CN115099172A - Method for analyzing characteristics of forming process of molten mass fragment bed - Google Patents
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Abstract
A method for analyzing characteristics of a melt scrap bed forming process mainly comprises the following steps: 1. carrying out geometric modeling and grid division; 2. modeling the shape of the fragments of the melt, selecting the materials of the fragments and the coolant, and setting initial parameters; 3. coupling EDEM software and Fluent software, and setting a calculation model and boundary conditions; 4. calculating a conservation equation of fluid mass, energy and momentum to obtain gas-liquid share, fluid state and temperature distribution; 5. calculating the solid-liquid interaction force and the heat transfer model to obtain the drag force and the heat transfer quantity of the fluid to the fragments; 6. calculating a solid collision mechanical model and a heat conduction model of the melt fragments; 7. calculating the position, the speed and the temperature distribution of the melt fragments at the next moment by combining the drag force and the heat transfer quantity information transmitted by the Fluent; 8. and judging whether the ending time is reached, if not, advancing according to the time step, and if so, outputting a calculation result. Based on the process of the present invention, the final melt scrap bed morphology characteristics can be predicted.
Description
Technical Field
The invention relates to the technical field of research on fluid-solid coupling mechanical action and heat transfer phase change of nuclear power plant severe accident reactor core melt fragments and a coolant, in particular to a method for analyzing characteristics of a melt fragment bed forming process.
Background
In the three-mile nuclear accident in 1979, the reactor core is melted down to melt part of the zirconium cladding nuclear uranium fuel of the fuel rod, so that radioactive substances leak out. The accident causes high attention of scholars in the international nuclear field to the serious accident of the nuclear reactor, and a serious accident management strategy is proposed for the accident: an In-Vessel Retention (IVR) strategy. The in-core molten material retention refers to that after a severe accident occurs in a nuclear power plant, the in-core molten material is retained in the pressure vessel by adopting a series of strategies or means so as to maintain the integrity of the pressure vessel, and therefore the consequences of the severe accident are limited within the boundary of a primary loop.
The international intensive research on the strategy of the molten material retention in the reactor is carried out, and the behaviors after the serious accident of the molten reactor core can be divided into the following aspects: the melt and water interact (including steam explosion stage, jet flow breaking), the fragments of the melt are settled and piled to form a fragment bed, the fragment bed is cooled, the fragment bed is remelted, and the dynamic behavior of a molten pool. The invention relates to a calculation method developed by analyzing characteristics of a melt fragment bed forming process, which mainly aims at a steam explosion process and a fragment bed cooling process, and relatively blanks the research on the fragment bed forming process and the fragment bed remelting process.
The research on the formation process of the fragment bed in the initial stage mainly utilizes experimental research, a large amount of experiments for injecting the molten materials into the water pool are internationally carried out on the research, and a series of mechanism models, semi-empirical formulas and empirical formulas are provided according to the experiments. On the basis of experiments and models, a large number of integrated serious accident analysis programs are developed, and a series of processes after the melt jet flow enters the water pool can be simulated. Nevertheless, due to the complexity of the various processes themselves and the limited experimental conditions (e.g., using simulated materials and non-prototype dimensions), there is still a great deal of uncertainty in the current knowledge and prediction of certain phenomena of severe accidents. The late process of melting the molten materials in the reactor is an area needing further research, because the late process not only influences the prediction of a power plant on the whole serious accident, but also is related to the dynamic evolution of the molten materials in the reactor on a pressure vessel, and is closely related to the safety of the nuclear reactor.
The molten material is cracked after contacting with the coolant water to form molten material fragments with indefinite size and shape, and the molten material fragments are driven by gravity to settle and are deposited in the reactor core supporting structure or the lower cavity of the reactor vessel to form a fragment bed, which is called a fragment bed forming process. The chip bed forming process plays a decisive role in determining the final shape of the chip bed, and the research on the process has great significance in improving the cooling performance of the chip bed, reducing the remelting risk of the chip bed and maintaining the integrity of a containment vessel of a pressure vessel, but the research on a calculation model of the chip bed forming process is relatively few, and the chip bed forming process belongs to an imperfect research field at home and abroad.
