Fuel element detection method and system based on neutron imaging and activation analysis

Abstract

The invention relates to the technical field of nondestructive testing of element content and uniformity of fuel elements, and provides a fuel element detection method and system based on neutron imaging and activation analysis. The detection method comprises the following steps: S1, installing a to-be-detected sample, and adjusting an imaging collimation hole to be aligned with a neutron beam current of a neutron source; s2, the thermal neutrons are collimated by the imaging collimation hole and then transmit the to-be-detected sample, and spatial distribution of uranium and poison elements of the to-be-detected sample is obtained through detection of a neutron imaging detector; s3, selecting a specific target area, switching the activation analysis collimation hole to align to a neutron beam of the neutron source, and adjusting the position of the to-be-detected sample, so that the specific target area aligns to the neutron beam of the neutron source; thermal neutrons bombard a specific target area after being collimated by the activation collimation hole, and are received by the gamma ray detector so as to analyze and obtain the element content of the specific target area. According to the method, distribution and content of uranium and toxic elements in the fuel element can be rapidly and accurately determined on the premise of nondestructive testing.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for the elemental content and uniformity of fuel elements. Specifically, it provides a fuel element testing method and system based on neutron imaging and activation analysis. Background Technology

[0002] With the development of nuclear power and nuclear propulsion technology, higher requirements are being placed on the operational lifespan and safety of fuel elements. The content and distribution of uranium and poison elements in fuel elements directly affect the efficiency and safety of the reactor, making it crucial to strictly control the content and distribution of uranium and poison elements in fuel elements.

[0003] Currently, the main methods for detecting the content and distribution of uranium and poison elements in fuel elements include chemical analysis, mass spectrometry, X-ray fluorescence analysis (XRF), and laser-induced breakdown spectroscopy (LIBS). These methods are mostly destructive analytical methods, and the detection process is complicated, which cannot meet the requirements of nuclear fuel element production.

[0004] Chinese patent CN111982940 A discloses a thermal neutron transmission imaging method and device based on a compact neutron source. Specifically, it discloses using a compact neutron source to provide external neutrons, which are then slowed down into thermal or ultrathermal neutrons by a neutron moderator. After slowing, the neutrons enter a neutron collimation channel, and the collimated thermal neutron beam is transmitted through the object being tested. The thermal neutrons passing through the object are detected by a thermal neutron image detector system, which converts them into a digitized transmission image, obtaining a two-dimensional spatial distribution of thermal neutron transmission intensity. This allows for the acquisition of the internal structure of the object and the spatial distribution of different materials. While this technology can obtain the elemental distribution of the object, it cannot determine the specific content of each element, nor can it rapidly and simultaneously determine the distribution and content of uranium and poison elements in fuel elements.

[0005] Chinese patent CN108918565A discloses a sample elemental distribution measurement device and method based on transient gamma-ray neutron activation analysis technology. Specifically, it discloses the use of a neutron generator to produce neutrons, which are then slowed down to obtain thermal neutrons. After collimation, a neutron beam is formed and used to bombard the sample, causing a radiocapture reaction with the nuclides in the sample to generate characteristic gamma rays. These characteristic gamma rays are detected and processed by data detection and processing; the energy and intensity of the gamma rays are analyzed to obtain the nuclide information corresponding to the measurement point. A measurement platform is used to rotate and move the sample according to a pre-set measurement step size, measuring at different positions to obtain the correspondence between sample position and nuclide content, thus realizing the spatial distribution information of the sample elements. While this method can achieve the specific nuclide content at a certain measurement point, obtaining the elemental spatial distribution information of the entire sample requires continuous rotation and movement of the sample, measuring information at different positions. The entire measurement process is time-consuming, and the correspondence between element content and spatial position is prone to errors. Furthermore, it cannot quickly and simultaneously determine the distribution and content of uranium and poison elements in fuel elements.

[0006] In summary, there is an urgent need to develop a detection method and system that can quickly and accurately determine the distribution and content of uranium and poison elements in fuel elements. Summary of the Invention

[0007] In view of the above-mentioned shortcomings in the prior art, the core objective of the present invention is to provide a fuel element detection method and system based on neutron imaging and activation analysis, which can quickly and accurately determine the distribution and content of uranium and poison elements in fuel elements under the premise of non-destructive testing.

