Method for calculating external exposure dose field of nuclear accident based on limited plume model and computer readable storage medium

Abstract

The application discloses a nuclear accident external exposure dose field calculation method based on a limited smoke cloud model and a computer readable storage medium, and solves the technical problems of poor matching, long calculation time and low efficiency of the prior art. First, the radionuclide source term file released by the nuclear accident and the corresponding original data are obtained; then, the source term nuclide information data matrix is calculated; then, the gamma ray linear attenuation coefficient and the air energy mass absorption coefficient of each nuclide are calculated according to the gamma ray energy of each nuclide; the number of grids and the number of grid points of each grid in the smoke cloud activity concentration field and the ground deposition activity field penetrated by the gamma rays of other grids are calculated; finally, the deposition external exposure dose and the smoke cloud external exposure dose of each grid are calculated, so that the nuclear accident external exposure dose field calculation is completed. The method can realize the automatic and refined calculation of the external exposure dose in the nuclear accident, and has high calculation efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a nuclear accident consequence evaluation method, in particular to a nuclear accident external exposure dose field calculation method based on a finite plume model and a computer readable storage medium. BACKGROUND

[0002] Although the safety of nuclear energy utilization is high, the risk of nuclear accidents still exists. When a nuclear accident occurs, airborne radioactive substances will move and diffuse in the atmosphere, and ultimately act on personnel and the environment through the ionizing radiation effect of high-energy rays. In order to cope with possible nuclear accidents, many countries have developed nuclear accident consequence evaluation and emergency decision support systems, and their external exposure dose models generally use a semi-infinite plume model or a list method for rapid calculation. However, the semi-infinite plume model does not consider the uneven distribution of the body source and the influence of topography, and under unfavorable diffusion weather conditions and within a few km of the release point, the calculation results differ by several times from the values derived using more rigorous calculation methods. In addition, for some radioactive deposition prediction models, the activity value of the radionuclide attached in the particle is converted to a dose field by spatial integration, and then a K factor is directly introduced to calculate the dose field distribution. The K factor is the dose rate value formed by a radio source with a certain geometric distribution at a specific location, which can be considered as the superposition of the dose rate values of multiple point sources at that location.

[0003] On this basis, more accurate finite plume models have been developed, such as the photon "range" method, the discrete point approximation method, and the graphical method. For example, Wang Xingyu, Shi Zhongqi, et al. published "A Finite Plume External Exposure Dose Calculation Method - Photon 'Range' Method [J]. Radiation Protection, 2001.(02)", which disclosed the principle of a finite plume model and divided the plume within 5 times the average free path of photons in air around the exposed person into some volume elements to calculate the external exposure dose. However, it did not disclose the specific calculation method, and it was unclear how to obtain the core parameters required for calculation.

[0004] Chen Xiaqiu et al. published "Comparison of Graphical Method and Discrete Point Approximation Method for Estimating External Exposure Dose from Finite Plume of Gamma Radionuclides in Atmospheric Discharge [J]. Radiation Protection, 1993.(05)", which disclosed a more simple and fast manual calculation method. However, this method has poor compatibility with existing computer models.

[0005] Li Xinpeng et al. published in "nuclear accident under the radiation risk prediction of airborne radionuclides[M]. Beijing: Tsinghua University Press, February 2023, the first edition", put forward a kind of non equidistant three-dimensional dose field fast calculation method based on NFFT, but this method only optimizes the integral calculation process, and lists the calculation results of one kind of radionuclide. However, nuclear accidents are of various forms, and the released radionuclides are of various types. After the concentration field and the settlement amount field are calculated by the atmospheric diffusion program, the external exposure dose field of all grids needs to be calculated. Therefore, if this calculation method is used to obtain the calculation results of all radionuclides, the calculation time is long, and the calculation efficiency is low. SUMMARY

[0006] The purpose of the present application is to solve the technical problems of the existing calculation method and the poor matching of the computer model, or the long calculation time and low efficiency, and to provide a nuclear accident external exposure dose field calculation method based on finite smoke cloud model and computer readable storage medium.

