Heat insulation guide structure suitable for control rod driving mechanism of pressurized water reactor nuclear power station

Abstract

The invention provides a heat insulation guide structure suitable for a control rod driving mechanism of a pressurized water reactor nuclear power station, relates to the technology of the control rod driving mechanism of the reactor of the pressurized water reactor nuclear power station, and particularly discloses an installation opening formed in a top cover of a reactor pressure vessel. A connecting pipe seat is detachably arranged at the end, arranged in the reactor pressure vessel, of the driving mechanism pipe seat, a second guide hole communicated with the first guide hole is formed in the connecting pipe seat, a guide cover is detachably arranged on the connecting pipe seat, a bypass flow structure used for flow guiding is arranged on the inner wall of the driving mechanism pipe seat, and the bypass flow structure is communicated with the first guide hole. The bypass flow structure realizes flow self-adaptive adjustment, maintains the flow speed in the guide hole to be stable, further reduces thermal stress concentration during rod falling of the control rod, reduces fluid resistance during rod falling, improves the rod falling speed and response efficiency, blocks reverse flow of a coolant and prevents heat from flowing upwards to the driving mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of control rod drive mechanisms for pressurized water reactor nuclear power plants, and in particular to a heat-insulating guide structure suitable for control rod drive mechanisms for pressurized water reactor nuclear power plants. Background Art

[0002] The control rod drive mechanisms of pressurized water reactor nuclear power plants are all designed with thermal insulation sleeve assemblies, which consist of parts such as thermal insulation sleeves and guide covers. They are installed in the drive mechanism pipe seat at the bottom of the sealed shell. Their main function is to reduce the heat transfer from the reactor coolant to the drive mechanism; at the same time, they provide a water squeezing channel when the drive mechanism drops the rods, ensuring the smooth drop of the drive rods; secondly, when the reactor pressure vessel top cover is closed, they guide the drive rod assembly into the hook assembly.

[0003] Due to the flow-induced vibration in the reactor pressure vessel top cover, the insulation sleeve assembly suffers significant wear at the supporting part where its end contacts the drive mechanism pipe seat, causing the insulation sleeve assembly to sink. In severe cases, the upper end of the insulation sleeve assembly may break, jamming the drive rod assembly, preventing the control rod from falling, causing a rod jam event, and posing a major safety hazard to reactor operation. Summary of the Invention

[0004] The object of the present invention is to provide a thermal insulation guide structure suitable for the control rod drive mechanism of a pressurized water reactor nuclear power plant. In view of the shortcomings of the existing technology, the present invention can maintain all the functions of the original thermal insulation sleeve assembly, eliminate the wear of the thermal insulation sleeve assembly caused by the vibration caused by the flow in the reactor, and eliminate the major safety hazards in the operation of the reactor caused by this.

[0005] The technical solution of the present invention is achieved as follows:

[0006] The present invention provides a heat-insulating guide structure suitable for a control rod drive mechanism of a pressurized water reactor nuclear power plant. The structure comprises a mounting opening opened at a top cover of a reactor pressure vessel, a drive mechanism pipe seat passing through the mounting opening, a first guide hole provided in the drive mechanism pipe seat, a detachable connecting pipe seat provided at an end of the drive mechanism pipe seat placed in the reactor pressure vessel, a second guide hole connected to the first guide hole provided in the connecting pipe seat, a detachable guide cover provided at the connecting pipe seat, a bypass structure for diverting flow provided on the inner wall of the drive mechanism pipe seat, and the bypass structure connected to the first guide hole.

[0007] In some technical solutions of the present invention, a sink groove is opened on the side of the drive mechanism pipe seat away from the reactor pressure vessel top cover. The inner diameter of the sink groove is larger than the inner diameter of the first guide hole. The sink groove and the first guide hole are combined to form a stepped guide channel.

[0008] In some technical solutions of the present invention, the bypass structure includes an annular groove, which is axially arranged on the inner wall of the first guide hole along the driving mechanism tube seat. Several axial holes are opened on the stepped surface formed by the sinking groove and the first guide hole, and the axial holes are all connected to the annular groove.

