Control rod drive mechanism

Abstract

To provide a control rod drive mechanism that can maintain the function of absorbing the impact force applied to the upper part of the control rod drive mechanism when the emergency stop function is activated. [Solution] The device comprises a hollow piston 11, a buffer sleeve 12 surrounding the hollow piston 11 from the outer circumference and having a flange portion 12b, an outer tube 13 surrounding the buffer sleeve 12 from the outer circumference, an orifice plate 14 attached to the inner circumferential surface 13k of the outer tube 13 so as to be located between the buffer sleeve 12 and the outer tube 13 and positioned opposite the upper surface 12e of the flange portion 12b, and at least one orifice 14b provided on the orifice plate 14, with fluid filling the space 15 between the flange portion 12b and the orifice plate 14.

Description

Technical Field

[0001] The present invention relates to a control rod drive mechanism.

Background Art

[0002] The control rod drive mechanism of a boiling water reactor has an emergency stop function (scram function) that quickly inserts a control rod between the fuel rods of the fuel assembly in the reactor when an emergency such as an earthquake occurs during the operation of the reactor, stops the nuclear fission reaction, and causes the reactor to make an emergency stop (scram).

[0003] When this function is activated, the control rod is instantaneously inserted between the fuel rods of the fuel assembly in the reactor, and a large impact force can be generated at the upper part of the control rod drive mechanism.

[0004] In order to reduce this impact force, in Patent Document 1, a plurality of disc springs are provided as a buffer mechanism at the upper part of the control rod drive mechanism.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, although the possibility is extremely small, the disc springs may have a reduced impact absorption function due to deformation, reduced rigidity, malfunction due to foreign matter混入 between the disc springs, etc.

[0007] An object of the present invention is to provide a control rod drive mechanism that can maintain a function of absorbing the impact force applied to the upper part of the control rod drive mechanism when the emergency stop function is activated.

Means for Solving the Problems

[0008] The present invention includes several means for solving the above problems, but one example is a hollow piston, a buffer sleeve surrounding the hollow piston from the outer circumference and having a flange, an outer tube surrounding the buffer sleeve from the outer circumference, an orifice plate attached to the inner surface of the outer tube so as to be located between the buffer sleeve and the outer tube and positioned opposite the upper surface of the flange, and at least one orifice provided in the orifice plate, wherein a fluid is filled into the space between the flange and the orifice plate. [Effects of the Invention]

[0009] According to the present invention, the orifice provided in the orifice plate can maintain its function of absorbing the impact force applied to the upper part of the control rod drive mechanism during an emergency shutdown of the reactor, thereby ensuring the safety of the reactor. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments. [Brief explanation of the drawing]

[0010] [Figure 1] This is a partial cross-sectional view of a control rod drive mechanism according to the first embodiment of the present invention. [Figure 2] This is a schematic diagram of a buffer sleeve and an orifice plate, which are technical features of the control rod drive mechanism according to the first embodiment of the present invention. [Figure 3] This is a schematic diagram of an enlarged perspective view of an orifice plate, which is a technical feature of the control rod drive mechanism according to the second embodiment of the present invention. [Figure 4] This is a schematic, enlarged perspective view of a spring provided between a buffer sleeve and an orifice plate, which is a technical feature of the control rod drive mechanism according to the third embodiment of the present invention. [Modes for carrying out the invention]

[0011] The configuration and operation of the control rod drive mechanism according to the first to third embodiments of the present invention will be described below with reference to the drawings. In each figure, the same reference numerals indicate the same part.

[0012] (First Embodiment) Figure 1 is a partial cross-sectional view of the control rod drive mechanism 1 according to the first embodiment of the present invention. Figure 2 is a perspective enlarged schematic view of the buffer sleeve 12 and orifice plate 14, which are technical features of the control rod drive mechanism 1 according to this embodiment.

[0013] The control rod drive mechanism 1 is a device for moving the control rod 3, which is protected by the control rod guide tube 2, in and out between the fuel rods of the fuel assembly in the reactor pressure vessel 4 filled with reactor water 4f, and comprises a hollow piston 11, a buffer sleeve 12, an outer tube 13, and an orifice plate 14.

[0014] The hollow piston 11 is a rod-shaped member that supports the control rod 3 and moves the control rod 3 up and down. The upper end of the hollow piston 11 reaches into the reactor pressure vessel 4, and the control rod 3 is connected to it via a coupling sput 11a. The lower end of the hollow piston 11 rests on the upper surface of the ball nut 11b.