[0007] To achieve the above-mentioned purpose, the technical solution provided by the present application is:

[0008] A nuclear accident external exposure dose field calculation method based on finite smoke cloud model, characterized in that it comprises the following steps:

[0009] 【1】respectively obtain the radionuclide source term file released by the nuclear accident, the smoke cloud activity concentration field and the ground deposition activity field file, and the corresponding grid number and the spatial distance size data of each grid;

[0010] 【2】extract the radionuclide type and activity data of each radionuclide from the radionuclide source term file, and read the source term radionuclide information data matrix of the corresponding radionuclide type from the pre-prepared radionuclide database; the source term radionuclide information data matrix includes radionuclide name, gamma ray energy of each radionuclide, corresponding yield and activity;

[0011] 【3】according to the gamma ray energy of each radionuclide, the gamma ray linear attenuation coefficient and air energy mass absorption coefficient of each radionuclide are calculated and added to the source term radionuclide information data matrix obtained in step 【2】;

[0012] 【4】based on the smoke cloud activity concentration field and the ground deposition activity field file, and the corresponding grid number and the spatial distance size data of each grid, the number of grids and the number of grid points in the smoke cloud activity concentration field and the ground deposition activity field that are penetrated by gamma rays from other grids are calculated;

[0013] 【5】Based on the source element nuclide information data matrix obtained in step 【3】 and the grid number and the grid point number obtained in step 【4】, the deposition external exposure dose and the cloud external exposure dose caused by each grid itself and other grids are calculated respectively by traversing all the grids of the cloud activity concentration field, so as to complete the calculation of the nuclear accident external exposure dose field based on the finite cloud model.

[0014] Further, in step 【3】, the gamma ray linear attenuation coefficient and the air energy mass absorption coefficient of each nuclide are obtained by spline function fitting according to the gamma ray energy of the corresponding nuclide.

[0015] Further, step 【4】 is specifically as follows:

[0016] 4.1. Based on the cloud activity concentration field and the ground deposition activity field file and the corresponding grid number and the spatial distance dimension data of each grid, the grid number penetrated by the gamma ray of any grid in the cloud activity concentration field and the ground deposition activity field is calculated respectively; wherein, the grid number penetrated by the gamma ray in the x-axis direction of the any grid is n x which is calculated by the following formula:

[0017] n x = fix (1000 / Δx) + 1

[0018] In the formula, fix is the rounding operation, and Δx is the distance dimension of the any grid in the x-axis direction;

[0019] The grid number penetrated by the gamma ray in the y-axis direction of the any grid is n y which is calculated by the following formula:

[0020] n y = fix (1000 / Δy) + 1

[0021] In the formula, Δy is the distance dimension of the any grid in the y-axis direction;

[0022] The grid number penetrated by the gamma ray in the z-axis direction is related to the uniformity of the grid height in the z-axis direction. When the grid height in the z-axis direction is uniform and unchanged, the grid number penetrated by the gamma ray in the positive direction of the z-axis is n z1 :

[0023] n z1 = fix (1000 / Δz) + 1

[0024] In the formula, Δz is the distance dimension of the any grid in the z-axis direction;

[0025] The grid number penetrated by the gamma ray in the negative direction of the z-axis is n' z1 :

[0026]

[0027] where z n is the layer number of the grid in the z-axis direction, and the first layer is close to the ground;

[0028] When the grid height in the z-axis direction varies with the atmospheric pressure, the number of grids n z2 penetrated by the γ-ray in the positive direction of the z-axis is related to the layer number z n of the grid in the z-axis direction:

[0029] n z2 = m - z n

[0030] where m satisfies The height of the grid layer with the layer number z n in the z-axis direction is denoted by hz z2 , and the number of grids n′ x penetrated by the γ-ray in the negative direction of the z-axis is:

[0031]

[0032] 4.2. Based on step 4.1, the number of grid points of the grid is obtained.

[0033] The number of grid points m x of the x-axis in the grid is: m x = 2n x + 1.

