Patent Number: 055703992
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a control rod and fuel supporting member gripping apparatus for gripping a control rod (hereinafter referred to as CR) and a fuel supporting member ( hereinafter referred to as FS) in order to remove and carry the CR and FS out of the reactor and to load the CR and FS again in the reactor, and also relates to a method of withdrawing the control rod and fuel supporting member gripping apparatus. Generally, the core of the boiling water reactor (BWR) is constructed as shown in FIG. 13 and a plurality of fuel assemblies 3 and CRs (control rods) 4 are mounted in a cylindrical core shroud 2 contained in a reactor pressure vessel 1. The top portions of these fuel assemblies 3 are supported by means of an upper lattice plate 5 and the bottom portions thereof are supported by means of a core supporting plate 7 through FSs (fuel supporting member) 6. The respective FSs 6 are supported by means of the core supporting plate 7 by engaging the cylindrical bottom portion thereof with an FS supporting engagement hole 7a as shown in FIG. 15. As shown in FIG. 16, the square top portion of the core supporting plate 7 has supporting engagement holes 6a, 6b, 6c, 6d for allowing the bottom of the fuel assembly 3 to engage therewith for supporting the fuel assembly 3 and has a cross shaped insertion hole for allowing the CR 4 to go through. The respective supporting engagement holes 6a-6d communicate with respective orifices 6e, 6f, 6g, 6h which are located on the sides of the supporting engagement holes in order to allow coolant to flow into the respective fuel assemblies 3 from the respective orifices 6e-6h through the respective supporting through holes 6a-6d. A through hole 6i which engages with a fixing pin 7b implanted on the core supporting plate 7 is provided on a square corner of the top portion of the FS 6 in order to fix the FS 6 onto the core supporting plate 7. On the other hand, the CR 4 is detachably connected to a control rod driving mechanism (hereinafter referred to as CRD) which is provided so as to vertically go through the bottom of the reactor pressure vessel 1 and the CR 4 is lifted up and down by means of each CRD 8 so as to be inserted into and pulled from the core. The CR 4 passes through a CR guide pipe 9 which is connected to the core supporting plate 7 so that the CR 4 is lifted up and down through a cross shaped insertion hole 4a formed among the four bodies of the fuel assemblies 3, 3, 3, 3 which are supported by means of the FS 6. A conventional coupling mechanism for the CR 4 and the CRD 8 is constructed in the form of a spud as shown in FIG. 17. As for the spud type coupling 10, a coupling spud 11 having locking pawls which are formed by incising the circumferential portion thereof so as to obtain, for example, four split parts is pushed up strongly by means of a driving piston, not shown, of the CRD 8 and then inserted into a gap around a lock plug 12 which is inserted into the engagement hole in the bottom portion 4b of the CR 4. Consequently, the coupling spud 11 is nipped between the internal face of the bottom portion 4b of the CR 4 and the external face of the lock plug 12 in order to connect the CR 4 with the CRD 8. By pushing up the lock plug 12 by means of an uncoupling rod 13 of the CRD 8 to resist the force of a spring 4c, the CR 4 is disconnected from and released from the CRD 8. When the CR 4 is removed from the CR driving mechanism in the reactor pressure vessel 1 and carried out of the core at the time of the periodic inspection of the BWR, first of all, the fuel assemblies 3 are pulled out of the core. However, since in the conventional BWR, the connection between the CR 4 and the CRD 8 is released by pushing the lock plug 12 strongly by means of the uncoupling rod 13, if such a foreign matter as clad or the like is caught between the lock plug 12 and the coupling stud 11, the lock plug 12 sticks firmly to the coupling spud 11, so that it may be impossible to disconnect the CR 4 from the CRD 8. To solve such a problem, recently a bayonet coupling 14 as shown in FIGS. 18A-18C has been sometimes employed as a connecting means for the CR 4 and the CRD 8. The bayonet coupling 14 has engaging protrusions 16 having a specified width which are disposed at every 90.degree. along the circumference thereof, the engaging protrusions protruding out of the internal face of an engaging hole 15 in the bottom portion 4b of the CR 4 in which the coupling spud 11 is to be inserted. By turning the bayonet coupling 14 or the CR 4 by 45.degree. along the circumference thereof as shown in FIG. 18B, the respective engaging protrusions 16 are moved along the external face of the respective coupling spuds 11 to reduce the diameter of the respective coupling spuds 11. Consequently, the lock plug 17 is nipped to connect the CR 4 with the CRD 8. If the CR 4 is turned further by 45.degree. or returned to its original position as shown in FIG. 18C, the respective coupling spuds 11 are moved to respective cavities of the engaging hole 15 to expand the diameter of the coupling spuds 11, thereby releasing connection between the CR 4 and the CRD 8. In the CR 4 which employs