Method for detecting boron distribution in a deposit of oxidized corrosion products

Abstract

A method for detecting the distribution of boron in the oxidation corrosion product deposition layer, using the prompt gamma activation technology to detect the total mass of boron elements inside the oxidation corrosion product deposition layer; according to the neutron radiography to obtain the geometric boundary of the corrosion product deposition layer, according to the Compton scattering information generated by the interaction of the prompt gamma rays generated by the oxidation corrosion product and the Compton radiography unit, the Compton cone is constructed within the geometric boundary obtained by neutron radiography, the origin of the gamma ray is reconstructed, and the pixelized image reconstruction is carried out by using the random origin set algorithm, the distribution image generated by the gamma ray is obtained, and the proportional distribution of the boron element in the oxidation corrosion product deposition layer is obtained. According to the obtained total concentration of boron element and the proportional distribution of boron element, the concentration distribution of boron element in the oxidation corrosion product deposition layer is calculated, which improves the existing method which can only measure the distribution of boron element in the limited depth of the surface of the corrosion product deposition layer and cannot obtain the internal element distribution information.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear reactor control, and particularly relates to a method for detecting boron distribution in an oxidation corrosion product deposition layer. BACKGROUND

[0002] Fe, Ni and other oxidation corrosion products in the primary loop of a pressurized water reactor are deposited on the surface of fuel cladding at the top of the reactor core, forming a thin oxidation corrosion product deposition layer. The oxidation corrosion product deposition layer has a loose porous structure, and boron is concentrated under the effect of boiling enhancement, and lithium borate with a negative temperature solubility coefficient is precipitated, resulting in uneven distribution of boron in the deposition layer. Since 10 B has a significant neutron absorption capacity, and the adsorption of boron in the corrosion product deposition layer will cause the core power distribution to deviate towards the bottom of the core, causing axial power deviation. The existing technology for detecting the boron distribution in the deposition layer extracts the fuel assembly in the reactor after shutdown to the outside of the reactor to prepare an oxidation corrosion product deposition layer sample for electron microscope (SEM) microscopic characterization and energy spectrum (EDS) element analysis, but such a method can only measure the boron element distribution in the limited depth of the surface of the corrosion product deposition layer, and cannot obtain the internal element distribution information. SUMMARY

[0003] The present application aims at the deficiency in the prior art that only the boron element distribution on the surface of the deposition layer can be characterized by the energy spectrum, and the distribution information of boron elements in the internal deposition layer cannot be accurately obtained, and proposes a method for detecting the boron distribution in the oxidation corrosion product deposition layer, which can obtain the boron element distribution in the internal oxidation corrosion product deposition layer.

[0004] The present application is realized by the following technical solutions:

[0005] The present application relates to a method for detecting the boron distribution in an oxidation corrosion product deposition layer, which first uses the prompt gamma activation technology to detect the total mass of boron elements in the internal oxidation corrosion product deposition layer, secondly uses the neutron radiography technology to obtain the thickness information of the oxidation corrosion product deposition layer and determine the calculation boundary, thirdly constructs a Compton cone in the calculation boundary confirmed by the neutron radiography technology according to the Compton scattering information generated by the interaction of the prompt gamma rays generated by the oxidation corrosion product and the Compton radiography unit, reconstructs the origin of the gamma rays, and then adopts the random origin set algorithm to reconstruct the pixelized image, obtains the distribution image generated by the gamma rays to obtain the proportional distribution of boron elements in the oxidation corrosion product deposition layer, and finally calculates the concentration distribution of boron elements in the oxidation corrosion product deposition layer according to the obtained total concentration and proportional distribution.

[0006] The prompt gamma activation technology refers to: the boron-containing oxidation corrosion product deposition layer is irradiated in a cold neutron beam, the neutron beam reacts with the nuclides in the thickness direction of the deposition layer and releases gamma rays, and the intensity of the characteristic gamma rays is determined by a high-purity germanium detector 10 The mass of B is specifically: the count rate of the characteristic gamma rays generated by each gram of boron element is , wherein: N A is the Avogadro constant; Q is the 10 capture cross section of the isotope of B; B is the isotope abundance of B; sigma is the neutron capture cross section; Phi is the neutron fluence rate; Gamma is the gamma ray yield; epsilon(E) is the detection efficiency of the gamma ray with energy E; and M is the atomic weight.

[0007] The Compton scattering information refers to: after the cold neutron beam irradiates the corrosion product deposition layer, the generated gamma rays undergo Compton scattering with the detector material in the Compton camera unit, the position of the scattering and the deposited energy are recorded in pixels, and comprehensive information is formed.

