CN106991511B - Inverse method and system of composite radiation source intensity for combination of point source, line source and surface source in nuclear power plant - Google Patents

Abstract

The invention discloses a composite radiation source intensity inversion method and system combining point sources, line sources and surface sources in nuclear power plants. The optical distance is calculated by the ray tracing method, and the coefficients of the equation system are calculated in combination with information such as materials and accumulation factors, and the source intensity is inversely deduced; then the dose rate is calculated for the detector position. Linear regression analysis calculates key parameters such as standard deviation, slope, intercept, and then calculates the quality factor to measure the acceptability of each calculation result; at the same time, a weighted iteration method is proposed to reduce the problem caused by detectors with large uncertainties. error, repeat the above steps many times in an iterative manner until the quality factor reaches a preset value, and obtain the desired radiation source intensity information.

Description

Inverse method and system of composite radiation source intensity for combination of point source, line source and surface source in nuclear power plant

technical field

The invention relates to a method and system for calculating the intensity of radiation sources in a nuclear power plant, in particular to a method and system for inversely deriving the intensity of a composite radiation source combined with a point source, line source, and surface source in a nuclear power plant.

Background technique

The radioactivity of a nuclear power plant comes from the active area of the fuel assembly in the pressure vessel, and the radiation source is mainly composed of fission products, actinides and corrosion activation products. During the operation of the system, the radiation source flows with the coolant through the primary circuit main system (including pressure vessel, main pump, voltage stabilizer, main pipeline, etc.), chemical container control system, etc. The radiation source is distributed on the surface of the coolant and related equipment. The radiation source itself is highly radioactive, and the daily activities of the staff during the normal operation of the nuclear power plant account for about 20% of the total annual dose. During the overhaul of the nuclear power plant, the dose received by the staff accounts for 80% of the total annual dose. %, during the overhaul of the nuclear power plant, the exposure dose is mainly reduced by shortening the residence time of the staff in the radiation area.

Radiation sources in nuclear power plants are widely distributed, especially after long-term use and overhaul, it is more and more difficult to infer the radiation intensity of radiation sources at various locations based on engineering experience. Therefore, in the calculation of many data, especially based on radiation sources In the calculation of intensity, it is difficult to obtain accurate basic information, which greatly affects the accuracy and practicability. At the same time, the current domestic protective facilities and means are not very complete, which also greatly increases the risk of exposure of workers. .

In the prior art, when it is necessary to estimate the intensity of the radiation source, the source term analysis method is generally used. First, the generation term (such as the inflow term, the decay generation term, etc.) and the disappearance term (such as the filter term) are determined according to the generation and disappearance of radioactive substances. , leakage term, etc.), and clarify the physical model of each item, then establish a nuclear concentration balance equation (group) for radioactive substances according to the above items, and finally solve the equation (group) simultaneously, however, there are a lot of simplifications in these calculation processes. and approximate calculation, so the results are often far from the real value, and there are many obstacles in practical application. In addition, considering the harm caused by the radiation source itself to the human body, the complex geometric structure inside the nuclear power plant, and the accuracy of radionuclides When the information is difficult to obtain, the uncertainty of the measured value of the nuclear power plant detector and other factors, the above methods have problems in terms of safety and accuracy, and it is urgent to improve or propose a new way to obtain the radiation source intensity.

Due to the above reasons, the inventor has conducted in-depth research on the existing methods for calculating source intensity information. According to experience, usually some radioactive components in a nuclear power plant can be simplified to a point source or a group of point sources, or can be simplified to a line A source or a group of line sources can also be simplified to one or a group of surface sources, such as a heat valve can be simplified to a point source, a pipeline can be simplified to a point source or multiple point sources, and a line source , some pipelines can also be simplified as a cylindrical surface source, discretization processing can be performed for the surface source and line source, and then the source intensity inversion can be obtained according to the discretized information to obtain the radiation source intensity information, so as to design a solution that can solve The method and system for the intensity inversion of the composite radiation source combined with the point source, line source and surface source of the nuclear power plant for the above problems.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned problems, the inventors have conducted keen research and designed a method and system for strong inversion of composite radiation sources combined with point source line sources and surface sources in nuclear power plants. The method and system can fully guarantee the radiation safety of the human body. In this method, a detector is placed at a predetermined position in the nuclear power plant, and a shielded detector is also placed at this position. The average energy of the gamma rays emitted by the radiation source is obtained; in addition, a plurality of detectors monitoring the radiation value of the nuclear power plant are also set up in the nuclear power plant to obtain the dose rate of some sampling points, using point nuclear integration and weighting At the same time, the normalized radiation source intensity is discretely spaced, and the ray tracing method is used to judge the space travel distance of the γ-ray emitted by each point source, line source and surface source, and calculate the optical distance. , carry out the calculation of the coefficients of the equation system in combination with the materials, accumulation factors and other information, and then invert the source intensity; then obtain the calculated value of the dose rate at the detector position, perform linear regression analysis on the measured value and calculated value, and obtain the standard deviation, Slope, intercept and other key parameters, and then obtain a quality factor that can represent the physical meaning, which can measure the acceptability of each calculation result; at the same time, a weighted iterative method is proposed to reduce the introduction of detectors with large uncertainties. The above steps are repeated several times in an iterative manner until the quality factor satisfies the preset conditions, and the desired radiation source intensity and the uncertainty of the radiation field result are obtained, thereby completing the present invention.

