JP2015021945A - Control rod drive mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control rod drive mechanism including a ball nut guide mechanism of which the replacement work and maintenance work are easy.SOLUTION: A control rod drive mechanism 50 includes a piston elevation mechanism 14 for raising and lowering a piston 19 to drive a control rod 5 and a drive unit 10 for driving the piston elevation mechanism, and inserts or extracts the control rod into or from a reactor core 3. The piston elevation mechanism includes a ball screw shaft 14a driven by the drive unit, a ball nut 15 engaged with the ball screw shaft to raise or lower the piston, a plurality of first rollers 16 attached to the peripheral edge of the ball nut, and a plurality of guide rails 55 which extend along a vertical direction and are engaged with corresponding first rollers to guide the first rollers. Each of the guide rails is held by a plurality of guide rings 54 surrounding the plurality of guide rails, and each of the guide rings is arranged along the guide rails in the vertical direction.

Description

  Embodiments of the present invention relate to a control rod drive mechanism (hereinafter referred to as CRD) used in a boiling water reactor (hereinafter referred to as BWR) as a light water reactor.

  First, a boiling water reactor (BWR) will be described with reference to FIG. FIG. 6 is a schematic longitudinal sectional view showing an example of the configuration of a boiling water reactor. As shown in FIG. 6, a coolant 2 that also serves as a moderator is accommodated in the reactor pressure vessel 1, and a core 3 is disposed at the center lower portion of the reactor pressure vessel 1. Surrounded by the core shroud 4. In addition, a large number of fuel assemblies (not shown) are loaded in the core 3, and control rods 5 are accommodated between the four fuel assemblies so that they can be inserted and removed from below.

  In this BWR, while the coolant 2 flows upward in the core 3, heat generated by the fission chain reaction is transmitted from the core 3 to be heated. The heated coolant 2 moves upward as a gas-liquid two-phase flow of water and steam, and is guided from the core 3 to the steam-water separator 6.

  The gas-liquid two-phase coolant is separated into water and steam by the steam separator 6. Among these, the steam passes through a steam dryer (not shown) and is sent from the main steam pipe to the steam turbine system to drive the steam turbine. Further, the steam that has driven the steam turbine is condensed in the condenser to become condensate, and then returned to the reactor pressure vessel 1 as feed water through the reactor condensate system and the feed water system.

  On the other hand, the water separated by the steam separator 6 flows down the downcomer section 7 and is guided to the lower part of the core 3 in a state of being mixed with the feed water sent through the reactor condensate system and the feed water system. Led to 3.

  Further, in the core 3 of the reactor pressure vessel 1, a control rod 5 is provided at the bottom of the CRD housing 9 provided through the bottom 1 a of the reactor pressure vessel 1 for starting and stopping the reactor and adjusting the reactor output. The CRD 8 connected to the flange 9a is taken in and out.

  As an example of the configuration of the CRD 8, an electrically driven CRD is shown in FIG. As shown in FIG. 7, the CRD 8 includes a ball screw shaft 14 a that is driven by a drive unit 10 provided below, and a ball nut 15 that is screwed to the ball screw shaft 14 a. A hollow piston 19 connected to the control rod 5 is placed on the upper surface of the ball nut 15.

  When the ball screw shaft 14a is rotationally driven by the drive unit 10, the ball nut 15 screwed to the ball screw shaft 14a slides and moves in the axial direction of the ball screw shaft 14a, that is, in the vertical direction. As the ball nut 15 moves up and down, the control rod 5 moves up and down via the piston 19. Thereby, the amount of insertion / extraction of the control rod 5 into the core 3 is adjusted, and the reactor output is controlled.

  Here, the above-described ball nut 15 will be further described in detail with reference to FIG. FIG. 8 shows an enlarged cross-sectional view of the ball nut 15 along the horizontal plane. As shown in FIG. 8, a plurality of rollers 16 are attached to the periphery of the ball nut 15 via pins 16a. The plurality of rollers 16 are arranged side by side in the circumferential direction of the ball screw shaft 14a. A mounting plate 18 extending in the vertical direction is installed between two adjacent rollers 16 among the plurality of rollers 16. When the mounting plate 18 contacts two adjacent rollers 16, the rotation of the ball nut 15 is restricted.

