Inspection device and method for inspecting nuclear reactor

Abstract

To provide a technology remotely inspecting a housing provided for a pressure vessel by excellent working property, on a suppressed device scale, by simple handling, and with excellent accuracy.SOLUTION: An inspection device 10 includes: a frame 30 hung in an open pressure vessel 27; a rod 31 which is supported by the frame 30 and is displaced in a longitudinal direction; a detection head 32 which is provided for an end of the rod 31 and is inserted through an upper opening 22a of the housing 21a going through a reactor bottom part of the pressure vessel 27; an engagement part 35 which is provided for a lower end of the frame 30 and engages an opening 29 adjacent to the upper opening 22a of the housing 21a.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE An embodiment of the present invention relates to a technique for remote, non-destructive inspection of a housing provided in a pressure vessel. [Background technology]

[0002] The housing of the accessory that is installed through the pressure vessel is subjected to the same level of steam pressure as the pressure vessel during operation of the reactor. Because such housings that serve as pressure boundaries are radioactive, non-destructive testing such as surface inspection and volume inspection are performed remotely to evaluate their soundness.

[0003] A technique has been proposed for non-destructive testing of the welded joints of the housing that penetrates the bottom of the pressure vessel, in which a flaw detection sensor is suspended from an operating tool fixed to the upper grid plate and inserted into the upper opening of the housing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2511583 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned technology, the flaw detection sensor is accessed independently from the operating tool to the upper opening of the housing in a suspended state. Therefore, the flaw detection sensor and its suspension member during transportation are easily interfered with by the cooling water and structures in the pressure vessel, and it is difficult to insert the flaw detection sensor into the upper opening of the housing, and the workability is poor.

[0006] Furthermore, the operating tool fixed to the upper lattice plate of the reactor pressure vessel needs to scan the suspended flaw detection sensor in the circumferential and vertical directions. Since the distance between the upper lattice plate and the welded part is about 9 m, when the inspection position is so far from the support part, the device that transmits the power required for the suspended member becomes large in scale, which increases the difficulty of handling.

[0007] In addition, the inspection position in the housing is determined by the length and rotation angle of the hanging member of the flaw detection sensor. However, since the distance between the operation tool fixed to the upper lattice plate and the flaw detection sensor inserted in the housing is long as described above, the deformation amount of the hanging member significantly contributes to the inspection position of the flaw detection sensor in the housing as an error.

[0008] An embodiment of the present invention has been made in consideration of the above circumstances, and aims to provide a technology for remotely inspecting a housing provided in a pressure vessel with excellent workability, a reduced equipment scale, simple handling, and excellent accuracy. [Means for solving the problem]

[0009] In the inspection device according to the embodiment, a frame is suspended from an open pressure vessel, a rod is supported by the frame and displaced in a longitudinal direction, and a detection head is provided at the tip of the rod and inserted from an upper opening of a housing that penetrates the bottom of the pressure vessel. and when the housing contains a neutron flux monitor, The housing is provided at the lower end of the frame. Opening adjacent to the upper opening Engagement portion that engages with When the housing is a housing for accommodating a control rod drive mechanism, the housing has an engagement portion provided at the lower end of the frame and engaging with an upper opening of the housing. . Effect of the Invention

[0010] According to an embodiment of the present invention, a technology is provided for remotely inspecting a housing provided in a pressure vessel with excellent workability, a reduced equipment scale, easy handling, and excellent accuracy. [Brief description of the drawings]

[0011] [Figure 1]1 is a cross-sectional view of a nuclear reactor to which an inspection device according to a first embodiment of the present invention is applied. [Diagram 2] 1 is a perspective view showing a state in which the inspection device according to the first embodiment is installed on a core support plate having an upper opening of a housing. [Diagram 3] 3A, 3B, and 3C are explanatory views of the operation of the inspection device according to the first embodiment, and FIG. 3D is a top view of a moving stage of the inspection device. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a detection head that inspects the inner circumferential surface of the housing in the first embodiment. [Diagram 5] FIG. 11 is a cross-sectional view showing a state in which an inspection device according to a second embodiment is installed in an upper opening of a housing in a nuclear reactor. [Figure 6] 10A and 10B are explanatory views of the operation of the inspection device according to the second embodiment. [Figure 7] 13A is an enlarged cross-sectional view of a detection head for inspecting the inner surface of a housing in the second embodiment, and (B) and (C) are enlarged cross-sectional views of an engagement portion in an inspection device installed in an upper opening of a housing in the second embodiment. [Figure 8] 3 is a flowchart illustrating steps of a nuclear reactor inspection method according to the first embodiment. [Figure 9] 10 is a flowchart illustrating steps of a nuclear reactor inspection method according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a cross-sectional view of a nuclear reactor 20 to which an inspection device 10A (10) according to a first embodiment of the present invention is applied. In the first embodiment, a flaw detection inspection of a welded portion and its heat-affected portion between a housing 21a that accommodates a neutron flux monitor (not shown) and a pressure vessel 27 in a boiling water reactor (BWR) will be described as an example.