Specifically, the object of the present invention is to provide the following aspects:

(1) A composite radiation source intensity inversion method for a combination of point sources, line sources and surface sources in a nuclear power plant, characterized in that the method comprises the following steps:

Step 1, use the detector to detect the dose rate D ₁ , D ₂ , D ₃ . . . D _i in the nuclear power plant,

Step 2: According to the detected dose rate information, an overdetermined equation system containing the intensity of the radiation source as shown in the following formula (1) is established,

(一)

(one)

Wherein, the coefficient matrix a _i,j of the overdetermined equation system is obtained by the following equations (2) and (3),

(two)

(三)

(three)

In formula (3), when the radiation source is a point source, p=0, M=1, N=1; when the radiation source is a line source, p=1, N=1; when the radiation source is a surface source , p=1;

In step 3, the intensity information of the radiation source is obtained by calculating the overdetermined equation system in step 2 by the least square method, and the intensity of the radiation source is the following formula (4)

S _j,0 =(a _j,i ·a _i,j ) ^-1 ·a _j,i ·D _i (4)

表示离散源强；M和N分别表示面源在二维坐标上离散后两个坐标轴上的离散标号；Among them, D _i represents the dose rate detected by the i-th detector; j represents the number of radiation sources; m represents the maximum value that the number of radiation sources can reach; S _j represents the intensity of the j-th radiation source; S _{j, 0} represents the intensity of the jth radiation source that is not iterated in the initial calculation; a _i,j represents the coefficient matrix, which is the dose response coefficient of the jth radiation source to the ith detector; BD(E,L(μ(E ), r ₀ →r _p ) represents the accumulation factor, which is a function of E and L(μ(E), r ₀ →r _p ); L(μ(E), r ₀ →r _p ) represents the optical distance, which is μ (E) and r ₀ →r _p function; μ(E) represents the cross-section/linear attenuation coefficient; r ₀ →r _p represents the distance from the radiation source to the detection point; C(E) represents the flux-dose conversion factor, which is A function of E; E represents energy, which is the average energy of gamma rays emitted by radiation sources in a nuclear power plant;

Indicates the discrete source intensity; M and N respectively represent the discrete labels on the two coordinate axes after the surface source is discrete in two-dimensional coordinates;

Preferably, after step 3, the method further comprises the following steps:

Step 4: Calculate the dose rate at the detector position according to the radiation source intensity information obtained in Step 3, D ₁ ', D ₂ ', D ₃ '...D _i ';

Step 5: Perform linear fitting on the dose rate information detected by the detector and the dose rate information at the position of the detector obtained by calculation to obtain a linear equation of the relationship between the two after fitting, and then obtain the fitting parameters. The combined parameters include: average uncertainty, goodness of fit and corresponding weight matrix;

Step 6: Iterate the new weight matrix obtained in Step 5 to the overdetermined equation system in Step 2 to obtain a weighted overdetermined equation, and then repeat Step 2, Step 3 and Step 4 until the desired radiation source intensity information is obtained. ;

Wherein, D _i ′ represents the calculated dose rate at the i-th detector position.

通过下式(五)获得：(2) The method for inversely inferring the intensity of a composite radiation source combined with a point source, line source, and surface source in a nuclear power plant according to the above (1), characterized in that when the radiation source is a surface source, the discrete source intensity

Obtained by the following formula (5):

(五)；

(five);

Among them, S _U (M) and S _V (N) represent the source intensity weight factor on the U coordinate axis and the source intensity weight factor on the V coordinate axis after the surface source is discretized on the two-dimensional coordinate, respectively;

Preferably, when the surface source is a cylindrical surface source, S _U (M) and S _V (N) are obtained by the following formulas (6) and (7), respectively:

(六)

(six)

(七)

(seven)

表示圆柱面源的角度；where η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, Z represents the height of the cylindrical surface source,

represents the angle of the cylindrical surface source;

Preferably, when the surface source is a spherical surface source, S _U (M) and S _V (N) are obtained by the following formulas (8) and (9), respectively:

(八)

(Eight)

(九)

(Nine)

表示球面源的垂直角度；where η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, θ represents the horizontal angle of the spherical source,

represents the vertical angle of the spherical source;

Preferably, when the surface source is a rectangular surface source, S _U (M) and S _V (N) are obtained by the following equations (10) and (11), respectively:

(十)

(ten)

(十一)

(eleven)

Among them, η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, Z represents the length of the rectangular surface source, and y represents the width of the rectangular surface source;

Preferably, when the surface source is a disk surface source, S _U (M) and S _V (N) are obtained by the following equations (12) and (13), respectively:

(十二)

(twelve)

(十三)

(Thirteen)

表示圆盘面源的角度，R表示圆盘面源的半径。where η _1,1 , η _1,2 , η _3,1 and η _3,2 all represent cosine distribution constants,

Represents the angle of the disk surface source, and R represents the radius of the disk surface source.

(3) The method for inversely estimating the intensity of the composite radiation source combined with the point source line source and surface source of the nuclear power plant according to the above (1), characterized in that, for the average energy E of the gamma rays emitted by the radiation source in the nuclear power plant , and its calculation method includes the following sub-steps:

Sub-step 1, select a predetermined position inside the nuclear power plant, the distance between the predetermined position and the radiation source is t, place a detector at the predetermined position, and collect the dose rate I ₀ detected by the detector,

Sub-step 2, retrieve the detector, and place the detector at the predetermined position after coating the outside of the detector with a shielding layer, and collect the dose rate I detected by the detector;

Alternatively, retrieve the detector, place a shield at a predetermined position, place the detector in the shield, and collect the dose rate I detected by the detector;

In sub-step 3, according to I and I ₀ obtained in sub-step 1 and step 2, calculate the mass attenuation coefficient μ of the cladding layer or shield by the following formula (14),

I/I ₀ =BDe ^-μt (fourteen)

In sub-step 4, according to the calculation result of sub-step 3, the average energy E of the gamma rays emitted by the radiation source is obtained.

(4) The method for inversely inferring the intensity of a composite radiation source combined with a point source, line source, and surface source in a nuclear power plant according to the above (1), characterized in that the method for calculating the optical distance L includes the following sub-steps:

Sub-step a, track the passing process of gamma rays from the radiation source to the detection point, and record the sequence of the gamma rays passing through the radiation area,

In sub-step b, the distance of each radiation area is calculated separately, combined with the linear weakening coefficient of the material of each radiation area, and finally the total optical distance L is obtained.

