Patent Number: 
Section: description

A CR/FS grapple according to an embodiment of the present invention will be explained in detail with reference to the accompanying drawings hereinafter. The CR/FS grapple according to one embodiment of the resent invention is employed such that, when a periodical inspection of the BWR, etc. is conducted, the CR/FS grapple is hung down into a reactor pressure vessel 1 (see FIG. 8) so as to release control rods 4 and a fuel support 6 from a core and, in turn, install the control rods 4 and the fuel support 6 from a fuel storage pool outside the reactor pressure vessel into the core. FIGS. 1 and 2 are vertical sectional views showing a schematic configuration of the CR/FS grapple according to the embodiment of the present invention. FIG. 1 is a front vertical sectional view while FIG. 2 is a side vertical sectional view. As shown in FIGS. 1 and 2, the CR/FS grapple according to the embodiment of the present invention comprises a main body frame 24 to which a separating frame 18 is fitted attachably/detachably by fitting bolts 31. A guide member 23 is provided at a lower end of the separating frame 18 to guide a hoist handle 4d (see FIG. 8) of the control rod 4. A square cylinder member 15 is provided in an inside of the separating frame 18 to be moved vertically by a predetermined width, but an upward movement of the square cylinder member 15 can be limited by a stopper 32 which is projected from an inner surface of the separating frame 18. A stud 14 is secured to an top end of the square cylinder member 15. The stud 14 is formed to have a square cylinder shape because a grid guide (not shown) which can guide the CR/FS grapple in passing through the upper grid 5 (see FIG. 8) can be attached to the stud 14. The stud 14 is connected to a hoist rope, etc. which is wound on an auxiliary hoist of a refueling machine. The CR/FS grapple can be picked up by the hoist rope, etc. and then inserted into the inside of the reactor pressure vessel 1 (see FIG. 8). A control rod holding air cylinder 17 is pivotally coupled to the square cylinder member 15 via a hinged coupling. A hook 16 which is formed of a hook-shaped member is pivotally coupled to a piston rod 17a of the air cylinder 17 via the hinged coupling. A bearing member 39 having a longitudinal hole 38 therein is provided on the separating frame 18. A pivot axis 40 is inserted into the longitudinal hole 38 and is movable vertically. Then, the hook 16 is fitted to the bearing member 39 via the pivot axis 40 such that such hook 16 can be pivoted and moved vertically. A limit switch 51 is provided in the close vicinity of the air cylinder 17. An operation state of the air cylinder 17 can be detected by the limit switch 51. The limit switch 51 is electrically connected to an indicator lamp 29 which is energized by a battery 28. The result detected by the limit switch 51 can be displayed by the indicator lamp 29. Therefore, the operator can check by eye whether or not the hook 16 is located in a hooking position. A control rod holding means 50 consists of the square cylinder member 15, the hook 16, and the air cylinder 17. Since the square cylinder member 15 can be moved up and down relative to the separating frame 18 by a predetermined width, the control rod holding means 50 can also be moved up and down relative to the separating frame 18. At that time, because the separating frame 18 is fixed to a main body frame 24, the control rod holding means 50 can be moved vertically relative to the main body frame 24 by a predetermined width, i.e., can be displaced relatively along a longitudinal direction of the control rod 4. A hoisting stroke of the control rod holding means 50 with respect to the separating frame 18 is designed to exceed a height of a projected portion of the hook 16 such that a mechanical lock mechanism can operate while keeping an engagement of the projection portion formed at the top end of the hook 16 with the hoist handle 4d (see FIG. 8) of the control rod 4. As shown in FIG. 2, a coupling releasing air cylinder 22 is fixed to the separating frame 18. A piston rod 22a of the coupling releasing air cylinder 22 is connected to a coupling releasing link mechanism 20 via an actuating rod 21. In this manner, the coupling releasing link mechanism 20 can be driven by the coupling releasing air cylinder 22. Also, an arm 19 is provided to extend along the actuating rod 21. The arm 19 is also provided such that it can be moved vertically relative to the separating frame 18. As shown in FIG. 3, during the exchange operation of the control rod 4, the arm 19 is inserted into a clearance between the control rod 4 and the cruciform through hole 4a of the fuel support 6 from the upper side. A coupling releasing means 60, which can uncouple the control rod 4 and the control rod drive mechanism 8 by virtue of a spud coupling, is composed of the coupling releasing link mechanism 20, the actuating rod 21, the coupling releasing air cylinder 22. As shown in FIG. 2, a damper mechanism 30 is provided to a top end of the air cylinder 22 to apply resistance to a piston rod 22a of the coupling releasing air cylinder 22 in its operation. The damper mechanism 30 constitutes an operational timing control mechanism which can uncouple the control rod 4 and control rod drive mechanism 8 by using the coupling releasing means 60 after the control rod holding means 50 has held the hoist handle 4d (see FIG. 8). A damper drive axis 30a of the damper mechanism 30 is connected to the piston rod 22a of the air cylinder 22. FIG. 4A, FIG. 4B, and FIG. 4C show an operation of the coupling releasing link mechanism 20 in the CR/FS grapple. As shown in FIG. 4A, FIG. 4B, and FIG. 4C, the coupling releasing link mechanism 20 includes a first arm 20a, a second arm 20b, and a third arm 20c.  