[0015] An elongated hole 11c is formed inside the hollow piston 11, extending in the axial direction of the hollow piston 11. A ball screw 11d, also extending in the axial direction of the hollow piston 11, is inserted into the hole 11c from below.

[0016] The ball screw 11d engages with the ball nut 11b and rotates circumferentially by the motor 5. As a result of the rotation of the ball screw 11d, the ball nut 11b moves up and down, causing the hollow piston 11 mounted on its upper surface to move up and down. This allows the control rod drive mechanism 1 to move the control rods 3 in and out between the fuel rods of the fuel assembly in the reactor pressure vessel 4, thereby controlling the nuclear fission reaction.

[0017] The buffer sleeve 12 is one of the components for absorbing the impact force applied to the upper part of the control rod drive mechanism when the emergency stop function is activated. It surrounds the hollow piston 11 from the outer circumference and has a flange. The buffer sleeve 12 is movable upward as the hollow piston 11 rises during a scrum.

[0018] Specifically, the buffer sleeve 12 has a tube portion 12a which is a tubular portion surrounding the hollow piston 11 from the outer periphery, and a flange portion 12b which is a flange-shaped portion protruding radially outward from the lower end of the tube portion 12a to the outside of the hollow piston 11.

[0019] The gap between the inner peripheral surface 12d of the tube portion 12a and the outer peripheral surface 11e of the hollow piston 11 is preferably narrowed to 1 mm or less in order to suppress the passage of the liquid discharged from the scram pipe 4d described later.

[0020] The flange portion 12b preferably has a guide roller 12f for suppressing friction with the hollow piston 11 on the inner peripheral surface 12d, with the upper surface 12e facing the lower surface 14a of the orifice plate 14 described later.

[0021] Also, the buffer sleeve 12 preferably has a cylindrical portion 12c which is a cylindrical portion extending downward from the outer periphery of the flange portion 12b. A stop piston 13g described later is disposed inside the cylindrical portion 12c.

[0022] The outer tube 13 is a cylindrical member surrounding the buffer sleeve 12 from the outer periphery, and is covered and protected by the control rod drive mechanism housing 4a.

[0023] A lower flange portion 13a is provided at the lower part of the outer tube 13, and is sandwiched between the lower flange 4b at the lower end of the control rod drive mechanism housing 4a and the upper flange 6a at the upper end of the spool piece 6.

[0024] The lower flange portion 13a of the outer tube 13, the lower flange 4b of the control rod drive mechanism housing 4a, and the upper flange 6a of the spool piece 6 are connected by bolts. Thereby, the outer tube 13 is connected to the control rod drive mechanism housing 4a. Therefore, the outer tube 13 is fixed to the control rod drive mechanism housing 4a in which the hollow piston 11 is housed so as not to be movable up and down.

[0025] The control rod drive mechanism housing 4a is fixed to the outer shell 4c of the reactor pressure vessel 4 by welding. Therefore, the outer tube 13 is attached to the outer shell 4c of the reactor pressure vessel 4 via the control rod drive mechanism housing 4a.

[0026] A scram pipe 4d is attached to the lower end flange 4b ​​of the control rod drive mechanism housing 4a. This pipe discharges a liquid (e.g., water) that allows the control rods 3 to be instantaneously inserted between the fuel rods of the fuel assemblies in the reactor pressure vessel 4 when the emergency stop function is activated. A scram passage 13b is provided in the lower flange portion 13a of the outer tube 13, which is a passage that communicates with the scram pipe 4d. The liquid discharged from the scram pipe 4d is discharged into the outer tube 13 via the scram passage 13b.

[0027] A cylindrical guide tube 13c is provided inside the outer tube 13, and the lower end of the guide tube 13c is supported by an inner flange portion 13d that protrudes radially inward from the lower end of the outer tube 13.

[0028] A guide rail 13e is provided on the inner circumferential surface of the guide tube 13c, running along the axial direction of the guide tube 13c. A guide roller 11f, provided on the ball nut 11b, and a guide roller 11g, provided on the lower part of the hollow piston 11, are assembled to the guide rail 13e. As a result, the circumferential rotation of the ball nut 11b and the hollow piston 11 is constrained, while they are able to move in the axial direction.