[0008] This invention is achieved through the following technical solution: This invention first provides a method for detecting fuel elements based on neutron imaging and activation analysis, comprising the following steps: S1 Preparation: Install the sample to be tested onto the testing stage and adjust the imaging collimation aperture to align with the neutron beam of the neutron source; S2 Neutron Imaging Detection: An external neutron source is used to provide neutrons, and fast neutrons are slowed down into thermal neutrons by a neutron moderator. After being collimated by the imaging collimation aperture, the thermal neutrons are transmitted to the sample to be detected. The thermal neutron beam passing through the sample is detected by the neutron imaging detector to obtain the spatial distribution image of uranium and poison elements in the sample. S3 Neutron Activation Analysis Detection: Based on the spatial distribution image of uranium and poison elements obtained in step S2, a specific target region is selected, the activation analysis collimation aperture is switched to align with the neutron beam of the neutron source, and the position of the sample to be detected is adjusted so that the specific target region is aligned with the neutron beam of the neutron source; external neutrons are provided by the neutron source, and fast neutrons are slowed down into thermal neutrons by a neutron moderator; after the thermal neutrons are collimated by the activation collimation aperture, the neutron beam bombards the specific target region, and the generated characteristic gamma-ray data is received and processed by a gamma-ray detector; thereby obtaining the elemental content of the specific target region.

[0009] The principle of neutron imaging detection is as follows: Uranium and other poison elements in the fuel element undergo reactions such as scattering, radiative capture, and fission with thermal neutrons. Regions with low uranium and poison element content allow thermal neutrons to pass through easily, while regions with higher uranium and poison element content have difficulty passing through. Therefore, the distribution of uranium and poison elements can be shown by observing the distribution of transmitted neutrons. The inventors previously discovered that, under conditions of a constant neutron source intensity, the distribution of transmitted neutron positions corresponds specifically to the distribution of uranium and poison elements in the fuel element.

[0010] The principle of activation analysis detection is as follows: incident thermal neutrons are captured by target nuclei, forming excited composite nuclei. Within an extremely short time (<10⁻¹⁴ s), the composite nuclei de-excite by emitting characteristic gamma rays. By measuring the energy and intensity of the characteristic gamma rays using a high-energy-resolution gamma-ray detector, the elemental types and contents in the sample can be determined. The inventors previously discovered that the energy of the emitted gamma rays can qualitatively analyze the types of uranium and poison elements in fuel elements, and that the intensity of the emitted gamma rays has a specific correlation with the content of uranium and poison elements in the fuel elements.

[0011] This invention creatively combines the advantages of neutron imaging detection technology and neutron activation analysis detection technology. First, it utilizes the specific correspondence between neutron transmission intensity and elemental distribution to acquire spatial distribution images of uranium and poison elements using a neutron imaging detector. Then, it switches to the activation analysis collimating aperture to precisely measure the energy and intensity of transient gamma rays in a specific target area determined by the imaging. Based on the energy of the transient gamma rays, the elemental types in the fuel element are analyzed. Based on the specific correspondence between the intensity of the transient gamma rays and the content of uranium and poison elements in the fuel element, the content of uranium and poison elements in that specific target area is quantitatively determined. Through this cascaded detection method of "first determining the elemental distribution in one step, and then anchoring the determination of elemental content in a specific area," the distribution and content of uranium and poison elements in fuel elements can be obtained rapidly, accurately, and non-destructively.

[0012] Preferably, the aforementioned specific target area is an area with abnormal element distribution and / or an area with a high incidence of historical defects.

[0013] Among them, the abnormal element distribution area refers to the area where the distribution of uranium and poison elements identified by neutron imaging deviates from the design standard, such as element-enriched areas (accumulated areas), element-deficient / sparse areas (blank areas, cracked areas), and unevenly distributed areas; the historical defect high-incidence area refers to the typical area where uranium and poison distribution problems are likely to occur, based on past fuel element detection failure records and reactor operation accident cases, such as the fuel element core end position.

[0014] By further detecting the content in the aforementioned specific target areas, potential safety hazards can be accurately identified, and effective detection of uranium and toxic elements in fuel elements can be achieved.

[0015] Preferably, the neutron source of the present invention is a high-current DD neutron source to match the detection purpose of uranium and poison elements in the fuel element.

