CN106815769A - The recombination radiation source strength backstepping method and system of nuclear power plant's point source line source combination - Google Patents
The recombination radiation source strength backstepping method and system of nuclear power plant's point source line source combination Download PDFInfo
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Abstract
The invention discloses the recombination radiation source strength backstepping method and the recombination radiation source strength backstepping system of point source line source combination of a kind of combination of nuclear power plant's point source line source, in the method, the close rate of multiple positions is obtained by detector, normalization radiation source intensity is spatially carried out discrete, optical distance is calculated using ray tracing method, the information such as bond material, buildup factor carry out the calculating of equation group coefficient, and backstepping goes out source strength；Then close rate calculating is carried out to detector position, linear regression analysis is carried out by measured value and calculated value, calculate the key parameters such as standard deviation, slope, intercept, and then calculate quality factor and weigh the acceptable degree of each result of calculation；The Weighted Iterative Methods are proposed simultaneously, the error that the larger detector of uncertainty is introduced is reduced, and using the mode of iteration, above steps may be repeated multiple times until quality factor reach pre-set value, obtains desired radiation source intensity information.
Description
Technical Field
The invention relates to a method and a system for calculating the intensity of a radiation source in a nuclear power plant, in particular to a method and a system for strongly pushing back a composite radiation source combined by a point source and a line source of a nuclear power plant.
Background
The radioactivity of a nuclear power plant comes from the active area of the fuel assemblies in the pressure vessel and the radiation source consists mainly of fission products, actinides and corrosion activation products. In the system operation, the radiation sources flow along with the coolant through a main loop system (including a pressure vessel, a main pump, a pressure stabilizer, a main pipeline and the like), a chemical vessel control system and the like, and the radiation sources are distributed on the surfaces of the coolant and related equipment. The radioactive source is strong in radioactivity, the dosage of daily activities of workers in normal operation of a nuclear power plant accounts for about 20% of the total annual dosage, the dosage of the workers accounts for 80% of the total annual dosage during overhaul of the nuclear power plant, and the exposure dosage is reduced mainly by shortening the stay time of the workers in a radiation area during overhaul of the nuclear power plant.
The radiation sources in the nuclear power plant are widely distributed, and particularly after long-time use and overhaul, the radiation intensity of the radiation sources at each position is more and more difficult to deduce according to engineering experience, so that when a lot of data are calculated, particularly in the calculation according to the radiation source intensity, because accurate basic information is difficult to obtain, the accuracy and the practicability are greatly influenced, and meanwhile, under the condition that the domestic current protection facilities and means are not complete, the irradiation risk of workers is greatly increased.
In the prior art, when the intensity of a radiation source needs to be calculated, a source item analysis method is generally adopted, firstly, generation items (such as inflow items, decay generation items and the like) and disappearance items (such as filtering items, leakage items and the like) of the radioactive substance are determined according to the generation and disappearance ways of the radioactive substance, physical models of the items are determined, then a nuclear concentration balance equation (set) is established for the radioactive substance according to the items, and finally the equation (set) is solved in a simultaneous manner The accuracy and the like are all problematic, and a new radiation source intensity acquisition way needs to be improved or proposed.
For the reasons, the inventor of the present invention has made intensive studies on the existing method for calculating the source intensity information, and according to experience, all radioactive components in a nuclear power plant can be simplified into a point source or a group of point sources, for example, a thermal valve can be simplified into a point source, a pipeline with uniform radioactivity can be simplified into a point source every several feet, and finally a group of point sources are formed, and can be simplified into a line source correspondingly in order to improve the calculation accuracy, so as to design a composite radiation source strong backward-pushing method for a nuclear power plant point source and line source combination and a composite radiation source strong backward-pushing system for a point source and line source combination, which can solve the above problems.
Disclosure of Invention
In order to overcome the problems, the inventor of the invention carries out intensive research and designs a composite radiation source strong backward-pushing method and a composite radiation source strong backward-pushing system of a point source and line source combination in a nuclear power plant, and the method and the system can obtain radiation source strong data under a complex geometric space structure in the nuclear power plant under the condition of fully ensuring the radiation safety of a human body; in the method, a detector is placed at a preset position in a nuclear power plant, and a detector with a shield is also placed at the position, so that the average energy of gamma rays emitted by a radiation source is obtained; in addition, a plurality of detectors for monitoring radiation values of the nuclear power plant are arranged in the nuclear power plant to obtain the dose rates of partial acquisition points, the normalized radiation source intensity is dispersed in space by using a point nuclear integration and weighted least square method combined mode, the passing path of gamma rays emitted by each radiation source in space is judged by using a ray tracing method, the optical distance is calculated, the calculation of the coefficients of an equation set is carried out by combining information such as materials and accumulation factors, and the source intensity is reversely deduced; then, a calculated value of the dose rate at the position of the detector is obtained, the measured value and the calculated value are subjected to linear regression analysis processing to obtain key parameters such as standard deviation, slope, intercept and the like, and further a quality factor capable of representing the physical meaning is obtained, and the quality factor can measure the acceptability of each calculation result; meanwhile, a weighted iteration method is provided, the error introduced by a detector with larger uncertainty is reduced, the steps are repeated for multiple times in an iteration mode until the quality factor meets the preset condition, and further the expected radiation source intensity and the uncertainty of the radiation field result are obtained, so that the method is completed.
