Method for emergency airborne radiation monitoring of nuclear power plant accidents

Abstract

The present application provides a kind of nuclear power plant accident emergency air radiation monitoring method, comprising the following steps: step one: preliminary generation of radioactive plume diffusion situation based on diffusion model;Step two: radiation dose rate estimation on the axis of radioactive plume;Step three: intervention boundary estimation of 5 kinds of operation intervention level OIL;Step four: actual intervention boundary determination based on ground gamma dose rate inversion calculation;Step five: air radiation monitoring task area determination and division;Step six: air radiation monitoring task planning;Step seven: air radiation monitoring flight control.The method proposed by the present application can scientifically determine the nuclear radiation situation of nuclear power plant nuclear accident, and can accurately divide and assign the radiation monitoring area.The present application can realize the optimization of air nuclear radiation monitoring task planning, the optimal matching of radiation monitoring task and radiation monitoring equipment, and can effectively improve the operation efficiency of air nuclear radiation monitoring equipment, and meet the needs of air radiation monitoring task for auxiliary decision-making.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nuclear radiation monitoring and application, and particularly relates to a nuclear power plant accident emergency air radiation monitoring method based on an optimization algorithm. BACKGROUND

[0002] Since the nuclear power plant accident hazard has the characteristics of wide nuclear radiation contamination range and long duration, therefore, rapid collection, transmission and processing of nuclear radiation monitoring information have a prerequisite role in timely organizing emergency rescue and reducing the influence of radiation hazards on emergency rescue decision-making. In the implementation of the nuclear emergency air radiation monitoring task, in order to complete the monitoring task in the shortest time and reasonably plan the task path and task allocation, it is necessary to scientifically plan the task of the air radiation monitoring equipment based on accurate measurement, so as to accurately obtain the monitoring data such as the range, dose rate and nuclide distribution of each radiation contaminated area in a short time. For air radiation monitoring, two cases of no wind and wind are distinguished, concentric circles, crosses, petal type and other flight methods are often used when there is no wind; when there is wind, serpentine return, scanning type and other flight methods are often used; these flight monitoring methods are mostly implemented according to the meteorological conditions and dose rate distribution, and cannot adapt to the needs of optimal monitoring path and task allocation under different emergency task environments. After the nuclear power plant accident, due to the restriction of factors such as topography and meteorological conditions, the area, shape and dose rate of the radiation hazard area are influenced to different degrees, and the differences of different hazard areas restrict the number and mode of the use of air radiation monitoring equipment. When performing the air radiation monitoring task under certain conditions, in order to minimize the task time and improve the monitoring efficiency, it is necessary to use optimization algorithm to scientifically allocate the monitoring task and optimize the radiation monitoring path under the constraint conditions of meeting the radiation situation demand and the index of air emergency monitoring equipment. SUMMARY

[0003] The present application aims at providing a fast and fine radiation monitoring method for emergency nuclear radiation monitoring of airborne radiation monitoring equipment after nuclear power plant accidents, which can be used for obtaining gamma radiation situation under various conditions and analyzing radionuclide distribution and radioactive plume diffusion. In order to solve the above technical problems and meet the needs of fast airborne radiation monitoring in nuclear power plant accident emergency and accurate acquisition of radiation situation in hazardous areas, attention should be paid to radioactive plume diffusion estimation, radiation dose rate estimation, intervention boundary estimation, gamma dose rate inversion estimation, monitoring task area and division, etc. The monitoring path and task allocation of airborne radiation monitoring are reasonably determined. The present application proposes an airborne nuclear radiation monitoring method based on task planning. On the basis of estimating the scope of nuclear radiation monitoring tasks, the method is constructed according to the idea of "monitoring task estimation, monitoring path optimization, condition limit constraint and task reasonable division", on the basis of fully considering the related constraint conditions, the related optimization algorithm and model are constructed, the monitoring path of airborne radiation monitoring equipment is optimized and the task is reasonably divided, the support efficiency of airborne emergency monitoring equipment is maximized, the task time limit is shortened, and the emergency benefit is maximized.

[0004] The present application is a nuclear power plant accident emergency airborne radiation monitoring method based on task planning, and the specific steps are as follows:

[0005] Step 1: Preliminary generation of radioactive plume diffusion situation based on diffusion model

[0006] Assuming that the release site of the nuclear power plant source is the source point, according to the Gaussian model, the continuous point source concentration distribution in the presence of wind is measured according to the following formula:

[0007]

[0008] In the formula, c(x,y,z) is the concentration of radioactive substances at any point in space, with the unit of Bq·m -3 ; x, y and z respectively represent the coordinate positions of any point in space left, right, front, back and up; Q is the source strength of the radioactive source, with the unit of Bq·s -1 ; u is the average wind speed, with the unit of m·s -1 ; k y and k z are the turbulent diffusion coefficients, with the unit of m.