(5) The method for inversely inferring the intensity of a composite radiation source combined with a point source, line source, and surface source in a nuclear power plant according to the above (1), characterized in that the least squares method is used to process the overdetermined equation system in step 2, and the radiation is obtained. The process of source strength information includes the following sub-steps:

用矩阵的形式表示为AX＝b；Substep 3-1, put the overdetermined system of equations

In the form of a matrix, it is expressed as AX=b;

Sub-step 3-2, find the normal equation A ^T AX=A ^T b of the matrix, that is, X=(A ^T A) ^-1 A ^T b;

Sub-step 3-3, use the triangular decomposition method of the symmetric matrix to solve the normal equation, denote G=A ^T A, where G is the symmetric matrix;

Sub-steps 3-4, use the triangular decomposition method to solve G=LDL ^T , where L is a small triangular matrix, and D is a diagonal matrix;

Substep 3-5, solve the lower triangular matrix equation system: LY ₁ =A ^T b;

Sub-steps 3-6, solve the diagonal matrix equation system: DY ₂ =Y ₁ ;

Sub-steps 3-7, solve the upper triangular matrix equation system: L ^T X=Y ₂ .

(6) The composite radiation source intensity inversion method for the combination of point sources, line sources and surface sources of nuclear power plants according to the above (2) is characterized in that, in step 5, linear fitting is performed by the following formula (15),

(十五)

(fifteen)

表 示估计的截距，

where is the estimated dose rate; is the estimated slope,

represents the estimated intercept,

表示计算出的探测器位置处剂量率的平均值，

表示探测器探测到的剂量率的平均值。n represents the maximum value that the number of detectors i can achieve,

represents the calculated mean of the dose rate at the detector position,

Indicates the average value of the dose rate detected by the detector.

(7) The method for inversely inferring the intensity of a composite radiation source combined with a point source, line source, and surface source in a nuclear power plant according to the above (6), characterized in that, in step 5, a weight function is obtained according to the uncertainty, and then the weight function is passed through the weight function. The weight matrix W is obtained, and the weight matrix W is obtained by the following formula (16),

(十六)

(sixteen)

表示平均拟合不确定度，

f_i表示第i个探测器位置的拟合不确定度；；

表示权重函数。where f is the fitting uncertainty,

is the mean fitting uncertainty,

f _i represents the fitting uncertainty of the i-th detector position;

represents the weight function.

(8) The combined radiation source intensity inversion method of the nuclear power plant point source line source area source combination according to the above (6), characterized in that:

In step 6, when S _i > 0 and the quality factor M reaches the maximum value, the weighted iteration is stopped, and the radiation source intensity information is output, and the output radiation source intensity information at this time is the desired radiation source intensity information;

Wherein, each time step 6 is performed, a quality factor M is obtained correspondingly, and the quality factor M is obtained by the following formula (17),

(十七)

(17)

where ^R2 represents the goodness of fit,

(9) A composite radiation source strong inversion system for a nuclear power plant point source line source area source combination, characterized in that the system is used to implement the nuclear power plant point source line source area source combination of claims 1-8. Intensive inversion method for composite radiation sources.

(10) The combined radiation source strong inversion system of the nuclear power plant point source line source surface source combination according to the above (9), characterized in that the system includes a detector, a gamma ray average energy calculation module and a radiation source intensity calculation module;

There are multiple detectors, including a predetermined position detector and a nuclear power plant radiation value monitoring detector,

The predetermined position detector is arranged in a predetermined position determined by the distance between the radiation area of the nuclear power plant and the radiation source, and the outside of the predetermined position detector is optionally covered with a detachable shielding layer;

The predetermined position detector is used to transmit the detected radiation dose rate information to the gamma ray average energy calculation module,

The nuclear power plant radiation value monitoring detectors are distributed in the radiation area of the nuclear power plant, and are used to transmit the respectively detected dose rate information in the nuclear power plant to the radiation source intensity calculation module,

The gamma ray average energy calculation module is used to calculate the average energy E of gamma rays,

The radiation source intensity calculation module is used to calculate the radiation source intensity in the nuclear power plant.

The beneficial effects of the present invention include:

(1) According to the composite radiation source intensity inversion method of the combination of point source line source and surface source of nuclear power plant provided by the present invention, under the condition of fully guaranteeing human body radiation safety, the point source and surface area under the complex geometrical space structure inside the nuclear power plant can be obtained. The source strength data of the source;

(2) According to the composite radiation source intensity inversion method for the combination of point source, line source and area source in a nuclear power plant provided by the present invention, through multiple iterative calculations, it is ensured that the source intensity information of the finally obtained point source, line source and area source is more accurate Tight real value, with high engineering application value.

Description of drawings

FIG. 1 shows an overall work flow diagram according to a preferred embodiment of the present invention.

Detailed ways

The present invention will be further described in detail below through the accompanying drawings and embodiments. The features and advantages of the present invention will become more apparent from these descriptions.

The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

According to the composite radiation source intensity inversion method provided by the nuclear power plant point source line source area source combination provided by the present invention, the method includes the following steps:

Step 1: Receive dose rate information D ₁ , D ₂ , D ₃ . . . D _i detected by detectors in the power plant. In order to detect the above multiple dose rates, multiple detectors need to be used. Multiple detectors can be placed in the nuclear power plant, or the existing detectors in the nuclear power plant can be directly used. The existing detectors in the nuclear power plant are the nuclear power plant radiation value monitoring detectors. The above two methods can also be used in combination. The location requirement is that there is no shield between the radiation source and the location, and the dose rate in the present invention is the radiation dose rate. In the present invention, the number of the detectors is greater than the number of radiation sources in the nuclear power plant.

