Repair and replacement heat insulation sleeve for control rod drive mechanism and its installation method

Abstract

This disclosure belongs to the field of nuclear power technology, specifically relating to a replaceable insulation sleeve for a control rod drive mechanism and its installation method. Structurally, the replaceable insulation sleeve of this disclosure moves the upper end of the insulation sleeve down to the through-hole port, retaining the line contact form, and structurally provides a rod-dropping and water-squeezing function; the remaining structural forms remain unchanged, meeting the functional requirements of the insulation sleeve. The entire replaceable insulation sleeve assembly is installed as a set and fixed to the lower port of the tube seat by welding. Simultaneously, due to the lowered support surface, the impact arm of flow-induced vibration is reduced, and with the addition of a positioning block, the service life of this replaceable insulation sleeve assembly is superior to the original structure. Furthermore, the wear rate is reduced by stabilizing radial wobble using the positioning block.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power technology, specifically relating to a maintenance and replacement type heat insulation sleeve for a control rod drive mechanism and its installation method. Background Technology

[0002] The control rod drive mechanism of a pressurized water reactor unit is abbreviated as CRDM. The thermal insulation sleeve assembly within the CRDM is mounted on the tube seat of the control rod drive mechanism located on the pressure vessel top cover. The installation method is radial clearance fit with no axial constraint. During unit operation, the thermal insulation sleeve is affected by vibrations induced by the primary circuit medium flow, causing abrasion at the upper end where it contacts the flange of tube seat 2, and collision and wear at the lower end with the through-piece of tube seat 2. Without preventative measures, long-term operation will lead to severe wear of the thermal insulation sleeve, resulting in serious malfunctions such as excessive subsidence, breakage and detachment, and wall thinning. Once the wear becomes irreparable and cannot be repaired, the thermal insulation sleeve needs to be replaced.

[0003] In related technologies, if the replacement is done from above the top cover, the structure of the heat shield does not need to be changed. However, due to the complex structure of the reactor pressure vessel top cover, the reactor top structure and control rod drive mechanism need to be dismantled to the maximum extent before replacing the heat shield. Furthermore, since the pressure vessel and control rod drive mechanism are nuclear-grade equipment, and the welds involved are also the pressure-bearing boundaries of the primary circuit, the dismantling and reinstallation verification procedures are complex. The specific replacement work involves cutting, beveling, re-welding, non-destructive testing, hydrostatic testing, and automated welding under high radiation environments, requiring complex processes, a long construction period, and poor safety and economic efficiency.

[0004] Given the various drawbacks of replacing the thermal insulation sleeve from above the top cover, the preferred replacement technique is to replace it from below the thermal insulation sleeve of the control rod drive mechanism in pressurized water reactor nuclear power units. This replacement technique is a special maintenance technique for nuclear-grade equipment. Furthermore, due to the relatively short operating life of domestic units, the settlement defects of the thermal insulation sleeve have not yet reached the point where replacement is necessary. Therefore, my country currently lacks technical reserves and application cases for replacing thermal insulation sleeves from below.

[0005] Replacing the insulation sleeve at the bottom involves the structural design and installation process design of the new insulation sleeve. Because the insulation sleeve has a suspension end at the top, a sleeve in the middle, and a flared cover at the bottom, with the end diameter larger than the sleeve, it exhibits an overall shape that is larger at the top and smaller at the bottom. If the original structure is used for installation from below, the end will not be able to pass through the pipe seat from below.