  As shown in FIG. 7, the ball nut 15 is accommodated in a guide tube 17 that extends along the vertical direction, and is guided along the guide tube 17 in the vertical direction. This guide tube 17 consists of an elongate hollow cylinder which consists of about 4 m in total length formed integrally.

Japanese Patent Laid-Open No. 11-23766

  The CRD 8 described above has a structure that allows the guide tube 17 to be removed during maintenance work. However, as described above, the guide tube 17 is formed of a long hollow cylinder having an overall length of about 4 m. For this reason, when performing the maintenance work, after removing the huge guide tube 17, the inner surface of the guide tube 17 is inspected and repaired, and the guide tube 17 is attached to the apparatus again. For this reason, much labor and time are required for the maintenance work.

  In addition, when an emergency occurs in the BWR, the reactor may be scrammed. During the scram, the piston 19 is rapidly pushed up in the guide tube 17 by the high pressure water. For this reason, the component (for example, latch member) installed in the outer periphery of the piston 19 and the inner surface of the guide tube 17 may come into contact with each other, and the guide tube 17 may be deformed minutely and locally. Although this minute and local deformation does not affect the scrum function, there is a risk of damaging other parts. Therefore, even if the deformation is local, the entire guide tube 17 has to be replaced. When exchanging the guide tube 17, not only a great deal of labor and time is required for the exchanging work, but also the parts cost is increased.

  The problem to be solved by the present invention is to provide a control rod drive mechanism having a ball nut guide mechanism that can easily perform replacement work and maintenance work instead of such a guide tube. .

  The control rod drive mechanism according to the embodiment includes a piston lifting mechanism that lifts and lowers a piston for driving the control rod, and a drive unit that drives the piston lifting mechanism, and the control rod is inserted into the core. Alternatively, the control rod is inserted into the core by pulling out the core and injecting high-pressure water during scram to push up the piston. The piston lifting mechanism includes a ball screw shaft driven by the drive unit, a ball nut that engages with the ball screw shaft and lifts the piston, and a plurality of first rollers attached to the periphery of the ball nut; And a plurality of guide rails extending along the vertical direction and engaging with the corresponding first roller to guide the first roller. Each guide rail is held by a plurality of guide rings surrounding the plurality of guide rails, and each guide ring is arranged in the vertical direction along the guide rail.

  According to the present invention, replacement work and maintenance work can be easily performed on the guide rail and guide ring for guiding the ball nut.

The longitudinal cross-sectional view which shows an example of a structure of the control-rod drive mechanism by one Embodiment. The expanded sectional view which shows the control rod drive mechanism in the horizontal cross section which crosses a ball nut. The perspective view which shows the guide ring and guide rail of the control-rod drive mechanism shown in FIG. The perspective view which shows the other example of a guide ring and a guide rail. The perspective view which shows the further another example of a guide ring and a guide rail. The expanded sectional view which expands and shows the control-rod drive mechanism in the horizontal cross section which crosses a piston. It is a longitudinal cross-sectional view for demonstrating the effect | action of a latch member, Comprising: (a) shows the state in which the piston is mounted in the ball nut, (b) shows the latch member to the guide ring side at the time of a scram. The state which protrudes and can contact | abut to the upper end part of a guide ring is shown. The schematic longitudinal cross-sectional view which shows an example of a structure of the prior art example of a boiling water reactor. FIG. 7 is a longitudinal sectional view showing the control rod drive mechanism shown in FIG. 6. The expanded sectional view which shows the control-rod drive mechanism shown in FIG. 7 in the horizontal cross section which crosses a ball nut.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view showing an example of the configuration of a control rod drive mechanism (CRD) according to an embodiment. The CRD 50 shown in FIG. 1 is used, for example, in the boiling water reactor described with reference to FIG. 6 in the background art. As shown in FIG. 1, the CRD 50 includes a so-called electric drive type control rod drive mechanism (FMCRD). Such a CRD 50 includes a piston 19 for driving the control rod 5, a piston lifting mechanism 14 that lifts and lowers the piston 19, and a drive unit 10 that drives the piston lifting mechanism 14.

