A method for inspecting defects in CRDM thermal insulation casing

Abstract

This application belongs to the field of thermal insulation sleeve defect inspection technology, and aims to solve the problem that nuclear power plants do not have a systematic CRDM thermal insulation sleeve defect inspection method and cannot systematically eliminate the safety hazards of the unit. This application discloses a CRDM thermal insulation sleeve defect inspection method, which systematically analyzes the pile-type movement and possible fault forms of the CRDM thermal insulation sleeve. Without disassembling any components, it measures the actual height, thickness, and cracks of the CRDM thermal insulation sleeve, calculates the height settlement and wall wear, and determines whether the position has moved downward, whether there is wall thinning at the lower pipe mouth, and whether there are cracks at the flange reduction part, thereby completing the systematic defect inspection of the CRDM thermal insulation sleeve. This application can improve the safety of nuclear reactor unit operation, optimize the in-service inspection content of core overhaul, provide technical guidance for the in-service inspection content of nuclear power plants, and provide a technical route and reference plan for the development of subsequent inspection equipment.

Description

Technical Field

[0001] The present application belongs to the technical field of thermal insulation sleeve defect inspection, and in particular relates to a CRDM thermal insulation sleeve defect inspection method. Background Art

[0002] like Figure 1 As shown, the CRDM thermal sleeve 3 (i.e., the control rod drive mechanism thermal sleeve) is a component of the control rod drive mechanism (CRDM). It consists of a flanged end, a thermal sleeve, and a guide cover. The upper portion is a flange, the middle portion is a straight tube section, and the lower portion is a flared end. Made of stainless steel, the CRDM thermal sleeve 3 is suspended from the conical inner wall of the CRDM tube base 2. This non-fixed, suspended installation structure allows clearance between the outer diameter of the sleeve and the inner bore of the tube base, leaving no longitudinal constraint. This allows for upward floating during rod drop, and can produce radial oscillation, circumferential rotation, and axial movement under the influence of in-core flow-induced vibrations. Located within the reactor pressure vessel head penetration, the CRDM thermal sleeve 3 is made of stainless steel and is a critical component relevant to nuclear safety. Its primary functions are to reduce the temperature difference between the inner and outer tube walls, minimize upward heat transfer, guide the drive rods during capping, and squeeze water during rod drop, optimizing rod drop time.

[0003] The in-pile movement of the CRDM thermal insulation sleeve 3 is relatively complex, and external experience feedback describes various fault forms. Currently, nuclear power plants lack a mature preventive inspection program to systematically guide the defect inspection work of the CRDM thermal insulation sleeve 3, posing a hidden danger to unit safety. Summary of the Invention

[0004] The purpose of this application is to provide a CRDM insulation sleeve defect inspection method to solve the problem that nuclear power plants have no systematic CRDM insulation sleeve defect inspection method and cannot systematically eliminate safety hazards of the units.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] This application provides a CRDM insulation sleeve defect inspection method, comprising:

[0007] Step 1: Determine the fault mode based on the in-pile movement of the CRDM thermal sleeve;

[0008] Step 2: Without disassembling any components, measure the actual height, thickness, and cracks of the CRDM thermal sleeve, and calculate the height settlement and wall wear. Use the height settlement to determine if the CRDM thermal sleeve has moved downward. Use the wall wear to determine if there is wall thinning between the CRDM thermal sleeve and the lower pipe opening of the CRDM pipe seat. Use crack measurement to determine if there are cracks in the flange reduction area of the CRDM thermal sleeve.

[0009] According to one embodiment of the present application, step 2 specifically includes:

[0010] Step 2.1: Position the height detection device below the CRDM insulation sleeve to be tested;

[0011] Step 2.2: Select a measurement reference and measure the height difference between the CRDM thermal insulation sleeve and the measurement reference;

[0012] Step 2.3: Calculate the difference between the height difference and the theoretical value to obtain the height settlement;

[0013] Step 2.4: Position the wall thickness detection device to the CRDM insulation sleeve to be tested under the top cover;

[0014] Step 2.5: Move the scanner from the inner bore of the CRDM insulation casing to the thinning point. Locate the target location by lifting the scanner. Use phased array ultrasound to measure the casing section to find the thinnest wall thickness.

[0015] Step 2.6: Calculate the difference between the measured wall thickness and the theoretical wall thickness to obtain the wall wear amount;

[0016] Step 2.7: Use a crack detection device to measure the reduced diameter position of the CRDM upper end to detect whether there are cracks in the reduced diameter part of the flange.

