Abstract:
A telescoping rod control cluster assembly change tool for moving control rod assemblies among fuel assemblies in a nuclear facility. The operation of the tool is completely mechanical and the telescoping feature enables the tool to have a relatively low profile when it is being moved and stored without housing a control rod assembly. Rigidly supported alignment cards guide a gripper that attaches to the control rod assembly as the control rod assembly is withdrawn into the tool with the alignment cards preventing any lateral or rotational movement of the gripper.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Provisional Application Ser. No. 61/316,956, filed Mar. 24, 2010, Attorney Docket NSD2010-003. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    This invention relates to a device for transporting control rod assemblies between fuel assemblies in a facility associated with a nuclear power generation plant and, more specifically, to a device for transferring control rod assemblies among fuel assemblies that uses an overhead crane as its primary lifting mechanism. 
         [0004]    2. Related Art 
         [0005]    Fuel for a nuclear reactor used to create steam and, ultimately, electricity, generally is in the form of fuel rods containing a fissile material. When fuel rods are being stored, the fuel rods are typically supported in nuclear fuel assemblies arranged as spaced parallel arrays. Fuel assemblies are stored in racks in a protective medium, such as water containing boric acid. In addition to the fuel rods, poison rods and/or water displacer rods are dispersed throughout the fuel assemblies to control the fission process. Poison rods generally include a plurality of elongated rods, each containing a neutron absorbent material, which fit in longitudinal openings, or thimbles, defined in the fuel assemblies. The top end of each poison rod is attached to a web or spider, thereby forming a poison rod assembly. A T-shaped bar or threaded hub is affixed to the top of the web or spider creating an easily accessible attachment point for lifting a poison rod assembly so it may be transferred from one fuel assembly to another. 
         [0006]    Because the poison rods, which are approximately 12 to 14 feet (3.66 to 4.27 meters) long, are only connected by the web or spider located at the top of the poison rod assembly, the lower end of the poison rods move freely, and, as such, can be difficult to reinsert within a second fuel assembly without the aid of a means for alignment. Prior art transfer devices provided comb assemblies as an alignment means. A comb assembly consists of at least two plates having slots corresponding to the rows of poison rods in the poison rod assembly. The plates are oriented at 90° to each other. As such, when the plates are positioned on top of each other, a grid is formed with an opening for a poison rod at each intersection of the slots. To provide extra stability, comb assemblies typically have two spaced grids. Each comb grid is typically formed of four plates, two plates with channels extending in one direction and two plates with channels extending in perpendicular direction. The plates are divided so that the comb assemblies may be moved aside while the web portion of the poison rod assembly is being lifted from the fuel assembly. Once the web portion of the poison rod assembly is above the comb assemblies, the comb assemblies are brought into place providing support and guidance for the poison rods. 
         [0007]    As shown in Hornack et al., U.S. Pat. No. 5,325,408, some prior art transfer devices use a winch located at the top of the transfer device to lift the poison rod assembly. Movement of the transfer device itself between fuel cells, is accomplished by a gantry crane in the fuel cell storage facility. Thus, this type of prior art lifting device consists of at least two lifting means, one to lift the transfer device itself, and one to lift the poison rod assembly within the transfer device. Burton et al., U.S. Pat. No. 6,327,322, recognize the advantage of the transfer device functioning with a single lifting mechanism. However, movement of the transfer device was still awkward because of the extended length of the transfer mechanism which was suspended from the gantry crane. 
         [0008]    According, a further improvement in the transfer mechanism is desired that will improve its reliability and ease of operation. 
