Nuclear reaction cooling liquid measuring rod

Abstract

The invention belongs to the field of nuclear industry detection, and particularly relates to a nuclear reaction cooling liquid measuring rod which comprises a shell, a core rod and a measuring assembly, a through hole is formed in the shell along the axis of the shell, the core rod is suspended in the through hole, and a uniform gap exists between the side face of the core rod and the inner wall of the shell; the shell and the core rod are fixedly connected with the measuring assembly at the same end, the shell and the core rod are both made of conductors, the nuclear reaction cooling liquid measuring rod is configured to be inserted into nuclear reaction cooling liquid at one end deviating from the measuring assembly, and the measuring assembly is used for measuring the resistance between the shell and the connecting end of the measuring assembly and the resistance between the core rod and the connecting end of the measuring assembly. The method has the effect of reducing nuclear radiation leakage in the observation process.

Description

Technical Field

[0001] The present application relates to the field of nuclear industry detection, and in particular to a nuclear reaction coolant measuring rod. Background Art

[0002] In the process of nuclear industry production, in order to reduce the temperature of the core, coolant needs to be introduced into the reactor pressure vessel, and the liquid level of the coolant is an important operating parameter of the reactor.

[0003] In order to observe the coolant level, relevant equipment needs to open a transparent observation window on the side wall of the reactor pressure vessel where the coolant is located, or connect a liquid level conduit to the side wall of the reactor pressure vessel. Under the principle of communicating vessels, the liquid level of the liquid level conduit reflects the coolant level.

[0004] However, both the liquid level duct and the observation window have weaker isolation capabilities against nuclear radiation than the reactor pressure vessel. Because of their direct contact with the reactor, the coolant also has high radioactivity, which poses a threat to the health and safety of operators. Summary of the invention

[0005] In order to solve the above problems and reduce nuclear radiation leakage during the observation process, the present application provides a nuclear reaction coolant measuring rod.

[0006] The present application provides a nuclear reaction coolant measuring rod adopting the following technical solution: A nuclear reaction coolant measuring rod comprises a shell, a core rod and a measuring assembly, wherein the shell has a through hole along its axis, the core rod is suspended in the through hole, and a uniform gap exists between the side of the core rod and the inner wall of the shell; the shell and the core rod are fixedly connected to the measuring assembly at the same end, the shell and the core rod are both made of conductors, the nuclear reaction coolant measuring rod is configured to be inserted into the nuclear reaction coolant at one end away from the measuring assembly, and the measuring assembly is used to measure the resistance between the connection end between the shell and the measuring assembly and the connection end between the core rod and the measuring assembly.

[0007] By adopting the above technical solution, the measurement of the nuclear reaction coolant level no longer relies on an observation window or a liquid level conduit, and the entire nuclear reaction coolant measuring rod is arranged in the reactor pressure vessel, thereby ensuring the sealing of the entire reactor core and the coolant and preventing the leakage of nuclear radiation; moreover, compared with the original manual observation, the measurement result of the present application is directly output as an electrical signal, and no manual participation is required, thereby reducing the frequency of contact between the staff and the reactor and further protecting the health and safety of the staff.

[0008] Optionally, one end of the shell away from the measuring component is closed by a soft film, and a conductive liquid is filled in a cavity formed by the soft film and the shell. The soft film can deform under a pressure difference so that the conductive liquid in the shell is flush with the nuclear reaction coolant outside the shell.

[0009] By adopting the above technical solution, the core rod of the measuring rod is immersed in the conductive liquid and has no direct contact with the nuclear reaction coolant, thereby preventing the nuclear reaction coolant from corroding the core rod and ensuring the stability of the measuring element and the accuracy of the measurement data; in addition, the conductivity of the conductive liquid can be adapted according to the range of the measuring component, avoiding excessively high accuracy requirements for the measuring component due to the small resistance of the nuclear reaction coolant.

[0010] Optionally, a diameter of the through hole at an end close to the soft membrane is larger than a diameter of an end close to the measuring component.

[0011] By adopting the above technical solution, the slight floating of the soft membrane will be amplified at the end of the shell close to the measuring component. By reasonably configuring the shape and size of the through hole, the volume of the liquid column between the upper and lower limit liquid levels in the through hole can correspond to only a small concave or convex part on the soft membrane, thereby achieving full-range mapping with smaller soft membrane deformation.