[0029] Furthermore, a stop piston 13g and a buffer sleeve 12 are mounted on the inner flange portion 13f that protrudes radially inward from the upper end of the guide tube 13c.

[0030] The stop piston 13g is a component that comes into contact with the large-diameter portion 11h, which increases in diameter downwards, located at the bottom of the rapidly rising hollow piston 11 when the emergency stop function is activated.

[0031] The stop piston 13g is provided with an annular portion 13h, which is a smaller diameter than the large diameter portion 11h, in order to contact the large diameter portion 11h of the hollow piston 11, and a cylindrical portion 13i that extends upward from the outer circumference of the annular portion 13h.

[0032] When the emergency stop function is activated, the stop piston 13g rises together with the hollow piston 11 as the large-diameter portion 11h of the rapidly rising hollow piston 11 comes into contact with the ring portion 13h. Then, the upper end of the cylindrical portion 13i of the stop piston 13g comes into contact with the lower surface of the flange portion 12b of the buffer sleeve 12, attempting to raise the buffer sleeve 12.

[0033] Furthermore, a coil spring 13j that expands and contracts in the axial direction of the hollow piston 11 is placed on the upper surface of the ring portion 13h of the stop piston 13g. The upper end of the coil spring 13j is in contact with the lower surface of the flange portion 12b of the buffer sleeve 12.

[0034] As a result, the emergency stop function is released, the hollow piston 11 descends, and the stop piston 13g, whose large-diameter portion 11h is no longer in contact with the ring portion 13h, is easily returned to its initial position by the coil spring 13j.

[0035] The orifice plate 14, along with the buffer sleeve 12, is a component that absorbs the impact force applied to the upper part of the control rod drive mechanism when the emergency stop function is activated. The orifice plate 14 is attached to the inner circumferential surface 13k of the outer tube 13 so as to be located between the buffer sleeve 12 and the outer tube 13, and is positioned opposite the upper surface 12e of the flange portion 12b of the buffer sleeve 12.

[0036] As a result, a space 15 is formed between the flange portion 12b and the orifice plate 14, and the space 15 is filled with fluid.

[0037] Furthermore, the orifice plate 14 is provided with at least one orifice 14b.

[0038] Furthermore, the gap between the outer circumferential surface 12g of the tube portion 12a of the buffer sleeve 12 and the inner circumferential surface 14c of the orifice plate 14 facing the outer circumferential surface 12g is preferably 1 mm or less in order to suppress the passage of liquid discharged from the scram piping 4d. In addition, it is preferable that a labyrinth shape is provided on the inner circumferential surface 14c of the orifice plate 14 facing the outer circumferential surface 12g of the tube portion 12a of the buffer sleeve 12.

[0039] Above the orifice plate 14, an upper guide 16, which is a cylindrical member having a through hole 16a in the center, is provided at intervals in the axial direction of the outer tube 13.

[0040] The upper guide 16 is a component that covers the opening at the upper end of the outer tube 13. The upper end surface of the upper guide 16 is covered by an inner flange 4e that protrudes radially inward from the upper end of the control rod drive mechanism housing 4a, preventing the upper guide 16 from flying upward due to the impact caused by the activation of the emergency stop function.

[0041] A cylindrical projection 2a, located at the lower end of the control rod guide tube 2, is attached to the upper part of the through hole 16a of the upper guide 16, and the control rod drive mechanism 1 and the control rod guide tube 2 are integrated together.

[0042] Furthermore, a hollow piston 11 is positioned inside the through hole 16a, and a guide roller 16c is provided on the side surface 16b of the through hole 16a to assist the vertical movement of the hollow piston 11.

[0043] When the emergency stop function is activated, the control rod drive mechanism 1 configured as described above discharges high-pressure liquid (high-pressure water) from the scram piping 4d into the outer tube 13 via the scram passage 13b.

[0044] The high-pressure water discharged into the outer tube 13 rapidly pushes the hollow piston 11 upward, initiating the insertion of the control rod 3 between the fuel rods of the fuel assembly.

[0045] As the hollow piston 11 rises, its large-diameter portion 11h comes into contact with the stop piston 13g, pushing the stop piston 13g upward. This causes the stop piston 13g to compress the coil spring 13j, attempting to push the buffer sleeve 12 upward. In other words, the hollow piston 11 pushes the buffer sleeve 12 upward, causing the buffer sleeve 12 to move in accordance with the hollow piston 11.

