A flow blocking plug for a control rod guide tube

Abstract

A flow-blocking plug for a control rod guide tube includes a flow-blocking plug installed at the upper end of the control rod guide tube, with a cylindrical shell at the lower part of the flow-blocking plug inserted into the control rod guide tube. The flow-blocking plug includes bolt holes, a circular boss, a cross-shaped flange, a drainage hole, and a cylindrical shell. The flow-blocking plug is connected to the upper end of the control rod guide tube via the cross-shaped flange. A drainage hole is provided on the cross-shaped flange. The top of the flow-blocking plug is a circular boss, with a bolt hole at the center of the circular boss, through which a lifting ring is installed. This invention achieves circumferential and radial positioning of the flow-blocking plug, and by evenly distributing a certain number of circular holes on the cross-shaped flange as drainage holes, only a small amount of coolant is allowed to flow into the control rod guide tube to cool the control rod drive mechanism. An internally recessed threaded hole is provided at the center of the upper circular boss of the flow-blocking plug for installing lifting rings and other tools, facilitating the installation and removal of the flow-blocking plug.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactor technology. Specifically, it relates to a flow-blocking plug for a control rod conduit. Background Technology

[0002] In high-flux engineering experimental nuclear reactors, control rods are inserted into the reactor core from bottom to top inside the pressure vessel to regulate reactor power. The coolant flow direction within the reactor also differs from that of conventional commercial pressurized water reactors; the coolant flows from top to bottom through the reactor core into the pressure vessel. Therefore, the normal movement direction of the drive line moving parts of the control rod drive mechanism is opposite to the coolant flow direction. This increases the resistance when the control rod is inserted into the core from bottom to top, thus increasing the lifting force required by the control rod drive mechanism. However, the maximum lifting force of a typical linear motor-type control rod drive mechanism is 700 N. In a high-flux reactor, the increased flow resistance on the drive line may lead to a longer control rod drop time, or even prevent the control rod from being lifted to the required core position, posing a safety hazard to the normal operation of the reactor.

[0003] In summary, to reduce the flow resistance of coolant to the movement of control rods, a flow-blocking element was designed and installed at the upper end of the control rod duct to limit the flow rate of coolant entering the control rod duct. This also reduces ineffective leakage in the core, allowing more coolant to flow through the core fuel assemblies and better meet the core thermal requirements. Summary of the Invention

[0004] The purpose of this invention is to design a flow-blocking element for use in high-flux nuclear reactors to limit (reduce) the coolant flow rate in the control rod conduit, preventing excessive pressure differential between the upper and lower ends of the conduit due to excessive coolant flow. This ensures that: (i) when the control rod needs to be lifted upwards for core insertion, the downward force of the coolant flowing from top to bottom in the conduit on the drive line moving parts is small, meaning the upward-moving control rod experiences less resistance from the coolant, keeping the lifting force required for lifting within a reasonable range for the drive mechanism; (ii) when the control rod needs to be lowered downwards, the downward force of the coolant flowing from top to bottom in the conduit on the drive line moving parts is small, meaning the downward-moving control rod experiences less thrust from the coolant, keeping the maximum impact force during the lowering process small and within the design tolerance range of the buffer assembly. Furthermore, by limiting (regulating) the coolant flow rate in the control rod conduit using the flow-blocking element, only a small amount of coolant is allowed to flow through the conduit to cool the control rod drive mechanism, minimizing ineffective core leakage.

[0005] The technical solution of the present invention is as follows: a flow-blocking plug for a control rod conduit, comprising a flow-blocking plug, the flow-blocking plug being installed at the upper end of the control rod conduit, and the cylindrical shell at the lower part of the flow-blocking plug being inserted into the control rod conduit;

[0006] The flow choke includes bolt holes, a circular boss, a cross-shaped flange, a water outlet, and a cylindrical shell. The flow choke is connected to the upper end of the control rod guide tube through the cross-shaped flange. A water outlet is opened on the cross-shaped flange. The top of the flow choke is a circular boss, and the center of the circular boss is a bolt hole. The flow choke is installed with a lifting ring through the bolt hole.