[0016] This invention also provides a fuel element detection system based on neutron imaging and activation analysis to achieve sequential cascaded detection of neutron imaging and activation analysis within the same detection system. The detection system of this invention includes a neutron source, a neutron moderator, a neutron collimator, a detection stage, a neutron imaging detector, and a gamma-ray detector; the neutron source, the neutron moderator, and the neutron collimator are sequentially arranged on one side of the detection stage; the neutron imaging detector and the gamma-ray detector are both located on the side of the detection stage away from the neutron collimator; both the neutron imaging detector and the gamma-ray detector are placed within a shield; the neutron collimator includes an imaging collimation aperture, an activation analysis collimation aperture, and an adjustment device for adjusting the imaging collimation aperture or the activation analysis collimation aperture to align with the neutron beam of the neutron source.

[0017] The detection system described above in this invention integrates a neutron imaging detector and a gamma ray detector within the same detection system. By adjusting the imaging collimation aperture or the activation analysis collimation aperture to align with the neutron beam of the neutron source through an adjustment device, it enables the qualitative detection of the distribution of uranium and poison elements in the fuel element and the quantitative analysis of the content of uranium and poison elements in a specific target area to be performed sequentially within the same detection system. This achieves non-destructive, rapid, and efficient control over the distribution and content of uranium and poison elements in the fuel element.

[0018] Preferably, the neutron imaging detector of the present invention and the neutron beam of the neutron source are located on the same straight line; the acute angle between the gamma-ray detector and the neutron beam of the neutron source is 30°~60°, preferably 45°.

[0019] This invention places the neutron imaging detector, gamma-ray detector, and high-current DD neutron source on opposite sides of the detection stage; the gamma-ray detector is placed at a 45° angle to the neutron beam, and the neutron imaging detector is placed on the neutron beam. This allows for the effective detection of transmitted neutrons and transient gamma rays while utilizing limited space to arrange shielding, reducing signal noise interference.

[0020] Preferably, the imaging collimation aperture is a conical channel, and the aperture diameter on the side closer to the neutron source is smaller than the aperture diameter on the side closer to the detection stage; and after collimation by the imaging collimation aperture, the neutron flux uniformity within the collimation aperture's field of view is greater than 85%, thus better meeting the requirements of neutron imaging detection.

[0021] Preferably, the activation analysis collimating orifice is a cylindrical orifice, and the ratio of thermal neutron flux in the 1cm*1cm region to that in the 3cm*cm region at the center of the activation analysis collimating orifice is not less than 0.4, to better meet the needs of activation analysis detection.

[0022] As a preferred embodiment, one type of neutron collimator of the present invention may have the following structure: the neutron collimator includes a collimator body, an imaging collimation aperture formed in the collimator body, and a shield plate rotatably disposed at one end of the collimator body away from the neutron source, wherein the shield plate has an activation analysis collimation aperture; when the shield plate blocks the imaging collimation aperture, the activation analysis collimation aperture is connected to the neutron beam of the neutron source.

[0023] Specifically, the collimator body can be a cylindrical or block-shaped collimator body made of B4C material; it can also be formed by filling a resin box with B4C particles. A rotating shaft is fixedly installed at the end of the collimator body away from the neutron source, and the shielding plate (B4C ceramic plate) can rotate along the rotating shaft. Preferably, a drive device can be configured to drive the shielding plate to rotate along the rotating shaft.

[0024] As a preferred embodiment, another structure of the neutron collimator of the present invention may be: the neutron collimator includes a collimator body, an imaging collimation hole opened in the collimator body, and a conical shielding member detachably engaged in the imaging collimation hole, wherein an activation analysis collimation hole is opened in the center of the conical shielding member; when the conical shielding member is engaged in the imaging collimation hole, the activation analysis collimation hole is connected to the neutron source.

[0025] Similarly, the collimator body can be a cylindrical or block-shaped collimator body made of B4C material; it can also be formed after filling a resin box with B4C particles. Preferably, a driving device can be configured to drive the conical shielding member to engage with or move away from the imaging collimation aperture.

[0026] This application selects a collimator made of B4C material. The elemental composition of the collimator does not fall within the range of uranium and poison elements in fuel elements, and will not affect neutron imaging or activation analysis, so as to meet the detection requirements of uranium and poison elements in fuel elements.