[0012] Optionally, a supporting net is provided at one end of the soft film away from the measuring component, for supporting the soft film and preventing the soft film from escaping from the through hole.

[0013] By adopting the above technical solution, the soft membrane is always located in the shell, avoiding the accidental situation that the soft membrane is attached to the outer wall of the shell by the rising liquid level of the nuclear reaction cooling fluid after it escapes from the shell under the action of the pressure difference.

[0014] Optionally, the soft film is in a circular ring shape, and a corrosion-resistant end sleeve is provided at one end of the core rod close to the soft film. The outer circle of the soft film is sealed and fixed to the shell, and the inner circle of the soft film is sealed and fixed to the corrosion-resistant end sleeve.

[0015] By adopting the above technical solution, when the liquid level of the nuclear reaction coolant rises and the soft film is concave under the action of the pressure difference, it will not interfere with the core rod.

[0016] Optionally, the core rod is a resistance rod with uniform electrical conductivity.

[0017] By adopting the above technical solution, the resistance change detected by the measuring component comes from two factors. First, after the liquid level rises, the conductive liquid between the core rod and the shell increases, and more paths are used for diversion, resulting in a decrease in resistance. Second, when the liquid level changes, the length of the core rod connected in series in the circuit changes, that is, the resistivity of the series resistance changes. Under the action of the two phases, the same liquid level height will lead to a greater parameter change and a higher measurement accuracy.

[0018] Optionally, a limiting ring is sleeved on the core rod, the limiting ring is conductive and has a gap with the shell, and when the nuclear reaction coolant reaches the upper limit liquid level, the liquid surface in the shell contacts the limiting ring.

[0019] By adopting the above technical solution, under the extreme water level, the minimum gap between the core rod and the shell is determined by the limit ring. The electrical conductivity of the liquid at this location is the lowest and the distance to the measuring component is closest. Therefore, when the nuclear reaction coolant reaches the extreme water level, a large proportion of the output current of the measuring component is diverted to the limit ring, and the resistance of the entire circuit drops sharply, thereby realizing the alarm function.

[0020] Optionally, the shell further includes a guide ring, which is disposed at one end of the shell close to the measuring component, and the guide ring is electrically connected to the measuring component.

[0021] By adopting the above technical solution, since the resistivity of the guide ring is small enough to be ignored compared to the entire circuit, no matter where the electrode of the measuring component is set, the voltage at the electrode is a fixed value after the constant voltage of the guide ring, thereby ensuring that the measurement data will not produce accidental fluctuations due to the electrode setting.

[0022] Optionally, both ends of the shell are provided with external threads.

[0023] By adopting the above technical solution, the nuclear reaction coolant measuring rod of the present application can be configured into the fuel rod array of the nuclear reactor and detachably connected to the upper and lower grids, making the structure inside the reactor pressure vessel more compact.

[0024] Optionally, the nuclear reaction coolant measuring rod also includes an end plug, which is threadedly connected to the through hole, and a fixing groove is provided at one end of the end plug close to the core rod, the core rod is inserted into the fixing groove and abuts against the end plug, and a plurality of evenly distributed guide grooves are provided on the side of the end plug, and the guide grooves penetrate the entire end plug along the axial direction of the end plug.

[0025] By adopting the above technical solution, one end of the core rod is fixed to the measuring assembly and the other end is fixed to the end plug, thereby ensuring the coaxiality of the core rod and the shell, reducing the core rod deviation caused by deflection, and further affecting the measurement data; and the guide groove opened on the side of the end plug can ensure the smooth flow of liquid inside and outside the shell, ensuring that the liquid level in the shell can correctly reflect the liquid level of the nuclear reaction coolant in the reactor pressure vessel.

