FR2574581A1 - Transfer tool for fuel rods - Google Patents

Abstract

A transfer tool for fuel rods has a tubular casing 10 of sufficient length to enable it to be suspended in a certain volume of water in which a set of fuel rods 12 is submerged, the upper end of the casing being above the water and the tool being aligned vertically over a chosen fuel rod which is at a short distance from the lower end of the tool. The casing has a cylinder at a distance from its ends, in which a plunger provided with a tubular push rod can slide from one end to the other of the cylinder. A control mechanism whose control can take two positions is attached to the upper end of the push rod of the plunger and has a member which can move freely downwards over a short path with the result that the control, taking up its second position, results in the release of the rod by placing in a release position a latching device fastened to the lower end of the push rod of the plunger. The position for releasing the rod is maintained until the rod returns to its original position, the latching device being maintained in its position for gripping the rod until the control has returned to the second position.

Description

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  Sets of fuel rods used in power plants

  nuclear are typically of the type comprising a group of combustion bars

  tables arranged in a square, each bar being retained individually and

  elastically so as to allow its removal and replacement when

  that a top holding mechanism is removed. When the fuel rods of an assembly are exhausted, the assembly is stored in a swimming pool or deep water tank because the

  bars are still radioactive and it is necessary to check periodically

  only, for each fuel rod, if it has coating defects or leaks. However, in this operation, no part of a bar can be less than 1.50 m to 1.80 m below the surface of the pool water; There are tools that allow you to grab and release individual fuel rods and then reintroduce them into the assembly.

  bars, but their operation is not reliable enough to satisfy

  to do at a high level of security and they are relatively ineffective, because to use them, it takes approximately half an hour for input,

  removing and reinserting a fuel rod to be checked and tested.

  The general object of the present invention is to provide a tool intended for removing a fuel rod from a set of spent rods to allow control and testing, to reintroduce it into the original rod assembly or in another, or to place it in a storage box or in a container, this makes it possible to carry out the handling of

  fuel rods safely and efficiently.

  This object is achieved according to the invention with a tool presenting itself

  in the form of a long tubular casing designed to be suspended from a lift

  teur-transporter, and a large part of which is in the pool containing the fuel assembly, the bars of which must be treated. The middle part of the casing is a cylinder containing a piston actuated by a pressurized fluid and equipped with a tubular connecting rod which can slide in leaktight manner in the ends of the cylinder and extending downwards.

  through the lower part of the housing, and provided with a locking device

  rusting bars. The tubular connecting rod also extends upwards in the upper end part of the housing and supports a control mechanism provided with a two-position control and an element extending downwards and passing through the piston rod. When the control is in its second position, a short push down is given to the control element.

  control which implements the position of the corresponding locking device

  laying down when the bar is released, a position which is maintained until

  that the bar is in its first position, and the position of the dispo-

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  lock sitive corresponding to entering the bar is then

maintained positively.

  In the use of such a tool, the casing is lowered on a

  fuel rod chosen, by means of the elevator, until its end

  lower mitd is only spaced a short predetermined distance apart

  of this bar above which it will be aligned. The hydraulic system

  used to drive the piston is actuated so as to place the piston at the lower end of the cylinder, the control being in its second position, and therefore advancing the locking device in its second position for releasing the bar, position in which the bar is then entered by returning the control to its first position. The pressurized fluid is then admitted into the cylinder below the piston to lift the bar from the assembly and to make it rise in the part

  bottom of the casing, the length of which is preferably such that it

  put the fuel rod to be contained therein over substantially its entire length. A specific object of the invention is to ensure that the means of

  locking is maintained in its independent bar gripping position

  especially the source of energy which actuates the control device. For this purpose, the locking means is positively held in this position, unless the control moves it to the second position, and

  until it does so, preferably by means of elastic means

  differentiated, automatically, to realize the position of

  gripping the bar of the locking means.

  A second specific aim of the invention is to ensure the maximum of

  safety in service, this goal being achieved by an interlocking device

  lage which prevents the unlocking of a bar, unless the piston is close

from its lowest position.