[0008] The construction of the origin of the Compton cone reconstructed gamma rays refers to: after the gamma rays undergo Compton scattering, the changes in energy and scattering angle satisfy: , wherein: E and E' respectively refer to the energy of the gamma rays before and after scattering, theta is the scattering angle, m e is the rest mass of an electron, and c is the speed of light. The direction of the scattered gamma rays, the energy before and after scattering, and the position where the scattering occurs are measured, the scattering angle is derived, and a cone with the scattering direction as the axis and the scattering position as the top of the cone is constructed, and the origin of the gamma rays is on the cone surface.

[0009] The random origin set algorithm refers to: dividing the reconstruction volume into voxels. Representative points on the origin cone cross section are randomly selected in the pre-defined image reconstruction volume, and a distribution histogram of the representative points is created as the radiation probability density of the prompt gamma rays. As the algorithm iteration proceeds, new representative points are generated on the prompt gamma ray origin cone, and the new prompt gamma ray radiation probability density is calculated. The updated representative point prompt gamma ray radiation probability density is compared until the iteration number or the preset convergence condition is met.

[0010] The present application relates to a kind of system for realizing the above-mentioned method, including: high purity germanium gamma ray detection unit, neutron radiography unit, Compton radiography unit and random origin collection unit, wherein: high purity germanium gamma ray detection unit is according to the prompt gamma ray generated in corrosion product deposition layer, carries out each element characteristic peak detection processing, obtains the total mass of B element after removing background interference and other factors;Neutron radiography unit carries out neutron imaging to sample, obtains the thickness of corrosion product deposition layer, provides the preset reference boundary of calculation for random origin collection algorithm;Compton radiography unit is according to the Compton scattering information recorded after the Compton scattering of gamma ray generated in corrosion product deposition layer and detector, constructs Compton cone, reconstructs the Compton cone of several sampling points of gamma ray origin;Random origin collection unit carries out the processing of pixelization reconstruction of gamma ray origin according to each Compton cone information, obtains the three-dimensional image generated by gamma ray, and then obtains the three-dimensional mass distribution result of boron element.

[0011] Technical effects

[0012] The present application combines prompt gamma activation technology, neutron radiography technology, Compton radiography unit and random origin algorithm, realizes the online measurement of boron element mass distribution in oxidation corrosion deposition layer.Compared with prior art, the present application can measure the boron element distribution in the entire deposition layer, improves the prior art that can only measure the boron element distribution in the limited depth of the surface of corrosion product deposition layer, and cannot obtain the internal element distribution information. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a schematic diagram of the principle of the present application;

[0014] Figure 2 It is the gamma spectrum measured for sample 0# of embodiment;

[0015] Figure 3 It is the gamma spectrum measured for sample 1# of embodiment;

[0016] Figure 4 It is the gamma spectrum measured for sample 2# of embodiment;

[0017] Figure 5 It is the actual sample of sample 1# (left) and sample 2# (right) of embodiment;

[0018] Figure 6 It is the imaging result of sample 1# of embodiment (the right side is local enlarged view);

[0019] Figure 7 It is the imaging result of sample 2# of embodiment (the right side is local enlarged view);

[0020] Figure 8 It is a schematic diagram of gamma ray Compton cone reconstruction;

[0021] Figure 9 Flow chart of random origin combination algorithm;

[0022] Figure 10 Resulting image of reconstructed gamma-ray source by random origin combination algorithm. DETAILED DESCRIPTION

[0023] As Figure 1 shown, the present embodiment relates to a method for detecting boron distribution in an oxide corrosion product deposition layer, comprising:

[0024] Step 1, irradiate the sample with a neutron beam by placing the sample of the oxide corrosion product deposition layer containing boron in the neutron beam. Due to the high penetration ability of neutrons, the neutron beam will react with the deposition layer, i.e. the sample in the thickness direction 10 B atomic nuclei, i.e. 10 B(n, α) 7 Li*, excited state 7 Li* decays to generate gamma rays with an energy of about 478 keV, and the intensity of the characteristic gamma rays is detected by a high-purity germanium detector to determine 10 the total amount of B, specifically including:

[0025] 1.1 Prepare the sample of the oxide corrosion product deposition layer containing boron elements, i.e. the samples 0#, 1# and 2# of the oxide corrosion product deposition layer not containing boron as the background.

[0026] 1.2 To avoid measurement deviations caused by factors such as changes in beam intensity during measurement, positioning errors of the beam and the sample, etc., the relative measurement method is used for boron elements, i.e. by simultaneously measuring the prompt gamma (selecting 465 keV gamma rays) intensity of Ni elements in the oxide corrosion product deposition layer sample to measure the mass ratio of B / Ni.

