated in step S2, the coolant invasion condition is judged by a water invasion model and the heat flux density of the heat conduction area is calculated, and the eruption heat transfer amount is calculated by a melt eruption model; S4, according to the decomposition state of the concrete, the gas film model or the slag film model is selected, and the interface heat transfer coefficient is calculated based on the calculation results of steps S2 and S3; S5, based on the interface heat transfer coefficient calculated in step S4, the ablation rate of the concrete is calculated, and the ablation distance is calculated according to the ablation rate; S6, the ablation distance calculated in step S5 is compared with the design safety thickness of the pit to realize quantitative evaluation of the safety of the pit structure.

2. The method of claim 1, wherein, In step S1, the debris melt diffusion model includes Ramacciotti model and Kunitz model, and the corresponding model is selected to calculate the viscosity according to the solid phase fraction of the melt; when the nonlinear enhancement effect of the solid phase fraction on the viscosity needs to be simulated, the Ramacciotti model is selected; when the characteristic that the viscosity tends to infinity when the solid phase fraction approaches 1.0 needs to be simulated, the Kunitz model is selected.

3. The method of claim 2, wherein, In the Ramacciotti model, the viscosity of the melt is: wherein is a constant; is given by the molten metal layer and the molten oxide layer of the debris; is the fraction of molten solid.

4. The method of claim 2, wherein, In the Kunitz model, the viscosity enhancement of the melt by the solid volume fraction Calculation: wherein, given by the molten metal layer and the molten oxide layer of the debris; is the molten solid fraction.

5. The method of claim 1, wherein, In step S3, the coolant invasion condition judging criterion of the water invasion model is that when the heat flux at the top of the melt < the dryout heat flux, the coolant is allowed to enter the solid shell; and the calculation formula of the dryout heat flux is: ​​ wherein, C dry is a dimensionless empirical constant; h lv is the latent heat of vaporization of water; ρ l is the density of water; ρ v is the density of water vapor; g is the acceleration due to gravity; v v is the dynamic viscosity of water vapor; N dry is a numerical constant; k c is the thermal conductivity of the solid shell; Δe sat is the specific enthalpy change from the melt temperature to the saturation temperature; C p is the specific heat capacity of the melt; Δe cr is the specific enthalpy change from the crack temperature to the saturation temperature; α T is the thermal expansion coefficient of the melt; T cr is the cracking temperature; T sat is the saturation temperature of the steam.

6. The method of claim 5, wherein, The eruption heat transfer amount calculation process of the melt eruption model includes: Calculating melt blow rate wherein, j melt is the rate of melt blow; is the entrainment factor; is the gas blow rate, Using the Ricou-Spalding relationship to calculate: , is the user defined entrainment multiplier, is the gas density; is the melt density; determining whether the melt meets the eruption condition: ≥ ; The heat of ejection is based on the enthalpy change of the ejected material The calculation, is the enthalpy difference for the ejected material to cool from the melt pool temperature to the coolant saturation temperature.

7. The method of claim 1, wherein, In step S4, when the gas film model is used to calculate the interface heat transfer coefficient, the calculation is classified according to the inclination angle of the gas film: When the inclination angle is < 15°: the bubble model is used, the convective heat transfer coefficient is calculated based on the momentum balance of Taylor unstable bubble unit, the radiation heat transfer is calculated combined with Stefan-Boltzmann law, and the total heat transfer coefficient is the sum of the convective heat transfer coefficient and the radiation heat transfer coefficient; When the inclination angle > 30°: Nusselt number for laminar flow , is the convective heat transfer coefficient for the inclined gas film in laminar flow, is the gas film thickness, is the thermal conductivity at the end of the turbulent flow , is the Prandtl number of the gas film, is the Reynolds number based on the gas film thickness, and the total heat transfer coefficient is obtained by combining the radiation heat transfer; When 15°≤ inclination angle≤ 30°: the distribution ratio of gas in the bubble and the film is determined based on the momentum balance, and the total heat transfer coefficient is calculated by combining the bubble model and the film flow model; The interface heat transfer coefficient is the total heat transfer coefficient of the gas film model.

8. The method of claim 1, wherein, In step S4, the heat transfer coefficient of the slag film model is calculated is calculated from the following equation: wherein, represents the convective heat transfer coefficient of the molten pool.

9. The method of claim 1, wherein, In step S5, the ablation rate v of the concrete ( abl ) is calculated from the following formula: wherein, is the heat flux through the air / slag film and the concrete contact interface; is the density of the concrete; is the enthalpy required to decompose a unit mass of concrete.

10. A molten material and concrete multiphase heat transfer and ablation diffusion computational system, comprising: It comprises: a debris melt diffusion module, configured to calculate the viscosity of the melt based on the physical parameters of the debris melt in the pit, and calculate the diffusion radius of the melt on the concrete bottom plate according to the viscosity, so as to determine the spatial distribution of the melt; a thermal parameter calculation module, configured to calculate the pool temperature and the boundary heat flux based on the spatial distribution and the known decay heat of the debris; a coolant heat transfer module, configured to judge the coolant invasion condition by a water invasion model and calculate the heat flux density of the heat conduction area based on the pool temperature and the boundary heat flux, and calculate the eruption heat transfer amount by a melt eruption model; an interface heat transfer module, configured to select the gas film model or the slag film model according to the decomposition state of the concrete, and calculate the interface heat transfer coefficient based on the pool temperature, the boundary heat flux and the eruption heat transfer amount; An ablation calculation module is configured to calculate an ablation rate of the concrete based on the interface heat transfer coefficient and to calculate an ablation distance according to the ablation rate; A safety evaluation module is configured to compare the ablation distance with a design safety thickness of the heap pit to realize quantitative evaluation of the safety of the heap pit structure.

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