[0027] Preferably, the neutron imaging detector is a direct neutron imaging detector with an imaging diameter of not less than 40 mm and a detection efficiency of not less than 30% for thermal neutrons.

[0028] Direct neutron imaging detectors use nuclear reaction to detect neutrons. When a neutron enters the sensitive volume of the detector, it reacts with neutron-sensitive elements (10B, 6Li, natGd) to produce charged particles. These charged particles then collide with the inner wall of the microchannel plate under the influence of the channel electric field, resulting in electron multiplication, which is then detected by subsequent electronics.

[0029] Compared to existing indirect neutron imaging detectors, which rely on the reaction of neutrons with neutron-sensitive elements to generate charged particles that excite a scintillator to produce fluorescence, followed by light conversion, reflection, and recording by a CCD camera, the direct neutron imaging detector of this application detects and records charged particles generated by the reaction of neutrons with neutron-sensitive elements without requiring light conversion, resulting in more intuitive detection results.

[0030] Preferably, the gamma-ray detector is a high-energy-resolution gamma-ray detector with a relative detection efficiency ≥40% and an energy resolution ≤2.0 keV at 1.332 MeV. It can accurately identify the characteristic gamma rays of uranium and poisonous elements.

[0031] Preferably, the detection stage is a three-dimensional moving stage that can hold the sample (fuel element) to be tested and translate and rotate it in three dimensions, so that a specific target area can be accurately aligned with the neutron beam of the neutron source.

[0032] Preferably, the neutron moderator is made of a hydrogen-containing neutron moderator material of a certain thickness; the shield is made of a hydrogen-containing neutron shield and a high-density gamma-ray shield of a certain thickness, requiring that after shielding, the neutron fluence entering the high-energy-resolution gamma-ray detector during the measurement time is not higher than 10. 7 cm -2 .

[0033] The present invention has at least the following advantages and beneficial effects: (1) This invention combines the advantages and disadvantages of neutron imaging detection and activation analysis detection. It designs a method to first obtain the distribution of uranium and poison elements through neutron imaging detection, and then obtain the element content of a specific target area through activation analysis detection. Through this cascade detection, the distribution and content of uranium and poison elements in the fuel element are detected respectively. The detection is completely non-destructive and the results are intuitive and accurate, with good application prospects.

[0034] (2) The present invention also includes a detection system that sequentially realizes neutron imaging detection and activation analysis detection, which can realize the cascade detection of the present invention in the same system, providing a hardware foundation for quickly obtaining intuitive and accurate distribution and content detection of uranium and poison elements.

[0035] (3) By setting up a neutron collimator that allows for easy adjustment of the collimation aperture for two different detection methods, the present invention achieves rapid switching between two detection methods and realizes a high degree of equipment integration of "one set of equipment with two functions". Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the fuel element detection system based on neutron imaging and activation analysis according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the neutron collimator in Embodiment 1 of the present invention, showing the imaging collimation aperture aligned with the neutron beam. Figure 3 This is a schematic diagram of the structure of the neutron collimator in Embodiment 1 of the present invention, showing the collimation aperture aligned with the neutron beam. Figure 4 This is a cross-sectional view of the neutron collimator in Embodiment 2 of the present invention, showing the collimation aperture aligned with the neutron beam.

[0037] In the picture: 1-DD neutron source, 2-neutron moderator, 3-neutron collimator, 31-collimator body, 32-imaging collimation aperture, 33-activation analysis collimation aperture, 34-shielding plate, 35-rotation shaft, 36-conical shielding component, 4-detection stage, 5-sample to be tested, 6-shielding body, 7-gamma ray detector, 8-neutron imaging detector. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments.

[0039] The following embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way.

[0040] Example 1 As attached Figure 1-3As shown, this embodiment provides a fuel element detection system based on neutron imaging and activation analysis, including a high-current DD neutron source 1, a neutron moderator 2, a neutron collimator 3, a detection stage 4, a neutron imaging detector 8, and a gamma-ray detector 7; the DD neutron source 1, the neutron moderator 2, and the neutron collimator 3 are sequentially arranged on one side of the detection stage 4; the neutron imaging detector 8 and the gamma-ray detector 7 are both located on the side of the detection stage 4 away from the neutron collimator 3; the neutron imaging detector 8 and the gamma-ray detector 7 are both placed inside a shield; the neutron collimator 3 includes an imaging collimation aperture 32, an activation analysis collimation aperture 33, and an adjustment device for adjusting the imaging collimation aperture 32 or the activation analysis collimation aperture 33 to align with the neutron beam of the DD neutron source 1.