the aforementioned bayonet coupling 14, no foreign matter such as clad or the like is caught between the lock plug 12 and the coupling spud 11 unlike the conventional spud type coupling 10. Thus, it is possible to release the CR 4 from the CRD 8 securely. It is necessary to turn the bayonet coupling 14 or the CR 4 axially by 45.degree. to release the CR 4 from the CRD 8. However, because the CR 4 is inserted through the cross shaped insertion hole 4a of the FS 6 which is fixed by the fixing pin 7b of the core supporting plate 7, it is not possible to turn the CR 4. If the CR 4 is turned forcibly, the CR 4 and the FS 6 may be damaged. If the CR 4 and the FS 6 are turned at the same time after the FS 6 is removed from the fixing pin 7b of the core supporting plate 7 so that the FS 6 is free, the top portion of the FS 6 collides with fuel assemblies in the lattice in the vicinity because the top portion thereof is square shaped, so that the fuel assemblies 3 may be damaged. FIG. 19A shows a plan view of the CR 4 and the FS 6 viewed from the upper side of the upper lattice plate 5 in a steady state. As shown in FIG. 19A, the CR 4 is located in the same direction as that of the upper lattice plate 5, and the FS 6 has a shape capable of passing the cell 5' formed to the upper lattice plate 5. The FS 6 is provided with projections 6' which can nip a pin 7b provided to the core supporting plate 7 to thereby prevent the FS 6 from rotating. The fuel assemblies, each having a square cross section, are positioned on the fuel assembly supporting through holes 6a, 6b, 6c, 6d formed to the FS 6. A reactor core is constituted by about 100 units of fuel assemblies, each unit including the thus arranged four fuel assemblies. When the CR 4 and the FS 6 now in the state of FIG. 19A are simultaneously gripped by the respective gripping devices and are then lifted to rotate them, the projections 6' of the FS 6 contact the surrounding fuel assemblies. This state is shown in FIG. 19B showing an arrangement in which the CR 4 and the FS 6 are rotated by 45.degree. from the arrangement shown in FIG. 19A. In this arrangement, the projections 6' project out of the cell 5', which may contact the fuel assembly disposed in the upper side cell and hence damage the same. In order to obviate such defect, as shown in FIG. 19C, sixteen fuel assemblies of the other four cells 5" surrounding the cell 5' now treated as well as the four fuel assemblies of the cell now treated have to be withdrawn upward from the core and conveyed to the fuel storage pool formed upper outside of the reactor pressure vessel, thus being troublesome and inconvenient in the prior art technology. SUMMARY OF THE INVENTION An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art described above and to provide a control rod and fuel supporting member gripping apparatus in which the CR and CRD, which are detachably connected by means of the bayonet coupling, can be released and disconnected from each other simply, securely and rapidly and in which the CR and the FS can be removed from the reactor pressure vessel and lifted up to be carried out thereof, and also provide a method of withdrawing the control rod and fuel supporting member gripping apparatus from a reactor core easily and effectively. This and other objects can be achieved according to the present invention by providing a control rod and fuel supporting member gripping apparatus for gripping a fuel supporting member and a control rod, the fuel supporting member being mounted on a core supporting plate located below an upper lattice plate within a reactor pressure vessel and having fuel assembly supporting engagement holes in which the bottom portions of a plurality of fuel assemblies are inserted to support the fuel assemblies and an insertion hole through which a control rod is passed, the control rod being detachably connected with a control rod driving mechanism by means of a bayonet coupling and being passed through a control rod passage so as to be lifted up and down freely in order to remove the fuel supporting member and the control rod from the core supporting plate and the control rod driving mechanism, the control rod and fuel supporting member gripping apparatus comprising: a gripping apparatus body hoisted elevationally liftably in an installed state within the reactor pressure vessel; a fuel supporting member gripping device disposed at a portion below the gripping apparatus body; a control rod gripping device disposed at a portion below the gripping apparatus body to be liftable up and down and rotatable with respect to the gripping apparatus body; and means for rotating the control rod gripping device with respect to the gripping apparatus body. In preferred embodiments of the present invention, the fuel supporting member gripping device includes a detection means for detecting a fact of settlement of the gripping apparatus body on the fuel supporting member gripping device. The gripping apparatus may further comprise a detection means for detecting a fact that a rotation angle of the control rod gripping device is rotated by an angle over a predetermined angle. An upper lattice plate is disposed above the gripping apparatus body at an