Abstract:
A new spring design for a strap employed in a grid of a nuclear reactor fuel assembly includes a pair of ligaments that each connect with the free portion of the retention plate. The ligaments each are equally spaced a certain distant from the termination of the slots within the strap body. The spring additionally includes a spring contact plate that is wider than the connections of the spring ligaments with the free portion to increase the surface area with which the spring contact plate is in contact with and retains the fuel rod, and thus reduces the contact stresses therebetween. The spring contact plate additionally includes an embossed spring contact member protruding outwardly therefrom reduces the frictional stresses on the fuel rod when it is inserted into and removed from the cell and during vibration of the fuel rod and/or the strap.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to nuclear reactor fuel assemblies and, more particularly, is directed to a spring design for a grid of a nuclear reactor fuel assembly. Specifically, the invention relates to an improved spring and dimple configuration for a retention plate of a grid strap. 
     2. Description of the Related Art 
     In most pressurized water nuclear reactors, the reactor core is comprised of a large number of elongated fuel assemblies. Conventional designs of these fuel assemblies include a plurality of fuel rods held in an organized array by a plurality of grids that are spaced axially along the fuel assembly length and are attached to a plurality of elongated thimbles of the fuel assembly. The thimbles typically receive control rods or instrumentation therein. Top and bottom nozzles on opposite ends of the fuel assembly are secured to the guide thimbles which extend slightly above and below the ends of the fuel rods. 
     The grids, as well known in the relevant art, are used to precisely maintain the spacing between the fuel rods in the reactor core, prevent rod vibration, provide lateral support for the fuel rods, and, to some extent, frictionally retain the rods against longitudinal movement. One type of conventional grid design includes a plurality of interleaved straps that together form an egg-crate configuration having a multiplicity of roughly diamond-shaped cells which individually accept the fuel rods and thimbles therein. The straps are configured such that the cells each include a plurality of relatively resilient springs and a plurality of relatively rigid dimples, the springs and dimples being formed into the metal of the interleaved straps and protruding outwardly therefrom. The springs and dimples of each cell frictionally engage or contact the respective fuel rod extending through the cell. Additionally, outer straps are attached together and peripherally enclose the inner straps to impart strength and rigidity to the grid. 
     One type of prior art strap is depicted generally at the numeral A 1  in FIG.  1  and the numeral A 2  in FIG.  2 . Straps A 1  and A 2  are identical but inverted views of identical straps, and thus include identical components. The specific components of the straps A 1  and A 2  thus will not be differentiated herein. The strap A 1  is in a “slots up” orientation and the strap A 2  is in a “slots down” orientation. 
     The straps A 1  and A 2  each include an elongated strap body C that is formed out of a strip of a sheet metal that is suited to a nuclear environment. The strap body C is formed with a plurality of slots E that are parallel with one another and that extend midway into the strap body C. Each strap body C includes a plurality of retention plates G thereon that are defined on the strap body C between adjacent slots E. Each retention plate G includes a free portion  1  that terminates on opposite sides at the slots E and a connected portion K that is defined within the strap body C and that terminates at imaginary sides that are aligned with the slots E. 
     A spring M and a pair of dimples O are formed in each retention plate G by stamping and cutting appropriate holes into the strap body C or by other known methods. Each spring M includes a first spring ligament Q, a second spring ligament S, and a spring contact plate U. The spring M is oriented at approximately a 45° angle with respect to a longitudinal axis that extends through the strap body C and that is substantially perpendicular with the slot E. 
     The first spring ligament Q extends between the connected portion K and the spring contact plate U. The second spring ligament S extends between the spring contact plate U and the free portion  1 . The retention plates G are each configured such that the spring M, and particularly the spring contact plate U, protrudes outwardly from the strap body C in a direction generally out of the plane of the paper of the paper of FIGS. 1 and 2. Similarly, the dimples O are configured to extend outwardly from the strap body C in a direction generally into the plane of the paper of FIGS. 1 and 2. The springs M thus protrude outwardly from the strap body C in a direction opposite the dimples O. 
     When the straps A 1  are interleaved with the straps A 2  by engaging the slots E of the straps A 1  with the slots E of the straps A 2 , a pair of springs M and two pairs of dimples O protrude into each cell. The springs M, with their first and second spring ligaments Q and S, are generally longer in length than the dimples O, and thus have a smaller spring constant than the dimples O. As such, the springs M are relatively resilient in comparison with the dimples O, which are relatively rigid. 