Some researchers in the field of severe accidents of nuclear reactors use mechanical analysis methods and Computational Fluid Dynamics (CFD) methods to simulate the formation process of the debris bed, for example, Discrete Element Method (DEM) is used to perform two-dimensional and three-dimensional numerical simulation on the formation process of the debris bed in severe accidents, Contact Dynamics (CD) is used to study the collapse and accumulation of molten core debris, and the porosity of the accumulation form of the debris bed is analyzed. However, the discrete medium mechanical analysis method can only complete the collision simulation among particles, and cannot meet the requirements of solid-liquid two-phase flow simulation. Some researchers have simulated the melt chips as a continuous medium, such as using the CFD method to study the interaction of melt and water, but the calculations did not match well with small scale mixing experiments.
Therefore, the present study provides a method for characterization of the formation process of a melt scrap bed, combining the method of discrete medium mechanical analysis and computational fluid dynamics.
Disclosure of Invention
In order to research the interaction process of fragments and a coolant and obtain the movement characteristics of molten mass fragments and the final shape of a fragment bed in the forming process of the fragment bed, the invention provides a method for analyzing the characteristics of the forming process of the molten mass fragments and the final shape of the fragment bed on the basis of the prior art aiming at the simulation of a molten accident of a reactor core of a nuclear power plant and the experimental simulation of the interaction of the molten mass and water, the method can research the interaction process of the molten mass solid fragments, the fluid-solid coupling interaction process of the molten mass solid fragments and a flowing coolant and the heat transfer and phase change phenomena in the heat transfer process of the molten mass solid fragments and the flowing coolant, has the advantages of high calculation speed and simple calculation setting, avoids a large amount of fussy pretreatment and aftertreatment, and can obtain the change process of the position, speed, temperature and resultant force of the molten mass fragments along with time in the sedimentation process of the particles of the molten mass fragments and the particles, the changes of gas-liquid volume fraction, fluid distribution, speed, pressure and temperature in a fluid domain along with time are obtained, the interaction force and the interphase heat transfer quantity between the solid of the melt and the fluid are obtained, the final fragment bed accumulation form, the porosity and the temperature distribution are obtained, and the movement process of the melt fragments, the gas-liquid boiling phenomenon, the solid-liquid temperature change process and the solid-liquid interphase interaction force in the fragment bed forming process can be analyzed and the final fragment bed form can be predicted according to the data.
In order to achieve the purpose, the invention adopts the following technical scheme to implement:
a method for characterization of a melt scrap bed formation process, comprising the steps of:
step 1: acquiring the characteristic information of the fragments of the molten material and the information of the core structure or experimental equipment of the nuclear reactor based on a calculation object in the simulation of the core fusion accident of the nuclear power plant reactor or the interaction experiment of the molten material and water, carrying out geometric modeling on the core structure or experimental equipment, the fragments of the molten material and the calculation domain of the fluid, and carrying out grid division on a geometric body;
step 2: modeling the shape and size of the melt fragments in EDEM software, setting basic information of material type, material thermophysical property, material mechanical property, mass or volume, initial speed and initial temperature of the melt fragments, setting information of material type, material thermophysical property and mechanical property of a nuclear reactor core structure or an experimental container, and setting contact mechanical parameters among the melt fragments and between the melt fragments and a wall surface; selecting a fluid name in Fluent software, and setting the form, the thermophysical property, the initial temperature, the initial speed and the distribution of the fluid in a calculation domain;
and step 3: the Fluent software is coupled with an adapter Interface provided by the EDEM software through the UDF function of the Fluent software, so that the melt fragment motion and flow field information of the two pieces of software can be mutually transmitted; selecting a contact mechanics model and a particle heat transfer model of the melt fragments in the EDEM software, and setting boundary conditions, calculation time step length, calculation time and data storage frequency for the release of the melt fragments; selecting a multi-phase flow model, a turbulence model, a gas-liquid evaporation and condensation model, a fluid-solid coupling drag force model and corresponding boundary conditions of fluid in Fluent software;