[0017] According to one embodiment of the present application, a method for calculating the height settlement includes:

[0018] Position the height check device below the CRDM insulation sleeve;

[0019] Select the fixed component on the top cover as the measurement reference. The measurement reference can be any one of the upper end face of the CRDM tube seat, the lower end face of the CRDM tube seat, and the lower end face of the bell mouth of the thermocouple tube seat.

[0020] Measure and calculate the height difference between the CRDM thermal insulation sleeve and the measurement benchmark, and calculate the height settlement.

[0021] According to one embodiment of the present application, with the upper end face of the CRDM tube seat as the measurement reference, the theoretical distance between the upper end face of the CRDM thermal insulation sleeve and the upper end face of the CRDM tube seat is h1, and the actual distance after settlement is h1'. The actual distance between the upper end face of the CRDM thermal insulation sleeve and the upper end face of the CRDM tube seat is measured to be h1', and the calculated height settlement is △h=h1'-h1.

[0022] According to one embodiment of the present application, taking the lower pipe opening of the CRDM pipe seat as the measurement reference, the theoretical relative distance between the lower pipe opening of the CRDM pipe seat and the upper end face of the bell mouth of the CRDM thermal insulation sleeve is h2, the actual distance between the two planes is measured as h2', and the height settlement is calculated to be △h=h2'-h2.

[0023] According to one embodiment of the present application, taking the lower end surface of the bell mouth of the thermocouple tube seat as the measurement reference, the theoretical value of the relative elevation difference between the bell mouth of the thermocouple tube seat and the bell mouth of the thermal insulation sleeve is h3, the measured value of the relative elevation difference is h3', and the calculated settlement height of the thermal insulation sleeve is △h=h3'-h3.

[0024] According to one embodiment of the present application, the wall thickness and crack detection of the CRDM thermal insulation sleeve is performed by first detecting the wall thickness and then detecting the cracks. The steps include:

[0025] The carrier carrying the phased array ultrasonic testing device moves to the position under the top cover corresponding to the CRDM insulation sleeve to be tested;

[0026] Using the vehicle's lifting mechanism and video inspection device, a scanner equipped with a phased array probe is transported from the inner bore of the CRDM insulation casing to the area where the wall thickness is reduced. The target position is locked by the lifting height, and phased array ultrasound is used to measure the casing section to find the thinnest wall thickness.

[0027] Compare with the theoretical wall thickness to obtain the wall wear amount;

[0028] The crack detection device is continuously lifted to the upper end diameter reduction position through the lifting mechanism, and the height position is preliminarily determined. The diameter reduction position is locked and the position is positioned according to the signal feedback from the phased array probe.

[0029] Perform a circular scan to check whether there are any cracks in the flange reduction area.

[0030] According to one embodiment of the present application, a method for calculating the wall thickness wear includes:

[0031] Position the wall thickness detection device below the CRDM insulation sleeve;

[0032] Lift the wall thickness measuring probe from inside the CRDM insulation sleeve;

[0033] Position the wall thickness measuring probe at the CRDM nozzle;

[0034] The wall thickness at the rubbing position between the CRDM thermal insulation sleeve and the CRDM pipe mouth was measured and compared with the original value to calculate the wall thickness wear.

[0035] According to one embodiment of the present application, a crack measurement method includes:

[0036] Position the crack detection device below the CRDM insulation sleeve;

[0037] Lift the crack detection probe from inside the CRDM insulation sleeve;

[0038] Position the crack detection probe at the flange reduction area at the upper end of the CRDM insulation sleeve;

[0039] The crack detection probe is used to scan the flange in the circumferential and axial directions to detect the flange reduction area.

[0040] According to one embodiment of the present application, the failure forms include wear of the end of the CRDM thermal insulation sleeve resulting in a drop in position, wear of the CRDM thermal insulation sleeve and the lower pipe opening of the CRDM pipe seat, and fatigue fracture of the necking transition zone of the upper end of the CRDM thermal insulation sleeve.

[0041] Compared with the prior art, the CRDM insulation sleeve defect inspection method provided by this application has the following beneficial effects:

[0042] This application improves the operational safety of nuclear reactor units and optimizes the in-service inspection content for core overhauls. It systematically analyzes the reactor motion and potential failure modes of CRDM thermal sleeves and provides specific inspection content and targeted inspection methods for CRDM thermal sleeves. This application provides technical guidance for in-service inspections at nuclear power plants and offers a technical roadmap and reference solutions for the development of subsequent inspection equipment.