     When the fuel rods are inserted into the cells and are in a compressive relation with the springs M and the dimples O protruding into the cell, the springs M, and to an extent the dimples O, are deflected away from the fuel rods and thus impart a residual retaining force against the fuel rods to hold the fuel rods in a given position. It can be seen, however, that since the first spring ligament Q connects with the connected portion K which terminates at an imaginary line within the strap body C, and the second spring ligament S connects with the free portion  1  which terminates at the slots E, the first spring ligament Q will have a higher spring constant and thus will be less resilient than the second spring ligament S. Such differential resilience has a tendency to impart a rotational force to the fuel rod. Such rotational forces have the effect of applying a torque to the fuel rods and of abrading or fretting holes into the fuel rods. Such wear on a fuel rod is preferably avoided due to the potential of releasing radioactive material into the primary cooling loop of the reactor. 
     In order to reduce the wear on fuel rods, it is thus desired to provided an improved spring design having an even deflection profile in directions both parallel and perpendicular with the longitudinal axis of the strap body. It is also desired to provide an improved spring design that will reduce the surface stress at the interface between the spring contact plate and the fuel rod. It is additionally preferred to configure the new spring design to minimize the abrasion that occurs to the fuel rod when the fuel rod is initially inserted and finally removed from the grid made up of the straps A 1  and A 2 . 
     SUMMARY OF THE INVENTION 
     A new spring design for a strap employed in a grid of a nuclear reactor fuel assembly includes a pair of ligaments that each connect with the free portion of the retention plate. The ligaments each are equally spaced a certain distant from the termination of the slots within the strap body. The spring additionally includes a spring contact plate that is wider than the connections of the spring ligaments with the free portion to increase the surface area with which the spring contact plate is in contact with and retains the fuel rod, and thus reduces the contact stresses therebetween. The spring contact plate additionally includes an embossed spring contact member protruding outwardly therefrom reduces the frictional stresses on the fuel rod when it is inserted into and removed from the cell and during vibration of the fuel rod and/or the strap. 
     Accordingly, an aspect of the present invention is to provide a strap for a grid of a nuclear reactor fuel assembly, the general nature of which can be stated as including an elongated strap body having a longitudinal axis and being formed with at least a first open slot and a second open slot, the at least first open slot extending along a first slot axis and the second open slot extending along a second slot axis, the first and second slot axes being substantially parallel and spaced apart and being oriented substantially perpendicular with the longitudinal axis, the at least first and second open slots each extending from a first edge of the strap body and each terminating at an end point, the end point being less than fully the distance from the first edge to a second and opposite edge of the strap body, the strap body including at least a first retention plate, the retention plate including a free portion and a connected portion, the free portion terminating on alternate sides at the at least first and second open slots, the connected portion terminating on alternate sides at the first and second slot axes within the strap body, with a spring being formed in the at least first retention plate by a first closed spring slot and a second closed spring slot, the spring protruding outwardly from the at least first retention plate in a first direction, and at least a first dimple being formed in the at least first retention plate by a first pair of closed dimple slots, the at least first dimple protruding outwardly from the at least first retention plate in a second direction substantially opposite the first direction, the spring including a first spring ligament, a second spring ligament, and a spring contact plate, the first and second spring ligaments each having a first connection at a first end thereof with the spring contact plate, the first and second spring ligaments each having a second connection with the free portion at a second end thereof, the second connections both being at the same distance from the longitudinal axis, the second connections each having a spring connection length along a direction perpendicular to the longitudinal axis the spring contact plate having a spring contact length along a direction perpendicular to the longitudinal axis, the spring contact length being greater than the spring connection lengths of either of the second connections. 