[0013] 1 discloses core support structures, such as a core shroud 28, an upper grid plate 25, and a core support plate 26, that exist after removing a top lid (not shown), a steam dryer (not shown), a steam separator (not shown), fuel assemblies (not shown), and other reactor internal structures. The core shroud 28 is a stainless steel cylinder that separates the upward flow of coolant inside, where the fuel assemblies are housed, from the downward flow of coolant in an outer annular region.

[0014] An upper grid plate 25 is fixed to the top of the core shroud 28, and a core support plate 26 is fixed to its bottom. The upper grid plate 25 is made of stainless steel plate-shaped beams arranged in a grid pattern, and supports the fuel assemblies in the lateral direction at the top of the fuel assemblies. The core support plate 26 is a stainless steel disk reinforced with beams, and supports the fuel assemblies in the vertical direction at the bottom of the fuel assemblies via fuel support brackets (not shown), and supports them in the lateral direction at the top opening 22a of the housing 21a.

[0015] The crane 13 installed on the top floor of the reactor 20 can reach any position on the horizontal plane with a two-axis rail 19. Furthermore, the lifting means 14 attached to the crane 13 allows the frame 30 of the inspection device 10 suspended from its tip to reach any position in the vertical direction. In the first embodiment, the inspection device 10A passes through the lattices of the upper lattice plate 25 and is suspended down to the upper surface of the core support plate 26, and the engagement part 35A (FIG. 3) engages with the opening 29 (FIG. 2) for the control rod guide tube. Then, the detection head 32 is inserted into the housing 21a that contains the neutron flux monitor (not shown).

[0016] Fig. 2 is a perspective view showing a state in which the nuclear reactor inspection device 10A according to the first embodiment is installed on a core support plate 26 having an upper opening 22a of a housing 21a. Figs. 3(A), (B), and (C) are side views of the nuclear reactor inspection device 10A according to the first embodiment. Fig. 3(D) is a top view of a moving stage 36 of the inspection device 10A.

[0017] Thus, the inspection device 10A (10) comprises a frame 30A (30) suspended over the open pressure vessel 27, a rod 31 supported by the frame 30A and displaceable in the longitudinal direction, a detection head 32 provided at the tip of the rod 31 and inserted through an upper opening 22a of a housing 21a which penetrates the bottom of the pressure vessel 27, and an engagement portion 35A provided at the lower end of the frame 30 and engaging with an opening 29 adjacent to the upper opening 22a of the housing 21a.

[0018] Furthermore, the inspection device 10 of the first embodiment has a motor 41 that rotates the screw 45 about its axis, a nut 42 that displaces the rod 31 according to the amount of rotation of the screw 45 that is screwed into it, a movable stage 36 fixed to the nut 42, a first gripping portion 11 provided on the movable stage 36 and that detachably holds the rod 31, and a second gripping portion 12 provided at a position on the frame 30 that is structurally integrated with the motor 41 and that detachably holds the rod 31 mutually exclusive to the first gripping portion 11.

[0019] The engagement portion 35 has a slide stage 15 that slides the frame 30 in the horizontal direction. The frame 30 has an internal space 37 that houses the detection head 32 until it is inserted into the upper opening 22 of the housing 21.

[0020] 2, the engagement portion 35 is inserted into an opening 29 for positioning the control rod guide tube adjacent to the housing 21a to be inspected. Then, a guide pin 24 for positioning a fuel support bracket (not shown) provided on the core support plate 26 is inserted into the notch 19, thereby determining the orientation of the inspection device 10A.

[0021] As shown in FIG. 3, in the frame 30A, a lower substrate 43 and an upper substrate 44 are connected at the four corners by supports 47, and further a top plate 48 is provided on the upper part, which are structurally integrated.

