Method for calculating wet deposition of radioactive aerosol plumes under rainfall meteorological conditions

Abstract

The present application relates to a kind of radioactive aerosol plume wet precipitation calculation method of rainfall weather condition, solve the problem that existing simulation does not have the wet precipitation diffusion transport influence calculation method of radioactive plume under the condition of complex flow field large scale considering the influence of precipitation situation;Including 1: based on (x0, y0, z0), establish two-dimensional coordinate system, determine the region to be calculated and grid division to it;2: based on precipitation type, precipitation intensity calculation wet precipitation removal coefficient Λ;3: based on Λ, calculate and record after time Δt, the ground deposition amount s1 of plume and after time Δt, the center position (x1, y1, z1) of plume, space distribution σ1;4: based on (x1,y1), σ1 and s1 calculate the plume particle deposition amount p1 (x,y) at any point (x,y) position in the region to be calculated;5: repeat step 2-step 4, until aerosol plume completely settles ground or escapes the boundary of the region to be calculated;6: after calculation, output record ground deposition result on grid point.

Description

Technical Field

[0001] The present invention relates to the technical field of numerical simulation of atmospheric diffusion of radioactive pollutants, and in particular to a method for calculating atmospheric diffusion and deposition processes of radioactive aerosol smoke clouds under complex meteorological conditions of rainfall. Background Art

[0002] Due to the radiation hazards of radionuclides, the release of radioactive aerosol particles into the air can cause serious damage to humans and the natural environment. For example, chemical explosions and nuclear power plant accidents, resulting in the formation of radioactive aerosol clouds due to nuclear leaks, diffuse and settle in the atmosphere, expanding the scope of radioactive hazards. In particular, immersion radiation and inhalation internal radiation from radioactive clouds can cause significant damage to tissues and organ cells in the human body. Strengthening research on the diffusion, transport, and sedimentation of aerosol clouds under complex conditions will facilitate rapid and accurate accident severity assessments and predictions of the scope and concentration distribution of accidental radioactivity. This, in turn, provides important guidance for emergency rescue, personnel evacuation, and other emergency response and protection plans.

[0003] The diffusion process of radioactive aerosol plume in the atmospheric environment is extremely complex. A large number of studies have been conducted on the settlement and diffusion transport law of radioactive aerosol plume at home and abroad. It is found that the distribution range and concentration distribution of the dispersion and transmission of radioactive aerosol in the atmosphere are related to the physical and chemical properties of the aerosol itself (such as density, particle size and diffusion coefficient), and also change with the surrounding environment. For example, Dong Xilin et al. found that different underlying surface topography can greatly affect the lifting, diffusion and deposition of radioactive material in the air. For example, the diffusion and transmission of the plume on the flat underlying surface is relatively stable, while the diffusion and transmission in the complex terrain area is relatively complex (Nuclear Power Plant Fire Safety and Accident Emergency[M]. Beijing Atomic Energy Press, 1999: 48-58). In addition, researchers found that meteorological conditions also have a great influence on the lifting, diffusion and deposition of the plume, such as wind speed, wind direction and atmospheric stability. For example, Wang Ke et al. found that the influence of flow field wind speed can accelerate the diffusion and deposition of radioactive plume, and affect its dispersion distance and transmission direction (Simulation of radioactive aerosol diffusion, migration and control measures, CHINA SCIENSE PAPER, Vol. 12. No. 5. Mar. 2017). Steven R. Hanna and Zhuo Jun et al. found that atmospheric stability also has a significant influence on the transmission of radioactive plume. For example, under the same wind speed, the more unstable the atmosphere, the stronger the dilution effect on the plume; on the contrary, the more stable the atmosphere, the weaker the dilution effect on the plume (Handbook on ATMOSPHERIC DIFFUSION [M], U.S. Department of Energy, 1981: 12-23, Dose Distribution of Radioactive Plume from Dirty Bomb Attack Simulated by Random Walk Method, Atomic Energy Science and Technology, Vol. 52. No. 6. Mar. 2018).