       SUMMARY OF THE INVENTION 
       [0009]    The foregoing object is achieved by a transfer device for moving a control rod assembly between fuel assemblies using an overhead crane. The control rod assembly has a plurality of spaced control rods which are supported from an overhead web or spider frame which aligns the control rod with guide thimble tubes in the fuel assemblies in which the control rods are designed to be inserted. In accordance with this embodiment, the transfer device includes an upper latch tube assembly having a longitudinal axis. An elongated inner member is slidably supported within the upper latch tube assembly is operable to telescope substantially coaxially with the longitudinal axis. A gripper assembly is supported from the elongated inner member and has an actuation arm reciprocably slidably supported within the elongated inner member to move substantially along the longitudinal axis a selected distance to actuate a gripper at one end of the gripper assembly. Another end of the gripper assembly is connected to an end of the elongated inner member which at another end includes a bail which is adapted to be attached to an overhead crane. An interlock assembly is attached to the upper latch tube assembly and selectively couples the elongated inner member to the upper latch tube assembly at one or another of two elevations along the longitudinal axis, with the one elevation being in a substantially extended position and the another elevation being in a substantially retracted position. An elongated enclosure assembly extends along the longitudinal axis and has a length at least substantially equal to the height of the control rod assembly. The length of the elongated closure assembly is substantially rigidly connected to one end of the upper latch tube assembly and has another end configured to key on the top of the fuel assembly or a can in which the fuel assembly is inserted. A plurality of alignment cards are laterally disposed in a spaced, tandem array along the length of the enclosure assembly with each of the alignment cards having openings that are aligned and sized to pass a control rod of the control rod assembly, so that the control rods are withdrawn into the enclosure assembly in alignment with the guide thimble tubes of the fuel assembly. The alignment cards further include a central opening through which the gripper assembly can pass through and at least some of the alignment cards central opening is sized to pass at least a portion of the elongated inner member. 
         [0010]    Preferably, the alignment cards prevent rotation of the gripper assembly whether or not the gripper assembly is attached to a control rod assembly. Desirably, the gripper assembly includes a central body having a generally rectangular cross section profile that fits in a corresponding central opening in at least some of the alignment cards. In one embodiment, the gripper assembly includes at least one laterally extending fin that fits in a corresponding slot in at least some of the alignment cards. Preferably, the gripper assembly includes a plurality of laterally extending fins that are spaced around a circumference of the gripper assembly and are desirably, equally spaced around the circumference of the gripper assembly. In another embodiment, a distal lateral end of the fin is contoured to have an enlarged cross section that fits in a corresponding opening in at least some of the alignment cards. Preferably, the contour is round and the distal lateral end of the fin has a bullet nose in at least one end in a direction of travel of the gripper assembly. Desirably, the distal lateral end of the fin has a bullet nose in an end on either side of the direction of travel of the gripper assembly. 
         [0011]    In another embodiment, the gripper assembly is biased in a latched condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A further understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
           [0013]      FIG. 1  is a perspective view of a spent nuclear fuel storage pool; 
           [0014]      FIG. 2  is a perspective view of a poison rod assembly partially withdrawn from a fuel cell; 
           [0015]      FIG. 3  is an elevational view of rod cluster control assembly change tool of this invention; 
           [0016]      FIG. 3A  is a cross sectional view of a rod cluster control change tool shown in  FIG. 3 ; 
           [0017]      FIG. 3B  is an elevational view, partially in section, of the rod cluster control change tool shown in  FIGS. 3 and 3A  with the latches of the upper latch tube assembly engaged in the upper slots of the inner support tube; 
           [0018]      FIG. 3C  is an elevational view, partially in section, of the rod cluster control change tool shown in  FIGS. 3 and 3A  with the latches of the upper latch tube assembly engaged in the lower slots in the inner support tube assembly; 
           [0019]      FIG. 4  is a perspective view of the upper latch tube assembly of the rod cluster control change tool shown in  FIG. 3 ; 
           [0020]      FIG. 5  is an elevational view partially in section of the upper latch tube assembly shown in  FIG. 4 ; 
           [0021]      FIG. 6  is an elevational view of the enclosure assembly of the rod cluster control change tube of  FIG. 3 ; 
           [0022]      FIG. 7  is an isometric view of the lower platform of the enclosure assembly shown in  FIG. 6 ; 
           [0023]      FIG. 8  is a plan view of an alignment card of the enclosure assembly shown in  FIG. 6 ; 
           [0024]      FIG. 9  is an isometric view of the inner support tube assembly of the rod cluster control change tube of this invention shown in  FIG. 3 ; 
           [0025]      FIG. 10  is a cross sectional view of the gripper assembly of the rod cluster control change tube shown in  FIG. 3 ; and 
           [0026]      FIG. 11  is a plan view of the gripper assembly shown in  FIG. 10 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    Referring to  FIG. 1 , there is illustrated a spent fuel storage pool  10  which contains a plurality of spent nuclear fuel racks  12 . The spent fuel pool  10  is a sealed enclosure comprised of concrete  14  and a sealed metallic liner  16 . The spent fuel pool  10  is filled with a shielding medium, such as water containing boric acid  18 . Each fuel rack  12  includes a plurality of vertically oriented spaced apart fuel cells  20 . Each cell  20  is sized to received a fuel assembly  50  (described below). Each cell  20  has a metallic can  22  affixed to the top of the cell  20 . The can  22  may include a square funnel to guide a fuel assembly  50  into its storage position. As shown in  FIG. 2 , the can  22  includes two bores  24 ,  26  in raised plates  25 ,  27  at diagonally opposite corners. The remaining corners of the can  22  define standoff plates  28 ,  30 . However, it should be appreciated that the fuel assembly top nozzle may have the bores  24 ,  26 , raised plates  25 ,  27  and standoff plates  28 ,  30 , without departing from the intent of this embodiment. 
