Nuclear island main equipment special-shaped inner cavity underwater in-service maintenance process

Abstract

The invention discloses an underwater in-service maintenance process for a special-shaped inner cavity of nuclear island main equipment. According to the process, an abnormal area is checked and positioned based on the preliminary morphology of an endoscope, a multi-stage inspection gauge is adopted to detect the notch or aperture size in a grading manner, a correction process is triggered by dynamically switching an inspection tool, and pollutants are accurately removed in combination with a directional high-pressure pulse cleaning technology. The remote control terminal achieves automatic switching of the inspection gauge, linkage adjustment of cleaning parameters and laser scanning three-dimensional deviation analysis, and closed-loop control is formed. Through the design of the tungsten carbide wear-resistant coating inspection gauge, the modular waterproof tool and the rigid connection structure of the safety rope, the detection precision, the cleaning efficiency and the operation stability are remarkably improved. The embodiment shows that the process can effectively shorten the maintenance period, improve the size recovery qualification rate, solve the problems of high false detection rate, incomplete cleaning and strong manual dependence of a traditional method, and provide efficient and reliable technical guarantee for safe operation of nuclear island equipment.

Description

Technical Field

[0001] The present invention relates to the production field, and particularly to an in-service underwater maintenance process for the special-shaped inner cavities of nuclear island main equipment. Background Art

[0002] The special-shaped inner cavities of nuclear island main equipment (such as the reactor pressure vessel notch, pipe connection parts, etc.) are long-term in high-temperature, high-pressure and strong radiation environments, and are prone to surface deterioration and geometric dimension deviation of the cavity due to corrosion, sediment attachment or mechanical stress, directly affecting the equipment sealing performance and operation safety. Traditional maintenance processes mostly adopt fixed-specification inspection tools (such as a single go-no-go gauge) combined with constant-pressure cleaning technology, which are difficult to adapt to the complex geometric features of special-shaped cavities, and have significant defects: the inspection tools cannot accurately identify the dimensional out-of-tolerance in local corrosion or deformation areas, resulting in an increased false inspection rate; the constant-pressure cleaning mode lacks the ability to directionally remove pollutants, easily causing incomplete cleaning or surface damage of the cavity. In addition, the inspection and cleaning processes rely on manual operation, with low automation, unable to achieve closed-loop control and dynamic correction, resulting in low maintenance efficiency and insufficient reliability.

[0003] The limitations of the prior art are further reflected in the tool design and control logic levels. Inspection tools generally have problems of poor adaptability and insufficient wear resistance. For example, ordinary steel inspection gauges are prone to wear and loss of accuracy after long-term use, and the waterproof sealing performance of the tool connection structure during underwater operation is insufficient, easily resulting in the risk of falling off due to water flow impact. At the same time, the existing solutions lack an intelligent parameter dynamic adjustment mechanism (such as the cleaning pressure changing adaptively with the thickness of pollutants, the automatic switching logic of inspection gauges), resulting in potential secondary pollution or operation interruption during the maintenance process. Although the industry has tried to improve the maintenance effect through basic cleaning devices or standardized processes, none of them have systematically solved the core requirements of high-precision detection, directional and efficient cleaning, and automated linkage of special-shaped cavities, and are difficult to meet the strict requirements of nuclear island equipment for safety and reliability. Summary of the Invention

[0004] In order to solve the above problems, the present invention proposes an in-service underwater maintenance process for the special-shaped inner cavities of nuclear island main equipment. Combining the shape, size and related characteristics of the workpiece, using the hole positions of the workpiece for positioning, it solves the problem that it is difficult to conduct internal inspection of the workpiece. This process can effectively save the inspection cycle, avoid repeated inspections, and at the same time avoid the influence of underwater impurities on the inspection results.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: An in-service underwater maintenance process for the special-shaped inner cavities of nuclear island main equipment, the method comprising the following steps: S1. Use an endoscope to conduct a preliminary morphological inspection of the special-shaped inner cavity, and identify the distribution of pollutants on the inner cavity surface and the areas with structural abnormalities; S2. Perform the first - level dimensional inspection on the notch or aperture of the special - shaped inner cavity using a thick - dimension double - groove inspection gauge. If the inspection is qualified, proceed to step S4; S3. If it is unqualified, switch to a thick - dimension single - groove inspection gauge for corrective inspection. After the corrective inspection is qualified, proceed to step S4; S4. Use a thin - dimension double - groove inspection gauge to perform the second - level precise dimensional inspection. If the inspection is qualified, end the process and terminate the process. If it is unqualified, proceed to step S5; S5. Start an underwater cleaning tool to perform directional high - pressure flushing on the abnormal area. After cleaning, use a thin - dimension single - groove inspection gauge to perform the third - level dimensional verification. If the verification is qualified, return to step S4 for re - inspection. After the re - inspection is qualified, terminate the process; if it is still unqualified, return to step S2 to re - perform the inspection with the thick - dimension double - groove inspection gauge until the inspection with the thin - dimension double - groove inspection gauge is qualified.

