A calibration method for a CT inspection system for nuclear fuel rod welds

Abstract

This invention relates to the field of non-destructive testing of nuclear fuel elements, and more particularly to a calibration method for a CT inspection system for nuclear fuel rod welds. The calibration method, based on the CT inspection system, includes the following steps: adjusting the detector's level; placing a small metal ball between the X-ray source and the detector, ensuring the ball is within the imaging area, and connecting the ball to a coordinate measuring machine (CMM) slide; adjusting the rotation angle of the CT inspection system to align with the CMM slide; adjusting the detector's in-plane rotation angle; adjusting the height difference; aligning the three points (sun, moon, and sphere); aligning the three points through the rotation center; and, within the adjusted CT inspection system, moving the metal ball to different positions, recording the movement distance and projected image coordinates, and calculating the surface area displacement (SOD) and surface area displacement (SDD) using the movement distance and projected image coordinates. This invention features a simple phantom and high accuracy.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing of nuclear fuel elements, and more particularly to a calibration method for a CT inspection system for nuclear fuel rod welds. Background Technology

[0002] Currently, some calibration methods for industrial CT inspection systems are patented. However, for X-ray CT inspection of nuclear fuel rod welds, no research results have been found on dedicated equipment with strong specificity. Furthermore, calibration methods specifically for CT inspection systems of nuclear fuel rod welds need improvement. Most methods require the manufacture of complex calibration phantoms, and manufacturing errors in these phantoms can affect calibration accuracy. Therefore, there is an urgent need in this field for a simple, high-precision calibration method. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a calibration method for a CT inspection system for nuclear fuel rod welds, which has a simple model and high accuracy.

[0004] This invention provides a calibration method for a CT inspection system for nuclear fuel rod welds, which is based on the CT inspection system and includes the following steps:

[0005] Step S1: Adjust the detector's level so that the detector plane is perpendicular to the movement trajectory of the Y-axis guide rail of the horizontal turntable;

[0006] Step S2: Place a small metal ball between the X-ray source and the detector, ensuring the metal ball is located within the imaging area and connected to the coordinate measuring machine slide. Adjust the rotation angle of the CT detection system so that the Y-axis guide rail of the horizontal turntable is parallel to the Y-axis guide rail of the coordinate measuring machine slide.

[0007] Step S3: Adjust the in-plane rotation angle of the detector to align the detector;

[0008] Step S4: Adjust the position of the metal ball along the Z-axis guide rail of the three-coordinate slide table so that the line connecting the focal point of the X-ray source and the center of the metal ball is perpendicular to the detector.

[0009] Step S5: Align the focal point of the X-ray source, the center point of the metal sphere, and the center point of the detector plane with the three points in a straight line;

[0010] Step S6: Adjust the three points to pass through the rotation center; or make the line connecting the X-ray source focus and the rotation center of the horizontal turntable parallel to the Y-axis guide rail of the horizontal turntable;

[0011] Step S7: In the adjusted CT detection system, the metal ball is moved to different positions, the moving distance and the projected image coordinates are recorded, and the distance from the focal point to the rotation center SOD and the distance from the focal point to the detector SDD are calculated using the moving distance and the projected image coordinates.

[0012] Furthermore, the CT detection system includes: a base, a lateral moving device, a slide, a radial moving device, a support frame, a horizontal turntable, a horizontal turntable Y-axis guide rail, a detector, and an X-ray source;

[0013] A lateral moving device is installed on the base, a slide is installed on the lateral moving device, a horizontal turntable is installed on the slide, a horizontal turntable Y-axis guide rail is installed on the horizontal turntable, a radial moving device is installed on the guide rail, a support frame is installed on the radial moving device, and a radiation source and a detector are respectively installed at the upper and lower ends of the support frame.

[0014] Further, step S2 specifically includes:

[0015] Step S2-1: Place a small metal ball between the X-ray source and the detector, so that the metal ball is located in the imaging area and is connected to the three-coordinate sliding table;

[0016] Step S2-2: Adjust the angle of the horizontal turntable until the projection position of the metal ball on the detector remains unchanged at 0° and 180°.

[0017] Step S2-3: Adjust the Y-axis guide rail of the horizontal rotary table and the Y-axis guide rail of the three-coordinate slide table to make them parallel.