[0022] A screw 45, which is connected to a motor 41 fixed to an upper substrate 44 and rotates about its axis, has its tip supported by a thrust bearing 46 provided on a lower substrate 43. In accordance with the amount of rotation of the screw 45, a moving stage 36 fixed to a nut 42 moves up and down.

[0023] The first gripping part 11 provided on the moving stage 36 and the second gripping part 12 provided on the upper substrate 44 are controlled to be mutually exclusive for attachment / detachment (hold / release) so that at least one of them grips the rod 31 to prevent it from dropping. The position where the second gripping part 12 is provided is not limited to the upper substrate 44, and it can be provided at any position on the structurally integrated frame 30.

[0024] The top plate 48 is provided with an attachment means (not shown) for attaching the tip of the lifting means 14 for suspending the inspection device 10. The top plate 48 also plays a role in preventing interference between the rod 31, which extends long upward, and the reactor internal structure when the detection head 32 is housed in the internal space 37 of the frame 30A.

[0025] The operation of the reactor inspection device 10A according to the first embodiment will be described with reference to Figures 3(A), (B), and (C). By operating the slide stage 15 from the state shown in Figure 3(A), the detection head 32 can be made to face the upper opening 22a of the housing 21a. When the first gripping part 11 is set to hold, the second gripping part 12 is set to release, and by driving the motor 41, the rod 31 can be displaced in the vertical direction together with the moving stage 36, as shown in Figures 3(A) and 3(B). This allows the detection head 32 to translate along the longitudinal direction inside the housing 21a.

[0026] When the second gripping unit 12 is in the hold setting, the first gripping unit 11 is in the release setting, and as shown in Figures 3(B) to 3(C), when the motor 41 is driven, only the moving stage 36 is displaced in the vertical direction while the position of the rod 31 remains fixed. By repeating the operations of Figures 3(B) and 3(C) in a stepwise manner in this way, the rod 31, which has a stroke infinitely longer than the screw 45, can be freely displaced from the upper limit to the lower limit.

[0027] 4 is an enlarged cross-sectional view of the detection head 32 that inspects the inner peripheral surface 23a of the housing 21a in the first embodiment. In this way, the detection head 32 rotates relative to the rod 31 by being driven by a motor (not shown). By such rotational and translational motion of the detection head 32, the sensor 38 can helically scan the inner peripheral surface 23a of the housing 21a. As a result, by moving the detection head 32 in only one stroke in the longitudinal direction of the housing 21a, the entire surface of the inner peripheral surface 23a can be inspected, and the inspection time can be shortened.

[0028] The detection head 32 is provided with a sensor 38 protruding from the outer circumferential surface. Various configurations are considered as mechanisms for protruding the sensor 38 when housed in the detection head 32, but it is effective to use air pressure or spring elasticity. In this way, by embedding the sensor 38 in the detection head 32 except when it faces the inner circumferential surface 23a of the housing 21a, it is possible to prevent the sensor 38 from interfering with surrounding structures and being damaged.

[0029] Furthermore, by arranging the multiple sensors 38 at equal intervals in the circumferential direction, the pitch of the spiral scan can be increased, further shortening the inspection time.

[0030] The sensor 38 may be, but is not limited to, one for eddy current testing or ultrasonic testing. The detection surface of the sensor 38 is provided with a probe shoe (not shown) that stabilizes the detection sensitivity by keeping the distance from the inner circumferential surface 23a constant. Each of the multiple sensors 38 arranged in the circumferential direction can be arranged with its posture changed to improve the S / N ratio of the detection signal of the sensor 38 and further improve the detection sensitivity of defects.

[0031] If the intervals between the multiple sensors 38 arranged in the circumferential direction are sufficiently close, the inner circumferential surface 23a of the housing 21a can be thoroughly inspected by translational motion only without rotational motion of the detection head 32. Also, a calibration specimen with an artificial flaw may be placed on the upper part of the housing 21a to calibrate the sensors 38.

[0032] The detection head 32 is provided with a biasing member 33 that biases the detection head 32 while contacting the inner circumferential surface 23a of the housing 21. By functioning such a biasing member 33, the detection head 32 receives reaction forces from the inner circumferential surface 23a of the housing 21 from all directions, and the central axes can be aligned with each other. Even if the inner diameter of the housing 21 changes, the shape of the biasing member 33 deforms, so that the alignment of the central axes of the detection head 32 and the housing 21 is not lost.

