Systems and methods for inspecting fuel pellets of nuclear fuel.

Abstract

An inspection system includes a support device (20) for supporting fuel pellets (4) of nuclear fuel such that the pellet axis (A) of each fuel pellet (4) coincides with a reference axis (B), and an optical measuring device (40) arranged for optically measuring the fuel pellets (4). The optical measuring device (40) includes a light emitter (42) configured to emit a light beam propagating along an optical axis (C) and a photodetector (46) arranged to receive the light beam (44), wherein each fuel pellet (4) interrupts the light beam (44) and generates a shadow projected onto the photodetector (46). The optical measuring device (40) includes a measuring module (48) configured to analyze the shadow to detect possible defects on the end face (10) and / or side face (8) of each fuel pellet (4).

Description

Technical Field

[0001] This invention relates to the technical field of manufacturing nuclear fuel rods, and more specifically, to the inspection of fuel pellets of nuclear fuel before they are inserted into the cladding of nuclear fuel rods. Background Technology

[0002] Nuclear fuel assemblies typically consist of bundles of nuclear fuel rods. Each fuel rod includes a tubular cladding that surrounds fuel pellets (hereinafter referred to as "fuel pellets") stacked within the tubular cladding. Fuel pellets are made of fissile material, such as enriched uranium dioxide.

[0003] Each fuel pellet is approximately rotationally symmetrical about its axis. Each fuel pellet has a generally cylindrical shape, comprising substantially cylindrical sides and two end faces. The two end faces are approximately symmetrical with respect to a central plane perpendicular to the pellet axis. Each fuel pellet is manufactured, for example, by sintering powdered fissile material.

[0004] In some pellets, each end face includes a central recess surrounded by an edge that is surrounded by a chamfer extending between the edge and side (preferably cylindrical) of the fuel pellet. The recess, edge, and chamfer are concentric and centered on the pellet axis.

[0005] Fuel pellets may have defects on the end face of the fuel pellet that affect nuclear fuel, namely, surface losses and / or protrusions on the end face of the fuel pellet.

[0006] The term "surface loss" refers to missing portions or dents on fuel pellets. Surface loss can result from fuel pellets breaking during handling on the production line (e.g., caused by impact).

[0007] Protrusions may include bubbles (dome-shaped protrusions that axially project from the end face caused by gases trapped during sintering), lips (material that axially project from the periphery of the end face, such as that caused by contact between cores during sintering), and flash (material that axially project from the periphery of the end face, such as that caused by tooling problems during pressing (e.g., breakage of the pressing punch)).

[0008] Any defects in fuel pellets can be harmful to nuclear fuel rods containing fuel pellets and nuclear fuel assemblies containing said fuel rods.

[0009] Fuel pellets can be inspected before being inserted into the cladding of nuclear fuel rods. For this purpose, fuel pellets are supplied to an automated inspection system, for example, which includes a conveying system for individually conveying fuel pellets. Such conveying systems are known, for example, according to EP2133290A1 and EP2273508A1.

[0010] For inspecting the end faces of fuel pellets, automated inspection systems can be equipped with image capture devices (e.g., matrix cameras) arranged to capture images of the end faces of fuel pellets being conveyed on a transport system and to analyze the captured images automatically. Therefore, the end faces of fuel pellets can be inspected simultaneously with the transport of the fuel pellets, for example, to detect the presence of surface defects or protrusions. The optical axis of the image capture device is, for example, coaxial with the pellet axis or forming a small angle with the pellet axis, for example, an angle between 0° and 30°.

[0011] However, inspecting the end faces of fuel pellets using such automated inspection systems is difficult, particularly in chamfered or recessed areas, and therefore not entirely reliable. In fact, chamfers and recesses are concave surfaces with different orientations and therefore different irradiation conditions compared to edges. The surface on which the fuel pellets are transported can also affect the irradiation condition of the end faces. Defects present on the end faces are only clearly visible at their edge locations in the frontal image of the end face captured by the image capture device, or may be difficult to detect. Reliable classification of end face surface damage in nuclear fuel fuel in chamfered areas, which often also affect pellet edges, is particularly important for improving the fuel pellet-cladding interaction in the reactor core. Furthermore, it is sometimes difficult to distinguish surface damage from protrusions in the frontal image of the end face. Therefore, defects in nuclear fuel fuel pellets may not be detected or correctly classified (surface damage or protrusions), and / or pellets without defects may be inappropriately rejected. Summary of the Invention

[0012] One object of the present invention is to provide an inspection system for inspecting fuel pellets of nuclear fuel, which is easy to operate, efficient and reliable, and particularly productive (e.g., 10 pellets per second).

[0013] To this end, the present invention proposes an inspection system for inspecting a fuel pellet of a nuclear fuel or a plurality of such fuel pellets arranged in a column, the fuel pellet being rotationally symmetrical about a pellet axis and having sides and two end faces. The inspection system includes a support device and an optical measuring device. The support device is used to support one or more fuel pellets such that the pellet axis of each fuel pellet coincides with a reference axis. The optical measuring device is arranged for optically measuring one or more fuel pellets. The optical measuring device includes a light emitter configured to emit a light beam propagating along an optical axis and a photodetector arranged to receive the light beam, wherein each fuel pellet interrupts the light beam and generates a shadow projected onto the photodetector. The optical measuring device includes a measuring module configured to analyze the shadow to detect possible defects on the end faces and / or sides of each fuel pellet.

[0014] Defects such as surface loss on the end face of the fuel pellet often affect the periphery of the end face of the fuel pellet, especially since the periphery of the end face is more susceptible to impact during pellet handling on the production line.

[0015] Defects such as protrusions on the end faces of fuel pellets often also affect the periphery of those end faces, especially since the periphery of the pressing punches is more prone to cracking at their circular edges, and because contact between pellets during sintering occurs at the edge locations.

[0016] In fuel pellets that include end faces each having a central recess surrounded by edges and chamfers, such defects can affect, for example, the edges and / or chamfers of the end faces.

[0017] Therefore, defects may give the fuel pellet an abnormal profile in the side view, which can be detected using an optical measurement device configured to project a light beam onto the side of the fuel pellet in a direction perpendicular to the pellet axis and measure the geometric parameters of the shadow cast by the fuel pellet with the interrupted light beam.

[0018] Optical measurements of the fuel pellets from the side can be performed while the fuel pellets are being transported in a direction parallel to the pellet axis, wherein the distance between the optical measurement device and the fuel pellets is constant.

[0019] In a particular implementation, the inspection system includes one or more of the following optional features, either individually or in any technically feasible combination:

[0020] - The measurement module is configured to measure at least one geometric parameter of the shadow to detect possible defects on the end face and / or side face of each fuel pellet;

[0021] - The measurement module is configured to measure at least one distance, at least one length and / or at least one area of ​​the shadow to detect potential defects on the end face and / or side face of each fuel pellet;

[0022] - The optical axis and a plane perpendicular to the reference axis define an angle between 0° and 45°, preferably between 0° and 25°;

[0023] - The optical axis is basically perpendicular to the reference axis;

[0024] - The support device is configured to allow each fuel pellet to rotate about its pellet axis;

[0025] - The measuring device is configured to analyze shadows during at least one complete rotation of each fuel pellet, so as to analyze the entire circumference of each end face and / or the entire circumference of each side face of each fuel pellet;

[0026] - The support device includes two cylindrical rollers parallel to each other, the rollers being configured to receive one or more fuel pellets positioned on the two rollers, wherein the pellet axis of each fuel pellet is parallel to the rollers;

[0027] - The two rollers can rotate in the same direction so that the fuel pellets or fuel pellet columns received on the two rollers can rotate about the pellet axis;

[0028] - The inspection system is configured to axially deliver (one or more) fuel pellets along a reference axis;

[0029] - The inspection system includes a propulsion device, which includes at least one propulsion member movable relative to a support device to move (one or more) fuel pellets along a reference axis;

[0030] - The support device is configured to axially deliver (one or more) fuel pellets along a reference axis while rotating each fuel pellet about its pellet axis, and the length of the beam extending in the direction of the reference axis is greater than the length of (one or more) fuel pellets plus the length of (one or more) fuel pellets traveling along the reference axis during at least one full rotation of the fuel pellets about their pellet axis;

[0031] - The beam is linear, and the shadow produced by each fuel pellet is segmented in shape. The measurement module is configured to measure the length of the shadow produced by each fuel pellet to determine the corresponding length of the fuel pellet and the presence of defects on the end face and / or sides of the fuel pellet.