         [0028]    Referring to  FIG. 2 , a poison rod assembly  40  is shown partially extracted from a fuel cell  20 . Each fuel assembly  50  is formed in part from fuel rods  52  which are intermixed with poison rods  42 . The fuel rods  52  are generally positioned on the periphery of the fuel assembly  50  and the poison rods  42  are generally positioned in an inner portion of the fuel assembly  50 . The poison rods  42  are joined at their top portions by a support web  44  which may take the form of the spider  44  illustrated in  FIG. 2  or other rudimentary web form such as that described in U.S. Pat. No. 6,327,322. A hub  46  is centrally attached to the support web  44  extending upwardly, forming an easily accessible attachment point for lifting the poison rod assembly  40 . When the poison rod assembly  40  is positioned within the fuel assembly  50 , each poison rod  42  is disposed within a thimble  48  mounted in the fuel assembly  50  between a top nozzle  32  and a bottom nozzle which is not shown. 
         [0029]    Referring to  FIG. 1 , a poison rod assembly transfer device  70  of the present invention is illustrated within a spent fuel pool  10 . The transfer device  70  is suspended within the spent fuel pool  10  by an overhead crane  60 . The overhead crane  60  is coupled to a moveable walkway  62  and gantry  63 . The moveable walkway  62  and the gantry  63  are mounted on walkway rails  64  located above the water line  18  of the spent fuel pool  10 . The crane  60 , moveable walkway  62  and gantry  63  are used to lift the transfer device  70  and a poison rod assembly  40  and move them between fuel cells  20 . The transfer device  70  is seated on a fuel cell  20  and attached to a poison rod assembly  40  as detailed below. Though, the transfer device discussed hereafter is described with regard to the movement of a poison rod assembly, it should be appreciated that the transfer device can also be employed to move any control rod assembly, such as an annular burnable absorber assembly, water displacement rod assembly, or neutron source assembly with only a modification to the gripper attachment point to provide a compatible coupling of the transfer device to the assembly to be moved. Similarly, the transfer device may be used in the main containment of such a facility to move control assemblies within the core of a nuclear reactor, though that might not be the most efficient use of the apparatus. 