[0043] This application systematically completes the CRDM insulation sleeve defect inspection without disassembling any components.

[0044] This application specifies the content and process technology for defect inspection of CRDM thermal sleeves, applicable to the CNP600, CNP1000, and Hualong One reactor types. By reviewing existing failure cases, studying the in-core movement of thermal sleeves, and analyzing common failure modes for these three reactor types, this application eliminates blind spots in defect inspection for CRDM thermal sleeves in nuclear power plants and implements systematic CRDM defect inspection, including processes for checking CRDM thermal sleeve settlement, wall wear, and cracks.

[0045] Furthermore, the present application provides three methods for measuring the height settlement of the thermal insulation sleeve, which respectively use the upper end face of the CRDM tube seat, the lower tube mouth of the CRDM tube seat, and the lower end face of the bell mouth of the thermocouple tube seat as measurement references.

[0046] Furthermore, the present application provides a process for measuring the wall thickness of the thermal insulation sleeve and detecting crack defects at the necking portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings required for the technical description.

[0048] Figure 1A partial schematic diagram of the installation of a CRDM thermal insulation sleeve in the prior art;

[0049] Figure 2 It is an overall schematic diagram of the installation of the CRDM thermal insulation sleeve in the prior art;

[0050] Figure 3 It is an overall cross-sectional schematic diagram of the installation of the CRDM thermal insulation sleeve in the prior art;

[0051] Figure 4 A schematic diagram of the distance between the CRDM thermal insulation sleeve and the upper end surface of the control rod guide tube in the prior art;

[0052] Figure 5 The installation dimension drawing of the CRDM thermal insulation sleeve and the lower pipe opening of the CRDM pipe seat in the prior art;

[0053] Figure 6 This is a comparison diagram of the CRDM thermal insulation casing in the prior art before and after settlement;

[0054] Figure 7 Schematic diagram of the height difference between the bell mouth of the thermal insulation sleeve and the bell mouth of the thermocouple in the prior art;

[0055] Figure 8 Schematic diagram of thinning the wall thickness of the CRDM thermal insulation sleeve in the prior art;

[0056] Figure 9 Schematic diagram of the crack location at the necking of the CRDM thermal insulation sleeve in the prior art;

[0057] Figure 10 Flowchart of the CRDM insulation sleeve defect inspection method provided in this application;

[0058] Figure 11 Flowchart of settlement detection provided for this application;

[0059] Figure 12 Flowchart of wall thickness detection provided for this application;

[0060] Figure 13 Flowchart of crack detection provided for this application.

[0061] Description of reference numerals:

[0062] 1. Thermocouple tube socket; 2. CRDM tube socket; 3. CRDM thermal insulation sleeve; 4. Top cover; 5. Biological shielding wall; 6. Control rod guide tube; 7. Control rod drive mechanism pressure shell; 8. Thermocouple tube socket bell mouth; 9. Small door; 10. Thermal insulation sleeve bell mouth. DETAILED DESCRIPTION

[0063] The following is further detailed description through specific implementation methods.

[0064] This application systematically analyzes the in-pile movement and possible fault forms of the CRDM thermal insulation sleeve, determines the inspection content of the CRDM thermal insulation sleeve 3, and adopts corresponding inspection methods in a targeted manner. Figures 1 to 9 As shown, the in-pile motion analysis of the CRDM thermal insulation sleeve 3 is as follows:

[0065] The CRDM thermal sleeve 3 has only two degrees of freedom constrained in space. This structural design allows for small-distance movement in the X and Y directions, as well as movement in the Z direction and rotation about the Z axis. Under the influence of coolant flow, the CRDM thermal sleeve 3 can move in radial direction, circumferential direction, and axial direction.

[0066] Since the CRDM thermal insulation sleeve 3 is a non-fixed component, it vibrates slightly under the impact of the coolant flow in the reactor, which may cause fretting wear or fracture cracks.

[0067] During the operation of the unit, the CRDM thermal insulation sleeve 3 is affected by the vibration caused by the flow of the primary circuit medium, resulting in friction between its upper end and the CRDM pipe base flange, and friction between its lower end and the CRDM pipe base penetration piece.

[0068] The defects of CRDM thermal insulation sleeve 3 mainly take the form of wear and fracture. After fracture, the control rod will fall into the control rod guide tube, and there is a risk of control rod jamming during the falling process, resulting in a rod jam event, which poses a serious risk to nuclear safety operation.