Step 2: According to the detected dose rate information, an overdetermined equation system containing the intensity of the radiation source is established, and the overdetermined equation system is the following formula (1),

(一)

(one)

In step 3, the intensity information of the radiation source is obtained by calculating the overdetermined equation system in step 2 by the least square method, and the intensity of the radiation source is the following formula (4)

S _j,0 =(a _j,i ·a _i,j ) ^-1 ·a _j,i ·D _i (4)

The coefficient matrix a _i,j of the overdetermined equation system is obtained by the following equations (2) and (3) after discretizing the surface source on the radiation space coordinates,

(two)

(三)；

(three);

In formula (3), when the radiation source is a point source, p=0, M=1, N=1; when the radiation source is a line source, p=1, N=1; when the radiation source is a surface source , p=1;

In the present invention, since there are many areas in a nuclear power plant that need to measure the intensity of radiation sources, there are also many radiation sources that need to be measured. surface source, and can be calculated by the above formula (3), when the radiation source is a point source, p=0, M=1, N=1; when the radiation source is a line source, p=1, N=1 ; when the radiation source is a surface source, p=1. When the radiation source is a point source, the radiation source can not be discretized, that is

After step 3, the intensity information of the radiation source can be obtained, but the intensity information may not be accurate enough, so continue the calculation through the following steps, in order to obtain the radiation source intensity information that is closer to the true value;

Step 4: Calculate the dose rate at the detector position according to the radiation source intensity information obtained in Step 3, D ₁ ', D ₂ ', D ₃ '...D _i ';

Step 5: Perform linear fitting on the dose rate information detected by the detector and the dose rate information at the position of the detector obtained by calculation to obtain a linear equation of the relationship between the two after fitting, and then obtain the fitting parameters. The combined parameters include: average uncertainty, goodness of fit, and corresponding weight matrix; the weight matrix described in the present invention can be an inner weight matrix or an outer weight matrix, and the obtaining method is the same, the difference lies in the outer weight matrix. Uncertainty is not calculated by the system, but the error range of the detector entered by operator means.

Step 6, iterate the weight matrix obtained in Step 5 to the overdetermined equation system in Step 2 to obtain a weighted overdetermined equation, and then repeat Step 2, Step 3 and Step 4 until the desired radiation source intensity information is obtained;

表示离散源强；M和N分别表示面源在二维坐标上离散后两个坐标轴上的离散标号。其中，所述探测点表示探测器的位置，更准确的说是探测器上接收到辐射信息的位置。In the present invention, D represents the dose rate detected by the detector; D _i represents the dose rate detected by the ith detector; i represents the number of detectors; j represents the number of radiation sources, and m represents the number of radiation sources The maximum value that can be reached; S represents the intensity of the radiation source; S _j represents the intensity of the j-th radiation source; S _j,0 represents the intensity of the j-th radiation source for which the initial calculation has not been iterated; a _i,j represents the coefficient matrix , is the dose response coefficient of the jth radiation source to the ith detector. In the present invention, it means the response coefficient of the point source to the detector and the response coefficient of the surface source to the detector after discretization; BD(E, L( μ(E),r ₀ →r _p ) represents the accumulation factor, which is a function of E and L(μ(E),r ₀ →r _p ); L(μ(E),r ₀ →r _p ) represents the optical distance , is a function of μ(E) and r ₀ →r _p , that is, the optical distance is a function of energy and actual distance; μ(E) represents the linear attenuation coefficient; r ₀ →r _p represents the distance from the radiation source to the detection point; C(E) represents the flux-dose conversion factor, which is a function of E; E represents energy, which is the average energy of the gamma rays emitted by the radiation source in the nuclear power plant; D _i ′ represents the calculated position of the i-th detector dose rate;

Indicates the discrete source intensity; M and N respectively represent the discrete labels on the two coordinate axes after the surface source is discrete in two-dimensional coordinates. Wherein, the detection point represents the position of the detector, more precisely, the position where the radiation information is received on the detector.

通过下式(五)获得：The discrete source intensity described in the present invention

Obtained by the following formula (5):

(五)；

(five);

Among them, S _U (M) and S _V (N) represent the source intensity weight factor on the U coordinate axis and the source intensity weight factor on the V coordinate axis after the surface source is discretized on the two-dimensional coordinate, respectively;

Preferably, when the surface source is a cylindrical surface source, S _U (M) and S _V (N) are obtained by the following formulas (6) and (7), respectively:

(六)

(six)

(七)

(seven)

表示圆柱面源的角度；即，Among them, η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, the default value of the cosine distribution constant is zero, which can be set according to the actual situation, Z represents the cylindrical surface source high,

represents the angle of the cylindrical surface source; that is,

Preferably, when the surface source is a spherical surface source, S _U (M) and S _V (N) are obtained by the following formulas (8) and (9), respectively:

(八)

(Eight)

(九)

(Nine)

表示球面源的垂直角度；即，当η_2,1＝0时S_U(M)＝cosθ_M-cosθ_M+1，Among them, η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant. The default value of the cosine distribution constant is zero, which can be set according to the actual situation, and θ represents the level of the spherical source. angle,

represents the vertical angle of the spherical source; that is, when η _2,1 =0 S _U (M)=cosθ _M -cosθ _M+1 ,

When η _2,1 ≠0: the value of S _U (M) is:

When η _2,1 =0

When η _2,1 ≠0:

Preferably, when the surface source is a rectangular surface source, S _U (M) and S _V (N) are obtained by the following equations (10) and (11), respectively:

(十)

(ten)

(十一)

(eleven)

Among them, η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, the default value of the cosine distribution constant is zero, which can be set according to the actual situation, Z represents the rectangular surface source length, y represents the width of the rectangular area source; i.e.

Preferably, when the surface source is a disk surface source, S _U (M) and S _V (N) are obtained by the following equations (12) and (13), respectively:

(十二)

(twelve)

(十三)

(Thirteen)

表示圆盘面源的角度，R表示圆盘面源的半径，即Among them, η _1,1 , η _1,2 , η _3,1 and η _3,2 all represent cosine distribution constants, and the default value of the cosine distribution constants is zero, which can be set according to the actual situation,

Represents the angle of the disk surface source, R represents the radius of the disk surface source, that is

When η _1,1 =0

When η _2,1 ≠ 0: the value of S _U (M) is

The accumulation factor described in the present invention is a professional term commonly used in this field, and can be explained and calculated with reference to the usual meaning in this field, and its general calculation formula is given in the present invention as follows:

The fitting formula of K ^x is as follows:

K(E,x)=cx ^a +d[tanh(x/X _k -2)-tanh(-2)]/[1-tanh(-2)];

where E is the photon energy, MeV; _x is the distance from the source point to the calculation point, mfp; b is the accumulation factor at a mean free path; a, c, d, X _k are empirical parameters, when the accumulation factor coefficient is selected, it can be Choose to use the logarithmic difference method, that is:

a(E _a )={a(E ₁ )·[log(E ₂ )-log(E _a )]+a(E ₂ )·[log(E _a )-log(E ₁ )]}/[log (E ₂ )-log(E ₁ )]