[0027] 1.3 Since Ni elements exist not only in the oxide corrosion product deposition layer but also in the cladding material at the bottom of the oxide corrosion product deposition layer, therefore, the Cr element which only exists in the cladding material needs to be selected as a relative monitor to correct the differences caused by factors such as changes in neutron beam intensity during measurement, positioning errors, etc. when measuring different samples.

[0028] As Figures 2-4 the characteristic peak of gamma rays with an energy of 835 keV is the prompt gamma rays generated by Cr elements. According to Figures 2-4 fitting, the count rates of gamma rays of the three samples are obtained, as shown in Table 1. 1.

[0029] Table 1 Count rates of gamma rays

[0030]

[0031] 1.4 The count rates of B (478 keV) and Ni (465 keV) in samples 1# and 2# were corrected respectively with the gamma ray count rate of sample 0# Cr as the reference value, and the results are shown in Table 2. 2.

[0032] Table 2 Corrected gamma ray count rates

[0033]

[0034] Since the energies of 478 keV and 465 keV are similar, it is approximately considered that the detection efficiencies of the gamma ray high-purity germanium detector for the two are equal, and thus the mass ratio of B to Ni in each sample can be calculated by m B / m Ni =(M B C B / σ B ) / (M Ni C Ni / σ Ni ), and the obtained results are the relative values of the total amount of boron element in the oxidation corrosion product deposition layer, as shown in Table 3.

[0035] Table 3 B / Ni mass ratio

[0036]

[0037] Step 2, the oxidation corrosion product deposition layer is photographed by using neutron photography to obtain its thickness data as the geometric boundary of the Compton photography unit and the random origin set unit.

[0038] As shown in Figure 5 , it is the oxidation corrosion product deposition layer (deposited on the surface of the fuel rod cladding), and the imaging field of view is about 6.9 cm x 6.9 cm, and the single-pixel size is about 3.375 μm. As shown in Figure 6 and 7 , by improving the resolution of the imaging system, the thickness of the oxidation corrosion product deposition layer can be clearly observed, which is about 64 μm and 47 μm respectively.

[0039] Step 3, as shown in Figure 8 , the scattering position and deposited energy of the Compton scattering between the prompt gamma rays and the detector material in the anti-Compton gamma measurement system are recorded by the Compton photography unit, so as to construct a Compton cone to reconstruct the origin of the gamma rays, specifically: the scattering angle is solved according to the scattering position, scattering direction and deposited energy before and after scattering, a Compton cone is constructed with the scattering direction as the axis, the scattering position as the cone top and 2 times the scattering angle as the top angle, so as to determine the position range of the gamma ray origin.

[0040] Step 4, asFigure 9 The pixelated image reconstruction is performed by using the random origin set algorithm to obtain the distribution of boron elements in the deposition layer of the oxidized corrosion product, and the spatial distribution of boron elements in the deposition layer is identified, which specifically includes:

[0041] 4.1 Randomly select a representative point r in the Compton cone of the origin of each gamma ray on the cone surface and the simulated body i ;

[0042] 4.2 Calculate the origin probability density: form a 3D histogram H spanning the entire volume for estimating the probability of the origin of the gamma ray at point x, and voxelize the simulated body. Fill the 3D histogram H with points r i to r x , and then normalize it to 1 to obtain the probability density of the origin of the gamma ray.

[0043] 4.3 Iteratively update the representative point for each cone of the origin of the gamma ray, which specifically includes:

[0044] a. Find a new point: randomly select a new representative point b on the surface and inside the simulated body i ; estimate r(b i ) and r(r i ) using the 3D histogram H in step 4.2 and generate a uniformly distributed random number UE∈[0,1];

[0045] b. If r(b i ) / [r(r i )-1 / N]>U, set r i =b i , otherwise keep the original representative point r i , where N is the number of gamma origin cones, and U is a uniformly distributed random number.

[0046] c. Update the probability density: update the 3D histogram H by subtracting 1 / N from the voxels containing the previous r i , and adding 1 / N to the count of the voxels containing the new r i .

[0047] d. After N iterations, the representative points r i to r N are obtained for generating the distribution image of the gamma ray generation.

[0048] 4.4 Build a three-dimensional space grid according to the real geometric boundary obtained in step 2, and for each point r i , accumulate the contribution of the voxel it is in according to the histogram H calculated in step 4.3, to obtain a three-dimensional pseudo-color image V(x,y,z), and the larger the value, the higher the origin probability.