[0006] In related technologies, the upper end structure of the insulation sleeve is designed as either a split or incomplete structure to achieve the purpose of passing through the sleeve. The split design uses a petal-shaped interlocking structure, where the upper and lower layers, inner and outer, are staggered and can retract inside the sleeve. After passing through the sleeve, they rely on the elasticity of the material to return to the designed size, and finally, the two layers are fixed together by welding. The incomplete design uses only materials with good elasticity and rigidity, making the upper end of the sleeve an incomplete structure, so that it can retract inside the sleeve under stress and return to the designed size through its own elasticity after passing through the sleeve. Although both structural forms conform to the original structural design and meet functional requirements, they achieve the lower installation process by reducing wall thickness, lowering strength, and sacrificing integrity. This results in a design service life of only 7-10 years, far below the service life requirements of pressure vessels. Summary of the Invention

[0007] To overcome the problems existing in related technologies, a maintenance and replacement type heat insulation sleeve for control rod drive mechanism and its installation method are provided.

[0008] According to one aspect of the present disclosure, a maintenance and replacement type heat insulation sleeve for a control rod drive mechanism is provided, the maintenance and replacement type heat insulation sleeve comprising: a horn cover, a sleeve, a support base, and an installation nozzle;

[0009] The horn cover and the sleeve are connected by a socket joint. The sleeve is long and tubular. The lower part of the sleeve has an end on the outside. The height from the end to the upper part of the sleeve is matched with the length of the sleeve inserted into the corresponding pipe seat, so that the height of the horn cover of each sleeve is the same after each sleeve is installed in the corresponding pipe seat.

[0010] The outer circumferential part of the sleeve has an end that extends radially outward, the support seat is a hollow stepped tube, the inner hole of the support seat has a stepped surface, and the sleeve is clamped on the stepped surface.

[0011] The installation nozzle is a hollow tube with a stop at the bottom. The installation nozzle is fitted onto the tube seat. The stop at the bottom of the installation nozzle is used to position the lower end of the tube seat. The installation nozzle is set at the opening on the support. The installation nozzle is fixedly connected to the tube seat on site and welded to the support. The hollow structure of the support and the installation nozzle are connected to form a cavity. The end of the sleeve can float up and down in the cavity.

[0012] In one possible implementation, multiple positioning components are installed sequentially from top to bottom in the upper middle part of the sleeve. Each positioning component includes multiple tile-shaped positioning blocks. The positioning blocks of each positioning component are fixedly connected to the outside of the sleeve and are evenly distributed around the axis of the sleeve. The positioning blocks are fitted with gaps in the gap between the tube and the tube seat.

[0013] In one possible implementation, the positioning blocks are welded to the outside of the sleeve.

[0014] In one possible implementation, the nozzle is welded to the support.

[0015] In one possible implementation, the nozzle is welded, spot-welded, or threaded to the pipe seat.

[0016] According to another aspect of the present disclosure, a method for installing a replaceable heat insulation sleeve for a control rod drive mechanism is provided. The method for assembling the replaceable heat insulation sleeve assembly includes:

[0017] Step 11: Pass the sleeve through the support seat so that the end of the sleeve contacts and engages with the stepped surface of the support seat.

[0018] Step 12: Install the horn cover at the lower end of the sleeve;

[0019] Step 13: Insert the installation nozzle into the sleeve from the upper end of the sleeve, so that the lower end face of the installation nozzle is in contact with the upper end face of the support base, and fix the lower end face of the installation nozzle to the upper end face of the support base by welding.

[0020] In one possible implementation, the installation method for the repairable and replaceable thermal insulation sleeve assembly includes:

[0021] Step 21: Under the top cover, at the position of the pipe seat to be replaced, lift the assembled maintenance and replacement heat insulation sleeve assembly upwards so that the installation nozzle covers the lower pipe opening of the pipe seat until the lower pipe opening of the pipe seat abuts the stop of the installation nozzle.

[0022] Step 22: Weld and fix the nozzle and the lower pipe opening of the pipe seat.