and 4, step 4: combining initial melt fragment particle information transmitted by EDEM software, regarding the melt fragments as solid phase fragments injected by a DPM model in Fluent software, and calculating a mass equation, a momentum equation and an energy equation by using a multiphase flow model in Fluent software to obtain gas-liquid share and distribution of a fluid domain, a fluid flow state and temperature distribution at the next moment; wherein, the gas-liquid share is calculated by using an evaporation and condensation model-Lee model, and as shown in formulas (1), (2) and (3), the gas-liquid phase-to-phase mass exchange can be calculated:
in the formula:
v-represents the vapor phase;
l-represents a liquid phase;
α v -steam volume fraction;
ρ v -steam density/kg m -3 ；
α l -volume fraction of liquid phase;
ρ l -density of liquid phase/kg. m -3 ；
T l -liquid phase temperature/K;
T sat -liquid phase saturation temperature/K;
c-adjustment factor, similar to relaxation time;
and 5: calculating drag force and interphase heat transfer quantity of fluid to the melt fragment particles by using a fluid-solid coupling mechanical model and a fluid-solid interphase heat transfer model, and transferring the drag force and the interphase heat transfer quantity to all the melt fragment particles in the EDEM software; the fluid-solid coupling mechanical model is as the following formula (4), and the fluid-solid heat transfer model is as the following formula (5):
in the formula:
s-represents the melt fragment particle phase;
f-represents a fluid phase;
m s -mass of particles/kg;
τ r -a particle relaxation time;
ρ s -density of the melt scrap particle phase/kg m -3 ；
ρ f -fluid phase density/kg · m -3 ；
h-convective heat transfer coefficient/W.m -2 ·K -1 ；
T s -melt scrap particle phase temperature/K;
A s particle surface area/m 2 ；
T ∞ -local temperature of continuous phase/K; epsilon s Particle emissivity (dimensionless);
sigma-stefin-boltzmann constant/W·m -2 ·K -4 ；
θ R -radiation temperature/K;
step 6: calculating mutual collision among the melt scrap particles by using a Hertz-Mindlin contact mechanical model represented by formula (6), formula (7) and formula (8), and calculating heat transfer quantity among the melt scrap particles by using a solid scrap particle heat conduction model represented by formula (9) and formula (10);
in the formula:
E * -equivalent young's modulus/Pa;
R * -equivalent radius/m;
δ n -the amount of normal overlap of the melt scrap particles/m;
beta-equivalent coefficient of restitution;
m * -equivalent mass/kg;
S n -normal stiffness/Pa · m;
F t e -represents the tangential spring force/N;
F t d -represents the tangential damping force/N;
S t -tangential stiffness/Pa · m;
δ t -the amount of tangential overlap of the melt chips particles/m;
m is mass/kg;
C p specific heat capacity/J.kg -1 ·K -1 ；
T-temperature/K;
q-quantity of Heat transfer between melt fragments/J.s -1 ；
Q p1p2 Between the melt fragment particle p1 and the particle p2Heat exchange amount/J · s -1 ；
h c -heat transfer coefficient/W.m -2 ·K -1 ；
ΔT p1p2 The temperature difference/K between the melt fraction particles p1 and p2
k p1 ,k p2 Thermal conductivity/W.m of melt scrap particles p1 and particles p2 -2 ·K -1 ；
And 7: combining the drag force and the interphase heat transfer quantity information of the melt fragment particles transmitted by UDF in Fluent software, calculating the position and the speed of the melt fragment particles at the next moment by using a Newton second law, and calculating the temperature distribution of the melt fragment particles by using a basic heat conduction model;
and step 8: repeating the steps 4 to 7 within the set calculation time, obtaining the change process of the position, the speed, the temperature and the resultant force of the fragments in the sedimentation process of the fragments of the melt at different moments along with the time, obtaining the change of the gas-liquid volume fraction, the fluid distribution, the speed, the pressure and the temperature of the fluid domain along with the time, obtaining the interaction force and the interphase heat transfer between the solid fragments of the melt and the fluid, and obtaining the final accumulation form, the porosity and the temperature distribution of the fragments of the melt bed. Through the data, the movement process of the molten mass fragments, the collision process of the molten mass fragments, the interaction process of the molten mass fragments and the fluid, the gas-liquid boiling phenomenon, the temperature change process of the fluid and the molten mass solid fragments in the forming process of the molten mass fragment bed can be analyzed, and the final molten mass fragment bed form can be predicted, so that the cooling performance of the fragment bed is improved, the remelting risk of the fragment bed is reduced, and the integrity of the containment vessel of the pressure vessel is maintained.