         [0030]    The transfer device  70  is shown in more detail generally in  FIGS. 3 ,  3 A,  3 B and  3 C, with different sections shown in more detail in the remaining figures. The transfer device  70  includes four basic sections; an upper latch tube section  100 , an inner support tube assembly  200 , an enclosure assembly  300  and a gripper assembly  400  which can generally be appreciate from  FIGS. 3 ,  3 A,  3 B and  3 C. The outer member is comprised of the upper latch tube assembly  100  and an enclosure assembly  300  which are rigidly connected at the flanges  102 ,  302 , respectively. The enclosure assembly  300  supports and protects the poison rod assembly  40  as it is extracted from the fuel cell  20 . In the preferred embodiment, the upper latch tube assembly  100  is tubular. The enclosure assembly  300  is fixed below the upper latch tube assembly  100 . The enclosure assembly  300  is an appropriate length to support substantially the full length of the poison rod assembly when it is drawn within the enclosure assembly. Inner support tube assembly  200  is slidably disposed within the upper latch tube assembly  100  and the enclosure assembly  300 , and is coupled at its lower end to the gripper assembly  400 . The gripper assembly  400  includes a gripper  402  at its distal end that rides within the enclosure assembly  300 , traveling substantially over the longitudinal length thereof. The inner support tube assembly  200  and upper latch tube assembly  100  can be selectively coupled by an interlock device  110 . The interlock device  110  locks the inner support tube assembly  200  in either an upper position  202  as shown in  FIG. 3C  or a lower position  204  as shown in  FIG. 3B . The inner support tube assembly  200  is attached to the crane  60  as shown in  FIG. 1  so that, when the inner support tube assembly  200  is not coupled to the upper latch tube assembly  100  and through the upper latch tube assembly  100  to the enclosure assembly  300  and the crane  60  is raised, enclosure assembly  300  and upper latch tube assembly  100  remain stationary and the inner support tube assembly  200  and gripper assembly  400  move vertically. When the interlock device  110  is engaged, however, inner support tube assembly  200  is coupled to the upper latch tube assembly  100  and the enclosure assembly  300  and raising the crane  60  raises the entire transfer device. It should be noted that the actuator  168  that operates the gripper  402  on the gripper assembly  400 , through the shaft  416  (as will be explained hereafter), has a cylinder  169  that blocks the lower latch openings  220 ,  222  ( FIG. 9 ) in the inner support tube assembly  200  when the inner support tube is fully inserted in the enclosure assembly  300  and the gripper  402  is activated. In this position, (shown in  FIG. 3B ), the cylinder prevents the interlock  110  from latching the inner support tube  200  to the upper latch tube assembly  100 . In that way, the poison rod assembly cannot be raised until it is fully supported in the enclosure assembly  300 . 
         [0031]    Thus, lifting of a poison rod assembly  40  is accomplished by an operator using the crane  60  to position the transfer device  70  over a fuel cell  20  containing a poison rod assembly  40 . Once the transfer device  70  is seated on the fuel cell  20 , the operator uses crane  60  to lower the inner support tube assembly  200  and the gripper assembly  400  until the gripper  402  engages the hub  46  of the poison rod assembly  40 . When the gripper  402  has engaged the hub  46 , the operator releases the interlock  110  and uses crane  60  to lift the inner support tube assembly  200 , the gripper assembly  400  and the poison rod assembly  40 . Once the poison rod assembly  40  is withdrawn from the fuel cell  20 , the operator may use the moveable gantry  63  to reposition the crane  60  and transfer device  70  above another fuel cell  20 . The transfer device  70  is seated on the second fuel cell  20  and the poison rod assembly  40  can be inserted into the second fuel cell  20 . When the poison rod assembly  40  is seated within the second fuel cell  20 , the gripper assembly  400  is disengaged from the poison rod assembly  40  and the transfer device  70  is removed. 
         [0032]    As shown in  FIGS. 6 ,  7  and  8 , the enclosure assembly  300  includes two C-members  304  held in spaced relationship by a number of horizontal guide plates (also referred to as alignment cards)  306  which are supported in a spaced tandem array along the length of the C-members  304 . It should be appreciated that the C-members could be replaced by four angle channels at the corners or a tubular housing. The C-members  304  define a preferably square, frame cavity  308  that has slotted guide bars  309  proximate the corners as shown in  FIGS. 6 and 8 . Each C-member  304  has an upper end  310 , located at the enclosure assembly upper end and a lower end  312  located at the enclosure assembly lower end. At the lower end  312  of the C-members  304  is a mounting pedestal  314 . The C-members  304  are attached to the mounting pedestal  314  and the mounting pedestal  314  has a central opening  316  that communicates with the central cavity  308  of the enclosure assembly  300 . The mounting pedestal can be better observed from the isometric view shown in  FIG. 7 . The central opening  316  in the pedestal  314  is sized to allow the poison rod assembly  40  to pass therethrough. The pedestal  314  communicates with the alignment cards  306  as the poison rod assembly is withdrawn. In operation, the poison rod assembly will be lifted through the pedestal  314  and alignment cards  306  by the gripper assembly  400  into a position within the frame of the enclosure assembly cavity  308 . The pedestal  314  lower surface has at least one projection  318  with the preferred embodiment having at least two projections  318  extending downwardly from diagonally opposite corners as shown in  FIG. 7 . The projections  318  are sized to engage the bore holes  24 ,  26  on the fuel rod assembly top nozzle or assembly can  22 . Thus, seating the transfer device  70  on the fuel cell  20  is accomplished by the operator lowering the device  70  until the projections  318  are seated within the bore holes  24 ,  26 . Once the projections  318  are so seated, the transfer device  70  is resting on the fuel cell can  20 . 
