Sealing device and application method

Abstract

The invention discloses a sealing device and an application method.The sealing device is applied to a chemical and volume control system and comprises a sealing pipe section, a plug bush flange and a blind flange, the sealing pipe section is connected with the plug bush flange, a pipe hole penetrating through the sealing pipe section in the axial direction is formed in the sealing pipe section, and the plug bush flange is connected with the blind flange; the plug bush flange is provided with a flange hole communicated with the pipe hole, and the blind flange and the plug bush flange are detachably connected to seal the flange hole. The leakage pipeline is sleeved with the sealing pipe section, the insertion sleeve flange and the blind flange form a detachable sealing structure, leakage of a radioactive coolant at the downstream of a leakage point is directly blocked, radioactive contamination outside a containment is avoided, an RCV pump or a main pump does not need to be stopped in the whole process, the requirement for full-power operation of a unit is met, the maintenance period is shortened, and the working efficiency is improved. And the method does not depend on an ice blockage process.

Description

Technical Field

[0001] This invention relates to the field of nuclear power technology, and in particular to a sealing device and its application method. Background Technology

[0002] During the operation of a nuclear power plant, the integrity and safety of the primary loop system are paramount. An abnormally high primary loop leakage rate can directly threaten the stability of the reactor coolant system (RCP) and even trigger rare accidents (such as the RCC-P condition III event). Taking Unit L2 of a certain nuclear power plant as an example, its current primary loop leakage rate is approximately 40 L / h, close to the internal yellow zone indicator of 46-92 L / h, and there is a risk of further increase. If the total leakage rate exceeds the limit of 2300 L / h specified in the technical specification (TS) and cannot be restored within 4 hours, it is necessary to enter Mode 3 within 6 hours and Mode 5 (where the coolant temperature is below 90°C) within 36 hours to reduce the leakage risk.

[0003] Current (improved) technical methods for addressing primary loop leakage have significant shortcomings: The existing technical solution involves confirming a high primary loop leakage rate and then continuing to monitor and address the leakage during a major overhaul of the unit (shutdown). Its advantages include minimal workload, no impact on full-power unit operation, and reduced refrigerant disposal during overhauls. However, its risks include potentially exceeding the ROP (Recovery Point of Operation) performance indicators (ROOs) used to monitor nuclear safety equipment operating parameters, formulate maintenance strategies, and manage spare parts, leading to a decline in the World Association of Nuclear Operators (WANO) performance indicators and the possibility of internal leakage expansion causing radiation accidents or forced unit shutdown. Furthermore, if the leakage rate continues to worsen, insufficient primary loop water may trigger a Loss of Coolant Accident (LOCA).

[0004] The existing technical solution 2 uses online flushing of the steam trap. Its advantages include not having to shut down the RCV (chemical and volumetric control system) pump and the main pump shaft seal, but it has the following problems: the defects may be aggravated during flushing, and preparations for passive retraction need to be made in advance; it may affect the operation of the RCV pump and the main pump; high-pressure flushing may damage the valve sealing surface or cause the copper sleeve to break, leading to the risk of water leakage; there is a lack of relevant experience, and if the sealing surface has already formed erosion pits, flushing cannot eliminate the leakage.

[0005] The existing technical solution three involves cutting off the main pump shaft seal injection and using an online ice blockage repair method to maintain the drain valve. Its advantage is that it can quickly eliminate defects without requiring retraction. However, it requires cutting off the main pump shaft seal injection, relying solely on the heat shield cooling water to maintain the main pump's normal operation, which carries the risk of main pump damage. Furthermore, filling and venting water is difficult. Simultaneously, the repair time is limited; for example, cutting and grinding the seal weld requires 12 hours, and replacing the valve requires 2 days. Moreover, the online cutting and sealing weld opening is large, and if ice blockage occurs, there is a significant potential risk of water leakage.

[0006] The existing technical solution four involves retracting the unit to repair the drain valve. Although the maintenance environment is safe and the problem can be completely solved, the main pump needs to be shut down, which directly affects the unit's operating efficiency and leads to a decrease in WANO indicators, resulting in high economic costs. Summary of the Invention

[0007] The purpose of this invention is to provide a sealing device and application method, which aims to solve the problems that existing solutions cannot simultaneously achieve safety, economy and rapid repair capability without shutting down the system.