[0009] In some technical solutions of the present invention, a spherical valve stem is slidably provided in the axial hole, and the arc surface of the spherical valve stem abuts against the inner side of the axial hole.

[0010] In some technical solutions of the present invention, the connecting pipe seat is threadedly connected to the guide cover.

[0011] In some technical solutions of the present invention, the side where the connecting pipe seat and the guide cover abut against each other is welded.

[0012] In some technical solutions of the present invention, the spherical valve stem includes a spherical part and a rod body. The spherical part and the rod body are integrally formed. A bearing surface is provided on the side of the spherical part facing away from the rod body. A strip hole is provided on the bearing surface. A circular blind hole connected to the strip hole is provided in the spherical part.

[0013] In some technical solutions of the present invention, the inner diameter of the axial hole is larger than the diameter of the annular groove.

[0014] In some technical solutions of the present invention, a guide groove adapted to the ball valve stem is opened in the drive mechanism pipe seat, the guide groove is coaxial with the axial hole, the guide groove is connected to the annular groove, and a part of the ball valve stem is embedded in the guide groove.

[0015] In some technical solutions of the present invention, an Ω sealing ring is installed between the drive mechanism tube seat and the installation port.

[0016] Compared with the prior art, the present invention has at least the following advantages or beneficial effects: by reducing the inner hole diameter of the upper section of the drive mechanism tube seat (consistent with the inner diameter of the original insulation sleeve), the drive mechanism tube seat is directly used to replace the guiding function of the original insulation sleeve, thereby reducing redundant components and reducing structural complexity. The drive mechanism tube seat, the connecting tube seat and the guide cover are quickly assembled through detachable connections, avoiding overall replacement and reducing maintenance costs; the guide cover and the connecting tube seat are combined to form a thermal barrier to isolate the direct thermal impact of the high-temperature coolant on the drive mechanism tube seat, thereby reducing the risk of heat conduction and thermal deformation; the annular groove and the axial The bypass flow structure formed by the holes diverts the coolant, balances the temperature distribution inside the tube seat, and avoids local overheating causing material fatigue; the ball valve stem cooperates with the bypass flow structure to realize adaptive flow adjustment, maintain the stability of the flow velocity in the main guide hole, and further reduce the thermal stress concentration when the control rod is dropped; the bypass flow structure formed by the annular groove and the axial hole provides a "water squeezing channel" for the control rod, reduces the fluid resistance when the rod is dropped, and improves the rod dropping speed and response efficiency. The ball valve stem automatically resets and closes the axial hole after the rod is dropped, blocking the reverse flow of the coolant, preventing heat from rising to the drive mechanism, and ensuring the safety of equipment operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic cross-sectional view of the installation structure of the present invention.

[0018] Figure 2 It is a schematic diagram of the installation structure of the annular groove and the axial hole in the present invention.

[0019] Figure 3 This is a schematic top view of the drive mechanism tube seat in the present invention.

[0020] Figure 4 It is a schematic cross-sectional view of the spherical valve stem in the present invention.

[0021] Figure 5 It is a schematic diagram of the top view of the spherical valve stem in the present invention.

[0022] Figure numerals: 1. drive mechanism pipe seat; 2. reactor pressure vessel top cover; 3. first guide hole; 4. sink groove; 5. ball valve stem; 6. second guide hole; 7. connecting pipe seat; 8. guide cover; 9. axial hole; 10. annular groove; 11. guide groove; 12. blind hole; 13. strip hole. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0025] Example

[0026] The present invention provides a heat-insulating guide structure suitable for a control rod drive mechanism of a pressurized water reactor nuclear power plant, such as Figure 1 、 Figure 2 As shown, this structure eliminates the original CRAD thermal sleeve assembly and improves the internal structure of the CRAD tube base 1, reducing the diameter of the inner hole in the upper section of the CRAD tube base 1. Specifically, the diameter of the inner hole in the upper section of the CRAD tube base 1 is reduced to match the inner diameter of the original thermal sleeve assembly, ensuring that the original thermal sleeve can guide the CRAD drive rod assembly.