  - A third specific goal is to ensure that the bars

  fuel will not be damaged during removal or replacement

  cement, this object being achieved by the use of pressurized water to drive the piston in either direction, as well as by adjustable means for controlling the pressure of the water so as to limit the forces exerted on the bar when it is removed or inserted into a fuel assembly. It is recommended, although this is not necessary, that the water be from the reservoir water and that the control is also actuated by the pressurized reservoir water., A fourth specific purpose consists in using an opening in the part lower crankcase, and this for several purposes, one of which is to provide, when the passage is open, a natural thermal circulation

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  of water around the bar when it is contained in the casing, another aim being to allow this passage to be connected by a conduit controlled by pump, to a fission product detector system for detecting coating defects fuel and to finally rinse the tool and drain the water. A fifth specific goal is to provide a tool designed for both assembly and service, this objective being achieved by the housing, the tubular piston rod and the control element of the gripping fingers.

composed of removable sections.

  A sixth specific object of the invention is to allow the con-

  bars, objective achieved by the use of one or more underwater television cameras mounted on the tool and adjusted so as to allow the tool to be placed precisely with respect to the chosen fuel bar or so to allow to precisely position a selected fuel rod relative to the location in which it must be introduced, and also to allow visual control of a grabbed bar

during its withdrawal.

  A specific seventh object of the invention is to provide a tool whose exposed surfaces will not be repeatedly wetted by

  contaminated and potentially radioactive pool water.

  Other objects of the invention will appear from the description

  attached to the preferred embodiment and the appended claims.

  There are a number of patents dealing with the problem of removing and replacing items such as control rods and fuel rods for nuclear reactors, and there are tools

for these applications.

  All the tools offered or existing have locking devices, which are means making it possible to control devices for grasping or releasing these elements, and means making it possible to remove these

  items seized or put them in a particular place.

  It has been proposed to use hydraulically controlled devices for such tools. US Patent 4,244,616 describes a cylinder intended to exert a permanent downward push on an element, the other operations being carried out by the displacement of a rod extending axially through the cylinder and actuating the device lock at

  by means of a handle located on its upper end.

  The use of a hydraulic control means for removing an element is described in US Patent No. 4,259,153, this means

  being mounted on a support external to the tool body.

  U.S. Patent No. 3,905,634 has described the use of -4 bellows at the bottom end of the tool to implement the

  locking and gripping positions.

  The applicant does not know of any prior art comprising the above patents and which could suggest a tool in accordance with the present invention, and in which a cylinder block and piston with long stroke and

  hydraulic control would be incorporated into the tool, a tubular connecting rod

  the two ends of the cylinder. A control element, responding to a two-position command, is fixed to the upper end of the connecting rod, to the lower end of which is fixed the locking device. The

  control device comprises an element extending downwards and passing through

  the piston and, when the control is in the second position, a short downward stroke takes place and places the locking device in its bar release position, position in which

  it is maintained until its control is in its first posi-

  tion in which it is positively maintained.

  The length of the cylinder is such that, when the piston passes from its low position, in which a bar can be grasped or released, to its high position, the element is freely pulled into the interior of the tool. The latter can then be ordered again so as to rest the bar seized in its original location or in another location, the block then driving the piston into its low position, and the

  locking then actuated by the control element for the release

ment of the latter.

  The accompanying drawings represent a preferred embodiment of the invention and: Figure 1 is a somewhat schematic view of a tool installed to remove or install fuel rods, the drawing of the tool being exploded for a purpose for simplification, FIG. 2 is a partial section, on a substantially enlarged scale, taken vertically through the upper end of the upper part of the tool, FIG. 3 is a similar section passing through the junction of the upper and central parts of the tool, Figure 4 is a similar section passing through the junction of the central and lower parts of the tool, Figure 5 is another similar section passing through the lower end of the tool, Figure 6 is a section partial, on a larger scale, of the locking device,

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  Figure 7 is a somewhat schematic side view of the control panel, and Figure 8 is a schematic view of the hydraulic system used

to order the tool.