[0009] Since the concentration distribution on the cross section of the smoke cloud is a normal distribution, the lateral diffusion coefficients σ y and σ z of the smoke cloud are:

[0010]

[0011] Substituting the above formula, it can be written as:

[0012]

[0013] Let z = 0, the ground concentration formula of radionuclide:

[0014]

[0015] In the formula: c(x, y, 0) is the concentration of radioactive material at a point on the ground, with units of Bq·m -3 ; Q is the source strength of the radioactive source, with units of Bq·s -1 ; u is the average wind speed, with units of m·s -1 ; σ y and σ z are the lateral dispersion coefficients of the plume, with units of m. The turbulent diffusion coefficient is shown in the table below.

[0016]

[0017] According to the above Gaussian dispersion model of radioactive plume, combined with the source strength of the radioactive source released by the nuclear power plant at that time, the average wind speed, the height of the radioactive source leakage position and other parameter conditions, the diffusion situation of the ground radioactive plume can be initially generated.

[0018] Step two: estimation of radiation dose rate on the axis of the radioactive plume

[0019] The ground gamma point source dose rate calculation formula is:

[0020]

[0021] In the formula: D is the air absorbed dose rate; A is the activity of the radioactive source, Γ is the irradiation rate constant corresponding to the nuclide; η is the linear attenuation coefficient corresponding to the nuclide; R is the distance between the point source and the monitoring point.

[0022] For the points in the direction of the radioactive plume diffusion (downwind), the radiation dose rate at a known position on the diffusion axis can be measured, and then the radiation dose rate at other downwind position points on the same axis can be measured by inverse proportion law. The calculation formula is as follows:

[0023]

[0024] In the formula: D1 is the measured radiation dose rate at r1, with units of mSv·h -1 ; D2 is the measured radiation dose rate at r2, with units of mSv·h -1 ; τ is the diffusion rate, which is related to atmospheric stability. Generally, it is 1.5 under normal weather conditions, 2 when the atmospheric stability is a or b, 1.5 when the atmospheric stability is c or d, and 1 when the atmospheric stability is e or f; r1, r2 are the distances of any two monitoring points from the radioactive source release position of the nuclear power plant, with units of m.

[0025] Step three: Intervention boundary estimation of OIL5

[0026] According to GB / T 41577-2022 "Emergency Operation Intervention Level of Nuclear Power Plant", the operation intervention level is divided into 9 types. According to the standard OIL5 type (preventive restriction of operation intervention level value of general food and milk, the measurement category is the dose rate around ground deposition), the dose rate limit value is 1uSv / h, and the protective action taken is food restriction.

[0027] At a fixed monitoring point with a known monitoring distance r1 in a certain area of a nuclear power plant, the measured γ dose rate is D1, and according to the OIL5 type operation intervention level boundary value 1uSv / h (D2), assuming the atmospheric stability diffusion rate is 1.5, based on the diffusion axis radiation dose rate formula

[0028]

[0029] The emergency radiation monitoring area of the airborne radiation monitoring equipment can be preliminarily estimated. Combined with the diffusion situation of the radioactive plume generated in the previous step one and the intervention boundary distance r2 in the downwind direction, the nuclear radiation monitoring task range can be preliminarily estimated, providing a basic reference for task planning.

[0030] Step four: Determination of actual intervention boundary based on ground γ dose rate inversion

[0031] For regional nuclear radiation monitoring, although the air track of the airborne radiation monitoring equipment is a very narrow straight line, the radioactive exposure of the airborne radiation monitoring equipment is from a large area ground source. The ground source is integrated according to the dose rate generated by multiple circular rings, and the airborne radiation monitoring equipment is located at the center of the circular ring. The dose rate at different heights can be calculated by the following formula.

[0032]

[0033] In the formula, Ψ is the radius of the large area source; r is the integral factor, corresponding to the radius of the circular ring; h is the flight height; ε is the surface contamination activity, representing the radioactivity per unit area, and Γ is the irradiation rate constant of the corresponding nuclide; is the linear attenuation coefficient of the corresponding nuclide.