[0026] In summary, the present application includes at least one of the following beneficial technical effects: 1. The measurement of the nuclear reaction coolant level no longer relies on an observation window or a liquid level guide tube. The entire nuclear reaction coolant measuring rod is set in the reactor pressure vessel, ensuring the sealing of the entire reactor core and coolant, and preventing nuclear radiation leakage; 2. The measurement results of the present application are directly output as electrical signals, which no longer requires human intervention, reduces the frequency of contact between workers and the reactor, and further protects the health and safety of workers; 3. Through the setting of soft film, the core rod does not come into direct contact with the nuclear reaction coolant, avoiding the influence of corrosion and radiation on the core rod, thereby ensuring the accuracy of the measurement data; 4. The diameter of the through hole near the soft membrane end is larger, so that the liquid level change at the soft membrane end is amplified and reflected to the measuring section, and only a small deformation is required to achieve obvious liquid level changes in the through hole; 5. A support net is provided on the outside of the soft film to prevent the soft film from being pressed to the outer wall of the shell by the liquid after it comes out. The soft film can be optionally set in a circular ring shape to avoid interference with the core rod during the concave process of the soft film; 6. The core rod is set as a resistance rod. The resistance measured by the measuring component is affected by the partial pressure of the conductive liquid itself and the length of the resistance rod exposed on the liquid surface. When the liquid level changes, the resistance of the core rod in series in the circuit changes, and the change trend is the same as the change trend of the liquid resistance. When the liquid level changes, the resistance changes more and the measurement data is more accurate. 7. A limit ring is set on the core rod. Under the limit water level, the minimum gap between the core rod and the shell is determined by the limit ring. The electrical conductivity resistance at this location is the lowest, and this location is closest to the measuring component. Therefore, when the nuclear reaction coolant reaches the upper limit liquid level, a large proportion of the output current of the measuring component is diverted to the limit ring, and the resistance of the entire circuit drops sharply, realizing the alarm function. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a cross-sectional schematic diagram of a nuclear reaction coolant measuring rod according to Example 1 of the present application; Figure 2 is an axial view of the end plug of Example 1 of the present application; Figure 3 is along Figure 2 Schematic diagram of the cross section along the AA line; Figure 4 This is a schematic diagram of a usage scenario of the nuclear reaction coolant measuring rod of Example 1 of the present application; Figure 5 A schematic cross-sectional view of a nuclear reaction coolant measuring rod at a high liquid level according to Example 2 of the present application; Figure 6 It is a cross-sectional schematic diagram of the nuclear reaction coolant measuring rod at a low liquid level in Example 2 of the present application.

[0028] Description of reference numerals: 1. Shell; 11. Through hole; 12. Soft film; 13. Support net; 14. Guide ring; 2. Core rod; 21. Limit ring; 22. Corrosion-resistant end sleeve; 3. Measuring assembly; 4. End plug; 41. Fixing groove; 42. Guide groove; 51. Fuel rod; 52. Stack; 53. Reactor pressure vessel; 61. Nuclear reaction coolant; 62. Conductive fluid. DETAILED DESCRIPTION

[0029] The following is combined with Figure 1-6 To further explain the present application in detail, it should be noted that the number of parts and size ratios in this embodiment are for illustration only and do not represent the actual device form of the embodiment.

[0030] In order to ensure that the core of the nuclear reactor is maintained at a safe operating temperature, during the nuclear industry production process, a certain depth of nuclear reaction coolant 61 is present in the reactor pressure vessel 53 for soaking the core. In order to observe the liquid level of the coolant, it is necessary to open an observation window or set a liquid level conduit on the side wall of the reactor pressure vessel 53. Due to direct or indirect contact with the core, the coolant itself has strong radioactivity, and the radiation protection performance of the observation window and the liquid level conduit is weaker than that of other parts of the reactor pressure vessel 53, which poses a hazard to the health and safety of the observers.

[0031] The embodiment of the present application discloses a nuclear reaction coolant measuring rod.

[0032] Example 1 Reference Figure 1 The nuclear reaction coolant measuring rod comprises a shell 1, a core rod 2, a measuring assembly 3 and an end plug 4. The shell 1 is a conductor cylinder with a through hole 11 provided in the axial direction, one end of which is fixedly connected to the measuring assembly 3 and the other end of which is fixedly connected to the end plug 4; the core rod 2 is suspended in the through hole 11 of the shell 1, one end of which is fixedly connected to the measuring assembly 3 and the other end of which is in contact with the end plug 4; the end plug 4 is made of insulating material or has an insulating layer on the surface. In addition to the fixing function, the measuring assembly 3 is also electrically connected to the shell 1 and the core rod 2 respectively, and is used to measure the resistance of the circuit in which the shell 1 and the core rod 2 are located.