[0023] The beneficial effects of this disclosure are as follows: The repairable and replaceable insulation sleeve of this disclosure structurally moves the upper end of the insulation sleeve down to the through-hole port, retaining the line contact form, and structurally possesses a water-squeezing function with a drop bar; the remaining structural forms remain unchanged, meeting the functional requirements of the insulation sleeve. The entire repairable and replaceable insulation sleeve assembly is installed as a set, fixed to the lower port of the pipe seat by welding. Simultaneously, due to the lowered support surface, the impact arm of flow-induced vibration is reduced, and with the addition of a positioning block, the service life of this invention's repairable and replaceable insulation sleeve assembly is superior to the original structure. Furthermore, the wear rate is reduced by stabilizing radial sway through the positioning block. This overcomes the drawbacks of related technologies using a "compressible insulation sleeve" structure, such as reduced strength and stiffness, shorter service life, and reliance on temporary emergency repairs. It achieves a permanent, full-life-cycle maintenance solution. Attached Figure Description

[0024] Figure 1 This is an installation scenario diagram of the original thermal insulation sleeve assembly in the relevant technology.

[0025] Figure 2 It is a cross-sectional view of the original thermal insulation sleeve assembly in the relevant technology.

[0026] Figure 3 This is a perspective view of a repairable and replaceable thermal insulation sleeve assembly exemplarily shown in this disclosure.

[0027] Figure 4 This is a cross-sectional view of a repairable and replaceable thermal insulation sleeve assembly exemplarily shown in this disclosure.

[0028] Figure 5 This is a perspective view of another state of the repairable and replaceable thermal insulation sleeve assembly exemplarily shown in this disclosure.

[0029] Figure 6 This is an exemplary perspective view of the installation of a repairable and replaceable thermal insulation sleeve assembly and a pipe fitting, as shown in this disclosure.

[0030] Figure 7 This is an exemplary sectional view of the installation of a repairable and replaceable thermal insulation sleeve assembly and a fitting, as shown in this disclosure.

[0031] Figure 8 This is a cross-sectional view of the connection between the support and the mounting nozzle, as exemplarily shown in this disclosure. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1 This is an installation scenario diagram of the original thermal insulation sleeve assembly in related technologies. Figure 2 This is a cross-sectional view of the original thermal insulation sleeve assembly in the relevant technology, such as... Figure 1 and Figure 2 As shown, in the related technology, the original heat insulation sleeve assembly 3 is suspended and installed in the CRDM pipe seat 2 by its upper end, and the pipe seat 2 is installed on the pressure vessel top cover 1. Figure 1 As shown, the upper surfaces of all the tube seats 2 are flush, and the lower tube opening of each tube seat 2 extends into the spherical surface of the inner cavity of the top cover 1 by about 50mm. Since the inner cavity of the top cover 1 is spherical, the lower tube openings of each tube seat 2 are at different heights.

[0034] Figure 3 This is a perspective view of a repairable and replaceable thermal insulation sleeve assembly exemplarily shown in this disclosure. Figure 4 This is a cross-sectional view of a repairable and replaceable thermal insulation sleeve assembly exemplarily illustrated in this disclosure. Figure 5 This is a perspective view of another state of the repairable and replaceable thermal insulation sleeve assembly exemplarily shown in this disclosure. Figures 3 to 5 As shown, the maintenance and replacement type thermal insulation sleeve assembly 5 includes: a horn cover 51, a sleeve 52, a support 53, and an installation nozzle 54.

[0035] The horn cover 51 and the sleeve 52 are connected by a socket joint. The sleeve 52 is a long tube in shape. The lower part of the sleeve 52 has an end 55 on the outside. The height of the end 55 to the upper end of the sleeve 52 is adapted to the length of the sleeve 52 inserted into the corresponding tube seat 2, so that after each tube sleeve 52 is installed in the corresponding tube seat, the height of the horn cover 51 of each tube sleeve 52 is flush.

[0036] Multiple sets (e.g., 2 sets) of positioning components are installed sequentially from top to bottom in the upper middle part of the sleeve 52. Each set of positioning components includes multiple (e.g., 3) tile-shaped positioning blocks 56. Each positioning block 56 is fitted with a gap between the tube 52 and the tube seat 2. The positioning blocks of each set of positioning components are fixedly connected (e.g., welded) to the outside of the sleeve 52 and are evenly distributed around the axis of the sleeve 52.