  Of the components constituting the CRD 50 described above, first, the drive unit 10 will be described. The drive unit 10 includes an electric motor 10a disposed vertically below, and a drive shaft mechanism 12 that transmits a rotational driving force from the electric motor 10a to the piston lifting mechanism 14. Among these, the drive shaft mechanism 12 is connected to the rotating shaft 11 of the electric motor 10a, and is connected to the gear coupling mechanism 12a that decelerates and outputs the rotational driving force of the electric motor 10a, and the gear coupling mechanism 12a. And a drive shaft 13 that transmits a driving force output by the ring mechanism 12a to the piston lifting mechanism 14.

  As shown in FIG. 1, an electromagnetic brake 21 is attached below the electric motor 10a, and the electric motor 10a can be stopped by operating the electromagnetic brake 21. A synchro position detector 22 is provided at the lower end of the electromagnetic brake 21, and the position of the control rod 5 can be detected by the synchro position detector 22. Further, a motor bracket 23 is disposed above the electric motor 10a and around the gear coupling mechanism 12a. A spool piece 24 as a primary cooling water partition is fixed to the upper portion of the motor bracket 23. Yes. In the spool piece 24, the drive shaft 13 of the drive unit 10 described above is supported.

  Next, the piston raising / lowering mechanism 14 driven by the drive shaft 13 of the drive unit 10 will be described. The piston lifting mechanism 14 includes a ball screw shaft 14 a connected to the drive shaft 13 of the drive unit 10, and a ball nut 15 that is screwed to the ball screw shaft 14 a and lifts the piston 19.

  FIG. 2 is an enlarged view of the CRD 50 in a horizontal cross section crossing the ball nut 15. As shown in FIG. 2, a plurality of first rollers 16 are attached to the periphery of the ball nut 15 via first pins 16a, and each first roller 16 is equally spaced in the circumferential direction of the ball screw shaft 14a. Are arranged side by side. More specifically, a pair of first rollers 16 are arranged symmetrically with respect to the center of the ball screw shaft 14a on each of two straight lines L1 passing through the center of the ball screw shaft 14a and orthogonal to each other. Each first roller 16 is rotatably supported by the first pin 16a, and the axial direction of the first pin 16a of each first roller 16 is orthogonal to the straight line L1 on which the first roller 16 is arranged. ing.

  Further, as shown in FIG. 2, the CRD 50 has a plurality of guide rails 55 extending in the vertical direction, and each guide rail 55 engages with the corresponding first roller 16 to cause the first roller 16 to move. It is designed to guide you. The plurality of guide rails 55 are arranged at equal intervals in the circumferential direction of the ball screw shaft 14 a corresponding to the first roller 16. More specifically, a pair of guide rails 55 are arranged symmetrically with respect to the center of the ball screw shaft 14a on each of two straight lines L1 passing through the center of the ball screw shaft 14a and orthogonal to each other.

  Each guide rail 55 is formed with a first groove 55a extending in the vertical direction, and the corresponding first roller 16 is inserted into the first groove 55a. As each first roller 16 is inserted into the first groove 55a of the corresponding guide rail 55 and engaged with the guide rail 55, the rotation of the ball nut 15 is restricted, and the ball nut 15 is moved vertically. Guided.

  Each guide rail 55 is held by a plurality of guide rings 54 surrounding the plurality of guide rails 55. FIG. 3A shows a perspective view of the guide rail 55 and the guide ring 54. As shown in FIG. 3A, each guide ring 54 is arranged in the vertical direction along the guide rail 55. In the illustrated example, the interval between the two adjacent guide rings 54 is equal to the interval between the other two adjacent guide rings 54, but is not limited thereto and may be different.