[0069] According to the analysis of empirical feedback information and the inspection results of the power plant, the CRDM thermal insulation sleeve 3 mainly has potential defects such as high settlement, wall wear and thinning, and cracks at the necking area.

[0070] Based on the above analysis, the present application provides a CRDM insulation sleeve defect inspection method, comprising the following steps:

[0071] Step 1: Analyze the in-pile movement of the CRDM thermal insulation sleeve 3 and determine the fault mode. The fault modes include downward movement of the CRDM thermal insulation sleeve 3, wear between the CRDM thermal insulation sleeve 3 and the lower pipe opening of the CRDM pipe base 2, and fatigue fracture in the necking transition zone at the upper end of the CRDM thermal insulation sleeve 3.

[0072] Step 2: Based on the identified fault type, without disassembling any components, use a detection device to measure the actual height, thickness, and cracks of the CRDM thermal insulation sleeve 3. This test determines whether the CRDM thermal insulation sleeve 3 has moved downward, whether the CRDM thermal insulation sleeve 3 has thinned at the friction point between the CRDM thermal insulation sleeve 3 and the through-piece end (between the CRDM thermal insulation sleeve 3 and the lower end of the CRDM pipe base 2), or whether the flange reduction area of the CRDM thermal insulation sleeve 3 has cracks.

[0073] Among them, the measurement results of the height settlement of the thermal insulation sleeve are used to determine whether the position of the CRDM thermal insulation sleeve 3 has moved downward, the measurement results of the wall thickness of the thermal insulation sleeve are used to determine whether there is wall thinning at the friction point between the CRDM thermal insulation sleeve 3 and the through-piece port, and the crack measurement results are used to determine whether there is a crack at the flange reduction point of the CRDM thermal insulation sleeve 3.

[0074] In step 2, the detection device includes three types of defect detection devices, using existing height detection devices, wall thickness detection devices, and crack detection devices. In crack detection, only the presence of cracks needs to be determined. If cracks are detected, the product is unqualified, and the judgment is made through ultrasonic signals.

[0075] In one embodiment, Figure 10 As shown, step 2 includes the following steps:

[0076] Step 2.1: Position the height detection device below the CRDM thermal insulation sleeve 3 to be tested;

[0077] Step 2.2: Select a fixed component on the top cover 4 as the measurement reference and measure the height difference between the CRDM thermal insulation sleeve 3 and the measurement reference;

[0078] Step 2.3: Calculate the difference between the height difference and the theoretical value to obtain the height settlement;

[0079] Step 2.4: Position the wall thickness detection device at the position of the CRDM insulation sleeve 3 to be tested below the top cover 4;

[0080] Step 2.5: Move the scanner from the inner hole of CRDM insulation casing 3 to the thinning point. Locate the target location by lifting the scanner. Use phased array ultrasound to measure the casing section to find the thinnest wall thickness.

[0081] Step 2.6: Calculate the difference between the measured wall thickness and the theoretical wall thickness to obtain the wall wear amount;

[0082] Step 2.7: Use a crack detection device to measure the reduced diameter position of the CRDM upper end to detect whether there are cracks in the reduced diameter part of the flange.

[0083] After completing the above steps, analyze the results of settlement inspection, wall thickness wear inspection, and crack inspection, and formulate corresponding treatment measures.

[0084] In step 1, determining the fault type includes:

[0085] Since the CRDM thermal insulation sleeve is a non-fixed component, it vibrates slightly under the impact of the coolant flow in the reactor, which can cause micro-wear or fracture cracks.

[0086] Under the influence of the reactor cooling bypass flow, the CRDM thermal insulation sleeve 3 and the CRDM tube base 2 move relative to each other, causing continuous wear. During unit operation, the CRDM thermal insulation sleeve 3 is affected by the vibration caused by the primary circuit medium flow, resulting in friction between its upper end and the flange joint of the CRDM tube base 2, and friction between its lower end and the penetration fitting of the CRDM tube base 2. Common failure modes are as follows:

[0087] Fault 1: The end of CRDM thermal insulation sleeve 3 is worn, causing its position to drop.

[0088] The joint between the upper end of the CRDM thermal insulation sleeve 3 and the flange surface of the CRDM pipe seat 2 is worn due to flow-induced vibration, causing the height position of the thermal insulation sleeve to drop.