[0027] Its specific structure includes a circular mounting opening in the reactor pressure vessel top cover 2, through which a drive mechanism tube base 1 is inserted. The drive mechanism tube base 1 is a tubular structure with a first guide hole 3. The end of the drive mechanism tube base 1 placed in the reactor pressure vessel is detachably provided with a connecting tube base 7. The connecting tube base 7 has a second guide hole 6 connected to the first guide hole 3. The connecting tube base 7 is detachably provided with a guide cover 8. A bypass flow structure for diverting flow is provided on the inner wall of the drive mechanism tube base 1, and the bypass flow structure is connected to the first guide hole 3. The control rod drop operation is as follows: the control rod enters the drive mechanism tube base 1 provided in the mounting opening of the reactor pressure vessel top cover 2, passes through the first guide hole 3 of the drive mechanism tube base 1, and extends into the guide cover 8 through the second guide hole 6 in the connecting tube base 7.

[0028] When the control rod is dropped, when the coolant flows in the guide hole, part of the fluid is diverted through the bypass structure on the inner wall of the drive mechanism tube seat 1 to form a bypass circulation. The detachable design of the drive mechanism tube seat 1 and the connecting tube seat 7 forms a continuous guide channel to ensure the precise positioning of the control rod; the bypass structure diverts the coolant through fluid dynamics to reduce the movement resistance of the control rod. The combination of the guide cover 8 and the connecting tube seat 7 isolates the direct heat conduction of the high-temperature coolant to the drive mechanism tube seat 1, reducing thermal stress. The bypass structure reduces the resistance of the control rod when dropping the rod in the guide hole, avoids sticking when dropping the rod, and reduces the friction between the control rod and the wall of the guide hole. The combination of the connecting tube seat 7 and the guide cover 8 prevents the high-temperature fluid from directly impacting the drive mechanism, thereby extending the life of the components. The detachable design facilitates the replacement of damaged components (such as the guide cover 8) and shortens the shutdown time.

[0029] In some technical solutions of the present invention, a recessed groove 4 is defined on the side of the drive mechanism tube base 1 facing away from the reactor pressure vessel top cover 2. The inner diameter of recessed groove 4 is larger than that of the first guide hole 3. The recessed groove 4 and the first guide hole 3 form a stepped guide channel. The recessed groove 4 forms a stepped transition with the first guide hole 3, increasing the entrance cross-sectional area. This allows the lateral deflection of the control rod due to inertia during entry to be constrained by the inner wall of recessed groove 4, which then gradually converges to the first guide hole 3. This stepped guide channel gradually corrects the control rod's posture and avoids hard collisions with the inner wall of the guide hole. Furthermore, the recessed groove 4 increases the coolant flow space, reduces eddy currents, and reduces local pressure loss.

[0030] In some technical solutions of the present invention, the bypass flow structure includes an annular groove 10, which is axially disposed on the inner wall of the first guide hole 3 of the drive mechanism tube seat 1. A plurality of axial holes 9, ranging from 3 to 6, are formed on the stepped surface formed by the sink 4 and the first guide hole 3. Each axial hole 9 is connected to the annular groove 10. When the control rod is dropped, after the coolant flows through the first guide hole 3, some of the fluid enters the axial holes 9 through the annular groove 10 and ultimately converges into the sink 4 area. The annular grooves 10 are evenly distributed along the circumference of the first guide hole 3, balancing the radial pressure within the guide hole. The axial holes 9 guide the fluid into the sink 4, forming a bypass circulation, providing a water squeezing channel for the control rod drive mechanism when dropping the rod, and reducing resistance during drop. The annular groove 10 evenly diverts the coolant to prevent local overheating that could cause tube seat deformation. Furthermore, the bypass fluid continuously flushes the sink 4 area through the axial holes 9, preventing particle deposition.