upper portion of the reactor pressure vessel and an upper plate is disposed on the upper lattice plate through a gripping apparatus body lifting device for lifting up and down the gripping apparatus body with respect to the upper lattice plate. The control rod gripping device comprises a hook means which is hung by a rotating member rotatably fixed to the upper plate in order to releasably grip a handle of the control rod, a first driving means for driving the control rod gripping device for making the hook perform gripping and releasing operations, a second driving means for lifting up and down the control rod lifting mechanism by raising the hook means, a third driving means having a reciprocal piston rod for driving a winding means, and a rotating device for rotating the rotating body clockwise or counterclockwise by connecting both ends of the winding means attached to a rotating member in rotational association with the rotating body to both ends of the reciprocal piston rod of the third driving means. Preferably, the first, second and third driving means are air cylinder assemblies. The first driving means includes a biasing means for maintaining the gripping operation of the hook means when a supply of fluid is eliminated. The first driving means is connected to a rope means for releasing the hook means at a time when the rope means is pulled to thereby forcibly perform the releasing action. The fuel supporting member gripping device comprises a first driving source which makes a pair of retractable gripping plungers protrude from the inside of the fuel supporting member into a pair of side holes communicating with the respective fuel assembly supporting engagement holes of the fuel supporting member and facing each other in a direction of a diameter thereof in order to grip the fuel supporting member, and a second driving source which grips the fuel supporting member by means of the gripping plungers and which hoist the fuel supporting member. The fuel supporting member gripping portion comprises a locking mechanism for holding the first drive source in the gripping position when the fuel supporting member is gripped by means of the first drive source and hoisted by means of a lifting mechanism in order to prevent the gripped fuel supporting member from being released. The first driving means includes a gripping state holding mechanism for maintaining the gripping state of the fuel supporting member when a driving supply is eliminated. The first driving means is connected to a rope and a pair of plungers are retracted from a pair of side holes to an inside of the fuel supporting member, when the rope is pulled, in order to forcibly release the fuel supporting member. In another aspect of the present invention, there is provided a method of withdrawing control rod and fuel supporting member from a reactor pressure vessel, in which the fuel supporting member is mounted on a core supporting plate located below an upper lattice plate within a reactor pressure vessel and has fuel assembly supporting engagement holes in which the bottom portions of a plurality of fuel assemblies are inserted to support the fuel assemblies and an insertion hole through which a control rod is passed and the control rod is connected to a control rod driving mechanism by means of a bayonet coupling and is passed through a control rod passage so as to be lifted up and down freely in order to remove the fuel supporting member and the control rod from the core supporting plate and the control rod driving mechanism, the method comprising the steps of: lifting upward the fuel supporting member from the core supporting plate by a predetermined distance; rotating the control rod by a predetermined angle to separate the control rod from the control rod driving mechanism; and withdrawing the fuel supporting member and the control rod from an upper portion of the reactor pressure vessel. According to the structures and characters of the present invention described above, generally, after the fuel assembly contained in a given lattice plate with a reactor pressure vessel is pulled out by means of a fuel exchanging device or the like, a body of the control rod and fuel supporting member gripping apparatus is hoisted in the lattice and lowered thereinto. After the lower portion of the apparatus body is settled on the upper surface of the FS, the fuel supporting member gripping device is operated to grip the FS, and in the similar manner, the control rod gripping device is operated to grip the control rod. Thereafter, only the FS is lifted upward to the predetermined level, at which the lower end of the FS is higher than the upper end of the CR, by driving the lift up and down mechanism disposed in the body of the gripping apparatus or by driving the hoist disposed to the upper portion of the apparatus body and lifting up the whole body by means of the hoisting wire, for example. Thereafter, the control rod gripping device is rotated with respect to the body of the gripping apparatus by means of a driving mechanism. Since the control rod is fixed to the control rod driving mechanism, the control rod is simultaneously rotated, thus being uncoupled from the control rod driving