     Another aspect of the present invention is to provide a nuclear reactor, the general nature of which can be stated as including at least a first fuel assembly, the at least first fuel assembly including at least a first fuel rod and at least a first grid, the at least first fuel rod being mounted on the at least first grid, the at least first grid including a plurality of straps, at least one of the straps including an elongated strap body having a longitudinal axis and being formed with at least a first open slot and a second open slot, the at least first open slot extending along a first slot axis and the second open slot extending along a second slot axis, the first and second slot axes being substantially parallel and spaced apart and being oriented substantially perpendicular with the longitudinal axis, the at least first and second open slots each extending from a first edge of the strap body and each terminating at an end point, the end point being less than fully the distance from the first edge to a second and opposite edge of the strap body, the strap body including at least a first retention plate, the retention plate including a free portion and a connected portion, the free portion terminating on alternate sides at the at least first and second open slots, the connected portion terminating on alternate sides at the first and second slot axes within the strap body, a spring being formed in the at least first retention plate by a first closed spring slot and a second closed spring slot, the spring protruding outwardly from the at least first retention plate in a first direction, at least a first dimple being formed in the at least first retention plate by a first pair of closed dimple slots, the at least first dimple protruding outwardly from the at least first retention plate in a second direction substantially opposite the first direction, the spring including a first spring ligament, a second spring ligament, and a contact plate, the first and second spring ligaments each having a first connection at a first end thereof with the spring contact plate, the first and second spring ligaments each having a second connection with the free portion at a second end thereof, the second connections both being at the same distance from the longitudinal axis, the second connections each having a spring connection length along a direction perpendicular to the longitudinal axis, the spring contact plate having a spring contact length along a direction perpendicular to the longitudinal axis, the spring contact length being greater than the spring connection lengths of either of the second connections. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiment of the invention, illustrative of the best mode in which Applicant has contemplated applying the principles of the invention, is set forth in the following description and is shown in the drawings and is particularly and distinctly pointed out and set forth in the appended Claims. 
     FIG. 1 is a front elevational view of a prior art strap in a “slots up” orientation; 
     FIG. 2 is a front elevational view of a prior art strap in a “slots down” orientation; 
     FIG. 3 is a top plan view of a grid of a fuel assembly that incorporates a plurality of straps in accordance with the present invention in a substantially hexagonal configuration within a schematic representation of a nuclear reactor; 
     FIG. 4 is a front elevational view of a portion of a strap in accordance with the present invention in accordance with the present invention in a “slots up” orientation; 
     FIG. 4A is an enlarged view of the left central portion of FIG. 4; 
     FIG. 4B is an enlarged view of the top left portion of FIG. 4; 
     FIG. 4C is an enlarged view of the bottom left portion of FIG. 4; 
     FIG. 5 is a front elevational view of a strap in accordance with the present invention in a “slots down” orientation; 
     FIG. 6 is a top plan view of the portion of the strap depicted in FIG. 4; 
     FIG. 7 is a sectional view as taken along line  7 — 7  of FIG. 4; and 
     FIG. 8 is a top plan view of a portion of a grid incorporating a plurality of the improved straps and depicting a fuel rod in one of the cells. 
     Similar numerals refer to similar parts throughout the specification. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A strap in accordance with the present invention is indicated at the numeral  4  in FIGS. 4-8. The strap  4  depicted in FIG. 4 is identical to the strap  4  depicted in FIG. 5, except that the strap  4  in FIG. 4 is in a “slots up” orientation and the strap  4  in FIG. 5 is in a “slots-down” orientation. A plurality of the straps  4  in each of the “slots-up” and “slots-down” orientations are interleaved to formed a grid  6  that is employed in a fuel assembly of a nuclear reactor  8 . The grid  6  includes a plurality of cells  10  (FIG. 8) that each carry a fuel rod  12 , a thimble tube (not shown), or other device therein, the cells  10  each being roughly diamond-shaped. While FIG. 8 generally depicts a portion of the grid  6  having four cells  10  therein, it is understood that each of the grids  6  employed in the nuclear reactor  8  include substantially more cells  10  than are shown in FIG.  8  and are configured like the grid  6  of FIG.  3 . 
     The straps  4  each include an elongated strap body  14  manufactured out of a sheet metal or other material that is appropriately suited to the reactive environment of a pressurized water nuclear reactor. The strap body  14  includes an imaginary longitudinal axis denoted by the line  16 . The strap body  14  is formed with a plurality of open slots  20  that each extend along an imaginary slot axis  24  that is oriented substantially perpendicular with the longitudinal axis  16 . 
     The open slots  20  each extend from a first edge  28  of the strap body  14  in the direction of a second edge  32  of the strap body  14 , yet terminate at an end point  34  that is between the first and second edges  28  and  32 . For reasons set forth more fully below, it is preferred that the end points  34  be at least nominally closer to the second edge  32  than to the first edge  28 , although the end point  34  may be equidistant from the first and second edges  28  and  32  without departing from the spirit of the present invention. 