[0034] The number of grid points m y of the y-axis in the grid is: m y = 2n y + 1.

[0035] When the grid height in the z-axis direction is uniform and constant, the number of grid points m z1 of the z-axis is:

[0036] m z1 = n′ z1 + n z1 .

[0037] When the grid height in the z-axis direction varies with the atmospheric pressure, the number of grid points m z2 of the z-axis is:

[0038] m z2 = n′ z2 + n z2 .

[0039] Further, in step 【5】, after the number of grids and the number of grid points of any grid penetrated by the gamma rays of other grids are calculated, the step of calculating the external exposure dose contribution of all gamma rays in each nuclide by parallel computing and discarding the gamma rays whose external exposure dose contribution in each nuclide is less than 1% by using the automatic truncation error is further included.

[0040] Further, in step 【5】, the formula for calculating the deposited external exposure dose is as follows:

[0041]

[0042] wherein D1 is the dose rate at the center height z0 position of any grid; f is the energy unit conversion coefficient; μ a is the air energy mass absorption coefficient of the kth gamma ray generated by the decay of the nuclide; q is the radioactivity; E k and FE k are the energy and the yield of the kth gamma ray generated by the decay of the nuclide, respectively; μ is the linear attenuation coefficient of the kth gamma ray generated by the decay of the nuclide; B(μr) = 1+kμr, wherein k=(μ-μ a ) / μ a S is the ground deposition source surface space; r is the distance between each point on the ground deposition source surface and the center height z0 position of any grid, and at this time,

[0043] Further, in step 【5】, the formula for calculating the external exposure dose of the smoke cloud is as follows:

[0044]

[0045] wherein D2 is the dose rate at the center height z0 position of any grid; V is the source volume space; r2 is the distance between each point on the source volume space and the center height z0 position of any grid, and at this time,

[0046] In addition, the application further provides a computer readable storage medium, which stores a computer program or instructions, and the special feature is that the computer program or instructions are executed by a processor to realize the steps of the method for calculating the external exposure dose field of a nuclear accident based on the limited smoke cloud model.

[0047] Compared with the prior art, the application has the following beneficial effects:

[0048] 1, The present application is first based on radionuclide source term file and pre-made nuclide database, and source term nuclide information data matrix is obtained; then the linear attenuation coefficient of gamma ray of each nuclide and air energy mass absorption coefficient are calculated and added to the source term nuclide information data matrix; then the number of grids and grid points of all grids in the calculated smoke cloud activity concentration field and ground deposition activity field which are penetrated by gamma rays of other grids are obtained; finally, the deposition external exposure dose and smoke cloud external exposure dose caused by each grid and other grids are calculated, so that the calculation of nuclear accident external exposure dose field based on finite smoke cloud model is completed, the method can realize automatic and refined calculation of external exposure dose in nuclear accident, and the calculation time is shorter and the calculation efficiency is higher.

[0049] 2, The present application can be applied to computer readable storage medium, and has higher matching with existing computer mode, and further improves the calculation efficiency.

[0050] 3, The deposition external exposure dose and smoke cloud external exposure dose calculated based on the present application are added to obtain the total external exposure dose, and the two can also be compared with the corresponding activity data, therefore, the application of data is more flexible and extensive.

[0051] 4, The present application can be used to solve the problem of refined calculation process of dose field formed by various nuclides in different distance grids. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 It is the flow chart of the embodiment of the present application.

[0053] Figure 2 It is the smoke cloud activity concentration data structure diagram in the embodiment of the present application.

[0054] Figure 3 It is the ground deposition activity data structure diagram in the embodiment of the present application. DETAILED DESCRIPTION

[0055] In order to make the purpose, advantages and characteristics of the present application clearer, the present application is further described in detail below in combination with the drawings and specific embodiments. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application, and the purpose is not to limit the protection scope of the present application.