         [0033]    The configuration of the alignment cards  306  is shown in  FIG. 8  and includes a number of round openings  320  through which the poison rods pass and slots  322  through which webs on the gripper assemblies  400  slide as will be described hereafter. The alignment cards  306  also include a central opening  324  which is configured to correspond to the central body shape of the gripper assembly  400 . Slotted guide bars  309  extend the full length of the C-members  304  and guide the gripper assembly  400  in between alignment cards  306 . 
         [0034]    As previously mentioned, the upper latch tube assembly  100  is fixed at its lower end  102  to an upper flange  302  of the enclosure assembly  300 . Thus, when the transfer device  70  is seated on a fuel cell  20 , enclosure assembly  300  and, therefore, upper latch tube assembly  100  are fixed in place. As noted above, inner support tube assembly  200  is slidably disposed within the upper latch tube assembly  100  and enclosure assembly  300 . Thus, as shown in  FIGS. 3 ,  3 B and  3 C, when the enclosure assembly  300  and upper latch tube assembly  100  are fixed in place, the inner support tube assembly  200  can slide between the upper position  202  and the lower position  204  within the enclosure assembly  300  and the upper latch tube assembly  100 . 
         [0035]    As shown in  FIG. 9 , a platform  206  is mounted at the upper end  208  of the inner support tube assembly  200 . The lifting platform  206  includes a medial opening  210  therethrough and a lifting bail  212  disposed above the platform  206 . The inner support tube assembly  200  passes through the medial hole  210  and has a flange  214  that contacts the upper surface of the platform  206 . The crane  60  is attached by conventional means to the bail  212 . Thus, raising or lowering the inner support tube assembly  200  or transfer device  70  is accomplished through the crane  60  acting upon platform  206 . Centering rails  226  center the inner support tube in the bushing  228  ( FIGS. 3B and 3C ) as the inner support tube assembly  200  moves within the enclosure assembly  300 . 
         [0036]    As shown in  FIGS. 3C ,  4 ,  5  and  9 , the interlock device  210  allows the upper latch tube assembly  100  and, thus, the enclosure assembly  300  to be locked in either the upper position  202  or the lower position  204  with respect to the inner support tube assembly  200 . In the upper position  202 , the inner support tube assembly  200  is raised so that the gripper assembly  400  is adjacent to the top of the frame of the enclosure assembly  300 . In the lower position  204 , the gripper assembly  400  is adjacent to the lower end of the enclosure assembly  300 , but, in the preferred embodiment, spaced above the mounting pedestal  314 . However, it should be appreciated, that, in the lower position the gripper  402  of the gripper assembly  400  could be at or just below the mounting pedestal  314 . When the inner support tube assembly  200  is in either locked position,  202  or  204 , raising or lowering the crane  60  will lift or lower the transfer device  70 . When the interlock device  110  is in an unlocked position, raising or lowering the crane  60  will slide the inner support tube assembly  200  and the gripper assembly  400  between the upper position  202  and the lower position  204  as shown in  FIGS. 3B and 3C  or allow the gripper assembly  400  to be lowered below the mounting pedestal  214  to engage a poison rod assembly  40 . 
         [0037]    The interlock device  110  is located adjacent to the upper end of the upper latch tube assembly  100 . The interlock device  110  includes a pair of latch members  112  and  114 , and a release mechanism  116 , which includes support collar assembly  118  linking members  120 ,  122 , a double clevis  124 , push rod  126 , spring  128 , and interlock support plate  130 . Additionally, the upper latch tube assembly  100  has two openings  132  and  134 , spaced 180° apart, located adjacent to the interlock device  110 . Finally, inner support tube assembly  200  has an upper pair of openings  216 ,  218  and a lower pair of openings  220 ,  222 , each spaced 180° apart as shown in  FIG. 9 . The upper openings  216  and  218 , are located proximal to the upper end of the inner support tube assembly  200  and the lower openings  220  and  222  are spaced approximately 13-15 feet (4-4.6 meters), just over the length of the poison rod assembly, below the upper openings  216 ,  218 . As will be detailed below, spring  128 , cooperating with linking members  120 ,  122  and push rod  126  urge the latch members  112 ,  114  to pass through the outer openings  132 ,  134  and either the upper or lower inner support tube assembly openings  116 ,  118 ,  120 ,  122  whereupon the inner support tube assembly  200  will be locked in place relative to the upper latch tube assembly  100 . 