[0032] - The beam of light is two-dimensional, and the shadow cast by each fuel pellet is also two-dimensional;

[0033] - The measurement module is configured to measure at least one length of the shadow produced by each fuel pellet to determine the corresponding length of the fuel pellet obtained between the end faces of the fuel pellet;

[0034] - The measurement module is configured to analyze the shadow produced by each fuel pellet by determining the position of the lateral plane of the fuel pellet and determining at least one axial distance between the lateral plane and the side of the shadow profile corresponding to the end face;

[0035] - The measurement module is configured to determine the position of the central transverse plane of the fuel pellet and to determine the length of the shadow generated by each fuel pellet between the central plane and the edge of the shadow's outline, so as to determine the corresponding length of the fuel pellet;

[0036] - The measurement module is configured to analyze the shadow produced by each fuel pellet by determining the position of an end lateral plane perpendicular to the fuel pellet axis for at least one end face or for each end face and calculating at least one axial distance between the end lateral plane and the side of the shadow profile corresponding to the end face.

[0037] - The end transverse plane is positioned as a point on the edge of the shaded outline corresponding to the end face or tangent to the line of the shaded outline corresponding to the end face.

[0038] - The measurement module is configured to calculate a number of axial distances at a number of discrete radial distances relative to the fuel pellet axis, and / or to calculate the distance between the end face and the end transverse plane on the measurement portion of the profile corresponding to the end face.

[0039] - The measuring section extends radially inward and / or radially outward from the intersection of the transverse plane of the end face and the edge of the profile corresponding to the end face;

[0040] - The measurement module is configured to determine a 3D map of at least a portion of at least one end face of each fuel pellet based on the analysis of the shadows produced by the fuel pellets (one or more).

[0041] - The measurement module is configured to generate a 3D image file that corresponds to the 3D map and encodes the 3D image representing the end face, and / or to generate a 2D image file that encodes the 2D image corresponding to the 3D map;

[0042] - The measurement module is configured to detect surface loss on the end face of each fuel pellet and / or protrusions on the end face of each fuel pellet and / or end capping on one end face and side face of each fuel pellet.

[0043] The present invention also proposes a method for inspecting fuel pellets of nuclear fuel that are rotationally symmetric about the pellet axis using the inspection system defined above. Attached Figure Description

[0044] The invention and its advantages will be better understood by reading the following description, which is given by way of non-limiting example only and with reference to the accompanying drawings, in which:

[0045] Figure 1 This is a partial cross-sectional view of nuclear fuel rods, showing the fuel pellets;

[0046] Figure 2 This is a front view of the end face of the fuel pellet;

[0047] Figure 3It is a schematic front view of an inspection system including a conveyor for transporting fuel pellets and an optical measuring device;

[0048] Figure 4 This is a schematic side view of the conveyor;

[0049] Figure 5 It is a schematic 3D diagram of a conveyor and an optical measuring device;

[0050] Figure 6 The image shows the shadow cast by a fuel pellet conveyed by a conveyor in an optical measuring device, and the geometric measurement performed on that shadow;

[0051] Figure 7 The image shows the shadow cast by a fuel pellet conveyed by a conveyor in an optical measuring device, and the geometric measurement performed on that shadow;

[0052] Figure 8 The image shows the shadow cast by a fuel pellet conveyed by a conveyor in an optical measuring device, and the geometric measurement performed on that shadow;

[0053] Figure 9 The image shows the shadow cast by a fuel pellet conveyed by a conveyor in an optical measuring device, and the geometric measurement performed on that shadow;

[0054] Figure 10 It is a schematic 3D diagram of the conveyor and another optical measuring device;

[0055] Figure 11 This is a front view of a fuel pellet, showing the composition of... Figure 10 The position of the beam of light generated by the optical measuring device relative to the fuel pellet;

[0056] Figure 12 It is a three-dimensional view of a core block with an end face that has a defect (in this case, surface loss);

[0057] Figures 13 to 15 It shows the rotation angle indication of the core. Figure 12 A graph of the distance measured on the core block;

[0058] Figure 16 The shadows cast by fuel pellets arranged in columns and conveyed by a conveyor in an optical measuring device are shown, as well as the geometric measurements performed on the shadows of some fuel pellets;

[0059] Figure 17 The image shows the shadow cast by a fuel pellet with an end cap defect. Detailed Implementation

[0060] Figure 1The nuclear fuel rods 2 shown comprise a stack of fuel pellets 4 (hereinafter referred to as "fuel pellets") encapsulated in a tubular cladding 6. Each fuel pellet 4 is made of fissile material such as enriched uranium dioxide.

[0061] exist Figure 1 In the image, a fuel pellet 4 is shown in cross-section, and the outlines of the other fuel pellets 4 are shown with dashed lines.

[0062] Each fuel pellet 4 is rotationally symmetrical about the pellet axis A. Each fuel pellet 4 has a side surface 8 and two end faces 10. The side surface 8 is preferably cylindrical around the pellet axis A.

[0063] The two end faces 10 are preferably symmetrical with respect to the central plane T of the fuel pellet 4. The central plane T is perpendicular to the pellet axis A.

[0064] Each end face 10 has, for example, a central disc-shaped portion 12, an edge 14, and an outer peripheral chamfer 16. The disc-shaped portion 12, the edge 14, and the outer peripheral chamfer 16 are concentric. The edge 14 is annular and surrounds the disc-shaped portion 12. The chamfer 16 is annular and surrounds the edge 14.

[0065] The disc-shaped portion 12 is, for example, shaped like a concave hemispherical surface. The disc-shaped portion 12 of each end face 10 defines a central recess on the end face 10, which is surrounded by an edge 14. The disc-shaped portion 12 of each end face 10 is not visible in the side view of the fuel pellet 4 because it is hidden by the sector of the edge 14.

[0066] Each end face 10 has an edge 14 that is, for example, conical in shape centered on the core axis A, or extends in a plane perpendicular to the core axis A. The edge 14 has, for example, only a very small taper. The angle between the edge 14 and the plane perpendicular to the core axis A includes, for example, between 0° and 5°.

[0067] Chamfer 16 is a conical shape centered on the pellet axis A. Chamfer 16 is inclined relative to the edge 14 and relative to the side surface 8. Chamfer 16 extends between the side surface 8 and the edge 14. Chamfer 16 is visible in the side view of the fuel pellet 4.

[0068] The angle between chamfer 16 and the plane perpendicular to the core axis A is strictly greater than the angle between edge 14 and the plane perpendicular to the core axis A.

[0069] like Figure 2 The diagram shows a front view of the fuel pellet 4. The end face 10 forms a first circle C1 at the transition between the central disc-shaped portion 12 and the edge 14, and a second circle C2 at the transition between the edge 14 and the chamfer 16. The disc-shaped portion 12 is located inside the first circle C1. The edge 14 is located between the first circle C1 and the second circle C2, and the chamfer 16 is located outside the second circle C2.

[0070] The outer radius of the disc-shaped part 12 is equal to the first radius R1 (the radius of the first circle C1), the inner radius of the edge 14 is equal to the first radius R1 and the outer radius of the edge 14 is equal to the second radius R2 (the radius of the second circle C2), the inner radius of the chamfer 16 is equal to the second radius R2 and the outer radius of the chamfer 16 is equal to the third radius R3.

[0071] Figure 3 and Figure 4 The inspection system 18 is configured for automated inspection of fuel pellets 4.

[0072] The inspection system 18 includes a support device 20 configured to receive fuel pellets 4, wherein the pellet axis A coincides with a reference axis B. The reference axis B is perpendicular to... Figure 3 The plane.