[0004] The rainfall condition also has a great influence on the lifting diffusion and deposition of the radioactive plume due to the collision and removal mechanism between the aerosol plume and the raindrop particles (Theoretical and observational study on below-cloud rain scavenging of aerosol particles, Journal of University of Chinese Academy of Sciences, Vol. 31. No. 3. May. 2014). At present, the atmospheric diffusion and radiation evaluation of the radioactive aerosol plume is mainly based on the Gaussian diffusion model (Influence of Weather Conditions on Consequence Assessment of Radiological Dispersal Device Attacks, Modern Applied Physics, Vol. 7. No. 1. Mar. 2016), which is suitable for small-scale calculation in a steady flow field and is not suitable for simulating large-scale plume diffusion in actual complex flow field conditions.

[0005] As described above, the rainfall has a great influence on the lifting diffusion and deposition of the radioactive plume, but there is no wet deposition diffusion transport influence calculation method for the radioactive plume under the condition of complex flow field and large scale considering the rainfall in the existing related simulation simulation. SUMMARY

[0006] The purpose of the present application is to solve the technical problem that there is no wet deposition diffusion transport influence calculation method for the radioactive plume under the condition of complex flow field and large scale considering the rainfall in the existing related simulation simulation, and to provide a radioactive aerosol atmospheric diffusion wet deposition calculation method for nuclear power plant accidents or nuclear attack caused by nuclear leakage;

[0007] The present application establishes a radioactive plume complex flow field large scale transport diffusion calculation model based on the random walk method, and provides an algorithm considering the influence of rainfall type and rainfall intensity on aerosol atmospheric diffusion. The technical scheme of the present application is as follows:

[0008] A radioactive aerosol plume wet deposition calculation method under rainfall meteorological conditions, characterized in that it comprises the following steps:

[0009] Step 1: based on the projection point (x0, y0, z0) of the center of the plume on the ground in the initial state, a two-dimensional coordinate system is established on the ground, the to-be-calculated region is determined, and the to-be-calculated region is divided into grids;

[0010] Step 2: calculate the wet deposition removal coefficient Λ based on the rainfall type and the rainfall intensity;

[0011] 2.1 Based on raindrop size D R , calculate raindrop terminal settling velocity U(D R ) and Reynolds number R e when raindrop falls;

[0012] 2.2 Based on D R , precipitation type and precipitation intensity, calculate raindrop spectrum distribution function N(D R ); based on aerosol smoke cloud particle size d p , calculate aerosol Schmidt number S c and aerosol terminal settling velocity U D ; based on R e , calculate dimensionless parameter S * ; based on U(D R ) and D R , calculate Stokes number S t of aerosol;

[0013] 2.3 Based on U D , N(D R ) and U(D R ), calculate collision probability K(d p , D R ); at the same time, based on R e , S c , S t and S * , calculate collision efficiency E(d p , D R );

[0014] 2.4 Calculate wet deposition removal coefficient Λ by formula ;

[0015] Step 3: Based on Λ, calculate and record the ground deposition amount s1 of the smoke cloud after time step Δt; at the same time, calculate the central position (x1, y1, z1) and spatial distribution σ1 of the smoke cloud after time step Δt;

[0016] Step 4: Based on (x1, y1), σ1 and s1, calculate the smoke cloud particle deposition amount p1(x, y) at any point (x, y) in the calculation area;

[0017] Step 5: Repeat steps 2-4 until the aerosol smoke cloud completely settles on the ground or escapes the boundary of the calculation area;

[0018] Step 6: After the calculation is completed, output the ground deposition results on the grid points.

[0019] Further, the step 2.1 comprises the following steps:

[0020] 2.11 Based on raindrop size D R , the terminal settling velocity of raindrops U(D R );

[0021]

[0022] 2.12 Based on raindrop size D R and the terminal settling velocity of raindrops U(D R ), the Reynolds number R when the raindrop falls is calculated by the following formula e ;

[0023] R e =D R U(D R )ρ a / 2μ a

[0024] Among them, ρ a is the density of air, μ a is the viscosity coefficient of air.