[0007] The cylindrical shell fits against the inner wall of the control rod guide tube.

[0008] The flow choke is fitted with four openings at the upper end of the control rod conduit via a cross-shaped flange.

[0009] The bolt holes are recessed.

[0010] There are multiple drainage holes.

[0011] There are 4 to 8 water outlets.

[0012] The diameter of the water flow hole 4 is 2-5mm.

[0013] The significant advantages of this invention are as follows: The flow-blocking plug element involved in this invention achieves circumferential and radial positioning of the flow-blocking plug by engaging with the opening on the upper sidewall of the control rod conduit through a cross-shaped flange. A certain number of evenly distributed circular holes on the cross-shaped flange serve as drainage holes, allowing only a small amount of coolant to flow into the control rod conduit to cool the control rod drive mechanism. An internally recessed threaded hole is provided at the center of the upper circular boss of the flow-blocking plug for installing tools such as lifting rings, facilitating the installation and removal of the flow-blocking plug. The lower part of the flow-blocking plug is a cylindrical shell structure that can extend into the conduit. The outer wall of the cylindrical shell fits against the inner wall of the conduit, preventing excessive coolant from flowing into the conduit. In summary, the flow-blocking plug effectively limits the coolant flow into the control rod conduit, while also reducing ineffective bypass flow in the reactor core and lowering the flow pressure difference between the upper and lower ends of the conduit. This effectively ensures that: (i) the lifting force required when the control rod is inserted into the reactor core from the bottom does not exceed the lifting force limit of the drive mechanism; and (ii) excessive impact force on the buffer assembly is avoided when the control rod is lowered from the reactor core. It provides an important safety guarantee for the normal operation of high-flux reactors. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the flow choke.

[0015] Figure 2 This is an assembly diagram showing the flow-blocking plug installed at the upper end of the control rod guide tube.

[0016] Figure 3 This is a top view of the flow choke.

[0017] In the diagram: 1—bolt hole; 2—circular boss; 3—cross flange; 4—drain hole; 5—cylindrical shell; 6—lifting ring; 7—flow plug; 8—control rod guide tube. Detailed Implementation

[0018] Many specific details are set forth in the following description to provide a full understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this application; therefore, this application is not limited to the specific embodiments disclosed below.

[0019] The terminology used in one or more embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the scope of one or more embodiments of this application. The singular forms “a,” “the,” and “the” used in one or more embodiments of this application and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” used in one or more embodiments of this application refers to and includes any or all possible combinations of one or more associated listed items.

[0020] It should be understood that although the terms first, second, etc., may be used to describe various information in one or more embodiments of this application, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first may also be referred to as second without departing from the scope of one or more embodiments of this application, and similarly, second may also be referred to as first.

[0021] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings.

[0022] like Figure 1 As shown, the flow-blocking plug 7 for the control rod guide tube of the present invention is integrally formed, including bolt hole 1, circular boss 2, cross-shaped flange 3, cylindrical shell 5, and water flow hole 4.

[0023] like Figure 2As shown, the flow choke 7 is installed at the upper end of the control rod conduit 8, and is positioned by engaging with the four openings at the upper end of the control rod conduit 8 through the cross-shaped flange 3. The cylindrical shell 5 at the lower part of the flow choke 7 is inserted into the control rod conduit 8 and fits against the inner wall of the control rod conduit 8, sealing the upper flow channel of the control rod conduit 8. By opening a certain number of water flow holes 4 on the cross-shaped flange 3, only a limited amount of coolant is allowed to flow into the control rod conduit 8 from the upper part to cool the relevant equipment. During reactor start-up and shutdown, the flow choke 7 is installed and removed by connecting to tools such as the lifting ring 6 through the recessed threaded hole 1 at the center of the circular boss 2 at the upper part of the flow choke 7. Under normal reactor operation, coolant flows from the reactor pressure vessel down through the control rod duct assembly and core fuel assemblies. Installing a flow-blocking plug 7 at the upper end of the control rod duct 8 reduces (limits) the coolant flow into the control rod duct 8, while also reducing ineffective bypass flow in the core and lowering the flow pressure difference between the upper and lower ends of the control rod duct 8. This ensures that: when the control rod is inserted into the core from the bottom, the required lifting force does not exceed the lifting force limit of the drive mechanism; and when the control rod is lowered from the core, excessive impact force on the buffer assembly is avoided.