[0073] The support device 20 is configured such that at least a portion of the fuel pellet 4 is visible in a view along the optical axis C without being obstructed by the support device 20. A portion of the fuel pellet 4 may be hidden by the support device 20 in a view along the optical axis C.

[0074] The support device 20 includes, for example, two cylindrical rollers 24 arranged parallel to each other. Each roller 24 extends along a corresponding roller axis D. These roller axes D are parallel. Each roller axis D is parallel to a reference axis B. The roller axes D are preferably substantially horizontal.

[0075] Each roller 24 has a cylindrical outer surface 26. The two rollers 24 preferably have the same outer diameter. The rollers 24 are spaced apart such that they do not contact each other. A gap 28 is defined between the two rollers 24.

[0076] The two rollers 24 are spaced apart and configured such that the fuel pellet 4 supported by the two rollers 24 has an angle perpendicular to the reference axis B. Figure 4 The top portion visible above the two rollers 24 in the side view of the image.

[0077] Optionally, the support device 20 includes a drive device 30, which is configured to drive the rollers 24 about their respective roller axes D in the same angular direction (e.g., Figure 3 , Figure 5 and Figure 10 (As indicated by arrow R). This allows the fuel pellet 4, supported on roller 24, to rotate in opposite angular directions about its pellet axis A.

[0078] Optionally, the support device 20 includes a moving device 32. Figure 4 The moving device 32 is configured to move the fuel pellet 4 along the roller 24 in the direction of movement (in Figure 4 As shown by arrow F, move axially to the right.

[0079] The moving device 32 includes, for example, a pushing member 34 that is driven to translate along the roller 24. The pushing member 34 includes a rod 36 that extends through a gap 28 defined between the rollers 24 and has a pushing head 38 that is arranged to contact the end face 10 of the fuel pellet 4 for axially pushing the fuel pellet 4 along the roller 24.

[0080] In the example shown, the pushing member 34 is preferably arranged such that when the core block 4 is supported by the roller 24, the pushing head 38 contacts the center of the disc-shaped portion 12 of the end face 10.

[0081] The moving device 32 may include a plurality of pushing members 34 driven by a conveyor (not shown) for moving a plurality of core blocks 4 simultaneously along the roller 24, as disclosed in EP2273508A1.

[0082] The inspection system 18 includes an optical measuring device 40. Figure 3 The optical measuring device 40 is arranged to measure the geometric parameters of the fuel pellet 4 supported by the support device 20.

[0083] The optical measuring device 40 includes a light emitter 42 configured to emit a light beam 44 along the optical axis C and a photodetector 46 configured to receive the light beam 44.

[0084] Preferably, the optical axis C is perpendicular to the reference axis B.

[0085] The beam 44 is preferably a parallel beam. The rays of the beam 44 are parallel to each other and parallel to the optical axis C.

[0086] The light emitter 42 and the photodetector 46 are arranged on both sides of the support device 20, such that the core block 4 supported by the support device 20 is located between the light emitter 42 and the photodetector 46. The core block 4 supported by the support device 20 intercepts a portion of the light beam 44.

[0087] When the chip 4 intercepts the beam 44, the chip 4 casts a shadow on the side of the photodetector 46 in a view along the optical axis C, the shadow corresponding to the outline of the chip 4.

[0088] The photodetector 46 is configured to detect the portion of the beam that has not been intercepted by the fuel pellet 4 and the portion of the beam 44 that has been intercepted by the fuel pellet 4, i.e., the shadow produced by the pellet 4.

[0089] Such optical measuring devices are sometimes called “thrubeam” or “throughbeam” optical measuring devices because they include a light emitter 42 for emitting a light beam 44 toward a photodetector 46, in which the object to be measured is placed.

[0090] The light emitter 42 and the photodetector 46 are preferably configured such that the extension of the light beam 44 along the reference axis B is greater than the expected total length of the chip 4 along the chip axis A. Therefore, the chip 4 can intercept the light beam 44 over its entire length.

[0091] As explained below, the fuel pellet 4 can rotate and move axially during the measurement, in which case the extension of the beam 44 is preferably greater than the length of the fuel pellet 4 plus the axial distance that the fuel pellet 4 travels along the support device 20 during at least one complete rotation of the fuel pellet 4 about the pellet axis A.

[0092] The optical measurement device 40 includes a measurement module 48 configured to detect defects on the end face 10 of the fuel pellet 4 by analyzing the shadow cast (or projected) by the fuel pellet 4 on the photodetector 46, particularly by measuring the geometric parameters of the shadow cast (or projected) by the fuel pellet 4 on the photodetector 46.

[0093] More specifically, the light detector 46 is configured to generate an image file including a representation of the shadows detected by the light detector 46, and the measurement module 48 is configured to process the image file to analyze the shadows, particularly by measuring the geometric parameters of the shadows.

[0094] The measurement module 48 is configured to measure, for example, at least one axial distance on the shadow (obtained along the core axis A), at least one length of the shadow (obtained along the core axis A), and / or at least one area of ​​the shadow, as will be illustrated below.

[0095] exist Figure 5 In the embodiment shown, the light emitter 42 is configured to emit a light beam 44, which has a two-dimensional shape in cross-section (i.e., in a plane perpendicular to the optical axis C).

[0096] The light emitter 42 has a light-emitting surface 50 having a cross-sectional shape of a light beam 44. The photodetector 46 has a photosensitive surface 52 having the shape of the light beam 44. The photosensitive surface 52 extends in the projection plane PP.

[0097] Such an optical measuring device is named an "area optical micrometer," "2D optical micrometer," or "profilometer." The light emitter 42 and the light detector 44 are named an area light emitter 42 and an area light detector 44.

[0098] The two-dimensional shape of beam 44 is, for example, a circle. Other shapes can be imagined, such as a rectangle.

[0099] like Figure 6 As shown, beam 44 projects a two-dimensional shadow of the illuminated portion of the chip 4 onto the photodetector 46, and more specifically, onto the photosensitive surface 52 of the photodetector 46. The outline of the shadow corresponds to the outline of the portion of the chip 4 illuminated by beam 44, which is supported by the support device 20.

[0100] In the example shown, the shadow corresponds to the outline of the upper part of the fuel pellet 4 extending above the roller 24, while the lower part of the pellet 4 is in the shadow of the roller 24.

[0101] The fuel pellet 4 supported by the support device 20 is considered to have a pellet axis A that coincides with the reference axis B, and the position of the pellet axis A is considered to be known when measuring the geometric parameters of the shadow.

[0102] like Figures 6 to 8 As shown, the measurement module 48 is configured, for example, to determine at least one length of the fuel pellet 4 obtained along the pellet axis A by measuring the corresponding length of the shadow of the fuel pellet 4 projected onto the photodetector 46.

[0103] The measuring module 48 is specifically configured to measure the length of the shadow along the pellet axis A between the two sides of the contour of the shadow produced by the end face 10 of the fuel pellet 4.

[0104] More specifically, Figure 6 As shown, the measurement module 48 is configured, for example, to measure the length L1 of the shadow of the fuel pellet 4 along the pellet axis A at a distance M1 from the pellet axis A, the distance M1 being greater than or equal to the inner radius (first radius R1) of the edge 14 and less than or equal to the outer diameter (second radius R2) of the edge 14.

[0105] At such a radial distance M1 from the pellet axis A, the length L1 of the shadow projected onto the photodetector 46 corresponds to the distance between two axially aligned edge portions of the end face 10 of the fuel pellet 4, which lie in the reference axial plane RAP containing the pellet axis A and perpendicular to the optical axis C.

[0106] Therefore, the length L1 of the shadow measured at this radial distance M1 corresponds to the edge-to-edge length of the fuel pellet 4 at a specific angular position around the pellet axis A (more specifically, at this position in the reference axial plane RAP).

[0107] At a distance from the core axis A that is less than the inner radius (first radius R1) of the edge 14, the shadow is blurred because each side of the shadow can correspond to two circumferentially spaced corner portions of the same edge 14. Therefore, defects such as surface damage that only affect one of these two portions will be hidden by the other portion on the profile projected onto the photodetector 46 and will not be detected.