[0041] Specifically, in this embodiment, a high-current DD neutron source 1 is used to provide external neutrons, and the maximum DD neutron yield is not less than 1 × 10⁻⁶ neutrons. 9 s -1 The stability of neutron yield within 4 hours of continuous operation is <±3%. After starting the high-current DD neutron source 1, the neutron yield and stability of the high-current DD neutron generator can be monitored using a gold-silicon surface barrier detector, a He-3 gas detector, etc.

[0042] Specifically, in this embodiment, the neutron moderator 2 is made of 6cm polyethylene, and after moderation, the thermal neutron content is not less than 22%; the neutron collimator 3 is made of B4C.

[0043] Specifically, in this embodiment, the neutron imaging detector 8 is a direct neutron imaging detector; and the gamma ray detector 7 is a high-energy-resolution gamma ray detector.

[0044] The detection system described in this embodiment integrates a neutron imaging detector 8 and a gamma ray detector 7 within the same detection system. By adjusting the imaging collimation aperture 32 or the activation analysis collimation aperture 33 to align with the neutron beam of the neutron source, the system can sequentially perform qualitative detection of the distribution of uranium and poison elements in the fuel element and quantitative analysis of uranium and poison elements in a specific target area within the same detection system. This enables non-destructive, rapid, and efficient control over the distribution and content of uranium and poison elements in the fuel element.

[0045] Further details are attached. Figure 2 and attached Figure 3As shown, the neutron collimator 3 includes a collimator body 31, an imaging collimation aperture 32 formed in the collimator body 31, and a shielding plate 34 rotatably disposed at the end of the collimator body 31 away from the neutron source. An activation analysis collimation aperture 33 is formed on the shielding plate 34. When the shielding plate 34 blocks the imaging collimation aperture 32, the activation analysis collimation aperture 33 is connected to the neutron beam of the neutron source. Specifically, the imaging collimation aperture 32 is a conical channel, and the aperture diameter on the side closer to the neutron source is smaller than the aperture diameter on the side closer to the detection stage 4; and after collimation by the imaging collimation aperture 32, the neutron flux uniformity within the collimation aperture's field of view is greater than 85%, to better adapt to neutron imaging detection requirements. The activation analysis collimation aperture 33 is a cylindrical aperture, and the thermal neutron flux ratio between the central 1cm*1cm region and the 3cm*cm region of the activation analysis collimation aperture 33 is not less than 0.4, to better adapt to activation analysis detection requirements.

[0046] Specifically, in this embodiment, the collimator body 31 is formed after filling a resin box with B4C particles. A rotating shaft 35 is fixedly installed at the end of the collimator body 31 away from the neutron source, and the shielding plate 34 (B4C ceramic plate) can rotate along the rotating shaft 35. This embodiment is equipped with a driving device (not shown in the figure) for driving the shielding plate 34 to rotate along the rotating shaft 35. This driving device can be a circumferential driving structure conventionally used in the art, which will not be described in detail here.

[0047] The testing platform 4 in this embodiment is a three-dimensional rotatable testing platform 4, and a fixture for loading fuel elements is configured on the testing platform 4; the specific structure of the three-dimensional rotating testing platform 4 and the specific structure of the fixture for holding the fuel elements are conventional designs in the field of testing equipment, and will not be described in detail here.

[0048] In this embodiment, a high-energy-resolution gamma-ray detector 7 (HPGe detector) is placed at a certain distance behind the detection stage 4 at an angle of 45° to the neutron beam. The detector has a relative detection efficiency of ≥40% and an energy resolution of ≤2.0keV (@1.332MeV). A direct neutron imaging detector 8 (gadolinium-doped MCP neutron detector) is placed on the neutron beam. The imaging diameter of the detector is not less than 40mm and the detection efficiency for thermal neutrons is not less than 30%. The detector is shielded by a shield made of heavy water, lead, or other materials.

[0049] This embodiment also provides a fuel element detection method based on neutron imaging and activation analysis, implemented using the above-mentioned detection system. Specifically, the detection method includes the following steps: S1 Preparation: Install the sample to be tested onto the detection stage 4, rotate the shield 34 so that the imaging collimation aperture 32 is aligned with the neutron beam of the neutron source (as shown in the attached diagram). Figure 2 (As shown).