  The transfer tool for fuel rods shown in the drawings has a housing indicated generally by the reference 10 and is shown in Figure 1 in suspended form and of length such that a significant part of its length is located inside a swimming pool or water tank 11, at a certain depth, inside which is a set of fuel rods indicated generally by 12. The means

  by which the housing 10 is thus maintained comprises a transport elevator

  conventional tor 13 carried by an overhead beam 14 and a pneumatic lifting block 15 connected to a reinforcement 16 which is provided with the upper end

of the tool.

  The housing 10 comprises three parts, namely the upper part A, the lower part 0lB and an intermediate part 10C. The extremities

  of the intermediate part 10C are removably assembled at the ends

  mites close to parts 10A and 10B by fittings marked so

general by reference 17.

  Each fitting 17, (see Figures 3 and 4), includes a sleeve 18 whose shape and dimensions are studied to adjust to the end

  close to the two housing parts to be assembled and which carry seals 18A.

  The two ends of each part of the housing have an annular groove

  laire 19, and each sleeve 18 is also provided with a pair of annular grooves 20 which are spaced so as to allow a collar 21 to be there

  retained as well as in the near groove 19 of a part of the casing.

  The sleeve 18 of each fitting 17 thus closes the ends close to the parts interconnected with the intermediate part O10C serving as a cylinder in which is mounted a piston block indicated generally by the reference 22. The piston block 22 (see FIG. 4) consists of a piston sleeve 23 having an upper end or enlarged cylindrical head 23A providing a shoulder 23B. The other end or lower end 23C of the piston sleeve 23 is threaded to receive a nut 24 having the shape of a sleeve whose internal diameter is identical to that of the piston sleeve and whose external diameter is the same as that of the head 23B. A compressible piston 25 is mounted on the sleeve of

  piston 23 and is retained between metal discs 26 and against the shoulder-

  ment 23B correctly compressed to seal with the walls of the cylinder 10C by adjusting the nut 24. The head 23A and the nut 24 have the same

axial length.

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  -6- The sleeves 18 are identical, but arranged in an opposite manner, and their axial cylindrical recesses 27 open into the cylinder 10C and have a shape and dimensions such that they freely receive the nut 24, in the case of the sleeve of the lower connector 17, or the head 23A in the case of the sleeve of the upper connector 18, and an axial length such that the engagement of a piston disc 26 with the sleeve prevents the closure of the passage 28 which opens into the cylinder. Each sleeve 18 is also provided with an opening 29 diametrically opposite to its opening 28, and communicating with the interior of the adjacent part 10A or 0lB by a passage 30. This last passage 30, which opens into the part 10A, serves as purge hole. The purpose of

  passage 30 leading into part 10B will be described below.

  Each sleeve 18 has an axial lumen opening into a socket 31 to seal it and is threaded to receive a sealing gland 32. The piston assembly 22 is fixed to a tubular piston rod 33 whose length is such that it can slide between the two sleeves 18. The piston rod 33 is shown with two sections, the section 33A fixed in the sleeve 23 and extending upwards in the upper part of the casing 10A and the section 33B fixed in the nut 24 and extending downward through the lower part 10A and a guide tube 34 which is held in the lower part 10B by a spacer 35 and by a terminal cap 36 (see FIG. 5). The end cap 36 has an annular groove 36A allowing it to be connected at the end

  lower part of lOB by a lock 21 in the same way as are inter-

  connected the three parts of the housing.

  As shown in Figures 1 and 8, the piston assembly is raised and lowered by the desired length, this stroke being four meters (by way of non-limiting example) for example by pumped water

  from a reservoir 37 by means of a conduit 38 equipped with a submersible pump

  geable 39 and controlled by a control 40. The duct 38 is provided with a valve 41 allowing the adjustment of the flow rate to and through the four-way valve 42 provided with a pipe 43 connected to the upper opening 28 and d a line 44 connected to the lower opening 28, each line serving to deliver pressurized water to one end of the cylinder 10C, the other end serving to return the water from the other end of the

  cylinder 10C towards the reservoir 37 via a pipe 45.