[0033] The steps of the method for inspecting a nuclear reactor using the inspection device according to the first embodiment will be described with reference to the flow chart in Fig. 8 (see Figs. 1, 2, and 3 as appropriate). First, one of the housings 21a to be inspected is selected (S11). Then, the crane 13 is moved in the open pressure vessel 27 to reach a position corresponding to the selected housing 21a (S12).

[0034] Then, the frame 30A is lowered so as to seat on the upper surface of the core support plate 26 (S13). The engagement portion 35A provided at the lower end of the frame 30A is engaged with the opening 29 for the control rod guide tube (S14). Furthermore, the slide stage 15 is operated to slide the frame 30 in the horizontal direction, and the detection head 32 is positioned opposite the upper opening 22a of the housing 21a.

[0035] Then, the first gripping unit 11 is set to the hold setting, and the second gripping unit 12 is set to the release setting, and the motor 41 is driven to displace the rod 31 supported by the frame 30A in the longitudinal direction (S15). In this manner, the detection head 32 provided at the tip of the rod 31 is inserted from the upper opening 22a of the housing 21a that houses the neutron flux monitor (S16).

[0036] While acquiring a detection signal of the inner circumferential surface 23a of the housing 21a from the sensor 38 (S17, S18; No, S19; No), the movable stage 36 is displaced to the lower limit position together with the rod 31 (S19; Yes). Then, the second gripping unit 12 is set to the hold setting, and the first gripping unit 11 is switched to the release setting (S20), and only the frame 30A is displaced to the upper limit position while maintaining the position of the rod 31 (S21).

[0037] Therefore, the first gripping unit 11 is again set to the hold setting, the second gripping unit 12 is switched to the release setting (S22), and while displacing the rod 31 again in the longitudinal direction, acquisition of the detection signal by the sensor 38 is resumed (S17). This flow from (S17) to (S22) is repeated until inspection of the entire inner circumferential surface 23a of the housing 21a to be inspected is completed (S18; Yes).

[0038] Then, the housing 21a to be inspected next is determined (S23; No, S11). Then, this flow from (S11) to (S23) is repeated until inspection of the inner circumferential surfaces 23a of all the housings 21a is completed (S23; Yes, END). Note that in the description, the detection signal by the sensor 38 is acquired only on the outward path from the top to the bottom of the housing 21a, but it may also be acquired only on the return path from the bottom to the top, or from both paths.

[0039] Second embodiment Next, a second embodiment of the present invention will be described with reference to Fig. 5 to Fig. 7. Fig. 5 is a cross-sectional view showing a state in which an inspection device 10B (10) according to the second embodiment is installed in an upper opening 22b of a housing 21b in a nuclear reactor 20. Figs. 6(A) and 6(B) are side views of the inspection device 10B according to the second embodiment. In Figs. 5 to 7, parts having the same configuration or function as those in Figs. 1 to 3 are indicated by the same reference numerals, and duplicated explanations will be omitted.

[0040] In the second embodiment, a flaw detection inspection of a welded portion and its heat-affected portion between a housing 21b that accommodates a control rod drive mechanism (not shown) in a boiling water reactor (BWR) and a pressure vessel 27 will be described as an example. In the second embodiment, the inspection device 10B passes through the lattices of the upper lattice plate 25, and further passes through an opening 29 for a control rod guide tube in the core support plate 26. The inspection device 10B is then lowered to the upper opening 22b of the housing 21b, and the detection head 32 is inserted into the housing 21b.

[0041] The inspection device 10B (10) comprises a frame 30B (30) suspended in the open pressure vessel 27, a rod 31 supported by the frame 30 and displaceable in the longitudinal direction, a detection head 32 inserted from the upper opening 22b of the housing 21b, and an engagement portion 35B (Figure 6(A)) provided at the lower end of the frame 30 and engaging with the upper opening 22b of the housing 21b.

[0042] 6, the frame 30B is provided with a motor 41 that rotates the screw 45, and a nut 42 that displaces the rod 31 according to the amount of rotation of the screw 45. The frame 30B has an internal space 37 that houses the detection head 32 until it is inserted into the upper opening 22b of the housing 21b.

[0043] The operation of the inspection device 10B according to the second embodiment will be described with reference to Figures 6(A) and 6(B). When the motor 41 is driven from the state shown in Figure 6(A), the rod 31 can be displaced in the vertical direction as shown in Figures 6(A) to 6(B), and the detection head 32 can be translated along the longitudinal direction inside the housing 21b.