[0033] Specific: The shell 1 is coaxially arranged with the through hole 11, and an internal thread is provided at one end of the through hole 11 close to the end plug 4 for fixing the end plug 4; a guide ring 14 surrounding the shell 1 is sleeved at one end of the shell 1 close to the measuring component 3, and the guide ring 14 is made of low-resistance material, and the parts in contact with the shell 1 are all conductive; an external thread is provided on the side wall of the shell 1 for detachable connection with the stack frame 52 of the nuclear reactor.

[0034] refer to Figure 2 , Figure 3The end plug 4 is a cylinder with an outer diameter corresponding to the through hole 11. An external thread matching the internal thread of the through hole 11 is provided on the side of the end plug 4. The end plug 4 has an end plug through hole along its axis. The diameter of the end plug through hole increases at the end close to the core rod 2 to form a bell mouth. In addition, a plurality of guide grooves 42 are provided along the busbar of the end plug 4, and the guide grooves 42 are distributed in a circular array with the axis of the end plug 4 as the center.

[0035] In another implementation of this embodiment, the end plug 4 is connected to the housing 1 through a keyway.

[0036] refer to Figure 1 The measuring component 3 is fixedly connected to one end of the housing 1 away from the end plug 4, is electrically connected to the guide ring 14, and is insulated from other parts of the housing 1 except the guide ring 14.

[0037] It should be noted that the measuring component 3 has no sealing effect on the through hole 11 of the housing 1 .

[0038] The core rod 2 is coaxially arranged with the shell 1 and the through hole 11, and the core rod 2 has no contact with the shell 1. In other words, there is a gap between the core rod 2 and the through hole 11; one end of the core rod 2 is fixedly connected and electrically connected to the measuring component 3, and the other end is inserted into the bell mouth of the end plug 4 and abuts against the end plug 4; the core rod 2 is provided with a limit ring 21 at a position close to the measuring component 3, and the gap between the limit ring 21 and the through hole 11 is smaller than the gap between the core rod 2 and the through hole 11.

[0039] Preferably, the core rod 2 is a resistance rod.

[0040] refer to Figure 4 The nuclear reaction coolant measuring rod is arranged in conjunction with the fuel rod 51 of the same group, and its diameter and length are the same as those of the fuel rod 51. One or more nuclear reaction coolant measuring rods are arranged in the nuclear reactor array and connected to the stacking rack 52 through the external thread arranged on the side wall of the shell 1. The whole composed of the nuclear reaction coolant measuring rod, the fuel rod 51 and the stacking rack 52 is placed in the reactor pressure vessel 53, and is immersed and cooled by the nuclear reaction coolant 61, and the upper limit liquid level of the nuclear reaction coolant 61 corresponds to the limit ring 21, and the lower limit liquid level corresponds to the end plug 4.

[0041] It should be noted that Figure 4 The number of fuel rods in the figure does not represent the actual arrangement. In a preferred implementation of this embodiment, in a 17*17 nuclear reactor array, there are a total of 280 fuel rods 51 and 9 nuclear reaction coolant measuring rods.

[0042] Preferably, in the case where stacking racks 52 are provided at both ends of the nuclear reaction coolant measuring rod and the fuel rod 51, the external threads at both ends of the shell 1 have opposite directions and the same number of threads, so as to complete the assembly with the two stacking racks 52 in one rotation process.

[0043] The implementation principle of Example 1 is: refer to Figure 4 The nuclear reaction coolant measuring rod of the present application is arranged in the nuclear reactor array, immersed in the coolant together with the fuel rod 51, and sealed by the reactor pressure vessel 53. When the liquid level of the nuclear reaction coolant 61 in the reactor pressure vessel 53 changes, the liquid level in the through hole 11 of the shell 1 changes accordingly under the action of the communicating vessel, and always remains flush with the outside of the shell 1.

[0044] refer to Figure 1 The resistance measured by the measuring assembly 3 is actually composed of three parts in series, namely, the part of the shell 1 exposed above the liquid surface, the part of the core rod 2 exposed above the liquid surface, and the shell 1, core rod 2 below the liquid surface plus the nuclear reaction coolant 61 between the two. For the embodiment in which the shell 1 and core rod 2 are made of low-resistance conductors, the resistance of the first two parts can be ignored. The measurement result is actually the parallel result of the nuclear reaction coolant 61 between the core rod 2 and the shell 1 below the liquid surface. As the liquid level rises, the resistance decreases, and as the liquid level drops, the resistance increases. The actual liquid level can be obtained based on the resistance by simply comparing the preset table parameters.

