A heat-insulating guide structure suitable for a control rod drive mechanism of a pressurized water reactor nuclear power plant

Abstract

The application discloses a heat insulation guide structure suitable for a control rod drive mechanism of a pressurized water reactor nuclear power plant, relates to the control rod drive mechanism technology of the pressurized water reactor nuclear power plant, and specifically discloses a mounting port arranged at a top cover of a reactor pressure vessel, a drive mechanism tube base is arranged in the mounting port, the drive mechanism tube base is provided with a first guide hole, and a connecting tube base is detachably arranged at an end of the drive mechanism tube base arranged in the reactor pressure vessel, the connecting tube base is provided with a second guide hole communicated with the first guide hole, the connecting tube base is detachably provided with a guide cover, a side flow structure for flow guiding is arranged on the inner wall of the drive mechanism tube base, the side flow structure is communicated with the first guide hole, the side flow structure realizes self-adaptive flow regulation, maintains the stability of flow velocity in the guide hole, further reduces the thermal stress concentration when the control rod falls, the side flow structure reduces the fluid resistance when the control rod falls, improves the falling speed and response efficiency of the control rod, and blocks the reverse flow of the coolant, so that the heat is prevented from rising to the drive mechanism.

Description

Technical Field

[0001] This invention relates to the technical field of reactor control rod drive mechanism in pressurized water reactor nuclear power plants, and more specifically, to a heat-insulating guide structure suitable for the control rod drive mechanism of pressurized water reactor nuclear power plants. Background Technology

[0002] All control rod drive mechanisms in pressurized water reactor nuclear power plants are designed with a heat insulation sleeve assembly. This assembly consists of a heat insulation sleeve and guide shrouds, and is installed in the drive mechanism tube seat at the bottom of the sealed shell. Its main function is to reduce the transfer of heat from the reactor coolant to the drive mechanism; at the same time, it provides a water squeezing channel when the drive mechanism lowers the rods to ensure smooth descent; and secondly, it guides the drive rod assembly into the claw assembly when the reactor pressure vessel top cover is closed.

[0003] Due to flow-induced vibration within the reactor pressure vessel top cover, significant wear occurs at the support portion of the heat shield assembly where it contacts the drive mechanism tube seat. This causes the heat shield assembly to sink, and in severe cases, the upper end of the heat shield assembly may break, jamming the drive rod assembly and preventing the control rod from falling, resulting in a rod jamming incident and posing a significant safety hazard to reactor operation. Summary of the Invention

[0004] The purpose of this invention is to provide a heat-insulated guide structure suitable for the control rod drive mechanism of a pressurized water reactor nuclear power plant. In view of the shortcomings of the prior art, this invention can maintain all the functions of the original heat insulation sleeve assembly, and eliminate the wear of the heat insulation sleeve assembly caused by in-core flow-induced vibration, thereby eliminating the major safety hazards to reactor operation caused by it.

[0005] The technical solution of this invention is implemented as follows:

[0006] This invention provides a heat-insulating guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant. It includes an installation port at the top cover of the reactor pressure vessel, a drive mechanism tube seat passing through the installation port, a first guide hole inside the drive mechanism tube seat, a detachable connecting tube seat at the end of the drive mechanism tube seat placed inside the reactor pressure vessel, a second guide hole communicating with the first guide hole inside the connecting tube seat, a detachable guide cover on the connecting tube seat, and a bypass structure for guiding flow on the inner wall of the drive mechanism tube seat, the bypass structure communicating with the first guide hole.

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

[0008] In some technical solutions of the present invention, the bypass structure includes an annular groove, which is axially disposed on the inner wall of the first guide hole along the drive mechanism tube seat. A plurality of axial holes are provided on the stepped surface formed by the sink and the first guide hole, and all the axial holes are connected to the annular groove.

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

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

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

[0012] In some technical solutions of the present invention, the ball valve stem includes a ball part and a rod body. The ball part and the rod body are integrally formed. A bearing surface is opened on the side of the ball part away from the rod body. A strip-shaped hole is opened on the bearing surface. A circular blind hole communicating with the strip-shaped hole is opened in the ball part.

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

[0014] In some technical solutions of the present invention, a guide groove adapted to the ball valve stem is provided in the tube seat of the drive mechanism. The guide groove is coaxial with the axial hole and communicates with the circumferential groove. A portion 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 mounting port.