[0006] In the preferred solution, the thickness of the thick - dimension double - groove inspection gauge is the upper limit value of the tolerance of the to - be - inspected notch + 0.1 mm, the thickness of the thin - dimension double - groove inspection gauge is the lower limit value of the tolerance - 0.05 mm, the thickness of the single - groove inspection gauge is the median value of the tolerance ± 0.03 mm, and a tungsten carbide wear - resistant coating is applied to the surface of all inspection gauges.

[0007] In the preferred solution, the corrective inspection in steps S2 and S3 includes: 3.1. Select the thick - dimension double - groove inspection gauge as the go - no - go gauge. The thickness of the double - groove inspection gauge is the upper limit value of the tolerance of the to - be - inspected notch. Insert the inspection tool vertically into the to - be - inspected part, and judge whether the dimension exceeds the tolerance range by the resistance during up - and - down movement; if the thick - dimension double - groove inspection gauge cannot pass through the notch, use the single - groove inspection gauge to measure the actual size of the notch; 3.2. Adjust the spraying parameters of the cleaning tool according to the measurement result to directionally remove the corrosion products or deposits that prevent the inspection gauge from passing through; 3.3. After cleaning, re - perform the inspection with the thick - dimension double - groove inspection gauge until it can pass through the notch.

[0008] In the preferred solution, the directional high - pressure flushing in step S5 is specifically as follows: 4.1. The cleaning nozzle adjusts the spraying angle through the guide rod according to the coordinates of the abnormal area located by the endoscope; 4.2. Adopt a pulse spraying mode, with a pressure of 30 - 50 MPa, the single - time spraying duration ≤ 5 s, and the intermittent duration ≥ 3 s; 4.3. After cleaning, verify the cleanliness in real - time through the endoscope. The cleanliness standard threshold is set as the surface pollutant coverage rate ≤ 2%.

[0009] In the preferred solution, the switching logic of the inspection gauges in steps S2 to S5 is realized through a remote control terminal. The following decision rules are built - in to the terminal: 5.1 If the thick-size double-groove inspection gauge fails three consecutive inspections, an alarm will be triggered and the cleaning process will be forced to start; 5.2 If the thin-size double-groove inspection gauge still fails after two cyclic inspections, it will automatically switch to the laser scanning module to generate a three-dimensional dimensional deviation report; 5.3 The scanning accuracy of the laser scanning module is ±0.01 mm, and the scanning frequency ≥ 10 Hz.

[0010] In a preferred solution, in step S5, the interlocking control between the thin-size single-groove inspection gauge and the cleaning tool includes: 6.1 When the thin-size double-groove inspection gauge fails the inspection, the cleaning nozzle automatically aligns with the corresponding groove opening, and the spraying distance is adjusted to 10 - 15 cm; 6.2 After cleaning, the thin-size single-groove inspection gauge slowly advances along the axis direction of the groove opening, with the advancing speed ≤ 2 mm / s, and the advancing resistance is monitored in real time and fed back to the control terminal; 6.3 If the advancing resistance exceeds the preset threshold, the cleaning spraying pressure or spraying angle will be automatically adjusted.

[0011] In a preferred solution, in step S5, the termination conditions of the process are: 7.1 The thin-size double-groove inspection gauge passes two consecutive inspections; 7.2 The cleanliness detected by the endoscope and the dimensional accuracy scanned by the laser both meet the operating standards of the nuclear island main equipment; 7.3 The total maintenance time does not exceed the preset threshold of 72 hours, otherwise an artificial intervention instruction will be triggered; 7.4 All the conditions described in 7.1 to 7.3 need to be met simultaneously.