[0108] The measurement module 48 is configured, for example, to measure the length L2 of the profile of the core 4 along the core axis A at a radial distance M2 from the core axis A, the radial distance M2 being greater than or equal to the inner diameter (second radius R2) of the chamfer 16 and less than or equal to the outer diameter (third radius R3) of the chamfer 16.

[0109] At such a radial distance M2 from the piston axis A, the length of the shadow projected onto the photodetector 46 corresponds to the distance between two axially aligned portions of the chamfer 16 of the end face 10 of the fuel pellet 4 located in the reference axial plane RAP.

[0110] Therefore, the length of the shadow measured at this radial distance M2 corresponds to the chamfer-to-chamfer distance of the fuel pellet 4 at a specific angular position around the pellet axis A (more specifically, at that angular position in the reference axial plane RAP).

[0111] At a distance from the core axis A that is less than the inner radius (second radius R2) of the chamfer 16, the length of the profile corresponds to the length of the core 4 obtained between the edges 14 of the end face 10.

[0112] like Figure 7 As shown, alternatively or optionally, the measurement module 48 is configured to determine the position of the central transverse plane MTP of the fuel pellet 4 in the shadow generated by the fuel pellet 4, and to measure at least one length of the shadow obtained between the central transverse plane MTP and the side of the shadow profile corresponding to the end face 10 of the fuel pellet 4, in order to determine the length of the fuel pellet 4.

[0113] The shadow outline of fuel pellet 4 includes two sides in the side view along the optical axis C that correspond to the outline of the end face 10 of the illuminated portion of fuel pellet 4.

[0114] In one example, the measurement module 48 determines the position of the central transverse plane MTP based on the portion of the two shaded sides corresponding to the end face 10 of the fuel pellet 4.

[0115] In one example where each end face 10 of the fuel pellet 4 has a disc-shaped portion 12, an edge 14, and a chamfer 16, each edge of the shaded contour is presented in the disc-shaped portion extending between the pellet axis A and the first radius R1 (where the disc-shaped portion 12 is in the shade of the edge 14), the edge portion corresponding to the contour of the edge 14 extending between the first radius R1 and the second radius R2, and the chamfer portion corresponding to the contour of the chamfer 16 extending between the second radius R2 and the third radius R3.

[0116] The disc-shaped portions of each edge are parallel. The edge portions of the end face line are not parallel when edge 14 is conical, but are parallel when edge 14 is planar. Due to the taper of the chamfer 16 of end face 10, the chamfered portion of the end face line is not parallel.

[0117] In one example, the measurement module 48 determines the position of the central plane MTP in the shadow as being located between two parallel portions of the shadow profile corresponding to the end face 10 of the fuel pellet 4.

[0118] like Figure 7 As shown, the pushing member 38 also projects a shadow onto the light detector 46, but the disk-shaped portion of the shadow's outline adjacent to it can still be detected by the measurement module 48.

[0119] The measurement module 48 is configured, for example, to measure the lengths L11, L12 of the shadow of the fuel pellet 4 at a radial distance M1 from the pellet axis A, between the central transverse plane MTP and each side of the shadow, wherein the radial distance M1 is greater than or equal to the inner radius (first radius R1) of the edge 14 and less than or equal to the outer diameter (second radius R2) of the edge 14.

[0120] Therefore, the lengths L11 and L12 of the shadow measured at this distance M1 correspond to the length from the edge of the fuel pellet 4 to the central transverse plane at a specific angular position around the pellet axis A (more specifically, at this position in the reference axial plane RAP).

[0121] The measurement module 48 is configured, for example, to measure the lengths L21, L22 of the shadow of the fuel pellet 4 at a radial distance M2 from the pellet axis A, along the central transverse plane T and the sides of the shadow, wherein the radial distance M2 is greater than or equal to the inner diameter (second radius R2) of the chamfer 16 and less than or equal to the outer diameter (third radius R3) of the chamfer 16.

[0122] The lengths L21 and L22 of the shadow correspond to the lengths of the chamfer to the mid-lateral plane of the fuel pellet 4 at a specific angular position around the pellet axis A (more specifically, at the visible angular position in the reference axial plane RAP).

[0123] Measuring the length of the shadow from the midline transverse plane MTP to each side of the shadow allows for the differentiation of corresponding defects on end face 10. The position of the midline transverse plane MTP is used as a reference. When determining the length between two portions of end face 10, the obtained length is relative, which in some cases (e.g., when a portion of one end face 10 has surface defects, while the corresponding portion of the other end face 10 has protrusions) will not allow for proper classification of defects.

[0124] like Figure 6 or Figure 7 As shown, the defect surface loss 16B affecting the chamfer 16 of the end face 10 of the core block 4 can be automatically detected as the chamfer-to-chamfer length or chamfer-to-center transverse plane length measured by the measurement module 48 being slightly shorter than the expected chamfer-to-chamfer length or the expected chamfer-to-center transverse plane length, for example, the difference from the expected length is E or E1.

[0125] like Figure 8 As shown, the defect protrusion 16C affecting the chamfer 16 of the end face 10 of the core block 4 can be automatically detected as the chamfer-to-chamfer length or chamfer-to-center transverse plane length L21 measured by the optical measurement module 48 being slightly longer than the expected chamfer-to-chamfer length or the expected chamfer-to-center transverse plane length, for example, the difference from the expected length is E2.

[0126] The technician understands that if the defect also affects the edge of the end face 10 located in the reference axial plane RAP, the defect will be presented in the same way as the edge-to-edge length or edge-to-central transverse plane length being shorter or longer than the expected edge-to-edge length or expected edge-to-central transverse plane length.

[0127] Optionally or alternatively, the measurement module 48 is configured to measure the area of ​​the shadow cast by the irradiated portion of the fuel pellet 4.

[0128] The measurement module 48 is configured, for example, to measure the area of ​​the shadow obtained between the two sides of the shadow profile corresponding to the end face 10 of the fuel pellet 4.

[0129] Optionally or alternatively, the measurement module 48 is configured to measure the area of ​​the shadow between each edge of the contour of the central transverse plane MTP and the end face 10 of the fuel pellet 4. The measurement module 48 thus calculates the area of ​​the shadow from the two end faces to the central transverse plane.

[0130] Defects (surface damage or protrusions) affecting the outer periphery of the end face 10 located in the reference axial plane RAP will alter the shadow cast by the fuel pellet 4, resulting in a shadow area that is either lower than expected (surface damage) or higher than expected (protrusion).

[0131] like Figure 9 As shown, alternatively or optionally, the measurement module 48 is configured to analyze the shadow produced by the fuel pellet 4 by determining at least one axial distance D1, D2, D3 (obtained along the fuel pellet axis A) between the end transverse plane ETP associated with the end face 10 and the shadow profile corresponding to the end face 10.

[0132] The end transverse plane ETP is, for example, a plane perpendicular to the fuel pellet axis A and positioned along the fuel pellet axis A to include a point or edge of the end face 10.

[0133] The measurement module 48 is configured, for example, to position the end transverse plane ETP of the shadow such that the end transverse plane ETP is tangent to or intersects the side of the shadow profile corresponding to the end face 10 at a specific radial distance from the fuel pellet axis A.

[0134] For example, the specific radial distance is selected such that the end transverse plane ETP is tangent to or intersects the edge of the shadow contour at a point on the edge portion corresponding to the inner edge of the edge 14, at the midpoint of the edge portion between the inner edge and the outer edge of the edge 14, at a point on the edge portion corresponding to the outer edge of the edge 14, at a point on the chamfered portion, at a point on the chamfered portion corresponding to the outer edge of the end face 10, or at the disc-shaped portion.

[0135] In a preferred embodiment, such as Figure 9 As shown, the end transverse plane ETP is tangent to the point of projection of the disc-shaped portion of the edge portion corresponding to the inner edge of the edge 14 or the outline of the shadow.

[0136] In the absence of defects, such as Figure 9 As shown, the point corresponding to the inner edge of the edge portion 14 and the disc-shaped portion define the same end transverse plane ETP.

