CN109580433B - Source term estimation method for diffusion of conventional explosive radioactive aerosol - Google Patents

Source term estimation method for diffusion of conventional explosive radioactive aerosol Download PDF

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CN109580433B
CN109580433B CN201811258555.0A CN201811258555A CN109580433B CN 109580433 B CN109580433 B CN 109580433B CN 201811258555 A CN201811258555 A CN 201811258555A CN 109580433 B CN109580433 B CN 109580433B
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aerosol
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苏自强
廉冰
董豫阳
康晶
陈海龙
王彦
杨洁
赵杨军
罗恺
于志翔
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China Institute for Radiation Protection
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N2015/0023—Investigating dispersion of liquids
    • G01N2015/0026—Investigating dispersion of liquids in gas, e.g. fog
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N2015/0042—Investigating dispersion of solids
    • G01N2015/0046—Investigating dispersion of solids in gas, e.g. smoke

Abstract

The invention discloses a method for estimating the diffusion source item of a conventional explosive radioactive aerosol, which comprises the following steps: aiming at the conventional explosion of the radioactive texture surface, the explosion equivalent is estimated, and the size of the explosion smoke cloud is estimated based on the explosion equivalent, wherein the size of the explosion smoke cloud comprises the following steps: the height of the explosion smoke cloud, the radius of the explosion smoke cloud, the volume of the explosion smoke cloud and the density of the explosion smoke cloud are used for estimating the generation share of the explosion aerosol and the particle size distribution of the explosion aerosol, estimating the influence of heavy gas effect on source items and setting nuclides needed to be concerned about in an explosion event. The method is based on the explosion equivalent, the explosive mass, the local wind speed and the like, comprehensively considers the size of the explosion smoke cloud, the generation portion of the explosion aerosol, the aerosol particle size distribution and the influence of heavy gas effect on the source item, forms a source item estimation method, is more in line with the actual situation, and has the effect superior to a point source diffusion model.

Description

Source term estimation method for diffusion of conventional explosive radioactive aerosol
Technical Field
The invention relates to the field of radiation environment influence evaluation, in particular to a source item estimation method for diffusion of conventional explosive radioactive aerosol. Namely a calculation method of radioactive aerosol diffusion source items generated by conventional explosion.
Background
Since the 21 st century, especially after the 9.11 th incident, the unconventional security threats represented by various terrorist explosions have become more serious, and the nuclear materials and facilities have become one of the main targets of terrorists due to their particularity, and the security problems of the nuclear materials and facilities have become a major concern.
IAEA (international atomic energy agency) has divided nuclear and radiation terrorist attacks into 4 main categories:
1. illegally obtaining radioactive materials (radioactive materials), manufacturing Radioactive Distribution Devices (RDDs), and performing radioactive attacks, such as dirty bombs;
2. nuclear facilities such as an attack Nuclear Power Plant (NPP) and the like cause nuclear accidents, and radioactive substances are released into the environment;
3. illegally obtaining special nuclear materials, manufacturing a rough nuclear device (IND), and carrying out nuclear explosion;
4. and illegally acquiring a complete nuclear weapon and carrying out nuclear explosion.
Of these, the 2 nd, 3 rd and 4 th have great influence, but since it is difficult for terrorists to obtain sufficient raw nuclear weapon material, and the manufacturing technique is difficult, and the protection measures for nuclear facilities and nuclear weapons are strict, the probability of occurrence is very low, and the nuclear and radiation terrorist attacks most likely to be implemented by terrorists are the use of "dirty bombs" to make terrorist events.
With the continuous expansion of the application range of nuclear technology, radioactive materials are more widely applied in the fields of industry, agriculture, medicine, military and the like. Terrorists can obtain radioactive materials through various ways such as theft, smuggling, illegal purchase and the like. Although a "dirty bomb" terrorist attack has not occurred to date, the threat of a "dirty bomb" terrorist attack is real.