         [0038]    Support collar  118  includes a collar  136 , pin supports  138 ,  140 , and pins  142 ,  144 . As shown in  FIGS. 4 and 5 , the support collar  136  is rectangular with an offset medial opening  146  therethrough, and a plurality of fasteners  148 . As shown in  FIG. 5 , the pin supports  138 ,  140  are disposed below the collar  136  held by fasteners  148  which are disposed within fasteners holes through the collar  136 . It should be appreciated that although not shown in the views illustrated in  FIGS. 4 and 5 , the pin supports  138 ,  140  extend on either side of the latch members  112 ,  114 . Each pin support  138 ,  140  has a flat body with a pin opening respectively for pins  142 ,  144  and a perpendicular mounting flange  150 ,  152 . The mounting flanges  150 ,  152  incorporate threaded fastener holes which cooperate with the fasteners  148  to attach the pin supports  142 ,  144  below and to the collar  136 . When disposed below the collar  136 , the pin supports  142 ,  144  form pairs with aligned pin openings through which the rotatable pins  142 ,  144  are disposed. Each pin  142 ,  144  is fixed to a linking member  120 ,  122  and to a latch member  112 ,  114 . 
         [0039]    In the preferred embodiment, as shown in  FIG. 5 , latch members  112 ,  114  are butterfly wing-shaped plates having a tab  154 , wheels  156  which ride in wheel cavities and axles  158  which fit through mounting holes in the tab. Opposing tabs  154 , one for each of the latch members  112 ,  114 , are shaped with a convex outer edge with notches  160  between outer edges of the tabs and the tab plates. Cavities for the wheels  156  are within either tab on the latch members  112 ,  114 . The wheels  156  are disposed within either wheel cavity and held in place by either axle  158 . The wheels  156  extend beyond the outer edges of the tabs. The latch members  112 ,  114  are fixed to either pin  142 ,  144  and rotate about the pin&#39;s axis. Latch members  112 ,  114  are attached to the pins  142 ,  144  so that the tabs  154  are proximal to the housing of upper latch tube assembly  100  and so that latch members  112 ,  114  are disposed below the support collar  136 . 
         [0040]    Referring again to  FIGS. 4 and 5 , interlock support plate  130  is rectangular having push rod opening  162 . Interlock support plate  130  is disposed adjacent to the top of the upper latch tube assembly  100 , above collar  136 . Collar assembly  118  is disposed about the upper latch tube assembly  100  above openings  132 ,  134 . Collar assembly tab opening  146  and support plate tab opening  162  are aligned vertically. Push rod  126  is slidably disposed through collar assembly tab opening  146  and support plate tab opening  162 . Push rod  126  has an upper end and a lower end. A ball knob  164  is disposed at the upper end of push rod  126 . Horizontal double clevis  124  is disposed at the lower end of push rod  126 . Linking members  120 ,  122  are flat, rectangular members having a pivot hole at one end and pin mounting holes for receiving the pins  142 ,  144  at the opposite end. Linking members  120 ,  122  are rotatably coupled about the pivots on the double clevis  124 , one linking member  120 ,  122  on either side of a double clevis  124 . As stated above, linking members  120 ,  122  are each fixedly attached to a pin  142 ,  144 ; this attachment is through the pin mounting holes in the double clevis. Push rod  126  has a flange  166  disposed at locations spaced above collar assembly  118 . Spring  128  is a helical coil spring wrapped around push rod  126  and positioned between collar  136  and flange  166 , thus biasing push rod  126  upward placing the latch members  112 ,  114  in a normally latched position. 