  Further, as shown in FIG. 3A, each guide ring 54 has a plurality of second grooves 54a extending in the vertical direction on the inner peripheral surface thereof, and corresponding guide rails 55 are provided in the respective second grooves 54a. Inserted and positioned. In the present embodiment, each guide rail 55 and each guide ring 54 are fastened by a small screw 56. Specifically, a plurality of female screws are formed on the outer surface side of each guide rail 55, and a through hole is formed in a portion of the guide ring 54 that overlaps with each female screw. The small screw 56 is screwed into the female screw of each guide rail 55 through the corresponding through hole of the guide ring 54. In the present embodiment, corresponding small screws 56 are screwed into four female screws of one guide rail 55, and one guide ring 54 and one guide rail 55 are fastened. But the connection means of each guide rail 55 and each guide ring 54 is not limited to such an example, These may be connected by various known connection means.

  Returning to FIG. 1, a hollow piston 19 is placed above the ball nut 15. FIG. 4 shows an enlarged horizontal section of the piston 19. As shown in FIG. 4, a plurality of second rollers 66 are attached to the periphery of the piston 19 via second pins 66a, and the plurality of second rollers 66 are equally spaced in the circumferential direction of the ball screw shaft 14a. Are arranged side by side. More specifically, as shown in FIG. 4, a pair of second rollers 66 are arranged symmetrically with respect to the center of the ball screw shaft 14a on each of two straight lines L2 that pass through the center of the ball screw shaft 14a and are orthogonal to each other. Has been. Each second roller 66 is rotatably supported by the second pin 66a, and the axial direction of the second pin 66a of each second roller 66 is orthogonal to the straight line L2 on which the second roller 66 is disposed. ing.

  Further, as shown in FIG. 4, each guide rail 55 engages with the second roller 66 of the piston 19 to guide the second roller 66 as well. Specifically, each second roller 66 is inserted into the corresponding first groove 55a. As each second roller 66 is inserted into the first groove 55a of the corresponding guide rail 55 and engaged with the guide rail 55, the rotation of the piston 19 is restricted and the piston 19 is guided in the vertical direction. It has become so.

  A latch mechanism 53 is provided on the lower peripheral edge of the piston 19. The latch mechanism 53 will be described with reference to FIGS. FIG. 5 is a longitudinal sectional view for explaining the operation of the latch mechanism, in which (a) shows a state in which the piston 19 is placed on the ball nut 15 at a normal time, and (b) The state in which the latch mechanism 53 is activated during the scram is shown. As shown in FIGS. 5A and 5B, the latch mechanism 53 includes a latch member 53a rotatably attached to the lower peripheral edge of the piston 19 via a pin 58, and the latch member 53a. A spring 59 provided between the piston 19 and the outer peripheral surface of the piston 19 for biasing the latch member 53a toward the guide ring 54.

  Among these, the latch member 53a is comprised from the rod-shaped member. The latch member 53a is rotatably attached to the peripheral edge of the piston 19 via a pin 58 provided at the upper end, and extends downward. At the lower end of the latch member 53a, a protruding latch-side engagement portion 53c that protrudes downward is formed. The latch-side engagement portion 53c can be engaged with a protruding nut-side engagement portion 15c that protrudes upward and is formed on the periphery of the upper end of the ball nut 15 positioned below. Specifically, the latch side engaging portion 53c can be accommodated in a space opened upward between the nut side engaging portion 15c of the ball nut 15 and the ball screw shaft 14a. And the latch side engaging part 53c is latched by these between the nut side engaging part 15c and the ball screw shaft 14a.

  Further, a flat latch side locking portion 53b is formed on the outer peripheral side of the piston 19 with respect to the latch side engaging portion 53c of the latch member 53a. The latch side latching part 53b is located above the lower end of the latch side engaging part 53c. As shown in FIG. 5B, when the latch member 53a is rotated so that the lower side of the latch member 53a protrudes toward the guide ring 54, the latch side locking portion 53b is flat on the upper surface of the guide ring 54. It will be in the state which can contact | abut to the ring-shaped latching | locking part 60 of shape.