[0056] The dose field calculation of semi-infinite smoke cloud is generally used in traditional nuclear accident consequence evaluation system, even if the finite smoke cloud model is used, the specific calculation process is not seen. In addition, nuclear accidents are various, and the released radionuclides are various, and after the concentration field is calculated by the atmospheric diffusion program, even the deposition amount field, the external exposure dose field of all grids needs to be calculated. Based on this, the present application designs a large number of different distance grid dose field automatic calculation process formed by various radionuclides, so that the external exposure dose of nuclear accident is automatically calculated and refined, and the calculation method can reduce the calculation time and improve the calculation efficiency.

[0057] As Figure 1 shown, the present embodiment provides a nuclear accident external exposure dose field calculation method based on a finite smoke cloud model, comprising the following steps:

[0058] 【1】Respectively acquire the radionuclide source term file released by the nuclear accident, the smoke cloud activity concentration field data file and the ground deposition activity field data file, and the corresponding grid number and the spatial distance size data of each grid. Figure 2 For three-dimensional space activity concentration data structure, Figure 3 two-dimensional space ground deposition activity data structure.

[0059] 【2】Extract the radionuclide type and activity data of each radionuclide from the radionuclide source term file, and read the source term radionuclide information data matrix corresponding to the radionuclide type from the pre-prepared radionuclide database. The source term radionuclide information data matrix includes radionuclide name, gamma ray energy (MeV) of each radionuclide and corresponding yield and activity.

[0060] The radionuclide database is a radionuclide information database prepared in advance, mainly including common radionuclide name, all gamma ray energy (MeV) generated by decay and corresponding yield, half-life and other information.

[0061] 【3】According to the gamma ray energy of each radionuclide, the gamma ray linear attenuation coefficient and air energy mass absorption coefficient of each radionuclide are calculated and added to the source term radionuclide information data matrix obtained in step 【2】.

[0062] In the present embodiment, the gamma ray linear attenuation coefficient and air energy mass absorption coefficient of each radionuclide are obtained by spline function fitting according to the gamma ray energy of the corresponding radionuclide.

[0063] 【4】Calculate the number of grids and grid points penetrated by gamma rays of other grids in any grid of the smoke cloud activity concentration field and the ground deposition activity field.

[0064] The embodiment considers the contribution of rays reaching the grid from other surrounding grids when calculating the dose of the grid. In particular, the contribution of ground-deposited nuclide rays is considered when calculating the air-external exposure dose, specifically:

[0065] 4.1, based on the smoke cloud activity concentration field and the ground-deposited activity field file, and their corresponding grid number and spatial distance size data of each grid, respectively calculate the number of grids in the smoke cloud activity concentration field and the ground-deposited activity field that are penetrated by γ rays from other grids; wherein, in the any grid, the number of grids penetrated by γ rays in the x-axis direction n x is calculated by the following formula:

[0066] n x = fix(1000 / Δx)+1

[0067] where fix is the rounding operation, and Δx is the distance size of the any grid in the x-axis direction.

[0068] The number of grids penetrated by γ rays in the y-axis direction n y is calculated by the following formula:

[0069] n y = fix(1000 / Δy)+1

[0070] where Δy is the distance size of the any grid in the y-axis direction.

[0071] The number of grids penetrated by γ rays in the z-axis direction is related to the uniformity of the grid height, and is divided into the number of penetrated grids in the positive z-axis direction and the negative z-axis direction. When the grid height in the z-axis direction is uniform and unchanged, the number of grids penetrated by γ rays in the positive z-axis direction (upward) n z1 :

[0072] n z1 = fix(1000 / Δz)+1

[0073] where Δz is the distance size of the grid point in the z-axis direction.

[0074] The number of grids penetrated by γ rays in the negative z-axis direction (downward) n' z1 :

[0075]

[0076] where z n is the layer number sequence of the grid point in the z-axis direction (close to the ground as the first layer).

[0077] When the grid height in the z-axis direction changes with atmospheric pressure, the expression of the number of grids penetrated by γ rays in the positive z-axis direction (upward) n z2 is related to the layer number sequence of the grid point in the z-axis direction z n :

[0078] n z2 = m - z n

[0079] wherein m satisfies z is the layer number in the z-axis direction n height of the grid layer of z.