[0025] Furthermore, the step 2.2 includes the following steps:

[0026] 2.2A based on D R , precipitation type and precipitation intensity, the raindrop spectrum distribution function N(D R );

[0027]

[0028] Among them, when the rainfall type is stratiform cloud, N0=2.1×10 4 P R -0.384 , P R is the precipitation intensity; b = 5.38P R -0.186 , dimensionless constant a=2.93; when the rainfall type is cumulonimbus, N0=0.4×10 3 P R -0.384 , b=1.74P R -0.186 , a=2.93; when the rainfall type is mixed cloud, N0=2.1×10 4 P R -0.384 , b=5.38P R -0.186 , a=2.93;

[0029] 2.2B is based on the cloud particle size d p , the aerosol Schmidt number S is calculated by the following formulas:c and aerosol terminal settling velocity U D ;

[0030] S c =μ a / (ρ a D diff )

[0031] Among them, D diff is the aerosol diffusion coefficient, satisfying D diff =k b TC c / (3πμ a d p ), k b is the Boltzman constant, T is the absolute temperature of the atmosphere, C c is the Cunningham slip correction coefficient, satisfying C c =1+2.493λ / d p +0.84(λ / d p )e -0.435dp / λ , λ is the mean free path of gas molecules;

[0032]

[0033] Among them, ρ p is the aerosol density, g represents the acceleration due to gravity;

[0034] 2.2C based on R e , the dimensionless parameter S is calculated by the following formula * ;

[0035] S * =[1.2+(1 / 12)ln(1+R e )] / [1+ln(1+R e )]

[0036] 2.2D based on U(D R ) and D R , the Stokes number S of the aerosol is calculated by the following formula t ;

[0037] S t =2τ p U(D R )C c / 2D R ;

[0038] Among them, τ p is the aerosol relaxation time,

[0039] Furthermore, the step 2.3 includes the following steps:

[0040] 2.3A based on U D 、N(D R ) and U(D R ), the collision probability K(d p ,D R );

[0041]

[0042] 2.3B based on R e 、S c 、S t and S * , the collision efficiency E(d p ,D R );

[0043]

[0044] Among them, ρ w and ρ p are water and aerosol densities, respectively; μ a and μ w are the viscosity coefficients of air and water, respectively.

[0045] Furthermore, the step 3 includes the following steps:

[0046] 3A is based on Λ and calculates and records the ground deposition of the smoke cloud s1 after Δt using the formula s1 = Λc0Δt, where c0 is the total mass of the aerosol in the initial state;

[0047] 3B calculates the center (x1, y1, z1) and spatial distribution σ1 of the smoke cloud after the time step Δt;

[0048] 3B1: According to the surface wind speed U 10 , the wind speed U(z1) at the center of the aerosol cloud after Δt is calculated using the following formula:

[0049] U(z1)=U 10 (z1 / 10) 1 / 7

[0050] Where z1 = z0 - U D Δt;

[0051] 3B2 Based on the wind speed U(z1), the coordinates (x1, y1) of the center of the aerosol cloud after Δt are calculated and recorded using the following formula;

[0052] x1=x0+U x Δt

[0053] y1=y0+U y Delta t

[0054] Wherein, U x And U y Respectively, the wind speed U(z1) in x and y axis direction projection size;

[0055] 3B3 according to the calculation of aerosol plume center position (x1, y1) after aerosol plume through Delta t, by the following formula calculation and record its spatial distribution sigma 1;

[0056]

[0057] Wherein, R is the aerosol plume diffusion transport horizontal projection point distance, satisfy Sigma 0 is the initial concentration distribution standard deviation.

[0058] Further, the step 3 also includes: based on Lambda, by the following formula calculation and record after time step Delta t, the total mass of aerosol plume c1;

[0059] C1=c0- Lambda c0 Delta t

[0060] Wherein, c0 is the initial state of aerosol total mass.