mechanism. During this rotating operation, since the FS is positioned above the upper end of the CR, the FS and the CD do not contact. Then, the entire body of the gripping apparatus is lifted upward by means of the wire rope and then moved to and stored in a pool disposed upper outside of the reactor pressure vessel. Therefore, according to the present embodiments, it is possible to grip and then remove the CR and the FS which are located within the reactor pressure vessel and hoist the CR and the FS to be carried out of the reactor pressure vessel. Thus, as compared with the conventional apparatus in which the CR and the FS are gripped separately by means of different gripping devices successively and carried out of the reactor pressure vessel after they are removed from the gripping devices, the present invention is capable of improving the working efficiency of hoisting operation markedly. Consequently, it is possible to improve the working efficiency of the BWR's periodic inspection markedly. Furthermore, the CR lifting air cylinder of the CR gripping portion makes it possible to adjust the hoisting height depending on the pressure of supplied air. Thus, by increasing the pressure of supplied air successively from low pressure to high pressure, it is possible to lift the hook to such an extent in which a play between the hook and the control rod gripped by the hook is eliminated and then hoist the hook higher. Thus, because the present invention is capable of relaxing a shock which occurs when the CR is hoisted by means of the hook all at once, it is possible to increase the completeness and safety of the CR when the CR is hoisted. Further, in the control rod rotating mechanism, the rotating members which rotate the rotating body which has the hook for gripping the handle of the CR are connected to the clockwise-counterclockwise rotating air cylinder through a wire in order to turn the rotating body. Thus, it is possible to reduce the load of the rotating force. If the supply of air to the control rod gripping air cylinder is interrupted when the CR is gripped by means of the hook which is actuated by the control rod gripping air cylinder, the gripping action of the control rod gripping air cylinder is maintained by the force of the biasing means, preferably, spring. Thus, even if the supply of air to the control rod gripping air cylinder is interrupted due to a breakage of the air hose or the like when the CR is gripped and hoisted by means of the hook, the hook does not release the CR. Thus, the safety operation can be assured. When the CR cannot be released due to a trouble in the control rod gripping air cylinder, it is possible to forcibly release the CR by pulling the rope. Because a pair of plungers are protruded into a pair of the existing side holes of the FS to support the FS, it is not necessary to make devices for the FS for assuring the gripping operation. Further, because a pair of plungers are inserted into a pair of side holes which faces each other with respect to the diameter of the FS to support and hoist the FS, the FS can be supported and hoisted stably with a balance with respect to the diameter thereof. Thus, it is possible to increase the reliability and the safety of supporting and hoisting the FS. When the FS is gripped by means of the FS gripping portion and hoisted, the gripping state is locked by the locking mechanism. Thus, it is possible to prevent the FS from dropping due to the action of releasing the fuel supporting member and damaging, thereby increasing the operational reliability and safety. If the supply of air to the FS gripping air cylinder is interrupted due to a breakage of the air hose when the FS is held by means of the FS gripping air cylinder, the gripping action of the FS gripping air cylinder is maintained by the force of the biasing means. Thus, if the supply of air to the FS gripping air cylinder is interrupted due to a breakage of the air hose when the FS is gripped and hoisted, the FS is held, thereby securing the safety operation. When the action of releasing the FS cannot be performed due to a trouble in the FS gripping air cylinder, it is possible to forcibly release the FS by pulling a rope. When the upper plate is settled on the upper lattice plate, the CR gripping portion is settled on the handle of the control rod, and the FS gripping portion is settled on the FS, the settlement of these portions are detected by means of respective settling detection devices. Thus, it is possible to confirm whether they are settled or not, as required, before the CR and the FS are gripped, removed and hoisted. As a result, the reliability of such a sequence of the operations can be increased and the operations can be performed smoothly. The looseness of the air hose and the cable is always absorbed by means of the cable absorbing mechanism. Thus, it is possible to reduce the possibility of a trouble which may occur when the air hose or the cable is hooked on other member due to such looseness, thereby increasing the operational reliability. The nature and further features of the present invention will be made more clear hereunder through the description made with reference to the accompanying drawings.