[0008] This invention provides a sealing device for use in chemical and volume control systems, comprising: a sealing pipe section, a socket flange, and a blind flange. The sealing pipe section is connected to the socket flange. The sealing pipe section has a pipe hole extending axially through the sealing pipe section. The socket flange has a flange hole communicating with the pipe hole. The blind flange and the socket flange are detachably connected to seal the flange hole.

[0009] Furthermore, it also includes: a plurality of connectors and a plurality of accessories, each of the connectors and one of the accessories being threadedly connected, and the plug flange and the blind flange being detachably connected through the connectors and the accessories.

[0010] Furthermore, it also includes a gasket disposed between the socket flange and the blind flange.

[0011] This invention also provides a method for applying a sealing device, comprising: Close the leak valve of the chemical and volume control system and cut the right-angle bend downstream of the leak valve; The prefabricated sealed pipe section is fitted onto the pressure-bearing pipe section downstream of the leakage valve, and the suction port of the vacuum negative pressure machine is connected to the pressure-bearing pipe section downstream of the leakage valve. The leaking water in the pressure-bearing pipe section downstream of the leaking valve is sucked away using the vacuum negative pressure machine, and the sealing pipe section is welded to the pressure-bearing pipe section downstream of the leaking valve. After welding is completed, the vacuum negative pressure machine is removed, and the blind flange is installed on the plug flange.

[0012] Furthermore, the prefabrication of the sealing pipe section includes: using the sum of the weld thickness (which meets the requirements of welding process and materials under a predetermined pressure) and the outer diameter of the pressure-bearing pipe section downstream of the leakage valve as the outer diameter of the sealing pipe section.

[0013] Furthermore, closing the leak valve of the chemical and volume control system and cutting the right-angle elbow downstream of the leak valve includes: cutting the pipe section on the outlet side 15-30mm upstream of the weld connecting the pipe section on the outlet side of the leak valve to the right-angle elbow and removing 30-35mm to facilitate the installation of the sealing device.

[0014] Furthermore, after closing the leak valve of the chemical and volume control system and cutting the right-angle bend downstream of the leak valve, the procedure includes: installing a plug at the inlet of the non-pressurized pipe section downstream of the leak valve to prevent downstream radioactive water from flowing back and causing contamination.

[0015] Furthermore, welding the sealing pipe section to the pressure-bearing pipe section downstream of the leakage valve includes: The sealing pipe section is welded to the pressure-bearing pipe section downstream of the leakage valve using a segmented welding method.

[0016] Furthermore, after welding the sealing pipe section to the pressure-bearing pipe section downstream of the leakage valve, the process includes: Perform flaw detection and penetrant testing on the welded area.

[0017] Furthermore, after installing the blind flange onto the socket flange, the process further includes: Verify whether the sealing device can withstand the predetermined pressure; If the sealing device cannot withstand the predetermined pressure, the sealing device shall be re-welded onto the pressure-bearing pipe section downstream of the leaking valve.

