Method for detecting boron distribution in oxidation corrosion product deposition layer

Abstract

The invention relates to a method for detecting boron distribution in an oxidation corrosion product deposition layer. The total mass of boron in the oxidation corrosion product deposition layer is detected by utilizing an instantaneous gamma activation technology; the method comprises the following steps: obtaining a geometric boundary of a deposition layer of a corrosion product according to neutron photography, constructing a Compton cone in the geometric boundary obtained by neutron photography according to instant gamma rays generated by the oxidation corrosion product and Compton scattering information generated by the action of a Compton photography unit, and reconstructing the origin of the gamma rays; and carrying out pixelated image reconstruction by adopting a random origin set algorithm to obtain a distribution image generated by gamma rays so as to obtain the proportional distribution of the boron element in the oxidation corrosion product deposition layer. According to the obtained total boron element concentration and boron element proportion distribution, boron element concentration distribution in the oxidation corrosion product deposition layer is calculated, and the defects that only boron element distribution in the limited depth of the surface of the corrosion product deposition layer can be measured and internal element distribution information cannot be obtained in an existing method are overcome.

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 whole deposition layer, improves the prior art that can only measure the boron element distribution in the limited depth of corrosion product deposition layer surface, and cannot obtain internal element distribution information. ACCURACY

[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 the random origin combination algorithm;

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

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

[0024] Step 1, by placing the sample of the oxide corrosion product deposition layer containing boron in the cold neutron beam, the neutron beam irradiates the sample. 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 high-purity germanium 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 changes in neutron beam intensity, positioning errors, etc. during the measurement of 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 the gamma rays of the three samples are obtained, as shown in Table 1. 1.

[0029] Table 1 Count rates of the gamma rays

[0030] 1.4 Using the gamma-ray count rate of sample 0# Cr as a reference value, the count rates of B (478 keV) and Ni (465 keV) in samples 1# and 2# were corrected, respectively. The results are as follows: As shown in Figure 2.

[0031] Table 2 Corrected Gamma ray count rate

[0032] Since the energies of 478 keV and 465 keV are similar, it can be approximated that the detection efficiency of the high-purity germanium gamma-ray detector is equal for both. Therefore, the mass ratio of B to Ni in each sample can be determined by m. B / m Ni =(M B C B / σ B ) / (M Ni C Ni / σ Ni The results were calculated to obtain the relative values ​​of the total boron content in the oxidative corrosion product deposit layer, as shown in Table 3.

[0033] Table 3 B / Ni mass ratio

[0034] Step 2: Use neutron radiography to photograph the oxide corrosion product deposit layer to obtain its thickness data, which is used as the geometric boundary for the Compton radiograph unit and the random origin set unit calculation.

[0035] like Figure 5 The image shown is a physical sample of the oxidation and corrosion product deposit (deposited on the surface of the fuel rod cladding). The photographic field of view is approximately 6.9 cm × 6.9 cm, and the single pixel size is approximately 3.375 μm. Figure 6 and 7 As shown, by increasing the resolution of the imaging system, the thicknesses of the oxidative corrosion product deposits can be clearly observed to be approximately 64 μm and 47 μm, respectively.

[0036] Step 3, as follows Figure 8 As shown, the Compton scattering position and deposition energy of the instantaneous gamma rays and the detector material in the anti-Compton gamma measurement system are recorded by the Compton photographic unit, thereby constructing a Compton cone to reconstruct the origin of the gamma rays. Specifically, the scattering angle is solved based on the scattering position, scattering direction and deposition energy before and after scattering, and a Compton cone is constructed with the scattering direction as the axis, the scattering position as the cone apex and twice the scattering angle as the vertex angle, thereby determining the location range of the gamma ray origin.

[0037] Step 4, as follows Figure 9As shown, 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:

[0038] 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 ;

[0039] 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.

[0040] 4.3 Update the representative point for each cone of the origin of the gamma ray iteratively, which specifically includes:

[0041] 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];

[0042] 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.

[0043] c. Update the probability density: update the 3D histogram H by subtracting 1 / N from the voxel containing the previous r i , and adding 1 / N to the count of the voxel containing the new r i .

[0044] d. After N iterations, the representative points r i to r N are obtained for generating the distribution image of the gamma ray generation.