  Lines 43 and 44 have return lines 46 and 47 each of which is connected to line 45 and which are provided with a safety & pressure valve

adjustable 48.

  In practice, the water from the reservoir 11 is used as a hydraulic source. For this purpose, a supply line 49 extends

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  down into the tank 11 and is provided with a control valve 50, a filter F and a pump 51 actuated by a switch 52 controlled by float. The tubular piston rod 33 has a nose 53 fixed at its lower end (see FIGS. 5 and 6) and a control 54 (see FIG. 3) in section 10A of the casing and fixed at the upper end of the latter. The control 54 is of the current type, actuated by hydraulic pressure, with a piston rod 54A which advances by a predetermined reduced stroke when

  pressurized fluid is applied to the control. Command 54 also has

  ment a spring 54B (see FIG. 8) used to return the piston rod 54A when the pressurized fluid no longer acts on the control. The piston rod 54A of the control 54 is connected to a tubular control element or rod 55 consisting of upper and lower sections 55A and 55B respectively, with a threaded interconnection 55C inside the assembly

piston 22.

  The control spring 54B is assumed to have no resistance.

  tance sufficient to ensure the implementation of a desired function and described below of the invention. For this reason, section 55B of the control element has, (see FIG. 5), a spring stop 56 which can slide in the tubular piston rod 33 and which maintains a return spring 57 under a suitable compression, acting against the nose 53 which has

  a support 58 opening into a counterbore 59.

  A locking device, indicated generally by the reference 60, see FIGS. 5 and 6, is actuated by the control 54, the

  role is to give element 55 a short blow down and is also

  ment controlled by the spring 57 whose role, when the control 54 is relieved of the hydraulic pressure, consists in positively effecting the return stroke of the element 55. The lower end of the element 55 comprises an element 61 having cam-shaped portions disposed opposite and extending freely between the fingers 65 in the nose 53 to grip the upper end of a fuel rod 66 which is shown

  as having a socket 67 provided with an internal annular recess 68.

  The gripping fingers 65 are held so as to be able to pivot in the bore 59 of the nose 53 by transverse pivots 69 housed between the cam-shaped parts 64 and 65 and have axially spaced cam-shaped parts 70 and 71; thus, when the rod 55 is biased downwards by the operation of the control 54, the cam 62 engages with the cams 70 of the fingers, the outer and lower ends of which are then pushed down one against the other and, when the hydraulic pressure is removed from the control 54, the spring 57 lifts the rod 55

  to bring the cams 65 into engagement with the cams 71 of the fingers, their ends

  external mites then being separated from each other. The outer ends of the fingers have shoulders disposed externally 65A and, when the control 54 is activated, they are positioned close enough to one another so that the shoulders 65A can be introduced into the socket of the fuel rod 67, the shoulders then being trapped in the annular recess 68 when the spring 57 is activated by the locking device. For fuel rods whose outer shoulders are to be gripped by the locking device, fingers are used which are spaced apart from each other in their fuel rod release position and which are drawn towards each other.

  others to perform the bar entry relationship.

  Returning to FIG. 8, it will be noted that a two-way valve 72, acting on the control 54, has a pipe 73 provided with a

  adjustable pressure regulating valve 74 connected to the inlet pipe

  pressure fluid 38, and a pipe 75 connected to the canali-

  sation 45 by which water is returned to the reservoir 37. A pipe 76 in communication with the control 54 has two functions: either to deliver a control pressure to the latter when the control valve is in its second position, or to remove of this command the hydraulic pressure

  when the control cam 72 is in its first position.

