CN106815453A - Nuclear power plant's ray radiation source strength backstepping method and ray radiation source strength backstepping system - Google Patents

Abstract

The invention discloses a method for reversing the intensity of a line source radiation source in a nuclear power plant and a system for reversing the intensity of a line source radiation source. The discretization is carried out on the surface, the optical distance is calculated by ray tracing method, the calculation of the coefficients of the equation system is carried out in combination with information such as materials and accumulation factors, and the source intensity is deduced inversely; Linear regression analysis calculates key parameters such as standard deviation, slope, and intercept, and then calculates the quality factor to measure the acceptability of each calculation result; at the same time, a weighted iterative method is proposed to reduce the noise introduced by detectors with large uncertainties. Error, the above steps are repeated multiple times in an iterative manner until the quality factor reaches a preset value, and the expected radiation source intensity information is obtained.

Description

Inverse method for line source radiation source intensity in nuclear power plant and line source radiation source intensity inverse estimation system

technical field

The invention relates to a calculation method and system for radiation source intensity in a nuclear power plant, in particular to a method for reversing the intensity of a line source radiation source in a nuclear power plant and a system for reversing the intensity of a line source radiation source.

Background technique

The radioactivity in nuclear power plants 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 main system of the primary circuit (including pressure vessels, main pumps, voltage stabilizers, main pipelines, etc.), the chemical container control system, etc., and the radiation sources are distributed on the surface of the coolant and related equipment. The radiation source itself is highly radioactive, and the dose received by the staff in their daily activities during normal operation of the nuclear power plant accounts for about 20% of the total annual dose, while 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, it is mainly to reduce the exposure dose by shortening the stay time of the staff in the radiation area.

The distribution of radiation sources in nuclear power plants is relatively wide, especially after long-term use and overhaul, it is more and more difficult to infer the radiation intensity of radiation sources at various positions based on engineering experience, so when calculating many data, especially based on radiation source In the calculation of intensity, the accuracy and practicability are greatly affected because it is difficult to obtain accurate basic information. At the same time, the current domestic protective facilities and means are not very complete, which also greatly increases the risk of workers being exposed .

In the prior art, when it is necessary to estimate the radiation source intensity, the source term analysis method is generally used. First, according to the production and disappearance pathways of radioactive substances, its production items (such as inflow items, decay production items, etc.) and disappearance items (such as filter items) are determined. , leakage items, etc.), and define the physical models of each item, then establish nucleon concentration balance equations (groups) for radioactive substances according to the above items, and finally solve the simultaneous equations (groups), but there are a lot of simplifications in these calculations and approximate calculation, so the result is 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 nuclear power plant detector measurement value 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 intensity of radiation sources.

Due to the above reasons, the present inventor has done in-depth research on the existing methods for calculating source intensity information. According to experience, usually the pipelines or components with uniform radioactivity in nuclear power plants can be simplified as a line source or a group of line sources, so that the design A strong inversion method of line source radiation source and a strong inversion system of line source radiation source in nuclear power plant can solve the above problems.

Contents of the invention

In order to overcome the above-mentioned problems, the present inventor has carried out intensive research, and designed a strong inversion method for line source radiation sources in nuclear power plants and a strong inversion system for line source radiation sources. The method and system can fully guarantee the safety of human body radiation. In this method, the line source intensity data under the complex geometric space structure inside the nuclear power plant is obtained; 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, and then the emission of radiation source is obtained. The average energy of gamma rays; in addition, multiple detectors are installed in the nuclear power plant to monitor the radiation value of the nuclear power plant to obtain the dose rate of some sampling points, using the combination of point nuclear integration and weighted least square method, and Discretize the intensity of the radiation source in space, use the ray tracing method to judge the travel distance of the gamma rays emitted by each discrete source in space and calculate the optical distance, and carry out the calculation of the coefficients of the equation system in combination with information such as materials and accumulation factors, and then inverse Introduce the source intensity; then obtain the calculated value of the dose rate at the detector position, and perform linear regression analysis on the measured and calculated values to obtain key parameters such as standard deviation, slope, and intercept, and then obtain a quality factor that can express physical meaning , the quality factor can measure the acceptability of each calculation result; at the same time, a weighted iterative method is proposed to reduce the error introduced by the detector with large uncertainty, and the above steps are repeated many times in an iterative way until the quality factor meets the predetermined value. The conditions established, and then the expected radiation source intensity and the uncertainty of the radiation field results are obtained, thereby completing the present invention.