     The longitudinal axis  16  is oriented substantially parallel with the first and second edges  28  and  32 . A plurality of exterior welding tabs  36  protrude outwardly from the first edge  28  in the plane of the strap body  14 , and a plurality of interior welding tabs  40  protrude outwardly from the second edge  32  in the plane of the strap body  14 . As is best shown in FIGS. 4 and 5, the exterior welding tabs  36  are disposed on alternate sides of each of the open slots  20 , and the interior welding tabs  40  are each centrally disposed along a slot axis  24 . As will be set forth more fully below, when a plurality of the straps  4  in the slots up orientation are interleaved with a plurality of the straps  4  in the slots down orientation, the interior welding tabs  40  are each interposed between a pair of the exterior welding tabs  36 , and a single weld can thus be applied to a confluence of the interior and exterior welding tabs  40  and  36  to fixedly retain the straps  4  in the desired interleaved configuration. 
     Each strap body  14  includes a plurality of retention plates  44  that are defined between adjacent slot axes  24 . Each retention plate  44  thus includes a free portion  48  that terminates on alternate sides thereof at adjacent open slots  20  and a connected portion  52  that terminates on alternate sides at adjacent slot axes  24  within the strap body  14 . 
     Each retention plate  44  includes a spring  56 , a first dimple  60 , and a second dimple  60  formed therein. It can be seen that the spring  56  and the first dimple  60  are disposed in the free portion  48 , and the second dimple  64  is disposed in the connected portion  52 . 
     The first and second dimples  60  and  64  are each formed by cutting a pair of closed dimple slots  68  in the strap body  14 . Similarly, the spring  56  is formed by cutting a first closed spring slot  72  and a second closed spring slot  76  in the strap body  14 . The first closed spring slot  72  is roughly U-shaped and includes a pair of compliance slots  80  and  84  that are connected with a connecting slot  88 , the connecting slot  88  connecting with one end of each of the compliance slots  80  and  84 . The second closed spring slot  76  is of a different configuration than the first closed spring slot  72 , yet still includes a pair of compliance slots  92  and  94  that are connected by a connecting slot  98 . It can be seen, however, that the connecting slot  98  extends between one end of the compliance slot  92 , yet connects with the compliance slot  94  at approximately the midpoint thereof. 
     The spring  56  includes a first ligament  102 , a second ligament  106 , and a spring contact plate  108 . The first ligament  102  extends between the spring contact plate  108  and a first leg  110  of the free portion  48 . The first leg  110  extends in a direction generally transverse to the longitudinal axis  16  and is bounded on one side by one of the open slots  20  and is bounded on the other side by the compliance slots  80  and  92 . Similarly, the second ligament  106  extends between the spring contact plate  108  and a second leg  112  of the free portion  48 , the second leg extending substantially transverse to the longitudinal axis  16  and being bordered generally by one of the open slots  20  and the compliance slots  84  and  94 . 
     The connections of the first and second ligaments  102  and  106  with the first and second legs  110  and  112 , respectively, each begin at a proximate point  114  with respect to the end point  34  and terminate at a distal point  116  with respect to the end point  34 . The distal point  116  is farther away from the end point  34  than the proximate point  114 , and the distance between the proximate point  114  and the distal point  116  is the spring connection length  118 , which is measured in a direction substantially perpendicular with the longitudinal axis  16 . 
     The proximate points  114  are each preferably the same distance away from the end points  34 . Similarly, the distal points  116  are equally spaced from the end points  34 . While it is preferred that the distance between the end points  34  and the proximate points  114  be at least one-half the spring connection lengths  118  to provide compliance to the first and second ligaments  102  and  106 , the aforementioned distance may be less than one-half depending upon the specific needs of the particular application without departing from the spirit of the present invention. Such identity between the connections of the first and second ligaments  102  and  106  with the first and second legs  110  and  112 , respectively, of the free portion  48 , gives the first and second ligaments  102  and  106  equal spring constants when deflected during use by a fuel rod  12  or during vibration or other movements within the nuclear reactor  8 . In this regard, it is understood that the term “spring constant” when used in relation to the first and second ligaments  102  and  106  refers to the overall deflection characteristic of the first and second ligaments  102  and  106  during deflection of the spring  56 , and thus additionally includes or incorporates the deflection characteristics of the first and second legs  110  and  112  as well as that of other appropriate elements of the reactor  8 . While other configurations of the spring  56  are possible in which the first and second ligaments  102  and  106  have non-identical connections with the first and second legs  110  and  112 , respectively, it is preferred that the first and second ligaments  102  and  106  nevertheless be configured to have equal spring constants in order to provide an even deflection profile both in the both longitudinal and transverse directions and to resist imparting rotative forces to the fuel rod  12 , as will be set forth more fully below. 