[0037] The sleeve 52 has an end 55 extending radially outward on the outer circumference of the middle part, and the support 53 is in the shape of a hollow stepped tube. The inner hole of the support 53 has a stepped surface, and the sleeve 52 is clamped on the stepped surface.

[0038] like Figure 6 and Figure 7 As shown, the mounting nozzle 54 is a hollow tube with a stop at the bottom. The mounting nozzle 54 is fitted onto the tube seat 2, and the stop at the bottom of the mounting nozzle 54 is used to position the lower end of the tube seat 2. Figure 8 As shown, the mounting nozzle 54 is located at the opening on the support 53 and is welded to the support 53. The hollow structures of the support 53 and the mounting nozzle 54 are interconnected to form a cavity, and the end 55 of the sleeve 52 can float up and down within the cavity. The mounting nozzle 54 and the pipe seat 2 are fixedly connected by any one of the following connection methods: welding, spot welding, or threaded connection.

[0039] In one possible implementation, see Figure 3 and Figure 4 The assembly method of the repair and replacement type thermal insulation sleeve assembly disclosed herein includes the following steps:

[0040] Step 11: Pass the sleeve 52 through the support 53 so that the end 55 of the sleeve 52 contacts and engages with the stepped surface of the support 53.

[0041] Step 12: Install the horn cover 51 at the lower end of the sleeve 52;

[0042] Step 13: Insert the installation nozzle 54 into the sleeve 52 from the upper end, so that the lower end face of the installation nozzle 54 fits against the upper end face of the support 53, and fix the lower end face of the installation nozzle 54 to the upper end face of the support 53 by welding.

[0043] In one possible implementation, see Figure 1 , Figure 6 and Figure 7The installation method of the repair and replacement type thermal insulation sleeve assembly disclosed herein includes the following steps:

[0044] Step 21: Under the top cover 1, at the position of the pipe seat 2 that needs to be replaced, lift the assembled maintenance and replacement heat insulation sleeve assembly upwards so that the installation nozzle 54 covers the lower pipe opening of the pipe seat 2 until the lower pipe opening of the pipe seat 2 abuts against the stop of the installation nozzle 54.

[0045] Step 22: Weld and fix the nozzle 54 and the lower pipe opening of the pipe seat 2.

[0046] The repairable and replaceable thermal insulation sleeve assembly disclosed herein has the following characteristics:

[0047] 1. Without altering the components of the insulation sleeve, the repairable and replacement insulation sleeve assembly 5 of this disclosure still consists of three parts: end 55, sleeve 52, and horn cover 51. To allow the insulation sleeve to be inserted from below the pipe seat 2, the position of the end 55 is lowered to the height of the lower port of the pipe seat 2, thus enabling bottom installation. Since the height of the lower port of the pipe seat 2 on the pressure vessel top cover varies, the specific height of the new sleeve installation end is determined based on the actual height of the pipe seat 2 on site.

[0048] 2. A support base is added. Due to the downward shift of end 55, the original conical surface on the pipe seat 2 can no longer be used as the end support surface. Therefore, a new type of special support base 53 and installation nozzle 54 for the insulation sleeve are added, and installed at the lower end of the pipe seat 2 by welding. The support base 53 and installation nozzle 54 serve to support the maintenance and replacement insulation sleeve assembly 5 and connect the pipe seat 2. At the same time, the inner cavity of the support base has sufficient space to maintain the floating effect of the sleeve 52 under fluid impact.