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

(1) a method for strong inversion of nuclear power plant line source radiation source, it is characterized in that, the method comprises the steps:

Step 1: use detectors 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, establish the overdetermined equations containing the intensity of the radiation source as shown in the following formula (1),

(one)

Wherein, the coefficient matrix a _i,j of the overdetermined equation system is obtained by the following formulas (two) and (three),

(two)

(three)

Step 3, calculate the overdetermined equation group in step 2 by the least square method to obtain the radiation source intensity information, and the radiation source intensity is the following formula (4)

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 j-th radiation source that has not been iterated in the initial calculation; a _i,j represents the coefficient matrix, which is the dose-response coefficient of the j-th radiation source to the i-th detector; Indicates the discrete coefficient of the line source; L _j indicates the discrete quantity of the jth radiation source; Indicates the normalized discrete source strength; BD(E,L(μ(E),r ₀ →r _p ) indicates 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 a function of μ(E) and r ₀ →r _p ; μ(E) represents the section/linear attenuation coefficient; r ₀ →r _p represents the radiation source to the detector 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 nuclear power plants.

(2) According to the nuclear power plant line source radiation source strong inversion method described in the above (1), it is characterized in that, after step 3, the method also includes 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 calculated dose rate information at the detector position to obtain the fitted linear equation of the relationship between the two, and then obtain the fitting parameters. Fitting 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 equations in step 2 to obtain the weighted overdetermined equations, and then repeat steps 2, 3 and 4 until the desired radiation source intensity information is obtained ;

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

(3) According to the above-mentioned nuclear power plant line source radiation source strong inversion method described in (1), it is characterized in that, for the average energy E of the gamma ray emitted by the radiation source in the nuclear power plant, its calculation method includes the following: step:

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, retrieving the detector, placing it at the predetermined position after it is covered with a shielding layer, and collecting the dose rate I detected by the detector;

Alternatively, retrieve the detector, place a shielding body at a predetermined position, then place the detector in the shielding body, 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, the mass attenuation coefficient μ of the cladding layer or shield is calculated by the following formula (5),

I/I ₀ = BDe ^-μt (5)

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) According to the nuclear power plant line source radiation source strong inversion method described in the above (1), it is characterized in that the method for calculating the optical distance L includes the following sub-steps,

Sub-step a, tracking the gamma-ray travel process from the discrete radiation source to the detection point, recording the sequence in which the gamma-ray passes through the radiation area,

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

(5) According to the above-mentioned nuclear power plant line source radiation source intensity inversion method described in (1), it is characterized in that the process of using the least squares method to process the overdetermined equations in step 2 and obtaining the radiation source intensity information includes the following Substeps:

Sub-step 3-1, the overdetermined equations It is expressed as AX=b in the form of matrix;

Substep 3-2, seek the normal equation A ^T AX=A ^T b of this matrix, namely X=(A ^T A) ^-1 A ^T b;

Sub-step 3-3, solve the equation with the triangular decomposition method of symmetric matrix, record G=A ^T A, wherein, G is a symmetric matrix;

Substep 3-4, utilize triangular decomposition method to solve G=LDL ^T , wherein L is a small triangular matrix, and D is a diagonal matrix;

Substep 3-5, solve lower triangular matrix equations: LY ₁ = ^AT b;

Sub-step 3-6, solving the diagonal matrix equations: DY ₂ =Y ₁ ;

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

(6) According to the nuclear power plant line source radiation source strong inversion method described in the above (2), it is characterized in that, in step five, linear fitting is carried out by the following formula (6),

(six)

in, Indicates the estimated dose rate; represents the estimated slope, represents the estimated intercept,

n represents the maximum value that the number of detectors i can reach, represents the average value of the calculated dose rate at the detector position, Indicates the average value of the dose rate detected by the detector.