[0012] In a preferred solution, in steps S2 to S5, a specific inspection tool is used for inspection, and the inspection tool includes a main body connection part and an inspection limit part; The main body connection part uses a thin-walled stainless steel steel pipe. The inner connection block and the outer connection block are respectively provided with M12 internal threads and M12 external threads. The rapid assembly and disassembly of the multi-layer structure are realized through thread meshing, and the welded joints of each layer of connecting rods are subjected to waterproof sealing treatment; The inspection limit part is a replaceable modular structure, which adapts to the geometric features of the groove opening or hole diameter of the special-shaped inner cavity, and includes a limit plate, a single-groove inspection gauge and a double-groove inspection gauge.

[0013] In a preferred solution, the limit plate is fixedly connected to the outer wall of the steel pipe of the main body connection part, and the single-groove inspection gauge and the double-groove inspection gauge are detachably connected to the steel pipe of the main body connection part; The single-groove inspection gauge includes a thick-size single-groove inspection gauge and a thin-size single-groove inspection gauge, and the double-groove inspection gauge includes a thick-size double-groove inspection gauge and a thin-size double-groove inspection gauge.

[0014] In a preferred solution, in step S5, the cleaning tool includes a cleaning host, a high-pressure pipeline, an electromagnetic switching valve, a cleaning guide rod, a cleaning hose, and a flexible protective nozzle. The total length of the cleaning guide rod after extension is 6.6 m. There are 3 circumferentially evenly distributed openings at the front end of the nozzle and 2 circumferentially evenly distributed openings at the rear end, with a total of 5 openings. The surface of the nozzle is coated with a polyurethane composite material protective layer; The end of the cleaning guide rod is connected to a lifting ring through a safety rope. One end of the safety rope is fixed to the support structure of the nuclear island main equipment or the safety belt of the operator, and the other end is rigidly connected to the cleaning guide rod to ensure the stability of the equipment during operation.

[0015] An in-service maintenance process for the special-shaped inner cavity of the nuclear island main equipment underwater has the following beneficial effects, including but not limited to: 1. Through the hierarchical switching mechanism of multi-level inspection gauges (thick-size double-groove, thin-size double-groove, single-groove inspection gauges), combined with precise design of parameters such as the upper tolerance value +0.1 mm and the lower tolerance value -0.05 mm, it effectively adapts to the complex geometric features of the special-shaped cavity. The surface of the inspection gauge is coated with a tungsten carbide wear-resistant coating, significantly improving the durability of the tool, avoiding size errors caused by long-term use, and ensuring long-term stability of the detection accuracy. At the same time, dynamically correcting the inspection logic (such as triggering the laser scanning module to generate a three-dimensional deviation report) further reduces the false detection rate and solves the problems of missed detection or misjudgment caused by poor adaptability of traditional tools; 2. Adopting the directional high-pressure pulse jet technology (pressure 30 - 50 MPa, single jet ≤ 5 s), combined with the real-time positioning of the endoscope and the angle adjustment of the guide rod, realizes the precise removal of pollutants. The cleanliness threshold (pollutant coverage rate ≤ 2%) is increased by more than 60% compared with the traditional process. The intermittent jet of the pulse mode (interval ≥ 3 s) effectively avoids damage to the cavity surface caused by continuous high pressure. At the same time, through the design of the polyurethane protective nozzle, the cavity is further protected from mechanical impact, taking into account both efficient cleaning and equipment integrity; 3. Based on the decision rules of the remote control terminal (such as triggering an alarm when 3 consecutive inspections fail, starting laser scanning when 2 cycles do not pass), the whole process of inspection gauge switching and cleaning parameter adjustment is automated. The linkage control of the thin-size single-groove inspection gauge and the cleaning nozzle (spraying distance 10 - 15 cm, propulsion speed ≤ 2 mm / s) forms a closed-loop feedback mechanism, which real-time monitors the propulsion resistance and adaptively adjusts the spraying parameters, reduces manual intervention, and the maintenance efficiency is increased by more than 40%; 4. The modular structure of the inspection tool (detachable single / double-slot inspection gauge, limit plate) is suitable for a variety of special-shaped cavity scenarios, combined with the waterproof sealing treatment of thin-walled stainless steel pipes (M12 threaded connection, welding seal) to ensure stable operation in underwater environments. The cleaning guide rod (total length 6.6m) is rigidly connected to the nuclear island support structure or operator through a safety rope, and the circumferential opening design of the nozzle (5 holes evenly distributed) and the polyurethane protective layer significantly reduce the risk of tool falling off and improve the safety of underwater operations; 5. Through strict setting of process termination conditions (passing two consecutive inspections, reaching the standards for cleanliness and dimensional accuracy, and 72-hour threshold control), invalid maintenance cycles are avoided, and the overall maintenance cycle is shortened by 30%. In addition, the application of intelligent early warning mechanisms (such as dust collector blockage prompts) and laser scanning modules (accuracy ±0.01mm) provides data support for the long-term stable operation of nuclear island equipment, indirectly reducing operation and maintenance costs and safety risks. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic cross-sectional view of a workpiece to be inspected according to the present invention; Figure 2 This is the overall flow chart of this process; Figure 3 This is a structural diagram of a specific inspection tool of the present invention; Figure 4 This is a physical picture of the cleaning nozzle of the present invention. DETAILED DESCRIPTION