[0018] Furthermore, step S2-2 specifically includes:

[0019] Step S221: At a 0° viewing angle, take an image of the metal ball with the detector and record the coordinate position L1 of the metal ball projected in the image; rotate the horizontal turntable 180 degrees and record the coordinate position L2 of the metal ball projected in the image.

[0020] Step S221: If the coordinate positions L1 and L2 are different, rotate the turntable by a small angle and return to step 221;

[0021] If the coordinate positions L1 and L2 are the same, the adjustment is complete, and the current rotation angle Ang1 of the horizontal turntable is recorded.

[0022] Furthermore, steps S2-3 specifically include:

[0023] Step S231: The metal ball moves along the Y-axis of the three-coordinate sliding table, moving closer to or away from the radiation source.

[0024] When the projected coordinates of the metal ball when it is close to the X-ray source are inconsistent with the projected coordinates of the metal ball when it is far away from the X-ray source, the metal ball is moved along the X-axis guide rail of the three-coordinate slide table, and the moving direction DirX is recorded.

[0025] Movement can be divided into the following two cases:

[0026] If the metal ball moves away from the X-ray source along the Y-axis guide rail of the three-coordinate slide table and the projected image of the ball keeps increasing, then the metal ball should be moved a small distance along the X-axis guide rail of the three-coordinate slide table in the direction that the projected image of the ball becomes smaller.

[0027] If the metal ball moves away from the X-ray source along the Y-axis guide rail of the three-coordinate slide, and the projected image of the ball first becomes smaller and then larger, then the metal ball should be moved a small distance along the X-axis guide rail of the three-coordinate slide, and the direction of movement should be the direction in which the projected image of the ball keeps getting larger.

[0028] Step S232: Repeat step S2-2, this time recording the angle Ang2 of the horizontal turntable and the rotation direction DirR:

[0029] Step S233: Repeat steps S231 and S232 until the projected coordinates of the metal ball when it is close to the X-ray source are the same as those when it is far away from the X-ray source. Then proceed to step S234. At this time, record the mechanical position coordinates L3 of the ball along the X-axis of the three-coordinate slide.

[0030] Step S234: The X-ray source and detector move synchronously along the Y-axis guide rail of the horizontal turntable, so that the X-ray source is closer to or farther away from the metal ball. When the projected coordinate position of the ball that is closer to the metal ball is inconsistent with the projected coordinate position of the ball that is farther away from the metal ball, the metal ball is moved along the DirX direction of the X-axis guide rail of the three-coordinate slide table.

[0031] When the image coordinates of the metal ball projected onto the detector U direction remain unchanged when it is close to or far from the radiation source, step S237 is executed to record the projection coordinates L4 of the metal ball.

[0032] Step S235: Rotate the horizontal turntable by a small angle in the DirR direction;

[0033] Step S236: Return to step S234;

[0034] Step S237: Subtract the position coordinates L3 and L4 of the metal ball to obtain the distance Ds that the focal point of the ray source needs to move;

[0035] Record the coordinates of the metal ball on the detector, that is, the coordinates (Us, Vs) of the X-ray source focus on the detector in the U and V directions.

[0036] The distance (Du, Dv) that the detector needs to move can be calculated by subtracting the coordinates (Us, Vs) of the focal point of the X-ray source on the detector in the U and V directions from the coordinates (Uc, Vc) of the detector center.

[0037] Record the angular position Ang3 of the horizontal rotary table. This angular position ensures that the Y-axis guide rail 2 of the horizontal rotary table and the Y-axis guide rail of the three-coordinate slide table are parallel.

[0038] Furthermore, step S3 specifically includes:

[0039] The metal ball moves along the X-axis guide rail of the three-coordinate slide to the left side of the detector, and the coordinate position (u1, v1) of the metal ball projected on the detector is recorded.

[0040] The metal ball moves along the X-axis guide rail of the three-coordinate slide to the right side of the detector, and the coordinate position (u2, v2) of the metal ball projected on the detector is recorded.

[0041] If v1 and v2 are not equal, adjust the in-plane rotation angle of the detector until v1 = v2, so that the detector is aligned.