Specifically, the present invention aims to provide the following:
(1) a composite radiation source strong backward pushing method of a point source and line source combination in a nuclear power plant is characterized by comprising the following steps:
step one, detecting dose rate D in a nuclear power plant by using a detector1,D2,D3…Di，
Step two, establishing an overdetermined equation set containing the radiation source intensity as shown in the following formula (one) according to the detected dose rate information,
(A)
Wherein the coefficient matrix a of the over-determined equation seti,jObtained by the following formulae (II) and (III),
(II)
(III)
In equation (three), i.e., when the radiation source is a point source, q is 0, and when the radiation source is a line source, q is 1;
step three, calculating the overdetermined equation set in the step two by a least square method to obtain the intensity information of the radiation source, wherein the intensity of the radiation source is represented by the following formula (IV)
Sj,0＝(aj,i·ai,j)-1·aj,i·Di(IV)
Wherein D isiIndicating the dose rate detected by the ith detector; j represents the number of radiation sources; m represents the maximum value which can be reached by the number of radiation sources; sjRepresenting the intensity of the jth radiation source, a discrete number of 1 when the radiation source is a point source; sj,0Representing the intensity of the jth radiation source for which the initial calculation was not iterated; a isi,jRepresenting a coefficient matrix which is the dose response coefficient of the jth radiation source to the ith detector;representing a line source dispersion coefficient; l isjRepresents a discrete number of jth radiation sources;representing normalized discrete source intensity; BD (E, L (. mu. (E), r)0→rp) Indicating an accumulation factor, E and L (. mu. (E), r)0→rp) A function of (a); l (. mu.E, r)0→rp) Denotes an optical distance, is μ (E) and r0→rpA function of (a); μ (E) represents a cross-sectional/linear attenuation coefficient; r is0→rpRepresenting the distance of the radiation source to the detection point; c (E) represents a flux-dose conversion factor, which is a function of E; e represents the energy, which is the average energy of gamma rays emitted by a radiation source in a nuclear power plant.
(2) The method for strongly backward pushing the composite radiation source of the nuclear power plant point source and line source combination is characterized in that after the third step, the method further comprises the following steps,
step four, calculating the dose rate D 'at the position of the detector according to the radiation source intensity information obtained in the step three'1,D′2,D′3…D′i；
And step five, performing 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 dose rate information and the dose rate information after fitting, and further obtain fitting parameters, wherein the fitting parameters comprise: average uncertainty, goodness-of-fit and corresponding weight matrix;
step six, iterating the new weight matrix obtained in the step five to the overdetermined equation set in the step two to obtain a weighted overdetermined equation, and further repeating the step two, the step three and the step four until the expected radiation source intensity information is obtained;
wherein, D'iRepresenting the calculated dose rate at the i-th detector position.
(3) The method for strongly backward estimating the composite radiation source of the nuclear power plant point source and line source combination is characterized in that, for the average energy E of the gamma rays emitted by the radiation source in the nuclear power plant, the method for calculating the average energy E comprises the following substeps:
substep 1, selecting a preset position in a nuclear power plant, wherein the preset position is at a distance t from a radiation source, placing a detector at the preset position, and collecting the dose rate I detected by the detector0，
Substep 2, retrieving the detector, covering a shielding layer on the outside of the detector, placing the detector at the preset position, and collecting the dose rate I detected by the detector;
or, the detector is taken back, a shielding body is placed at a preset position, then the detector is placed in the shielding body, and the dosage rate I detected by the detector is collected;
substep 3, I and I obtained according to substeps 1 and 20The mass attenuation coefficient μ of the clad or shield is calculated by the following formula (five),
I/I0＝BDe-μt(V)
And a substep 4 of obtaining the average energy E of the gamma rays emitted by the radiation source according to the calculation result of the substep 3.
(4) The method for strongly backward pushing a composite radiation source of a nuclear power plant point source and line source combination is characterized in that the method for calculating the optical distance L comprises the following substeps,
a sub-step a of tracking the passing process of the gamma ray from the radiation source to the detection point, recording the sequence of the gamma ray passing through the radiation region,
and a substep b, respectively calculating the distance of each radiation area, and finally calculating the total optical distance L by combining the linear attenuation coefficient of the material of each radiation area.