[0031] In some technical solutions of the present invention, a ball valve stem 5 slides within the axial bore 9, with the arc surface of the ball valve stem 5 abutting against the inner side of the axial bore 9. When the control rod is dropped, the coolant flow rate changes, and the ball valve stem 5 slides within the axial bore 9, adjusting the flow channel opening through the contact between the ball portion and the bore wall. The high-pressure fluid pushes the ball valve stem 5 toward the sink 4, expanding the flow channel. When the control rod is dropped, the lifting force exerted by the fluid on the ball valve stem 5 gradually decreases, and the ball valve stem returns to its original position due to gravity, narrowing the flow channel formed between the ball valve stem 5 and the axial bore 9. After the ball valve stem is fully returned, the axial bore 9 is sealed, thus closing the bypass flow structure for coolant circulation, preventing reactor coolant from flowing upstream and reducing the transfer of reactor coolant heat to the control rod drive mechanism. This structure dynamically adjusts the bypass flow rate to maintain a constant flow velocity within the main guide bore. The tight contact between the ball portion and the bore wall prevents reverse flow of coolant, thereby improving system safety.

[0032] In some technical solutions of the present invention, the connecting pipe base 7 is threadedly connected to the guide cover 8. The connecting pipe base 7 and the guide cover 8 are fixed by screwing together and can be removed and replaced when necessary. The threaded connection provides axial preload to ensure that the guide cover 8 does not loosen in a vibrating environment.

[0033] In some technical solutions of the present invention, the abutting side of the connecting pipe base 7 and the guide cover 8 is welded. After the threaded connection, the joint surface of the connecting pipe base 7 and the guide cover 8 is welded to achieve a double fixation. Welding eliminates thread gaps, completely blocks leakage paths, and forms a redundant seal. The welded structure resists the risk of thread loosening caused by high-frequency vibration. Together, the two prevent seal failure caused by thread corrosion.

[0034] In some technical solutions of the present invention, the ball valve stem 5 includes a spherical portion and a stem. The spherical portion and the stem are integrally formed. The side of the spherical portion facing away from the stem is cut to form a bearing surface. The bearing surface is provided with a strip hole 13. A circular blind hole 12 is provided in the spherical portion and communicates with the strip hole 13. This facilitates the operator's installation of the spherical valve stem 5 in the axial hole 9. The outer diameter of the stem is smaller than the inner diameter of the axial hole 9.

[0035] In some technical solutions of the present invention, the inner diameter of the axial hole 9 is larger than the diameter of the annular groove 10. This ensures sufficient and unrestricted bypass flow. The large-diameter axial hole 9 serves as the main bypass channel, while the annular groove 10 is used only for pressure equalization. The large-diameter axial hole 9 reduces the probability of impurity retention and prevents clogging, while also reducing bypass flow resistance and improving cooling efficiency.

[0036] In some technical solutions of the present invention, a guide groove 11 adapted for the ball valve stem 5 is defined within the drive mechanism socket 1. The guide groove 11 is coaxial with the axial hole 9 and communicates with the annular groove 10. A portion of the ball valve stem 5 is embedded within the guide groove 11. The body of the ball valve stem 5 is embedded within the guide groove 11, restricting it to sliding only in the axial direction. The guide groove 11 constrains the motion trajectory of the ball valve stem 5, preventing it from deflecting or getting stuck, ensuring that the valve stem remains coaxial with the axial hole 9, maintaining sealing, and distributing the force applied to the valve stem, reducing wear on one side of the ball valve stem 5.

[0037] In some technical solutions of the present invention, an Ω sealing ring is installed between the drive mechanism tube socket 1 and the mounting opening. The Ω sealing ring is welded between the drive mechanism tube socket 1 and the mounting opening. When pressurized, it expands radially to fill the gap between the drive mechanism tube socket 1 and the mounting opening. The Ω-shaped structure maintains resilience at high temperatures, accommodating the differential thermal expansion between the tube socket and the top cover. The higher the system pressure, the greater the compressive force of the sealing surface formed by the Ω-shaped structure, minimizing the risk of leakage.