(7) According to the strong inversion method of nuclear power plant line source radiation source described in the above (6), it is characterized in that, in step 5, the weight function is obtained according to the uncertainty, and then the weight matrix W is obtained through the weight function, and the The weight matrix W is obtained by the following formula (7),

(seven)

where f represents the fitting uncertainty, represents the average fitting uncertainty, f _i represents the fitting uncertainty of the i-th detector position; represents the weight function.

(8) According to the nuclear power plant line source radiation source strong inversion method described in the above (6), it is 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, a quality factor M is correspondingly obtained each time step 6 is performed, and the quality factor M is obtained by the following formula (8),

(Eight)

Among them, ^R2 represents the goodness of fit,

(9) A nuclear power plant line source radiation source strong inversion system, characterized in that the system is used to implement the nuclear power plant line source radiation source strong inversion method described in claims 1-8.

(10) According to the nuclear power plant line source radiation source strong inversion system described in the above (9), it is 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 predetermined position detectors and nuclear power plant radiation value monitoring detectors,

The predetermined position detector is arranged at a predetermined position within the radiation area of the nuclear power plant at a predetermined distance from the radiation source, and is optionally covered with a detachable shielding layer outside the predetermined position detector;

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 for calculating the radiation source intensity in a nuclear power plant.

The beneficial effects that the present invention has include:

(1) The line source radiation source intensity inversion method for nuclear power plants provided by the present invention can obtain the line source intensity data under the complex geometric space structure inside the nuclear power plant under the condition of fully ensuring the radiation safety of the human body;

(2) According to the inversion method of the nuclear power plant line source radiation source intensity provided by the present invention, through multiple iterative calculations, it is ensured that the finally obtained line source source intensity information is closer to the real value, which has high engineering application value.

Description of drawings

Fig. 1 shows an overall working flow chart according to a preferred embodiment of the present invention.

detailed description

The present invention will be further described in detail through the drawings and examples below. Through these descriptions, the features and advantages of the present invention will become more apparent.

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 superior or better than other embodiments.

According to the nuclear power plant line source radiation source strong inversion method provided by the present invention, the method comprises the following steps:

Step 1, _receiving the dose rate information D ₁ , D ₂ , D ₃ . Place multiple detectors in the nuclear power plant, or directly use the existing detectors in the nuclear power plant. The existing detectors in the nuclear power plant are radiation value monitoring detectors in nuclear power plants. The above two methods can also be used in combination. For the above detectors 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 detectors is greater than the number of radiation sources in a nuclear power plant.

Step 2, according to the detected dose rate information, establish an overdetermined equation system containing radiation source intensity, the overdetermined equation system is the following formula (1),

(one)

Step 3, calculate the overdetermined equation group in step 2 by the least square method to obtain the radiation source intensity information, and the radiation source intensity 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 of} the overdetermined equation system is obtained by the following formulas (two) and (three),

(two)

(three),

After step three, the intensity information of the radiation source has been obtained, but the intensity information may not be accurate enough, so the calculation is continued through the following steps in order to obtain the intensity information of the radiation source closer to the real 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 calculated dose rate information at the detector position to obtain the fitted linear equation of the relationship between the two, 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 is divided into inner weight matrix or outer weight matrix, and its calculation method is consistent, and the difference is that the outer weight matrix Uncertainty is not calculated by the system, but the error range of the detector entered by operator means.