In the evaluation of radiation environment influence, the source item refers to the type, form and quantity (which can be called as source intensity) of the radioactive nuclide used by, carried by or generated by the source and the physicochemical morphological characteristics of the radioactive nuclide. Currently, analog calculation is mostly performed in a point source form in environmental impact evaluation, and a virtual point source form is also mostly adopted in an explosion event. The point sources have identifiable ranges that can be distinguished from other sources of contamination, simplifying the calculations in the form of one point in the mathematical model.
However, for an explosive event, whether initiated by accident or intentionally, a simple point source diffusion model is difficult to solve for atmospheric diffusion of explosive pollutants. The source terms required by the outcome calculation model of an explosion event (accident) are: after the explosion is over, a stable cloud (explosion cloud) is formed, which begins to diffuse under atmospheric action, with the instantaneous aerosol characteristics.
The size of the explosive smoke cloud and the source characteristics such as the distribution of internal substances affect the concentration of radioactive substances on the ground and in the air from the area near the explosive point to the area of several kilometers or more, and other consequences, so the problem of the explosive source needs to be considered in the evaluation of the consequences. The prior art lacks corresponding research and analysis, and has no corresponding forming technical scheme.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a conventional explosive radioactive aerosol diffusion source item estimation method, and provides a source item calculation method for establishing an explosive event consequence evaluation model.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for estimating the diffusion source term of a conventional explosive radioactive aerosol comprises the following steps:
aiming at the conventional explosion of the radioactive texture surface, the explosion equivalent is estimated,
estimating the size of the explosion cloud based on the explosion equivalent, the size of the explosion cloud comprising: height of the detonation smoke cloud, radius of the detonation smoke cloud, volume of the detonation smoke cloud, and density of the detonation smoke cloud, wherein:
when the height of the explosion smoke cloud is estimated, the explosion equivalent and the local wind speed are integrated,
the explosive equivalent is taken into account when estimating the radius of the explosive cloud,
the explosive quality and the volume of the explosive cloud are integrated when the density of the explosive cloud is estimated,
the explosive aerosol generation fraction and the aerosol particle size distribution were estimated,
the effect of heavy gas effects on the source terms is estimated and the nuclides of interest needed to set the explosive event.
Further, as mentioned above, the method for estimating the source term of the conventional explosive radioactive aerosol diffusion means to convert the explosive energy into TNT equivalent with a conversion relationship of 4.19MJ (megajoule) 1 kgTNT.
Further, the method for estimating the source term of the diffusion of the conventional explosive radioactive aerosol, which estimates the size of the explosive smoke cloud based on the explosive equivalent weight specifically includes:
the height of the explosion smoke cloud is estimated by the following formula,
h(w,t,v)＝(6.3±1.0)×w0.29±0.03×t0.5±0.05stability or neutrality
h(w,t,v)＝(6.3±1.0)×w0.29±0.013×t(0.7±0.013)-(0.03±0.002)vInstability of the film
Wherein:
h is the effective height that the smoke cloud can reach, and the unit is m,
w is the explosive TNT equivalent, the applicable range of the explosive equivalent is between 0.25kg and 100kg,
t is the time to reach the effective altitude, in units of s,
v is the local wind speed, in m/s,
the radius of the explosion smoke cloud is estimated by the following formula,
R(w)＝3.5w0.375
the volume of the explosion smoke cloud is estimated by the following formula,
V＝πR2h
the density of the explosive cloud is estimated by the following formula,
ρ＝ρa+(Wd+WE)/V
wherein:
rho is the density of the explosive smoke cloud and has the unit of kg/m3，
ρaIs the air density in kg/m3，
WdIs the mass of the explosive, and the unit is kg,
WEis the total mass in kg of other materials contained in the explosive material.