[0034] Through a large number of test comparisons, for the same height, as the radius of the source increases, the dose rate gradually increases, and when the source radius reaches 100m or more, the dose rate change is no longer obvious, so the source radius in the formula can be taken as 100 meters. The formula can be expressed as:

[0035]

[0036] When performing the emergency monitoring task, assuming that the airborne radiation monitoring device flies at a certain height of 1 meter, measures a certain contamination point dose rate value, and through the above dose rate inversion formula, the surface contamination activity (ε) of the contamination point can be measured; and the dose rate value 1 meter away from the contamination point can be inversely calculated. In the estimation of the intervention boundary, the airborne radiation monitoring device should appropriately reduce the flight speed, and compare the real-time ground gamma dose rate value obtained by inversion with the 5 types of operation intervention dose rate value, and then determine the actual intervention boundary.

[0037] Step five: determination and division of the airborne radiation monitoring task area

[0038] According to GB / T 41577-2022 “Nuclear Power Plant Emergency Operation Intervention Level”, in the early emergency monitoring stage, the key monitoring range on land is 30 km, and according to the radioactive pollution situation, the monitoring range can be gradually expanded to 50 km; for a large amount of radioactive release caused by a severe accident of a reactor with a thermal power of ≥1000 MW, the monitoring range may need to be expanded to 80 km or even further. The specific emergency monitoring area should be reasonably determined according to the estimated nuclear radiation monitoring task range, diffusion situation estimation map and national standard requirements. According to the nuclear emergency plan of each nuclear power plant, the emergency plan area includes the plume emergency plan area and the ingestion emergency plan area. The plume emergency plan area is the emergency area centered on the nuclear power plant, which is divided into the inner area (radius generally 5 km) and the outer area (radius generally 10 km) of the plume; the radius of the ingestion emergency plan area is generally 30 km or 50 km. According to this, based on the downwind of the dominant wind direction, the contaminated sector is divided into different monitoring ranges with a radius of 5 km, (5-10) km, (10-30) km, (30-50) km, etc. Specifically, within a radius of 5 km, the task area is equivalent to a rectangular area with a length of 5 km and a width of the distance between the thermal line and the longitudinal estimated intervention boundary; within a radius of 5-10 km, the task area is equivalent to a rectangular area with a length of 5 km and a width of the distance between the thermal line and the longitudinal estimated intervention boundary; within a radius of 10-30 km, the task area is equivalent to a rectangular area with a length of 20 km and a width of the distance between the thermal line and the longitudinal estimated intervention boundary; within a radius of 30-50 km, the task area is equivalent to a rectangular area with a length of 20 km and a width of the distance between the thermal line and the longitudinal estimated intervention boundary.

[0039] The airborne radiation monitoring adopts the method of equidistant parallel lines, covering the entire monitoring area along the equidistant lines parallel to the vertical line of the thermal line in the direction of plume diffusion. The spacing between different task area monitoring lines can be determined according to the following formula:

[0040]

[0041] In the formula, d is the spacing between radiation monitoring parallel lines; D bTo monitor the natural background dose rate of the environment; D z To generate a dose rate at 1 meter from the radionuclide.

[0042] The scanning parallel line spacing for air monitoring in different monitoring areas such as 5 km, (5-10) km, (10-30) km, (30-50) km, etc. is d1, d2, d3, d4, respectively. 3、 d4. The corresponding different monitoring areas can further refine the monitoring method. The 5 km range monitoring area can be refined into a grid area; the (5-10) km, (10-30) km, (30-50) km range monitoring area uses a scanning parallel turn-back method. The actual air radiation monitoring task area should be determined in combination with the preliminary estimated nuclear radiation monitoring task range and the above monitoring method.

[0043] Step six: Air radiation monitoring task planning

[0044] First, the total distance of air gamma radiation monitoring is calculated. According to the determined air nuclear radiation monitoring task range, the total distance of air radiation monitoring path needs to be calculated, and the calculation formula is:

[0045]

[0046] In the formula, S represents the total distance of air radiation monitoring, unit: km; s1, s2, s3, s4 represent the horizontal distance of monitoring ranges with radii of 5 km, 5-10 km, 10-30 km, 30-50 km, respectively; l1, l2, l3, l4 represent the distance between the hot wire and the longitudinal estimated intervention boundary in the direction of the smoke plume for different monitoring radii, unit: m; d1, d2, d3, d4 represent the radiation monitoring parallel line spacing in the monitoring range with radii of 5 km, 5-10 km, 10-30 km, 30-50 km, respectively, unit: m.

[0047] Second, the air gamma radiation monitoring time calculation and task allocation. After estimating the total air radiation monitoring task, based on the number of emergency equipment, performance, and related range, task radius, monitoring speed, and related constraints such as tolerable cumulative dose, the air radiation monitoring time and monitoring task are scientifically allocated.