[0046] As the buffer sleeve 12 moves in accordance with the hollow piston 11, the fluid filling the space 15 between the flange 12b of the buffer sleeve 12 and the orifice plate 14 is compressed and flows out of the space 15 through the orifice 14b of the orifice plate 14. At this time, the pressure loss caused by the fluid passing through the orifice 14b causes a damping force to act on the hollow piston 11, and the insertion speed of the hollow piston 11 and the control rod 3 is reduced.

[0047] Subsequently, the upward movement of the hollow piston 11 and the control rod 3 stops when the upper surface 12e of the flange portion 12b of the buffer sleeve 12 comes into contact with the lower surface 14a of the orifice plate 14, or when the upper end of the tube portion 12a of the buffer sleeve 12 comes into contact with the upper guide 16.

[0048] Therefore, in this embodiment, the control rod drive mechanism 1, the pressure loss caused by the fluid filling the space 15 between the flange portion 12b and the orifice plate 14 passing through the orifice 14b can apply a damping force to the hollow piston 11, thereby suppressing the impact force that may occur when the hollow piston 11 stops.

[0049] Furthermore, at least one orifice 14b provided in the orifice plate 14 is unlikely to experience a decrease in shock absorption function due to deformation, reduced rigidity, or malfunction caused by the inclusion of foreign matter. Therefore, it can maintain its function of absorbing the shock force applied to the upper part of the control rod drive mechanism during an emergency shutdown of the reactor, thereby ensuring the safety of the reactor.

[0050] Furthermore, the damping effect on the upward velocity of the buffer sleeve 12 is considered to be primarily influenced by the shape of the orifice 14b. Therefore, it is thought that only the shape of the orifice 14b needs to be changed to obtain the required damping force. This means that in performance verification tests, only the orifice plate 14 needs to be used as the test specimen, thus reducing the amount of work involved.

[0051] [effect] The control rod drive mechanism 1 according to this embodiment comprises a hollow piston 11, a buffer sleeve 12 surrounding the hollow piston 11 from the outer circumference and having a flange portion 12b, an outer tube 13 surrounding the buffer sleeve 12 from the outer circumference, an orifice plate 14 attached to the inner circumferential surface 13k of the outer tube 13 so as to be located between the buffer sleeve 12 and the outer tube 13 and positioned opposite the upper surface of the flange portion 12b, and at least one orifice 14b provided on the orifice plate 14, with fluid filling the space 15 between the flange portion 12b and the orifice plate 14.

[0052] This allows the orifice 14b provided in the orifice plate 14 to maintain its function of absorbing the impact force applied to the upper part of the control rod drive mechanism during an emergency shutdown of the reactor, thereby ensuring the safety of the reactor.

[0053] In this embodiment, the control rod drive mechanism 1 is preferably provided with a labyrinth shape on the inner surface of the orifice plate facing the outer surface of the buffer sleeve. This prevents the fluid filling the space 15 between the flange 12b and the orifice plate 14 from flowing out from between the buffer sleeve 12 and the orifice plate 14. Therefore, it is possible to prevent the shock absorption function of the orifice 14b from being hindered.

[0054] (Second Embodiment) Figure 3 is a perspective view and enlarged schematic diagram of orifice plates 214a and 214b, which are technical features of the control rod drive mechanism 201 according to the second embodiment of the present invention.

[0055] The difference between the orifice plate of this embodiment and the orifice plate 14 of the first embodiment is that the orifice plate consists of multiple orifice plates (two orifice plates 214a and 214b in Figure 3) arranged in the axial direction of the hollow piston 11.

[0056] It is preferable that the orifices 14b of two adjacent orifice plates 214a and 214b among the multiple orifice plates are arranged on different axes AX1 and AX2.

[0057] Furthermore, the control rod drive mechanism 201 according to this embodiment may include at least one beam 214c between the multiple orifice plates 214a and 214b to maintain the spacing between the multiple orifice plates 214a and 214b. This allows the spacing between the multiple orifice plates 214a and 214b to be maintained even when the buffer sleeve 12 comes into contact with the orifice plate 214a.