  The long stroke of the piston 22 requires that the pipe 76 going to the control 54 from the two-way control valve 72 be equipped with a wound and elastic end portion 76A of sufficient length in the upper part IOA to adapt to a such a race. The part 76A is connected to the pipe 76 by a terminal cap 77 provided with a seal 78 and an annular groove 77A necessary to allow its coupling to the housing part 10A by a latch 21. A bleed or breather assembly 79 , connected to the end cap 77 is placed in communication with the inside of the casing part 10A by a passage 80 passing through the end cap 77. If we now return to the operation of the tool, it is

  normally positioned as shown in Figure 1 with the lower end

  of the guide tube 34 separated by a short distance above the selected fuel rod from the block 12 and aligned with the latter, the piston being above its low position. When the control valve 72 is normally placed in its first position, so that the spring

  57 resiliently but positively holds the fingers 65 in their positions

  bar entry, the operator located at station 81 passes the control valve 72 to its other position (second position) where the

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  pressurized fluid delivered to the control 54 causes the advancement of the control element 55 and the cam action on the fingers 65 to move the latter into their closed position or bar release position, into which they can enter the bar sleeve 67. The control valve 42 is now adjusted to deliver the pressurized water to the cylinder 10C, advancing the tubular rod 33 until the fingers 65 are located

  inside the sleeve 67, and the piston 25 is next. lowered. The opera-

  The valve now places the control valve 72 in its first position to release the control 54 from the control pressure, so that the spring 57 again positively returns the fingers 65 to their gripping positions.

bar and keeps them there.

  The operator now places the valve 42 in its position where the pressurized water drives the piston 25 upwards, the grab bar 66 being withdrawn from the bar assembly upwards and entering section 10B of the casing, section the length of which allows the bar to be stored there. The current fuel rods being 3.60 m long, the section LOB is preferably substantially longer, for example 3.90 m. The bar being in the part 10B, the opening 29 being at the lower end of the cylinder lOC allows normal thermal circulation of the water in the tank in this section. If you wish to be alerted of coating leaks, a tube (not

  shown) is connected to the opening 29 and to the intake of a per-

  pumping the water from the lOB part through a fission product detection system. Neither the pump nor the detector are shown. A thermostatic relief valve 82 can be actuated to allow circulation through the part 1OC if the temperature at

  the interior reaches a predetermined value during such a test.

  To allow the tool to be positioned precisely with respect to a selected fuel rod, the guide tube 34 is equipped with one and preferably with two sets of supports 83 and 84, each of which serves to support

  an underwater television camera 85 adjusted so as to be able to see the former

  end of the head of a fuel rod to be extracted, the fuel rod being removed from the set of bars examined, and the position of the tool relative to the chosen location for its return or its replacement

being fixed precisely.

  Due to the depth at which the fuel rods are located, it is recommended to have other means enabling the position of the piston 22 to be displayed. To this end and by way of example, such means (see FIG. 5) , the control 54 is shown capable of a collar 86 carrying a magnet 87 which interacts with a conventional block of magnetic reading switch 88 providing visual information on the following position of the piston thanks to a series of lamps not shown, at the rate of a lamp for each switch, and thus lit when

  the magnet 87 is aligned transversely with the switch.

  It is of course important that a bar removed from the bar set is not released prematurely. To this end and as an example

  means to accomplish this function, the switch 88A of the stack

  of switches 88 which represents the position of the piston 25 when it is close enough to its low position so that the locking device can be safely placed in its position corresponding to the release of the bar, is used to excite the solenoid that opens the valve

  normally closed 89 located in line 73. In this posi-

  tion of the piston 25i the bar release position of the locking device must be opened before the piston 25 reaches its lower position so that a bar can be gripped and, in the case of a gripped bar, the latter will then be practically rested when released and then completely rested when the piston is at

  bottom, position in which the series of switches 88B is closed.

  Referring to Figure 7, the control panel 90 located at the operator station 81 is shown with the control handle 91 for the valve 42 and the control handle 92 for the valve 72. The television screen 93 allows the observer to observe the locking device and the bar being withdrawn or replaced while the control 94 allows the valve 41 to be adjusted to control or vary the speed of movement of the piston and the force exerted by the latter in the

both directions.

