Spent nuclear fuel defect inspection system using radioactivity

Abstract

The present invention relates to a spent nuclear fuel rod radiation inspection system using radioactivity for inspecting minute defects, such as cracks, in spent nuclear fuel rods, comprising a nuclear fuel pellet, which is a nuclear fuel rod, and a collimator; a cladding corresponding to the part inspecting defects in the nuclear fuel rod surrounds the nuclear fuel pellet, and in the event that minute defects, such as cracks, exist in the spent nuclear fuel rod, radioactivity is emitted through the cladding surrounding the nuclear fuel pellet, and the collimator is composed of a fixed primary collimator and a rotating secondary collimator. A radiation detector made of a scintillator is installed inside a secondary collimator, a primary collimator hole is formed in the primary collimator, and a secondary collimator hole is formed in the secondary collimator, and radiation sensors of SiPM (silicon photomultiplier) are attached to both ends of the radiation detector made of a scintillator inside the collimator, and defect inspection of the inspection area of ​​the nuclear fuel fillet cladding is performed through a field of view formed by aligning the primary collimator hole of the collimator with the rotating secondary collimator hole.

Description

Technology Field

[0001] The present invention relates to a spent nuclear fuel defect inspection system capable of rapidly and accurately measuring radiation emitted from minute defects occurring in spent nuclear fuel fuel rods to determine the location of the defects. Background Technology

[0003] A measuring device for measuring partial defects in stored or transported spent nuclear fuel assemblies in real time using a scintillator is described in Korean Registered Patent Publication No. 10-2096289 (April 2, 2020).

[0004] A device for measuring partial defects in spent nuclear fuel assemblies includes one or more radiation-electrical signal converters, a measuring instrument for measuring electrical signals generated from photovoltaics of the radiation-electrical signal converters, and a position control unit that performs the role of positioning each radiation-electrical signal converter to a location for measuring partial defects in spent nuclear fuel assemblies.

[0005] A radiation-to-electrical signal converter includes a scintillator that converts radiation emitted from a post-nuclear fuel assembly into visible light, and a photovoltaic cell that generates an electric current or voltage (hereinafter referred to as an "electrical signal") from the visible light emitted from the scintillator.

[0006] The position control unit is configured to control each radiation-to-electrical signal converter to be inserted to a certain depth between each fuel rod or fuel pin (fuel rod) constituting the spent fuel assembly when measuring partial defects in the spent fuel assembly.

[0007] Korean Registered Patent Publication No. 10-0977290 (August 23, 2010) describes a device for determining defects in spent fuel assemblies and a method for determining defects using the same, which calculates the dose ratio of neutrons and gamma rays emitted from spent fuel assemblies to determine whether defects occur on the surface of spent fuel assemblies and the location of the defects.

[0008] The defect detection device for spent nuclear fuel assemblies is equipped with a radiation detection sensor comprising a neutron detection sensor and a gamma ray detection sensor that are integrally combined to generate visible light by reacting with neutrons and gamma rays emitted from the spent nuclear fuel assembly, respectively.

[0009] It consists of a pair of cables composed of optical fibers, each connected to a neutron measurement sensor and a gamma ray measurement sensor to transmit visible light generated from the neutron measurement sensor and the gamma ray measurement sensor, respectively, and a photoelectric converter that converts the visible light transmitted through the pair of cables into electrical signals corresponding to the magnitude of the visible light.

[0010] The configuration includes a microprocessor that calculates the dose ratio of neutrons and gamma rays emitted from a spent fuel assembly based on an electrical signal converted by a photoelectric converter, and determines whether the spent fuel assembly is defective or where the defect is located by comparing the calculated dose ratio of neutrons and gamma rays with the dose ratio of neutrons and gamma rays emitted from a spent fuel assembly without defects. Prior art literature

[0012] Korean Registered Patent Publication KR 10-2096289 B1 Korean Registered Patent Publication KR 10-0977290 B1 The problem to be solved

[0013] Spent nuclear fuel generated after combustion in a nuclear reactor contains radioactive materials, and to ensure safety, the connection status of spent fuel rods is inspected periodically during the planned preventive maintenance period.

[0014] Since major defects in spent nuclear fuel manifest as minute flaws, such as cracks in the fuel rods, inspection equipment is required to easily identify the presence of defects and pinpoint their exact locations.

[0015] Therefore, the purpose of the present invention is to provide a spent nuclear fuel inspection system that determines the location of defects by rapidly and accurately measuring radiation emitted from cracks, which are longitudinal microscopic defects occurring in spent nuclear fuel rods, while shortening the inspection time for spent nuclear fuel defects by reducing the number of inspection movements. means of solving the problem

[0017] The spent nuclear fuel rod radiation inspection system using radioactivity for inspecting minute defects, such as cracks, in spent nuclear fuel rods according to the present invention includes a nuclear fuel pellet, which is a nuclear fuel rod, and a collimator.