[0048] The air radiation monitoring time is calculated according to the following formula:

[0049]

[0050] In the formula, S represents the total distance of air radiation monitoring, unit: km; n represents the number of air radiation monitoring equipment, unit: pieces; v represents the radiation monitoring speed of air radiation monitoring equipment, unit: km / h.

[0051] Related constraints:

[0052]

[0053] Based on the above constraints, in the case of a given number of air radiation devices, through reasonable task allocation, the air radiation monitoring task can be optimized within the specified task time.

[0054] Third, the contaminated area is identified. The main function of the isotope identification is to identify the ground or air radioisotope category, to prove the type, distribution and influence range of the radioisotope leaked by the nuclear power plant accident. Since the isotope identification process can be alternately performed during the gamma dose rate monitoring, only need to be selected on the gamma dose rate monitoring route, and the isotope identification should be performed near the hot line or at the point with high radiation intensity. The identification should be suspended for more than 30 seconds at the corresponding position, and then the monitoring should be performed after the identification is completed. The isotope identification is divided into real-time identification and preset time identification, and the specific application method is determined by the emergency personnel according to the actual situation.

[0055] Step seven: Air radiation monitoring flight control

[0056] Combined with the task planning of each air radiation monitoring device, combined with the GIS map, the air radiation monitoring path of each monitoring device is generated, and imported into the air radiation monitoring device control end. The air radiation monitoring device can perform radiation monitoring according to the task planning path after reaching the task area, or can optimize the radiation monitoring path in real time according to the actual measurement.

[0057] During the execution of the task, the flight speed of the monitoring device is too fast, which will affect the accuracy of the geographical reference position of the sensor data; at the same time, the data update rate of the detector of different monitoring devices is different, some are slower, and the faster flight speed will cause the dose rate distribution to be too sparse. In order to generate more accurate radiation situation, the flight speed should be determined according to the sensitivity of the detector, the data update speed and the sampling distance should not exceed 10 meters, and the flight speed of the device should be reasonably determined.

[0058] During the execution of the task, the flight height of the monitoring device should not be too high. The radiation dose rate is inversely proportional to the square of the distance, and the flight height should be as low as possible to detect effective radiation data. Considering the difficulty of long-distance control of air radiation monitoring devices due to terrain and objects, the flight height cannot be too low. When the air radiation monitoring device monitors along the scanning parallel line, its radiation detection system scans the surface source determined by the farthest detection distance, and the boundary condition is determined by its flight height. Since the detector has a sampling period, there are some areas that are not monitored by the detector during continuous flight. Therefore, the two intersecting surface sources should be tangent to determine the flight height of the monitoring device, as shown in the following formula.

[0059]

[0060] In the formula: P represents the farthest detection distance of the aerial radiation detector, unit: m; v represents the radiation monitoring speed of the aerial radiation monitoring device, unit: km / h; t' represents the sampling period of the detector, unit: s; d represents the monitoring line spacing of the aerial radiation monitoring device in different task areas, unit: m.

[0061] In order to improve the accuracy of aerial monitoring data, at least hovering once near the intersection position of the scanning parallel line and the smoke plume hot line, each hovering for about 10 seconds, to accurately measure the actual radiation dose rate value of the point, thereby providing reliable data support for generating accurate nuclear radiation situation. After the flight is completed, the monitoring data of each monitoring device is integrated and situation fusion, and finally displayed in the form of radiation situation heat map on the GIS map.

[0062] The application provides a quick and fine radiation monitoring method for the aerial radiation monitoring device to perform emergency nuclear radiation monitoring after the nuclear power plant accident, which can provide decision support for the aerial radiation monitoring device to optimize the monitoring path and reasonably distinguish the tasks, maximize the support efficiency of the aerial emergency monitoring device, shorten the task time limit, and maximize the emergency benefit BRIEF DESCRIPTION OF DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly described below. The drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creating creative labor.

[0064] Figure 1 It is a flow chart of a nuclear power plant accident emergency aerial radiation monitoring method.

[0065] Figure 2 It is a ground radioactive contamination distribution map.

[0066] Figure 3a And Figure 3b It is a radioactive smoke plume diffusion situation map.

[0067] Figure 4 It is a schematic diagram of the aerial nuclear radiation monitoring task area.