[0089] Fault 2: The CRDM insulation sleeve 3 and the lower pipe opening of the CRDM pipe seat 2 are worn. Figure 8 As shown in the figure, the circled position is the location where the CRDM insulation sleeve rubs against the pipe seat, resulting in thinning of the wall thickness.

[0090] Based on external experience feedback, this area is also a common wear area and needs to be inspected.

[0091] Fault 3: Fatigue fracture in the necking transition area of the upper end of the CRDM thermal insulation sleeve 3, such as Figure 9 As shown in the figure, the circled position is the location where cracks are likely to occur at the reduced diameter of the CRDM insulation sleeve.

[0092] In the transition area below the upper end, fatigue fracture occurs due to stress concentration and medium flow conditions in the reactor top cover.

[0093] like Figure 2 and Figure 3 As shown, inspection and repair of the CRDM thermal sleeve 3 must be performed in the storage room of the top cover 4. Due to the high radioactive environment in this location, the storage room is shielded by a biological shielding wall 5. A small door 9 serves as the entrance and exit of the biological shielding wall when the top cover 4 is stored in the storage room. The biological shielding wall 5 provides radiation protection, and the small door 9 provides access for maintenance equipment. The internal exposure dose rate of the CRDM tube base 2 is approximately 30-100 mSv / h, and the ambient dose rate at a distance of 100 mm from the CRDM tube base 2 can reach approximately 10 mSv / h. Considering the operating space, the radiation resistance of tools, and the personnel radiation dose limit, the entire process of thermal sleeve inspection of in-service units must be carried out using remote-controlled mechanical and intelligent methods.

[0094] like Figure 4 As shown, the control rod guide tube 6 is a component on the upper internal components of the reactor. It has an installation gap h requirement with the CRDM thermal insulation sleeve 3. After the CRDM thermal insulation sleeve 3 settles, the gap between them will become smaller.

[0095] like Figure 5 and Figure 9 As shown, the CRDM pressure housing 7 is a component of the CRDM, installed on the CRDM tube seat 2, and is a circuit pressure boundary.

[0096] For fault 1, the height settlement of the CRDM thermal insulation sleeve is measured and calculated. The height settlement of CRDM thermal insulation sleeve 3 is calculated. After completing the height settlement defect inspection, it can be determined whether the height settlement will cause nuclear safety risks.

[0097] Select the measurement reference surface and measure the height settlement of the CRDM thermal insulation sleeve. Figure 6 and Figure 7 As shown, the selection of the measurement reference surface includes: taking the upper end surface of the CRDM tube base 2 as the measurement reference ( Figure 6 ), take the lower end surface of CRDM tube base 2 as the measurement reference ( Figure 6 ), take the lower end surface of the thermocouple bell mouth 8 as the measurement reference ( Figure 7 The purpose of selecting the measurement reference surface is to measure the deviation between the installation height of the CRDM thermal insulation sleeve 3 and the theoretical position.

[0098] The height settlement of the CRDM thermal insulation sleeve 3 will cause changes in three dimension chains: the height difference h3 of the CRDM thermal insulation sleeve 3 relative to the thermocouple bell mouth 8 will become larger; the length h2 of the CRDM thermal insulation sleeve 3 extending from the CRDM tube seat 2 will become larger; and the height difference h1 of the CRDM thermal insulation sleeve 3 relative to the upper end surface of the CRDM tube seat 2 will become larger.

[0099] Based on the changes in the dimensions of the three dimensional chains caused by the height settlement of the CRDM thermal insulation sleeve 3, a specific measurement process (for example, non-contact or contact measurement methods such as laser scanning measurement) is adopted to measure these three dimensions (h3, h2, h1). By comparing them with the theoretical values, the height settlement of the CRDM thermal insulation sleeve 3 can be obtained. Figure 11 As shown, the detection steps are as follows:

[0100] S11: The height inspection device moves below the top cover 4 and is positioned below the target to be inspected (ie, the CRDM thermal insulation sleeve 3).

[0101] S12: Select a fixed component on the top cover 4 as a measurement reference. The measurement references include the upper end face of the CRDM tube base, the lower end face of the CRDM tube base, and the lower end face of the flare of the thermocouple tube base. During implementation, only one measurement reference needs to be selected.

[0102] S13: Measure and calculate the height difference between the CRDM thermal insulation sleeve 3 and the measurement reference, calculate the difference between the height difference and the theoretical value, and obtain the height settlement.