(5) The method for strongly backward pushing the composite radiation source of the nuclear power plant point source and line source combination is characterized in that the overdetermined equation set in the second step is processed by using a least square method, and the process of obtaining the intensity information of the radiation source comprises the following substeps:
substep 3-1. solving the overdetermined system of equationsExpressed in matrix form as AX ═ b;
substep 3-2, solving the normal equation A of the matrixTAX＝ATb, i.e. X ═ ATA)-1ATb；
Substep 3-3, solving equation by trigonometric decomposition of symmetric matrix, and recording G ═ ATA, wherein G is a symmetric matrix;
substeps 3-4, solving for G ═ LDL by trigonometric decompositionTWherein L is a small triangular matrix and D is a diagonal matrix;
substeps 3-5, solving the lower triangular matrix equation system LY1＝ATb；
Substeps 3-6, solving the diagonal matrix equation set: DY (DY)2＝Y1；
And substeps 3-7, solving an upper triangular matrix equation set: l isTX＝Y2。
(6) The method for strongly backward pushing the composite radiation source of the nuclear power plant point source and line source combination is characterized in that in the fifth step, linear fitting is performed according to the following formula (six),
(VI)
Wherein,represents the estimated dose rate;which is indicative of the slope of the estimate, the estimated intercept is represented as a function of,
n represents the maximum number of detectors i can reach,representing the calculated average value of the dose rate at the detector position,representing the average value of the dose rate detected by the detector.
(7) The method for strongly backward pushing the composite radiation source of the nuclear power plant point source and line source combination is characterized in that, in the fifth step, a weight function is obtained according to uncertainty, and then a weight matrix W is obtained through the weight function, wherein the weight matrix W is obtained through the following formula (VII),
(seven)
Where f represents the uncertainty of the fit,the mean fit uncertainty is represented as a function of,fifitting uncertainty representing ith detector position；；Representing a weight function.
(8) The method for strongly backward pushing the composite radiation source of the nuclear power plant point source and line source combination is characterized in that,
in step six, when SiIf the quality factor M is greater than 0, stopping the weighting iteration when the quality factor M reaches the maximum value, and outputting the intensity information of the radiation source, wherein the output intensity information of the radiation source is the expected intensity information of the radiation source;
wherein, each time step six is executed, a quality factor M is obtained correspondingly, the quality factor M is obtained by the following formula (eight),
(eight)
Wherein R is2The goodness of fit is expressed,
(9) a composite radiation source strong backstepping system of a nuclear power plant point source and line source combination is characterized by being used for executing the composite radiation source strong backstepping method of the nuclear power plant point source and line source combination according to claims 1-8.
(10) The composite radiation source strong backward-pushing system of the nuclear power plant point source and line source combination according to the above (9), wherein the system comprises a detector, a gamma ray average energy calculation module and a radiation source intensity calculation module;
the detector is provided with a plurality of detectors, including a preset position detector and a nuclear power plant radiation value monitoring detector,
the preset position detector is arranged at a preset position with a determined distance from a radiation source in a radiation area of a nuclear power plant, and a detachable shielding layer is optionally coated outside the preset position detector;
the preset position detector is used for transmitting the detected radiation rate information to the gamma ray average energy calculating module,
the nuclear power plant radiation value monitoring detectors are distributed in a radiation area of the nuclear power plant and used for transmitting respectively detected dose rate information in the nuclear power plant to the radiation source intensity calculating module,
the gamma ray average energy calculating module is used for calculating the average energy E of gamma rays,
the radiation source intensity calculating module is used for calculating the intensity of the radiation source in the nuclear power plant.
The invention has the advantages that:
(1) according to the composite radiation source strong backward pushing method for the point source and line source combination of the nuclear power plant, provided by the invention, radiation source strong data under a complex geometric space structure in the nuclear power plant can be obtained under the condition of fully ensuring the radiation safety of a human body;
(2) according to the composite radiation source strong backward pushing method of the point source and line source combination of the nuclear power plant, provided by the invention, the finally obtained radiation source intensity information is ensured to be more close to the true value through repeated iterative calculation, and the method has a very high engineering application value.
Drawings
Fig. 1 shows an overall workflow diagram according to a preferred embodiment of the present invention.
Detailed Description
The invention is explained in more detail below with reference to the figures and examples. The features and advantages of the present invention will become more apparent from the description.
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.
The invention provides a strong backward pushing method for a composite radiation source of a point source and line source combination of a nuclear power plant, which comprises the following steps:
step one, receiving dose rate information D detected by a detector in a power plant1,D2,D3…DiIn the present invention, a plurality of detectors may be placed in a power plant, or a detector already existing in the nuclear power plant may be directly utilized, the detector already existing in the nuclear power plant is a nuclear power plant radiation value monitoring detector, or the two methods may be used in combination, where the position of the detector is required to be: there is no shield between the radiation source and the location, and the dose rate in the present invention is the irradiation dose rate. In the invention, the number of detectors is greater than the number of radiation sources in the nuclear power plant.