[0044] A guide 49 that can be fixed to the core support plate 26 is provided on the frame 30B at the top of the inspection equipment 10B. The function of this guide 49 makes it possible to reduce the shaking of the inspection equipment 10B during inspection. In addition, by configuring this guide 49 to be detachable from the main body of the frame 30B, it is possible to easily handle the equipment on the operating floor.

[0045] Fig. 7(A) is an enlarged cross-sectional view of a detection head 32 for inspecting an inner peripheral surface 23b of a housing 21b in the second embodiment. Figs. 7(B) and (C) are enlarged cross-sectional views of an engagement portion 35B (35) of an inspection device 10B installed in an upper opening 22b of a housing 21b in the second embodiment.

[0046] 7(B) and (C), the engaging portion 35B has a clamp member 16 that clamps the upper opening 22b of the housing 21b. The clamp member 16 receives a biasing force from compressed air or the like and protrudes from the inner peripheral surface of the engaging portion 35B to press a part of the outer peripheral surface of the housing 21b near the upper opening 22b.

[0047] In the drawings, the clamp member 16 is composed of two pressing members 17, 18 which cooperate to move in a direction perpendicular to each other by receiving a biasing force from compressed air or the like. However, there is no limitation on the configuration of the clamp member 16, and any suitable member may be used as long as it can detachably clamp the engagement portion 35B of the inspection device 10B and the upper opening 22b of the housing 21b. If the clamp member 16 is disposed at three or more locations at equal intervals in the inner circumferential direction of the engagement portion 35B, the central axes of the detection head 32 and the housing 21b can be aligned with each other.

[0048] Moreover, the detection head 32 rotates relative to the rod 31 when driven by the motor 39. Such rotational and translational motion of the detection head 32 allows the sensor 38 to spirally scan the inner circumferential surface 23b of the housing 21b. Furthermore, the detection head 32 is provided such that the sensor 38 protrudes from the side circumferential surface.

[0049] Based on the flow chart of Fig. 9, the steps of the method for inspecting a nuclear reactor using the inspection device according to the second embodiment will be described (see Figs. 5, 6, and 7 as appropriate). First, one of the housings 21b to be inspected is selected (S31). Then, the crane 13 is moved in the open pressure vessel 27 to reach a position corresponding to the selected housing 21b (S32). Then, the frame 30B is lowered (S33), and the engagement portion 35B provided at the lower end is engaged with the upper opening 22b (S34).

[0050] Then, the clamp member 16 clamps the engagement portion 35B to the upper opening 22b of the housing 21b, and the rod 31 supported by the frame 30B is displaced in the longitudinal direction (S35). Then, the motor 41 is driven to insert the detection head 32 provided at the tip of the rod 31 from the upper opening 22b of the housing 21b that accommodates the control rod drive mechanism (S36).

[0051] While acquiring a detection signal of the inner circumferential surface 23b of the housing 21b from the sensor 38 (S37, S38; No), the detection head 32 is displaced to the lower limit position of the housing 21b (S39; Yes). This completes the inspection of the entire inner circumferential surface 23b of the housing 21b to be inspected.

[0052] Then, the housing 21b to be inspected next is determined (S39; No, S31). Then, this flow from (S31) to (S39) is repeated until inspection of the inner circumferential surfaces 23b of all the housings 21b is completed (S39; Yes, END). Note that in the description, the detection signal by the sensor 38 is acquired only on the outward path from the top to the bottom of the housing 21b, but it may also be acquired only on the return path from the bottom to the top, or from both paths.

[0053] According to at least one of the embodiments of the reactor inspection device described above, an engagement portion that engages with the upper opening or an adjacent opening of the housing is provided at the lower end of the frame, so that the housing provided in the pressure vessel can be remotely inspected with excellent workability, a reduced equipment scale, simple handling, and excellent accuracy. Note that, although the above-mentioned embodiment has been described as an example of a pressure vessel of a reactor, it can also be used in chemical plants and the like as long as it is a pressure vessel provided with a housing.