[0103] For different measurement benchmarks, the corresponding insulation sleeve settlement height (height settlement) can be calculated as follows:

[0104] (1) Take the upper end surface of CRDM tube seat 2 as the measurement reference

[0105] like Figure 6 As shown in the figure, the theoretical distance between the upper end surface of the CRDM thermal insulation sleeve 3 and the upper end surface of the CRDM tube base 2 is h1, and the actual distance after settlement is h1'. The actual distance between the upper end surface of the CRDM thermal insulation sleeve 3 and the upper end surface of the CRDM tube base 2 is measured using endoscopic visual measurement technology, which is h1'. By calculating the difference, the settlement height of the thermal insulation sleeve can be calculated as △h = h1' - h1.

[0106] (2) Take the lower nozzle of CRDM pipe seat 2 as the measurement reference

[0107] like Figure 6 As shown in the figure, the lower pipe opening of the CRDM pipe seat 2 and the upper end surface of the flare mouth 10 of the thermal insulation sleeve are selected as the measurement reference planes. The theoretical relative distance between the two planes is h2. The actual distance between the two planes measured by the existing visual measurement technology is h2'. The settlement height of the thermal insulation sleeve can be calculated as △h=h2'-h2.

[0108] (3) The lower end surface of the thermocouple tube holder bell mouth 8 is used as the measurement reference

[0109] like Figure 7 As shown in the figure, since the settlement of the CRDM thermal sleeve 3 causes the elevation of the sleeve flare 10 to decrease, and the thermocouple base flare 8 is a fixed structure, the thermocouple base flare 8 can be used as a measurement reference. By measuring the relative height between the two flares, the height settlement of the CRDM thermal sleeve 3 can be indirectly calculated. The theoretical value of the relative elevation difference between the thermocouple base flare 8 and the thermal sleeve flare 10 is h3, and the measured value is h3'. Therefore, the calculated insulation sleeve settlement height is Δh = h3' - h3.

[0110] For fault 2 and fault 3, since the wall thickness detection position is low and the crack detection position is high, this application adopts the method of detecting the wall thickness first and then the crack detection. The CRDM insulation sleeve 3 is installed in the CRDM pipe seat 2. There are two parts that need to be detected, see Figure 8 and Figure 9One area is where the CRDM thermal insulation sleeve 3 rubs against the lower end of the CRDM pipe base 2 (this area is on the CRDM thermal insulation sleeve 3), and the circumferential wall thickness needs to be measured to determine whether the wall thickness has been reduced. The other area is the flange neck at the upper end of the CRDM thermal insulation sleeve 3 (this area is on the CRDM thermal insulation sleeve 3), which is at risk of fatigue fracture and needs to be inspected for cracks.

[0111] The entire inspection process is carried out in the chamber below the top cover 4 after it is positioned in the storage room. Existing dedicated inspection equipment is required and installed on a transport cart via a predetermined dedicated interface. The transport cart uses its own positioning function to transport the inspection equipment to the bottom of the CRDM insulation sleeve 3 to be inspected. The inspection equipment has positioning jacking and video inspection functions, and is equipped with a scanner with a phased array probe for automatic scanning. At the same time, existing phased array instruments (crack detection device and wall thickness detection device) are used for automatic analysis to detect wall thickness and cracks.

[0112] The steps for detecting the wall thickness and cracks of the CRDM thermal insulation sleeve 3 include:

[0113] S21: A transport vehicle carrying a phased array ultrasonic testing device automatically moves to a position below the top cover 4 corresponding to the CRDM thermal insulation sleeve 3 to be tested. The phased array ultrasonic testing device installed on the transport vehicle is an existing device that can detect both cracks and wall thickness.

[0114] S22: Using the vehicle's lifting mechanism and video inspection device, a scanner equipped with a phased array probe is transported from the inner bore of CRDM insulation casing 3 to the thinning area. The target location is roughly determined by the lifting height. Phased array ultrasound is used to measure the casing section, automatically analyzing and finding the thinnest wall thickness. The video inspection device is an existing device equipped with a video-assisted positioning system.

[0115] S23: Compare with the theoretical wall thickness to obtain the wall thickness wear amount.

[0116] S24: Continue to lift the crack detection device to the reduced diameter position of the upper end through the lifting mechanism, roughly determine the height position based on the height, accurately lock the reduced diameter position based on the signal feedback of the phased array probe, and perform position positioning.

[0117] S25: Perform a circular scan to check whether there are any cracks in the flange reduction area.

[0118] For fault 2, the wall thickness wear of the CRDM thermal insulation sleeve 3 is measured and calculated. After completing the wall thickness wear defect inspection, it can be determined whether the wall thickness wear will cause nuclear safety risks.