         [0041]    Thus, the interlock device  110  engages the inner support tube assembly  200  and the upper latch tube assembly  100  in a similar fashion, regardless of whether the inner support tube assembly  200  is in its upper position  202  or its lower position  204 . Accordingly, the following description shall address the operation of the interlock device  110  as if the inner support tube assembly  200  is in its upper position  202  and tabs  154  on the latch members  112 ,  114  pass through the inner support tube assembly lower openings  220 ,  222 . It is understood, however, that the following description is equally applicable to operation of the interlock device  110  with the inner member upper openings  216 ,  218 . 
         [0042]    If crane  60  is lifting the inner support tube assembly  200 , attached to the bail  212 , while tabs  254  of latch members  112 ,  114  pass through the inner support tube assembly  200  lower openings  220 ,  222 , the inner support tube assembly  200  will slide within the upper latch tube assembly until the lower edge of lower openings  220 ,  222  of the inner support tube assembly  200  contact the notches  160  on the latch members  112 ,  114 . When the lower edges of the lower openings  220 ,  222  contact the notches  160 , the inner support tube assembly  200  is prevented from sliding within the upper latch tube assembly  100 . At this point, raising the crane  60  will lift the entire transfer device  70  as the lifting force is transferred from the inner support tube assembly  200  through the interlock device  110  to the upper latch tube assembly  100 . 
         [0043]    In operation, as push rod  126  is biased upward by spring  128 , push rod  126  lifts the double clevis  124 . The double clevis  124 , in turn, lifts linking members  120 ,  122 . Linking members  120 ,  122  act upon the pins  142 ,  144  which, in turn, acts upon the latch members  112 ,  114 , biasing latch members  112 ,  114  toward the inner support tube assembly  200 . Tabs  154  of the latch members  112 ,  114  pass through the openings  132 ,  134  in the upper latch tube assembly  100 . When the inner support assembly  200  is in either its upper position  202  or its lower position  204 , tabs  154  of latch members  112 ,  114 , also pass through either inner support tube assembly  200  upper openings  216 ,  218  or lower openings  220 ,  222 . Thus, when the push rods  126  is in its upper position and the openings  132 ,  134  in the upper latch assembly are aligned with the inner support tube assembly openings  216 ,  218  or  220 ,  222 , the latch members  112 ,  114  are in the locked position. 
         [0044]    To release the interlock device  110  and allow the inner support tube assembly  200  to slide within the upper latch tube assembly  100 , an operator must operate the release mechanism  116  by pressing the ball knob  164  which will counteract the force of the spring  128  acting on the push rod  286  and push the rod  126  into its lower position. When push rod  126  is in its lower position, push rod  126  lowers double clevis  124 . Double clevis  124 , in turn, lowers linking members  120 ,  122 . Linking members  120 ,  122  act upon pins  142 ,  144  which, in turn, act upon the latch members  112 ,  114 , rotating latch members  112 ,  114  away from the inner support tube assembly  200  and the upper latch tube assembly  100 . Tabs  154  of latch members  112 ,  114  are then removed from the upper latch tube assembly  100  openings  132 ,  134  and either inner support tube assembly  200  upper openings  216 ,  218  or lower openings  220 ,  222 . Thus, when the push rod  126  is in its upper position the latch members  112 ,  114  are in the unlocked position. 
         [0045]    With the latch members  112 ,  114  in the unlocked position, inner support tube assembly  200  can slide freely within the upper latch tube assembly  100 . As the inner support tube assembly  200  slides up or down within the upper latch tube assembly  100 , the inner support tube assembly  100  openings either upper or lower  216 ,  218  or  220 ,  222 , will no longer be aligned with the outer member openings  132 ,  134 . Instead, as the inner support tube assembly  200  is being raised or lowered, the outer surface of the inner support tube assembly  200  is exposed through the openings  132 ,  134  in the upper latch tube assembly  100 . Once the outer surface of the inner support tube assembly  200  is exposed through the upper latch tube assembly  100  openings  132 ,  134  the operator may release the ball knob  164  and allow latch members  112 ,  114  to be biased by the spring  128  towards the housing of the upper latch tube assembly  100 . Wheels  156  will now contact the outer surface of the inner support tube assembly  200  allowing the inner support tube assembly outer surface to slide between the latch members  112 ,  114 . When the inner support tube assembly  200  reaches either its upper position  202  or its lower position  204 , the inner support tube assembly openings, either upper or lower,  216 ,  218  or  220 ,  222 , will align with the upper latch tube assembly openings  132 ,  134  and latch members  112 ,  114  will close, once again locking the inner support tube assembly  200  within the upper latch tube assembly  100 . 