[0018] The cladding corresponding to the part inspecting for defects in the nuclear fuel rod of the present invention surrounds the nuclear fuel pellet, and in the event that minute defects such as cracks exist in the spent nuclear fuel rod, radioactivity is released through the cladding surrounding the nuclear fuel pellet.

[0019] The collimator of the present invention is composed of a fixed primary collimator and a rotating secondary collimator. A radiation detector made of a scintillator is installed inside the secondary collimator, and a primary collimator hole is formed in the primary collimator and a secondary collimator hole is formed in the secondary collimator.

[0020] Radiation sensors of SiPM (silicon photomultiplier) are attached to both ends of a radiation detector consisting of a scintillator inside the collimator of the present invention.

[0021] A defect inspection of the inspection area of ​​the nuclear fuel fillet cladding is performed through a field of view formed by aligning the primary collimator hole of the collimator of the present invention with the rotating secondary collimator hole.

[0022] The primary collimator of the present invention is fixed in a form in which a collimator hole is drilled in the defect measurement portion of a nuclear fuel fillet, which is a nuclear fuel rod, and the secondary collimator surrounds the scintillator of a radiation detector and is located inside the primary collimator, and the secondary collimator has a secondary collimator hole drilled in the same position as the primary collimator hole of the primary collimator, so that it is structured to be able to rotate in order to inspect the radioactivity of the spent nuclear fuel rod.

[0023] When the secondary collimator hole of the present invention rotates and coincides with the primary collimator hole, the radioactivity of the spent nuclear fuel in that direction is measured.

[0024] When the secondary collimator hole and the primary collimator hole of the present invention coincide to inspect radioactivity, the portion without the primary and secondary collimator holes performs the role of shielding and reducing background radiation emitted from a fuel rod other than the spent nuclear fuel rod for which the radioactivity inspection is being performed.

[0025] In this invention, the rail can move in the X and Y axis directions by means of a movable rail installed on the ceiling, and the tapping motor installed on the rail is controlled by the control unit to move it to an accurate position, and the rotation of the secondary collimator for measuring radiation can also be controlled.

[0026] Using the radioactivity inspection system for spent nuclear fuel rods that inspects minute defects according to the present invention, each of the four spent nuclear fuel rods is inspected in 1 / 4 portions according to the size of the irradiation field (FOV) (500) of the nuclear fuel fillet generated when the secondary collimator and the primary collimator coincide, and the remaining portions are inspected in 1 / 4 portions by moving the radiation detector.

[0027] The inspection of a nuclear fuel fillet, which is one fuel rod of the present invention, determines defects by summing the information through four movements.

[0028] In the defect inspection system of the present invention, the Z-axis position (lengthwise direction) of the scintillator, which determines the defect location when radiation is detected, is calculated using the formula [lengthwise defect location = LM1 / M1+M2] (where M1 and M2 are the total number of radiations obtained from the radiation sensors located at both ends of the scintillator, and L is the length of the scintillator) using signals obtained from radiation sensors placed at both ends, which is the Z-axis direction where radioactivity is high.

[0029] In order to minimize the influence of background radiation incident from various directions in the present invention, shielding is arranged in a grid shape, and by using multiple defect inspection systems, the number of movements and measurements of radiation detectors can be reduced, thereby shortening the inspection time. Effects of the invention

[0031] The spent nuclear fuel defect inspection system utilizing radioactivity according to the present invention simplifies the efficient inspection and detection system for longitudinal (Z-axis) defects by using a cylindrical scintillator and radiation sensors attached to both ends. Furthermore, by departing from the conventional inspection method of individually inspecting spent nuclear fuel rods using a radioactivity detection system, it reduces the number of inspection movements, thereby effectively shortening the spent nuclear fuel defect inspection time. Brief explanation of the drawing

[0033] FIGS. 1(a) and (b) are schematic diagrams of a spent nuclear fuel fuel rod radioactivity inspection system and a field-of-view (FOV) inspection method according to the present invention. FIGS. 2(a) and (b) illustrate a method of moving a spent nuclear fuel defect inspection system according to the present invention and a method of inspecting a defective part of spent nuclear fuel by rotating a secondary collimator of the defect inspection system. FIG. 3 illustrates a method for inspecting defective parts of spent nuclear fuel rods and a method for arranging them using a plurality of defect inspection systems according to the present invention. Specific details for implementing the invention

[0034] Since spent nuclear fuel generated after combustion in a reactor contains radioactive materials, the fuel rods are periodically inspected during the planned preventive maintenance period for the presence of minute defects, such as cracks, to ensure safety.