Further, the method for estimating the source term of the diffusion of the conventional explosive radioactive aerosol includes:
calculating the mass fraction of the airborne radioactive substance, using the following formula,
F＝2.378(WT/WE)-0.6383 WT≥5WE
F＝1.0 WT<5WE
wherein:
WTis the TNT equivalent, in kg,
WEis contained in the exploderThe total mass of the other materials in the fry mass, in kg,
the particle size distribution of the airborne radioactive substance is usually lognormal distributed with the mass, the particle size distribution of the airborne radioactive substance is calculated, the following formula is adopted,
Figure BDA0001843348480000041
wherein:
FRis the particle diameter d1And d2The mass fraction of the gas-carrying substance in between,
d1and d2Respectively two particle sizes, d1>d2The unit is a number of microns,
m is a mass median diameter in μm, obtained experimentally,
g is the geometric standard deviation, an empirical value,
erfc is a complementary error function.
Further, the conventional method for estimating the source term of the explosive radioactive aerosol diffusion as described above is divided into two groups according to the particle size of more than 15 μm and the particle size of 15 μm or less when calculating the particle size distribution of the airborne radioactive material,
the part with the particle size of more than 15 μm and less than 100 μm is calculated according to the particles and divided into four groups according to the ground reflection coefficient: d is more than 15 and less than or equal to 30 mu m, d is more than 30 and less than or equal to 47 mu m, d is more than 47 and less than or equal to 75 mu m, d is more than 75 and less than or equal to 100 mu m,
fractions having a particle size of 15 μm or less, considered as gases, were divided into three groups: d is more than 0 and less than or equal to 1 mu m, d is more than 1 and less than or equal to 10 mu m, d is more than 10 and less than or equal to 15 mu m,
more than 100 μm are independently used as a group,
the fractions within the different fractions are determined from this particle size fraction.
Further, as described above, the method for estimating the source term of diffusion of a conventional explosive radioactive aerosol, where the method for estimating the influence of Heavy Gas effects on the source term adopts an IIT Heavy Gas Model-I instantaneous release Heavy Gas Model, specifically including:
gravity settling, using the following formula:
Figure BDA0001843348480000042
wherein:
dR/dt is the change rate of the radius of the smoke cloud along with time, and the unit is m/s,
ρais the density of air, in kg/m3，
K is the gravity settling coefficient of the smoke cloud,
Δ ρ is the density difference between the cloud and air in kg/m3，
Air entrainment, using the following formula:
Figure BDA0001843348480000051
wherein:
α*to control the parameters of the side draw rate,
ue is the velocity of the top entrainment, which is the Raphson number Ri and the radial turbulence velocity UlAs a function of (c).
Further, as described above in a conventional method for estimating the source term of explosive radioactive aerosol diffusion, the source term estimation is started after a stable smoke cloud is formed after explosion, and the temperature of the smoke cloud and the temperature of the surrounding atmosphere are considered to be equal.
The invention has the beneficial effects that: based on the explosion equivalent, the explosive mass, the local wind speed and the like, the size of the explosion smoke cloud, the generation share of the explosion aerosol, the aerosol particle size distribution and the influence of heavy gas effect on the source item are comprehensively considered to form a source item estimation method, which is more in line with the actual situation and has the effect superior to a point source diffusion model.
Drawings
FIG. 1 is a graph of the effect of heavy gas on the height and radius of the source term in accordance with the present invention. Wherein:
a is a graph of the height h over time.
And b is a graph of the change of the radius R with time.
FIG. 2 is a block diagram of a method of the present invention.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
Fig. 2 is a flowchart illustrating a method for estimating a source term of a conventional explosive radioactive aerosol diffusion according to an embodiment of the present invention, where the method mainly includes:
aiming at the conventional explosion of the radioactive texture surface, the explosion equivalent is estimated,
estimating the size of the explosion cloud based on the explosion equivalent, the size of the explosion cloud comprising: height of the detonation smoke cloud, radius of the detonation smoke cloud, volume of the detonation smoke cloud, and density of the detonation smoke cloud, wherein:
when the height of the explosion smoke cloud is estimated, the explosion equivalent and the local wind speed are integrated,
the explosive equivalent is taken into account when estimating the radius of the explosive cloud,
the explosive quality and the volume of the explosive cloud are integrated when the density of the explosive cloud is estimated,
the explosive aerosol generation fraction and the aerosol particle size distribution were estimated,
the effect of heavy gas effects on the source term is estimated and the nuclear species of interest needed to set the explosive event ("dirty bomb" explosive event).