         [0046]    The upper portion of the inner support tube assembly  200  was described with respect to  FIG. 9 .  FIG. 11  is a cross sectional view of the lower portion of the gripper assembly  400  which is attached through a rod extension, not shown, to the lower portion  224  of the inner support tube assembly  200 . The gripper assembly includes two sets of laterally extending fins  404  and  406 . Each set of fins includes four separate fins  408  that are equal distantly spaced by 90° around a central hub  410  that has a generally square cross section with the fins extending from the corners of the square central hub  410  as shown in the cross sectional view illustrated in  FIG. 11 . Each of the fins has an axially extended rounded distal ends that terminates axially at either end in a bullet nose. The intermediate lateral sections of the fins  414  ride in the slots  322  of the alignment cards  306  while the distal ends of the fins  412  ride in the rounded openings  320  within some of the slots  322 , the central hub  410  rides in the central opening  324  of the alignment cards  306  all of which assure that the gripper assembly will maintain its orientation as it moves axially within the enclosure assembly  300 . The distal ends of the fins  412  ride on the slotted guide bars  309  in between the alignment cards for continued support over the length of the enclosure assembly  300 . The gripper  402  at the distal axial end of the gripper assembly  400  is activated by an axially slidable central shaft  416  which is connected to the actuator handle  168  shown in  FIG. 4 . The actuator handle is maintained in position by a locking pin  170 . Movement of the central shaft  416  in a direction toward the gripper  402  spreads the gripper and will lock the gripper within the poison rod assembly hub  46 . The design of the gripper increases actuator locking force with any increase in downward load. A spring or springs  418  are captured on either side of a spring spacer  420  and the lower spring is captured between the spacer and the central fin hub  410 . The spring or springs  418  are compressed in the gripper assembly and compensate for the approximately sixty percent of the actuator rod weight, and preferably, though not shown in  FIG. 10 , biases the gripper  402  in a normally locked position. 
         [0047]    In operation, the transfer device  70  is seated on a fuel cell  20  as described above. For the purpose of understanding the operation of the transfer device, at this time assume that the inner support tube assembly  200  is in its lower locked position  204 . The operator then releases the interlock device  110  and uses the crane  60  to lower the gripper assembly  400  onto the poison rod assembly  40 . The gripper  402  will fit into the hub  46 . The operator then activates the actuator handle  68  locking the hubs to the gripper and inserts the locking pin  70  to secure the connection. The operator then uses the crane  60  and the ball knob  64  to lift the inner support tube assembly  200  there by raising the gripper  402  and poison rod assembly  40  into the enclosure assembly  300  cavity  308 . The interlock device  110  will not latch into the support tube  200 , as a cylinder blocks the upper support tube latch opening. Once the inner support tube assembly  200  reaches its upper position  202 , the interlock device  110  will engage. After the interlock device  110  has been engaged in the upper position, crane  60  lifts the transfer device  70  off the fuel cell  20 . The operator then uses the gantry  64  to reposition the transfer device  70  over a different fuel cell  20 . The transfer device  70  is then seated on the second fuel cell  20  as described above. Once the transfer device is seated on the second fuel cell, the operator releases the interlock device  110  by depressing the ball knob  164  and lowers the crane  60  thereby lowering the poison rod assembly  40  into the new fuel cell  20 . After the poison rod assembly  40  is inserted into a second fuel cell  20 , the operator releases the actuation handle  168  by withdrawing the locking pin  170  and pulling up on the handle to unlatch the poison rod assembly  40  from the gripper assembly  400 . The operator then raises the crane  60  to lift the inner support tube assembly  200  until the interlock device  110  engages the lower openings  220 ,  222 . Once the interlock device  110  is engaged in the lower openings  220 ,  222  in the inner support tube assembly  200 , the crane  60  may lift the transfer device  70  off the fuel cell  20 . Transporting the transfer device  70  in the telescoped condition with the inner support tube assembly  200  telescoped within the upper latch tube assembly  100  and the enclosure assembly  300  makes movement of the transfer device less awkward and easier to control. 
         [0048]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.