Step 6, iterating the weight matrix obtained in step 5 to the overdetermined equations in step 2 to obtain the weighted overdetermined equations, and then repeating steps 2, 3 and 4 until the desired radiation source intensity information is obtained;

In the present invention, D represents the dose rate detected by the detector; Di represents the dose rate detected by the i-th detector; _i represents the number of detectors; j represents the number of radiation sources; m represents the number of radiation sources The maximum value that can be achieved; S represents the intensity of the radiation source; S _j represents the intensity of the jth radiation source; S _j,0 represents the intensity of the jth radiation source that has not been iterated in the initial calculation; a _i,j represents the coefficient matrix , is the dose response coefficient of the jth radiation source to the ith detector; Indicates the discrete coefficient of the line source; L _j indicates the discrete quantity of the jth radiation source; Indicates the normalized discrete source strength; BD(E,L(μ(E),r ₀ →r _p ) indicates 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 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 gamma rays emitted by the radiation source in the nuclear power plant; D _i ' represents the calculated dose rate at the position of the i-th detector. Wherein, the detection point represents the position of the detector, more precisely, the position on the detector where radiation information is received.

The accumulation factor described in the present invention is a professional term commonly used in the art, and can be explained and calculated with reference to the usual meaning in the art. The calculation formula provided in the present invention in general is 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, you can 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, retrieving the detector, placing it at the predetermined position after it is covered with a shielding layer, and collecting the dose rate I detected by the detector;

Alternatively, retrieve the detector, place a shielding body at a predetermined position, then place the detector in the shielding body, 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, the mass attenuation coefficient μ of the cladding layer or shield is calculated by the following formula (5),

I/I ₀ = BDe ^-μt (5)

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 said look-up table can be a material section table, which is recorded in ANSI/ANS 6.4.3, "Gamma-ray Attenuation Coefficients and Buildup Factor for Engineering Materials", American Nuclear Society, 1991. pages 16-67. In the present invention, all radiant energy is calculated with the above average energy. If the energy difference in different areas of the nuclear power plant is relatively large, it can be considered to calculate the area separately, that is, the average energy and the intensity of the radiation source can be calculated separately.

In a preferred embodiment, the method for calculating the optical distance L includes the following sub-steps, sub-step a, tracking the gamma-ray travel process from the radiation source to the detection point, recording the order in which the gamma-ray passes 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 r _p represents the position of the detection point. In sub-step b, the distance of each radiation area is calculated separately, combined with the linear attenuation coefficient of the material of each radiation area, and finally the total optical distance L is obtained.

Specifically, when calculating the γ-ray travel distance, the space is described by the method of combinatorial geometry, and the space of different media is divided into different regions. The distance Di between the intersection point of the gamma ray and each primitive and the entrance and the distance Do between the exit and the exit are calculated respectively. Find all primitive numbers plus and minus with "+" and "-" in each area, this process may 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 the area; if there are "-" primitives in this area, then all "+" primitives in this area must satisfy the starting point r ₀ in all "+" primitives, and all "-" primitives must Satisfied that the starting point r ₀ does not contain this ray, 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, all "+" primitives in this area must satisfy that the end point r _p is located in all "+" primitives, then the termination area of the ray can be considered is the region; if there are "-" primitives in this region, then all "+" primitives in this region must satisfy the terminal r _p in all "+" primitives, and all "-" primitives must satisfy the end point r _p that does not contain this ray, then the end area of the ray is considered to be this area.

(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 γ-ray starting region number, the minimum exit distance Do of all "+" primitives in the starting region is the exit distance of the γ-ray starting region. If there is a "-" basic body in the starting area of the γ-ray, first all "+" basic bodies in the initial area take the smallest exit distance Do, and then all "-" basic bodies take the smallest entrance distance Di, and take 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 entrance distance of the primitive is less than or equal to the entrance distance of the area and When it is less than the exit distance of the basic body (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 "-" basic body in the γ-ray area number, for all For "+" primitives, the primitive import distance is less than or equal to the region's import distance and less than the primitive's exit distance (Di<=Zin<Do), and for all "-" primitives, the primitive import distance is greater than the region import distance Or when the exit distance of the basic body is less than or equal to the area entrance distance (Di>Zin or Do<=Zin), this 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 exit distance Zo of each area that the ray passes through:

If there is no "-" basic body in the adjacent area obtained above, the exit distance of this area is the smallest among all "+" basic body exit distances Do, and the entrance distance of this area is the exit distance of the previous area; If there is a "-" primitive in the adjacent area obtained above, first find the smallest one of the exit distance Do of all "+" primitives, and find the smallest one of the entrance distance Di of all "-" primitives , 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) In the case of the end point in the outermost area, first find all the primitive numbers aa in the outermost layer, for the area in which the "+" primitive includes the primitive aa, and the "-" primitive does not include the primitive aa When , look for whether there is a "-" primitive whose entrance distance of the "-" primitive in the ray passes through the area is greater than the entrance distance of the area (Di(k,minus(i,m))>Zi(k,n)), if If it exists, the exit distance of the area is the smallest among the entrance distances Di of all "-" primitives. If it does not exist, the exit distance of the area is the ray length.