The conventional explosion of the radioactive texture surface refers to the conventional explosion of the radioactive texture surface such as 'dirty bomb' explosion and the like.
Further, the estimation of the explosion equivalent refers to converting the energy of explosion into the TNT equivalent, and the conversion relation is 4.19MJ (megajoule) ═ 1 kgTNT.
The explosives adopted by conventional explosion can be different, and for convenience of calculation, in the dirty bomb explosion scene, the explosive explosion energy is converted into TNT equivalent.
Further, estimating the size of the explosion smoke cloud based on the explosion equivalent specifically comprises:
the height of the explosion smoke cloud is estimated by the following formula,
h(w,t,v)＝(6.3±1.0)×w0.29±0.03×t0.5±0.05stability or neutrality
h(w,t,v)＝(6.3±1.0)×w0.29±0.013×t(0.7±0.013)-(0.03±0.002)vInstability of the film
Wherein:
h is the effective height that the smoke cloud can reach, and the unit is m,
w is the explosive TNT equivalent, the applicable range of the explosive equivalent is between 0.25kg and 100kg,
t is the time to reach the effective altitude, in units of s,
v is the local wind speed, in m/s,
the formula for t is a function of the explosive equivalent, using the following formula,
t(w)＝(28.0±1.1)w(0.33±0.4)，
the radius of the explosion smoke cloud is estimated by the following formula,
R(w)＝3.5w0.375
as for the radius of the smoke cloud formed after explosion, because the radius is slightly influenced by the environment and is greatly influenced by the explosion equivalent,
the volume of the explosion smoke cloud is estimated by the following formula,
V＝πR2h
the density of the explosive cloud is estimated by the following formula,
ρ＝ρa+(Wd+WE)/V
wherein:
rho is the density of the explosive smoke cloud and has the unit of kg/m3，
ρaIs the air density in kg/m3，
WdIs the mass of the explosive, and the unit is kg,
WEis the total mass in kg of other materials contained in the explosive material.
The process of 'dirty bomb' explosion is mainly divided into three stages:
stage one: rapid diffusion of explosive substances generated in an explosion. This process heats the air near the explosion point. Typically lasting from a few tenths of a millisecond to a second, is the fastest and least affected by meteorological conditions for the entire process.
And a second stage: the explosive material, hot air and entrained dust create expansion and elevation of the smoke cloud. At this stage, the average temperature within the cloud is significantly higher than the ambient temperature. The size and vertical velocity of the smoke cloud are determined by the average density within the smoke cloud, the ambient environmental conditions, the viscosity and velocity of the air, and the temperature distribution within the smoke cloud. If the explosive volume is relatively large, the heat in the cloud may continue to increase because of the presence of products of sustained combustion after the explosion. At this stage, the effective process of cooling the smoke cloud is radioactive, transformation of the smoke cloud, heat transfer to the environment, and expansion of the smoke cloud. This process lasts from a few seconds to tens of seconds.
And a third stage: the cloud continues to expand and rise. At this stage, the average temperature of the cloud is close to that of the surrounding environment, the cloud continues to increase the inertial force of the internal gas, and the expansion of the cloud is mainly due to diffusion and turbulence. This phase lasts for hundreds of seconds in a particularly large explosion and ends when it reaches the effective altitude.
When studying the size of the smoke cloud at the beginning of the explosion, the assumption is made that the heat rise of the smoke cloud after the explosion is rapid, before most diffusion, i.e. expansion precedes diffusion.