[0068] Figure 5 It is a schematic diagram of the aerial nuclear radiation monitoring path. DETAILED DESCRIPTION

[0069] The implementation data of the present application is derived from the comprehensive application practice of air radiation monitoring equipment. According to the actual demand of the operation of the nuclear emergency monitoring equipment in the air radiation monitoring task, the diffusion state of the ground radioactive plume is determined through the Gaussian diffusion model of the radioactive plume and the related parameters; the ground gamma point source dose rate calculation formula is used to estimate the radiation dose rate on the axis of the radioactive plume; the estimated intervention boundary based on 5 types of operation intervention levels (OIL); the actual intervention boundary determined based on the ground gamma dose rate inversion calculation; the downwind land sector of the dominant wind direction at different task radii is distinguished by different monitoring methods, and the air radiation monitoring task area is refined; the air radiation monitoring task quantity is estimated, and the scientific task allocation is carried out based on the related constraints; and the air radiation monitoring flight speed, height, hovering and other actions are precisely controlled around the radiation situation.

[0070] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described in the following with the drawings in the embodiments, and the described embodiments of the present application are only a part of the embodiments of the present application, not all the embodiments.

[0071] Figure 1 The flow chart of the nuclear power plant accident emergency air radiation monitoring method of the present application. The following will take the air radiation monitoring of the radiation hazard area of a nuclear power plant accident as an example, and the implementation steps are as follows:

[0072] Step one: preliminary generation of radioactive plume diffusion state based on diffusion model

[0073] Suppose that the source strength of the radioactive source released by the nuclear power plant is 1.5×10 22 Bq / s, the average wind speed is 5 m / s, the height of the radioactive source leakage position is 26 m, and the atmospheric stability is C. According to the ground concentration formula of the radioactive nuclide:

[0074]

[0075] The ground radioactive material concentration of each point can be calculated, and the ground radioactive contamination distribution as shown in Figure 2 , and the radioactive plume diffusion state as shown in Figure 3a and Figure 3b .

[0076] Step two: estimation of radiation dose rate on the axis of the radioactive plume

[0077] Suppose that the main nuclide released by the nuclear power plant is 235 U. According to the ground concentration formula of the radioactive nuclide, the activity of the radioactive material on the axis of the radioactive plume at a distance of 50 meters from the leakage position is about 9.5885×10 18 Bq·m -3The irradiation rate constant of the nuclide is 8.9 x 10 -2 The linear attenuation coefficient of the nuclide is 0.7, and the distance between the point source and the airborne radiation monitoring device is 50 meters. According to the ground gamma point source dose rate calculation formula, the dose rate value at a distance of 50 meters from the release position of the radioactive plume on the axis can be estimated to be about 1.9 mSv / h.

[0078] The ground radiation dose rate can be obtained in real time by using the fixed radiation monitoring device of the nuclear power plant itself. Assuming that the fixed monitoring device is 100 meters away from the release position of the radioactive plume, the measured dose rate value is 0.8 mSv / h. According to the radiation dose rate calculation formula of the other downwind position points on the axis:

[0079]

[0080] When the atmospheric stability is C, the diffusion rate is taken as 1.5. According to the formula, the dose rate at a distance of 1000 meters from the release position of the radioactive plume is 0.025 mSv / h. Thus, the radiation dose rate distribution can be estimated, as shown in Table 1.

[0081] Table 1 Estimated values of dose rate at different distances from the release position of the nuclear power plant

[0082] r(km) 0.5 1.0 5.0 10.0 30.0 50.0 [D1 (mSv / h)] 0.0716 0.025 0.0023 0.00046 0.00015 0.00007

[0083] Step three: Intervention boundary estimation of the five operation intervention levels (OIL)

[0084] According to the gamma dose rate measured by a fixed monitoring point in a certain area of the nuclear power plant, according to the diffusion axis radiation dose rate formula and the boundary value of the five operation intervention levels (1 uSv / h), the boundary distance of the emergency radiation monitoring area of the airborne radiation monitoring device in the downwind direction is preliminarily estimated to be about 8617 meters.

[0085] Step four: Determination of the actual boundary of the five operation intervention levels based on the inversion estimation of the ground gamma dose rate

[0086] Through a large number of test comparisons, for the same height, as the radius of the surface source increases, the dose rate gradually increases, and when the source radius reaches more than 100 meters, the dose rate no longer changes obviously. The radius of the surface source can be taken as 100 meters. The dose rate formula of the airborne radiation monitoring device at different heights can be expressed as:

[0087]

[0088] When performing emergency monitoring tasks, assuming that the airborne radiation monitoring equipment flies at a height of 50 meters, measures the dose rate value of a contaminated point, and through the above dose rate inversion formula, the surface contamination activity (ε) of the contaminated point can be measured. With the help of the computing chip of the monitoring equipment, the dose rate value 1 meter away from the ground radioactive source can be quickly inverted and calculated. On the scanning parallel lines about 8.4-9 kilometers away from the release position, the airborne radiation monitoring equipment can appropriately shorten the interval between the parallel lines, compare the real-time measured ground gamma dose rate value with the 5-class operating intervention level dose rate value, and then accurately determine the actual monitoring intervention boundary.