Tracing to the area IPend where r _p point is located and the exit distance of the ray is equal to the length of the ray is terminated. Thus, the travel distance of gamma rays is obtained.

Then calculate the number of times the ray passes through the area and the distance traveled each time:

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

Obtain the γ section μ _n by using the γ mass attenuation coefficient and the material of the region medium;

Through the above-mentioned travel process of recording gamma rays passing through the area, the optical distance of each area is calculated 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 process of using the least square method to process the overdetermined equations in step 2 and obtaining the radiation source intensity information includes the following sub-steps:

Sub-step 3-1, the overdetermined equations It is expressed as AX=b in the form of matrix;

Substep 3-2, seek the normal equation A ^T AX=A ^T b of this matrix, namely X=(A ^T A) ^-1 A ^T b;

Sub-step 3-3, solve the equation with the triangular decomposition method of symmetric matrix, record G=A ^T A, wherein, G is a symmetric matrix;

Substep 3-4, utilize triangular decomposition method to solve G=LDL ^T , wherein L is a small triangular matrix, and D is a diagonal matrix;

Substep 3-5, solve lower triangular matrix equations: LY ₁ = ^AT b;

Sub-step 3-6, solving the diagonal matrix equations: DY ₂ =Y ₁ ;

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

Wherein, X=(A ^T A) ^-1 A ^T b corresponds to S _j,0 =(a _i,j ^T ·a _i,j ) ^-1 ·a _i,j ^T ·D _i , through the sub From step 3-1 to sub-step 3-7, the calculated value of the intensity of the radiation source is obtained, and the least square method described in the present invention is a common overdetermined equation solution method in the field.

In a preferred embodiment, in step five, linear fitting is carried out by the following formula (6),

(six)

in, Indicates the estimated dose rate; represents the estimated slope, represents the estimated intercept,

n represents the maximum value that the number of detectors i can reach, represents the average value of the calculated 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 Confidence for iterative calculations. In step five, the weight function is obtained according to the uncertainty, and then the weight matrix W is obtained through the weight function, and the weight matrix W is obtained by the following formula (7),

(seven)

where 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 six, the judging condition for obtaining the desired radiation source intensity information is when S _i >0, and the quality factor M reaches the maximum value, that is, when S _i >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 expected radiation source intensity, which is also the radiation source intensity closest to the real value.

The purpose of the present invention is to obtain the radiation source intensity closest to the true value, and 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 radiation source intensity closest to the true value, the weighted iterative process of step 4 to step 6 is given in the present invention, and the conditions for the termination of the iteration are finally set, so as to reduce the workload as much as possible while ensuring the accuracy of the result, Shorten the operation time and improve the efficiency of data acquisition. According to the above-mentioned weighted iteration method and the criterion of iteration termination. In addition, the intensity of the radiation source obtained in the present invention is more accurate than the intensity of the radiation source obtained by the source item analysis method, and is closer to the real value, and can ensure that the obtained value and the real value are within an order of magnitude. In a preferred embodiment, a quality factor M is correspondingly obtained each time step 6 is performed, and the quality factor M is obtained by the following formula (8),

(Eight)

Among them, ^R2 represents the goodness of fit,

In a preferred embodiment, the overdetermined system of equations The matrix form of is shown in the following formula (9)

(Nine)

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 formula (10),

(ten),

Among them, S ^* represents the intensity of the radiation source considering the error, and then 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 i-th detector. For a line source, the radiation source in space The coordinates (A, B, C) are discrete, then the response coefficient of the discrete point source to the detector is

After the above equations are discretized, they become

for The acquisition of , taking the radiation source S ^* ₁ as an example, discretize the radiation source on the one-dimensional coordinate of space, then It can be obtained by the following formula (11),

(eleven)

in,

which is

Among them, X _L represents the coordinate after discretization; Indicates the cosine constant, which can be entered manually, and the default value is 0; L indicates the discrete quantity, that is, the number of divisions when the line source is divided into several divisions for discrete calculation.