     The spring contact plate  108  includes a spring contact member  120  that is an embossment protruding outwardly from a spring border  122 , the spring border  122  being the portion of the spring contact plate  108  that has not been embossed outwardly to form the spring contact member  120 . The spring contact member  120  is a portion of the spring contact plate  108  that comes into physical contact with the fuel rod  12 . The spring contact member  120  thus is of a spring contact length  126  measured in a direction substantially perpendicular with the longitudinal axis  16 . 
     The spring contact length  126  is advantageously greater than the spring connection lengths  118  to reduce the stresses imparted by the spring contact member  120  on the fuel rod  12 . More specifically, by providing an extended or enlarged spring contact member  120  having an expanding spring contact length  126  in comparison with the spring connection lengths  118 , the retention force imparted by the spring  56  to the fuel rod  12  is distributed across the contact area between the spring contact member  120  and the fuel rod  12 , and by increasing the area of the spring contact member  120 , as evidenced by the enhanced spring contact length  126 , the stresses imparted by the spring  56  to the fuel rod  12  are relatively reduced. Not only is the normal force between the spring contact member  120  and fuel rod  12  distributed over a relatively greater area and thus the normal stresses are correspondingly reduced, but any stresses resulting from frictional forces due to sliding or vibration of the fuel rods  12  with respect to the grid  6  are likewise reduced. Such reduced stresses advantageously diminish the likelihood of abrasion or fretting of the fuel rods  12 , with consequent reduction in the likelihood of fretting failure of the fuel rods  12 . 
     The spring contact member  120  is advantageously embossed to have curved or arcuate upper and lower edges to resist digging by the edge of the spring contact plate  108  into the fuel rod  12  during installation and removal of the fuel rod  12  in the cell  10  (FIG. 7.) Moreover, the side edges of the spring contact member  120  are likewise curved to reduce such digging or gouging by the side edges during vibration of the reactor  8  or in the event of other movement phenomena (FIG. 6.) Additionally, it can be seen that by providing both a spring border  122  as well as a spring contact member  120  embossed outwardly therefrom, the spring border  122  provides strength in directions transverse to and parallel with the longitudinal axis  16 , which resists deflection of and damage to the spring contact member  120  when the fuel rod  12  is initially installed and ultimately removed from the nuclear reactor  8  in the transverse direction. 
     Each of the first and second dimples  60  and  64  include a pair of dimple ligaments  130  and a dimple contact plate  134 . The dimple ligaments  130  of the first dimple  60  extend between the dimple contact plate  134  and the free portion  48 . Similarly, the dimple ligaments  130  of the second dimple  64  extend between the associated dimple contact plate  134  and the connected portion  52 . 
     The pair of dimple ligaments  130  of the first dimple  60  are each disposed an equal distance from the first edge  28  and are each of an equal dimple connection length  142  with the free portion  48  to provide equal spring constants and a constant deflection profile in both the longitudinal and transverse directions. Similarly, the dimple ligaments  130  of the second dimple  64  are each disposed an equal distance away from the second edge  32  and are each of an equal dimple connection length  142  with the connected portion  52  to provide equal spring constants and an equal deflection profile in both the longitudinal and transverse directions. 
     Each of the dimple contact plates  134  includes a dimple contact member  138  that is an embossment protruding outwardly from a dimple border  140 , which is the portion of the dimple contact plate  134  that is not embossed outwardly to form the dimple contact member  138 . The dimple contact member  138  is preferably configured with rounded or arcuate upper and lower edges to resist the edge of the dimple contact plate  134  from gouging the fuel rod  12  during installation and removal of the fuel rod  12  from the cell  10 . The dimple contact member  138  is the portion of the dimple contact plate  134  that is physically in contact with the fuel rod  12 , and is of a dimple contact length  146 , measured in a direction substantially perpendicular with the longitudinal axis  16 . The connections of the dimple ligaments  130  of the first dimple  60  are of a dimple connection length  142  measured in a direction substantially perpendicular to the longitudinal axis  16  that is less than the associated dimple contact length  146  of the dimple contact plate  134  thereof. Similarly, the dimple ligaments  130  of the second dimple  64  are of a dimple connection length  142  measured in a direction substantially perpendicular to the longitudinal axis  16  that is less than the associated dimple contact length  146  of the dimple contact plate  134  thereof. 