[0042] Further, step S4 specifically includes:

[0043] Step S4-1: Move the metal ball along the Y-axis guide rail of the three-coordinate slide table. Move the metal ball a certain distance towards the X-ray source and record its projected image coordinates (Unear, Vnear); move the metal ball a certain distance away from the X-ray source and record its projected image coordinates (Ufar, Vfar).

[0044] Step S4-2: If Vfar and Vnear are inconsistent, and Vfar is less than Vnear, then the metal ball is moved a small distance along the direction of decreasing V coordinates of the projected image on the Z-axis guide rail of the three-coordinate slide table; if Vfar is greater than Vnear, then the metal ball is moved a small distance along the direction of increasing V coordinates of the projected image on the Z-axis guide rail of the three-coordinate slide table.

[0045] Then return to step S4-1;

[0046] If Vfar = Vnear, then stop adjusting.

[0047] Further, step S5 specifically includes:

[0048] After adjustments in steps S2 and S4, the focal point of the X-ray source and the metal ball are aligned.

[0049] Adjust the detector position based on Du and Dv obtained in step S2, align the detector center with the focal point of the X-ray source, and achieve a straight line between the focal point of the X-ray source, the center point of the metal ball, and the center point of the detector plane.

[0050] Further, step S6 specifically includes:

[0051] Based on the radiation source movement distance Ds obtained in step S2,

[0052] Simultaneously translate the X-ray source, the metal ball, and the detector by a distance Ds, so that the line connecting the center of the X-ray source and the center of the detector passes through the rotation center of the horizontal turntable.

[0053] Alternatively, step S6 may specifically include:

[0054] Move the metal ball to position Ds and return it to position B2;

[0055] Adjust and move the ray source in the opposite direction of the DirZ direction, Ds;

[0056] Adjust the distance between the X-ray source and the metal ball, change the magnification ratio, and record the coordinate positions of the projected images of the ball under two different magnification ratios. When the coordinate positions remain unchanged, the accuracy of the X-ray source focus movement is verified, ensuring that the line connecting the X-ray source focus and the rotation center is parallel to the Y-axis guide rail of the horizontal turntable.

[0057] Furthermore, step S7 specifically includes:

[0058] Move the metal ball along the X-axis and Z-axis guide rails of the three coordinate system, and image it at four positions. Record the image coordinates p1, p2, p3, and p4 of the metal ball projected onto the detector U direction, respectively.

[0059] Determine the distance L that the metal ball moves along the guide rail in the X-axis direction and the distance H that it moves along the guide rail in the Z-axis direction of the three coordinate system;

[0060] The distance from the focal point to the rotation center (SOD) and the distance from the focal point to the detector (SDD) are calculated as follows:

[0061] (1);

[0062] (2).

[0063] Compared with the prior art, the calibration method of the present invention for the CT inspection system of nuclear fuel rod welds uses a single metal sphere phantom to image the sphere and repeatedly adjust the mechanism to make the system meet the geometric relationship of CT imaging, and finally calculates the geometric parameters of the system for CT image reconstruction. Attached Figure Description

[0064] Figure 1 A schematic diagram showing the structure of the metal ball and the CT detection system;

[0065] Figure 2 A simplified diagram illustrating a metal ball and a CT detection system;

[0066] Figure 3 A flowchart illustrating the calibration method of this invention;

[0067] Figure 4 This indicates the first adjustment state when adjusting the rotation angle of the CT detection system;

[0068] Figure 5 This indicates adjustment state two when adjusting the rotation angle of the CT detection system;

[0069] Figure 6 This indicates adjustment state three when adjusting the rotation angle of the CT detection system;

[0070] Figure 7 This indicates adjustment status four when adjusting the rotation angle of the CT detection system;

[0071] Figure 8 A schematic diagram showing the movement of the metal ball during actual measurement;

[0072] In the picture,

[0073] 1-Horizontal turntable; 2-Horizontal turntable Y-axis guide rail; 3-Radiation source; 4-Three-coordinate slide table Y-axis guide rail; 5-Three-coordinate slide table X-axis guide rail; 6-Three-coordinate slide table Z-axis guide rail; 7-Detector; 8-Metal ball.

[0074] C is the rotation center of the horizontal turntable, and B, B1, and B2 are different positions of the metal ball. Detailed Implementation

[0075] To further understand the present invention, embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the present invention.