According to the present invention, there is provided a nuclear power plant line source radiation source strong inversion system, which is used to implement the nuclear power plant line source radiation source strong inversion method described above in the present invention.

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 predetermined position detectors and nuclear power plant radiation value monitoring detectors,

The predetermined position detector is arranged at a predetermined position determined by the distance between the nuclear power plant radiation area 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 of 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 for calculating the gamma ray average energy;

The radiation value monitoring detectors of the nuclear power plant are distributed in the radiation area of the nuclear power plant, respectively located at 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 for calculating the radiation source intensity in a nuclear power plant.

Experimental example:

Taking room NB281 in the nuclear island of Daya Bay Nuclear Power Plant Unit 1 as the experimental object, this room is used to place radioactive waste water collection barrels in the nuclear island control area. The source strength of radioactive liquid in the waste water collection barrels is 0.7586E+10MeV/ cm ³ .s (or 4.2898E+14/s). Simplify the waste water collection bucket into 4 vertical line sources, install a detector every 50cm in the middle of the waste water collection bucket, a total of five detectors, the detection values obtained by each detector are 2.032mSv/hr, 0.685 mSv/h, 0.255mSv/h, 0.1446mSv/h, 0.0929mSv/h, namely D ₁ , D ₂ , D ₃ , D ₄ , D ₅ in the present invention, according to the average energy acquisition method and The average energy obtained by the system is 1.3MeV. Using the source strength inversion method and system provided by the present invention, the four point source strengths obtained respectively are

1.4836E+12MeV/(cm.s) (or 1.1869E+14MeV/s),

1.0739E+12MeV/(cm.s) (or 0.8591E+14MeV/s),

1.2566E+12MeV/(cm.s) (or 1.0053E+14MeV/s),

1.2635E+12MeV/(cm.s) (or 1.0108E+14MeV/s).

It can be seen from the final results that the obtained sum of the radiation intensity of the four line sources is basically consistent with the real value of the radiation intensity of the radiation source, so it can be explained that the method and system provided by the present invention can obtain radiation source intensity information close to the real value.

The present invention has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and serve as illustrations only. On this basis, various replacements and improvements can be made to the present invention, all of which fall within the protection scope of the present invention.

Claims (10)