[0045] Preferably, when the core rod 2 is a resistor rod, when the liquid level changes, in addition to the above changes, the resistance of the part of the core rod 2 located on the liquid surface will also change and be connected in series to the circuit. Specifically, when the liquid level rises, the resistance of the core rod 2 connected in series to the circuit decreases, and the total resistance decreases; when the liquid level drops, the resistance of the core rod 2 connected in series to the circuit increases, and the total resistance increases. Because the change trend of this part of the resistance with the liquid level is in the same direction as the above resistance change trend, that is, when the core rod 2 is a resistor rod, the same liquid level change will be reflected as a larger resistance parameter change, thereby achieving higher measurement accuracy.

[0046] When the nuclear reaction coolant 61 in the reactor pressure vessel 53 reaches the upper limit liquid level, the liquid level in the shell 1 contacts the limit ring 21, and the minimum gap between the core rod 2 and the shell 1 is determined by the distance between the limit ring 21 and the inner wall of the shell 1, and the resistance value measured by the measuring component 3 jumps and decreases; when the nuclear reaction coolant 61 in the reactor pressure vessel 53 reaches the lower limit liquid level, there is no nuclear reaction coolant 61 between the shell 1 and the core rod 2, and the circuit is broken, and the voltage tends to infinity, which serves as an alarm.

[0047] Example 2 Reference Figure 5 , Figure 6 The difference between this embodiment and embodiment 1 is that: In this embodiment, there is no end plug 4, and the end of the through hole 11 away from the measuring component 3 is closed by the soft film 12. A support net 13 is provided on the side of the soft film 12 away from the measuring component 3. The diameter of the support net 13 is larger than the diameter of the through hole 11 and is fixed to the shell 1. A pressure sensor is provided between the support net 13 and the shell 1.

[0048] The core rod 2 is provided with a corrosion-resistant end sleeve 22 at one end away from the measuring assembly 3 , and the end surface of the corrosion-resistant end sleeve 22 away from the end of the core rod 2 is flush with the end surface of the shell 1 away from the measuring assembly 3 .

[0049] The soft film 12 is preferably an elastic annular film, the outer circle of the annular film is sealed and fixed to the housing 1 , and the inner circle of the annular film is sealed and fixed to the corrosion-resistant end sleeve 22 .

[0050] When the liquid level of the nuclear reaction coolant 61 rises, the soft film 12 is recessed into the gap between the core rod 2 and the shell 1 under the action of the pressure difference; when the liquid level of the nuclear reaction coolant 61 drops, the soft film 12 is close to the support net 13 under the action of the pressure difference until it is received by the support net 13.

[0051] The cavity formed by the soft film 12 and the shell 1 is filled with conductive liquid 62. In normal working state, under the action of the communicating vessel, the liquid level of the conductive liquid 62 in the shell 1 changes with the change of the liquid level of the nuclear reaction coolant 61 outside the shell 1. When the nuclear reaction coolant 61 reaches the upper limit liquid level, the conductive liquid 62 contacts the limit ring 21.

[0052] Preferably, the through hole 11 is enlarged at one side close to the soft film 12 to form a bell mouth, and the position of the core rod 2 corresponding thereto is a cylinder with a constant diameter.

[0053] The implementation principle of Example 2 is: The side of the soft film 12 close to the core rod 2 is in contact with the conductive liquid 62, and the side of the soft film 12 away from the core rod 2 is in contact with the nuclear reaction coolant 61. Since the liquid pressure is determined by the product of the contact area, gravity acceleration, liquid depth and liquid density, on both sides of the soft film 12, the gravity acceleration and the contact area are approximately equal, and the liquid density is in a fixed ratio. Therefore, when the soft film 12 is in a force balance state, the conductive liquid 62 in the shell 1 and the nuclear reaction coolant 61 outside the shell 1 are in a fixed ratio relative to the depth of the soft film 12. When the density of the conductive liquid 62 is equal to that of the nuclear reaction coolant 61, the liquid levels inside and outside the shell 1 are flush.