[0024] The flow-blocking plug structure 7 involved in this invention is as follows: Figure 1 As shown, it is installed on the upper end 8 of the control rod guide tube, as... Figure 2 As shown, circumferential and radial positioning can be achieved by engaging the cross-shaped flange 3 in the middle of the choke with the four openings at the upper end of the conduit. The cylindrical shell 5 with openings at the lower part of the choke is inserted into the conduit and basically fits against the inner wall of the conduit, which can reduce the amount of coolant flowing into the conduit. By opening a certain number of water flow holes 4 on the cross-shaped flange, a small amount of coolant is allowed to flow into the control rod conduit to cool the drive mechanism. During the start-up and shutdown of the high flux reactor, the internally recessed threaded hole 1 at the center of the upper circular boss 2 of the choke can be connected to tools such as lifting rings, thereby realizing the installation and removal of the choke. Under normal operating conditions of a high-flux reactor, coolant flows from top to bottom from the reactor pressure vessel through the control rod duct assembly, core fuel assembly, beryllium sleeve assembly, and secondary support assembly. Installing a flow-blocking plug at the upper end of the control rod duct can reduce (limit) the flow rate of coolant into the duct, while also reducing ineffective bypass flow in the core and lowering the flow pressure difference between the upper and lower ends of the duct. This ensures that: (i) the lifting force required when the control rod is inserted into the core from the bottom does not exceed the lifting force limit of the drive mechanism, and (ii) the impact force on the buffer assembly is avoided when the control rod is lowered from the core.

[0025] The present invention relates to a flow-restricting plug element for limiting the coolant flow rate in a control rod duct in a high-flux nuclear reactor, comprising an upper circular boss, a middle cross-shaped flange, and a lower cylindrical shell. The upper circular boss has a recessed bolt hole at its center for installing lifting rings, facilitating the installation and removal of the flow-restricting plug. The middle cross-shaped flange mates with the opening at the upper end of the control rod duct, providing circumferential and radial positioning and restriction for the flow-restricting plug. Additionally, a number of drainage holes are provided on the flange, allowing a small amount of coolant to flow into the control rod duct to cool the drive mechanism. The coolant flow rate and flow pressure differential (resistance) in the control rod duct can be adjusted by changing the number of holes (4-8) and their diameter (2-5 mm). The lower cylindrical shell extends into the control rod duct and essentially fits against the inner wall of the duct, preventing excessive coolant from flowing into the duct.

[0026] The above description is merely a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this patent shall be included within the scope of protection of this patent.

[0027] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0028] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0029] The preferred embodiments disclosed above are merely illustrative of this application. The optional embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this application. These embodiments are selected and specifically described in this application to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to better understand and utilize this application.

Claims

1. A flow-blocking plug for a control rod conduit, characterized in that: Includes a flow choke (7), which is installed at the upper end of the control rod conduit (8), and the cylindrical shell (5) at the lower part of the flow choke (7) is inserted into the control rod conduit (8); The flow choke (7) includes a bolt hole (1), a circular boss (2), a cross flange (3), a water outlet (4), and a cylindrical shell (5); the flow choke (7) is connected to the upper end of the control rod guide tube (8) through the cross flange (3); the cross flange (3) has a water outlet (4); the top of the flow choke (7) is a circular boss (2), the center of the circular boss (2) is a bolt hole (1), and the flow choke (7) is fitted with a lifting ring (6) through the bolt hole (1); The cylindrical shell (5) fits against the inner wall of the control rod guide tube (8); The flow choke (7) is fitted with the four openings at the upper end of the control rod guide tube (8) via the cross-shaped flange (3); The bolt hole (1) is an inset type; There are 4 to 8 water outlets (4); The diameter of the water flow hole (4) is 2~5mm.

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