[0061] Further, the step 4 specifically is: by the following formula calculation and record the aerosol particle deposition amount p1(x, y) at any point (x, y) on the ground position:

[0062]

[0063] Compared with the prior art, the beneficial effects of the present application are as follows:

[0064] 1、The present application establishes a simulation method for the influence of rainfall type and precipitation intensity on the diffusion process of radioactive aerosol plume for complex flow field large scale situation, realizes the calculation of surface environmental concentration change and ground deposition distribution of radioactive aerosol plume, and the calculation results show that rainfall intensity and rainfall type have great influence on the transport or deposition of radioactive aerosol plume, which further provides important technical support for developing nuclear leakage emergency rescue plan, personnel emergency protection evacuation and attack safety protection under complex rainfall meteorological conditions.

[0065] 2、The present application is based on solving the problem of wet deposition effect calculation of aerosol plume atmospheric diffusion process under complex rainfall meteorological conditions, realizes the effective simulation of aerosol plume wet deposition effect under rainfall condition by establishing the corresponding relationship between rainfall parameters (rainfall intensity and rainfall type) and removal coefficient in wet deposition, and can give the aerosol ground deposition distribution and surface environmental concentration change.

[0066] 3. The method proposed in the present invention can solve different practical problems based on the actual situation of radioactive aerosol source terms, such as the computational study of the effects of rainfall on the diffusion and deposition distribution of radioactive particulate matter caused by nuclear power plant accidents and nuclear attacks, and provide technical support for the formulation of emergency rescue plans for nuclear accidents or personnel evacuation under complex meteorological conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 Schematic diagram of radioactive aerosol source term, calculation area and grid setting in an embodiment of the present invention;

[0068] Figure 2 is a flow chart of an embodiment of the present invention;

[0069] Figure 3 Calculation results of the effects of stratiform cloud rainfall on radioactive aerosol cloud deposition in an embodiment of the present invention, where (a) is for a precipitation intensity of 1 mm / hr, and (b) is for a precipitation intensity of 10 mm / hr;

[0070] Figure 4 The following are the calculation results of the deposition of radioactive aerosol smoke clouds at different times for stratiform cloud rainfall with a precipitation intensity of 1 mm / hr in the examples of the present invention, where (a) is 1.0 hr, (b) is 2.0 hr, (c) is 3.0 hr, and (d) is 12.0 hr.

[0071] Figure 5 In the embodiment of the present invention, the 24-hour smoke cloud deposition calculation results are shown for the cases where the precipitation intensity is 1 mm / hr and the rainfall types are stratiform (CZY), mixed (HHY), and cumulonimbus (JYY), respectively. (a) is the 24-hour smoke cloud deposition calculation result for stratiform (CZY), (b) is the 24-hour smoke cloud deposition calculation result for mixed (HHY), and (c) is the 24-hour smoke cloud deposition calculation result for cumulonimbus (JYY). DETAILED DESCRIPTION

[0072] The present invention proposes a method for calculating the influence of rainfall meteorological conditions on the wet deposition of radioactive aerosol smoke clouds, which is used to solve the problem of surface concentration change and ground deposition distribution prediction during the atmospheric transport and diffusion of radioactive smoke clouds under complex flow field and large-scale conditions. Figure 2 As shown in the figure: the concentration distribution and initial position of the aerosol cloud at the initial moment are determined according to the release source of the aerosol cloud; then the aerosol atmospheric diffusion parameters and wet deposition removal coefficient are determined according to the meteorological conditions of rainfall type and precipitation intensity. The diffusion parameters include Schmidt number, Stokes number and C cSlip correction coefficient, etc.; the wet deposition calculation method is used to calculate the atmospheric transport and diffusion process of aerosol smoke clouds in rainfall, and the ground deposition distribution of aerosol smoke clouds is recorded. The present invention can simulate the wet deposition process of aerosol smoke clouds under different rainfall types and rainfall intensities, and give the ground radioactive aerosol deposition distribution.