A top end of the first arm 20a is pivotally coupled to a bottom end of the actuating rod 21, a bottom end of the first arm 20a is pivotally coupled to one end of the second arm 20b, and the other end of the second arm 20b is pivotally coupled to a middle portion of the third arm 20c.  In addition, one end of the third arm 20c is pivotally coupled to the arm 19. As shown in FIG. 4A, FIG. 4B, and FIG. 4C in sequence, when the piston rod 22a is lifted upward by driving the air cylinder 22, the first arm 20a and the second arm 20b can be pulled up and also the third arm 20c can be pulled up until a horizontal position while being pivoted. Further, a bend-shaped switching member 20d is swingably and pivotally coupled to the third arm 20c. A limit switch 33 is provided over the switching member 20d.The limit switch 33 is electrically connected to an indicator lamp 29 shown in FIG. 1. On/off states of the limit switch 33 can be displayed by the indicator lamp 29. As shown in FIG. 1 and FIG. 2, a pair of fuel support holding plungers 25 are provided on a bottom surface of the main body frame 24. A pair of fuel support holding air cylinders 26 for driving these holding plungers 25 are provided on the fuel support holding plungers 25. Limit switches 27 are provided in the neighborhood of the air cylinders 26 respectively. Operation states of the air cylinders 26 can be detected by the limit switches 27 and then detected results can be displayed by the indicator lamp 29. Then, a fuel support holding means 70 which can hold the fuel support 6 (see FIG. 11) is composed of the fuel support holding plungers 25 and the fuel support holding air cylinders 26. The fuel support holding plungers 25 have contact pieces 34 respectively. As shown in FIG. 5, the contact pieces 34 can be moved back and forth by a fuel support holding link mechanism 35. A pair of contact pieces 34 are arranged at positions corresponding to a pair of opposing orifices 6e (f, g, h) of the fuel support 6 shown in FIG. 11. Stepped portions 34a on which the upper portions of the orifices 6e (f, g, h) are placed are formed on the contact pieces 34 respectively. The fuel support holding link mechanism 35 has a first arm 35a and a second arm 35b. One end of the first arm 35a is pivotally coupled to a rear end of the contact piece 34, and the other end of the first end 35a is pivotally coupled to one end of the second arm 35b, and the other end of the second arm 35b is pivotally coupled to outer peripheral wall 25a (see FIG. 1) of the fuel support holding plunger 25. In addition, a bottom end of the actuating rod 36 which is coupled to the piston rod of the air cylinder 26 is pivotally coupled to a pivotable portion between the first arm 35a and the second arm 35b.  FIG. 6 is a schematic system diagram showing a piping system for supplying a working air to a control rod holding air cylinder 17 and a coupling releasing air cylinder 22 in the CR/FS grapple. As can be seen from FIG. 6, the control rod holding air cylinder 17 and the coupling releasing air cylinder 22 employ commonly a set of low and high pressure working air sources. In general, the working air sources which can be employed in the nuclear power plant consist of two sets of low and high pressure working air sources. Hence, a set of working air sources are commonly used for the control rod holding air cylinder 17 and the coupling releasing air cylinder 22, while a set of remaining working air sources can be used to operate the fuel support holding air cylinders 26. Therefore, there is no case where the site has lack of the working air sources. FIG. 7 shows a modification in which a flow restrict mechanism 37 is provided in place of the damper mechanism 30 as an operational timing control mechanism in the CR/FS grapple. In this modification, a flow restrict mechanism 37 is provided in the middle of a low pressure side working fluid pipe 41 connected to the coupling releasing air cylinder 22. Next, referring to FIGS. 1 and 8, when the control rods 4 and the fuel support 6 are picked up from the inside of the water-filled reactor pressure vessel 1, operations performed during the periodical inspection of the BWR by using the CR/FS grapple according to the present embodiment will be explained. At the time when the lifting operation of the control rods 4 and the fuel support 6 is to be carried out, the fuel assemblies 3 fitted in predetermined grids have already been taken out from the inside of the reactor pressure vessel 1 by the refueling machine, etc. and the control rods 4 have been descended to their full pull-out states. At first, a hoist rope wound on an auxiliary hoist, etc. of the refueling machine (not shown) is connected to the stud 14 of the CR/FS grapple, and then the CR/FS grapple is hung down inside of the reactor pressure vessel 1 to be inserted into the preselected grid. Thus, the separating frame 18 and the main body frame 24 are seated on the control rod 4 and the fuel support 6 respectively. Then, a compressed air is supplied from an air system (working air source) of the refueling machine to the control rod holding air cylinder 17, the coupling releasing air cylinder 22, and the fuel support holding air cylinders 26 respectively. At that time, since the operational timing control mechanism composed of the damper mechanism 30 or the flow restrict mechanism 37 is provided to the coupling releasing air cylinder 22, movement of the coupling releasing air cylinder 22 is delayed relative to that of the control rod holding air cylinder 17 in operation. Therefore, at first the hook 16 of the control rod holding means 50 holds the hoist handle 4d of the control rod 4 and then the third arm 20c of the coupling releasing link mechanism 20 of the coupling releasing means 60 pulls up the release handle 4e of the control rod 4, whereby the coupled state of the control rod 4 and the control rod drive mechanism 8 by using the spud coupling can be released. Like the above, since the operational timing control mechanism is provided, a holding operation of the control rod 4 can be effected by the control rod holding means 50 before the coupled state is released by the coupling releasing means 60. Since the time difference in the operations of the control rod holding air cylinder 17 and the coupling releasing air cylinder 22 is caused by the operational timing control mechanism composed of the damper mechanism 30 or the flow restrict mechanism 37, a time difference can be generated in their respective operations even though the common working air source is employed for the control rod holding air cylinder 17 and the coupling releasing air cylinder 22. In addition, since the common working air source is employed for both air cylinders 17, 22, a time difference can be caused without fail in their operation even when a pressure of the supplied air from the working air source is varied. The operation when the hoist handle 4d of the control rod 4 is held by the control rod holding means 50 will be explained hereunder. After the separating frame 18 is seated on the control rod 4, the piston rod 17a is drawn in by driving the control rod holding air cylinder 17 to pivot the hook 16 such that the hook 16 is shifted to the hooked position shown in FIG. 1. At that time, an operation state of the control rod holding air cylinder 17 can be detected by the limit switch 51 and then the detection result can be displayed on the indicator lamp 29. Accordingly, the operator can check by eye whether or not the hook 16 is located in its hooking position. Next, when the stud 14 is lifted by winding the hoist rope of the auxiliary hoist in this state, only the control rod holding means 50 which consists of the hook 16, the control rod holding air cylinder 17, and the square cylinder member 15 can be lifted up together with the stud 14 while the separating frame 18 is still seated on the control rod 4. Then, the hook 16 grasps the hoist handle 4d of the control rod 4 and lifts it. At that time, it can be detected by sensing a weight applied to the hoist rope whether or not the hook 16 of the control rod holding means 50 has held the hoist handle 4d of the control rod 4. In this way, prior to lifting-up of an entire CR/FS grapple, it can be checked or confirmed whether the control rod 4 is held by the control rod holding means 50, or not. Also, under the condition that the hoist handle 4d is grasped and then lifted up by the hook 16, a hooked state by the hook 4 can be held by a self-weight of the control rod 4 since the hook 16 is formed like a hook-shape. As a result, the control rod 4 is prevented from dropping down and also safety can be maintained even if either supply of the compressed air to the control rod holding air cylinder 17 has been lost or operations have been performed wrong. Subsequently, an operation performed when the coupled state of the control rod 4 and the control rod drive mechanism 8 by the spud coupling is released by the coupling releasing means 60 will be explained hereunder. First of all, when the piston rod 22a is lifted up by driving the coupling releasing air cylinder 22, the first arm 20a and the second arm 20b can be pulled up and also the third arm 20c can be pulled up to its horizontal position while it is being pivoted, as shown in FIG. 4A, FIG. 4B, and FIG. 4C in order. Next, the overall coupling releasing link mechanism 20 as well as the arm 19 can be lifted up by rising up the piston rod 22a further from the state shown in FIG. 4C. Then, the release handle 4e of the control rod 4 can be pulled up by the third arm 20c, so that the coupling of the control rod 4 and the control rod drive mechanism 8 can be released. In addition, the switching member 20d can be pivoted when the third arm 20c is engaging with the release handle 4e and thus the limit switch 33 can be pushed up by one end of the switching member 20d. Then, the limit switch 33 is operated to switch its