Further, the estimating of the generation fraction of the explosive aerosol and the aerosol particle size distribution specifically includes:
calculating the mass fraction of the airborne radioactive substance, using the following formula,
F＝2.378(WT/WE)-0.6383 WT≥5WE
F＝1.0 WT<5WE
wherein:
WTis the TNT equivalent, in kg,
WEis contained in an explosive substanceThe total mass of the material is kg,
the particle size distribution of the airborne radioactive substance is usually lognormal distributed with the mass, the particle size distribution of the airborne radioactive substance is calculated, the following formula is adopted,
Figure BDA0001843348480000081
wherein:
FRis the particle diameter d1And d2The mass fraction of the gas-carrying substance in between,
d1and d2Respectively two particle sizes, d1>d2The unit is a number of microns,
m is the mass median diameter, the value of m is 5, the unit is mum, and the m is obtained according to domestic experiments,
g is the geometric standard deviation, the value of g is 4, which is an empirical value,
erfc is a complementary error function.
The particle size of the aerosol particles affects the diffusion process after the formation of the explosive cloud, the deposition rate of the particles and the gas in the atmospheric environment is different, and the aerosol can generate some characteristics of heavy gas due to the existence of the particles. Evaluating the post-detonation particle scale problem involves two calculations:
(1) calculating the mass fraction of the substance that becomes airborne radioactive due to the explosion;
(2) the mass fraction of all airborne substances in the particle size range which can have a detrimental health effect on humans is calculated.
When calculating the particle size distribution (aerosol particle size distribution) of the airborne radioactive substance, the invention divides the aerosol into two groups and seven groups according to the particle size,
the two groups refer to the particle size of more than 15 μm and the particle size of less than or equal to 15 μm.
The part with the grain diameter more than 15 μm and less than 100 μm is calculated according to the particles and divided into four groups according to the ground reflection coefficient,
the fraction having a particle size of 15 μm or less, considered as a gas, aerosol particles having a particle size of 15 μm or less are divided into three groups,
the seven particle size groups are specifically: d is more than 0 and less than or equal to 1 mu m, d is more than or equal to 1 and less than or equal to 10 mu m, d is more than or equal to 10 and less than or equal to 15 mu m, d is more than 15 and less than or equal to 30 mu m, d is more than 30 and less than or equal to 47 mu m, d is more than 47 and less than or equal to 75 mu m, and d is more than 75 and less than or equal. The particles having a particle size of 100 μm or more (excluding the number) are individually grouped. The invention determines the fraction within the different fractions on the basis of this particle size fraction.
It should be noted that: according to the summary of the relevant documents of the aerosol, the particles with the smallest aerosol deposition rate are about 1 μm in particle size, some books are different from guiding rules, and the aerosol with the particle size below 10 μm is regarded as gas, so the invention takes the two points as the basis to group the aerosols with the particle size of 15 μm or less.
Examples are as follows:
a uranium mass of 4kg and a TNT equivalent weight of 0.5kg were selected and the calculated particle size groups are given in Table 1.
TABLE 1 particle size groups and fraction of each group
Figure BDA0001843348480000091
Further, the estimating of the influence of the Heavy Gas effect on the source term adopts an IIT Heavy Gas Model-I instantaneous Heavy Gas release Model, which specifically comprises:
gravity settling, using the following formula:
Figure BDA0001843348480000092
wherein:
dR/dt is the change rate of the radius of the smoke cloud along with time, and the unit is m/s,
ρais the density of air, in kg/m3，
K is the gravity settling coefficient of the smoke cloud, the value is 1,
Δ ρ is the density difference between the cloud and air in kg/m3，
Air entrainment, using the following formula:
Figure BDA0001843348480000093
wherein:
α*to control the parameters of the side draw rate,
ue is the velocity of the top entrainment, which is the Raphson number Ri and the radial turbulence velocity UlAs a function of (a) or (b),
cloud cluster heating adopts the following formula:
Figure BDA0001843348480000101
wherein:
t is the temperature of the smoke cloud in units of,
dT/dT is the amount of change in the smoke cloud temperature over time,
delta Ta is the difference between the temperature of the smoke cloud and the temperature of the air in units of,
cp is the specific heat capacity of the released substance, in J/(kg ℃ C.),
m is the mass of the released substance,
qc is the rate of heat exchange of the smoke cloud due to turbulent and forced exchanges, depending on the temperature difference between the ground and the smoke cloud and various thermodynamic properties of the material,
cpa is the specific heat capacity of the entrained air,
ma is the mass of air entrained.