[0018] This invention discloses a sealing device and its application method. The sealing device is applied to a chemical and volumetric control system and includes: a sealing pipe section, a socket flange, and a blind flange. The sealing pipe section is connected to the socket flange. The sealing pipe section has an axially penetrating pipe hole. The socket flange has a flange hole communicating with the pipe hole. The blind flange and the socket flange are detachably connected to seal the flange hole. By fitting the sealing pipe section onto the outside of the leaking pipe, and forming a detachable sealing structure with the socket flange and the blind flange, this invention can directly block the leakage of radioactive coolant downstream of the leak point, avoiding radioactive contamination outside the containment. It eliminates the need to shut down the RCV pump or main pump, meeting the unit's full-power operation requirements, avoiding economic losses from downtime maintenance, shortening the maintenance cycle, and eliminating the need for ice-blocking processes. Furthermore, by providing the pipe hole and flange hole, a vacuum negative pressure pump can continuously drain leaked water from the pipe hole and flange hole, thereby keeping the welding area dry and ensuring welding quality. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A simplified flowchart of the RCV system; Figure 2 A simplified flowchart of the main pump shaft seal injection module; Figure 3 A simplified flowchart of the leakage module; Figure 4 A simplified flow chart of the inlet exhaust module of the charging pump; Figure 5 A simplified flowchart of the low-flow module for the top-charge pump; Figure 6 A simplified flow chart of the main pump shaft seal return water module; Figure 7 A simplified flowchart of the charging pump inlet and outlet and the charging circuit module; Figure 8 This is a schematic diagram of the sealing device. Figure 9 A schematic diagram of the sealed pipe section and the socket flange; Figure 10 This is a flowchart illustrating the application method of the sealing device. Figure 11 A structural schematic diagram of the sealing pipe section and the socket flange from another perspective; Figure 12This is a schematic diagram showing the downstream side of the leaking valve after cutting. Figure 13 This is a schematic diagram illustrating the working principle of a sealing device welded downstream of a leaking valve. Figure 14 This is a schematic diagram showing the sealing device welded downstream of the leaking valve. Explanation of the labels in the diagram: 1. Sealed pipe section; 2. Insert flange; 3. Blind flange; 4. Pipe hole; 5. Flange hole; 6. Connecting parts; 7. Matching parts. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be understood that, when used in this specification and the appended claims, the terms “comprising” and “including” indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0023] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0024] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0025] Please see Figures 1-7The Chemical and Volume Control System (RCV) is a major auxiliary system of the Reactor Coolant System (RCP). The RCV system consists of drain lines, charging lines, low-pressure drain lines, excess drain lines, shaft seal injection and return water lines, purification units, and other pipelines, providing chemical, volumetric, and reactivity control for the reactor coolant system. During normal operation, high-temperature, high-pressure water drawn from the RCP system is depressurized through one of three parallel depressurization orifice plates (RCV001 / 002 / 003DI) and the drain control valve (RCV013VP). It is then cooled twice by heat exchangers (RCV001EX and RCV002RF) to become low-temperature, low-pressure water. After passing through a filtration and demineralization bed purification unit, it enters the volume control tank (RCV002BA).

[0026] The RCV002BA containment tank serves as a buffer for the primary loop water load, removing gas fission products and controlling the primary loop hydrogen content, while also providing positive head for the charging pumps. Three RCV charging pumps are arranged in rows A and B. Normally, one pump in row B operates, drawing water from the RCV002BA containment tank, pressurizing it to 177 bar, and then injecting it into the primary loop via the charging flow regulating valve RCV046VP, adjusting the primary loop water load to the programmed value. The charging and venting processes exchange heat in the regenerative heat exchanger RCV001EX, reducing the venting flow temperature to prevent vaporization and heating the charging flow to prevent cryogenic water from entering the reactor core. When the RCP pressure drops below 30 bar, due to excessive resistance in the venting orifice plate, a low-pressure venting pipeline needs to be activated. This pipeline originates from the outlet header of the residual heat removal system (RRA) pump, flows through RCV310VP to the downstream of the venting orifice plate, and then into RCV002BA. The primary loop pressure is controlled by RCV013VP.

[0027] The RCV also supplies shaft seal water to the RCP main pump. A dedicated shaft seal water pipeline is located on the outlet header of the charging pump. After passing through one of two parallel-operating filters to remove solid impurities, the water enters the No. 1 shaft seal of the main pump. Part of the shaft seal water flows downwards to cool and lubricate the main pump bearings before entering the primary loop system; the other part flows upwards, through the No. 1 shaft seal return water pipeline, and after solid particles are removed by the shaft seal return water filter RCV005FI, it enters the shaft seal return water heat exchanger RCV003RF. After cooling, it returns to the inlet of the RCV charging pump. The shaft seal flow rate is adjusted by adjusting RCV061VP to maintain it within the normal range. The shaft seal water flow rate of each main pump is individually adjusted locally by regulating RCV067 / 068 / 069VP.

[0028] The reactor coolant loop (RCP) primarily circulates the coolant, transferring the heat generated by nuclear fission in the reactor core to the secondary coolant loop via a steam generator. This steam drives the turbine generator and simultaneously cools the reactor core, preventing fuel assemblies from burning out or being damaged. Furthermore, the coolant, light water, slows down the fast neutrons produced by fission into thermal neutrons (high-energy neutrons are converted into low-energy neutrons), maintaining the chain fission reaction. The coolant also contains boric acid, which absorbs neutrons; adjusting the boron concentration controls reactivity to compensate for burnup and xenon toxicity. The RCP system includes a pressurizer to maintain the primary loop pressure at a set absolute pressure of 155 bar.