[0080] Meanwhile, the expression of the number of grid layers n' through which the γ-ray in the negative direction (downward) of the z-axis direction penetrates is: z2

[0081]

[0082] 4.2, on the basis of step 4.1, the number of grid points of any grid is obtained, that is, the number of grid points m of the x-axis in any grid x is: m x = 2n x + 1

[0083] the number of grid points m of the y-axis y is: m y = 2n y + 1;

[0084] when the grid height of the z-axis is uniform and constant, the number of grid points m of the z-axis z1 :

[0085] m z1 = n' z1 + n z1 ;

[0086] when the grid height of the z-axis changes with atmospheric pressure, the number of grid points m of the z-axis z2 :

[0087] m z2 = n' z2 + n z2 .

[0088] 【5】Based on the source element nuclide information data matrix obtained in step 【3】 and the grid number and grid point number calculated in step 【4】, all grids of the plume activity concentration field are traversed to calculate the deposition external exposure dose and the plume external exposure dose caused by each grid and other grids, respectively, so as to complete the calculation of the nuclear accident external exposure dose field based on the finite plume model.

[0089] The traversal mode of this embodiment is:

[0090] ①First, traverse the z-axis direction. When the grid height of the z-axis direction is uniform and constant, start from the first layer of the ground. When the layer number of the grid in the z-axis direction is less than or equal to the number of grid layers n​z1 When the grid layer number in z-axis direction is greater than the grid number n z1 , only the contribution of the external exposure of the surrounding cloud activity at each height layer is considered; in both cases, the total grid points affected by the γ-rays in z-axis direction of the grid in z-axis direction are m z1 . When the grid height in z-axis direction changes with atmospheric pressure, starting from the first layer on the ground, when the grid layer number in z-axis direction is less than or equal to the grid number n z2 , the exposure dose calculation of the layer grid considers the contribution of the external exposure of the ground deposition activity and the contribution of the external exposure of the surrounding cloud activity at each height layer; when the grid layer number in z-axis direction is greater than the grid number n z2 , only the contribution of the external exposure of the surrounding cloud activity at each height layer is considered; in both cases, the total grid points affected by the γ-rays in z-axis direction of the grid in z-axis direction are m z2 .

[0091] ②In each z-axis height layer, starting from the leftmost layer in x-axis direction, the grid affected by the γ-rays in x-axis direction is n x , and the grid affected by the γ-rays in y-axis direction is n y . For the exposure dose of each horizontal grid (x, y), n x symmetrical grids in x-axis horizontal direction are considered, that is, the grid points traversed in x-axis horizontal direction are m x , n y symmetrical grids in y-axis horizontal direction are considered, that is, the grid points traversed in y-axis horizontal direction are m y , and the external exposure contributions of these grid points to the cloud formed by the γ-rays and the ground deposition of each horizontal grid (x, y) are calculated one by one. When the grid (x, y) is at the edge of the space, there is no symmetrical grid, and the non-existent symmetrical grid is directly set to zero.

[0092] Because there are many kinds of nuclear species released in a nuclear accident, each kind of nuclear species has a different number of γ-rays with different energies, therefore, the total number of all the remaining rays after the rays whose contribution sum is less than 1% are discarded is taken as the total amount, specifically: after the grid number and the grid points number penetrated by the γ-rays of other grids are calculated, the grid is regarded as a volume source, for the external exposure dose contribution of all the γ-rays of each kind of nuclear species in the volume source, parallel computing is used, and the γ-rays whose external exposure dose contribution sum is less than 1% of each kind of nuclear species are discarded by using automatic truncation error.