[0137] The use of this end transverse plane ETP is advantageous because defects such as protrusions should not intersect with the end transverse plane ETP. Otherwise, gaps may be created with adjacent pellets in the pellet column of the nuclear fuel rods, which would be detrimental to the operation of the fuel rods.

[0138] Furthermore, in the presence of significant protrusions or surface defects, the position of the end lateral plane ETP may be unstable, potentially leading to erroneous measurements (e.g., confused measurements of axial distances D1, D2, and D3). The closer the point used to construct the end lateral plane ETP is to the axis of the core, the greater the likelihood of a stable end lateral plane ETP.

[0139] Each axial distance D1, D2, and D3 is determined as a distance obtained along the fuel pellet axis A, measured between the corresponding radial distances M1, M3, M3 from the fuel pellet axis A, between the edges of the end transverse plane ETP and the shaded contour corresponding to the end face 10.

[0140] The measurement module 48 is configured to, for example, determine multiple axial distances D1, D2, D3 obtained at discrete radial distances M1, M2, M3.

[0141] The measurement module 48 is configured to, for example, determine a first axial distance D1 at a first radial distance M1, a second axial distance D2 at a second radial distance M2, and / or a third axial distance D3 at a third radial distance M3.

[0142] For example, a first radial distance M1 corresponding to the edge 14 is selected, a second radial distance M2 corresponding to the chamfer 16 is selected, and a third radial distance M3 corresponding to the outer edge of the end face 10 (i.e., in this example, the junction between the chamfer 16 and the side surface 8 of the fuel pellet 4) is selected. The third radial distance M3 is equal to the third radius R3 here.

[0143] Figure 9 The end face 10 of the shown core 4 has a slightly tapered edge 14. This allows for the illustration of an example of a non-zero first axial distance D1. In another example, the edge 14 can be radial, i.e., each edge 14 extends in a plane perpendicular to the core axis A, whereby the first axial distance D1 is considered approximately zero.

[0144] In an alternative embodiment, the measurement module 48 is configured to measure the axial distance relative to the transverse plane ETP of the end face over the entire length of the measurement portion MP of the shaded contour corresponding to the end face 10, the measurement portion MP being located between two radial distances relative to the fuel pellet axis A, for example, between a first radial distance M1 and a third radial distance M3 as shown here.

[0145] Using the midline transverse plane (MTP) and / or the end transverse plane (ETP) as references for calculating distances, lengths, and / or areas allows for better classification of defects, for example, in cases where one side has surface damage and the other side has a protrusion.

[0146] Optionally, the measurement module 48 is configured to check the validity of the end lateral plane ETP by measuring the total length of the fuel pellet 4 at the lowest point of the field of view (i.e., at the distance closest to the fuel pellet axis A, at which the outline of the fuel pellet 4 is projected without disturbance or obstruction from the support device 20 and / or the moving device 32).

[0147] In one exemplary embodiment, the measurement module 48 is configured such that if a deviation in the total length of the fuel pellet 4 is detected at the inner edge of the edge 14 or in the disc-shaped portion 12, these measurements are deemed unreliable and the fuel pellet 4 is rejected. In practice, such a deviation could be due to large defects (surface damage or protrusions) in the edge or recessed area.

[0148] exist Figure 10 In the embodiment shown, the light emitter 42 is configured to emit a light beam 44, which has a one-dimensional shape in cross-section (i.e., in a plane perpendicular to the optical axis C).

[0149] The beam 44 preferably has the shape of a straight segment in cross-section. The straight segment extends parallel to the pellet axis A of the fuel pellet 4 supported on the support device 20.

[0150] The light-emitting line 54 of the light emitter 42 has the shape of a beam 44. The photosensitive line 56 of the photodetector 46 also has the shape of a beam 44.

[0151] Such an optical measuring device 40 is named a "linear optical micrometer". The light emitter 42 and the light detector 44 are named linear light emitter 42 and linear light detector 44.

[0152] The optical measuring device 40 that can be used is either the Micro-Epsilon optoCONTROL 2520 or the Keyence series LS-9000.

[0153] The beam 44 is emitted onto a portion of the fuel cell 4, and the length of the beam 44 intercepted by the fuel cell 4, i.e. the length of the shadow cast or produced by the fuel cell 4 on the photodetector 46, corresponds to the apparent length of that irradiated portion of the fuel cell 4.

[0154] The measurement module 48 is configured to measure the length of the irradiated portion of the fuel pellet 4 based on the light detected by the photodetector 46 and, in particular, the length of a portion of the beam 44 that has been intercepted by the fuel pellet 4.

[0155] like Figure 11 As shown, beam 44 intersects the reference plane RP at a radial distance M1 or M2 from the core axis A.

[0156] The beam 44 is emitted, for example, at a radial distance M1 from the core axis A to the core 4 supported by the support device 20, the radial distance M1 being greater than or equal to the inner radius (first radius R1) of the edge 16 and less than or equal to the outer diameter (second radius R2) of the edge 14.

[0157] At such a radial distance M1 from the axis A of the fuel pellet, the length of the intercepted beam 44 corresponds to the distance between two axially aligned edge portions of the end face 10 of the fuel pellet 4, which is substantially located in the reference axial plane RAP, i.e., the edge-to-edge length of the fuel pellet 4 at an angular position in the reference axial plane RAP.

[0158] Therefore, surface loss affecting these edge portions can be detected. A length shorter than expected indicates that surface loss affects one or both of these edge portions. Protrusions affecting these edge portions can also be detected. A length longer than expected indicates that a protrusion affects one or both of these edge portions.

[0159] If beam 44 is emitted at a distance from the core axis A below the inner diameter (first radius R1) of edge 14, the interception length of beam 44 can correspond to two circumferentially spaced edge portions on each end face 10, such that a defect on one of the two edge portions can be hidden by the other edge portion.

[0160] Alternatively, beam 44 is emitted at a radial distance M2 from the core axis A, which is greater than or equal to the inner diameter (second radius R2) of chamfer 16 and less than or equal to the outer diameter (third radius R3) of chamfer 16.

[0161] At such a radial distance M2 from the axis A of the fuel pellet, the length of the intercepted beam 44 corresponds to the distance between two axially aligned chamfered portions of the end face 10 of the fuel pellet 4, which are substantially located in the reference axial plane RAP, i.e., the chamfer-to-chamfer length of the fuel pellet 4 at the angular position in the reference axial plane RAP.

[0162] Therefore, surface damage affecting these chamfered sections can be detected. A length shorter than expected indicates that surface damage affects one or both of these chamfered sections. Protrusions affecting these chamfered sections can also be detected. A length longer than expected indicates that a protrusion affects one or both of these chamfered sections.

[0163] The optical measuring device 40 allows for the measurement of the distance between two axially aligned chamfered portions of the end face 10 located in the reference plane RP and / or the distance between two axially aligned edge portions of the end face 10 located in the reference plane RP.

[0164] The above description of the measurement of the geometric parameters of the shadow cast by the fuel pellet 4 on the photodetector 46 by the measurement module 48 for a corner position of the fuel pellet 4 has been performed.

[0165] Optionally, the support device 20 is configured to rotate the fuel pellet 4 about the pellet axis A while measuring the shadow produced by the fuel pellet 4 with the optical measuring device 40, so as to allow the determination of the corresponding geometric parameters of the fuel pellet 4 at multiple angular positions (i.e., at multiple positions along the circumference of the end face 10, preferably along the entire circumference of the end face 10) of the fuel pellet 4 about the fuel pellet axis (i.e., at multiple positions along the circumference of the end face 10, preferably along the entire circumference of the end face 10).

[0166] Therefore, when the optical measuring device 40 performs measurements of the edge-to-edge length, the edge-to-central transverse plane length, the chamfer-to-chamfer length, the chamfer-to-central transverse plane length, and / or the distance from the end transverse plane to the end face for the entire circumference of the fuel pellet 4, the drive device 30 drives the roller 24 in the same angular direction (see...). Figure 3 Rotate along the arrow R) to drive fuel pellet 4 to rotate around pellet axis A.