  As shown in FIG. 5A, the piston 19 is placed on the ball nut 15 in a normal state. At this time, the latch side engaging portion 53 c of the latch member 53 a supported by the piston 19 is engaged with the nut side engaging portion 15 c of the ball nut 15. Accordingly, the latch member 53a is accommodated in the guide ring 54. On the other hand, at the time of scrum, as shown in FIG. 5B, high-pressure water is injected, and the piston 19 is lifted away from the ball nut 15 by the high-pressure water. At this time, due to the urging of the spring 59, the lower side of the latch member 53a protrudes outward toward the guide ring 54 and faces the ring-side locking portion 60 on the upper surface of the guide ring 54. Thereafter, it is assumed that the high-pressure water is depressurized due to some cause and the piston 19 is lowered. However, since the latch member 53a protrudes toward the guide ring 54 and faces the ring-side locking portion 60, the latch-side locking portion 53b of the latch member 53a contacts the ring-side locking portion 60 of the guide ring 54. . As a result, the state in which the control rod 5 is inserted can be maintained without the piston 19 being greatly lowered.

  Further, as described above, at the time of scram, the piston 19 rises and the lower side of the latch member 53a protrudes outward toward the guide ring 54 side. At this time, in order to prevent the latch member 53a from coming into contact with the lower surface of the guide ring 54 to prevent the piston 19 from being lifted, the lower portion of the guide ring 54 in the longitudinal section shown in FIGS. The inclined surface 57 is inclined upward from the outside toward the inside.

  As shown in FIG. 1, a hollow piston tube 19a extending in the vertical direction is connected to the upper part of the piston 19, and the piston 19 is connected via a coupling 20 by bayonet coupling installed at the upper end of the piston tube 19a. And connected to the control rod 5. A ball screw shaft 14a extends into the hollow space of the piston 19 and the hollow space of the piston tube 19a.

  The operation of the present embodiment configured as described above will be described with reference to the drawings.

  First, the normal operation will be described. When the electric motor 10 a is driven, the ball screw shaft 14 a rotates via the rotating shaft 11 and the driving shaft 13. When the ball screw shaft 14a rotates in this way, the ball nut 15 screwed to the ball screw shaft 14a slides on the outer periphery of the ball screw shaft 14a and moves in the axial direction of the ball screw shaft 14a, that is, in the vertical direction. To do. Specifically, as shown in FIG. 2, when the ball screw shaft 14 a is rotated and the ball nut 15 slides on the ball screw shaft 14 a, each first roller 16 engages with the corresponding guide rail 55. As a result, the rotation of the ball nut 15 is restricted, and the ball nut 15 is guided in the vertical direction.

  When the ball nut 15 is moved in the vertical direction, the piston 19 placed on the ball nut 15 is also moved in the vertical direction in conjunction with the ball nut 15. Specifically, each second roller 66 of the piston 19 engages with the corresponding guide rail 55 and is moved in the vertical direction while being restricted from rotating.

  When the ball nut 15 is moved in the vertical direction, the control rod 5 connected to the piston 19 via the piston tube 19 a and the coupling 20 also moves in the vertical direction in conjunction with the piston 19. As the control rod 5 moves in the vertical direction, the amount of insertion or withdrawal of the control rod 5 into the core 3 is adjusted, and the furnace output is controlled.

  Next, a case where an emergency situation occurs in the BWR and the reactor is scrammed will be described. During scram of the nuclear reactor, high-pressure drive water is rapidly supplied from the scram insertion pipe 25 connected to the lower flange 9 a of the CRD housing 9 into the cylinder 31 below the piston 19 through the water injection port 26. When the high pressure driving water is rapidly filled in the cylinder 31, the piston 19 is separated from the ball nut 15 and rapidly pushed upward, and the control rod 5 is inserted into the core 3 at a high speed. At this time, the piston 19 is separated from the ball nut 15 and the engagement between the latch side engaging portion 53c of the latch member 53a and the nut side engaging portion 15c of the ball nut 15 is released as shown in FIG. Thus, the latch member 53 a protrudes outward toward the guide ring 54 side by the urging force of the spring 59, and comes into a state in which the latch member 53 a can contact the upper end portion of the guide ring 54. Thereafter, even if the high pressure water is depressurized for some reason and the piston 19 descends, the latch member 53a protrudes toward the guide ring 54, so that the latch side latching portion 53b of the latch member 53a is connected to the guide ring 54. The ring side latching part 60 contacts. As a result, the state in which the control rod 5 is inserted can be maintained without the piston 19 being greatly lowered.