[0093] The dose calculation formula used in this embodiment is:

[0094]

[0095] D is dose rate, Gy / s; f is energy unit conversion coefficient 1.6x10 -13 , J / MeV, μ a is air energy mass absorption coefficient of the kth γ-ray produced by the decay of the nuclide, m 2 / kg; q is radioactivity, Bq; E k and FE k are energy (MeV) and yield of the kth γ-ray produced by the decay of the nuclide, respectively; μ is linear attenuation coefficient of the kth γ-ray produced by the decay of the nuclide, 1 / m; B(μr) = 1+kμr, and k = (μ-μ a ) / μ a , r is the distance between each point in space and the center height z0 of the calculation grid, m; when calculating the cloud external exposure dose, V is the source volume space, and when calculating the ground deposition external exposure, V is the source surface space, and the triple integral is reduced to a double integral.

[0096] The above-mentioned automatic truncation error mode is specifically that the coefficient μ a · q · E k · FE k of each γ-ray in each nuclide is combined, that is, the product of the mass absorption coefficient, activity, energy and the corresponding yield, and all the combinations of the nuclides are taken as the basis for arranging the size, the contribution of the error truncation to the calculation efficiency is analyzed, and the rays with a contribution sum below 1% are discarded.

[0097] As described above, in the present embodiment, the formula for calculating the deposition external exposure dose of each nuclide on any grid is:

[0098]

[0099] In the formula, D1 is the dose rate at the center height z0 (related to the position of the grid and the spatial distance size of the z-axis) of the grid; S is the ground deposition source surface space, and r is the distance between each point on the ground deposition source surface and the center height z0 of the grid, at this time,

[0100] The formula for calculating the cloud external exposure dose of each nuclide on any grid is:

[0101]

[0102] In the formula, D2 is the dose rate at the center height z0 of any grid; V is the source volume space; r is the distance between each point on the source volume space and the center height z0 of the grid, at this time,

[0103] When the calculation of the nuclear accident external exposure dose field based on the limited smoke cloud model is completed, the smoke cloud external exposure and ground deposition external exposure dose field data are output, the file format of the data is the same as the smoke cloud activity concentration field data structure and file format, and the data structure shown in Figure 2 or Figure 3 is output, facilitating subsequent processes to display the external exposure dose generated by the smoke cloud and the external exposure deposited on the ground, and the total external exposure dose can be obtained by adding the two external exposure doses, or the data can also be compared with the corresponding activity data.

[0104] The present application reads the nuclide species and its activity from the source item file, prepares the source nuclide information data for dose calculation, and adopts fitting calculation to obtain the mass absorption coefficient and linear absorption coefficient of gamma rays for dose calculation, which is suitable for nuclear pollution diffusion dose consequence calculation in different scenarios. In addition, based on the present application, a large number of dose field automatic calculation processes of different distance grids and multiple nuclides can be designed, so that the external exposure dose in a nuclear accident can be automatically and finely calculated, the calculation time is greatly shortened, and the calculation efficiency is significantly improved.

[0105] The embodiment also provides a computer readable storage medium having a computer program or instructions stored thereon, and the computer program or instructions are executed by a processor to realize the steps of the nuclear accident external exposure dose field calculation method based on the limited smoke cloud model.