[0073] The specific steps include:

[0074] like Figure 1 As shown, the initial position of the aerosol cloud (the position of the aerosol cloud at t = 0 (x0, y0, z0)), the standard deviation of the concentration distribution at the initial moment σ0, the total mass c0 of the aerosol cloud and the particle size d are determined according to the aerosol cloud release source. p ;

[0075] In this example, the center of the aerosol cloud at the initial moment is 500m above the ground, the aerosol cloud concentration is Gaussian distributed in the horizontal direction, the standard deviation of the distribution at the initial moment σ0 is 100m, the total aerosol radioactivity is 1Bq, and the aerosol particle size d p 20 μm, with a density of 2.6×10 3 kg / m 3 ;

[0076] Meteorological conditions are as follows: wind speed at 10 m above ground is 3 m / s, wind speed is exponentially distributed with height, the distribution index is 1 / 7, and atmospheric stability is level B;

[0077] Step 1: Based on the projection point (x0, y0, z0) of the aerosol cloud center on the ground in the initial state, a two-dimensional coordinate system is established on the ground. In this two-dimensional coordinate system, the area to be calculated is divided and meshed to obtain the grid resolution G.

[0078] like Figure 1 As shown in the figure, the ground projection point (x0, y0, z0) of the center of the aerosol cloud in the initial state is taken as the coordinate origin, and the wind direction is the positive direction of the x-axis to establish a two-dimensional rectangular coordinate system, and the ground calculation area (x min , x max ), (y min ,y max ); Draw a grid based on the ground calculation area of ​​aerosol smoke cloud wet deposition and actual needs to obtain the grid spatial resolution G;

[0079] In this embodiment, the calculation area and grid are divided as follows: the calculation interval is -10000m≤x≤10000m, -50000m≤y≤50000m, and the recording grid spatial resolution is G=200m×200m;

[0080] Step 2: Calculate the wet deposition removal coefficient Λ based on precipitation type, precipitation intensity, and aerosol particle size;

[0081] The clearance coefficient Λ is mainly determined by the collision probability K(d p ,D R ) and collision efficiency E(d p ,D R ) consists of two parts, and the calculation formula is as follows:

[0082]

[0083] Among them, K(d p ,D R ) represents the particle size d p The aerosol cloud particles and particle size are D R The probability of raindrops colliding, E(d p ,D R ) indicates the particle size D R The raindrops and particle size are d p The probability of collision and merger of aerosol cloud particles when their trajectories intersect;

[0084] K(d p ,D R ) is calculated as follows:

[0085]

[0086] Among them, U D and U(D R ) represent the terminal settling velocities of aerosol particles and raindrop particles, respectively, N(D R ) is the raindrop spectrum distribution function, which represents the concentration distribution of raindrop particle diameters;

[0087] Specific: Raindrop terminal settling velocity U(D R )satisfy:

[0088]

[0089] Aerosol terminal settling velocity U D satisfy:

[0090]

[0091] Among them, ρ p is the aerosol density, which is 997.45 kg.m -3 , g represents the acceleration due to gravity; μ a is the viscosity coefficient of air, which is 1.832×10 -5 kg.m -1 .s -1 ;

[0092] C c =1+2.493λ / d p +0.84(λ / d p )e -0.435dp / λ , λ is the mean free path of gas molecules, and its value is 6.73×10 - 8 m;

[0093] N(D R ) is calculated as:

[0094]

[0095] Among them, when the rainfall type is stratiform cloud, N0=2.1×10 4 P R -0.384 , unit: m -3 / mm;P R is the precipitation intensity; b = 5.38P R -0.186 , unit: mm -1 ; dimensionless constant a=2.93; when the rainfall type is cumulonimbus, N0=0.4×10 3 P R -0.384 , b=1.74P R -0.186 , a=2.93; when the rainfall type is mixed cloud, N0=2.1×10 4 P R -0.384 , b=5.38P R -0.186 , a=2.93;

[0096] Collision efficiency E(d p ,D R ) characterizes the probability of collision when the raindrop and aerosol tracks intersect. In this paper, the Brownian diffusion collision mechanism, inertial collision mechanism, and interception collision clearance mechanism are considered. A semi-empirical expression of collision efficiency is obtained by dimensionless analysis and coupling with experimental data to realize the calculation of collision efficiency:

[0097]

[0098] Among them, ρ w and ρ p are the densities of water and aerosol particles, respectively; μ a and μ w are the viscosity coefficients of air and water, respectively, and their values ​​are 1.832×10 -5 kg.m -1 .s -1 and 9.591kg.m-1 .s -1 ;

[0099] R e is the Reynolds number of raindrop falling, and the calculation formula is R e = D R U(D R )ρ a / 2μ a , wherein U(D R ) is the terminal falling speed of raindrop, ρ a is the density of air, and the value is 1.193 kg.m -3 ;

[0100] S c is the Schmidt number of aerosol, and the calculation formula is S c = μ a / (ρ a D diff ), wherein ρ a is the air density, and the value is 1.193 kg.m -3 , and D diff is the diffusion coefficient of aerosol, and satisfies D diff =k b TC c / (3πμ a d p ), k b is the Boltzman constant (the value is 1.38054×10 -23 ), T is the absolute temperature of atmospheric environment (the value is 298 K), and C c is the Cunningham slip correction coefficient, and satisfies C c =1+2.493λ / d p +0.84(λ / d p )e -0.435dp / λ , λ is the average free path of gas molecules, and the value is 6.73×10 -8 m;

[0101] S t is the Stokes number of aerosol, and the formula is S t =2τ p U(D R )C c / 2D R ; wherein τ p is the relaxation time of aerosol, and the calculation formula is

[0102] S* is a dimensionless parameter, and satisfies: S * =[1.2+(1 / 12)ln(1+R e )] / [1+ln(1+Re )];

[0103] Step 3: Based on the wet deposition removal coefficient Λ obtained in step 2, calculate and record the total mass c1 of the aerosol cloud and the ground deposition s1 after the time step Δt. At the same time, calculate the center position (x1, y1, z1) and spatial distribution σ1 of the suspended aerosol after the time step Δt.

[0104] A. Based on the wet deposition removal coefficient Λ obtained in step 2, calculate and record the total mass c1 of the suspended aerosol after the time step Δt using the following formula:

[0105] c1=c0-Λc0Δt

[0106] Wherein, c0 is the total amount of aerosol in the initial state;

[0107] B. Based on the wet deposition removal coefficient Λ obtained in step 2, calculate and record the ground deposition amount s1 of the suspended aerosol after the time step Δt using the following formula:

[0108] s1=Λc0Δt;

[0109] C. Calculate the center position (x1, y1, z1) and spatial distribution σ1 of the suspended aerosol after the time step Δt;

[0110] C1: According to the surface wind speed U 10 Calculate the wind speed U(z1) at the center of the aerosol cloud (height z1) after the time step Δt. The calculation formula is as follows:

[0111] U(z1)=U 10 (z1 / 10) 1 / 7

[0112] Where z1 = z0 - U D Δt;

[0113] C2: Based on the wind speed U(z1), obtain and record the center position (x1, y1, z1) of the aerosol cloud after the time step Δt;

[0114] The calculation formula for the change in the center position of the aerosol cloud is:

[0115]

[0116] Among them, U x and U y are the projections of wind speed U(z) in the x- and y-axis directions respectively;

[0117] C3: Calculate and record the spatial distribution σ1 of the aerosol cloud based on its central position (x1, y1) after the time step Δt.

[0118] The calculation formula is as follows:

[0119]

[0120] Among them, R is the distance of the horizontal projection point of the aerosol cloud diffusion transport, satisfying σ0 is the standard deviation of the concentration distribution at the initial moment;

[0121] Step 4: Calculate the aerosol particle deposition amount p1(x, y) at any point (x, y) on the ground based on the center position (x1, y1), the spatial distribution σ1, and the ground deposition amount s1 calculated in step 3;

[0122] Based on the center position (x1, y1), the spatial distribution σ1, and the ground deposition s1 calculated in step 3, calculate and record the aerosol particle deposition p1(x, y) at any point (x, y) on the ground using the following formula:

[0123]

[0124] Step 5: Repeat steps 2 to 4, and calculate and record the distribution of ground subsidence after different time steps, until the aerosol cloud is completely settled on the ground or escapes the boundary;

[0125] Step 6: After the calculation is completed, output the ground settlement results at the recorded grid points.