[0029] Furthermore, the main pumps are electric pumps, with one main pump in each loop. These pumps drive the coolant to circulate within the primary loop pressure boundary, ensuring a sufficient flow of coolant through the reactor core. This continuously transfers the heat generated by the reactor to the secondary side of the steam generator, ensuring that the reactor core does not deviate from the operating conditions of nucleation boiling. Unless otherwise specified, only main pump No. 1 is shown in this document.

[0030] Furthermore, the purification unit removes radioactive ions, such as cesium, from the reactor coolant, purifying the primary coolant. It can also intermittently remove cationic lithium from the coolant and adjust the pH of the primary coolant. A downstream filter removes resin debris lost from the purification unit.

[0031] like Figures 1-7 As shown, the green pipelines represent the inlet and outlet of the charging pump and the charging circuit pipelines; the red pipelines represent the discharge pipelines; the purple pipelines represent the small flow pipelines of the charging pump; the yellow pipelines represent the inlet exhaust pipelines of the charging pump; the light blue pipelines represent the main pump shaft seal injection pipelines; and the blue pipelines represent the main pump shaft seal return water pipelines.

[0032] During a routine inspection, a rapid drop in the level of the control tank L2RCV002BA was observed, with a calculated drop rate of approximately 26 L / h. On-site temperature monitoring indicated an internal leak in the steam trap L2RCV577VP. Inspection of the downstream inspection port L2RPE206IC revealed water. Multiple leakage rate tests (T2RCP010, 4 hours) were performed, with the highest result being 41.28 L / h, meeting the requirements of the technical specifications (which define the boundaries of normal reactor operation and represent the minimum technical rules that must be followed to ensure the safety of the public and personnel during normal operation) and the oversight program (which ensures effective monitoring of safety system performance through regular inspections of critical safety equipment and systems). Regarding potential leaks within the containment (which isolates the environment from gases and facilities within the containment, provides shielding, and prevents damage to equipment from projectiles), inspections of the L2RX building for temperature, pressure, and radioactivity showed no abnormal changes. Based on these findings, the leak was determined to be an internal leak in the steam trap L2RCV577VP. To solve the problem of internal leakage in steam traps, this embodiment designs a method of inserting a large-diameter pipe section of the same material into the leaking pipeline, using a vacuum negative pressure machine to divert the water downstream of the leaking pipe opening, and welding the large-diameter pipe section upstream to seal the leaking water. The invention will be described in detail below through specific embodiments.

[0033] Please see Figure 8 and Figure 9 This embodiment provides a sealing device for use in chemical and volume control systems, including: a sealing pipe section 1, a socket flange 2, and a blind flange 3. The sealing pipe section 1 is connected to the socket flange 2. The sealing pipe section 1 is provided with a pipe hole 4 that extends axially through the sealing pipe section 1. The socket flange 2 is provided with a flange hole 5 that communicates with the pipe hole 4. The blind flange 3 and the socket flange 2 are detachably connected to seal the flange hole 5.

[0034] This embodiment connects the sealing pipe section 1 to the outside of the leaking pipe, and the insert flange 2 and blind flange 3 form a detachable sealing structure, which can directly block the leakage of radioactive coolant downstream of the leak point, avoid radioactive contamination outside the containment, and does not require the shutdown of the RCV pump or main pump throughout the process, meeting the requirements for full-power operation of the unit, avoiding economic losses caused by downtime maintenance, shortening the maintenance cycle, and eliminating the need to rely on ice plugging technology. At the same time, by setting the pipe hole 4 and flange hole 5, the leaking water can be continuously drained from the pipe hole 4 and flange hole 5 through the vacuum negative pressure machine, thereby keeping the welding area dry and ensuring the quality of the welding.

[0035] The sealing pipe section 1 is made of RCC-2 grade stainless steel (Z2CN18.10), with an outer diameter designed according to the pressure-bearing pipe section downstream of the leak point (such as the outlet pipe section of the steam trap L2RCV577VP), and a pressure-bearing capacity of 177-200 bar.g. A flange hole 5 is provided at the end of the sealing pipe section 1, communicating with the through hole of the insert flange 2. The insert flange 2 has a flange standard of 1 / 2" ANSI B16.5 1500LB, is made of the same material as the sealing pipe section 1, and is welded to the end of the sealing pipe section 1 or integrally formed with the end of the sealing pipe section 1. The blind flange 3 has a flange standard of 1 / 2" ANSI B16.5 1500LB, is made of RCC-2 grade stainless steel, and is detachably connected to the insert flange 2 via connector 6 and matching parts 7.