[0167] Performing one or more measurements on the circumference of the end face 10 of the fuel pellet 4 can help automatically detect defects on the end face 10 and / or distinguish surface damage or protrusions of different shapes.

[0168] When measurements are performed for each of a plurality of angular positions of fuel pellet 4 around fuel pellet axis A, where applicable, a central transverse plane MTP and / or an end transverse plane ETP are determined for each angular position of fuel pellet 4 to calculate the associated distance, length and / or area.

[0169] Angular positions can be discrete.

[0170] In one example, the number of angular positions being measured is greater than or equal to 360, specifically 390. This allows measurements to be performed on angular positions at angular intervals of 1° or less between two sequential angular positions.

[0171] Figure 12 This is a perspective view of a fuel pellet 4 having three surface losses S1, S2, and S3 distributed on the circumference of the end face 10 of the fuel pellet 4. The three surface losses S1, S2, and S3 exhibit different shapes.

[0172] Figures 13 to 15 This shows the reference. Figure 9 The graph shows the axial distances D1, D2, and D3 measured at different radial distances M1, M2, and M3 during the discussion, which vary with the angular position of fuel pellet 4 around the fuel pellet axis A.

[0173] Each graph shows curves C1, C2, and C3 representing the measured values ​​of the corresponding axial distances D1, D2, and D3 (vertical axis) as the angular position (horizontal axis) of fuel pellet 4 changes.

[0174] In the example shown, each curve C1, C2, C3 extends mainly close to the expected values ​​V1, V2, V3, including three valleys where curves C1, C2, C3 move away from the expected values ​​V1, V2, V3, each valley corresponding to one of the three surface losses S1, S2, S3.

[0175] As shown here, the valleys extend downwards relative to the expected values ​​V1, V2, V3 and correspond to surface losses S1, S2, S2. Defects such as protrusions will produce peaks that extend upwards relative to the expected values ​​V1, V2, V3.

[0176] In one example, the measurement module 48 is configured to establish corresponding curves C1, C2, C3 for the measured values ​​of the corresponding axial distances D1, D2, D3 that vary with the angular position of the fuel pellet 4 for each radial distance M1, M2, M3.

[0177] For example, measurement module 48 is configured to detect peaks and / or valleys, and to identify defects when the difference between the peak or valley value and the expected value V1, V2, V3 is higher than a detection threshold. Exceeding the threshold indicates that the change exceeds manufacturing tolerances and is a defect in fuel pellet 4.

[0178] Advantageously, the measurement module 48 is configured to classify defects by analyzing each curve C1, C2, C3.

[0179] In one example, measurement module 48 is configured to measure the width of each valley, the sum of the widths of all valleys, the depth of each valley, the width of each peak, the sum of the widths of all peaks, and / or the height of each peak to classify each detected defect. The width of a valley or the width of a peak corresponds to the angular extension of the defect.

[0180] Advantageously, the measurement module 48 is configured to classify defects based on measurements of the width of each valley, the sum of the widths of all valleys, the depth of each valley, the width of each peak, the sum of the widths of all peaks, and / or the height of each peak.

[0181] For surface loss, the width of the valley is generally more important than the depth of the valley (for chip quality).

[0182] In one example, measurement module 48 is configured to classify defects characterized by a valley whose width is greater than its height as surface loss.

[0183] For protrusions, the height of the peak is generally more important than the width of the valley (for chip quality).

[0184] In one example, the measurement module 48 is configured to classify defects characterized by a peak height greater than its height as protrusions.

[0185] Furthermore, measuring the axial distance along the entire measuring section MP and along the entire circumference of the end face 10 allows for the generation of a 3D map of points in an annular region of the end face 10 centered on the fuel pellet axis B and corresponding to the measuring section MP.

[0186] The measurement module 48 can then be configured to compare the 3D image with the expected image to detect and / or classify defects on the end face 10 of the fuel pellet 4.

[0187] In addition, 3D maps can be used to generate images, which can be presented to an operator, for example, to check the detection performed by the measurement module 48.

[0188] In one example, the measurement module 48 is configured to generate a 3D image file based on the measurements performed above, which corresponds to the 3D diagram and encodes a 3D image representing the end face 10.

[0189] Optionally or alternatively, the measurement module 48 is configured to generate a 2D image file that encodes a 2D image corresponding to the 3D image, wherein the 3D bumps of the end face 10 are encoded in the 2D image, for example, in grayscale or in color.

[0190] In one example, the 2D image represents a strip with two parallel sides, one corresponding to the outer peripheral edge of end face 10 and the other corresponding to the inner edge of edge 14.

[0191] Alternatively or optionally, the 2D image represents a disc-shaped portion having an outer edge corresponding to the outer peripheral edge of the end face 10 and an inner edge corresponding to the inner edge of the edge 14.

[0192] Optionally, the support device 20 is configured to translate the core block 4 along the core block axis A while rotating the core block 4 and measuring it with the optical measuring device 40. This allows the core block 4 to be inspected on its circumference while being conveyed along the roller 24.

[0193] Axial movement is provided to the fuel pellet 4, for example by the moving device 32, and the pushing member 34 is conveyed along the roller 24, thereby pushing the fuel pellet 4 along the roller 24.

[0194] Preferably, when each end face 10 has a disc-shaped portion 12, an edge 14, and a chamfer 14, the pushing member 34 is configured to contact the center of the disc-shaped portion 12 of the end face 10 of the fuel pellet 4 to push the fuel pellet 4 without contacting the edge 14 and / or the chamfer 14 (more specifically, without contacting or concealing the edge portion and / or the chamfer portion located in the reference axial plane RAP). Therefore, the pushing member 34 will at least not intercept the beam 44 in the area of ​​the measurement distance.

[0195] The light emitter 42 and the light detector 46 are preferably configured such that the extension of the light beam 44 along the core axis A is greater than the length of the core 4 plus the distance traveled by the fuel core 4 during at least one complete rotation of the fuel core 4 around the core axis A.

[0196] This allows the geometric parameters of the fuel pellet 4 to be measured over the entire circumference of the end face 10 while the beam 44 is intercepted as the fuel pellet 4 travels between the light emitter 42 and the light detector 46.

[0197] In one embodiment, the light emitter 42 and the light detector 46 are preferably configured such that the extension of the light beam 44 along the fuel cell axis A allows for simultaneous measurement of multiple fuel cells (e.g., two fuel cells, three fuel cells, or more fuel cells).

[0198] In embodiments using a two-dimensional light emitter 42 and a two-dimensional light detector 46, the light detector 46 includes, for example, a matrix light sensor, which is a light sensor comprising a plurality of photosensitive pixels arranged in a matrix.

[0199] Advantageously, the photodetector 46 is configured to activate only a portion of the area covered by the photodetector sufficient to perform one or more measurements operated by the measurement module 48, while the remainder of the photodetector remains inactive.

[0200] Figure 6 The box AF above shows an example of a possible working part of a light sensor. Figure 6 The remaining part corresponds to the non-working portion of the optical sensor.

[0201] The working part can be less than 20% of the area of ​​the light sensor, or even less than 10% of the area of ​​the light sensor.

[0202] Using only a portion of the light sensor allows for faster processing via the light detector 46. Furthermore, it simplifies the analysis performed by the measurement module 48, as only the relevant portions of the shadow appear in the data acquired by the light detector 46, and the locations of the edges, points, and planes required for measurement are identified more easily and quickly. Therefore, it allows for increased productivity, i.e., an increase in the number of fuel pellets processed per unit time.

[0203] In one example, the light emitter 42 is configured to emit a light beam in the form of light pulses, preferably based on instructions from the photodetector 46. Thus, the light emitter 42 is driven by the photodetector 46, and the photodetector 46 is therefore configured to instruct the light emitter 42 to emit light pulses.

[0204] In a known manner, the light detector 46 is capable of capturing 'images' at a given frequency (i.e., a given number of images per unit time). The time between two consecutive images captured by the light detector 46 corresponds to the time required to collect data from the light sensor of the light detector 46 (specifically from multiple pixels of the light sensor).