Compared with the prior art, the invention has the following advantages:
the analysis method can accurately solve the collision between the fragments of the molten material and the wall surface, and simultaneously considers the interaction force between the fragments of the molten material and the fluid and the heat exchange between phases; aiming at irregular melt fragments, the invention can combine regular particles to form irregular melt fragments with different sizes and irregular shapes, so that the fragment movement characteristics in the fragment bed forming process are more real. And the EDEM software and the Fluent software are very convenient to couple, the advantages of high calculation speed and calculation setting exist, a large amount of complicated pre-treatment and post-treatment are avoided, and large-scale calculation can be carried out, so that the safety of the reactor is more efficiently and accurately evaluated.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
FIG. 2 is a schematic diagram of a chip bed formation experiment.
Fig. 3a and 3b are schematic views of the shapes of the elongated chips and the elongated bent chips, respectively.
FIG. 4 is a schematic view showing the form of a chip bed formed by stacking chips of a melt.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Step 1: acquiring the characteristic information of the fragments of the molten material and the information of the core structure or experimental equipment of the nuclear reactor based on a calculation object in the simulation of the core fusion accident of the nuclear power plant reactor or the interaction experiment of the molten material and water, carrying out geometric modeling on the core structure or experimental equipment, the fragments of the molten material and the calculation domain of the fluid, and carrying out grid division on a geometric body;
step 2: modeling the shape and size of the melt fragments in EDEM software, setting basic information of material type, material thermophysical property, material mechanical property, mass or volume, initial speed and initial temperature of the melt fragments, setting information of material type, material thermophysical property and mechanical property of a nuclear reactor core structure or an experimental container, and setting contact mechanical parameters among the melt fragments and between the melt fragments and a wall surface; selecting a fluid name in Fluent software, and setting the form, the thermophysical property, the initial temperature, the initial speed and the distribution of the fluid in a calculation domain;
and step 3: the method comprises the following steps that 1, the Fluent software and an adapter Interface provided by the EDEM software are coupled through the UDF function of the Fluent software, so that the melt fragment motion and flow field information of the two pieces of software can be transmitted mutually; selecting a contact mechanics model and a particle heat transfer model of the melt fragments in the EDEM software, and setting boundary conditions, calculation time step length, calculation time and data storage frequency for the release of the melt fragments; selecting a multi-phase flow model, a turbulence model, a gas-liquid evaporation and condensation model, a fluid-solid coupling drag force model and corresponding boundary conditions of fluid in Fluent software;
and 4, step 4: combining initial melt fragment particle information transmitted by EDEM software, regarding the melt fragments as solid phase fragments injected by a DPM model in Fluent software, and calculating a mass equation, a momentum equation and an energy equation by using a multiphase flow model in Fluent software to obtain gas-liquid share and distribution of a fluid domain, a fluid flow state and temperature distribution at the next moment; wherein, the gas-liquid share is calculated by using an evaporation and condensation model-Lee model, and as shown in formulas (1), (2) and (3), the gas-liquid phase-to-phase mass exchange can be calculated:
in the formula:
v-represents the vapor phase;
l-represents a liquid phase;
α v -steam volume fraction;
ρ v -steam density/kg m -3 ；
α l -volume fraction of liquid phase;
ρ l -density of liquid phase/kg. m -3 ；
T l -liquid phase temperature/K;
T sat -liquid phase saturation temperature/K;
c-adjustment factor, similar to relaxation time;
and 5: calculating the drag force of fluid to the melt fragment particles and the interphase heat transfer quantity by using a fluid-solid coupling mechanical model and a fluid-solid phase heat transfer model, and transferring the drag force and the interphase heat transfer quantity to all the melt fragment particles in the EDEM software; the fluid-solid coupling mechanical model is as the following formula (4), and the fluid-solid heat transfer model is as the following formula (5):