[0036] In this embodiment, it also includes: a plurality of connectors 6 and a plurality of matching parts 7, each connector 6 and each matching part 7 being threadedly connected, and the insert flange 2 and the blind flange 3 being detachably connected through the connectors 6 and the matching parts 7.

[0037] Connector 6 is a high-strength bolt, which can be M16×1.5 in size and made of Inconel 625 material, with a nickel-plated surface for rust prevention. Matching part 7 is a nut, which can also be made of Inconel 625 material.

[0038] During actual installation, first ensure that the connection surfaces of the insert flange 2 and the blind flange 3 are clean and free of impurities to avoid affecting the tightness of the connection. Next, thread the connector 6 through the corresponding mounting holes on the insert flange 2 and the blind flange 3 in sequence, and then screw the matching part 7 onto the connector 6, tightening it to the specified torque to ensure the stability and reliability of the connection. During use, the equipment may be subjected to external forces such as vibration and impact, requiring regular inspection of the connection between the connector 6 and the matching part 7 for looseness, wear, or other issues. If any damage is found to the connector 6 or the matching part 7, it should be replaced promptly to prevent safety hazards such as leakage between the insert flange 2 and the blind flange 3 due to connection problems, ensuring the safe and stable operation of the entire system.

[0039] The detachable connection between the insert flange 2 and the blind flange 3 is achieved through connector 6 and accessory 7, significantly reducing maintenance costs and complexity, and improving equipment maintainability. Simultaneously, the threaded connection provides excellent self-locking properties, ensuring stable connection force and preventing easy loosening of the insert flange 2 and blind flange 3 after connection. This guarantees the sealing and stability of the entire system and effectively prevents media leakage. Furthermore, using multiple connectors 6 and accessory 7 increases the number of connection points, distributing stress at the connection points and further enhancing the connection strength between flanges. This allows the system to withstand greater external forces and internal pressures, improving equipment safety and reliability.

[0040] In this embodiment, a gasket (not shown in the figure) is also included, which is disposed between the insert flange 2 and the blind flange 3.

[0041] When connecting insert flange 2 and blind flange 3, even if the flange surfaces are machined to be very flat, it is difficult to achieve absolute smoothness and zero gaps. Gaskets have good elasticity and compressibility, which can fill the small unevenness and gaps between the flange surfaces, forming a reliable sealing barrier and effectively preventing the leakage of high-pressure media.

[0042] Gaskets can be non-metallic, such as polytetrafluoroethylene (PTFE) gaskets, semi-metallic, such as spiral wound metal gaskets, or metallic, such as flat metal gaskets.

[0043] In practical applications, the appropriate gasket is selected based on the properties of different media in the pipeline, the pressure and temperature of the pipeline system, without imposing too many restrictions.

[0044] In this embodiment, the thickness of the gasket is in the range of 3mm-6mm. For example, a gasket with a thickness of 4.4mm can be used between the insert flange 2 and the blind flange 3.

[0045] Please see Figure 10-14 This embodiment also provides a method for applying a sealing device, including: S101: Close the leak valve of the chemical and volume control system and cut the right-angle bend downstream of the leak valve; In this embodiment, temporary supports (W258.566) need to be removed to make room for operation before shutting off leak valves (such as steam traps RCV577VP) in the chemical and volume control system.

[0046] Please see Figure 12 The upstream pipeline is located to the left of the leaking valve, with a pressure equal to the outlet pressure of the charging pump (177 bar.g), which is also the primary circuit pressure boundary. The downstream pipeline is located to the right of the leaking valve. The downstream pipeline has the same pressure rating as the upstream pipeline, but the pipeline from the first pipe joint bend downstream of the valve to the downstream section is not designed to be pressurized. Therefore, the pipeline downstream of the leaking valve (such as the RCV577VP steam trap) must be cut open and welded on the pressurized section.

[0047] Specifically, closing the leak valve and cutting the right-angle elbow downstream of the leak valve includes: cutting the pipe section on the outlet side 15-30mm upstream of the weld connecting the pipe section on the outlet side of the leak valve to the right-angle elbow and removing 30-35mm to facilitate the installation of the sealing device.