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Claims (27)

  1. Transfer tool for fuel rod, characterized in that it comprises a tubular casing (10) of such a length that it can be suspended from a location located above the water in a tank , in which a set of fuel rods is stored at a significant depth, the lower portion of the casing extending downward in the water and being aligned vertically on a rod. (66) selected from the bars of this assembly, and the lower end of the tool being near said bar and directly above it, elements (18) spaced axially inside said casing and spaced from the ends of the latter to produce a cylinder, a piston ( 22) being able to slide in the latter, a means controlled by pressurized fluid controlled by a valve and in communication with said cylinder and being able to give an alternative movement to said piston between lower and upper positions, a   tubular connecting rod (33) which can slide through the elements which define   feels this cylinder and connected to said piston to move with the latter, a bar locking means (60) which can assume bar release and bar gripping positions and connected to the lower end of said piston rod, and a means capable of implementing said positions and comprising a control fixed to the upper end of said piston rod, a control element (54) being in the piston rod and being able to move between the first and second positions, said control element capable of being moved by said control in said second position, the control element being connected to the locking means so that such movement achieves and maintains the bar release position, said control means also comprising means controlling said control element except when said control is used   to make such a move, to establish positively and to conserve   to the bar gripping position of the locking means, so that, with the means actuated by hydraulic pressure serving to bring said piston into its low position, and with said control used to effect said movement, said locking means is positioned for enter the selected bar, said bar being entered when this command is not   thus employed, then withdrawn when said hydraulic fluid actuated means   Pressure die is used to drive the piston upwards, said cylinder and the bottom part of the casing being long enough that the gripped bar can be freely removed from the set of bars and entered into said bottom part, so that, the means actuated by fluid under pressure being actuated to return the piston to its low position, the bar   seizure can be pushed down, rested and released in its place -12- -12- 2574581 ment original or in another.   2. Fuel rod transfer tool according to claim   1, characterized in that a control (72) for the control device   de is situated outside the upper end part of the casing, said control having first and second positions, the displacement being effected in the second position to implement the bar release position of the locking means, and a coupling between said control and the control element which comprises an elastic coil (76A) provided with a sufficient number of turns inside the upper part of the casing to adapt to the stroke of the piston from its position   upper to its lower position.   3. Fuel rod transfer tool according to claim 2, characterized in that the control device is actuated by a fluid under pressure.   4. Fuel rod transfer tool according to claim   3, characterized in that the hydraulic pressure used for action-   The control element and the hydraulic pressure used to move the piston alternately are supplied by pressurized water from a tank.   5. Fuel rod transfer tool according to claim 4, characterized in that the water in the tank is water supplied by the   tank in which the set of fuel rods is located.   6. Transfer tool for fuel rod according to claim 1, characterized in that the means actuated by hydraulic pressure comprises outside the casing a control (41) which can adjust the pressure of the fluid delivered to the piston and consequently its speed of displacement and the force exerted by the latter.   7. Transfer tool for fuel rod according to claim   1, characterized by the fact that the tool comprises at least one tele-video camera   underwater vision (85) attached to the lower end of the tool and an observation screen above the water and adjacent to the portion of the end   upper part of the tool, the camera being adjusted so that the location   ment for or from a fuel rod can be observed and that one can   examine a removed or reinstalled fuel rod.   8. Fuel rod transfer tool according to claim 1, characterized in that the tool comprises a guide tube (34) to   the interior and supported by the lower part of the housing which receives free-   the piston rod and the locking means.   9. Fuel rod transfer tool according to claim 8, characterized in that at least one underwater television camera 13- is fixed to the guide tube, an observation screen being located above the water and adjacent to the upper end portion of the tool, the camera being adjusted so that one can observe the location intended for or occupied by a fuel rod and that one can examine a fuel rod in progress withdrawal or replacement. 10. Fuel rod transfer tool according to claim   1, characterized in that the lower portion of the casing has one or   groove (29) adjacent to its upper end allowing a stored bar to be cooled by thermal circulation upwards from the open end of the casing, and to rinse it through said opening or   said lower portion of the housing.   11. Fuel bar transfer tool according to claim, characterized in that said lower portion comprises a   relief valve (82) thermostatically actuated and operable   born to allow such thermal circulation in the case where a system   fission product detector is connected to said opening.   