In a preferred embodiment, the method for calculating the average energy E of the gamma rays emitted by the radiation source in the nuclear power plant includes the following sub-steps:

Sub-step 1, select a predetermined position inside the nuclear power plant, the distance between the predetermined position and the radiation source is t, place a detector at the predetermined position, and collect the dose rate I ₀ detected by the detector,

Sub-step 2, retrieve the detector, and place the detector at the predetermined position after coating the outside of the detector with a shielding layer, and collect the dose rate I detected by the detector;

Alternatively, retrieve the detector, place a shield at a predetermined position, place the detector in the shield, and collect the dose rate I detected by the detector;

In sub-step 3, according to I and I ₀ obtained in sub-step 1 and step 2, calculate the mass attenuation coefficient μ of the cladding layer or shield by the following formula (14),

I/I ₀ =BDe ^-μt (fourteen)

Sub-step 4, according to the calculation result of sub-step 3, look up the table to obtain the average energy E of the gamma rays emitted by the radiation source. The table of the look-up table may be a material section table described in ANSI/ANS 6.4.3, "Gamma-ray Attenuation Coefficients and Buildup Factor for Engineering Materials", American Nuclear Society, 1991. pp. 16-67. In the present invention, all the radiation energy used is calculated by the above average energy. If the energy difference in different areas in the nuclear power plant is large, it can be considered to measure the area separately, that is, measure the average energy separately, and measure the intensity of the radiation source separately.

In a preferred embodiment, the method for calculating the optical distance L includes the following sub-steps, sub-step a, tracking the passing process of the gamma rays from the radiation source to the detection point, and recording the sequence of the gamma rays passing through the radiation area, That is, the distance r ₀ →r _p from the radiation source to the detection point is calculated by the ray tracing method, where r ₀ represents the position of the radiation source and the position r _p of the detection point. In sub-step b, the distance of each radiation area is calculated separately, combined with the linear weakening coefficient of the material of each radiation area, and finally the total optical distance L is obtained.

Specifically, when calculating the travel distance of gamma rays, the space is described by the combined geometric method, and the space of different media is divided into different regions. Find the distance Di between the intersection of the gamma ray and each primitive and the entrance and the distance Do between the exit and the exit, respectively. Find all primitive numbers plus and minus with "+" and "-" in each area. This process can include the following six steps,

(1) Determination of the area number Ipstart where the starting point r ₀ of each line is located:

If there is no "-" primitive in a certain area, then all "+" primitives in this area must satisfy that the starting point r ₀ is located in all "+" primitives, then it can be considered that the starting area of the ray is this region; if there are "-" primitives in the region, then all "+" primitives in the region must satisfy the starting point r ₀ in all "+" primitives, and all "-" primitives must If the starting point r ₀ of this ray is not included, then the starting area of the ray is considered to be this area.

(2) Determination of the area number Ipend where the end point r _p of each line is located:

Similarly, if there is no "-" primitive in a certain area, then all the "+" primitives in this area must satisfy that the end point r _p is located in all the "+" primitives, then the termination area of the ray can be considered is the region; if there are "-" primitives in the region, then all "+" primitives in the region must satisfy that the end point _rp is located in all "+" primitives, and all "-" primitives must satisfy the end point _rp that does not contain this ray, then the end region of the ray is considered to be this region.

(3) Determination of the area exit distance Zo corresponding to the area number where the starting point r ₀ of each line is located:

If there is no "-" primitive in the starting area number of the gamma ray, the minimum of the distance Do of the extraction exit of all the "+" primitives in the starting area is the exit distance of the gamma ray starting area. If there is a "-" primitive in the starting area of gamma rays, firstly, all the "+" primitives in the starting area take the smallest distance Do from the exit, and then take the smallest distance Di from the entrance for all the "-" primitives. The maximum value of the two is the exit distance of the gamma ray starting region.

(4) Determination of the number IP of each area that the ray passes through:

When the end point is not in the outermost area, if there is no "-" primitive in the area number, the adjacent sub-area is judged first. For all "+" primitives, the primitive entrance distance is less than or equal to the area's entrance distance and When it is less than the exit distance of the primitive (Di<=Zin<Do), this area is the adjacent area of the previous area, and the corresponding area number IP is obtained; if there is a "-" primitive in the γ-ray area number, for all "+" primitives, the primitive inlet distance is less than or equal to the zone's inlet distance and less than the primitive's outlet distance (Di <= Zin < Do), and for all "-" primitives, the primitive inlet distance is greater than the zone inlet distance Or when the basic body exit distance is less than or equal to the area entrance distance (Di>Zin or Do<=Zin), the area is the adjacent area of the previous area, and the corresponding area number IP is obtained.

(5) Determination of the entrance distance Zi and the exit distance Zo of each area that the ray passes through:

If there is no "-" primitive in the adjacent area obtained above, the exit distance of this area is the smallest among all the "+" primitive exit distances Do, and the entrance distance of this area is the exit distance of the previous area; If there are "-" primitives in the adjacent area obtained above, first find the smallest one of all the "+" primitives taking the exit distance Do, and then find the smallest one of all the "-" primitives' inlet distances Di , and then take the maximum value of the two as the exit distance of this area, and the entrance distance of this area is the exit distance of the previous area.

(6) When the end point is in the outermost area, first find all the primitive numbers aa in the outermost layer. For the area in which the "+" primitive contains the primitive aa, and the "-" primitive does not contain the primitive aa When the ray passes through the region, find whether there is a "-" primitive whose entrance distance of the "-" primitive is greater than that of the region (Di(k,minus(i,m))>Zi(k,n)), if If it exists, the area exit distance takes the smallest of all "-" primitive entrance distances Di. If it does not exist, the area exit distance is the ray length.

The tracking is terminated when the area _IPend where the rp point is located and the ray exit distance is equal to the ray length. Thus, the travel distance of the gamma rays is obtained.

Then calculate the number of times the ray travels through the area and the distance for each travel:

If the passing area number of the ray is not 0, then the passing distance of the γ-ray in this area is equal to the entrance distance of the area minus the exit distance of the area, and the number of γ-ray passing through is increased by 1; if the passing area number of the γ-ray is 0, stop tracking.