[0048] The cutting location should be chosen 15-30mm upstream of the weld connecting the outlet pipe section of the leakage valve and the right-angle elbow. Avoid directly cutting the existing weld or its heat-affected zone (approximately 10-15mm), as this could damage the mechanical properties of the original weld joint (such as reduced hardness and toughness). The 30-35mm cut length is precisely calculated based on the actual installation dimensions of the insert flange, gasket, and blind flange. The combined thickness of the gasket and blind flange is typically around 28.7mm, therefore 30-35mm ensures sufficient installation space for the gasket and blind flange.

[0049] In this embodiment, after closing the leak valve and cutting the right-angle bend downstream of the leak valve, the following steps are taken: installing a plug on the pipe opening of the non-pressurized section downstream of the leak valve to prevent downstream radioactive water from flowing back and causing pollution.

[0050] The non-pressurized pipeline downstream of the right-angle bend remains on site for subsequent restoration of the original design. The cut right-angle bend pipe section is stored in the warehouse. After the overhaul, the leaking valve (such as the steam trap RCV577VP) is replaced with a qualified leaking valve after pressure testing. The plug is then removed and the downstream pipeline and right-angle bend are re-welded to restore the original design configuration.

[0051] S102: Fit the prefabricated sealed pipe section onto the pressure-bearing pipe section downstream of the leakage valve, and connect the suction port of the vacuum negative pressure machine to the pressure-bearing pipe section downstream of the leakage valve; Please participate Figure 11 Before fitting the prefabricated sealing pipe section onto the pressure-bearing pipe section downstream of the leak valve, the outer diameter of the prefabricated sealing pipe section needs to be determined. Specifically, the prefabricated sealing pipe section includes the sum of the weld thickness that meets the welding process and material requirements under the predetermined pressure and the outer diameter of the pressure-bearing pipe section downstream of the leak valve as the outer diameter of the sealing pipe section.

[0052] By fitting a sealing pipe section over the original pressure-bearing pipe section, and designing the outer diameter of the sealing pipe section to equal the outer diameter of the pressure-bearing pipe section plus the weld thickness, it is possible to ensure that the sealed pipe section completely covers the welded area of ​​the pressure-bearing pipe section downstream of the leaking valve after welding. This forms an integral pressure-bearing structure of "double-walled pipe + full-circumference weld". For example, if the outer diameter of the pressure-bearing pipe section is 33.4mm + the weld thickness is 6mm, the outer diameter of the sealing pipe section is 39.4mm. This maximizes the stress-bearing area of ​​the welded joint, thereby evenly distributing the shear force of the high-pressure medium on the weld and preventing localized stress concentration.

[0053] In this embodiment, the specific calculation process for the weld thickness that meets the allowable welding process and materials under a predetermined pressure is as follows: Determine the design input parameters, as shown in Table 1; Table 1 Next, calculate the weld thickness T using the following formula. 焊缝 : T 焊缝 =P×D o / (2S×E×n).

[0054] In a specific embodiment, T can be calculated by substituting the example values ​​in Table 1 into the above formula. 焊缝 =17.7×219 / (2×138×0.85×3.0)=5.51mm. According to engineering specifications, the weld thickness must be rounded up to the standard value; in this example, T is used. 焊缝 =6mm.

[0055] Then the outer diameter of the sealed pipe section can be calculated to be 219 mm + 6 mm, which is 225 mm.

[0056] Next, please refer to Figure 13 To prevent the uncontrolled discharge of radioactive water and radiation exposure to personnel during welding due to continuous leakage from the leaking valve, and to avoid welding failure caused by continuous leakage, this embodiment uses a vacuum negative pressure machine to draw away the leaking water downstream of the leaking pipe. Specifically, the suction port of the vacuum negative pressure machine is fitted onto the pressure-bearing pipe section downstream of the leaking valve, and then the vacuum negative pressure machine is used to continuously draw away the leaking water from the downstream pipe opening of the leaking valve to ensure a dry environment during welding. After welding is completed, the vacuum negative pressure machine is removed.

[0057] S103: Use the vacuum negative pressure machine to suck away the leaked water in the pressure-bearing pipe section downstream of the leaking valve, and weld the sealing pipe section to the pressure-bearing pipe section downstream of the leaking valve; In this embodiment, welding the sealing pipe section to the pressure-bearing pipe section downstream of the leakage valve includes: The sealing pipe section and the pressure-bearing pipe section downstream of the leakage valve are welded using a segmented welding method.