[0017] Example 1: Maintenance of the internal notch of the reactor pressure vessel; (e.g. Figure 1 ) Application scenario: There are special-shaped notches inside the reactor pressure vessel of a nuclear power plant. Due to long-term high temperature and high pressure environment, local corrosion and oxide layer deposition occur, and underwater in-service maintenance is required; The first step is to check the appearance and size: 1.1. Use an endoscope (resolution 1080p, waterproof grade IP68) to scan the notch area and identify three corrosion points and one sediment-covered area; 1.2. Use thick double-slot inspection gauge (thickness = slot tolerance upper limit + 0.1mm, i.e. 32.1mm) to conduct first-level dimensional inspection, and find that the thickness of two slots is out of tolerance due to corrosion (actual measurement is 31.8mm, out of tolerance by 0.3mm), triggering the correction inspection process; Step 2: Correction inspection and cleaning: 2.1. Switch to the thick size single slot inspection gauge (thickness = tolerance median ± 0.03mm, i.e. 31.5mm) to measure the actual size of the slot and determine that the corrosion depth is 0.7mm; 2.2. Adjust the parameters of the cleaning nozzle: set the injection pressure to 45 MPa, pulse mode (inject for 4 seconds / intermittent for 3 seconds), position the guide rod to the corroded area, and remove the oxide layer directionally. After cleaning, the endoscope inspection shows that the pollutant coverage rate drops to 1.5%; Step 3. Precision re-inspection and closed-loop control: 3.1. Conduct the second-level inspection using a thin-size double-groove inspection gauge (thickness = lower tolerance limit value - 0.05 mm, i.e., 31.45 mm). One of the groove openings still fails to meet the standard; 3.2. Trigger the linkage control: the cleaning nozzle automatically aligns with this groove opening, adjust the injection distance to 12 cm. After secondary cleaning, verify using a thin-size single-groove inspection gauge (thickness 31.5 mm). The propulsion resistance is stable within 50 N (threshold ≤ 60 N), and the re-inspection passes; Step 4. Termination conditions and results: The thin-size double-groove inspection gauge passes the inspection continuously for 2 times. The laser scan shows that the dimensional deviation ≤ ±0.02 mm, and the total maintenance time is 48 hours. The generated report shows: the cleanliness compliance rate is 100%, and the dimensional recovery qualification rate is 98%.

[0018] Example 2: Maintenance of the pipe connection part of the steam generator: Application scenario: The aperture of the pipe connection part of the steam generator is reduced due to the accumulation of radioactive sediments, and underwater precision maintenance is required; Step 1. Abnormality location and automated detection: 1.1. The endoscope inspection finds that the sediment coverage rate at the pipe connection reaches 15%, and the actual measured aperture is 49.5 mm (design tolerance 50 ± 0.2 mm); 1.2. The remote control terminal automatically calls a thick-size double-groove inspection gauge (thickness = 50.2 + 0.1 = 50.3 mm) for inspection. Due to the obstruction of sediments, it cannot pass, trigger an alarm and start the cleaning process; Step 2. Directional cleaning and intelligent correction: 2.1. Switch the cleaning nozzle to the circumferential injection mode (3 holes at the front end + 2 holes at the rear end), increase the pressure to 50 MPa, and pulse injection (5 seconds / 3 seconds) to remove sediments directionally; 2.2. After cleaning, measure using a thick-size single-groove inspection gauge (thickness = 50.0 mm). The aperture recovers to 50.1 mm, but still does not meet the requirements of the thin-size double-groove inspection gauge (49.95 mm); Step 3. Laser scanning and parameter optimization: 3.1. The system automatically switches to the laser scanning module (accuracy ±0.01 mm, scanning frequency 15 Hz), generates a three-dimensional deviation map showing that the thickness of the local residual sediment is 0.08 mm; 3.2. Adjust the nozzle angle to 30° according to the scanning data. After secondary cleaning, the thin-size double-groove inspection gauge passed smoothly, and the measured hole diameter was 49.98 mm. Step 4. Safety protection and efficiency verification: 4.1. The inspection tool was quickly replaced with a thin-size single-groove inspection gauge through an M12 thread, and there was no leakage in the waterproof seal test. 4.2. The total maintenance time was 36 hours, the cleanliness met the standard (coverage rate 1.2%), and the tool stability test showed that the vibration amplitude was <0.1 mm and there was no risk of falling off.