in the formula:
s-represents the melt fragment particle phase;
f-represents a fluid phase;
m s -mass of particles/kg;
τ r -a particle relaxation time;
ρ s -density of the melt scrap particle phase/kg m -3 ；
ρ f -fluid phase density/kg · m -3 ；
h-convection heat transfer coefficient/W.m -2 ·K -1 ；
T s -melt scrap particle phase temperature/K;
A s -particle surface area/m 2 ；
T ∞ -local temperature of continuous phase/K; epsilon s -particle emissivity (dimensionless);
sigma-stefan-boltzmann constant/W.m -2 ·K -4 ；
θ R -the radiation temperature/K;
step 6: calculating mutual collision among the melt fragment particles by using a Hertz-Mindlin contact mechanical model represented by formula (6), formula (7) and formula (8), and calculating heat transfer quantity among the melt fragment particles by using a solid fragment particle heat conduction model represented by formula (9) and formula (10);
in the formula:
E * -equivalent young's modulus/Pa;
R * -equivalent radius/m;
δ n -the amount of normal overlap of the melt scrap particles/m;
beta-equivalent coefficient of restitution;
m * -equivalent mass/kg;
S n -normal stiffness/Pa · m;
F t e -represents the tangential spring force/N;
F t d -represents the tangential damping force/N;
S t -tangential stiffness/Pa · m;
δ t -the amount of tangential overlap of the melt scrap particles/m;
m is mass/kg;
C p specific heat capacity/J.kg -1 ·K -1 ；
T-temperature/K;
q-quantity of Heat transfer between melt fragments/J.s -1 ；
Q p1p2 The quantity of heat exchange/J.s between the melt scrap particles p1 and the particle p2 -1 ；
h c -heat transfer coefficient/W.m -2 ·K -1 ；
ΔT p1p2 The temperature difference/K between the melt fraction particles p1 and p2
k p1 ,k p2 Thermal conductivity/W.m of melt chip particles p1 and of particle p2 -2 ·K -1 ；
And 7: combining the drag force and the interphase heat transfer quantity information of the melt fragment particles transmitted by UDF in Fluent software, calculating the position and the speed of the melt fragment particles at the next moment by using a Newton second law, and calculating the temperature distribution of the melt fragment particles by using a basic heat conduction model;
and 8: and (4) repeating the step (4) to the step (7) within the set calculation time, obtaining the change process of the position, the speed, the temperature and the resultant force of the fragments along with time in the sedimentation process of the fragments of the melt at different moments, obtaining the change of the gas-liquid volume fraction, the fluid distribution, the speed, the pressure and the temperature of a fluid domain along with time, obtaining the interaction force and the interphase heat transfer quantity between the solid fragments of the melt and the fluid, and obtaining the final accumulation form, the porosity and the temperature distribution of the melt fragment bed. Through the data, the movement process of the molten mass fragments, the collision process of the molten mass fragments, the interaction process of the molten mass fragments and the fluid, the gas-liquid boiling phenomenon, the temperature change process of the fluid and the molten mass solid fragments in the forming process of the molten mass fragment bed can be analyzed, and the final molten mass fragment bed form can be predicted, so that the cooling performance of the fragment bed is improved, the remelting risk of the fragment bed is reduced, and the integrity of the containment vessel of the pressure vessel is maintained.
In conclusion, the geometric modeling and the grid division of the calculation object are completed through the steps 1 to 3, the calculation of a conservation equation, a fluid-solid coupling interaction force model and an interphase heat transfer model is completed through the steps 4 to 5, and the gas-liquid share, the fluid state, the temperature distribution of the fluid domain and the drag force and the heat transfer quantity of the fluid domain to the molten mass fragments are obtained; and (4) completing calculation of a contact mechanics model, a solid fragment particle heat conduction model and a Newton's second law through the steps 6 to 7 to obtain the position, the speed and the temperature distribution of the melt fragment particles. By integrating the steps, simulation analysis is carried out on the characteristics of the forming process of the molten mass fragment bed, the final accumulation form, porosity and temperature distribution of the molten mass fragment bed are obtained, analysis of coolable performance of the fragment bed is facilitated, the remelting risk of the fragment bed is reduced, and the integrity of the containment vessel of the pressure vessel is maintained.