[0058] Specifically, based on the length of the butt weld between the sealed pipe section and the pressure-bearing pipe section (assuming it is 120mm), it is divided into 6 sections, each with a length of 20mm.

[0059] Each segment is numbered S1 to S6, and the welding sequence is S3→S1→S5→S2→S4→S6 (staggered segment welding method to reduce deformation).

[0060] Then, the pressure pipe section is preheated, with the preheating temperature controlled at 150~250℃.

[0061] Next, use an infrared thermometer to monitor the preheating temperature to ensure uniformity.

[0062] Then, spot welding is performed on each section of the weld (at 5mm intervals) to form a temporary fixation.

[0063] Then, the root pass welding is carried out in the order of number S3→S1→S5, with each weld length being 10mm (completed in two stages).

[0064] The surface oxide layer should be cleaned immediately after welding.

[0065] Next, filler soldering is performed in sequence S2→S4→S6, with the interpass temperature controlled at 150~200℃.

[0066] Then, complete the cover weld in sequence S1→S3→S5 to ensure uniform weld formation. After each section of the root pass, fill pass, and cover weld is completed, use an ultrasonic flaw detector to inspect for internal defects.

[0067] After the inspection of the cover weld is completed, the weld area is annealed by heating to 300~350℃ and holding for 1 hour to eliminate residual stress. The cooling rate is controlled below 200℃ / h to prevent hot cracking.

[0068] Once fully cooled, the welding of the sealing section to the pressure-bearing section downstream of the leaking valve is completed.

[0069] This embodiment utilizes staggered segmented back-welding and skip-welding methods to disperse the heat-affected zone and reduce post-weld deformation. Each weld segment is completed independently, avoiding uneven cooling caused by continuous heating of long welds and saving construction time. Segmented inspection and interlayer cleaning ensure timely defect detection, improving weld pass rate.

[0070] In this embodiment, after welding the sealing pipe section to the pressure-bearing pipe section downstream of the leakage valve, the following steps are included: Perform flaw detection and penetrant testing on the welded area.

[0071] Specifically, the flaw detection procedure is as follows: Use sandpaper to roughen the surface of the weld and surrounding base material to Ra ≤ 6.3 μm; then apply glycerin coupling agent to the inspection area, ensuring the probe adheres to the surface; next, scan in a zigzag pattern along the weld axis, covering the entire weld cross-section; subsequently, inspect according to the standard that no incomplete fusion, cracks, or dense porosity longer than 3 mm is allowed. If any of these are present, the flaw detection is deemed unqualified; if none are present, the flaw detection is deemed qualified.

[0072] The process of penetrant testing is as follows: Remove the oil stain and scale on the weld surface with acetone, and the cleaning range ≥ 25 mm on both sides of the weld; Then use a solvent-removable penetrant (such as DPT-5) for spraying, with a uniform spraying thickness, and the penetration time is 15 min; Then use non-woven paper dipped in cleaning agent to gently wipe the surface, and avoid excessive wiping that may blur the defect display; Then spray white dry powder developer, and the developing time is 10 min; Subsequently, observe under natural light (illuminance ≥ 300 lx). If no red linear or circular display traces are found, it is judged as qualified. If red linear or circular display traces are found, it is judged as unqualified.

[0073] In this embodiment, by standardizing the flaw detection and penetrant testing processes, the quality of the welds in the primary circuit of the nuclear power plant is ensured to meet the stringent safety requirements.

[0074] S104: After welding is completed, remove the vacuum negative pressure machine and install the blind flange on the socket flange.

[0075] Please refer to Figure 14 , specifically, fasten the blind flange with connecting parts and matching parts. At the final stage of fastening the blind flange, the leaked water in the pressure-bearing pipe section downstream of the leakage valve may have been pressurized to 177 bar.g. However, at this time, the final seal of the blind flange can be achieved by continuing to fasten the connecting parts and matching parts. After fastening is completed, the socket flange and the blind flange serve as the pressure-bearing boundary and can block the leaked water in the leakage valve.

[0076] Among them, during the installation of the blind flange, gaskets need to be installed between the socket flange and the blind flange to achieve the seal between the socket flange and the blind flange.