[0019] In summary, through the implementation of hierarchical inspection, directional cleaning, and intelligent linkage, the present invention significantly improves the accuracy and efficiency of maintaining the special-shaped inner cavity of the main equipment in the nuclear island, while ensuring the safety of underwater operations, and has broad engineering application value.

[0020] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention; any reference signs in the claims should not be regarded as limiting the claimed claims.

Claims

1. An in-service maintenance process for the special-shaped inner cavity of the main equipment in the nuclear island underwater, characterized in that, The process includes the following steps: S1. Use an endoscope to conduct a preliminary morphological inspection of the special-shaped inner cavity, and identify the distribution of contaminants on the inner cavity surface and the areas with structural abnormalities; S2. Use a thick-size double-groove inspection gauge to conduct a first-level dimension inspection on the groove opening or hole diameter of the special-shaped inner cavity. If the inspection is qualified, proceed to step S4; S3. If it is unqualified, switch to a thick-size single-groove inspection gauge for corrective inspection. After the corrective inspection is qualified, proceed to step S4; S4. Use a thin-size double-groove inspection gauge to conduct a second-level precision dimension inspection. If the inspection is qualified, end the process and terminate the process. If it is unqualified, proceed to step S5; S5. Start an underwater cleaning tool to conduct directional high-pressure flushing on the abnormal area. After the cleaning is completed, use a thin-size single-groove inspection gauge to conduct a third-level dimension verification. If the verification is qualified, return to step S4 for re-inspection. After the re-inspection is qualified, the process terminates; if it is still unqualified, return to step S2 to re-perform the thick-size double-groove inspection gauge inspection until the thin-size double-groove inspection gauge inspection is qualified.

2. The in-service maintenance process for the special-shaped inner cavity of the nuclear island main equipment underwater according to claim 1, characterized in that The thickness of the thick-size double-groove inspection gauge is the upper limit value of the tolerance of the groove opening to be inspected + 0.1 mm, the thickness of the thin-size double-groove inspection gauge is the lower limit value of the tolerance - 0.05 mm, and the thickness of the single-groove inspection gauge is the median value of the tolerance ± 0.03 mm. And a tungsten carbide wear-resistant coating is coated on the surface of all inspection gauges.

3. The in-service maintenance process for the special-shaped inner cavity of the main equipment in the nuclear island underwater according to claim 1, characterized in that, The corrective inspection described in steps S2 and S3 includes: 3.

1. Select a thick-size double-groove inspection gauge as a go / no-go gauge. The thickness of the double-groove inspection gauge is the upper limit value of the tolerance of the groove opening to be inspected. Insert the inspection tool vertically into the part to be inspected, and judge whether the dimension exceeds the tolerance range by the resistance of up and down movement; if the thick-size double-groove inspection gauge cannot pass through the groove opening, use a single-groove inspection gauge to measure the actual size of the groove opening; 3.

2. Adjust the spraying parameters of the cleaning tool according to the measurement results to directionally remove the corrosion products or deposits that prevent the inspection gauge from passing through; 3.

3. After cleaning, re-perform the thick-size double-groove inspection gauge inspection until it can pass through the groove opening.

4. The underwater in-service maintenance process for the special-shaped inner cavity of the main equipment in the nuclear island according to claim 1, characterized in that, The directional high-pressure flushing in step S5 is specifically: 4.

1. The cleaning nozzle adjusts the spraying angle through the guiding rod according to the coordinates of the abnormal area located by the endoscope; 4.

2. Adopt a pulse spraying mode, with a pressure of 30 - 50 MPa, the single spraying duration ≤ 5 s, and the intermittent duration ≥ 3 s; 4.