The aerosol formed after the explosion of the dirty bomb mainly comprises products after the explosion and the combustion of the explosive, products after the combustion or the oxidation of radioactive substances, dust and the like which are absorbed into the smoke cloud. The gas products after explosive combustion are mainly carbon oxides, sulfur oxides, nitrogen compounds and the like, and the molecular weights of the compounds are not much different from the molecular weight of air and are gases; the solid particles such as radioactive aerosol particles and dust are not continuous gas like gas, and the distance between the solid particles is far larger than the distance between air molecules, so that the solid particles can be used for preparing the gasConsidering that the density of the aerosol is the sum of the density of air and the density of radioactive substances and dust, so that the density of the aerosol is greater than that of air, it can be regarded as heavy gas, and the heavy gas effect should be considered to affect the explosive source item of the dirty bomb. The standard for judging heavy gas effect is density difference<0.0001kg/m3And also as a criterion for the loss of the heavy gas effect.
In the prior art, three equations of a box model are used for heavy gas effect judgment, and are correlated with each other, so that calculation is troublesome.
The invention adopts an IIT Heavy Gas Model-I instantaneous release Heavy Gas Model, the side entrainment is considered to enter, the entrainment speed Ue depends on UlAnd Ri formula as follows:
Ue＝α′UlRi-1
in the above formula, the first and second carbon atoms are,
Figure BDA0001843348480000111
wherein:
α' is the entrainment constant, the IIT Heavy Gas Model-I Model recommends a value of 0.8,
Ulis that the radial turbulence rate is proportional to the friction speed U, UlParameter a is related to atmospheric stability, as shown in table 2:
TABLE 2 stability vs. parameter a
Figure BDA0001843348480000112
g is the gravity acceleration, 9.8m/s is taken,
ls is the turbulence length, which is a function of height, and the expression for ls is given by Taylor (1970) as follows:
ls＝5.88h0.48。
as mentioned above, the density of the aerosol is the sum of the air density and the density of the radioactive material and the dust, and thus the density of the plume after entrainment of air can be considered as the ratio of the sum of the mass of the entrained air and the mass of the initial plume to the volume after entrainment of air, i.e.:
Figure BDA0001843348480000113
wherein:
a is the initial mass of the smoke cloud,
and M is the increased volume of entrained air multiplied by the density of the air, M ═ R2h-400). times.1.293, and obtaining the following by taking the derivatives of the two sides of the formula:
Figure BDA0001843348480000114
as can be seen from the foregoing, the present invention,
Figure BDA0001843348480000115
thus, it is possible to obtain
Figure BDA0001843348480000121
The parameters calculated in the previous step are brought in and simplified to obtain
Figure BDA0001843348480000122
While
Figure BDA0001843348480000123
And substituting the parameters to obtain the result of R, and solving h by using MATLAB.
In the 'dirty bomb' explosion scene, the source term estimation is started after stable smoke cloud is formed after explosion, the temperature of the smoke cloud is equal to the temperature of the surrounding atmosphere, and therefore the radius R of the explosion smoke cloud and the effective height h which the smoke cloud can reach are obtained without considering cloud cluster heating. For example, fig. 1 is a graph showing the results of the effects of heavy gas on the spread of smoke cloud calculated when the mass of uranium is 4kg and the TNT equivalent amount is 0.5 kg. Wherein: FIG. 1.a is a graph of the height h as a function of time. FIG. 1.b is a graph of the change of radius R with time.