[0076] In this invention, the three-axis slide has guide rails in three directions: the X-axis guide rail, the Y-axis guide rail, and the Z-axis guide rail; the three are perpendicular to each other.

[0077] In a CT scan system, the Y-axis guide rail of the horizontal turntable is a radial guide rail.

[0078] This invention uses a single metal ball as a calibration phantom. By imaging the metal ball and repeatedly adjusting the mechanism, the system satisfies the geometric relationship of CT imaging. Finally, the geometric parameters of the system are calculated for CT image reconstruction.

[0079] An embodiment of the present invention discloses a calibration method for a CT inspection system for nuclear fuel rod welds, which is based on the CT inspection system for calibration.

[0080] like Figure 1 and Figure 2As shown, the CT detection system includes: a base, a lateral moving device, a slide, a radial moving device, a support frame, a horizontal rotary table 1, a horizontal rotary table Y-axis guide rail 2, a detector 7, and a radiation source 3.

[0081] A transverse moving device is installed on the base, a slide is installed on the transverse moving device, a horizontal turntable 1 is installed on the slide, a horizontal turntable Y-axis guide rail 2 is installed on the horizontal turntable 1, a radial moving device is installed on the horizontal turntable Y-axis guide rail 2, a support frame is installed on the radial moving device, and a radiation source 3 and a detector 7 are respectively installed at the upper and lower ends of the support frame.

[0082] Driven by the horizontal turntable 2, the X-ray source 3 and the detector 7 rotate around the metal sphere 8.

[0083] A small metal ball 8 is fixed on a three-coordinate slide, and the small metal ball 8 is a calibration model.

[0084] The three-coordinate sliding stage is used in conjunction with the CT detection system to complete the calibration.

[0085] Since the Y-axis guide rail 4 of the coordinate measuring machine slide table is not parallel to the Y-axis guide rail 2 of the horizontal rotary table during installation, it is necessary to adjust the angle of the horizontal rotary table to make the Y-axis guide rail 4 of the coordinate measuring machine slide table parallel to the Y-axis guide rail 2 of the horizontal rotary table in preparation for subsequent calibration.

[0086] Calibration method as follows Figure 3 As shown, the specific steps include:

[0087] Step S1: Adjust the level of detector 1 so that the plane of detector 7 is perpendicular to the movement trajectory of the Y-axis guide rail of the horizontal turntable;

[0088] Specifically:

[0089] Place the level on the plane of detector 7, measure the levelness along the horizontal and vertical sides of detector 7, and adjust the attitude of detector 7 by screws so that the level reading is close to 0 with an error of 0.01 degrees.

[0090] Step S2: Place a small metal ball 8 between the X-ray source 3 and the detector 7, so that the small metal ball 8 is located in the imaging area and is connected to the three-coordinate slide; adjust the rotation angle of the CT detection system so that the Y-axis guide rail 2 of the horizontal turntable is parallel to the Y-axis guide rail 4 of the three-coordinate slide.

[0091] Step S2 specifically includes:

[0092] Step S2-1: Place a small metal ball 8 between the X-ray source 3 and the detector 7, so that the small metal ball 8 is located in the imaging area, and the small metal ball 8 is connected to the three-coordinate sliding table;

[0093] Step S2-2 specifically includes:

[0094] Step S221: At a 0° viewing angle, the detector 7 captures an image of the metal ball and records the coordinate position L1 of the metal ball 8 projected in the image; the horizontal turntable is rotated 180 degrees and the coordinate position L2 of the metal ball 8 projected in the image is recorded.

[0095] Step S222: If the coordinate positions L1 and L2 are different, rotate the turntable by a small angle and return to step 221;

[0096] If coordinate positions L1 and L2 are the same, such as Figure 4 As shown, the adjustment is complete. Record the current rotation angle Ang1 of the horizontal turntable 1.

[0097] The minute angle is 1°.

[0098] Step S2-3: Adjust the Y-axis guide rail 2 of the horizontal rotary table and the Y-axis guide rail 4 of the three-coordinate slide table to make them parallel.

[0099] like Figure 4 In the middle, the position of metal ball 8 is B1, and the adjustment starts from this position;

[0100] Specifically, it includes:

[0101] Step S231: The metal ball moves along the Y-axis guide rail 5 of the three-coordinate slide table, moving closer to or further away from the radiation source 3.