[0049] As Figure 10 shown, the gamma ray source position and intensity reconstructed by the random origin set algorithm is highly consistent with the actual source, which embodies the accuracy of the random origin set algorithm in characterizing the boron concentration and its distribution in the oxidation corrosion product deposition layer.

[0050] The above specific embodiments can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present application, the protection scope of the present application is subject to the claims and is not limited by the above specific embodiments, and each implementation scheme within the scope is subject to the present application.

Claims

1. A method for detecting the distribution of boron in a deposit layer of an oxidation corrosion product, characterized in that Firstly, the total mass of boron element in the oxidation corrosion product deposition layer is detected by using the prompt gamma activation technology; secondly, the thickness information of the oxidation corrosion product deposition layer is obtained by using the neutron radiography technology to determine the calculation boundary; thirdly, the Compton scattering information generated by the interaction between the prompt gamma rays generated by the oxidation corrosion product and the Compton radiography unit is used to construct the Compton cone within the calculation boundary confirmed by the neutron radiography technology, the origin of the gamma rays is reconstructed, the pixelized image reconstruction is performed by using the random origin set algorithm, the distribution image generated by the gamma rays is obtained to obtain the proportional distribution of the boron element in the oxidation corrosion product deposition layer; finally, the concentration distribution of the boron element in the oxidation corrosion product deposition layer is calculated according to the obtained total concentration and proportional distribution. The calculation boundary refers to that the thickness data of the oxidation corrosion product deposition layer is obtained by taking a neutron radiograph to serve as the geometric boundary for the calculation of the Compton radiography unit and the random origin set unit. The Compton scattering information refers to that after the cold neutron beam is irradiated to the corrosion product deposition layer, the Compton scattering of the generated gamma rays is recorded in pixels to form the comprehensive information.

2. The method of claim 1, wherein the method is characterized by: The aforementioned instantaneous gamma activation technology refers to irradiating a boron-containing oxide corrosion product deposit layer with a cold neutron beam. The neutron beam reacts with nuclides along the thickness direction of the deposit layer, releasing gamma rays. The intensity of the characteristic gamma rays is then determined using high-purity germanium detectors. 10 The mass of B, specifically: the characteristic gamma-ray count rate produced per gram of boron. , where: N A Avogadro's constant; Q is the number of captured neutrons. 10 B isotopic abundance; σ is neutron capture cross section; Φ is neutron fluence rate; Γ is gamma-ray yield; ε(E) is the detection efficiency of gamma rays with energy E; M is atomic weight.

3. The method of claim 1, wherein the method is characterized by: The origin of the Compton cone reconstruction gamma ray is that after the Compton scattering of the gamma ray, the energy and scattering angle change satisfy: , wherein E and E' respectively indicate the energy of the gamma ray before and after scattering, θ is the scattering angle, m e is the rest mass of the electron, and c is the speed of light; the direction of the scattered gamma ray, the energy before and after scattering, and the position where the scattering occurs are measured, the scattering angle is derived, a cone with the scattering direction as the axis and the scattering position as the top of the cone is constructed, and the origin of the gamma ray is on the cone surface.

4. The method of claim 1, wherein the method is characterized by: The random origin set algorithm refers to that the reconstruction volume is divided into voxels; the representative points on the origin cone section are randomly selected in the predefined image reconstruction volume, and the distribution histogram of the representative points is created as the radiation probability density of the prompt gamma rays; With the iteration of the algorithm, new representative points are generated on the prompt gamma ray origin cone, and the new prompt gamma ray radiation probability density is calculated; the updated representative point prompt gamma ray radiation probability density is compared until the iteration number or the preset convergence condition is met.

5. A system for detecting the distribution of boron in an oxide corrosion product layer that implements the method of any one of claims 1-4, wherein, It comprises: a high-purity germanium gamma ray detection unit, a neutron radiography unit, a Compton radiography unit and a random origin set unit, wherein: the high-purity germanium gamma ray detection unit detects the characteristic peaks of each element according to the prompt gamma rays generated in the corrosion product deposition layer to obtain the total mass of the B element after removing the background interference factors; the neutron radiography unit performs neutron imaging on the sample to obtain the thickness of the corrosion product deposition layer to provide the reference boundary for the random origin set algorithm; the Compton radiography unit records the Compton scattering information after the Compton scattering of the gamma rays generated by the corrosion product deposition layer and the detector to perform the processing of constructing the Compton cone to reconstruct the origin of the gamma rays to obtain the Compton cone of a plurality of sampling points; the random origin set unit performs the processing of pixelized reconstruction of the origin of the gamma rays according to the Compton cone information to obtain the three-dimensional image generated by the gamma rays and further obtain the three-dimensional mass distribution result of the boron element.

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