[0205] The photodetector 46, configured to drive the emitter 42 to emit light pulses, allows the light emitter 42 to be synchronized with the photodetector 46.

[0206] In addition, each “image” is captured by the light detector 46 using the exposure time (i.e., the duration for which the light sensor is exposed to the beam of light emitted by the light emitter 42).

[0207] Preferably, the photodetector 46 and the light emitter 42 are configured such that the light beam is emitted only during a portion of the exposure time when the image is captured. For this purpose, the emission of the light beam begins after the start of the exposure time and / or ends before the end of the exposure time.

[0208] In one implementation, the duration of the light pulse emitted by the light emitter 42 for capturing the image is strictly shorter than the exposure time of the light detector 46 for capturing the image. In one example, the exposure time is 450 microseconds (μs) or less, while the duration of the light pulse includes between 50 and 100 μs.

[0209] This allows for a sharper shadow and thus enhances the accuracy of measurements operated by the measurement module 48, i.e., when the fuel pellet 4 rotates about the fuel pellet axis A and / or moves axially along the fuel pellet axis A.

[0210] Furthermore, especially when using electroluminescent diodes (or LEDs) as light sources to generate light, this allows for reduced motion blur, increased expected lifetime of (one or more) light sources, and / or increased light intensity compared to permanent lighting.

[0211] In various examples, the measurement module 48 is preferably configured to compare geometric parameters (e.g., distance, length, or area) with expected values ​​and to emit a defect signal when the geometric parameters differ from the expected values. Therefore, the fuel pellets can be retrieved for further inspection and / or rejection.

[0212] In various examples, the measurement module 48 is provided, for instance, as a computer program executed by a data processing unit 58 comprising a memory 60 and a processor 62, wherein the computer program is stored in the memory 60 and the processor 62 is configured to execute the computer program stored in the memory 60. Alternatively, the measurement module 48 is provided as a programmable logic device (“PLD”), such as a field-programmable gate array (“FPGA”) or an application-specific integrated circuit (“ASIC”).

[0213] The inspection system 18 allows for the execution of a method for inspecting fuel pellet 4 of nuclear fuel that is rotationally symmetric about the pellet axis A. The method includes positioning the fuel pellet 4 on a support device 20 and using an optical measuring device 40 to determine at least one geometric parameter of the shadow cast by the fuel pellet 4 in order to detect possible defects on the end face 10 of the fuel pellet 4.

[0214] The inspection method includes, for example, measuring the edge-to-edge length or edge-to-center plane length of the fuel pellet 4 at one or more locations on the circumference of the edge 14, preferably over the entire circumference of the edge 14, and / or measuring the chamfer-to-chamfer length or chamfer-to-center plane length of the fuel pellet 4 at one or more locations on the circumference of the chamfer 16, preferably over the entire circumference of the chamfer 16.

[0215] Measurements at different locations or along the entire circumference are performed by rotating the fuel pellet 4 about the pellet axis A and optionally advancing the fuel pellet 4 along the pellet axis A while measuring the length, so as to measure the length while the fuel pellet 4 is being conveyed along the support device 20.

[0216] Thanks to this invention, optical measurements of the geometric parameters of fuel pellets can be performed reliably and with good accuracy. Optical measurements allow for the detection of defects affecting the periphery of the end face of fuel pellet 4, typically defects such as surface damage and protrusions. Rotation of the fuel pellet about its axis allows for inspection of the entire circumference of the end face of the fuel pellet.

[0217] Because the distance between the fuel pellet and the components of the optical measurement device remains constant, optical measurements can be performed even when the fuel pellet is being transported axially, using a beam emitted along an optical axis perpendicular to the pellet axis.

[0218] An optical measuring device provided as a 2D optical micrometer (or profilometer) allows for the measurement of multiple lengths and / or areas of the shadow cast by the irradiated portion of the fuel pellet 4.

[0219] The optical measuring device provided by the linear optical micrometer allows for the measurement of a length, such as edge-to-edge length or chamfer-to-chamfer length.

[0220] However, compared to 2D optical micrometers, linear optical micrometers have the advantage of very high measurement frequencies (e.g., above or equal to 2 kHz) for standard and commercial off-the-shelf devices, while maintaining the same measurement accuracy (from 1 to 15 μm).

[0221] Multiple linear optical micrometers can be combined in the same or different reference axial planes RAP to obtain different lengths of fuel pellet 4.

[0222] In one example, the inspection system includes two optical measuring devices provided by a linear optical micrometer, which are arranged to measure different lengths of the fuel pellet 4.

[0223] In a particular example where the end face 10 of the fuel pellet 4 has a disc-shaped portion 12, an edge 14, and a chamfer 16, the inspection system 18 includes a first linear optical micrometer arranged to measure the edge-to-edge length of the fuel pellet 4 and a second linear optical micrometer arranged to measure the chamfer-to-chamfer length of the fuel pellet 4.

[0224] The inspection system 18 and its operation have been described in more detail in conjunction with the fuel pellet 4, which includes end faces 10, each having a disc-shaped portion 12, an edge 14, and a chamfer 16.

[0225] The inspection system 18 can also be used to inspect fuel pellets 4 with end faces 10 of different shapes.

[0226] Specifically, the inspection system 18 can also be used to inspect fuel pellets 4 with end faces 10 without chamfers 16, i.e., only the edge 14 defines the extension between the side face 8 and the disc-shaped portion 12. The edge 14 has, for example, only a very slight taper. The angle between the edge and the plane perpendicular to the pellet axis A includes, for example, between 0° and 5°.

[0227] Alternatively, the inspection system 18 can also be used to inspect annular fuel pellets, i.e., the disc-shaped portion 12 is replaced by an axial orifice extending from one end face 10 to the other end face 10 through the fuel pellet 4.

[0228] It is important to note that Figure 4 The moving device 32 shown is designed to push onto the disc-shaped portion 12 and may not provide satisfactory operation for fuel pellets with annular designs (i.e., no disc-shaped portion 12 on each end face 10). The moving device 32 can therefore be adapted to push on another surface of the fuel pellet 4, or to inspect the fuel pellet 4 when it is stationary along the pellet axis A.

[0229] The measurements performed on the shadows cast by the fuel pellet 4 are adjusted according to the shape of the end face 10 of the fuel pellet 4. In particular, the end face to end face length, the end face to midline transverse plane length, or the end face to end transverse plane distance is obtained at an appropriate radial distance from the pellet axis A based on the profile of the end face in a side view along the optical axis of the optical measuring device.

[0230] In the illustrated embodiment, the inspection system 18 is configured such that the optical axis C is perpendicular to the reference axis B and therefore perpendicular to the fuel pellet axis A. The shadow projected onto the photodetector 46 thus corresponds to the edge profile of the fuel pellet 4, including its end face 10.

[0231] In other embodiments, the optical axis C is tilted relative to the fuel pellet axis A, that is, neither perpendicular to nor parallel to the fuel pellet axis A.

[0232] If the optical axis C is tilted relative to the fuel pellet axis A, the shadow projected onto the photodetector 46 will be different compared to the case where the optical axis C is perpendicular to the fuel pellet axis A.

[0233] However, the orientation of the optical axis C can be selected to facilitate the detection of specific defects on specific surfaces of fuel pellets.

[0234] The optical axis C can be selected to be tangent to, for example, a specific portion of an end face 10 (e.g., the corner sector of edge 14 or the corner sector of chamfer 16).

[0235] Preferably, the optical axis C and the transverse plane perpendicular to the fuel pellet axis A define an angle between 0° and 25°. The 0° angle corresponds to the optical axis C perpendicular to the fuel pellet axis A.

[0236] In the example above, a single fuel pellet 4 is inspected. While multiple fuel pellets 4 can certainly be inspected continuously using the support device 20 and / or the moving device 32, each fuel pellet 4 is inspected individually, with the fuel pellets 4 axially spaced apart from each other.