[0049] 3. Adding positioning blocks: Due to the approximately 5mm gap between the sleeve 52 and the pipe seat 2, radial tilting and swaying will occur under the impact of the fluid medium inside the stack, resulting in contact and rubbing, which accelerates the rate of wear settlement and wall thickness reduction. To address this, a set of positioning blocks 56 is added to the sleeve, increasing the number of positioning blocks from one set to two sets. These blocks are arranged axially on the sleeve to stabilize the radial swaying.

[0050] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or technical improvements to the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A replaceable heat insulation sleeve for a control rod drive mechanism, characterized in that, The repair and replacement type thermal insulation sleeve includes: a horn cover, a sleeve, a support base, and an installation nozzle; The horn cover and the sleeve are connected by a socket. The sleeve is long and tubular in shape. The outer side of the middle part of the sleeve has a radially outward-extending end. The height of the end to the top of the sleeve is matched with the length of the sleeve inserted into the corresponding tube seat, so that the height of the horn cover of each sleeve is the same after each sleeve is installed in the corresponding tube seat. The support base is a hollow stepped tube with a stepped surface inside the support base, and the sleeve is clamped on the stepped surface. The installation nozzle is a hollow tube with a stop at the bottom. The installation nozzle is fitted onto the tube seat. The stop at the bottom of the installation nozzle is used to position the lower end of the tube seat. The installation nozzle is set at the opening on the support seat. The installation nozzle is fixedly connected to the tube seat on site and welded to the support seat. The hollow structure of the support seat and the installation nozzle are connected to form a cavity. The end of the sleeve can float up and down in the cavity. When installing the replacement insulation sleeve, under the top cover, corresponding to the position of the pipe seat to be replaced, lift the assembled replacement insulation sleeve upwards so that the installation nozzle covers the lower pipe opening of the pipe seat until the lower pipe opening of the pipe seat abuts the stop of the installation nozzle. Then, weld the installation nozzle and the lower pipe opening of the pipe seat to fix them.

2. The control rod drive mechanism repair and replacement type heat insulation sleeve according to claim 1, characterized in that, Multiple positioning components are installed sequentially from top to bottom in the upper middle part of the casing. Each positioning component includes multiple tile-shaped positioning blocks. The positioning blocks of each positioning component are fixedly connected to the outside of the casing and are evenly distributed around the axis of the casing. The gaps between the positioning blocks are fitted in the gap between the casing and the pipe seat.

3. The control rod drive mechanism repair and replacement type heat insulation sleeve according to claim 2, characterized in that, Each positioning block is welded to the outside of the sleeve.

4. The control rod drive mechanism repair and replacement type heat insulation sleeve according to claim 1, characterized in that, The nozzle is welded to the support base.

5. The control rod drive mechanism repair and replacement type heat insulation sleeve according to claim 1, characterized in that, The nozzle is installed by welding or threading it to the pipe seat.

6. A method for installing a replaceable heat insulation sleeve for a control rod drive mechanism, characterized in that, The method is implemented based on the control rod drive mechanism repairable and replaceable heat insulation sleeve as described in any one of claims 1 to 5, and the assembly method of the repairable and replaceable heat insulation sleeve assembly includes: Step 11: Pass the sleeve through the support seat so that the end of the sleeve contacts and engages with the stepped surface of the support seat. Step 12: Install the horn cover at the lower end of the sleeve; Step 13: Insert the installation nozzle into the sleeve from the upper end of the sleeve, so that the lower end face of the installation nozzle is in contact with the upper end face of the support base, and fix the lower end face of the installation nozzle to the upper end face of the support base by welding.

7. The method according to claim 6, characterized in that, The installation methods for repairable and replaceable thermal insulation sleeve assemblies include: Step 21: Under the top cover, at the position of the pipe seat to be replaced, lift the assembled maintenance and replacement heat insulation sleeve assembly upwards so that the installation nozzle covers the lower pipe opening of the pipe seat until the lower pipe opening of the pipe seat abuts the stop of the installation nozzle. Step 22: Weld and fix the nozzle and the lower pipe opening of the pipe seat.

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