[0102] When the projected coordinates of the metal ball 8 when it is close to the X-ray source 3 are inconsistent with the projected coordinates of the metal ball 8 when it is far away from the X-ray source 3, the metal ball 8 is moved along the guide rail 4 of the three-coordinate slide table in the X-axis direction, and the moving direction DirX is recorded.

[0103] Movement can be divided into the following two cases:

[0104] If the metal ball 8 moves away from the X-ray source along the Y-axis guide rail 4 of the coordinate sliding table, and the projected image of the ball keeps increasing, then the metal ball 8 should be moved a small distance along the X-axis guide rail 5 of the coordinate sliding table, in the direction that the projected image of the ball decreases; that is... Figure 5 In the middle, the metal ball 8 moves from position B1 to position B2;

[0105] The minute distance is 0.5mm;

[0106] If the metal ball moves along the Y-axis guide rail 4 of the coordinate measuring machine away from the X-ray source, and the projected image of the ball first decreases and then increases, then the metal ball 8 should be moved along the X-axis guide rail 5 of the coordinate measuring machine in the direction in which the projected image of the ball continuously increases; that is... Figure 6 In the middle, the metal ball 8 moves from position B2 to position B1;

[0107] Step S232: Repeat step S2-2, this time recording the angle Ang2 of the horizontal turntable 1 and the rotation direction DirR:

[0108] Step S233: Repeat steps S231 and S232 until the projected coordinates of the metal ball 8 when it is close to the X-ray source 3 are the same as the projected coordinates of the metal ball 8 when it is far away from the X-ray source 3. Then proceed directly to step S234. At this time, record the mechanical position coordinates L3 of the ball along the X-axis of the three-coordinate slide.

[0109] Step S234: Make the X-ray source 3 and detector 7 move synchronously along the Y-axis guide rail 2 of the horizontal turntable, so that the X-ray source 3 moves closer to or further away from the metal ball 8, thereby adjusting the imaging magnification ratio;

[0110] When the projected coordinates of the metal ball 8 when it is close to the metal ball 8 are inconsistent with the projected coordinates when it is far away from the metal ball 8, then the metal ball 8 is moved along the DirX direction of the guide rail 5 of the three-coordinate slide table; for example Figure 7 In the middle, the metal ball 8 moves from position B2 to position B3;

[0111] When the image coordinates of the metal ball projected onto the detector U direction remain unchanged as the X-ray source 3 approaches or moves away from the metal ball 8, step S237 is executed to record the projection coordinates L4 of the metal ball 8 at this time.

[0112] Step S235: Rotate the horizontal turntable 1 by a small angle in the DirR direction; the small angle is 0.1 degrees;

[0113] Step S236: Return to step S234;

[0114] Step S237: Subtract the position coordinates L3 and L4 of the metal ball 8 to obtain the distance Ds that the focal point of the ray source 3 needs to move;

[0115] Record the coordinates of the metal ball 8 on the detector 7, that is, the coordinates (Us, Vs) of the X-ray source focus in the U and V directions on the detector 7.

[0116] The distance (Du, Dv) that detector 7 needs to move can be calculated by subtracting the coordinates (Us, Vs) of the focal point of the X-ray source on the detector in the U and V directions from the coordinates (Uc, Vc) of the center of detector 7.

[0117] Record the angular position Ang3 of the horizontal rotary table 1. This angular position ensures that the Y-axis guide rail 2 of the horizontal rotary table and the Y-axis guide rail 4 of the three-coordinate slide table are parallel.

[0118] Step S3: Adjust the in-plane rotation angle of the detector to align the detector;

[0119] Specifically, it includes:

[0120] The metal ball 8 moves along the X-axis guide rail 5 of the three-coordinate slide table to the left side of the detector 7, and the coordinate position (u1, v1) of the metal ball 8 projected onto the detector 7 is recorded;

[0121] The metal ball 8 moves along the X-axis guide rail 5 of the three-coordinate slide table to the right side of the detector, and the coordinate position (u2, v2) of the metal ball 8 projected on the detector 7 is recorded.

[0122] If v1 and v2 are not equal, adjust the in-plane rotation angle of the detector, that is, rotate it around the Y-axis.