on/off state and as a result the displaying state of the indicator lamp 29 is changed, whereby the operator can check or confirm by eye that the release handle 4e of the control rod 4 has been actuated. Operations effected when the fuel support 6 is held by the fuel support holding means 70 are explained hereinbelow. Prior to starting the holding operation of the fuel support 6, the contact pieces 34 and the fuel support holding link mechanism 35 are positioned at locations shown by chain double-dashed lines in FIG. 5. The actuating rod 36 is moved upward from this location by driving the fuel support holding air cylinders 26. Thus, the contact pieces 34 are caused to advance to the orifices 6e (f, g, h) of the fuel support 6 and thus advance further more than the position indicated by solid lines in FIG. 5. Forward movements of the contact pieces 34 are continued until the first arm 35a and the second arm 35b are positioned from their downward-convex alignment to their linear alignment, and then the contact pieces 34 are switched to their backward movements when the first arm 35a and the second arm 35b are shifted from their linear alignment to their upward-convex alignment. Then, at the time point when the piston rods of the fuel support holding air cylinders 26 and the actuating rod 36 reach their upper limit positions of lifting strokes, the backward movements of the contact pieces 34 are stopped and therefore the contact pieces 34 are positioned, as shown by the solid lines in FIG. 5. At this time, operation states of the fuel support holding air cylinders 26 can be detected by the limit switches 27 and the detected results can then be displayed by the indicator lamps 29 respectively. Accordingly, the operator can check or confirm by eye whether or not the contact pieces 34 are in their held positions. Then, in the situation indicated by the solid lines in FIG. 5, when the CR/FS grapple is pulled up by winding up the hoist rope of the auxiliary hoist, the upper portions of the orifices 6e (f, g, h) of the fuel support 6 are put on the stepped portions 34a of the contact pieces 34 so that the CR/FS grapple as well as the fuel support 6 can be pulled up together. Since both forward and backward movements of the contact pieces 34 can be prevented in the situation that the upper portions of the orifices 6e (f, g, h) of the fuel support 6 are put on the stepped portions 34a of the contact pieces 34, the fuel support 6 can be prevented from dropping down to thus maintain safety even if either supply of the compressed air to the control rod holding air cylinder 17 has been lost at the worst or wrong operations have been effected. As described above, the CR/FS grapple can be lifted upward after the control rods 4 have been held by the control rod holding means 50 and also the fuel support 6 has been held by the fuel support holding means 70, so that the control rods 4 and the fuel support 6 can be lifted up simultaneously and carried out together from the reactor pressure vessel 1. The CR/FS grapple according to the embodiment of the present invention may be employed when the control rods 4 and the fuel support 6 are carried into the inside of the reactor pressure vessel 1 and then installed therein. In this case, the control rods 4 and the fuel support 6 maybe lifted up and installed simultaneously. In the CR/FS grapple according to the embodiment of the present invention, since the separating frame 18 may be detached from the main body frame 24 by releasing the fitting bolts 31 (see FIG. 2), the fuel support holding means 70 and an assembly consisting of the control rod holding means 50 and the coupling releasing means 60 can be employed independently respectively as separate bodies. As a consequence, in a case that the control rods 4 cannot be pulled out until their full pull-out states due to a failure of the control rod drive mechanism 8, at first only the fuel support 6 can be lifted up by using the fuel support holding means 70 to be picked out from the reactor pressure vessel 1, and then the control rods 4 are hoisted by the control rod holding means 50 and the coupling releasing means 60 to be taken out from the reactor pressure vessel 1. As described above, according to the CR/FS grapple of the embodiment of the present invention, since both the control rods 4 and the fuel support 6 can be held by the control rod holding means 50 and the fuel support holding means 70 and also the coupled state of the control rods 4 and the control rod drive mechanism 8 by using the spud coupling can be released by the coupling releasing means 60, there is no necessity of executing the coupling releasing operation from the pedestal side of the bottom of the reactor, unlike the aforesaid related art. Therefore, an efficiency of the exchange operation of the control rods 4 can be improved by reducing the term of the periodical inspection and the exposure of the operator. More particularly, in contrast to the prior operation, it is possible to reduce the operation time by about thirty minutes per control rod 4. The typical operation time of the prior operation was about 55 minutes per control rod 4. Therefore, about 55% of the operation time can be reduced by using the present CR/FS grapple.