12. Fuel rod transfer tool according to claim   1, characterized in that the control element is rigid.   13. Fuel rod transfer tool according to claim 12, characterized in that the control element extends downward through the piston rod from the upper end into the end lower of it.   14. Fuel rod transfer tool according to claim 12, characterized in that the control means allowing the control element to be held in a position which retains the locking means in the bar gripping position is elastic and is retained by the lower end of the piston rod and connected to the control element. 15. fuel rod transfer tool according to claim 1, characterized in that the control means by which the control element is held in a position retaining by means of locking its bar gripping position, is elastic and incorporated by control means so as to resiliently place and hold the control element in said position.   16. Fuel rod transfer tool according to claim 1, characterized in that a measuring means is located outside the casing adjacent to its upper end portion to provide   visual information such as the location of the locking means.   17. Fuel rod transfer tool according to claim 16, characterized in that the measuring means comprises a bench -1} 4- -2574581   switches (88) fixed to the outside of the upper part of the casing and a magnet (87) supported by the control (54) which actuates any switch of said bench laterally to the latter.   18. Fuel bar transfer tool according to claim 1, characterized in that a means is provided to prevent the operation of the control so as to implement the bar release position of the locking means, unless the piston is in a predetermined position such that a fuel rod would be at least partially   rested in a desired location.   19. Fuel rod transfer tool according to claim 18, characterized in that a signaling means is actuated when   the piston is in said predetermined position.   20. Fuel bar transfer tool according to claim 19, characterized in that a signaling means can be actuated   when the piston is in said lower position.   21. Fuel bar transfer tool according to claim 18, characterized in that a magnetically controlled switch (88) is mounted outside the upper part of the casing in a position representing said predetermined position of the piston and a magnet (87) is movable with the control (54) and actuates said switch when it is located laterally to the latter, and that a means controlled by the action of such a switch makes the operation of such a control effective for activate the control which implements the bar release position of the locking means.   22. Fuel rod transfer tool according to claim 21, characterized in that the control is actuated by a pressurized fluid system which includes a two-position valve control and that an electrically controlled valve normally blocks the flow pressurized fluid to this valve and is actuated to open said valve   when said switch is actuated.   23. Fuel rod transfer tool according to claim 1, characterized in that the casing comprises three tubular sections (1OA, lOB, 10C), end caps and removable couplings between said sections and said end caps, as said connecting rod piston has two sections (33A, 33B) detachably connected to opposite ends of the piston, and the control member has two sections   removably interconnected in the center of the piston rod.   24. Fuel rod transfer tool according to claim 1, characterized in that the control element comprises at its lower part first and second cam-shaped parts (65) axially spaced and located in the end lower of said piston rod, and that the locking means comprises a pair of gripping fingers (65A) for bars rotatably coupled to said lower end of piston rod between said cam-shaped portions, each finger having a first and a second cam-shaped part located with the pivot axis (69) between them and which are spaced and arranged so that, when the said control element is moved in one direction, the first cam-shaped parts of that -that are brought in   taken with the first cam parts of the fingers and realize the posi-   bar release of the latter and that, when the control element is moved in the opposite direction, the second cam-shaped parts brought into engagement with the second cam-shaped parts of the fingers   and realize the gripping positions of the bars of the latter.   25. Fuel rod transfer tool according to claim   23, characterized in that a spring (57) supported on the lower end   of the piston rod is connected to the control element and can be actuated to elastically oppose the movement of the control element in a direction of release of the bars from a predetermined position in   which fingers are in their bar grab positions.   26. Transfer tool for fuel rod according to claim-   tion 1, characterized in that a control means 81e comprises a portion located above the water and an immersed portion, said immersed portion being connected to the lower end of the tool in a position allowing inspection a fuel rod when removed and returned to the   same set of bars or to another, then released.   27. Fuel rod transfer tool according to claim 1, characterized in that at least one control means comprises an examination portion situated above the water and an underwater portion fixed to the end lower part of the tool, said portion located above the water   being located adjacent to the upper end portion of the   til and the underwater portion of the tool being positioned so that one can observe the location of a fuel rod or intended for it and examine a fuel bar being removed or returned in place.