[0035] The present invention relates to a spent nuclear fuel defect inspection system capable of rapidly and accurately measuring radiation emitted from minute defects (cracks) occurring in spent nuclear fuel fuel rods to determine the location of the defects.

[0036] Hereinafter, the spent nuclear fuel defect inspection system according to the present invention will be described in more detail with reference to the attached drawings.

[0037] If minute defects exist in spent nuclear fuel rods, radiation is emitted from radioactive materials through the defective areas, and the radioactivity of the normal parts and the defective parts of the spent nuclear fuel rods appears significantly different.

[0038] The location of the defect can be easily identified by utilizing the fact that the radioactivity of the normal part and the defective part of the fuel rod appears significantly different.

[0039] Because existing equipment for inspecting defects through radiation measurement uses individual radiation measuring instruments, the measurement time increased when performing inspections of spent nuclear fuel rods in all directions (X, Y, Z).

[0040] In addition, if radiation detectors are made larger to shorten measurement time, the volume increases, and the space between spent nuclear fuel rods becomes very narrow, which limits their use.

[0041] FIGS. 1(a) and (b) are schematic diagrams of a spent nuclear fuel fuel rod radioactivity inspection system and a field-of-view (FOV) inspection method according to the present invention.

[0042] The present invention is an inspection system for rapidly and accurately measuring radiation emitted from minute defects occurring in spent nuclear fuel rods to determine the location of the defects, and to miniaturize the inspection system, a cylindrical scintillator identical in size to the spent nuclear fuel is used in the longitudinal direction.

[0043] Radiation sensors are attached to each end of the scintillator to identify high-radiation ranges.

[0044] In addition, two collimators are used for shielding and radiation focusing to increase the accuracy of radioactivity measurement in the inspection system.

[0045] By utilizing the radiation signal measured by the radiation sensor, X, Y, and Z coordinates with high radioactivity can be obtained.

[0046] The inspection system of the present invention has a limited field of view (FOV) because it uses a collimator that focuses radiation, but the miniaturized detection system can move between spent nuclear fuel rods using a rail installed separately on the ceiling.

[0047] By aggregating the radioactivity information measured after moving the inspection system, the entire spent nuclear fuel rod can be inspected in a short period of time, and by deploying multiple small detectors, the time required to determine the presence of defects through radioactivity inspection can be further shortened.

[0048] A spent nuclear fuel rod radiation inspection system (100) using radiation to inspect for minute defects such as cracks in spent nuclear fuel rods is configured to include a nuclear fuel rod, a nuclear fuel pellet (200), and a collimator (300).

[0049] The cladding (210) covers the nuclear fuel pellet (200) and corresponds to the part that actually inspects for defects in the nuclear fuel rod.

[0050] Radioactivity is emitted through the cladding (210) when there are fine defects, such as cracks, in the spent nuclear fuel rods.

[0051] In the case of the presence of fine defects, such as cracks, in the spent nuclear fuel rods, radioactivity is released through the cladding (210) surrounding the nuclear fuel pellets (200).

[0052] The collimator (300) consists of a fixed primary collimator (310) and a rotating secondary collimator (320).

[0053] A radiation detector (400) made of a scintillator is installed inside the secondary collimator (320).

[0054] A first collimator hole (311) is formed in the first collimator (310), and a second collimator hole (321) is formed in the second collimator (320).

[0055] Defect inspection can be performed in the inspection area (220) of the cladding (210) of the nuclear fuel fillet (200) through the field of view (500) formed by aligning the primary collimator hole (311) of the collimator and the rotating secondary collimator hole (321).

[0056] Radiation sensors (600) of a SiPM (silicon photomultiplier) are attached to both ends of a radiation detector (400) which is made of a scintillator with a length equal to the length of a fuel fillet (200) inside a collimator (300).

[0057] It is preferable that a small SiPM be used as the radiation sensor and that a radiation detector made of a scintillator usable at room temperature be used as the radiation detector material, and when using a radiation detector made of a scintillator, it is advantageous to use a scintillator with a high atomic number and density.

[0058] In addition, since radiation is emitted from all fuel fillets of spent nuclear fuel, shielding of the radiation detector made of a scintillator is essential, and in the inspection system, first and second collimators (310, 320) are used to detect by shielding and limiting the direction of radiation.