[0089] Step five: Airborne radiation monitoring task area determination and division

[0090] According to the radiation dose rate calculation formula of other downwind position points on the axis:

[0091]

[0092] The natural background is usually 0.1 uSv / h, and it can be estimated that the distance from the nuclear power plant release position to the normal natural background is about 40 km; According to the estimated radiation dose rate at a distance of 30 km from the release position, it is about 0.15 uSv / h, which is not much different from the natural background. According to GB / T 41577-2022 “Nuclear Power Plant Emergency Operating Intervention Level”, in the early emergency monitoring stage, the land key monitoring range is 30 km. Through estimation, the downwind boundary distance of the 5-class operating intervention level boundary value is about 9 km.

[0093] Based on the above factors, in order to accurately generate the nuclear radiation situation, the land sector radius (0-5) km, (5-10) km, (10-30) km, etc. in the downwind direction of the dominant wind direction is implemented respectively. Scanning type parallel foldback radiation monitoring. The (30-50) km range does not implement radiation monitoring. The schematic diagram of the airborne nuclear radiation monitoring task area is shown in Figure 4 .

[0094] According to the different task area monitoring line spacing, the following formula can be referred to for determination;

[0095]

[0096] The scanning parallel line spacing of airborne monitoring in three different monitoring areas is 40 meters, 80 meters, and 140 meters, respectively.

[0097] Step six: Airborne radiation monitoring task planning

[0098] According to the total distance calculation formula of the airborne radiation monitoring path:

[0099]

[0100] To further improve the accuracy of task planning, the longitudinal estimated intervention boundary distance is taken every 5 km in the monitoring area of (10-30) km. The hot wire and longitudinal estimated intervention boundary distance of different monitoring radiuses are assumed to be 0.5 km, 1 km, 1.5 km, 2 km, 2.5 km, and 3 km, respectively. It is estimated that the total monitoring distance is about 703 km. It is assumed that the maximum monitoring range of a single air monitoring device is 400 km, the maximum telemetry distance is 100 km, the maximum allowed cumulative dose of the detector is 100 Gy, the maximum air monitoring speed is 50 km / h, and there are 2 air radiation monitoring devices. According to the formula, it can be calculated that the air radiation monitoring time is at least 7 h. If the situation is urgent, the superior needs to quickly determine the ground radiation situation, the radiation monitoring of the smoke emergency plan area can be carried out first, and it is estimated that the air radiation monitoring time is at least 2.5 h. The schematic diagram of the air nuclear radiation monitoring path is shown in Figure 5 .

[0101] Step seven: air radiation monitoring flight control

[0102] Combined with the task planning of air radiation monitoring equipment and GIS map, the air radiation monitoring path of each monitoring equipment is generated and imported into the control end of air radiation monitoring equipment. Assuming that the detector of air radiation monitoring equipment updates data every 1 second, combined with the limitation that the sampling distance should not exceed 10 meters, the speed of air radiation monitoring should be maintained at about 36 km / h.

[0103] Assuming that the farthest detection distance of the detector of air radiation monitoring equipment at the boundary of the smoke emergency plan inner area is 100 meters, the flight speed of air radiation monitoring equipment is 10 m / s, the sampling period is 1 s, and the parallel line spacing of the inner area is 40 m, according to the flight height calculation formula, the flight height of air radiation monitoring equipment is about 97 m. According to the estimated value of the dose rate of the boundary of the smoke emergency plan outer area and the sensitivity of the detector, the ratio of the flight height of the outer area to the inner area of the smoke emergency plan is about 1:2, so the air flight height of the outer area of the smoke emergency plan is about 50 m.

[0104] At least hover near the intersection position of each scanning parallel line and smoke hot wire for about 10 seconds each time to accurately measure the actual radiation dose rate value of the point. After the flight is completed, the monitoring data of each monitoring equipment is integrated and situation fusion, and finally displayed in the form of radiation situation heat map on the GIS map.

[0105] While the foregoing specific embodiments of the application have been described in some detail to provide a thorough understanding of the application, it should be apparent that the application is not limited to the specifics of the foregoings as these can, of course, vary. As can be seen, the application can be carried out by specifically constructing devices in accordance with the teaching herein or by practicing acts consistent with the principles of this application. For a better understanding of the application, its operating principles and other objects and advantages, reference should be made to the drawings and to the accompanying descriptive matter.