[0123] Until v1 = v2, thus aligning detector 7;

[0124] Step S4: Adjust the position of the metal ball 8 along the Z-axis of the three-coordinate slide table guide rail 6 so that the line connecting the focal point of the X-ray source and the center of the ball is perpendicular to the detector 7.

[0125] Specifically, it includes:

[0126] Step S4-1: Move the metal ball 8 along the Y-axis guide rail 4 of the three-coordinate slide table. Move the metal ball a certain distance towards the X-ray source and record its projected image coordinate position (Unear, Vnear); move the metal ball a certain distance away from the X-ray source and record its projected image coordinate position (Ufar, Vfar).

[0127] Step S4-2: If Vfar and Vnear are inconsistent, and Vfar is less than Vnear, then move the metal ball a small distance along the direction of decreasing V coordinates on the Z-axis guide rail of the three-coordinate slide table; if Vfar is greater than Vnear, then move the metal ball a small distance along the direction of increasing V coordinates on the Z-axis guide rail of the three-coordinate slide table; then return to step S4-1.

[0128] If Vfar = Vnear, then stop adjusting;

[0129] The minute distance is 0.5mm;

[0130] Step S5: Align the focal point of the X-ray source, the center point of the metal sphere, and the center point of the detector plane with the three points in a straight line;

[0131] Specifically, it includes:

[0132] After adjustments in steps S2 and S4, the focal point of the X-ray source and the metal ball are aligned.

[0133] Adjust the detector position according to Du and Dv obtained in step S2, align the detector center with the X-ray source focus, and achieve a straight line between the X-ray source focus, the center point of the metal ball, and the center point of the detector plane.

[0134] Step S6: Adjust the three points to pass through the rotation center; or make the line connecting the focal point of the X-ray source and the rotation center of the horizontal turntable parallel to the Y-axis guide rail 2 of the horizontal turntable;

[0135] Specifically, it includes:

[0136] Based on the radiation source movement distance Ds obtained in step S2,

[0137] Simultaneously translate the X-ray source 3, the metal ball 8, and the detector 7 by a distance Ds, so that the line connecting the center of the X-ray source 3 and the center of the detector 7 passes through the center of the horizontal turntable rotation 1.

[0138] Alternatively, step S6 may specifically include:

[0139] Move the metal ball 8 to position Ds, returning it to position B2, as shown. Figure 7 As shown;

[0140] Adjust and move the ray source 3 in the opposite direction of the DirZ direction by Ds;

[0141] Adjust the distance between the X-ray source 3 and the metal ball 8, change the magnification ratio, and record the coordinate positions of the projected images of the ball under two different magnification ratios. When the coordinate positions remain unchanged, the accuracy of the X-ray source focus movement is verified, ensuring that the line connecting the X-ray source focus and the rotation center is parallel to the Y-axis guide rail 2 of the horizontal turntable.

[0142] After adjusting steps S1 to S6, the CT detection system and calibration device are adjusted.

[0143] Step S7: In the adjusted CT detection system, the metal ball 8 is moved to different positions, the moving distance and the projected image coordinates are recorded, and the distance from the focal point to the rotation center SOD and the distance from the focal point to the detector SDD are calculated using the moving distance and the projected image coordinates.

[0144] Step S7 specifically includes:

[0145] like Figure 8 As shown, the metal ball is moved along the X-axis guide rail 5 and the Z-axis guide rail 6 of the three coordinate system, and images are formed at four positions. The image coordinates p1, p2, p3, and p4 of the metal ball projected onto the detector U direction are recorded respectively.

[0146] Determine the distance L that the metal ball moves along the guide rail in the X-axis direction and the distance H that it moves along the guide rail in the Z-axis direction of the three coordinate system;

[0147] The distance from the focal point to the rotation center (SOD) and the distance from the focal point to the detector (SDD) are calculated as follows:

[0148] (1);

[0149] (2).