[0059] The primary collimator (310) is used in a fixed form with a collimator hole drilled in the defect measurement area of ​​the nuclear fuel fillet (200), which is a nuclear fuel rod.

[0060] The secondary collimator (320) surrounds the scintillator of the radiation detector and is located inside the primary collimator.

[0061] The secondary collimator (320) has a secondary collimator hole (321) drilled at the same location as the primary collimator hole (311) of the primary collimator (310), so that it is structured to be able to rotate in order to inspect the radioactivity of the spent nuclear fuel rod.

[0062] Therefore, when the secondary collimator hole (321) rotates and aligns with the primary collimator hole (311), the radioactivity of the spent nuclear fuel in that direction is measured.

[0063] In addition, when the secondary collimator hole (321) and the primary collimator hole (311) coincide to test for radioactivity, the part without the primary and secondary collimator holes (311, 321) serves to shield and reduce background radiation emitted from a fuel rod other than the spent nuclear fuel rod for which the radioactivity test is being performed.

[0064] FIG. 1(b) illustrates in detail the field of view (FOV) generated when the primary and secondary collimator holes (311, 321) align.

[0065] FIGS. 2(a) and (b) illustrate a method of moving a spent nuclear fuel defect inspection system according to the present invention and a method of inspecting a defective part of spent nuclear fuel by rotating a secondary collimator of the defect inspection system.

[0066] The movement of the spent nuclear fuel defect inspection system using radioactivity is controlled by a moving rail (700) installed on the ceiling, so that the rail (700) can move in the X and Y axis directions, and the tapping motor installed on the rail is controlled by the control unit to move it to an accurate position, and the rotation of the secondary collimator (320) for radioactivity measurement can also be controlled.

[0067] Depending on the size of the irradiation field (FOV) generated when the secondary collimator (320) and the primary collimator (310) are aligned, each of the four spent nuclear fuel fuel rods can be inspected.

[0068] The remaining parts can be inspected in quarters by moving the radiation detector (400).

[0069] Therefore, the inspection of a nuclear fuel fillet (200), which is a single fuel rod, determines defects by summing the information through four movements.

[0070] In this way, partial inspection information of four fuel rods can be collected in a single movement, and the data can be aggregated through the movement of the detector to inspect the radioactivity of all spent nuclear fuel rods, specifically the fuel fillets.

[0071] Defects in spent nuclear fuel rods can be determined by the measured radioactivity value.

[0072] If a defect exists, radioactivity appears higher compared to normal areas.

[0073] When radiation is detected in a defect inspection system, the Z-axis position (lengthwise direction) of the scintillator that determines the defect location can be calculated using the following formula where high radioactivity is observed, using signals obtained from radiation sensors (500) placed at both ends.

[0075] [Longitudinal defect location in the Z-axis direction = LM1 / M1+M2]

[0076] Here, M1 and M2 are the total number of radiations acquired by radiation sensors located at both ends of the scintillator, and L is the length of the scintillator.

[0078] FIG. 3 illustrates a method for inspecting defective parts of spent nuclear fuel rods and a method for arranging them using a plurality of defect inspection systems according to the present invention.

[0079] Inspection time can be further reduced by deploying multiple defect inspection systems.

[0080] A shield (800) can be installed and arranged in a grid shape to minimize the impact of background radiation incident from various directions on the defect inspection system.

[0081] By using multiple defect inspection systems, the number of times the radiation detector (400) moves and measures can be reduced, thereby shortening the inspection time.

[0082] As described above, the defect inspection system of the present invention can efficiently inspect defects in the longitudinal Z-axis direction by using a cylindrical scintillator and radiation sensors attached to both ends.

[0083] By moving away from the existing inspection method of individually inspecting spent nuclear fuel rods using a radiation detection system, the number of inspection movements can be reduced, thereby significantly shortening the time required for inspecting defects in spent nuclear fuel.

[0084] To improve the accuracy of setting the field of view (FOV) and measuring radioactivity for the inspection area of ​​spent nuclear fuel rods, a fixed primary collimator and a rotatable secondary collimator can be used, and a shield can be used to shield ambient background radiation, thereby improving the reliability of defect inspection.

[0085] In addition, by deploying multiple defect inspection systems, the time required to inspect spent nuclear fuel defects can be reduced compared to using a single inspection system due to a reduction in the number of moves.

[0086] Although the present invention has been described in detail through representative embodiments above, those skilled in the art will understand that various modifications can be made to the above-described embodiments within the scope of the present invention.