3. After cleaning, verify the cleanliness in real time through the endoscope. The cleanliness standard threshold is set as the surface contaminant coverage rate ≤ 2%.

5. The in-service maintenance process for the special-shaped inner cavity of the main nuclear island equipment underwater according to claim 1, characterized in that, The switching logic of the inspection gauges described in steps S2 to S5 is realized through a remote control terminal. The following judgment rules are built into the terminal: 5.

1. If the thick-size double-groove inspection gauge fails the inspection continuously for 3 times, trigger an alarm and forcibly start the cleaning process; 5.

2. If the thin-size double-groove inspection gauge still fails after 2 cycles of inspection, automatically switch to the laser scanning module to generate a three-dimensional dimension deviation report; 5.

3. The scanning accuracy of the laser scanning module is ± 0.01 mm, and the scanning frequency ≥ 10 Hz.

6. The underwater in-service maintenance process for the special-shaped inner cavity of the main equipment in the nuclear island according to claim 1, wherein, In step S5, the interlocking control between the thin-size single-groove inspection gauge and the cleaning tool includes: 6.

1. When the thin-size double-groove inspection gauge fails the inspection, the cleaning nozzle automatically aligns with the corresponding groove opening, and the spraying distance is adjusted to 10 - 15 cm; 6.2 After the cleaning is completed, the thin-size single-groove inspection gauge is slowly pushed along the axis direction of the groove opening, and the pushing speed is ≤ 2 mm / s. The pushing resistance is monitored in real time and fed back to the control terminal; 6.3 If the pushing resistance exceeds the preset threshold, the cleaning injection pressure or injection angle is automatically adjusted.

7. The in-service maintenance process for the special-shaped inner cavity of the main equipment in the nuclear island underwater according to claim 1, characterized in that In step S5, the termination conditions of the process are: 7.1 The thin-size double-groove inspection gauge passes the inspection twice continuously; 7.2 The cleanliness detected by the endoscope and the dimensional accuracy of the laser scanning both meet the operating standards of the nuclear island main equipment; 7.3 The total maintenance time does not exceed the preset threshold of 72 hours, otherwise an artificial intervention instruction is triggered; 7.4 All the conditions described in 7.1 to 7.3 need to be satisfied simultaneously.

8. The underwater in-service maintenance process for the special-shaped inner cavity of the main nuclear island equipment according to claim 1, characterized in that, In steps S2 to S5, a specific inspection tool is used for inspection. The inspection tool includes a main body connection part and an inspection limit part; The main body connection part uses a thin-walled stainless steel steel pipe. The inner connection block and the outer connection block are respectively provided with M12 internal threads and M12 external threads. The rapid assembly and disassembly of the multi-layer structure are realized through thread meshing, and the welding joints of each layer of connecting rods are subjected to waterproof sealing treatment; The inspection limit part is a replaceable modular structure, which adapts to the geometric features of the groove opening or hole diameter of the special-shaped inner cavity, and includes a limit plate, a single-groove inspection gauge and a double-groove inspection gauge.

9. The in-service maintenance process for the special-shaped inner cavity of the nuclear island main equipment underwater according to claim 8, characterized in that, The limit plate is fixedly connected to the outer wall of the steel pipe of the main body connection part, and the single-groove inspection gauge and the double-groove inspection gauge are detachably connected to the steel pipe of the main body connection part; The single-groove inspection gauge includes a thick-size single-groove inspection gauge and a thin-size single-groove inspection gauge, and the double-groove inspection gauge includes a thick-size double-groove inspection gauge and a thin-size double-groove inspection gauge.

10. The in-service maintenance process for the special-shaped inner cavity of the main equipment in the nuclear island underwater according to claim 1, characterized in that, In step S5, the cleaning tool includes a cleaning host, a high-pressure pipeline, an electromagnetic switching valve, a cleaning guide rod, a cleaning hose and a flexible protective nozzle. There are 3 circumferentially evenly distributed openings at the front end of the nozzle and 2 circumferentially evenly distributed openings at the rear end, and the surface of the nozzle is coated with a polyurethane composite material protective layer; The end of the cleaning guide rod is connected to a hanging ring through a safety rope. One end of the safety rope is fixed to the support structure of the nuclear island main equipment or the safety belt of the operator, and the other end is rigidly connected to the cleaning guide rod to ensure the stability of the equipment during the operation process.

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