[0119] In one embodiment, Figure 12 As shown in the figure, the wall thickness detection specifically includes the following steps:

[0120] S31, the wall thickness detection device moves under the top cover 4 and is positioned below the target to be inspected (i.e., the CRDM insulation sleeve 3);

[0121] S32, lifting the wall thickness measuring probe from the inside of the CRDM thermal insulation sleeve 3;

[0122] S33, positioning the wall thickness measuring probe at the CRDM pipe orifice;

[0123] S34. Measure the wall thickness at the location where the CRDM thermal insulation sleeve and the CRDM pipe mouth rub against each other, and compare it with the original value (original value - measured wall thickness = wall thickness wear) to obtain the wall thickness wear.

[0124] For fault 3, fatigue fracture detection is carried out on the necking transition zone of the upper end of the CRDM thermal insulation sleeve 3. The necking position is locked and the necking part is checked for cracks. After completing the crack defect inspection, it can be determined whether the crack will cause nuclear safety risks.

[0125] In one embodiment, Figure 13 As shown, crack detection specifically includes the following steps:

[0126] S41, the crack detection device moves under the top cover 4 and is positioned below the target to be inspected (i.e., the CRDM insulation sleeve 3);

[0127] S42, lifting the crack detection probe from the inside of the CRDM thermal insulation sleeve 3;

[0128] S43, positioning the crack detection probe at the flange reduction portion of the upper end of the CRDM thermal insulation sleeve 3;

[0129] S44. Use the crack detection probe to scan circumferentially and axially to detect the flange reduction area.

[0130] In view of the three common failure modes of the CRDM thermal insulation sleeve 3 mentioned above, combined with the structure of the CRDM thermal insulation sleeve 3, without disassembling any components, use inspection equipment to measure the actual height, thickness, cracks and other parameters of the CRDM thermal insulation sleeve 3, and determine whether the position of the CRDM thermal insulation sleeve 3 has moved downward, whether there is wall thickness thinning at the friction part with the through-piece port, and whether there are cracks at the flange reduction part, so as to conduct analysis and formulate corresponding treatment measures.

[0131] The height of the CRDM thermal insulation sleeve 3 is measured by using a carrying trolley equipped with a height measuring device, with the upper end surface of the CRDM tube base 2 as the measurement reference, or with the lower tube mouth of the CRDM tube base 2 as the measurement reference, or with the lower end surface of the bell mouth of the thermocouple tube base as the measurement reference.

[0132] The crack and wall thickness detection adopts the method of carrying trolley positioning and phased array ultrasonic scanning. Its main purpose is to determine whether the wall thickness of the insulation sleeve is thinned and whether cracks are generated at the necking.

[0133] This application establishes an inspection system for typical defects of CRDM thermal insulation sleeves for M310 and improved reactor types, and comprehensively summarizes the hidden defects involved in CRDM thermal insulation sleeves, which facilitates targeted inspection of defects and has guiding significance for defect troubleshooting.

[0134] This application develops three processes for measuring the height settlement of isolation casings, which are convenient for implementation using different technical means, making the measurement scheme diverse.

[0135] This application develops a process for measuring the wall thickness of the thermal insulation sleeve and detecting crack defects at the necking point, which points out the process ideas for the development of subsequent measurement equipment.

[0136] The above description is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed in this application should be covered by the scope of protection of the present application.

Claims

1. A CRDM insulation sleeve defect inspection method, characterized in that: include: Step 1: Determine the failure mode based on the in-pile movement of the CRDM thermal sleeve. Failure modes include wear of the CRDM thermal sleeve end causing it to drop, wear between the CRDM thermal sleeve and the lower nozzle of the CRDM pipe seat, and fatigue fracture in the necking transition zone of the CRDM thermal sleeve's upper end. Step 2: Without disassembling any components, measure the actual height, thickness, and cracks of the CRDM thermal sleeve, and calculate the height settlement and wall wear. First, use the height settlement to determine whether the CRDM thermal sleeve has moved downward. Then, use the wall wear to determine whether there is wall thinning between the CRDM thermal sleeve and the lower pipe opening of the CRDM pipe seat. Finally, use crack measurement to determine whether there are cracks in the flange reduction area of the CRDM thermal sleeve. Step 2 specifically includes: Step 2.1: Position the height detection device below the CRDM insulation sleeve to be tested; Step 2.2: Select a measurement reference and measure the height difference between the CRDM thermal insulation sleeve and the measurement reference; Step 2.3: Calculate the difference between the height difference and the theoretical value to obtain the height settlement; Step 2.4: Position the wall thickness detection device to the CRDM insulation sleeve to be tested under the top cover; Step 2.5: Move the scanner from the inner bore of the CRDM insulation casing to the thinning point. Locate the target location by lifting the scanner. Use phased array ultrasound to measure the casing section to find the thinnest wall thickness. Step 2.6: Calculate the difference between the measured wall thickness and the theoretical wall thickness to obtain the wall wear amount; Step 2.7: Use a crack detection device to measure the reduced diameter position of the CRDM upper end to detect whether there are cracks in the reduced diameter part of the flange.