[0016] Compared with the prior art, the present invention has at least the following advantages or beneficial effects: By reducing the inner diameter of the upper section of the drive mechanism tube seat (which is consistent with the inner diameter of the original heat insulation sleeve), the drive mechanism tube seat directly replaces the guiding function of the original heat insulation sleeve, reducing redundant parts and structural complexity; the drive mechanism tube seat, connecting tube seat, and guide cover are detachably connected to achieve rapid assembly, avoiding overall replacement and reducing maintenance costs; the guide cover and connecting tube seat together form a thermal barrier, isolating the high-temperature coolant from the direct thermal shock to the drive mechanism tube seat, reducing the risk of heat conduction and thermal deformation; the circumferential groove and axial... The bypass structure formed by the orifices diverts the coolant, equalizes the temperature distribution inside the tube seat, and avoids local overheating that could lead to material fatigue. The ball valve stem, in conjunction with the bypass structure, enables adaptive flow regulation, maintaining a stable flow velocity within the main orifice and further reducing thermal stress concentration during control rod drop. The bypass structure formed by the circumferential groove and axial orifice provides a "water-squeezing channel" for the control rod, reducing fluid resistance during drop, improving drop speed and response efficiency. After drop, the ball valve stem automatically resets and seals the axial orifice, blocking the reverse flow of coolant and preventing heat from rising to the drive mechanism, thus ensuring safe operation of the equipment. Attached Figure Description

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

[0018] Figure 2 This is a schematic diagram of the installation structure of the circumferential groove and the axial hole in this invention.

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

[0020] Figure 4 This is a cross-sectional view of the ball valve stem in this invention.

[0021] Figure 5 This is a top view of the ball valve stem in this invention.

[0022] Reference numerals: 1. Drive mechanism pipe seat; 2. Reactor pressure vessel top cover; 3. First guide hole; 4. Settling tank; 5. Ball valve stem; 6. Second guide hole; 7. Connecting pipe seat; 8. Guide cover; 9. Axial hole; 10. Circumferential groove; 11. Guide groove; 12. Blind hole; 13. Strip hole. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] Example

[0026] This invention provides a heat-insulated guide structure suitable for the 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 heat insulation sleeve assembly of the control rod drive mechanism and improves the internal structure of the drive mechanism tube seat 1 by reducing the inner diameter of the upper section of the drive mechanism tube seat 1. Specifically, the inner diameter of the upper section of the drive mechanism tube seat 1 is reduced to match the inner diameter of the original heat insulation sleeve assembly, ensuring the original heat insulation sleeve's guiding function for the drive rod assembly of the control rod drive mechanism.

[0027] Its specific structure includes a circular mounting port located at the top cover 2 of the reactor pressure vessel. A drive mechanism tube seat 1 is installed inside the mounting port. The drive mechanism tube seat 1 is a tubular structure with a first guide hole 3 inside. A connecting tube seat 7 is detachably installed at the end of the drive mechanism tube seat 1 inside the reactor pressure vessel. The connecting tube seat 7 has a second guide hole 6 communicating with the first guide hole 3. A guide cover 8 is detachably installed on the connecting tube seat 7. A bypass structure for guiding flow is provided on the inner wall of the drive mechanism tube seat 1, and the bypass structure communicates with the first guide hole 3. The control rod dropping operation is as follows: the control rod enters from the drive mechanism tube seat 1 located in the mounting port at the top cover 2 of the reactor pressure vessel, passes through the first guide hole 3 of the drive mechanism tube seat 1, and extends into the guide cover 8 through the second guide hole 6 in the connecting tube seat 7.

[0028] When the control rod is dropped, the coolant flows in the guide hole, and 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 accurate positioning of the control rod. The bypass structure diverts the coolant through fluid dynamics, reducing the resistance to the movement of the control rod. The combination of the guide cover 8 and the connecting tube seat 7 isolates the high-temperature coolant from direct heat conduction to the drive mechanism tube seat 1, reducing thermal stress. The bypass structure reduces the resistance when the control rod is dropped in the guide hole, preventing jamming and reducing friction between the control rod and the guide hole wall. The combination of the connecting tube seat 7 and the guide cover 8 prevents the high-temperature fluid from directly impacting the drive mechanism, extending component life. The detachable design facilitates the replacement of damaged components (such as the guide cover 8) and shortens downtime.