Step two, establishing an overdetermined equation set containing the intensity of the radiation source according to the detected dose rate information, wherein the overdetermined equation set is a formula (one) as follows,
(A)
Step three, calculating the overdetermined equation set in the step two by a least square method to obtain the intensity information of the radiation source, wherein the intensity of the radiation source is represented by the following formula (IV)
Sj,0＝(aj,i·ai,j)-1·aj,i·Di(IV)
System of said overdetermined system of equationsNumber matrix ai,jObtained by the following formulae (II) and (III),
(II)(III) the first step of the method,
in the formula (iii), q is 0 for point and 1 for line; that is, when the radiation source is a point source, q is 0, and when the radiation source is a line source, q is 1;
in the invention, because a plurality of areas in which the intensity of the radiation source needs to be measured and calculated exist in one nuclear power plant, a plurality of radiation sources need to be measured and calculated, in different areas or aiming at different radiation sources, the radiation sources can be simulated into point sources or line sources, and can be measured and calculated through the formula (III), when the radiation source is a point source, the q is 0, and when the radiation source is a line source, the q is 1. When the radiation source is a point source, the point source may not be discretely treated, i.e., Lj＝0，ai,j＝a1 i,j。
After the third step, the intensity information of the radiation source can be obtained, but the intensity information may not be accurate enough, so the calculation is continued through the following steps to obtain the intensity information of the radiation source closer to the true value;
step four, calculating the dose rate D 'at the position of the detector according to the radiation source intensity information obtained in the step three'1,D′2,D′3…D′i；
And step five, performing 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 dose rate information and the dose rate information after fitting, and further obtain fitting parameters, wherein the fitting parameters comprise: average uncertainty, goodness-of-fit and corresponding weight matrix; the weight matrix in the present invention can be an internal weight matrix or an external weight matrix, and the obtaining method is consistent, except that the uncertainty of the external weight matrix is not calculated by the system, but is the error range of the detector input by the operator means.
Step six, iterating the weight matrix obtained in the step five to the overdetermined equation set in the step two to obtain a weighted overdetermined equation, and further repeating the step two, the step three and the step four until expected radiation source intensity information is obtained;
in the invention, D represents the dosage rate detected by a detector; diIndicating the dose rate detected by the ith detector; i represents the number of detectors; j represents the number of radiation sources; m represents the maximum value which can be reached by the number of radiation sources; s represents the intensity of the radiation source; sjRepresents the intensity of the jth radiation source; sj,0Representing the intensity of the jth radiation source for which the initial calculation was not iterated; a isi,jRepresenting a coefficient matrix which is the dose response coefficient of the jth radiation source to the ith detector;representing a line source dispersion coefficient; l isjRepresents a discrete number of jth radiation sources, the discrete number being 1 when the radiation source is a point source;representing normalized discrete source intensity; BD (E, L (. mu. (E), r)0→rp) Indicating an accumulation factor, E and L (. mu. (E), r)0→rp) A function of (a); l (. mu.E, r)0→rp) Denotes an optical distance, is μ (E) and r0→rpI.e. the optical distance is a function of the energy and the actual distance; μ (E) represents a linear attenuation coefficient; r is0→rpRepresenting the distance of the radiation source to the detection point; c (E) represents a flux-dose conversion factor, which is a function of E; e represents energy, which is the average energy of gamma rays emitted by a radiation source in a nuclear power plant; d'iRepresenting the calculated dose rate at the i-th detector position. Wherein the detection points represent the position of the detector, more precisely theIs the location on the detector at which the radiation information is received.
The accumulation factor described in the present invention is a term commonly used in the art, and can be explained and calculated with reference to the ordinary meaning in the art, and the general formula of the calculation is given as follows:
wherein KxThe fitting formula of (a) is as follows:
K(E,x)＝cxa+d[tanh(x/Xk-2)-tanh(-2)]/[1-tanh(-2)]；
where E is photon energy, MeV;xdistance from source point to calculated point, mfp; b is the accumulation factor at one mean free path; a, c, d, XkFor the empirical parameters, when the accumulation factor coefficient is selected, a logarithmic difference mode can be selected, that is:
a(Ea)＝{a(E1)·[log(E2)-log(Ea)]+a(E2)·[log(Ea)-log(E1)]}/[log(E2)-log(E1)]
in a preferred embodiment, the method for calculating the mean energy E of gamma rays emitted by a radiation source in a nuclear power plant comprises the following sub-steps:
substep 1, selecting a preset position in a nuclear power plant, wherein the preset position is at a distance t from a radiation source, placing a detector at the preset position, and collecting the dose rate I detected by the detector0，
Substep 2, retrieving the detector, covering a shielding layer on the outside of the detector, placing the detector at the preset position, and collecting the dose rate I detected by the detector;
or, the detector is taken back, a shielding body is placed at a preset position, then the detector is placed in the shielding body, and the dosage rate I detected by the detector is collected;
substep 3, I and I obtained according to substeps 1 and 20The mass attenuation coefficient μ of the clad or shield is calculated by the following formula (five),
I/I0＝BDe-μt(V)
And a substep 4, obtaining the average energy E of the gamma rays emitted by the radiation source by looking up a table according to the calculation result of the substep 3. The table of the lookup table may be a material section table, which is presented at pages 16-67 of ANSI/ANS 6.4.3, "Gamma-ray attenuation Coefficients and Buildup Factor for Engineering Materials", American Nuclear Society, 1991. In the invention, all the used radiation energy is calculated by using the average energy, and if the energy difference of different areas in the nuclear power plant is large, the area can be considered to be independently measured, namely the average energy is independently measured, and the radiation source intensity is independently measured.
In a preferred embodiment, the method for calculating the optical distance L comprises the sub-steps of a tracking the course of the gamma rays passing from the radiation source to the detection point, and recording the sequence of the gamma rays passing through the radiation zone, i.e. calculating the distance r from the radiation source to the detection point by ray tracing0→rpWherein r is0Indicating the position of the radiation source, indicating the position r of the detection spotp. And a substep b, respectively calculating the distance of each radiation area, and finally calculating the total optical distance L by combining the linear attenuation coefficient of the material of each radiation area.