Further, the nuclide needed to be concerned by the set explosion event is selected according to the following principle:
(1) ease of acquisition of radioactive materials;
(2) a greater number of possibilities can be obtained;
(3) the use and the manufacture are simple;
(4) easy shielding;
(5) higher activity levels;
(6) a sufficiently long half-life.
The method specifically comprises the following steps:
60Co、137Cs、192Ir、90Sr、241Am、252Cf、238Pu。
currently, the most commonly used isotopes in the medical, scientific and industrial industries are likely to be the commercial sources for "dirty bombs" and are set as nuclides of interest.
The properties of the isotopes most commonly used in the medical, scientific and industrial industries are listed in table 3.
TABLE 3 commercial sources that may be used for "dirty bombs
Figure BDA0001843348480000124
Figure BDA0001843348480000131
In addition, uranium also requires attention in addition to the several nuclides mentioned above because:
(1) the application is wide, the uranium is easy to obtain, the domestic and foreign control of the uranium is relaxed, and the application of the uranium in the civil aspect is also very wide.
(2) Emitters, which are primarily alpha-rays, low-energy beta-rays and gamma-rays, are easier to shield than Co and Cs, and are also convenient for terrorists to operate.
(3) Most of the detectors at present are used for detecting gamma rays, and the gamma ray detector is difficult to detect alpha rays, which causes certain difficulty for detecting uranium oxide after the explosion of a dirty bomb.
(4) Inhalation and ingestion of uranium can cause chemical and radiological hazards to the human body.
(5) Uranium is widely known as the primary material for making nuclear weapons, and if the material of a "dirty bomb" is uranium, it may cause greater panic than other nuclear materials not known.
The invention has the beneficial technical effects that: on the basis of basic conditions such as explosion equivalent, explosive mass, local wind speed and the like, the influences of the size of explosion smoke cloud, the generation portion of explosion aerosol, aerosol particle size distribution and heavy gas effect on source items are fully considered, and nuclides needing attention are listed. Compared with a point source, the source item estimation method provided by the invention is more suitable for the situation of 'dirty bomb' explosion in practice.
The invention can provide a preliminary basis for emergency plan and decontamination work of the place where the dirty bomb explosion event occurs, provides a basis for calculating the diffusion of radioactive substances in city streets, and provides a material and a theoretical basis for further research on the dirty bomb terrorist attack event in the future.
The present invention is not limited to the above specific embodiments, and those skilled in the art can derive other embodiments according to the technical solutions of the present invention, which also belong to the technical innovation scope of the present invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.

Claims (3)

1.A method for estimating the diffusion source term of a conventional explosive radioactive aerosol comprises the following steps:
aiming at the conventional explosion of the radioactive texture surface, the explosion equivalent is estimated,
estimating the size of the explosion cloud based on the explosion equivalent, the size of the explosion cloud comprising: height of the detonation smoke cloud, radius of the detonation smoke cloud, volume of the detonation smoke cloud, and density of the detonation smoke cloud, wherein:
when the height of the explosion smoke cloud is estimated, the explosion equivalent and the local wind speed are integrated,
the explosive equivalent is taken into account when estimating the radius of the explosive cloud,
the explosive quality and the volume of the explosive cloud are integrated when the density of the explosive cloud is estimated,
the explosive aerosol generation fraction and the aerosol particle size distribution were estimated,
estimating the influence of heavy gas effect on source items and setting the nuclide of interest required by the explosion event;
the estimation of the explosion equivalent refers to converting the explosion energy into TNT equivalent, and the conversion relation is 4.19MJ (megajoule) which is 1 kgTNT;
the estimating of the size of the explosion smoke cloud based on the explosion equivalent specifically comprises:
the height of the explosion smoke cloud is estimated by the following formula,
h(w,t,v)＝(6.3±1.0)×w0.29±0.03×t0.5±0.05stability or neutrality
h(w,t,v)＝(6.3±1.0)×w0.29±0.013×t(0.7±0.013)-(0.03±0.002)vInstability of the film
Wherein:
h is the effective height that the smoke cloud can reach, and the unit is m,
w is the explosive TNT equivalent, the applicable range of the explosive equivalent is between 0.25kg and 100kg,
t is the time to reach the effective altitude, in units of s,
v is the local wind speed, in m/s,
the radius of the explosion smoke cloud is estimated by the following formula,
R(w)＝3.5w0.375
the volume of the explosion smoke cloud is estimated by the following formula,
V＝πR2h
the density of the explosive cloud is estimated by the following formula,
ρ＝ρa+(Wd+WE)/V
wherein:
rho is the density of the explosive smoke cloud and has the unit of kg/m3，
ρaIs the air density in kg/m3，
WdIs the mass of the explosive, and the unit is kg,
WEis the total mass of other materials contained in the explosive substance in kg;
the estimating of the generation portion of the explosive aerosol and the aerosol particle size distribution specifically comprises the following steps:
calculating the mass fraction of the airborne radioactive substance, using the following formula,
F＝2.378(WT/WE)-0.6383 WT≥5WE
F＝1.0 WT<5WE
wherein:
WTis the TNT equivalent, in kg,
WEis the total mass of other materials contained in the explosive substance, in kg,
the particle size distribution of the airborne radioactive substance is usually lognormal distributed with the mass, the particle size distribution of the airborne radioactive substance is calculated, the following formula is adopted,
Figure FDA0002940462760000021
wherein:
FRis the particle diameter d1And d2The mass fraction of the gas-carrying substance in between,
d1and d2Respectively two particle sizes, d1>d2The unit is a number of microns,
m is a mass median diameter in μm, obtained experimentally,
g is the geometric standard deviation, an empirical value,
erfc is a complementary error function;
the method for estimating the influence of the Heavy Gas effect on the source item adopts an IIT Heavy Gas Model-I instantaneous release Heavy Gas Model, and specifically comprises the following steps:
gravity settling, using the following formula:
Figure FDA0002940462760000022
wherein:
dR/dt is the change rate of the radius of the smoke cloud along with time, and the unit is m/s,
ρais the density of air, in kg/m3，
K is the gravity settling coefficient of the smoke cloud,
Δ ρ is the density difference between the cloud and air in kg/m3，
Air entrainment, using the following formula:
Figure FDA0002940462760000031
wherein:
α*to control the parameters of the side draw rate,
ue is the rate of top entrainment, which is the Raphson number Ri and the radial turbulenceSpeed UlAs a function of (c).
2. The method for estimating the source term of a conventional explosive radioactive aerosol diffusion according to claim 1, wherein: when calculating the particle size distribution of the airborne radioactive substance, the method is divided into two groups according to the particle size of more than 15 μm and the particle size of less than or equal to 15 μm,
the part with the particle size of more than 15 μm and less than 100 μm is calculated according to the particles and divided into four groups according to the ground reflection coefficient: d is more than 15 and less than or equal to 30 mu m, d is more than 30 and less than or equal to 47 mu m, d is more than 47 and less than or equal to 75 mu m, d is more than 75 and less than or equal to 100 mu m,
fractions having a particle size of 15 μm or less, considered as gases, were divided into three groups: d is more than 0 and less than or equal to 1 mu m, d is more than 1 and less than or equal to 10 mu m, d is more than 10 and less than or equal to 15 mu m,
more than 100 μm are independently used as a group,
the fractions within the different fractions are determined from this particle size fraction.
3. The method for estimating the source term of a conventional explosive radioactive aerosol diffusion according to claim 1, wherein: the source term estimation begins after a stable cloud of smoke is formed after the explosion, at which point the temperature of the cloud of smoke and the temperature of the surrounding atmosphere are considered to be equal.
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