[0050] S2 Neutron Imaging Detection: A high-current DD neutron source 1 is activated to provide external neutrons, and the 2.45 MeV DD fast neutrons are slowed down into thermal neutrons by a neutron moderator 2. The thermal neutrons are collimated through an imaging collimation aperture 32 and then transmitted to the sample under test. The thermal neutron beam passing through the sample is detected by a neutron imaging detector 8 to obtain a spatial distribution image of uranium and poison elements in the sample. Since, under a certain neutron source intensity, the distribution of transmitted neutron positions corresponds specifically to the distribution of uranium and poison elements in the fuel element, the spatial distribution image of uranium and poison elements obtained in this step is compared with the spatial distribution image of uranium and poison elements in a standard fuel element to identify anomalous element distribution areas as one of the specific target areas for the next step.

[0051] S3 Neutron Activation Analysis Detection: Based on the spatial distribution image of uranium and poison elements obtained in step S2, select a specific target area and switch the activation analysis collimating aperture 33 to align with the neutron beam generated by the neutron source (as shown in the attached image). Figure 3 As shown in the diagram, the three-dimensional detection stage 4 is adjusted to position the sample to be tested, aligning the specific target area with the neutron beam generated by the neutron source. The high-current DD neutron source 1 is activated to provide external neutrons, and the fast neutrons are slowed down into thermal neutrons by the neutron moderator 2. After the thermal neutrons are collimated by the activated collimation aperture, the neutron beam bombards the specific target area, and the generated characteristic gamma-ray data is received and processed by the gamma-ray detector 7, thereby obtaining the elemental content of the specific target area. Since the energy of the transient gamma rays can qualitatively analyze the types of uranium and poison elements in the fuel element, the intensity of the transient gamma rays has a specific correspondence with the content of uranium and poison elements in the fuel element. That is, the content of uranium and poison elements corresponding to this area can be obtained from the characteristic gamma-ray data of this step.

[0052] The aforementioned specific target areas were selected sequentially from regions with abnormal elemental distribution and regions with a high incidence of historical defects, in order to achieve precise control over the content of uranium and toxic elements.

[0053] The detection system and method described in this embodiment enable effective detection of the distribution and content of uranium and poison elements in fuel elements.

[0054] Example 2 This embodiment also provides a fuel element detection system based on neutron imaging and activation analysis. The only difference between this system and the one provided in Embodiment 1 is that the neutron collimator 3 in this embodiment includes a collimator body 31, an imaging collimation hole 32 formed in the collimator body 31, and a conical shielding member 36 detachably mounted in the imaging collimation hole 32. An activation analysis collimation hole 33 is formed at the center of the conical shielding member 36. When the conical shielding member 36 is mounted in the imaging collimation hole 32, the activation analysis collimation hole 33 is connected to the neutron source. Similarly, the collimator body 31 in this embodiment is formed after filling a resin box with B4C particles.

[0055] The detection system in this embodiment can also effectively detect the distribution and content of uranium and poison elements in fuel elements.

[0056] In summary, the detection system and method provided by this invention first rapidly acquire the spatial distribution of uranium and poison elements using a direct neutron imaging detector 8, and then switch to an activation analysis collimator to accurately measure the content of uranium and poison elements in the target area based on the characteristics of the imaging-locked target region. This achieves both a visual representation of the elemental distribution and quantitative analysis of the content in a specific region, overcoming the limitations of existing technologies that can only detect a single distribution or content. The detection results are intuitive and highly accurate.

[0057] Meanwhile, this invention reduces invalid detection processes by pre-locating key areas through imaging; the collimator can rotate to switch between imaging and activation analysis functions, eliminating the need to build multiple additional detection systems. The equipment has high integration, is easy to operate, and significantly shortens the detection cycle, meeting the detection efficiency requirements for mass production of nuclear fuel elements.