[0126] Different initial particle size or precipitation intensity parameters can be set, and the aerosol wet deposition process under different particle sizes and rainfall conditions can be calculated.

[0127] Figure 3 (a) Figure 3 (b) The distribution of ground radioactive fallout under stratiform clouds and precipitation intensities of 1 mm / hr and 10 mm / hr are given respectively. The results show that the greater the precipitation intensity, the more significant the wet deposition effect on aerosol particles, resulting in a smaller deposition range. Figure 4 (a) Figure 4 (b) Figure 4 (c) and Figure 4 (d) The calculation results of the precipitation of radioactive aerosol smoke at different times when the rainfall type is stratiform cloud and the precipitation intensity is 1 mm / hr; Figure 5 (a) Figure 5 (b) Figure 5(c) are the 24-hour smoke cloud deposition calculation results under the conditions of precipitation intensity of 1 mm / hr and rainfall types of stratiform cloud (CZY), mixed cloud (HHY) and cumulonimbus cloud (JYY), respectively. The results show that different rainfall types have different effects on the wet deposition of aerosol particles. In terms of deposition range, cumulonimbus cloud (JYY) type rainfall has the most obvious effect on the wet deposition of aerosol particles, followed by mixed cloud (HHY) and stratiform cloud (CZY) rainfall types. The above results show that the present invention can well calculate the range of aerosol smoke cloud deposition at different rainfall intensities and different rainfall types at different times under complex meteorological conditions.

Claims

1. A method for calculating the wet deposition of radioactive aerosol smoke clouds under rainfall meteorological conditions, characterized in that: The following steps are involved: Step 1: Based on the projection point (x0, y0, z0) of the smoke cloud center on the ground in the initial state, a two-dimensional coordinate system is established on the ground, the area to be calculated is determined, and the area to be calculated is meshed; Step 2: Calculate the wet deposition removal coefficient Λ based on precipitation type and precipitation intensity; 2.1 Based on raindrop size D R , calculate the raindrop terminal settling velocity U(D R ) and the Reynolds number R when the raindrop falls e ; 2.2 Based on D R , precipitation type and precipitation intensity to calculate the raindrop spectrum distribution function N(D R ); Based on the aerosol cloud particle size d p Calculation of aerosol Schmidt number S c and aerosol terminal settling velocity U D ; Based on R e Calculate the dimensionless parameter S * Based on U(D R ) and D R , calculate the Stokes number S of the aerosol t ; 2.3 Based on U D 、N(D R ) and U(D R ), calculate the collision probability K(d p ,D R ); Based on R e 、S c 、S t and S * Calculate the collision efficiency E(d p ,D R ); 2.4 Through the formula Calculate the wet deposition removal coefficient Λ; Step 3: Based on Λ, calculate and record the ground settlement s1 of the smoke cloud after the time step Δt; at the same time, calculate the center position (x1, y1, z1) and spatial distribution σ1 of the smoke cloud after the time step Δt; Step 4: Calculate the cloud particle deposition amount p1(x,y) at any point (x,y) in the calculation area based on (x1,y1), σ1, and s1; Step 5: Repeat steps 2 to 4 until the aerosol cloud is completely settled on the ground or escapes the boundary of the area to be calculated; Step 6: After the calculation is completed, the ground settlement results at the recorded grid points are output; The step 4 is specifically as follows: calculate and record the aerosol particle deposition amount p1(x, y) at any point (x, y) on the ground using the following formula:

2. The method for calculating the wet deposition of radioactive aerosol clouds under rainfall meteorological conditions according to claim 1, characterized in that: The step 2.1 includes the following steps: 2.11 Based on raindrop size D R , the terminal settling velocity of raindrops U(D R ); 2.12 Based on raindrop size D R and the terminal settling velocity of raindrops U(D R ), the Reynolds number R when the raindrop falls is calculated by the following formula e ; R e =D R U(D R )r a / 2m a Among them, ρ a is the density of air, μ a is the viscosity coefficient of air.