[0045] 4.4 According to the true geometric boundary obtained in step 2, establish a three-dimensional space grid, and according to the histogram H calculated in step 4.3, accumulate the contribution of each point r i in the voxel it is located in to obtain a three-dimensional pseudo-color image V(x, y, z), and the larger the value, the higher the origin probability.

[0046] AsFigure 10 As shown, the reconstructed gamma ray source positions and intensities by the random origin set algorithm are 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.

[0047] 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 within the scope is subject to the present application.

Claims

1. A method for detecting boron distribution within an oxide corrosion product deposit layer, characterized in that, First, the total mass of boron within the oxide corrosion product deposit layer was detected using transient gamma activation technology. Second, neutron radiography was used to obtain the thickness information of the oxide corrosion product deposit layer and determine the calculation boundary. Third, based on the Compton scattering information generated by the interaction between the transient gamma rays generated by the oxide corrosion products and the Compton radiography unit, a Compton cone was constructed within the calculation boundary confirmed by neutron radiography to reconstruct the origin of the gamma rays. Then, a random origin set algorithm was used for pixelated image reconstruction to obtain the distribution image of gamma ray generation, thereby obtaining the proportional distribution of boron within the oxide corrosion product deposit layer. Finally, based on the obtained total concentration and proportional distribution, the boron concentration distribution within the oxide corrosion product deposit layer was calculated.

2. The method for detecting boron distribution in the oxide corrosion product deposit layer according to claim 1, characterized in that, 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 for detecting boron distribution in the oxide corrosion product deposit layer according to claim 1, characterized in that, The Compton scattering information refers to the comprehensive information formed by the Compton scattering of gamma rays generated after a cold neutron beam irradiates the corrosion product deposit layer, and the location of the scattering and the energy of the deposit are recorded pixel by pixel.

4. The method for detecting boron distribution in the oxide corrosion product deposit layer according to claim 1, characterized in that, The aforementioned construction of the Compton cone to reconstruct the origin of gamma rays refers to the following: after the gamma rays undergo Compton scattering, the changes in energy and scattering angle satisfy the following: Where: E and E' refer to the energies of the gamma rays before and after scattering, respectively; θ is the scattering angle; m e Let c be the electron's rest mass and c be the speed of light. By measuring the direction of the scattered gamma rays, their energy before and after scattering, and the location where scattering occurs, the scattering angle can be derived. Thus, a cone with the scattering direction as its axis and the scattering location as its apex can be constructed. The origin of the gamma rays is on the surface of this cone.

5. The method for detecting boron distribution in the oxide corrosion product deposit layer according to claim 1, characterized in that, The aforementioned random origin set algorithm refers to: dividing the reconstructed volume into voxels; randomly selecting representative points on the origin cone section within a predefined image reconstructed volume, and creating a distribution histogram of the representative points as the radiation probability density of the transient gamma rays; As the algorithm iterates, new representative points are generated on the transient gamma-ray origin cone, and new transient gamma-ray radiation probability densities are calculated. The transient gamma-ray radiation probability densities of the updated representative points are compared until the number of iterations or the preset convergence condition is met.

6. A system for detecting boron distribution in an oxidation corrosion product deposition layer that implements the method of any one of claims 1-5, characterized in that, include: The system comprises a high-purity germanium gamma-ray detection unit, a neutron radiography unit, a Compton radiography unit, and a random origin ensemble unit. Specifically: the high-purity germanium gamma-ray detection unit detects and processes the characteristic peaks of each element based on the transient gamma rays generated in the corrosion product deposit layer, obtaining the total mass of element B after removing background interference and other factors; the neutron radiography unit performs neutron imaging on the sample to obtain the thickness of the corrosion product deposit layer, providing a reference boundary for the random origin ensemble algorithm; the Compton radiography unit constructs Compton cones to reconstruct the gamma-ray origin based on the Compton scattering information recorded after the gamma rays generated in the corrosion product deposit layer undergo Compton scattering with the detector, obtaining Compton cones at several sampling points; and the random origin ensemble unit performs pixel-based reconstruction of the gamma-ray origin based on the Compton cone information, obtaining a three-dimensional image of the gamma-ray generation, and thus the three-dimensional mass distribution of element boron.

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