     As can be seen in FIGS. 6 and 7, the spring  56  and the first and second dimples  60  and  64  protrude outwardly from the plane of the strap body  14  in order to operatively engage the fuel rods  12 . More specifically, the springs  56 , as depicted in FIGS. 4 and 5, protrude in a direction generally out of the plane of FIGS. 4 and 5, and the first and second dimples  60  and  64  protrude in a direction opposite the spring  56 , and thus extend generally into the plane of FIGS. 4 and 5. 
     With the springs  56  protruding from the strap body in a first direction and with the first and second dimples  60  and  64  protruding from the strap body  14  in a 30 second opposite direction, it can be seen from FIG. 8 that the spring  56  of any given retention plate  44  protrudes into a cell  10  that is different than the cell  10  into which the first and second dimples  60  and  64  of the same retention plate  44  protrude. As is best shown in FIG. 8, each cell  10  is bordered by four retention plates  44  in a roughly diamond-shaped configuration, with the cell  10  having two springs  56 , two first dimples  60 , and two second dimples  64  protruding into it. As to any given retention plate  44 , the spring  56  thereof protrudes into a given cell  10 , and the first and second dimples  60  and  64  thereof protrude into an adjacent cell  10 . 
     As is best shown in FIG. 4 and 5, the dimple contact plates  134  of the first and second dimples  60  and  64  lie along a dimple axis  154  that is substantially perpendicular with the longitudinal axis  16 . Similarly, the springs contact plate  108  can be said to lie along a spring contact axis  150  that is oriented substantially perpendicular with the longitudinal axis  16 . The spring contact axis  150  and the dimple axis  154  are parallel and spaced from one another. It thus can be seen that the spring contact plate  108  is offset from the dimple contact plates  134  of the first and second dimples  60  and  64  with respect to the longitudinal axis  16 . The offset relation between the spring contact plate  108  and the dimple contact plates  134  is further illustrated in FIGS. 6 and 8. 
     Moreover, as can be seen in FIGS. 6 and 8, the offset relation of the spring contact plate  108  from the dimple contact plates  134  necessitates that the spring contact member  120  be oriented in a direction that is generally non-coplanar with the balance of the strap  4 . Similarly, the dimple contact members  138  are generally non-coplanar with the balance of the strap  4 . 
     It can thus be seen that the improved configuration of the retention plate  44  of the present invention, with the improved configurations of the spring  56 , the first dimple  60 , and the second dimple  64 , advantageously results in fewer stresses and stresses of lesser magnitude to the fuel rods  12 . Such reduced stresses result in a reduced likelihood of fretting damage to the fuel rods  12  by eliminating or at least substantially reducing the twisting forces applied to the fuel rods  12 , by reducing the contact stresses of the springs  56  and first and second dimples  60  and  64  on the fuel rods  12 , and by resisting gouging of the fuel rods  12  during installation into and removal from the grid  6 . 
     The “horizontal” nature of the springs  56  and the first and second dimples  60  and  64  obtained by configuring the first and second ligaments  102  and  106  of the spring at the same vertical distance from the first edge  28 , and by similarly configuring the dimple ligaments  130  of the first and second dimples  60  and  64  to be of equal distances from the first and second edges  28  and  32 , respectively, and by providing identity of the spring connection lengths  118  and dimple connections lengths  142 , advantageously results in each of the springs  56  and first and second dimples  60  and  64  having an even deflection profile in directions both parallel with and transverse to the longitudinal axis  16 . Moreover, by providing spring contact lengths  126  that are greater than the spring connection lengths  118 , and by providing dimple contact lengths  146  that are greater than the dimple connection lengths  142 , the springs  56  and first and second dimples  60  and  64  advantageously apply relatively reduced normal contact stresses and consequently reduced frictional stresses to the fuel rods  12 . Still additionally, by providing spring contact members  120  and dimple contact members  138  in the form of embossments having curved or arcuate upper end lower edges, the likelihood of the fuel rods  12  being gouged by the springs  56  and the first and second dimples  60  and  64  during installation and removal of the fuel rods  12  into and from the grids  6  is advantageously reduced. 
     While a particular embodiment of the present invention has been described herein, it is understood that various changes, additions, modifications, and adaptations may be made without departing from the scope of the present invention, as set forth in the following Claims.