  As described above, according to the present embodiment, the plurality of guide rails 55 extending in the vertical direction engage with the corresponding first roller 16 of the ball nut 15 to guide the first roller 16. Each guide rail 55 is held by a plurality of guide rings 54 surrounding the plurality of guide rails 55. For this reason, at the time of maintenance and inspection of the guide ring 54 or the guide rail 55 constituting the guide mechanism of the ball nut 15, a part of the target guide ring 54 or the guide rail 55 is removed and the inspection of these parts 54 and 55 is performed. And after performing repairs, these parts 54 and 55 can be attached again. As described above, when the guide ring 54 or the guide rail 55 is maintained and inspected, a part of the guide ring 54 and the guide rail 55 can be removed and the maintenance and inspection work can be performed. Therefore, the maintenance and inspection work can be easily performed. it can. Further, when replacing the parts 54 and 55 constituting the guide mechanism, only the guide ring 54 or the guide rail 55 to be replaced needs to be replaced, so that the part cost can be saved.

  Furthermore, since each guide ring 54 is arranged vertically along the guide rail 55, it is not necessary to remove the guide ring 54 and the guide rail 55 at the time of maintenance and inspection of the guide ring 54 or the guide rail 55. In this case, the inner surface of the guide ring 54 and the inner surface of the guide rail 55 can be inspected using the space between the adjacent guide rings 54. For this reason, the maintenance and inspection work of the guide ring 54 and the guide rail 55 can be easily performed.

  Further, when the guide mechanism of the ball nut 15 is composed of a plurality of guide rings 54 and a plurality of guide rails 55, when the parts constituting the guide mechanism of the ball nut 15 are integrally incorporated in the hollow cylindrical tube. In comparison, the material cost can be greatly reduced while maintaining the required strength of the guide mechanism.

  Further, according to the present embodiment, the piston 19 is guided along the corresponding guide rail 55 via each second roller 66 and is urged toward the guide ring 54 side by the lower peripheral edge of the piston 19. A latch member 53a is rotatably attached. The latch member 53a is engaged by the ball nut 15 at normal times, and when the piston 19 is lifted away from the ball nut 15 at the time of scram, the latch member 53a protrudes toward the guide ring 54 and protrudes to the upper end of the guide ring 54. It is possible to abut. Therefore, even when the high pressure water is depressurized for some reason and the piston 19 is lowered during the scram, the latch member 53a can come into contact with the upper end portion of the guide ring 54. As a result, the state in which the control rod 5 is inserted can be maintained without the piston 19 being greatly lowered.

  In the above-described embodiment, the control rod 5 and the piston 19 are separated from the ball nut 15 during scram. In this case, the sync position detector 22 cannot detect the position of the control rod 5. In this case, the position of the control rod 5 is detected by a magnet 27 attached to the lower end of the piston 19 and a position detector 29 having a built-in reed switch 28 operated by magnetic force. However, some of the components constituting the CRD 50 are provided inside the reactor pressure vessel 1, the position detector 29 is installed outside the CRD 50, and the upper end thereof is from the bottom 1 a of the reactor pressure vessel 1. Is located below, the entire stroke of the control rod 5 cannot be detected.

  The position detector 29 is configured to be able to detect 0%, 10%, 40%, and 60% of the position of the control rod 5 determined by the specification value of the insertion time during scrum. Further, the position of 100% of the control rod 5 is determined by the specification value of the insertion time at the time of the scrum, and this is detected by another mechanism.