[0029] In some technical solutions of this invention, a groove 4 is provided on the side of the drive mechanism tube seat 1 away from the reactor pressure vessel top cover 2. The inner diameter of the groove 4 is larger than the inner diameter of the first guide hole 3. The groove 4 and the first guide hole 3 together form a stepped guide channel. The groove 4 and the first guide hole 3 form a stepped transition. The groove 4 increases the inlet cross-sectional area, so that the lateral displacement caused by inertia when the control rod enters is constrained by the inner wall of the groove 4, and then gradually converges to the first guide hole 3. The stepped guide channel gradually corrects the attitude of the control rod and avoids hard collision with the inner wall of the guide hole. In addition, the groove 4 increases the coolant flow space, reduces the generation of eddies, and reduces local pressure loss.

[0030] In some technical solutions of this invention, the bypass structure includes an circumferential groove 10, which is axially disposed on the inner wall of the first guide hole 3 along the drive mechanism tube seat 1. A plurality of axial holes 9 are formed on the stepped surface of the settling tank 4 and the first guide hole 3, with the number of axial holes being 3-6. All axial holes 9 are connected to the circumferential groove 10. When the control rod drops, after the coolant flows through the first guide hole 3, some fluid enters the axial holes 9 through the circumferential groove 10 and finally flows into the settling tank 4 area. The circumferential groove 10 is evenly distributed circumferentially along the first guide hole 3, balancing the radial pressure within the guide hole. The axial holes 9 guide the fluid into the settling tank 4, forming a bypass circulation, providing a water-squeezing channel for the control rod drive mechanism when dropping the rod, reducing resistance during the drop. The circumferential groove 10 evenly distributes the coolant, preventing local overheating that could cause tube seat deformation, and the bypass fluid continuously flushes the settling tank 4 area through the axial holes 9, preventing particle deposition.

[0031] In some technical solutions of this invention, a spherical valve stem 5 is slidably disposed within the axial hole 9, with the arc surface of the spherical valve stem 5 abutting against the inner side of the axial hole 9. When the control rod is lowered, the coolant flow rate changes, and the spherical valve stem 5 slides within the axial hole 9. The flow channel opening is adjusted by the contact between the spherical part and the hole wall. The high-pressure fluid pushes the spherical valve stem 5 towards the settling tank 4, expanding the flow channel. When the control rod is lowered, the lifting force exerted by the fluid on the spherical valve stem 5 gradually decreases, and the spherical valve stem returns to its original position by gravity, narrowing the flow channel formed between the spherical valve stem 5 and the axial hole 9. After the spherical valve stem is fully returned to its original position, the axial hole 9 is closed. This closes the bypass structure that allows coolant flow, preventing reactor coolant from flowing upstream and reducing the transfer of reactor coolant heat to the control rod drive mechanism. The above structure dynamically adjusts the bypass flow rate, maintains a constant flow velocity into the main hole, and the tight fit between the spherical part and the hole wall can block the reverse flow of coolant, improving system safety.

[0032] In some technical solutions of the present invention, the connecting pipe seat 7 and the guide cover 8 are threadedly connected. The connecting pipe seat 7 and the guide cover 8 are fixed by threaded engagement and can be disassembled and replaced if necessary. The threaded connection provides axial preload to ensure that the guide cover 8 does not loosen under vibration.

[0033] In some technical solutions of this invention, the connecting pipe seat 7 and the guide cover 8 are welded together on the side where they abut against each other. After the threaded connection, welding is performed on the mating surface of the connecting pipe seat 7 and the guide cover 8 to form a double fixation. Welding eliminates thread gaps, completely blocks the leakage path, and forms a redundant seal. The welded structure resists the risk of thread loosening caused by high-frequency vibration. The two work together to avoid the problem of seal failure caused by thread corrosion.

[0034] In some technical solutions of this invention, the ball valve stem 5 includes a ball portion and a rod body. The ball portion and the rod body are integrally formed. A bearing surface is formed by cutting the side of the ball portion away from the rod body. A strip-shaped hole 13 is formed on the bearing surface. A circular blind hole 12 communicating with the strip-shaped hole 13 is formed inside the ball portion. This facilitates the operator to install the ball valve stem 5 in the axial hole 9. The outer diameter of the rod body is smaller than the inner diameter of the axial hole 9.

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

[0036] In some technical solutions of the present invention, a guide groove 11 adapted to the ball valve stem 5 is provided in the drive mechanism tube seat 1. The guide groove 11 is coaxial with the axial hole 9 and communicates with the circumferential groove 10. The ball valve stem 5 is partially embedded in the guide groove 11. The rod body of the ball valve stem 5 is embedded in the guide groove 11, restricting it to slide only along the axial direction; the guide groove 11 constrains the movement trajectory of the ball valve stem 5, avoids deflection and jamming, ensures that the valve stem is always coaxial with the axial hole 9, maintains sealing performance, and the guide groove 11 distributes the force on the valve stem, reducing unilateral wear of the ball valve stem 5.