Specifically, when the traveling distance of the gamma ray is calculated, the space is described by a combined geometric method, and the spaces of different media are divided into different regions. And respectively calculating the distance Di between the intersection point of the gamma ray and each basic body and the inlet and the distance Do between the intersection point of the gamma ray and each basic body and the outlet. All the basic body numbers plus and minus are found in each area, with "+" and "-", which may include the following six steps,
(1) each timeStarting point r of line0Determination of the region number Istart:
if there is no "-" element in a region, then all "+" elements in that region must satisfy the starting point r0In all "+" basis volumes, then the starting area of the ray can be considered to be that area; if there are "-" elements in the region, then all "+" elements in the region must satisfy the starting point r0In all "+" basis bodies, and all "-" basis bodies must satisfy the starting point r not containing the ray0Then the starting region of the ray is considered to be that region.
(2) End point r of each linepDetermination of the region number Ipend:
similarly, if there is no "-" element in a region, then all "+" elements in that region must meet the end point rpIn all "+" elementary volumes, then the ending area of the ray can be considered to be that area; if there are "-" elements in the zone, then all "+" elements in the zone must meet the end point rpIn all "+" basic bodies and all "-" basic bodies must satisfy the end point r not containing the raypThen the termination region of the ray is considered to be that region.
(3) Starting point r of each line0Determining the area outlet distance Zo corresponding to the area number:
if there is no "-" basic body in the gamma-ray starting region number, the smallest of the distances Do of taking out the basic bodies of all "+" in the starting region is the outlet distance of the gamma-ray starting region. If there are "-" basic bodies in the gamma-ray starting region, the minimum distance Do is taken out of all "+" basic bodies in the starting region, and then the minimum distance Di is taken out of all "-" basic bodies in the starting region, and the maximum value of the distances is taken as the outlet distance of the gamma-ray starting region.
(4) Determination of the number IP of each region through which the ray passes:
under the condition that the end point is not in the outermost zone, if no basic body exists in the zone number, firstly, judging adjacent sub-zones, and for all the plus basic bodies, when the inlet distance of the basic body is less than or equal to the inlet distance of the zone and less than the outlet distance of the basic body (Di < ═ Zin < Do), the zone is an adjacent zone of the previous zone, and solving a corresponding zone number IP; if the gamma ray area number has "-" basic bodies, the inlet distance of the basic bodies is less than or equal to the inlet distance of the area and less than the outlet distance (Di < ═ Zin < Do) of the basic bodies for all "+" basic bodies, and when the inlet distance of the basic bodies is greater than the inlet distance of the area or the outlet distance of the basic bodies is less than or equal to the inlet distance (Di > Zin or Do < ═ Zin) of the area for all "-" basic bodies, the area is the adjacent area of the previous area, and the corresponding area number IP is calculated.
(5) Determination of the entrance distance Zi and exit distance Zo of each zone traversed by the ray:
if there is no "-" basic body in the adjacent area, the outlet distance of the area is the minimum of the outlet distances Do of all "+" basic bodies, and the inlet distance of the area is the outlet distance of the previous area; if there is "-" basic body in the adjacent area, the smallest distance Do between the take-out ports of all "+" basic bodies is first determined, the smallest distance Di between the take-in ports of all "-" basic bodies is then determined, the largest value of the two distances is taken as the outlet distance of the area, and the inlet distance of the area is the outlet distance of the previous area.
(6) In the case that the end point is in the area of the outermost layer, firstly, finding all base body numbers aa of the outermost layer, and when the "+" base body in the area contains the base body aa and the "-" base body does not contain the area of the base body aa, finding whether the "-" base body exists, wherein the inlet distance of the "-" base body in the area is larger than the inlet distance (Di (k, minus (i, m)) > Zi (k, n)) of the area, if the "-" base body exists, taking the outlet distance of the area as the minimum of the inlet distances Di of all the "-" base bodies, and if the "-" base body does not contain the base body aa, taking the outlet distance of the area as.
Track to rpThe area IPend where the point is located and the ray exit distance is equal to the ray length. Thereby obtaining the traveling path of the gamma ray.
And then calculating the times of the ray passing through the area and the distance of each passing:
if the number of the passing area of the ray is not 0, the passing distance of the gamma ray in the area is equal to the distance of the inlet of the area minus the distance of the outlet of the area, and the passing times of the gamma ray is added with 1; if the passing area number of the gamma ray is 0, stopping tracking.
Gamma section mu is obtained by utilizing gamma mass attenuation coefficient and material of regional mediumn；
Through the above-mentioned process of recording the passing process of gamma ray passing through the area, the optical distance of each area is respectively calculated and then summed, namely:where N denotes the number of radiation areas, which is mainly determined by the environment inside the building.