[0106] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A method for calculating an external exposure dose field in a nuclear accident based on a limited plume model, characterized in that, The method comprises the following steps: 【1】. Respectively obtaining a radionuclide source term file released by a nuclear accident, a cloud activity concentration field and a ground deposition activity field file, and corresponding grid number and spatial distance dimension data of each grid; 【2】. Extracting nuclide types and activity data of each nuclide from the radionuclide source term file, and reading out a source term nuclide information data matrix of the corresponding nuclide type from a pre-prepared nuclide database; the source term nuclide information data matrix comprises a nuclide name, γ-ray energy of each nuclide, and corresponding yield and activity; 【3】. According to the γ-ray energy of each nuclide, the γ-ray linear attenuation coefficient and the air energy mass absorption coefficient of each nuclide are calculated and added to the source term nuclide information data matrix obtained in step 【2】; 【4】. Based on the cloud activity concentration field and the ground deposition activity field file, and the corresponding grid number and spatial distance dimension data of each grid, the grid number and grid point number of any grid in the cloud activity concentration field and the ground deposition activity field that is penetrated by γ-rays from other grids are calculated; then the external exposure dose contribution of all γ-rays in each nuclide is calculated by parallel computing, and γ-rays with a total external exposure dose contribution of less than 1% in each nuclide are discarded by using an automatic truncation error method; 【5】. Based on the source term nuclide information data matrix obtained in step 【3】 and the grid number and grid point number obtained in step 【4】, all grids in the cloud activity concentration field are traversed to calculate the deposition external exposure dose and cloud external exposure dose of each grid caused by itself and other grids, thereby completing the calculation of the nuclear accident external exposure dose field based on the limited cloud model; The calculation formula of the deposition external exposure dose is: ； wherein D1 is the dose rate at any grid center height z0 position; f is the energy unit conversion factor; μ a is the air energy mass absorption coefficient of the kth γ-ray generated by the decay of the nuclide; q is the radioactivity; and FE k are the energy and the corresponding yield of the kth γ-ray generated by the decay of the nuclide, respectively; μ is the linear attenuation coefficient of the kth γ-ray generated by the decay of the nuclide; wherein k = (μ-μ a ) / μ a , S is the ground deposition source surface space; r is the distance between each point on the ground deposition source surface and the height z0 position of any grid center, at this time, ; The calculation formula of the cloud external exposure dose is: ； In the formula, D2 is the dose rate at any grid center height z0 position; V is the source volume space; r is the distance from each point on the source volume space to the any grid center height z0 position, at which time, .

2. The nuclear accident external exposure dose field calculation method based on the limited cloud model according to claim 1, characterized in that: In step 【3】, the γ-ray linear attenuation coefficient and the air energy mass absorption coefficient of each nuclide are obtained by spline function fitting according to the γ-ray energy of the corresponding nuclide.

3. The method for calculating the external exposure dose field of a nuclear accident based on a limited cloud model according to claim 1, characterized in that, Step 【4】 is specifically: 4.1, based on the cloud activity concentration field and the ground deposition activity field file, and the corresponding grid number and the spatial distance size data of each grid, respectively calculate the number of grids in any grid of the cloud activity concentration field and the ground deposition activity field which is penetrated by γ-rays of other grids; wherein, in the any grid, the number of grids penetrated by γ-rays in the x-axis direction This is calculated by the following formula: ； where fix is a rounding operation, is the distance dimension of the grid in the x-axis direction; number of grids penetrated by the γ-rays in the y-axis direction is calculated by the following equation: ； In the formula, is the distance dimension of the grid in the y-axis direction; The uniformity of the number of grid in the z-axis direction of the γ-ray penetration is related to the uniformity of the grid height in the z-axis direction. When the grid height in the z-axis direction is uniform and unchanged, the number of grid in the z-axis direction of the γ-ray penetration is : ； In the formula, is the distance dimension of the grid in the z-axis direction; number of grids penetrated by the negative z-axis direction gamma rays : ； In the formula, z n is the layer number of the grid in the z-axis direction, wherein the layer closest to the ground is the first layer; The number of grids penetrated by the γ-ray in the positive direction of the z-axis when the grid height in the z-axis direction changes with the atmospheric pressure The expression is related to the number of layers z of the grid in the z-axis direction for any one of the grids, that is: n ​ ； In the formula, m satisfies , represents the height of the grid layer in the z-axis direction with the number of layers z n of the penetrating γ-rays in the negative z-axis direction; and the expression of the number of the penetrating γ-rays in the positive z-axis direction is: ​ ； 4.

2. On the basis of step 4.1, the grid point number of the any grid is obtained; The number of grid points of the x-axis in any of the grids is: ; The number of grid points of the y axis is: ; When the grid height in the z-axis direction is uniform and constant, the number of grid points in the z-axis direction is represented as: ； When the grid height in the z-axis direction changes with the atmospheric pressure, the number of grid points in the z-axis is represented as: 。 4. A computer readable storage medium having stored thereon a computer program or instructions, characterized in that, The computer program or instructions are executed by the processor to realize the steps of the nuclear accident external exposure dose field calculation method based on the limited cloud model according to any one of claims 1 to 3.

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