[0054] refer to Figure 5 When the nuclear reaction coolant 61 in the reactor pressure vessel 53 reaches the upper limit liquid level, the liquid level in the shell 1 contacts the limit ring 21, and the minimum gap between the core rod 2 and the shell 1 is determined by the distance between the limit ring 21 and the inner wall of the shell 1. The resistance value measured by the measuring component 3 jumps and decreases.

[0055] refer to Figure 6 When the nuclear reaction coolant 61 in the reactor pressure vessel 53 reaches the lower limit liquid level, and the hydraulic pressure provided by the nuclear reaction coolant 61 cannot balance the hydraulic pressure brought by the conductive liquid 62, the side of the soft membrane 12 away from the core rod 2 is provided with a balancing force by the support net 13, and the pressure sensor reading increases, which serves as an alarm.

[0056] The core rod 2 in this embodiment is isolated from the nuclear reaction coolant 61, thereby avoiding the corrosion and radioactive influence of the nuclear reaction coolant 61 on the core rod 2, thereby ensuring the reliability of the reading.

[0057] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A nuclear reaction coolant measuring rod, characterized in that: It comprises a shell (1), a core rod (2) and a measuring assembly (3), wherein the shell (1) is provided with a through hole (11) along its axis, the core rod (2) is suspended in the through hole (11), and a uniform gap exists between the side surface of the core rod (2) and the inner wall of the shell (1); The shell (1) and the core rod (2) are fixedly connected to a measuring component (3) at the same end; the shell (1) and the core rod (2) are both made of conductors; the nuclear reaction coolant measuring rod is configured such that an end thereof facing away from the measuring component (3) is inserted into the nuclear reaction coolant (61); the measuring component (3) is used to measure the resistance between the connection end between the shell (1) and the measuring component (3) and the connection end between the core rod (2) and the measuring component (3).

2. The nuclear reaction coolant measuring rod according to claim 1, characterized in that: One end of the shell (1) away from the measuring component (3) is closed by a soft film (12), and a conductive liquid (62) is filled in a cavity formed by the soft film (12) and the shell (1). The soft film (12) can deform under a pressure difference so that the conductive liquid (62) in the shell (1) is flush with the nuclear reaction coolant (61) outside the shell (1).

3. The nuclear reaction coolant measuring rod according to claim 2, characterized in that: The diameter of the through hole (11) at an end close to the soft membrane (12) is larger than the diameter at an end close to the measuring component (3).

4. The nuclear reaction coolant measuring rod according to claim 2, characterized in that: A supporting net (13) is provided at one end of the soft film (12) away from the measuring component (3) for supporting the soft film (12) and preventing the soft film (12) from falling out of the through hole (11).

5. The nuclear reaction coolant measuring rod according to claim 2, characterized in that: The soft film (12) is in the shape of a ring. A corrosion-resistant end sleeve (22) is provided at one end of the core rod (2) close to the soft film (12). The outer circle of the soft film (12) is sealed and fixed to the shell (1), and the inner circle of the soft film (12) is sealed and fixed to the corrosion-resistant end sleeve (22).

6. The nuclear reaction coolant measuring rod according to claim 1, characterized in that: The core rod (2) is a resistance rod with uniform electrical conductivity.

7. The nuclear reaction coolant measuring rod according to claim 1, characterized in that: A limit ring (21) is sleeved on the core rod (2); the limit ring (21) is conductive and has a gap with the shell (1); when the nuclear reaction coolant (61) reaches an upper limit liquid level, the liquid surface in the shell (1) contacts the limit ring (21).

8. The nuclear reaction coolant measuring rod according to claim 1, characterized in that: The housing (1) further comprises a guide ring (14), wherein the guide ring (14) is arranged at one end of the housing (1) close to the measuring component (3), and the guide ring (14) is electrically connected to the measuring component (3).

9. The nuclear reaction coolant measuring rod according to claim 1, characterized in that: External threads are provided at both ends of the housing (1).

10. The nuclear reaction coolant measuring rod according to claim 1, characterized in that: The nuclear reaction coolant measuring rod further comprises an end plug (4), the end plug (4) being threadedly connected to the through hole (11), a fixing groove (41) being provided at one end of the end plug (4) close to the core rod (2), the core rod (2) being inserted into the fixing groove (41) and abutting against the end plug (4), a plurality of evenly distributed guide grooves (42) being provided on the side surface of the end plug (4), the guide grooves (42) penetrating the entire end plug (4) along the axial direction of the end plug (4).

Images