[0077] Furthermore, after installing the blind flange on the socket flange, it further includes: Verify whether the sealing device can withstand a predetermined pressure; If the sealing device cannot withstand the predetermined pressure (such as 177 bar.g, etc., and the specific value can be determined according to the actual situation), then re-weld the sealing device on the pressure-bearing pipe section downstream of the leakage valve.

[0078] If the sealing device can withstand the predetermined pressure, reinstall the temporary support W258.566 to support the drain pipe section downstream of the right-angle elbow remaining on site.

[0079] In this embodiment, through the above method, it is possible to avoid the risk of radioactive water entering the nuclear auxiliary building due to the expansion of leakage during excessive maintenance, thus causing radiation risks to personnel and the environment; at the same time, it can avoid on-line high-pressure flushing, which may damage the valve sealing surface and further expand the leakage; it can also avoid the risk of main pump damage and unit withdrawal caused by the inability to ensure that the ice plug can withstand a pressure of 177 bar during ice plug maintenance; and it can also avoid the economic losses caused by shutdown maintenance.

[0080] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

[0081] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusivity.

[0082] The term "comprises" implies that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A sealing device for use in chemical and volume control systems, characterized in that, include: The system includes a sealing pipe section, a socket flange, and a blind flange. The sealing pipe section is connected to the socket flange. The sealing pipe section has a pipe hole that extends axially through the sealing pipe section. The socket flange has a flange hole that communicates with the pipe hole. The blind flange and the socket flange are detachably connected to seal the flange hole.

2. The sealing device according to claim 1, characterized in that, Also includes: A plurality of connectors and a plurality of fittings are provided, each connector and each fitting being threadedly connected, and the insert flange and the blind flange being detachably connected via the connectors and fittings.

3. The sealing device according to claim 1, characterized in that, Also includes: A gasket is disposed between the insert flange and the blind flange.

4. A method of applying the sealing device as described in any one of claims 1-3, characterized in that, include: Close the leak valve of the chemical and volume control system and cut the right-angle bend downstream of the leak valve; The prefabricated sealed pipe section is fitted onto the pressure-bearing pipe section downstream of the leakage valve, and the suction port of the vacuum negative pressure machine is connected to the pressure-bearing pipe section downstream of the leakage valve. The leaking water in the pressure-bearing pipe section downstream of the leaking valve is sucked away using the vacuum negative pressure machine, and the sealing pipe section is welded to the pressure-bearing pipe section downstream of the leaking valve. After welding is completed, the vacuum negative pressure machine is removed, and the blind flange is installed on the plug flange.

5. The application method according to claim 4, characterized in that, The prefabrication of the sealing pipe section includes: using the sum of the weld thickness (which meets the requirements of welding process and materials under a predetermined pressure) and the outer diameter of the pressure-bearing pipe section downstream of the leakage valve as the outer diameter of the sealing pipe section.

6. The application method according to claim 4, characterized in that, The step of closing the leak valve of the chemical and volume control system and cutting the right-angle elbow downstream of the leak valve includes: cutting the pipe section on the outlet side 15-30mm upstream of the weld connecting the pipe section on the outlet side of the leak valve to the right-angle elbow and removing 30-35mm to facilitate the installation of the sealing device.

7. The application method according to claim 4, characterized in that, After closing the leak valve of the chemical and volume control system and cutting the right-angle bend downstream of the leak valve, the procedure includes: installing a plug at the inlet of the non-pressurized pipe section downstream of the leak valve to prevent downstream radioactive water backflow from causing contamination.

8. The application method according to claim 4, characterized in that, Welding the sealing pipe section to the pressure-bearing pipe section downstream of the leakage valve includes: The sealing pipe section is welded to the pressure-bearing pipe section downstream of the leakage valve using a segmented welding method.

9. The application method according to claim 4, characterized in that, After welding the sealing pipe section to the pressure-bearing pipe section downstream of the leakage valve, the process includes: The welded area is subjected to flaw detection and penetrant testing.

10. The application method according to claim 4, characterized in that, After installing the blind flange onto the socket flange, the process further includes: Verify whether the sealing device can withstand the predetermined pressure; If the sealing device cannot withstand the predetermined pressure, the sealing device shall be re-welded onto the pressure-bearing pipe section downstream of the leaking valve.

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