Claims

1. A method for emergency airborne radiation monitoring in nuclear power plant accidents, characterized in that: The steps include the following: Step 1: Generate the initial diffusion pattern of the radioactive plume based on the diffusion model; including: estimating the concentration distribution of continuous point sources under windy conditions and generating the initial diffusion pattern of the ground radioactive plume. Step 2: Estimation of radiation dose rate along the axis of the radioactive plume; including: calculating the ground gamma point source dose rate along the axis of the radioactive plume and estimating the radiation dose rate in the downwind direction using the inverse proportionality law; Step 3: Estimation of the intervention boundaries for OIL at the five intervention levels; including: determining the boundary dose rate values ​​for the five intervention levels and estimating the location of the boundaries for the five intervention levels; Step 4: Determine the actual intervention boundary based on ground gamma dose rate inversion calculation; including: clarifying the dose rate calculation formula of airborne radiation monitoring equipment, inverting and calculating the dose rate value 1 meter away from the contamination point, and determining the actual boundary of the five types of operational intervention levels through real-time inversion calculation; Step 5: Determining and dividing the airborne radiation monitoring task area; including: clarifying the division of the airborne radiation monitoring area according to the prevailing wind direction, clarifying the formula for the spacing between scanning radiation monitoring lines, and calculating the spacing between the parallel lines of each radiation monitoring area. Step Six: Airborne Radiation Monitoring Mission Planning; including: calculating the total airborne gamma radiation monitoring distance, calculating the airborne gamma radiation monitoring time and allocating tasks based on constraints, and planning tasks for nuclide identification; Step 7: Flight control for airborne radiation monitoring; including: mission planning path generation and import, airborne flight speed, altitude control and precise hovering measurement control, and generation of nuclear radiation situation heat map based on GIS map.

2. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 1, characterized in that: In step one, assuming the location of the nuclear power plant's radioactive source release is the source point, the concentration distribution of continuous point sources under wind conditions is measured according to the following formula based on the Gaussian model: In the formula: c(x,y,z) represents the concentration of radioactive material at any point in space, with units of Bq·m³. -3 x, y, z represent the left-right, front-back, and up-down coordinates of any point in space, respectively; Q is the source intensity of the radiation source, measured in Bq·s. -1 ; u is the average wind speed, measured in meters per second (m·s). -1 ;k y ,k z This is the turbulent diffusion coefficient, with units of meters (m). Since the concentration distribution across the cross-section of the smoke cloud follows a normal distribution, the lateral diffusion coefficient σ of the smoke cloud... y and σ z for: Substituting into the above formula, it can be written as: Setting z = 0, we obtain the formula for the ground concentration of radionuclides: In the formula: c(x,y,0) represents the concentration of radioactive material at a point on the ground, with units of Bq·m³. -3 Q represents the source intensity of the radioactive source, measured in Bq·s. -1 ; u is the average wind speed, measured in meters per second (m·s). -1 ;σ y and σ z denoted as the lateral diffusion coefficient of the smoke cloud, with units of meters (m).

3. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 1, characterized in that: In step two, the formula for calculating the ground-based gamma point source dose rate is as follows: In the formula: D is the air absorbed dose rate; A is the activity of the radioactive source; Γ is the irradiation rate constant of the corresponding nuclide; η is the linear attenuation coefficient of the corresponding nuclide; and R is the distance between the point source and the monitoring point.

4. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 3, characterized in that: For points along the direction of radioactive plume diffusion, the radiation dose rate at a known location on the diffusion axis is measured, and then the radiation dose rate at other downwind locations on the same axis is measured using an inverse proportionality principle. The calculation formula is as follows: In the formula: D1 is the radiation dose rate measured at r1, with units of mSv·h -1 ; D2 is the radiation dose rate measured at r2, in mSv·h. -1 τ is the diffusion rate, and r1 and r2 are the distances between any two monitoring points and the source of the nuclear power plant's radioactive source, in meters.

5. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 1, characterized in that: In step four, the area source is integrated based on the dose rates generated by multiple rings. The airborne radiation monitoring equipment is located at the center of the rings, and its dose rate at different altitudes is calculated using the following formula: In the formula: Ψ is the radius of the large surface source; r is the integration factor, corresponding to the radius of the ring; h is the flight altitude; ε is the surface contamination activity, representing the radioactivity activity per unit area; and Γ is the exposure rate constant of the corresponding nuclide. This represents the linear attenuation coefficient of the corresponding nuclide.

6. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 5, characterized in that: For the same height, the dose rate gradually increases with the increase of the radius of the area source. When the source radius reaches more than 100m, the dose rate change is no longer significant. Therefore, the area source radius is taken as 100m. The formula is expressed as: When performing emergency monitoring tasks, if the airborne radiation monitoring equipment flies at a certain altitude of one meter and measures the dose rate value of a certain contamination point, the surface pollution activity ε of the contamination point is measured by using the dose rate inversion formula; then the dose rate value at a distance of 1 meter from the contamination point is calculated by inversion; near the estimated intervention boundary, the airborne radiation monitoring equipment should appropriately reduce its flight speed, and the actual intervention boundary is determined by comparing the ground γ dose rate value obtained in real time with the dose rate values ​​of five types of operational interventions.

7. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 1, characterized in that: In step five, the contaminated sector downwind of the prevailing wind direction is divided into different monitoring ranges with radii of 5km, 5–10km, 10–30km, and 30–50km. Specifically: within a radius of 5km, the task area is equivalent to a rectangular area with a length of 5km and a width equal to the distance between the hotline and the longitudinal estimated intervention boundary; within a radius of 5–10km, the task area is equivalent to a rectangular area with a length of 5km and a width equal to the distance between the hotline and the longitudinal estimated intervention boundary; within a radius of 10–30km, the task area is equivalent to a rectangular area with a length of 20km and a width equal to the distance between the hotline and the longitudinal estimated intervention boundary; within a radius of 30–50km, the task area is equivalent to a rectangular area with a length of 20km and a width equal to the distance between the hotline and the longitudinal estimated intervention boundary.

8. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 7, characterized in that: Airborne radiation monitoring uses equidistant parallel lines, with equidistant lines parallel to the vertical lines of the heat lines in the direction of plume diffusion covering the entire monitoring area. The spacing between monitoring lines in different mission areas is determined with reference to the following formula. In the formula: d is the spacing between parallel lines used for radiation monitoring; D b The natural background dose rate of the radiation monitoring environment; D z The dose rate produced by the radionuclide at a distance of 1 meter.

9. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 1, characterized in that: In step six, the total distance for airborne gamma radiation monitoring is calculated. Based on the determined scope of the airborne nuclear radiation monitoring mission, the total distance of the airborne radiation monitoring path needs to be calculated, and the calculation formula is as follows: In the formula: S represents the total distance for airborne radiation monitoring, in km; s1 s2 s3 s4 represent the lateral distances of the monitoring ranges with radii of 5km, 5-10km, 10-30km, and 30-50km, respectively; l1 l2 l3 l4 represent the distances between the hotlines of different monitoring radii in the plume diffusion direction and the longitudinal estimated intervention boundary, respectively, in meters; d1, d2, d3, and d4 represent the spacing between parallel radiation monitoring lines within monitoring ranges of radii of 5km, 5–10km, 10–30km, and 30–50km, respectively, in meters. Time calculation and task allocation for airborne gamma radiation monitoring; After estimating the total workload of airborne radiation monitoring, the airborne radiation monitoring time and monitoring tasks should be scientifically allocated based on the number and performance of emergency equipment used to perform the tasks, as well as relevant constraints such as flight range, mission radius, monitoring speed, and tolerable cumulative dose. The duration of airborne radiation monitoring is determined according to the following formula: In the formula: S represents the total distance of airborne radiation monitoring, in km; n represents the number of airborne radiation monitoring devices, in units; v represents the radiation monitoring speed of the airborne radiation monitoring equipment, in km / h; Relevant constraints: Nuclide identification is performed on the contaminated area. Since the nuclide identification process is carried out alternately during gamma dose rate monitoring, it is only necessary to select locations on the gamma dose rate monitoring route, focusing on locations near the hot line or with high radiation intensity. During identification, the nuclide should be hovered at the corresponding location for more than 30 seconds, and monitoring should be carried out after the identification is completed.

10. The method for emergency airborne radiation monitoring in nuclear power plant accidents according to claim 1, characterized in that: In step seven, when the airborne radiation monitoring equipment monitors along the scanning parallel line, its radiation detection system scans the surface source determined by the farthest detection distance, and the boundary conditions are determined by its flight altitude. Because the detector has a sampling period, some areas may not be detected during continuous flight. Therefore, the flight altitude of the monitoring equipment must be determined by the tangency of the two intersecting surface sources, as shown in the formula: In the formula: P represents the farthest detection distance of the airborne radiation detector, in meters; v represents the radiation monitoring speed of the airborne radiation monitoring equipment, in km / h; t' represents the sampling period of the detector, in seconds. d represents the distance between monitoring lines in different mission areas of the airborne radiation monitoring equipment, in meters.

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