[0037] In some technical solutions of this invention, an Ω-shaped sealing ring is installed between the drive mechanism tube seat 1 and the mounting port. The Ω-shaped sealing ring is welded between the drive mechanism tube seat 1 and the mounting port. After being compressed, it expands radially to fill the gap between the drive mechanism tube seat 1 and the mounting port. The Ω-shaped structure maintains resilience at high temperatures, adapting to the thermal expansion difference between the tube seat and the top cover. The higher the system pressure, the greater the sealing force of the sealing surface formed by the Ω-shaped structure, resulting in an extremely low risk of leakage.

[0038] Preferably, the entire control rod drive mechanism is manufactured at the control rod drive mechanism equipment manufacturing plant, including the overall sealing shell (including the drive mechanism tube 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 its installation on the reactor pressure vessel top cover 2 are completed, or the overall sealing shell of the control rod drive mechanism (including the drive mechanism tube seat 1 part) is installed on the reactor pressure vessel top cover 2. At the same time, the threaded connection and anti-loosening welding of the guide tube of the guide cover 8 assembly to the drive mechanism tube seat 1 are completed.

[0040] At the nuclear power plant site, after installing the ball valve stem, the other components of the control rod drive mechanism are installed. After completing the welding of the Ω-shaped sealing ring weld on the pressure shell of the control rod drive mechanism, a hydrostatic test is conducted on the pressure shell of the control rod drive mechanism. After the hydrostatic test is completed, the guide cover 8 of the guide cover 8 assembly is installed onto the connecting pipe seat 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. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A heat-insulated guide structure suitable for the control rod drive mechanism of a pressurized water reactor nuclear power plant, characterized in that, It includes an installation port opened at the top cover (2) of the reactor pressure vessel, a drive mechanism tube seat (1) passing through the installation port, a first guide hole (3) inside the drive mechanism tube seat (1), a connecting tube seat (7) detachably provided at the end of the drive mechanism tube seat (1) placed inside the reactor pressure vessel, a second guide hole (6) communicating with the first guide hole (3) inside the connecting tube seat (7), a guide cover (8) detachably provided on the connecting tube seat (7), and a bypass structure for guiding the flow on the inner wall of the drive mechanism tube seat (1), the bypass structure communicating with the first guide hole (3); The drive mechanism tube seat (1) has a groove (4) on the side away from the reactor pressure vessel top cover (2). The inner diameter of the groove (4) is larger than the inner diameter of the first guide hole (3). The groove (4) and the first guide hole (3) together form a stepped guide channel. The bypass structure includes an annular groove (10), which is axially disposed on the inner wall of the first guide hole (3) along the drive mechanism tube seat (1). A plurality of axial holes (9) are provided on the stepped surface formed by the sink (4) and the first guide hole (3), and the axial holes (9) are all connected to the annular groove (10).

2. The heat-insulated guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 1, characterized in that, A ball valve stem (5) is slidably disposed inside the axial hole (9), and the arc surface of the ball valve stem (5) abuts against the inner side of the axial hole (9).

3. A heat-insulated guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 1 or 2, characterized in that, The connecting tube seat (7) is threadedly connected to the guide cover (8).

4. The heat-insulating guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 3, characterized in that, The connecting tube seat (7) and the guide cover (8) are welded together on the side that abuts against each other.

5. A heat-insulated guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 2, characterized in that, The ball valve stem (5) includes a ball part and a rod body. The ball part and the rod body are integrally formed. A bearing surface is provided on the side of the ball part away from the rod body. A strip hole (13) is provided on the bearing surface. A circular blind hole (12) connected to the strip hole (13) is provided in the ball part.

6. A heat-insulated guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 1 or 2, characterized in that, The inner diameter of the axial hole (9) is larger than the diameter of the circumferential groove (10).

7. A heat-insulated guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 5, characterized in that, The drive mechanism tube seat (1) is provided with a guide groove (11) adapted to the ball valve stem (5). The guide groove (11) is coaxial with the axial hole (9). The guide groove (11) is connected to the circumferential groove (10). A portion of the ball valve stem (5) is embedded in the guide groove (11).

8. A heat-insulated guide structure for a control rod drive mechanism in a pressurized water reactor nuclear power plant according to claim 1, characterized in that, An Ω sealing ring is installed between the drive mechanism tube seat (1) and the mounting port.

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