In a preferred embodiment, the process of processing the over-determined equation set in step two by using the least square method and obtaining the radiation source intensity information comprises the following sub-steps:
substep 3-1. solving the overdetermined system of equationsExpressed in matrix form as AX ═ b;
substep 3-2, solving the normal equation A of the matrixTAX＝ATb, i.e. X ═ ATA)-1ATb；
Substep 3-3, solving equation by trigonometric decomposition of symmetric matrix, and recording G ═ ATA, wherein G is a symmetric matrix;
substeps 3-4, solving for G ═ LDL by trigonometric decompositionTWherein L is a small triangular matrix and D is a diagonal matrix;
substeps 3-5, solving the lower triangular matrix equation system LY1＝ATb；
Substeps 3-6, solving the diagonal matrix equation set: DY (DY)2＝Y1；
And substeps 3-7, solving an upper triangular matrix equation set: l isTX＝Y2。
Wherein X is (A)TA)-1ATb and Sj，0＝(ai，j T·ai，j)-1·ai，j T·DiCorrespondingly, the calculated value of the intensity of the radiation source is obtained through the substep 3-1 to the substep 3-7, and the least square method is a general overdetermined equation solving method in the field.
In a preferred embodiment, in step five, a linear fit is performed by the following equation (six),
(VI)
Wherein,represents the estimated dose rate;which is indicative of the slope of the estimate, the estimated intercept is represented as a function of,
n represents the maximum number of detectors i can reach,representing the calculated average value of the dose rate at the detector position,representing the average value of the dose rate detected by the detector.
In a preferred embodiment, after the linear fitting, the average uncertainty, the goodness of fit, the quality factor, the weighting function and the corresponding weight matrix of the linear fitting are obtained, respectively, and the quality factor represents the reliability of the current iteration calculation. In the fifth step, a weight function is obtained according to the uncertainty, and a weight matrix W is obtained through the weight function, wherein the weight matrix W is obtained through the following formula (seven),
(seven)
Where f represents the uncertainty of the fit,fia fit uncertainty representing an ith detector position;the mean fit uncertainty is represented as a function of,representing a weight function.
In a preferred embodiment, in step six, the judgment condition for obtaining the expected radiation source intensity information is when Si> 0, and the quality factor M reaches a maximum value, i.e. when SiAnd when the quality factor M reaches the maximum value, stopping the weighting iteration and outputting the radiation source intensity information, wherein the radiation source intensity information is the expected radiation source intensity finally obtained and is the radiation source intensity closest to the true value.
The invention aims to obtain the intensity of the radiation source closest to the true value, the reliability of the intensity of the radiation source obtained in the step three is low, and the error between the intensity of the radiation source and the true value is large, so in order to improve the accuracy of the value, namely to obtain the intensity of the radiation source closest to the true value, the invention provides the weighted iteration process from the step four to the step six, and finally sets the condition of iteration termination, so as to reduce the workload as much as possible under the condition of ensuring the accurate result, shorten the operation time and improve the efficiency of data acquisition. According to the weighted iteration method and the judgment standard of iteration termination. In addition, the intensity of the radiation source obtained by the method is more accurate than that obtained by a source item analysis method, is closer to a real value, and can ensure that the obtained value and the real value are within an order of magnitude. In a preferred embodiment, each time step six is executed, a quality factor M is obtained accordingly, which is obtained by the following formula (eight),
(eight)
Wherein R is2The goodness of fit is expressed,
in a preferred embodiment, the superFixed equation setIn the form of a matrix, see the following formula (nine)
(nine)
Wherein the error introduced by each detector is represented; considering the physical implications, the error caused at each detection point can be considered to be caused by the radiation source, and the above equation is simplified to the following equation (ten),
(ten) the steps of (a) and (b),
wherein S*Representing the intensity of the radiation source considering errors, P represents point, namely a point source, L represents line, namely a line source, k is used for representing the number of the line sources, and the line sources are numbered in sequence from j +1 to j + k; the coefficient matrix a can be found by the above formulai,jEquivalent to the dose response coefficient of the jth radiation source to the ith detector, the response coefficient of the discrete point source to the detector is
Q is 0 for point source point and 1 for line source line; that is, when the radiation source is a point source, q is 0, and when the radiation source is a line source, q is 1;
for a line source, the radiation source is discretized in spatial coordinates (A, B, C), and the response coefficient of the discrete point source to the detector is then
The above equation system becomes after being dispersed
For theWith a radiation source S* 1For example, the radiation source is scattered in one-dimensional space coordinates, thenCan be obtained by the following formula (eleven),
(eleven)
Wherein,
namely, it is
Wherein, XLRepresenting the discretized coordinates;the cosine constant is represented, and the value can be artificially input and is generally 0; l represents the discrete number, i.e. the number of parts into which the line source is divided when performing the discrete calculation by dividing the line source into several parts.
According to the invention, the composite radiation source strong backstepping system of the nuclear power plant point source and line source combination is provided, and is used for executing the composite radiation source strong backstepping method of the nuclear power plant point source and line source combination.