Obtain the γ cross-section μ _n using the γ mass attenuation coefficient and the material of the zone medium;

其中，N表示辐射区域的数量，该数量主要是由厂房内部环境决定的。By recording the passing process of the γ-ray passing through the area, the optical distance of each area is obtained separately and then summed, namely:

Among them, N represents the number of radiation areas, which is mainly determined by the internal environment of the plant.

In a preferred embodiment, the least squares method is used to process the overdetermined equation system in step 2, and the process of obtaining the intensity information of the radiation source includes the following sub-steps:

用矩阵的形式表示为AX＝b；Substep 3-1, put the overdetermined system of equations

In the form of a matrix, it is expressed as AX=b;

Sub-step 3-2, find the normal equation A ^T AX=A ^T b of the matrix, that is, X=(A ^T A) ^-1 A ^T b;

Sub-step 3-3, use the triangular decomposition method of the symmetric matrix to solve the normal equation, denote G=A ^T A, where G is the symmetric matrix;

Sub-steps 3-4, use the triangular decomposition method to solve G=LDL ^T , where L is a small triangular matrix, and D is a diagonal matrix;

Substep 3-5, solve the lower triangular matrix equation system: LY ₁ =A ^T b;

Sub-steps 3-6, solve the diagonal matrix equation system: DY ₂ =Y ₁ ;

Sub-steps 3-7, solve the upper triangular matrix equation system: L ^T X=Y ₂ .

相对应，通过所述子步骤3-1至子步骤3-7得到辐射源强度的计算数值，本发明中所述的最小二乘法为本领域中通用的超定方程解算方法。where X=(A ^T A) ^-1 A ^T b and

Correspondingly, the calculated value of the intensity of the radiation source is obtained through the sub-steps 3-1 to 3-7, and the least squares method described in the present invention is a common method for solving overdetermined equations in the art.

In a preferred embodiment, in step 5, linear fitting is performed by the following formula (15),

(十五)

(fifteen)

表 示估计的截距，

where is the estimated dose rate; is the estimated slope,

represents the estimated intercept,

表示计算出的探测器位置处剂量率的平均值，

表示探测器探测到的剂量率的平均值。n represents the maximum value that the number of detectors i can achieve,

represents the calculated mean of the dose rate at the detector position,

Indicates the average value of the dose rate detected by the detector.

In a preferred embodiment, after the linear fitting, the average uncertainty, goodness of fit, quality factor, weighting function and corresponding weight matrix of the linear fitting are obtained respectively, and the quality factor represents the current Confidence of iterative computations. In step 5, a weight function is obtained according to the uncertainty, and then a weight matrix W is obtained through the weight function, and the weight matrix W is obtained by the following formula (16),

(十六)

(sixteen)

表示权重函数。 Among them, f represents the fitting uncertainty, f _i represents the fitting uncertainty of the i-th detector position; represents the average fitting uncertainty,

represents the weight function.

In a preferred embodiment, in step 6, the judgment condition for obtaining the desired radiation source intensity information is when _Si > 0, and the quality factor M reaches the maximum value, that is, when _Si > 0, and the quality When the factor M reaches the maximum value, the weighted iteration is stopped, and the radiation source intensity information is output. The radiation source intensity information is the final desired radiation source intensity, which is also the radiation source intensity closest to the true value.

The purpose of the present invention is to obtain the radiation source intensity closest to the true value, but the reliability of the radiation source intensity obtained in step 3 is relatively low, and the error between it and the true value will be relatively large, so in order to improve the accuracy of the value , that is, to obtain the intensity of the radiation source closest to the true value, the weighted iterative process from steps 4 to 6 is given in the present invention, and the conditions for iterative termination are finally set, so as to reduce the workload as much as possible while ensuring the accuracy of the results, Shorten the operation time and improve the efficiency of data acquisition. According to the above-mentioned weighted iteration method and the judgment criteria of iteration termination. In addition, the radiation source intensity obtained in the present invention is more accurate and closer to the true value than the radiation source intensity obtained by the source term analysis method, and can ensure that the obtained value and the true value are within an order of magnitude. In a preferred embodiment, each time step 6 is performed, a quality factor M is obtained correspondingly, and the quality factor M is obtained by the following formula (17),

(十七)

(17)

where ^R2 represents the goodness of fit,

的矩阵形式见下式(十八)In a preferred embodiment, the overdetermined system of equations

The matrix form of , see the following formula (18)

(十八)

(eighteen)

Among them, ε represents the error introduced by each detector; considering the physical meaning, in fact, the error caused by each detection point can be considered to be caused by the radiation source, then the above equation is simplified to the following equation (19),

(十九)，

(nineteen),

Furthermore, it can be found that the coefficient matrix a _i,j is equivalent to the dose response coefficient of the jth radiation source to the ith detector, wherein the dose response coefficient of the detector is calculated by using the point kernel integration technique. Integral technique is a routine calculation method in the art.

Provided according to the present invention is a combined radiation source strong inversion system of a nuclear power plant point source line source area source combination, the system is used for implementing the nuclear power plant point source line source area source combination compound radiation source described above in the present invention Strong inversion method.

Preferably, the system includes a detector, a gamma ray average energy calculation module and a radiation source intensity calculation module;

There are multiple detectors, including a predetermined position detector and a nuclear power plant radiation value monitoring detector,

The predetermined position detector is arranged in a predetermined position determined by the distance between the radiation area of the nuclear power plant and the radiation source, and the outside of the predetermined position detector is optionally covered with a detachable shielding layer; the predetermined position distance The distance to the radiation source can appear as a known quantity in subsequent calculations;

The predetermined position detector is used to transmit the detected radiation dose rate information to the gamma ray average energy calculation module, so as to calculate the gamma ray average energy;

The nuclear power plant radiation value monitoring detectors are distributed in the radiation area of the nuclear power plant, respectively located at the key positions described in the present invention, and are used to transmit the respectively detected dose rate information in the nuclear power plant to the radiation source intensity calculation module,

The gamma ray average energy calculation module is used to calculate the average energy E of gamma rays,

The radiation source intensity calculation module is used to calculate the radiation source intensity in the nuclear power plant.