[0054] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention described in the claims and their equivalents, as well as the scope and spirit of the invention. In addition, although a boiling water reactor (BWR) has been described as an example, housings and the like provided in pressure vessels of other nuclear reactors can also be inspected. [Explanation of symbols]

[0055] 10 (10A, 10B)... inspection device, 11... first gripping part, 12... second gripping part, 13... crane, 14... lifting means, 15... slide stage, 16... clamping member, 17, 18... pressing member, 19... rail, 20... reactor, 21 (21a, 21b)... housing, 22 (22a, 22b)... upper opening, 23 (23a, 23b)... inner peripheral surface, 24... guide pin, 25... upper grid plate, 26... core support plate, 27... pressure Force vessel, 28...core shroud, 29...opening, 30 (30A, 30B)...frame, 31...rod, 32...detection head, 33...actuating member, 35 (35A, 35B)...engagement portion, 36...moving stage, 37...internal space, 38...sensor, 39...motor, 41...motor, 42...nut, 43...lower board, 44...upper board, 45...screw, 46...thrust bearing, 47...support, 48...top plate, 49...guide.

Claims

1. a frame that is lowered onto the open pressure vessel; A rod supported by the frame and displaceable in a longitudinal direction; a detection head provided at the tip of the rod and inserted from an upper opening of a housing penetrating the bottom of the pressure vessel; The housing contains a neutron flux monitor, An inspection device having an engagement portion provided at a lower end of the frame, the engagement portion being adapted to engage with an opening adjacent to the upper opening of the housing.

2. a frame that is lowered onto the open pressure vessel; A rod supported by the frame and displaceable in a longitudinal direction; a detection head provided at the tip of the rod and inserted from an upper opening of a housing penetrating the bottom of the pressure vessel; The housing houses a control rod drive mechanism, An inspection device having an engagement portion provided at a lower end of the frame and adapted to engage with an upper opening of the housing.

3. In the inspection device according to claim 1 or 2, The detection head is an inspection device that rotates relative to the rod.

4. In the inspection device according to any one of claims 1 to 3, The detection head is an inspection device in which a sensor is provided so as to protrude from a side peripheral surface.

5. In the inspection device according to any one of claims 1 to 4, The inspection device includes a detection head having a biasing member that biases the inner circumferential surface of the housing while contacting the inner circumferential surface of the housing.

6. In the inspection device according to any one of claims 1 to 5, The frame of the inspection device has a space for accommodating the detection head until it is inserted into the upper opening of the housing.

7. In the inspection device according to any one of claims 1 to 6, The frame is A motor for rotating the screw; and a nut that displaces the rod according to the amount of rotation of the screw that is screwed into the nut.

8. In the inspection device according to claim 7, wherein the housing contains a neutron flux monitor, A moving stage fixed to the nut; a first gripping part provided on the moving stage and configured to detachably grip the rod; an inspection device having a second gripping portion provided at a position on the frame that is structurally integrated with the motor, and configured to detachably grip the rod mutually exclusive with the first gripping portion;

9. In the inspection device according to claim 8, The engagement portion is an inspection apparatus having a slide stage that slides the frame in a horizontal direction.

10. An inspection device according to any one of claims 2 to 7, wherein the housing accommodates a control rod drive mechanism, The engagement portion of the inspection device has a clamp member that clamps the upper opening of the housing.

11. In the inspection device according to claim 8 or claim 9, The frame is suspended down to the upper surface of a core support plate placed inside a reactor pressure vessel, the engagement portion engages with an opening for a control rod guide tube, and the detection head is inserted into the housing which contains the neutron flux monitor.

12. In the inspection device according to claim 10, The frame is suspended up to an upper opening of the housing that houses the control rod drive mechanism that moves the control rod inside the reactor pressure vessel, and the detection head is inserted into the inspection device.

13. In the inspection device according to claim 12, An inspection device in which a guide capable of being fixed to a core support plate disposed inside a reactor pressure vessel is provided on an upper portion of the frame.

14. suspending the frame over the open pressure vessel so that the frame rests on an upper surface of a core support plate disposed within the pressure vessel; a step of engaging an engagement portion provided at a lower end of the frame with an opening for a control rod guide tube; Displacing a rod supported by the frame in a longitudinal direction; and inserting the detection head provided at the tip of the rod through the bottom of the pressure vessel from an upper opening of a housing that houses a neutron flux monitor.

15. suspending the frame over the open pressure vessel; a step of penetrating an engagement portion provided at a lower end of the frame through a reactor bottom of a pressure vessel and engaging with an upper opening of a housing that accommodates a control rod drive mechanism; Displacing a rod supported by the frame in a longitudinal direction; and inserting a detection head provided at the tip of the rod from the upper opening of the housing.

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