Preferably, the system comprises a detector, a gamma ray average energy calculation module and a radiation source intensity calculation module;
the detector is provided with a plurality of detectors, including a preset position detector and a nuclear power plant radiation value monitoring detector,
the preset position detector is arranged at a preset position with a determined distance from a radiation source in a radiation area of a nuclear power plant, and a detachable shielding layer is optionally coated outside the preset position detector; the distance of the predetermined position from the radiation source may appear as a known quantity in a subsequent calculation;
the preset position detector is used for transmitting the detected radiation dose rate information to the gamma ray average energy calculating module for calculating the average gamma ray energy;
the nuclear power plant radiation value monitoring detectors are distributed in the radiation area of the nuclear power plant, are respectively positioned at the key positions in the invention, and are used for transmitting the respectively detected dose rate information in the nuclear power plant to the radiation source intensity calculation module,
the gamma ray average energy calculating module is used for calculating the average energy E of gamma rays,
the radiation source intensity calculating module is used for calculating the intensity of the radiation source in the nuclear power plant.
Experimental example:
an NB281 room in a nuclear island of a unit of a nuclear power station No. 1 of a Bay great bay is taken as an experimental object, the room is a place for placing a radioactive wastewater collecting barrel in a nuclear island control area, the wastewater collecting barrel is a cylindrical container, and the intensity of an internal radioactive liquid source is 0.7586E +10MeV/cm3S (or 4.2898E + 14/s). The upper half part of the cylindrical container is simplified into 2 point sources, the lower half part is simplified into 2 line sources vertical to the bottom surface of the cylinder, and the waste is treatedOne detector is arranged at intervals of 50cm at the middle part of the water collecting barrel, and the detection values obtained by each detector are respectively 2.032mSv/hr, 0.685mSv/h, 0.255mSv/h, 0.1446mSv/h and 0.0929mSv/h, namely D in the invention1,D2,D3,D4,D5The average energy obtained by the average energy obtaining method and the average energy obtained by the average energy obtaining system provided by the invention is 1.3MeV, the source intensity of 2 points obtained by adopting the source intensity reverse pushing method and the source intensity reverse pushing system provided by the invention are 1.1037E +14MeV/s and 1.2694E +14MeV/s respectively, and the source intensity of 2 line sources is 1.1698E +12MeV/(cm.s) (or 0.9358E +14MeV/s) and 1.1766E +12MeV/(cm.s) (or 0.9413E +14MeV/s) respectively.
From the final result, the sum of the obtained four radiation intensities is basically consistent with the true value of the radiation intensity of the radiation source, so that the method and the system provided by the invention can obtain the radiation source intensity information close to the true value.
The present invention has been described above in connection with preferred embodiments, but these embodiments are merely exemplary and merely illustrative. On the basis of the above, the invention can be subjected to various substitutions and modifications, and the substitutions and the modifications are all within the protection scope of the invention.
Claims (10)
1. A composite radiation source strong backward pushing method of a point source and line source combination in a nuclear power plant is characterized by comprising the following steps:
step one, detecting dose rate D in a nuclear power plant by using a detector1,D2,D3…Di；
Step two, establishing an overdetermined equation set containing the radiation source intensity as shown in the following formula (one) according to the detected dose rate information,
(A)
Wherein the coefficient matrix a of the over-determined equation seti,jObtained by the following formulae (II) and (III),
(II)
(III);
in equation (iii), q is 0 when the radiation source is a point source, and q is 1 when the radiation source is a line source;
step three, processing the overdetermined equation set in the step two by a least square method to obtain the intensity information of the radiation source shown in the following formula (four),
Sj,0＝(aj,i·ai,j)-1·aj,i·Di(IV);
wherein D isiIndicating the dose rate detected by the ith detector; j represents the number of radiation sources; m represents the maximum value which can be reached by the number of radiation sources; sjRepresents the intensity of the jth radiation source; sj,0Representing the intensity of the jth radiation source for which the initial calculation was not iterated; a isi,jRepresenting a coefficient matrix which is the dose response coefficient of the jth radiation source to the ith detector;representing a line source dispersion coefficient; l isjRepresents a discrete number of jth radiation sources, the discrete number being 1 when the radiation source is a point source;representing normalized discrete source intensity; BD (E, L (. mu. (E), r)0→rp) Indicating an accumulation factor, E and L (. mu. (E), r)0→rp) A function of (a); l (. mu.E, r)0→rp) Denotes an optical distance, is μ (E) and r0→rpA function of (a); μ (E) represents a cross-sectional/linear attenuation coefficient; r is0→rpRepresenting the distance of the radiation source to the detection point; c (E) represents a flux-dose conversion factor, which is a function of E; e represents the energy, which is the average energy of gamma rays emitted by a radiation source in a nuclear power plant.
2. The method of strongly backward pushing from a source of composite radiation combined with a point source of nuclear power plant as claimed in claim 1, wherein after step three, the method further comprises the steps of,
step four, calculating the dose rate D 'at the position of the detector according to the radiation source intensity information obtained in the step three'1,D′2,D′3…D′i；
And step five, performing 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 dose rate information and the dose rate information after fitting, and further obtain fitting parameters, wherein the fitting parameters comprise: average uncertainty, goodness-of-fit and corresponding weight matrix;
step six, iterating the weight matrix obtained in the step five to the overdetermined equation set in the step two to obtain a weighted overdetermined equation, and further repeating the step two, the step three and the step four until expected radiation source intensity information is obtained;
wherein, D'iRepresenting the calculated dose rate at the i-th detector position.