Experimental example:

The room NB281 in the nuclear island of Daya Bay Nuclear Power Station Unit 1 is used as the experimental object. This room is used to place the radioactive wastewater collection barrel in the nuclear island control area. The wastewater collection barrel is a cylindrical container, and the internal radioactive liquid source strength is 0.7586E+10MeV/cm ³ .s (or 4.2898E+14/s). The upper part of the cylindrical container is simplified to 2 point sources, the middle part is simplified to 1 cylindrical surface source, and the lower part is simplified to 2 line sources, and a detector is installed every 50cm in the middle part of the waste water collection bucket, a total of Five detectors, the detection values obtained by each detector are respectively 2.032mSv/hr, 0.685mSv/hr, 0.255mSv/hr, 0.1446mSv/hr, 0.0929mSv/hr, namely D ₁ , D in the present invention ₂ , D ₃ , D ₄ , D _{5 ,} according to the average energy acquisition method and system provided by the present invention, the average energy obtained is 1.3MeV, and the source intensity inversion method and system provided by the present invention are used to obtain two point source intensities respectively. They are 7.0856E+13MeV/s, 7.1763E+13MeV/s, and the source strengths of the two line sources are 2.6677E+12MeV/(cm.s) (or 7.1228E+13MeV/s), 2.7132E+12MeV/(cm, respectively. .s) (or 7.2441E+13MeV/s), the source intensity of one surface source is 2.9225E+10MeV/(cm ² .s) (or 7.3413E+13MeV/s).

It can be seen from the final result that the sum of the obtained intensities of the five radiation sources is basically consistent with the true value of the radiation intensity of the radiation source, so it can be shown that the method and system provided by the present invention can obtain radiation source intensity information close to the true value.

The present invention has been described above with reference to the preferred embodiments, but these embodiments are only exemplary and serve only for illustrative purposes. On this basis, various substitutions and improvements can be made to the present invention, which all fall within the protection scope of the present invention.

Claims (15)

1. a composite radiation source strong inversion method of a nuclear power plant point source line source surface source combination, is characterized in that, this method comprises the steps: Step 1, use the detector to detect the dose rates D ₁ , D ₂ , D ₃ . . . D _i in the nuclear power plant; Step 2: According to the detected dose rate information, an overdetermined equation system containing the intensity of the radiation source as shown in the following formula (1) is established,

Wherein, the coefficient matrix a _i,j of the overdetermined equation system is obtained by the following equations (2) and (3),

In formula (3), when the radiation source is a point source, p=0, M=1, N=1; when the radiation source is a line source, p=1, N=1; when the radiation source is a surface source , p=1; In step 3, the overdetermined equation system in step 2 is processed by the least squares method, and the intensity information of the radiation source shown in the following formula (4) is obtained, S _j,0 =(a _j,i ·a _i,j ) ^-1 ·a _j,i ·D _i (4); Among them, D _i represents the dose rate detected by the i-th detector; j represents the number of radiation sources; m represents the maximum value that the number of radiation sources can reach; S _j represents the intensity of the j-th radiation source; S _{j, 0} represents the intensity of the jth radiation source that is not iterated in the initial calculation; a _i,j represents the coefficient matrix, which is the dose response coefficient of the jth radiation source to the ith detector; BD(E,L(μ(E ), r ₀ →r _p ) represents the accumulation factor, which is a function of E and L(μ(E), r ₀ →r _p ); L(μ(E), r ₀ →r _p ) represents the optical distance, which is μ (E) and r ₀ →r _p function; μ(E) represents the cross-section/linear attenuation coefficient; r ₀ →r _p represents the distance from the radiation source to the detection point; C(E) represents the flux-dose conversion factor, which is A function of E; E represents energy, which is the average energy of gamma rays emitted by radiation sources in a nuclear power plant;

Indicates the discrete source intensity; M and N respectively represent the discrete labels on the two coordinate axes after the surface source is discrete in two-dimensional coordinates. 2. The composite radiation source strong inversion method of the combination of point sources, line sources and surface sources in a nuclear power plant according to claim 1, after step 3, the method further comprises the following steps: Step 4: Calculate the dose rate at the detector position according to the radiation source intensity information obtained in Step 3, D′ ₁ , D′ ₂ , D′ ₃ . . . D′ _i ; Step 5: Perform linear fitting on the dose rate information detected by the detector and the dose rate information at the position of the detector obtained by calculation to obtain a linear equation of the relationship between the two after fitting, and then obtain the fitting parameters. The combined parameters include: average uncertainty, goodness of fit and corresponding weight matrix; Step 6, iterate the weight matrix obtained in Step 5 to the overdetermined equation system in Step 2 to obtain a weighted overdetermined equation, and then repeat Step 2, Step 3 and Step 4 until the desired radiation source intensity information is obtained; Among them, D′ _i represents the calculated dose rate at the i-th detector position. 3 . The composite radiation source intensity inverse method for combining point sources, line sources and surface sources of nuclear power plants according to claim 1 , wherein when the radiation source is a surface source, the discrete source intensity

Obtained by the following formula (5):

Among them, S _U (M) and S _V (N) respectively represent the source intensity weighting factor on the U coordinate axis and the source intensity weighting factor on the V coordinate axis after the surface source is discretized in two-dimensional coordinates. 4. The composite radiation source strong inversion method of the combination of point source line source and surface source of nuclear power plant according to claim 3, is characterized in that, when described surface source is cylindrical surface source, S _U (M) and S _V (N) are obtained by the following formulas (6) and (7), respectively:

where η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, Z represents the height of the cylindrical surface source,

Represents the angle of the cylindrical surface source. 5. The composite radiation source strong inversion method of the combination of point source line source surface source in nuclear power plant according to claim 3, is characterized in that, when described surface source is spherical surface source, S _U (M) and S _V ( N) are obtained by the following formulas (eight) and (nine), respectively:

where η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, θ represents the horizontal angle of the spherical source,