  That is, as shown in FIG. 5, a cylinder 31 in which the piston 19 moves up and down is disposed below the disc spring mechanism 30 for braking the control rod 5 and the piston 19 during scram. A coil spring 32 and a stop piston 33 are provided above the cylinder 31. As shown in FIG. 2, a long guide ribbon 39 extending in the vertical direction is connected to the stop piston 33, and a magnet 34 shown in FIG. 1 is attached below the guide ribbon 39. The guide ribbon 39 is accommodated in a groove formed on the outer peripheral surface of the guide ring 54. The guide ribbon 39 is guided along the vertical direction by each band 42 attached so as to cover the groove of the corresponding guide ring 54.

  By such a mechanism, when the control rod 5 reaches the 100% position, the piston 19 pushes up the stop piston 33 somewhat, whereby the magnet 34 is pushed up somewhat via the guide ribbon 39, and the position detector 29 is moved. The 100% position is detected by the built-in reed switch 28.

  Next, an example of a method for detecting abnormality of the CRD 50 will be described. The CRD 50 is further provided with a separation detection mechanism for detecting that the control rod 5 and the piston 19 are separated from the ball nut 15 in order to prevent the control rod 5 from being dropped.

  That is, as shown in FIG. 1, a magnet holder 36 containing a magnet 35 is slidably fitted to the drive shaft 13 in the spool piece 24, and a coil spring 37 is provided below the magnet holder 36. ing. A separation detector 38 incorporating a reed switch is installed outside the CRD 50.

  With such a structure, the control rod 5 and the piston 19 are suspended due to frictional resistance between the control rod 5 and the fuel assembly during the pulling operation of the control rod 5. When separated from above, the load on the control rod 5 and the piston 19 acting on the magnet holder 36 is released. For this reason, the coil spring 37 extends and the magnet 35 is pushed up, and the reed switch of the separation detector 38 is activated. Thereby, it is detected that the control rod 5 and the piston 19 are separated from the ball nut 15.

≪Modification≫
Note that various modifications can be made to the above-described embodiment. Hereinafter, an example of modification will be described with reference to the drawings. In the following description and the drawings used in the following description, the same reference numerals as those used for the corresponding parts in the above embodiment are used for the parts that can be configured in the same manner as the above embodiment, A duplicate description is omitted.

  In the above-described embodiment, as shown in FIG. 3A, an example in which the guide rings 54 are integrally formed has been described. However, the configuration of the guide rings 54 is not limited to the above-described configuration. FIG. 3B shows another configuration example of the guide ring. In the example illustrated in FIG. 3B, some of the guide rings 61 among the plurality of guide rings can be divided into a plurality of portions 61 a and 61 b provided in the circumferential direction. Specifically, the guide ring 61 is configured as a pair, and in the boundary region, one portion 61a has a belt-like convex portion 64a extending in the circumferential direction of the guide ring 61, and the other portion 61b is And a recess 64b that engages with a belt-like protrusion 64a extending in the circumferential direction.

  According to such a modification, the guide ring 61 can be partly removed to perform maintenance work or replacement work, so that the work can be performed more efficiently.

  In the above-described embodiment, as shown in FIG. 3A, an example in which the guide rails 55 are integrally formed has been described. However, the configuration of the guide rails 55 is not limited to the above-described configuration. FIG. 3C shows another configuration example of the guide rail. In the example illustrated in FIG. 3C, some of the guide rails 62 among the plurality of guide rails can be divided into a plurality of portions 62a and 62b provided in the vertical direction. Specifically, in the boundary region of the guide rail 62, one portion 62a has a convex portion 65a that tapers downward from above, and the other portion 62b has a concave portion 65b that engages with the convex portion. Have.

  According to such a modification, the guide rail 62 can be partly removed and maintenance work and replacement work can be performed, so that the work can be performed more efficiently.

  Although not specifically mentioned in the above-described embodiment, as shown in FIG. 4, the rotation of the second roller 66 in the contour of each second roller 66 of the piston 19 in the cross section along the horizontal plane. The edge 66b farthest outward from the shaft is in contact with the guide rail 55. However, it is not limited to such an example. In the cross section along the horizontal plane, a gap is provided between the edge of the second roller 66 of the piston 19 that is farthest outward from the rotation axis of the second roller 66 and the guide rail 55. Also good. According to such a configuration, when the piston 19 moves in the vertical direction, the second roller 66 of the piston 19 inserted into the first groove 55a of the guide rail 55 receives resistance from the guide rail 55 more than necessary. It is possible to prevent the guide rail 55 from being restrained more than necessary.