[0087] Therefore, the scope of the rights of the present invention should not be limited to the described embodiments, but should be determined by the claims set forth below as well as all modifications or variations derived from the claims and equivalent concepts. Explanation of the symbols

[0089] 100: Fuel rod radiation inspection system 200: Nuclear fuel pellet 210: Cladding 220: Inspection area 310: 1st collimator 311: Primary Collimator Hole 320: Secondary collimator 321: Secondary Collimator Hole 400: Radiation detector 500: Field of View 600: Radiation sensor 700: Rail 800: Shield

Claims

Claim 1 A spent nuclear fuel rod radiation inspection system (100) using radiation to inspect minute defects such as cracks in spent nuclear fuel rods comprises a nuclear fuel pellet (200) which is a nuclear fuel rod and a collimator (300), and a cladding (210) corresponding to the part inspecting defects in the nuclear fuel rod surrounds the nuclear fuel pellet (200), and in the event that minute defects such as cracks exist in the spent nuclear fuel rod, radiation is emitted through the cladding (210) surrounding the nuclear fuel pellet (200), and the collimator (300) is composed of a fixed primary collimator (310) and a rotating secondary collimator (320), and a radiation detector (400) made of a scintillator is installed inside the secondary collimator (320), and the primary A spent nuclear fuel rod radiation inspection system using radioactivity, characterized in that a primary collimator hole (311) is formed in the collimator (310) and a secondary collimator hole (321) is formed in the secondary collimator (320), and a radiation sensor (600) of a SiPM (silicon photomultiplier) is attached to both ends of a radiation detector (400) made of a scintillator inside the collimator (300), and a defect inspection of an inspection area (220) of the cladding (210) of a nuclear fuel fillet (200) is performed through a field of view (500) formed by aligning the primary collimator hole (311) of the collimator with the rotating secondary collimator hole (321). Claim 2 A spent nuclear fuel rod radiation inspection system using radiation, characterized in that, in claim 1, the primary collimator (310) is fixed in a form having a collimator hole drilled in the defect measurement area of ​​the nuclear fuel fillet (200), which is a nuclear fuel rod, the secondary collimator (320) surrounds the scintillator of the radiation detector and is located inside the primary collimator (310), and the secondary collimator (320) has a secondary collimator hole (321) drilled in the same position as the primary collimator hole (311) of the primary collimator (310), so as to be structured to rotate in order to inspect the radioactivity of the spent nuclear fuel rod, and when the secondary collimator hole (321) rotates and coincides with the primary collimator hole (311), the radioactivity of the spent nuclear fuel in that direction is measured. Claim 3 A spent nuclear fuel rod radiation inspection system using radiation according to claim 2, characterized in that when the secondary collimator hole (321) and the primary collimator hole (311) coincide to inspect radiation, the portion without the primary and secondary collimator holes (311, 321) performs the role of shielding and reducing background radiation emitted from a fuel rod other than the spent nuclear fuel rod for which radiation inspection is being performed. Claim 4 A spent nuclear fuel rod radiation inspection system using radiation according to claim 3, characterized in that the rail (700) can move in the X and Y axis directions by means of a moving rail (700) installed on the ceiling, and the tapping motor installed on the rail is controlled by a control unit to move it to an accurate position, and the rotation of a secondary collimator (320) for radiation measurement can also be controlled. Claim 5 A method for inspecting defective areas of a spent nuclear fuel fillet using radioactivity, characterized by using a radioactivity-based spent nuclear fuel fuel rod radioactivity inspection system (100) for inspecting minute defects according to any one of claims 1 to 4, inspecting 1 / 4 portions of four spent nuclear fuel fuel rods according to the size of the irradiation field (FOV) (500) of the nuclear fuel fillet (400) generated when the secondary collimator (320) and the primary collimator (310) coincide, inspecting the remaining portions in 1 / 4 portions through the movement of a radiation detector (400), and determining defects by summing the information through four movements for the inspection of a nuclear fuel fillet (200), which is one fuel rod. Claim 6 In claim 5, the Z-axis position (longitudinal direction) of the scintillator, which determines the defect location when radiation is detected in the defect inspection system, is calculated using the following formula in which high radioactivity is observed using a signal obtained from radiation sensors (500) placed at both ends, thereby determining the longitudinal defect location. [Longitudinal defect location in the Z-axis direction = LM1 / M1+M2] Here, M1 and M2 are the total number of radiations obtained from radiation sensors located at both ends of the scintillator, and L is the length of the scintillator. Claim 7 A method for inspecting defective parts of a spent nuclear fuel rod using radioactivity, characterized in that, in claim 6, shielding bodies (800) are arranged in a grid shape to minimize the influence of background radiation incident from various directions, and multiple defect inspection systems are used to reduce the number of movements and measurements of radiation detectors (400), thereby shortening the inspection time.

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