1. A strong inversion method for nuclear power plant line source radiation source, is characterized in that, the method comprises the steps: Step 1, using detectors 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, establish the overdetermined equations containing the intensity of the radiation source as shown in the following formula (1), (one) Wherein, the coefficient matrix a _i,j of the overdetermined equation system is obtained by the following formulas (two) and (three), (two) (three); Step 3, process the overdetermined equations in step 2 by the least square method, and obtain the radiation source intensity information shown in the following formula (4), S _j,0 ＝(a _j,i ·a _i,j ) ^-1 ·a _j,i ·D _i (four); 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 j-th radiation source that has not been iterated in the initial calculation; a _i,j represents the coefficient matrix, which is the dose-response coefficient of the j-th radiation source to the i-th detector; Indicates the discrete coefficient of the line source; L _j indicates the discrete quantity of the jth radiation source; Indicates the normalized discrete source strength; BD(E,L(μ(E),r ₀ →r _p ) indicates 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 a function of μ(E) and r ₀ →r _p ; μ(E) represents the section/linear attenuation coefficient; r ₀ →r _p represents the radiation source to the detector 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 nuclear power plants. 2. The strong inversion method for nuclear power plant line source radiation source according to claim 1, characterized in that, after step 3, the method also includes 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 calculated dose rate information at the detector position to obtain the fitted linear equation of the relationship between the two, and then obtain the fitting parameters. Fitting parameters include: average uncertainty, goodness of fit and corresponding weight matrix; Step 6, iterating the weight matrix obtained in step 5 to the overdetermined equations in step 2 to obtain the weighted overdetermined equations, and then repeating steps 2, 3 and 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 strong inversion method of nuclear power plant line source radiation source according to claim 1, characterized in that, for the average energy E of the gamma rays emitted by the radiation source in the nuclear power plant, its measuring method comprises 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, retrieving the detector, placing it at the predetermined position after it is covered with a shielding layer, and collecting the dose rate I detected by the detector; Alternatively, retrieve the detector, place a shielding body at a predetermined position, then place the detector in the shielding body, 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, the mass attenuation coefficient μ of the cladding layer or shield is calculated by the following formula (5), I/I ₀ = BDe ^-μt (5) 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 strong inversion method for nuclear power plant line source radiation source according to claim 1, characterized in that the method for calculating the optical distance L comprises the following sub-steps, Sub-step a, tracking the gamma-ray travel process from the discrete radiation source to the detection point, recording the sequence in which the gamma-ray passes through the radiation area, In sub-step b, the distance of each radiation area is calculated separately, combined with the linear attenuation coefficient of the material of each radiation area, and finally the total optical distance L is obtained. 5. The strong inversion method of nuclear power plant line source radiation source according to claim 1, characterized in that the process of using the least squares method to process the overdetermined equations in step 2, and obtaining the radiation source intensity information includes the following sub-steps : Sub-step 3-1, the overdetermined equations It is expressed as AX=b in the form of matrix; Substep 3-2, seek the normal equation A ^T AX=A ^T b of this matrix, namely X=(A ^T A) ^-1 A ^T b; Sub-step 3-3, solve the equation with the triangular decomposition method of the symmetric matrix, record G=A ^T A, wherein, G is a symmetric matrix; Substep 3-4, utilize triangular decomposition method to solve G=LDL ^T , wherein L is a small triangular matrix, and D is a diagonal matrix; Substep 3-5, solve lower triangular matrix equations: LY ₁ = ^AT b; Sub-step 3-6, solving the diagonal matrix equations: DY ₂ =Y ₁ ; Sub-step 3-7, solving the upper triangular matrix equation system: L ^T X = Y ₂ . 6. The strong inverse method for nuclear power plant line source radiation source according to claim 2, is characterized in that, in step 5, carry out linear fitting by following formula (6), (six) in, Indicates the estimated dose rate; represents the estimated slope, represents the estimated intercept, n represents the maximum value that the number of detectors i can reach, represents the average value of the calculated dose rate at the detector position, Indicates the average value of the dose rate detected by the detector. 7. The strong inversion method of nuclear power plant line source radiation source according to claim 6, characterized in that, in step 5, the weight function is obtained according to the uncertainty, and then the weight matrix W is obtained through the weight function, and the weight matrix W is obtained by the following formula (7), (seven) where f represents the fitting uncertainty, represents the average fitting uncertainty, f _i represents the fitting uncertainty of the i-th detector position; represents the weight function. 8. The strong inversion method for nuclear power plant line source radiation source according to claim 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 radiation source intensity information output at this time is the desired radiation source intensity information; Wherein, a quality factor M is correspondingly obtained each time step 6 is performed, and the quality factor M is obtained by the following formula (8), (Eight) Among them, ^R2 represents the goodness of fit, 9. A nuclear power plant line source radiation source strong inversion system, characterized in that the system is used to implement the nuclear power plant line source radiation source strong inversion method described in claims 1-8. 10. The nuclear power plant line source radiation source strong inversion system according to claim 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 predetermined position detectors and nuclear power plant radiation value monitoring detectors, The predetermined position detector is arranged at a predetermined position within the radiation area of the nuclear power plant at a predetermined distance from the radiation source, and is optionally covered with a detachable shielding layer outside the predetermined position detector; 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 for calculating the radiation source intensity in a nuclear power plant.