[0150] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0151] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A calibration method for a CT inspection system for nuclear fuel rod welds, characterized in that, Calibration based on a CT detection system includes the following steps: Step S1: Adjust the detector's level so that the detector plane is perpendicular to the movement trajectory of the Y-axis guide rail of the horizontal turntable; Step S2: Place a small metal ball between the X-ray source and the detector, ensuring the metal ball is located within the imaging area and connected to the coordinate measuring machine slide. Adjust the rotation angle of the CT detection system so that the Y-axis guide rail of the horizontal turntable is parallel to the Y-axis guide rail of the coordinate measuring machine slide. Specifically, it includes: Step S2-1: Place a small metal ball between the X-ray source and the detector, so that the metal ball is located in the imaging area and is connected to the three-coordinate sliding table; Step S2-2: Adjust the angle of the horizontal turntable until the projection position of the metal ball on the detector remains unchanged at 0° and 180°. Step S2-3: Adjust the Y-axis guide rail of the horizontal rotary table and the Y-axis guide rail of the three-coordinate slide table to make them parallel; Step S2-3 specifically includes: Step S231: The metal ball moves along the Y-axis of the three-coordinate sliding table, moving closer to or away from the radiation source. When the projected coordinates of the metal ball when it is close to the X-ray source are inconsistent with the projected coordinates of the metal ball when it is far away from the X-ray source, the metal ball is moved along the X-axis guide rail of the three-coordinate slide table, and the moving direction DirX is recorded. Movement can be divided into the following two cases: If the metal ball moves away from the X-ray source along the Y-axis guide rail of the three-coordinate slide table and the projected image of the ball keeps increasing, then the metal ball should be moved a small distance along the X-axis guide rail of the three-coordinate slide table in the direction that the projected image of the ball becomes smaller. If the metal ball moves away from the X-ray source along the Y-axis guide rail of the three-coordinate slide, and the projected image of the ball first becomes smaller and then larger, then the metal ball should be moved a small distance along the X-axis guide rail of the three-coordinate slide, and the direction of movement should be the direction in which the projected image of the ball keeps getting larger. Step S232: Repeat step S2-2, this time recording the angle Ang2 of the horizontal turntable and the rotation direction DirR: Step S233: Repeat steps S231 and S232 until the projected coordinates of the metal ball when it is close to the X-ray source are the same as those when it is far away from the X-ray source. Then proceed to step S234. At this time, record the mechanical position coordinates L3 of the ball along the X-axis of the three-coordinate slide. Step S234: The X-ray source and detector move synchronously along the Y-axis guide rail of the horizontal turntable, so that the X-ray source is closer to or farther away from the metal ball. When the projected coordinate position of the ball that is closer to the metal ball is inconsistent with the projected coordinate position of the ball that is farther away from the metal ball, the metal ball is moved along the DirX direction of the X-axis guide rail of the three-coordinate slide table. When the image coordinates of the metal ball projected onto the detector U direction remain unchanged when it is close to or far from the radiation source, step S237 is executed to record the projection coordinates L4 of the metal ball. Step S235: Rotate the horizontal turntable by a small angle in the DirR direction; Step S236: Return to step S234; Step S237: Subtract the position coordinates L3 and L4 of the metal ball to obtain the distance Ds that the focal point of the ray source needs to move; Record the coordinates of the metal ball on the detector, that is, the coordinates (Us, Vs) of the X-ray source focus on the detector in the U and V directions. The distance (Du, Dv) that the detector needs to move can be calculated by subtracting the coordinates (Us, Vs) of the focal point of the X-ray source on the detector in the U and V directions from the coordinates (Uc, Vc) of the detector center. Record the angular position Ang3 of the horizontal rotary table. This angular position ensures that the Y-axis guide rail of the horizontal rotary table and the Y-axis guide rail of the three-axis slide table are parallel. Step S3: Adjust the in-plane rotation angle of the detector to align the detector; Step S4: Adjust the position of the metal ball along the Z-axis guide rail of the three-coordinate slide table so that the line connecting the focal point of the X-ray source and the center of the metal ball is perpendicular to the detector. Step S5: Align the focal point of the X-ray source, the center point of the metal sphere, and the center point of the detector plane with the three points in a straight line; Step S6: Adjust the three points to pass through the rotation center; or make the line connecting the X-ray source focus and the rotation center of the horizontal turntable parallel to the Y-axis guide rail of the horizontal turntable; Step S7: In the adjusted CT detection system, the metal ball is moved to different positions, the moving distance and the projected image coordinates are recorded, and the distance from the focal point to the rotation center SOD and the distance from the focal point to the detector SDD are calculated using the moving distance and the projected image coordinates.

2. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 1, characterized in that, The CT detection system includes: a base, a lateral moving device, a slide, a radial moving device, a support frame, a horizontal turntable, a horizontal turntable Y-axis guide rail, a detector, and a radiation source; A lateral moving device is installed on the base, a slide is installed on the lateral moving device, a horizontal turntable is installed on the slide, a horizontal turntable Y-axis guide rail is installed on the horizontal turntable, a radial moving device is installed on the guide rail, a support frame is installed on the radial moving device, and a radiation source and a detector are respectively installed at the upper and lower ends of the support frame.

3. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 1, characterized in that, Step S2-2 specifically includes: Step S221: At a 0° viewing angle, take an image of the metal ball with the detector and record the coordinate position L1 of the metal ball projected in the image; rotate the horizontal turntable 180 degrees and record the coordinate position L2 of the metal ball projected in the image. Step S222: If the coordinate positions L1 and L2 are different, rotate the turntable by a small angle and return to step 221; If the coordinate positions L1 and L2 are the same, the adjustment is complete, and the current rotation angle Ang1 of the horizontal turntable is recorded.

4. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 2, characterized in that, Step S3 specifically includes: The metal ball moves along the X-axis guide rail of the three-coordinate slide to the left side of the detector, and the coordinate position (u1, v1) of the metal ball projected on the detector is recorded. The metal ball moves along the X-axis guide rail of the three-coordinate slide to the right side of the detector, and the coordinate position (u2, v2) of the metal ball projected on the detector is recorded. If v1 and v2 are not equal, adjust the in-plane rotation angle of the detector until v1 = v2, so that the detector is aligned.

5. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 1, characterized in that, Step S4 specifically includes: Step S4-1: Move the metal ball along the Y-axis guide rail of the three-coordinate slide table. Move the metal ball a certain distance towards the X-ray source and record its projected image coordinates (Unear, Vnear); move the metal ball a certain distance away from the X-ray source and record its projected image coordinates (Ufar, Vfar). Step S4-2: If Vfar and Vnear are inconsistent, and Vfar is less than Vnear, then the metal ball is moved a small distance along the direction of decreasing V coordinates of the projected image on the Z-axis guide rail of the three-coordinate slide table; if Vfar is greater than Vnear, then the metal ball is moved a small distance along the direction of increasing V coordinates of the projected image on the Z-axis guide rail of the three-coordinate slide table. Then return to step S4-1; If Vfar = Vnear, then stop adjusting.

6. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 1, characterized in that, Step S5 specifically includes: After adjustments in steps S2 and S4, the focal point of the X-ray source and the metal ball are aligned. Adjust the detector position based on Du and Dv obtained in step S2, align the detector center with the focal point of the X-ray source, and achieve a straight line between the focal point of the X-ray source, the center point of the metal ball, and the center point of the detector plane.

7. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 1, characterized in that, Step S6 specifically includes: Based on the radiation source movement distance Ds obtained in step S2, Simultaneously translate the X-ray source, the metal ball, and the detector by a distance Ds, so that the line connecting the center of the X-ray source and the center of the detector passes through the rotation center of the horizontal turntable. Alternatively, step S6 may specifically include: Move the metal ball to position Ds and return it to position B2; Adjust and move the ray source in the opposite direction of the DirZ direction, Ds; Adjust the distance between the X-ray source and the metal ball, change the magnification ratio, and record the coordinate positions of the projected images of the ball under two different magnification ratios. When the coordinate positions remain unchanged, the accuracy of the X-ray source focus movement is verified, ensuring that the line connecting the X-ray source focus and the rotation center is parallel to the Y-axis guide rail of the horizontal turntable.

8. The calibration method for a CT inspection system for nuclear fuel rod welds according to claim 1, characterized in that, Step S7 specifically includes: Move the metal ball along the X-axis and Z-axis guide rails of the three coordinate system, and image it at four positions. Record the image coordinates p1, p2, p3, and p4 of the metal ball projected onto the detector U direction, respectively. Determine the distance L that the metal ball moves along the guide rail in the X-axis direction and the distance H that it moves along the guide rail in the Z-axis direction of the three coordinate system; The distance from the focal point to the rotation center (SOD) and the distance from the focal point to the detector (SDD) are calculated as follows: （1）； （2）。

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