2. The CRDM insulation sleeve defect inspection method according to claim 1 is characterized in that: The calculation methods of height settlement include: Position the height check device below the CRDM insulation sleeve; Select the fixed component on the top cover as the measurement reference. The measurement reference can be any one of the upper end face of the CRDM tube seat, the lower end face of the CRDM tube seat, and the lower end face of the bell mouth of the thermocouple tube seat. Measure and calculate the height difference between the CRDM thermal insulation sleeve and the measurement benchmark, and calculate the height settlement.

3. The CRDM insulation sleeve defect inspection method according to claim 2, characterized in that: Taking the upper end face of the CRDM pipe seat as the measurement reference, the theoretical distance between the upper end face of the CRDM thermal insulation sleeve and the upper end face of the CRDM pipe seat is h1, and the actual distance after settlement is h1'. The actual distance between the upper end face of the CRDM thermal insulation sleeve and the upper end face of the CRDM pipe seat is measured as h1', and the calculated height settlement is △h = h1'-h1.

4. The CRDM insulation sleeve defect inspection method according to claim 2, characterized in that: Taking the lower nozzle of the CRDM pipe seat as the measurement reference, the theoretical relative distance between the lower nozzle of the CRDM pipe seat and the upper end face of the bell mouth of the CRDM thermal insulation sleeve is h2, and the actual distance between the two planes is h2'. The calculated height settlement is △h = h2'-h2.

5. The CRDM insulation sleeve defect inspection method according to claim 2, characterized in that: Taking the lower end face of the bell mouth of the thermocouple tube holder as the measurement reference, the theoretical value of the relative elevation difference between the bell mouth of the thermocouple tube holder and the bell mouth of the thermal insulation sleeve is h3, and the measured value of the relative elevation difference is h3'. The calculated settlement height of the thermal insulation sleeve is △h = h3'-h3.

6. The CRDM insulation sleeve defect inspection method according to claim 1, characterized in that: The wall thickness and crack detection of CRDM thermal insulation sleeves are carried out by first detecting the wall thickness and then detecting the cracks. The steps include: The carrier carrying the phased array ultrasonic testing device moves to the position under the top cover corresponding to the CRDM insulation sleeve to be tested; Using the vehicle's lifting mechanism and video inspection device, a scanner equipped with a phased array probe is transported from the inner bore of the CRDM insulation casing to the area where the wall thickness is reduced. The target position is locked by the lifting height, and phased array ultrasound is used to measure the casing section to find the thinnest wall thickness. Compare with the theoretical wall thickness to obtain the wall wear amount; The crack detection device is continuously lifted to the upper end diameter reduction position through the lifting mechanism, and the height position is preliminarily determined. The diameter reduction position is locked and the position is positioned according to the signal feedback from the phased array probe. Perform a circular scan to check whether there are any cracks in the flange reduction area.

7. The CRDM insulation sleeve defect inspection method according to claim 1, characterized in that: The calculation method of wall thickness wear includes: Position the wall thickness detection device below the CRDM insulation sleeve; Lift the wall thickness measuring probe from inside the CRDM insulation sleeve; Position the wall thickness measuring probe at the CRDM nozzle; The wall thickness at the rubbing position between the CRDM thermal insulation sleeve and the CRDM pipe mouth was measured and compared with the original value to calculate the wall thickness wear.

8. The CRDM insulation sleeve defect inspection method according to claim 1, characterized in that: Crack measurement methods include: Position the crack detection device below the CRDM insulation sleeve; Lift the crack detection probe from inside the CRDM insulation sleeve; Position the crack detection probe at the flange reduction area at the upper end of the CRDM insulation sleeve; The crack detection probe is used to scan the flange in the circumferential and axial directions to detect the flange reduction area.

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