Indicates the vertical angle of the spherical source. 6. The composite radiation source strong inverse method for combining point sources, line sources, and surface sources of nuclear power plants according to claim 3, wherein when the surface sources are rectangular surface sources, S _U (M) and S _V (N) are obtained by the following equations (10) and (11), respectively:

Among them, η _2,1 , η _2,2 , η _3,1 and η _3,2 all represent the cosine distribution constant, Z represents the length of the rectangular surface source, and y represents the width of the rectangular surface source. 7. The composite radiation source strong inverse method for combining point sources, line sources, and surface sources of nuclear power plants according to claim 3, wherein when the surface sources are disc surface sources, S _U (M) and S _V (N) is obtained by the following equations (12) and (13), respectively:

where η _1,1 , η _1,2 , η _3,1 and η _3,2 all represent cosine distribution constants,

Represents the angle of the disk surface source, and R represents the radius of the disk surface source. 8 . The method for strong inversion of composite radiation sources combined with point source line sources and surface sources in a nuclear power plant according to claim 1 , wherein, for the average energy E of the gamma rays emitted by the radiation sources in the nuclear power plant, its The calculation method includes the following sub-steps: Sub-step 1, select a predetermined position inside the nuclear power plant, the distance between the predetermined position and the radiation source is t, place a detector at the predetermined position, and collect the dose rate I ₀ detected by the detector, Sub-step 2, retrieve the detector, and place the detector at the predetermined position after coating the outside of the detector with a shielding layer, and collect the dose rate I detected by the detector; Alternatively, retrieve the detector, place a shield at a predetermined position, place the detector in the shield, and collect the dose rate I detected by the detector; In sub-step 3, according to I and I ₀ obtained in sub-step 1 and step 2, calculate the mass attenuation coefficient μ of the cladding layer or shield by the following formula (14), I/I ₀ =BD(E,L(μ(E),r ₀ →r _p )e ^-μt (fourteen) In sub-step 4, according to the calculation result of sub-step 3, the average energy E of the gamma rays emitted by the radiation source is obtained. 9 . The composite radiation source intensity inverse method for combining point sources, line sources and surface sources of nuclear power plants according to claim 1 , wherein the method for calculating the optical distance L comprises the following substeps: 10 . Sub-step a, track the passing process of gamma rays from the radiation source to the detection point, and record the sequence of the gamma rays passing through the radiation area, In sub-step b, the distance of each radiation area is calculated separately, combined with the linear weakening coefficient of the material of each radiation area, and finally the total optical distance L is obtained. 10 . The composite radiation source intensity inversion method for the combination of point sources, line sources, and surface sources in a nuclear power plant according to claim 1 , wherein the least squares method is used to process the overdetermined equations in step 2, and the radiation source intensity is obtained. 11 . The information process includes the following sub-steps: Substep 3-1, put the overdetermined system of equations

In the form of a matrix, it is expressed as AX=b; Sub-step 3-2, find the normal equation A ^T AX=A ^T b of the matrix, that is, X=(A ^T A) ^-1 A ^T b; Sub-step 3-3, use the triangular decomposition method of the symmetric matrix to solve the normal equation, denote G=A ^T A, where G is the symmetric matrix; Sub-steps 3-4, use the triangular decomposition method to solve G=LDL ^T , where L is a small triangular matrix, and D is a diagonal matrix; Substep 3-5, solve the lower triangular matrix equation system: LY ₁ =A ^T b; Sub-steps 3-6, solve the diagonal matrix equation system: DY ₂ =Y ₁ ; Sub-steps 3-7, solve the upper triangular matrix equation system: L ^T X=Y ₂ . 11. The composite radiation source intensity inversion method for the combination of point sources, line sources and surface sources of nuclear power plants according to claim 2, characterized in that, in step 5, linear fitting is performed by the following formula (15),

in,

represents the estimated dose rate;

represents the estimated slope,

represents the estimated intercept,

n represents the maximum value that the number of detectors i can achieve,

represents the calculated mean of the dose rate at the detector position,

Indicates the average value of the dose rate detected by the detector. 12 . The composite radiation source intensity inverse method for combining point sources, line sources and surface sources of nuclear power plants according to claim 11 , wherein in step 5, after linear fitting, a weight function is obtained according to the uncertainty, Then, the weight matrix W is obtained through the weight function, and the weight matrix W is obtained by the following formula (16),

where f is the fitting uncertainty,

is the mean fitting uncertainty,

f _i represents the fitting uncertainty of the i-th detector position;

represents the weight function. 13. The method for strong inversion of a composite radiation source combined with a point source, line source, and surface source in a nuclear power plant according to claim 11, characterized in that: In step 6, i represents the number of detectors; j represents the number of radiation sources; S represents the intensity of the radiation source; S _j represents the intensity _of the _jth radiation source; When the maximum value is reached, the weighted iteration is stopped, and the radiation source intensity information is output, and the output radiation source intensity information at this time is the desired radiation source intensity information; Wherein, each time step 6 is performed, a quality factor M _is obtained correspondingly, and the quality factor M _is obtained by the following formula (17),

where ^R2 represents the goodness of fit,

14. A combined radiation source strong inversion system of a nuclear power plant point source line source area source combination, characterized in that the system is used to execute the nuclear power plant point source line source area source combination of claims 1-13. Radiation source strong inversion method. 15. The combined radiation source strong inversion system of nuclear power plant point source line source surface source combination according to claim 14, characterized in that, the system comprises a detector, a gamma ray average energy calculation module and a radiation source intensity calculation module ; There are multiple detectors, including a predetermined position detector and a nuclear power plant radiation value monitoring detector, The predetermined position detector is arranged in a predetermined position determined by the distance between the radiation area of the nuclear power plant and the radiation source, and the outside of the predetermined position detector is optionally covered with a detachable shielding layer; The predetermined position detector is used to transmit the detected radiation dose rate information to the gamma ray average energy calculation module, The nuclear power plant radiation value monitoring detectors are distributed in the radiation area of the nuclear power plant, and are used to transmit the respectively detected dose rate information in the nuclear power plant to the radiation source intensity calculation module, The gamma ray average energy calculation module is used to calculate the average energy E of gamma rays, The radiation source intensity calculation module is used to calculate the radiation source intensity in the nuclear power plant.

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