The effect of the present invention will be described below with reference to specific calculation targets, and the debris bed formation experiment shown in fig. 2 will be taken as an example. First, melt fragment characteristic information and nuclear reactor core structure or experimental information, such as equipment size, melt fragment regular form, fragment mass, fragment volume, material, fragment and coolant temperature, are acquired, the experimental schematic diagram is shown in fig. 2, and the melt fragment regular form of long-strip-shaped fragment and long-strip-shaped bent fragment is shown in fig. 3a and 3 b. And finishing geometric modeling, grid division and initial parameter setting based on the information. In the EDEM software, selecting a Hertz-Mindlin model as a collision mechanical model; in Fluent software, a multiphase flow model is set as a texture model, and a turbulence model is set as a readable K-epsilon model. After the calculation is started, the melt fragments are released from the bottom of the hopper, the mechanical and heat transfer interaction among the melt fragments, between the melt fragments and the wall surface, and between the melt fragments and the coolant can be calculated according to the steps 4 to 7, and the change of the movement characteristics, the fluid movement characteristics and the solid-liquid temperature distribution of the melt fragments along with the time in the step 8 can be obtained. Finally, the result is output, the accumulation form, the porosity and the temperature distribution of the fragment bed of the melt shown in the figure 4 can be obtained, the analysis of the coolable performance of the fragment bed is facilitated, the risk of remelting of the fragment bed is reduced, and the integrity of the containment of the pressure vessel is maintained.
Claims (1)
1. A method for characterizing a melt scrap bed forming process, comprising: the method comprises the following steps:
step 1: acquiring the characteristic information of the fragments of the molten material and the information of the core structure or experimental equipment of the nuclear reactor based on a calculation object in the simulation of the core fusion accident of the nuclear power plant reactor or the interaction experiment of the molten material and water, carrying out geometric modeling on the core structure or experimental equipment, the fragments of the molten material and the calculation domain of the fluid, and carrying out grid division on a geometric body;
step 2: modeling the shapes and the sizes of the fragments of the molten material in EDEM software, setting basic information of the material types, the material thermophysical properties, the material mechanical properties, the mass or the volume, the initial speed and the initial temperature of the fragments of the molten material, setting information of the material types, the material thermophysical properties and the mechanical properties of a reactor core structure or an experimental container of a nuclear reactor, and setting contact mechanical parameters among the fragments of the molten material and between the fragments of the molten material and a wall surface; selecting a fluid name in Fluent software, and setting the form, the thermophysical property, the initial temperature, the initial speed and the distribution of the fluid in a calculation domain;
and step 3: the Fluent software is coupled with an adapter Interface provided by the EDEM software through the UDF function of the Fluent software, so that the melt fragment motion and flow field information of the two pieces of software can be mutually transmitted; selecting a contact mechanics model and a particle heat transfer model of the melt fragments in the EDEM software, and setting boundary conditions, calculation time step length, calculation time and data storage frequency for the release of the melt fragments; selecting a multi-phase flow model, a turbulence model, a gas-liquid evaporation and condensation model, a fluid-solid coupling drag force model and corresponding boundary conditions of fluid in Fluent software;
and 4, step 4: combining initial melt fragment particle information transmitted by EDEM software, regarding the melt fragments as solid phase fragments injected by a DPM model in Fluent software, and calculating a mass equation, a momentum equation and an energy equation by using a multiphase flow model in Fluent software to obtain gas-liquid share and distribution of a fluid domain, a fluid flow state and temperature distribution at the next moment; wherein, the gas-liquid share is calculated by using an evaporation and condensation model-Lee model, and as shown in formulas (1), (2) and (3), the gas-liquid phase-to-phase mass exchange can be calculated:
in the formula:
v-represents the vapor phase;
l-represents a liquid phase;
α v -steam volume fraction;
ρ v -steam density/kg m -3 ；
α l -volume fraction of liquid phase;
ρ l -density of liquid phase/kg. m -3 ；
T l -liquid phase temperature/K;
T sat -liquid phase saturation temperature/K;
c-adjustment factor, similar to relaxation time;
and 5: calculating drag force and interphase heat transfer quantity of fluid to the melt fragment particles by using a fluid-solid coupling mechanical model and a fluid-solid interphase heat transfer model, and transferring the drag force and the interphase heat transfer quantity to all the melt fragment particles in the EDEM software; the fluid-solid coupling mechanical model is as the following formula (4), and the fluid-solid heat transfer model is as the following formula (5):
in the formula:
s-represents the melt fragment particle phase;
f-represents a fluid phase;
m s -mass of particles/kg;
τ r -a particle relaxation time;
ρ s -density of the melt scrap particle phase/kg m -3 ；
ρ f -fluid phase density/kg · m -3 ；
h-convective heat transfer coefficient/W.m -2 ·K -1 ；
T s -melt scrap particle phase temperature/K;
A s -particle surface area/m 2 ；
T ∞ -local temperature of continuous phase/K; epsilon s Particle emissivity (dimensionless);
sigma-stefan-boltzmann constant/W.m -2 ·K -4 ；
θ R -radiation temperature/K;
step 6: calculating mutual collision among the melt fragment particles by using a Hertz-Mindlin contact mechanical model represented by formula (6), formula (7) and formula (8), and calculating heat transfer quantity among the melt fragment particles by using a solid fragment particle heat conduction model represented by formula (9) and formula (10);
in the formula:
E * -equivalent young's modulus/Pa;
R * -equivalent radius/m;
δ n -the amount of normal overlap of the melt scrap particles/m;
beta-equivalent coefficient of restitution;
m * -equivalent mass/kg;
S n -normal stiffness/Pa · m;
F t e -represents the tangential spring force/N;
F t d -represents the tangential damping force/N;
S t -tangential stiffness/Pa · m;
δ t -the amount of tangential overlap of the melt chips particles/m;
m is mass/kg;
C p specific heat capacity/J.kg -1 ·K -1 ；
T-temperature/K;
q-quantity of Heat transfer between melt debris particles/J.s -1 ；
Q p1p2 The amount of heat exchange between the melt scrap particles p1 and particles p 2/J.s -1 ；
h c -heat exchangecoefficient/W.m -2 ·K -1 ；
ΔT p1p2 The temperature difference/K between the melt fraction particles p1 and p2
k p1 ,k p2 Thermal conductivity/W.m of melt scrap particles p1 and particles p2 -2 ·K -1 ；
And 7: combining the drag force and the interphase heat transfer quantity information of the melt fragment particles transmitted by UDF in Fluent software, calculating the position and the speed of the melt fragment particles at the next moment by using a Newton second law, and calculating the temperature distribution of the melt fragment particles by using a basic heat conduction model;
and 8: repeating the steps 4 to 7 within the set calculation time, obtaining the change process of the position, the speed, the temperature and the resultant force of the fragments in the sedimentation process of the fragments of the melt at different moments along with the time, obtaining the change of the gas-liquid volume fraction, the fluid distribution, the speed, the pressure and the temperature of the fluid domain along with the time, obtaining the interaction force and the interphase heat transfer between the solid fragments of the melt and the fluid, and obtaining the final accumulation form, the porosity and the temperature distribution of the fragments of the melt bed. Through the data, the movement process of the molten mass fragments, the collision process of the molten mass fragments, the interaction process of the molten mass fragments and the fluid, the gas-liquid boiling phenomenon, the temperature change process of the fluid and the molten mass solid fragments in the forming process of the molten mass fragment bed can be analyzed, and the final molten mass fragment bed form can be predicted, so that the cooling performance of the fragment bed is improved, the remelting risk of the fragment bed is reduced, and the integrity of the containment vessel of the pressure vessel is maintained.
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