[0058] [effect] The orifice plates of the control rod drive mechanism 201 according to this embodiment are a plurality of orifice plates 214a, 214b arranged in the axial direction of the hollow piston 11. By installing a plurality of orifice plates 214a, 214b, the pressure loss when the fluid filled in the space 15 between the flange portion 12b and the orifice plate 214a flows toward the upper guide 16 can be increased. As a result, a further damping force acts on the hollow piston 11, further reducing the upward speed of the hollow piston 11 and further suppressing the impact caused by the hollow piston 11.

[0059] In this embodiment, it is preferable that the orifices 14b of two adjacent orifice plates 214a and 214b of the control rod drive mechanism 201 are arranged on different axes (for example, axes AX1 and AX2). This allows the direction of travel of the liquid passing through the orifice 14b of orifice plate 214a along axis AX1 to be shifted to axis AX2 of the orifice 14b of orifice plate 214b. As a result, the pressure loss when the fluid filling the space 15 between the flange portion 12b and the orifice plate 214a flows toward the upper guide 16 can be further increased. Consequently, a greater damping force acts on the hollow piston 11, further reducing the upward speed of the hollow piston 11 and further suppressing the impact caused by the hollow piston 11.

[0060] (Third embodiment) Figure 4 is a schematic, enlarged perspective view of a spring 317 located between a buffer sleeve 12 and an orifice plate 14, which is a technical feature of the control rod drive mechanism 301 according to the third embodiment of the present invention.

[0061] The difference between the control rod drive mechanism 301 according to this embodiment and the control rod drive mechanism 1 according to the first embodiment is that a spring 317 is provided between the flange portion 12b of the buffer sleeve 12 and the orifice plate 14.

[0062] [effect] In this embodiment, the control rod drive mechanism 301 is provided with a spring 317 between the flange portion 12b of the buffer sleeve 12 and the orifice plate 14. Therefore, the control rod drive mechanism 301 can prevent the space 15 between the flange portion 12b and the orifice plate 14 from narrowing due to the buffer sleeve 12 malfunctioning and rising, etc., by the spring 317. In addition, after the scram is released, the spring 317 extends, making it easier for the buffer sleeve 12 to return to its initial position, and the space 15 between the flange portion 12b and the orifice plate 14 can be quickly restored.

[0063] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0064] The embodiments of the present invention may also be as follows. For example, the above-described embodiment shows that the outer circumference of the disc-shaped orifice plate 14 is attached to the inner surface 13k of the outer tube 13. However, the invention is not limited thereto, and a cylindrical portion extending toward the upper guide 16 and contacting or connecting with the upper guide 16 may be provided on the outer circumference of the orifice plate 14 to increase the rigidity of the orifice plate 14. [Explanation of Symbols]

[0065] 1, 201, 301…Control rod drive mechanism, 3…Control rod, 4…Reactor pressure vessel, 11…Hollow piston, 12…Buffer sleeve, 12b…Flange, 12e…Top surface, 13…Outer tube, 13g…Stop piston, 13k…Inner surface, 14, 214a, 214b…Orifice plate, 14a…Bottom surface, 14b…Orifice, 14c…Inner surface, 15…Space, 16…Upper guide, 317…Spring

Claims

1. A hollow piston and A buffer sleeve having a flange surrounds the hollow piston from the outer circumference, The outer tube surrounds the buffer sleeve from the outer circumference, An orifice plate is attached to the inner circumferential surface of the outer tube so as to be located between the buffer sleeve and the outer tube, and is positioned opposite the upper surface of the flange, The orifice plate comprises at least one orifice, A control rod drive mechanism characterized in that a fluid is filled in the space between the flange portion and the orifice plate.

2. A control rod drive mechanism according to claim 1, A control rod drive mechanism characterized in that a labyrinth shape is provided on the inner surface of the orifice plate facing the outer surface of the buffer sleeve.

3. A control rod drive mechanism according to claim 1, A control rod drive mechanism characterized in that the orifice plate is a plurality of orifice plates arranged in the axial direction of the hollow piston.

4. A control rod drive mechanism according to claim 3, A control rod drive mechanism characterized in that the orifices of two adjacent orifice plates among the plurality of orifice plates are arranged on different axes.

5. A control rod drive mechanism according to claim 1, A control rod drive mechanism characterized in that a spring is provided between the flange portion and the orifice plate.

6. A control rod drive mechanism according to claim 1, The buffer sleeve is movable upward as the hollow piston rises during a scrum. The control rod drive mechanism is characterized in that the outer tube is fixed to the housing in which the hollow piston is housed so as not to be able to move up or down.

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