  In addition, embodiment is an illustration and the range of invention is not limited to it, For example, it can also be set as the modification which combined FIG. 3B and FIG. 3C.

DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 1a ... Bottom part, 2 ... Coolant, 3 ... Reactor core, 4 ... Core shroud, 5 ... Control rod, 6 ... Steam separator, 7 ... Downcomer part, 8 ... Control rod drive device (CRD) 9) CRD housing, 9a ... Lower flange, 10 ... Drive unit, 10a ... Electric motor, 11 ... Rotating shaft, 12 ... Drive shaft mechanism, 12a ... Gear coupling mechanism, 13 ... Drive shaft, 14 ... Piston lifting mechanism, 14a ... Ball screw shaft, 15 ... Ball nut, 15c ... Nut side engaging part, 16 ... First roller, 16a ... First pin, 17 ... Guide tube, 18 ... Mounting plate, 19 ... Piston, 19a ... Piston tube, 20 ... Coupling, 21 ... Electromagnetic brake, 22 ... Synchro position detector, 23 ... Motor Racket 24 ... Spool piece 24a ... Mounting flange 25 ... Scram insertion pipe 26 ... Inlet 27 ... Magnet 28 ... Reed switch 29 ... Position detector 30 ... Belleville spring mechanism 31 ... Cylinder 32 ... Coil spring, 33 ... Stop piston, 34 ... Magnet, 35 ... Magnet, 36 ... Magnet holder, 37 ... Coil spring, 38 ... Separation detector, 39 ... Guide ribbon, 40 ... Machine screw, 41 ... Pin, 42 ... Band, 50 ... Control rod drive mechanism (CRD), 53 ... Latch mechanism, 53a ... Latch member, 53b ... Latch side locking part, 53c ... Latch side engagement part, 54 ... Guide ring, 54a ... Second groove, 55 ... Guide Rail, 55a ... 1st groove, 56 ... Screw, 57 ... inclined surface 58 ... pin 59 ... spring, 60 ... ring side locking portion, 61 ... guide ring, 62 ... guide rail, 66 ... second roller, 66a ... second pin

Claims (5)

A piston elevating mechanism that elevates and lowers a piston for driving the control rod; and a drive unit that drives the piston elevating mechanism. The control rod is inserted into or extracted from the core, and a high pressure is applied during scram. In a control rod drive mechanism that injects water and pushes up the piston to insert the control rod into the core,
The piston lifting mechanism includes a ball screw shaft driven by the driving unit, a ball nut that engages with the ball screw shaft and lifts the piston,
A plurality of first rollers attached to the periphery of the ball nut;
A plurality of guide rails extending along the vertical direction and engaging with the corresponding first roller to guide the first roller;
Each guide rail is held by a plurality of guide rings surrounding the plurality of guide rails,
Each guide ring is arranged in the up-and-down direction along the guide rail, The control rod drive mechanism characterized by things. The piston is guided along the guide rail via a plurality of second rollers,
A latch member biased toward the guide ring side is rotatably attached to the lower peripheral edge of the piston,
During normal times, the latch member is engaged by the ball nut and fits within the guide ring,
When the piston is lifted away from the ball nut at the time of scram, the latch member protrudes outward toward the guide ring side and can come into contact with the upper end portion of the guide ring. The control rod drive mechanism according to claim 1.   In the horizontal section, a gap is provided between the edge of the contour of each second roller of the piston that is farthest outward from the rotation axis of the second roller and the guide rail. The control rod drive mechanism according to claim 2.   4. The control rod drive mechanism according to claim 1, wherein the guide ring can be divided into a plurality of portions provided in a circumferential direction. 5.   5. The control rod drive mechanism according to claim 1, wherein the guide rail can be divided into a plurality of portions provided in a vertical direction.