[0237] In another example, such as Figure 16 As shown, the inspection system 18 can be configured to simultaneously inspect multiple fuel pellets 4 stacked in a column 64 of fuel pellets 4, where the fuel pellet axes A are coaxial. The fuel pellets 4 of the column 64 are in contact with each other. More specifically, the facing end faces 10 of each pair of adjacent fuel pellets 4 in the column 64 are in contact with each other.

[0238] In this configuration, the measurement module 48 is configured to simultaneously perform measurements on multiple fuel pellets 4 of the cylinder 4. This is in Figure 16 The above is achieved by measuring each fuel pellet simultaneously ( Figure 16The three fuel pellets on the surface are shown with the central transverse plane MTP and the end transverse plane ETP, as well as the distances measured with reference to these planes (see double arrows).

[0239] The post 64 may be stationary during inspection. Alternatively, during inspection, the post 64 may be rotated such that each fuel pellet 4 rotates about its fuel pellet axis A, and / or the post 64 may be moved axially such that each fuel pellet 4 moves along its fuel pellet axis A. Thus, each end face 10 of each fuel pellet 4 of the post 64 can be inspected along the entire circumference of the end face 10.

[0240] Simultaneous inspection of multiple fuel pellets 4 arranged in columns 64 can be achieved by either using at least one 2D optical micrometer or using at least one linear optical micrometer, as described above for inspecting one fuel pellet 4 at a time.

[0241] For clarity of the accompanying drawings, such as Figure 16 As shown, only the three fuel pellets 4 of column 64 are checked simultaneously (fuel pellets 4 that define the reference plane). In practice, more than three fuel pellets 4 can be checked simultaneously, especially more than ten fuel pellets, such as approximately twenty fuel pellets 4.

[0242] In addition, Figure 16 The above only shows some measurements using the central transverse plane MTP and the end transverse plane ETP; however, of course all the different measurements described above for a single fuel pellet 4 are also applicable to multiple fuel pellets 4 being examined simultaneously.

[0243] In the example above, the inspection system 18 is configured to detect defects on the end face 10 of each fuel pellet 4.

[0244] Optionally or alternatively, the inspection system 18 may be configured to detect defects affecting the side 8 of the fuel pellet 4, particularly near each end face 10 or in the joint area between the side 8 and each end face 10.

[0245] In fact, a possible defect in fuel pellet 4 is an end cap crack, that is, a circumferential crack near the outer edge of end face 10, which is either on end face 10 itself or on the side face 8 near end face 10.

[0246] Figure 17 The shadow cast by fuel pellet 4 in a 2D optical micrometer is shown, which is reflected on end face 10. Figure 17 The outline of the shadow near the left side of the fuel pellet 4 corresponds to the end cap crack on the side 8.

[0247] For comparison, fuel pellet 4 has another end face 10 ( Figure 17 There are no end cap cracks near the right side.

[0248] The measurement module 48 of the inspection system 18 is configured, for example, to detect that the portion of the shadow outline corresponding to the side 8 of the fuel pellet 4 is not straight and / or to detect patterns such as indentations 66 in the portion of the shadow outline corresponding to the side 8.

[0249] The detection of defects affecting the side 8 of fuel pellet 4 can be achieved using Figure 17 The 2D optical micrometer shown can be used for detection, or an inspection system 48 including a linear optical micrometer can be used. In the latter case, it can be detected as an interruption of the linear shadow neatly generated by the fuel pellet 4 at one end of the linear shadow.

[0250] In a general manner, the inspection system 48 is able to detect any defects that affect the shadows cast by the fuel pellet 4, which interrupts the beam of light between the light emitter and the photodetector.

Claims

1. An inspection system for inspecting a fuel pellet (4) of nuclear fuel or a plurality of such fuel pellets (4) arranged in a column (64), the fuel pellet (4) being rotationally symmetrical about a pellet axis (A) and having sides (8) and two end faces (10), the inspection system comprising a support device (20) for supporting the fuel pellet (4) such that the pellet axis (A) of each fuel pellet (4) coincides with a reference axis (B), the optical measurement device (40) being arranged for optically measuring the fuel pellet (4), the optical measurement device (40) comprising being configured to emit a light beam propagating along an optical axis (C). The light emitter (42) and the photodetector (46) arranged to receive the light beam (44), wherein each fuel pellet (4) interrupts the light beam (44) and produces a shadow projected onto the photodetector (46), the optical measurement device (40) includes a measurement module (48) configured to analyze the shadow to detect possible defects on the end face (10) and / or the side face (8) of each fuel pellet (4), and the measurement module (48) is configured to analyze the shadow produced by each pellet (4) by determining at least one axial dimension (L1, L2) at a expected radial distance (M1, M2) from the axis (A) of the pellet.

2. The inspection system according to claim 1, wherein, The measurement module (48) is configured to measure at least one geometric parameter of the shadow to detect possible defects on the end face (10) and / or the side face (8) of each fuel pellet (4).

3. The inspection system according to claim 1, wherein, The optical axis (C) and the plane perpendicular to the reference axis (B) define an angle between 0° and 45°.

4. The inspection system according to claim 1, wherein, The optical axis (C) and the plane perpendicular to the reference axis (B) define an angle between 0° and 25°.

5. The inspection system according to claim 1, wherein, The support device (20) is configured to rotate each fuel pellet (4) about its pellet axis (A).

6. The inspection system according to claim 5, wherein, The measurement module (48) is configured to analyze the shadow during at least one complete rotation of each fuel pellet (4) in order to analyze the entire circumference of each end face (10) and / or the entire circumference of the side face (8) of each fuel pellet (4).

7. The inspection system according to claim 1, wherein, The inspection system is configured to axially transport the fuel pellets (4) along the reference axis (B).

8. The inspection system according to claim 1, wherein, The beam (44) is linear, and the shadow produced by each fuel pellet (4) is segmented in shape. The measurement module (48) is configured to measure the length of the shadow produced by each fuel pellet (4) to determine the corresponding length of the fuel pellet (4) and the presence of defects on the end face (10) and / or the side face (8) of the fuel pellet (4).

9. The inspection system according to claim 1, wherein, The beam (44) is two-dimensional, and the shadow cast by each fuel pellet (4) is two-dimensional.

10. The inspection system according to claim 1, wherein, The measurement module (48) is configured to analyze the shadow generated by each fuel pellet (4) by determining the position of the lateral plane of the fuel pellet (4) and determining at least one axial distance between the lateral plane and the side of the shadow profile corresponding to the end face (10).

11. The inspection system according to claim 1, wherein, The measurement module (48) is configured to determine the position of the central transverse plane (MTP) of the fuel pellet (4) and to determine the length of the shadow generated by each fuel pellet (4), the length of which is taken between the central transverse plane (MTP) and the edge of the shadow's outline, to determine the corresponding length of the fuel pellet (4).

12. The inspection system according to claim 1, wherein, The measurement module (48) is configured to analyze the shadow produced by each fuel pellet (4) by determining the position of the end transverse plane (ETP) of the end face (10) perpendicular to the pellet axis (A) for at least one end face (10) or for each end face (10) and calculating at least one axial distance (D1, D2, D3) between the end transverse plane (ETP) and the side of the shadow profile corresponding to the end face (10).

13. The inspection system according to claim 1, wherein, The measurement module (48) is configured to determine a 3D map of at least a portion of at least one end face (10) of each fuel pellet (4) based on the analysis of the shadows produced by the fuel pellets (4).

14. The inspection system according to claim 13, wherein, The measurement module (48) is configured to generate a 3D image file that corresponds to the 3D diagram and encodes a 3D image representing the end face (10) and / or to generate a 2D image file that encodes a 2D image corresponding to the 3D diagram.

15. The inspection system according to claim 1, wherein, The measurement module (48) is configured to detect surface loss on the end face (10) of each fuel pellet (4) and / or protrusions on the end face (10) of each fuel pellet (4) and / or end capping between one of the end faces (10) and the side face (8) of each fuel pellet (4).

16. A method for inspecting fuel pellets of nuclear fuel using the inspection system according to claim 1, wherein the fuel pellets are rotationally symmetric about a pellet axis (A).

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