3. The method for calculating the wet deposition of radioactive aerosol clouds under rainfall meteorological conditions according to claim 2, characterized in that: The step 2.2 includes the following steps: 2.2A based on D R , precipitation type and precipitation intensity, the raindrop spectrum distribution function N(D R ); Among them, when the rainfall type is stratiform cloud, N0=2.1×10 4 P R -0.384 , P R is the precipitation intensity; b = 5.38P R -0.186 , dimensionless constant a=2.93; when the rainfall type is cumulonimbus, N0=0.4×10 3 P R -0.384 , b=1.74P R -0.186 , a=2.93; when the rainfall type is mixed cloud, N0=2.1×10 4 P R -0.384 , b=5.38P R -0.186 , a=2.93; 2.2B is based on the cloud particle size d p , the aerosol Schmidt number S is calculated by the following formulas: c and aerosol terminal settling velocity U D ; S c =μ a / (r a D diff ) Among them, D diff is the aerosol diffusion coefficient, satisfying D diff =k b TC c / (3πμ a d p ), k b is the Boltzman constant, T is the absolute temperature of the atmosphere, C c is the Cunningham slip correction coefficient, satisfying C c =1+2.493λ / d p +0.84(λ / d p )e -0.435dp / λ , λ is the mean free path of gas molecules; Among them, ρ p is the aerosol density, g represents the acceleration due to gravity; 2.2C based on R e , the dimensionless parameter S is calculated by the following formula * ; S * =[1.2+(1 / 12)ln(1+R e )] / [1+ln(1+R e )] 2.2D based on U(D R ) and D R , the Stokes number S of the aerosol is calculated by the following formula t ; S t =2τ p U(D R )C c / 2D R ; Among them, τ p is the aerosol relaxation time, 4. The method for calculating the wet deposition of radioactive aerosol clouds under rainfall meteorological conditions according to claim 3, characterized in that: The step 2.3 includes the following steps: 2.3A based on U D 、N(D R ) and U(D R ), the collision probability K(d p ,D R ); 2.3B based on R e 、S c 、S t and S * , the collision efficiency E(d p ,D R ); Among them, ρ w and ρ p are water and aerosol densities, respectively; μ a and μ w are the viscosity coefficients of air and water, respectively.

5. The method for calculating the wet deposition of radioactive aerosol clouds under rainfall meteorological conditions according to claim 4, characterized in that: The step 3 comprises the following steps: 3A is based on Λ and calculates and records the ground deposition of the smoke cloud s1 after Δt using the formula s1 = Λc0Δt, where c0 is the total mass of the aerosol in the initial state; 3B calculates the center (x1, y1, z1) and spatial distribution σ1 of the smoke cloud after the time step Δt; 3B1: According to the surface wind speed U 10 , the wind speed U(z1) at the center of the aerosol cloud after Δt is calculated using the following formula: U(z1)=U 10 (z1 / 10) 1 / 7 Where z1 = z0 - U D Δt; 3B2 Based on the wind speed U(z1), the coordinates (x1, y1) of the center of the aerosol cloud after Δt are calculated and recorded using the following formula; x1=x0+U x Δt y1=y0+U y Δt Among them, U x and U y are the projections of wind speed U(z1) in the x- and y-axis directions respectively; 3B3 Based on the coordinates (x1, y1) of the center of the aerosol cloud after Δt, calculate and record its spatial distribution σ1 using the following formula; Among them, R is the distance of the horizontal projection point of the aerosol cloud diffusion transport, satisfying σ0 is the standard deviation of the concentration distribution at the initial moment.

6. The method for calculating the wet deposition of radioactive aerosol clouds under rainfall meteorological conditions according to claim 5, characterized in that: The step 3 further includes: based on Λ, calculating and recording the total mass c1 of the aerosol cloud after the time step Δt by the following formula; c1=c0-Λc0Δt Where c0 is the total mass of aerosol in the initial state.

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