[0038] Preferably, the control rod drive mechanism is manufactured at a control rod drive mechanism equipment manufacturing plant, including the manufacturing of the integral sealing shell (including the drive mechanism pipe seat 1 part), the guide cover 8 assembly and the ball valve stem.

[0039] At the reactor pressure vessel manufacturing plant, the manufacturing of the drive mechanism tube seat 1 and the installation of the drive mechanism tube seat 1 on the reactor pressure vessel top cover 2 are completed, or the installation of the control rod drive mechanism integral sealing shell (including the drive mechanism tube seat 1 part) on the reactor pressure vessel top cover 2 is completed, and at the same time, the threaded connection and anti-loosening welding between the guide tube of the guide cover 8 assembly and the drive mechanism tube seat 1 are completed.

[0040] At the nuclear power plant site, after installing the ball valve stem, the other CRAM components are installed. After completing the Ω sealing ring weld on the CRAM pressure hull, a hydrostatic test is performed on the CRAM pressure hull. After the hydrostatic test is completed, the guide hood 8 of the guide hood 8 assembly is mounted on the connecting pipe base 7 using threaded connections and anti-loosening welding.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A heat-insulating guide structure suitable for a control rod drive mechanism of a pressurized water reactor nuclear power plant, characterized in that: The invention comprises a mounting opening opened at the top cover (2) of the reactor pressure vessel, wherein a drive mechanism pipe seat (1) is penetrated in the mounting opening, wherein the drive mechanism pipe seat (1) has a first guide hole (3), wherein the end of the drive mechanism pipe seat (1) placed in the reactor pressure vessel is detachably provided with a connecting pipe seat (7), wherein the connecting pipe seat (7) has a second guide hole (6) connected to the first guide hole (3), wherein the connecting pipe seat (7) is detachably provided with a guide cover (8), and a bypass structure for diverting flow is provided on the inner wall of the drive mechanism pipe seat (1), wherein the bypass structure is connected to the first guide hole (3).

2. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: A sink groove (4) is provided on the side of the drive mechanism pipe seat (1) facing away from the reactor pressure vessel top cover (2); the inner diameter of the sink groove (4) is larger than the inner diameter of the first guide hole (3); and the sink groove (4) and the first guide hole (3) are combined to form a stepped guide channel.

3. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 2, characterized in that: The bypass structure comprises an annular groove (10), which is arranged on the inner wall of the first guide hole (3) along the axial direction of the drive mechanism pipe seat (1); a plurality of axial holes (9) are opened on the stepped surface formed by the sinking groove (4) and the first guide hole (3), and the axial holes (9) are all connected to the annular groove (10).

4. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 3, characterized in that: A spherical valve stem (5) is slidably provided in the axial hole (9), and the arc surface of the spherical valve stem (5) abuts against the inner side of the axial hole (9).

5. A heat-insulating guide structure suitable for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to any one of claims 1 to 4, characterized in that: The connecting pipe seat (7) is threadedly connected to the guide cover (8).

6. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 5, characterized in that: The connecting pipe seat (7) and the guide cover (8) are welded together on one side where they abut against each other.

7. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 4, characterized in that: The ball valve stem (5) comprises a ball portion and a rod body, the ball portion and the rod body being integrally formed, a bearing surface being provided on the side of the ball portion facing away from the rod body, a strip hole (13) being provided on the bearing surface, and a circular blind hole (12) being provided in the ball portion and communicating with the strip hole (13).

8. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 3 or 4, characterized in that: The inner diameter of the axial hole (9) is larger than the diameter of the annular groove (10).

9. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 4 or 7, characterized in that: A guide groove (11) adapted to the spherical valve stem (5) is provided in the drive mechanism pipe seat (1), the guide groove (11) is coaxial with the axial hole (9), the guide groove (11) is communicated with the annular groove (10), and a part of the spherical valve stem (5) is embedded in the guide groove (11).

10. The heat-insulating guide structure for a control rod drive mechanism of a pressurized water reactor nuclear power plant according to claim 1, characterized in that: An Ω sealing ring is installed between the drive mechanism pipe seat (1) and the installation port.

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