[0058] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A method for detecting fuel elements based on neutron imaging and activation analysis, characterized in that, Includes the following steps: S1 Preparation: Install the sample to be tested onto the testing stage and adjust the imaging collimation aperture to align with the neutron beam of the neutron source; S2 Neutron Imaging Detection: An external neutron source is used to provide neutrons, and fast neutrons are slowed down into thermal neutrons by a neutron moderator. After being collimated by the imaging collimation aperture, the thermal neutrons are transmitted to the sample to be detected. The thermal neutron beam passing through the sample is detected by the neutron imaging detector to obtain the spatial distribution image of uranium and poison elements in the sample. S3 Neutron Activation Analysis Detection: Based on the spatial distribution image of uranium and poison elements obtained in step S2, a specific target region is selected, the activation analysis collimation aperture is switched to align with the neutron beam of the neutron source, and the position of the sample to be detected is adjusted so that the specific target region is aligned with the neutron beam of the neutron source; external neutrons are provided by the neutron source, and fast neutrons are slowed down into thermal neutrons by a neutron moderator; after the thermal neutrons are collimated by the activation collimation aperture, the neutron beam bombards the specific target region, and the generated characteristic gamma-ray data is received and processed by a gamma-ray detector; thereby obtaining the elemental content of the specific target region.

2. The fuel element detection method based on neutron imaging and activation analysis according to claim 1, characterized in that, The specific target area is an area with abnormal element distribution and / or an area with a high incidence of historical defects.

3. A detection system applied to the fuel element detection method based on neutron imaging and activation analysis according to claim 1 or 2, characterized in that, This includes a neutron source, a neutron moderator, a neutron collimator, a detection stage, a neutron imaging detector, and a gamma-ray detector; The neutron source, the neutron moderator, and the neutron collimator are sequentially arranged on one side of the detection stage; the neutron imaging detector and the gamma ray detector are both located on the side of the detection stage away from the neutron collimator; the neutron imaging detector and the gamma ray detector are both placed inside a shielding body; The neutron collimator includes an imaging collimation aperture, an activation analysis collimation aperture, and an adjustment device for adjusting the imaging collimation aperture or the activation analysis collimation aperture to align with the neutron beam of the neutron source.

4. The fuel element detection system based on neutron imaging and activation analysis according to claim 3, characterized in that, The neutron imaging detector and the neutron beam of the neutron source are located on the same straight line; the acute angle between the gamma ray detector and the neutron beam of the neutron source is 30°~60°.

5. The fuel element detection system based on neutron imaging and activation analysis according to claim 3, characterized in that, The imaging collimation aperture is a conical channel, and the aperture diameter on the side closer to the neutron source is smaller than the aperture diameter on the side closer to the detection stage; and after collimation by the imaging collimation aperture, the neutron flux uniformity within the collimation aperture field of view is greater than 85%.

6. The fuel element detection system based on neutron imaging and activation analysis according to claim 3, characterized in that, The activation analysis collimation aperture is a cylindrical aperture, and the ratio of thermal neutron flux in the 1cm*1cm region to that in the 3cm*cm region at the center of the activation analysis collimation aperture is not less than 0.

4.

7. The fuel element detection system based on neutron imaging and activation analysis according to claim 3, characterized in that, The neutron collimator includes a collimator body, an imaging collimation hole formed in the collimator body, and a shield plate rotatably disposed at the end of the collimator body away from the neutron source. The shield plate is provided with an activation analysis collimation hole. When the shielding plate blocks the imaging collimation aperture, the activation analysis collimation aperture and the neutron beam of the neutron source are connected.

8. The fuel element detection system based on neutron imaging and activation analysis according to claim 3, characterized in that, The neutron collimator includes a collimator body, an imaging collimation hole opened in the collimator body, and a conical shielding member that is detachably locked in the imaging collimation hole. The center of the conical shielding member is provided with an activation analysis collimation hole. When the conical shielding component is inserted into the imaging collimation aperture, the activation analysis collimation aperture and the neutron beam of the neutron source are connected.

9. The fuel element detection system based on neutron imaging and activation analysis according to any one of claims 3 to 8, characterized in that, The neutron collimator is made of B4C.

10. The fuel element detection system based on neutron imaging and activation analysis according to any one of claims 3 to 8, characterized in that, The neutron imaging detector is a direct neutron imaging detector with an imaging diameter of not less than 40 mm and a detection efficiency of not less than 30% for thermal neutrons. The gamma ray detector is a high-energy-resolution gamma ray detector with a relative detection efficiency of ≥40% and an energy resolution of ≤2.0keV at 1.332MeV.

Images