3. The method for strongly backward pushing a composite radiation source of a nuclear power plant point source and line source combination according to claim 1, wherein the method for calculating the average energy E of gamma rays emitted by a radiation source in the nuclear power plant comprises the following sub-steps:
substep 1, selecting a preset position in a nuclear power plant, wherein the preset position is at a distance t from a radiation source, placing a detector at the preset position, and collecting the dose rate I detected by the detector0，
Substep 2, retrieving the detector, covering a shielding layer on the outside of the detector, placing the detector at the preset position, and collecting the dose rate I detected by the detector;
or, the detector is taken back, a shielding body is placed at a preset position, then the detector is placed in the shielding body, and the dosage rate I detected by the detector is collected;
substep 3, I and I obtained according to substeps 1 and 20The mass attenuation coefficient μ of the clad or shield is calculated by the following formula (five),
I/I0＝BDe-μt(V)
And a substep 4 of obtaining the average energy E of the gamma rays emitted by the radiation source according to the calculation result of the substep 3.
4. The method of strongly backward pushing a composite radiation source of a nuclear power plant point source combination according to claim 1, wherein the method of calculating the optical distance L comprises the sub-steps of,
a sub-step a of tracking the passing process of the gamma ray from the radiation source to the detection point, recording the sequence of the gamma ray passing through the radiation region,
and a substep b, respectively calculating the distance of each radiation area, and finally calculating the total optical distance L by combining the linear attenuation coefficient of the material of each radiation area.
5. The method for strongly backward pushing the composite radiation source of the nuclear power plant point source and line source combination according to claim 1, wherein the overdetermined equation set in the second step is processed by using a least square method, and the process of obtaining the intensity information of the radiation source comprises the following sub-steps:
substep 3-1. solving the overdetermined system of equationsExpressed in matrix form as AX ═ b;
substep 3-2, solving the normal equation A of the matrixTAX＝ATb, i.e. X ═ ATA)-1ATb；
Substeps 3-3Solving equation by trigonometric decomposition of symmetric matrix, and recording G as ATA, wherein G is a symmetric matrix;
substeps 3-4, solving for G ═ LDL by trigonometric decompositionTWherein L is a small triangular matrix and D is a diagonal matrix;
substeps 3-5, solving the lower triangular matrix equation system LY1＝ATb；
Substeps 3-6, solving the diagonal matrix equation set: DY (DY)2＝Y1；
And substeps 3-7, solving an upper triangular matrix equation set: l isTX＝Y2。
6. The method for strongly backward pushing a composite radiation source of a nuclear power plant point source combination according to claim 2, is characterized in that in the fifth step, a linear fitting is performed by the following formula (six),
(VI)
Wherein,represents the estimated dose rate;which is indicative of the slope of the estimate, the estimated intercept is represented as a function of,
n representsThe maximum value that can be reached by the number i of detectors,representing the calculated average value of the dose rate at the detector position,representing the average of the dose rate detected by the detector.
7. The method for strongly backward pushing a composite radiation source of a nuclear power plant point source and line source combination is characterized in that in the fifth step, a weight function is obtained according to uncertainty, and then a weight matrix W is obtained through the weight function, wherein the weight matrix W is obtained through the following formula (seven),
(seven)
Where f represents the uncertainty of the fit, the mean fit uncertainty is represented as a function of,fia fit uncertainty representing an ith detector position;representing a weight function.
8. The method of claim 6, wherein the composite radiation source comprises a nuclear power plant point source and a nuclear power plant point source,
in step six, when SiGreater than 0, and quality factorStopping the weighted iteration when the number M reaches the maximum value, and outputting the intensity information of the radiation source, wherein the output intensity information of the radiation source is the expected intensity information of the radiation source;
wherein, each time step six is executed, a quality factor M is obtained correspondingly, the quality factor M is obtained by the following formula (eight),
(eight)
Wherein R is2The goodness of fit is expressed,
9. a composite radiation source strong backstepping system of a nuclear power plant point source and line source combination is characterized by being used for executing the composite radiation source strong backstepping method of the nuclear power plant point source and line source combination according to claims 1-8.
10. The system of claim 9, comprising a detector, a gamma ray mean energy calculation module, and a radiation source intensity calculation module;
the detector is provided with a plurality of detectors, including a preset position detector and a nuclear power plant radiation value monitoring detector,
the preset position detector is arranged at a preset position with a determined distance from a radiation source in a radiation area of a nuclear power plant, and a detachable shielding layer is optionally coated outside the preset position detector;
the preset position detector is used for transmitting the detected radiation rate information to the gamma ray average energy calculating module,
the nuclear power plant radiation value monitoring detectors are distributed in a radiation area of the nuclear power plant and used for transmitting respectively detected dose rate information in the nuclear power plant to the radiation source intensity calculating module,
the gamma ray average energy calculating module is used for calculating the average energy E of gamma rays,
the radiation source intensity calculating module is used for calculating the intensity of the radiation source in the nuclear power plant.
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