Patent Number: 048572640
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The composite of FIGS. 1A And 1B (referred to hereinafter as FIG. 1) is an elevational view, partly in cross-section, of a pressurized water reactor 10 comprising a pressure vessel 12 including an upper dome, or head assembly, 12a, cylindrical sidewalls 12b, and a bottom closure 12c comprising the base of the reactor 10. Plural radially oriented inlet nozzles 11 and outlet nozzles 13 (only one (1) of each appearing in FIG. 1) are formed in the sidewall 12b, adjacent the upper, annular end surface 12d of the sidewall 12b. Whereas the cylindrical sidewall 12b may be integrally joined, as by welding, to the bottom closure 12c, the head assembly 12a is removably received on the upper, annular end surface 12d of the sidewall 12b and secured thereto. The sidewall 12b further defines an inner, generally annular mounting ledge 12e for supporting various internal structures as later described. Within the bottom closure 12c, as schematically indicated, is so-called bottom-mounted instrumentation 14. The lower barrel assembly 16 comprises a generally cylindrical sidewall 17 affixed at its lower end to a lower core plate 18, which is received on mounting support 18b, as generally schematically illustrated. The cylindrical sidewall 17 extends substantially throughout the axial height of the vessel 12 and includes an annular mounting ring 17a at the upper end thereof which is received on the annular mounting ledge 12e thereby to support the assembly 16 within the vessel 12. As will be rendered more apparent hereafter, the sidewall 17 is solid in the vicinity of the inlet nozzles 11, but includes an aperture 17b having a nozzle ring 17c mounted therein which is aligned with and closely adjacent to the outlet nozzle 13, for each such nozzle. An upper core plate 19 is supported on a mounting support 17d affixed to the interior surface of the cylindrical sidewall 17 at a position approximately one-half the axial height thereof. Fuel rod assemblies 20 are positioned in generally vertically oriented, parallel axial relationship within the lower barrel assembly 16 by bottom mounts 2 carried by the lower core plate 18 and by pin-like mounts 23 carried by, and extending through, the upper core plate 19. Flow holes 18a and 19a (only two of which are shown in each instance) are provided in predetermined patterns, extending substantially throughout the areas of the lower and upper core plates 18 and 19, respectively. The flow holes 18a permit passage of a reactor coolant fluid into the lower barrel assembly 16 in heat exchange relationship with the fuel rod assemblies 20, which comprise the reactor core, and the flow holes 19a permit passage of the core output flow into the inner barrel assembly 24. A neutron reflector and shield 21 is mounted interiorly of the cylindrical sidewalls 17, in conventional fashion. The inner barrel assembly 24 includes a cylindrical sidewall 26 which is integrally joined at its lower edge to the upper core plate 19. The sidewall 26 has secured to its upper, open end, an annular mounting ring 26a which is received on an annular hold-down spring 27 and supported along with the mounting ring 17a on the mounting ledge 12e. The sidewall 26 further includes an aperture 26b aligned with the aperture 17b and the output nozzle 13. Within the inner barrel assembly 24, and densely packed within the cylindrical sidewall 26, are positioned a plurality of rod guides in closely spaced, parallel axial relationship; for simplicity of illustration, only two such rod guides are shown in FIG. 1, namely rod guide 28 housing a cluster 30 of radiation control rods (RCC) and a rod guide 32 housing a cluster 34 of water displacement rods (WDRC). The rods of each RCC cluster 30 and of each WDRC cluster 34 are mounted individually to the respectively corresponding spiders 147 and 90. Mounting means 36 and 37 are provided at the respective upper and lower ends of the RCC rod guide 28 and, correspondingly, mounting means 38 and 39 are provided at the respective upper and lower ends of the WDRC rod guide 32. The lower end mounting means 37 and 39 rigidly mount the respective rod guides 28 and 32 to the upper core plate 19, as illustrated for the RCC rod guide mounting means 37 by bolt 37'. The upper mounting means 36 and 38 mount the respective rod guides 28 and 32 to a calandria assembly 50, and particularly to a lower calandria plate 52. The calandria assembly 50, in more detail, comprises a generally cylindrical, flanged shell 150 formed of a composite of the flange 50a, an upper connecting cylinder 152 which is welded at its upper and lower edges to the flange 50a and to the upper calandria plate 54, respectively, and a lower connecting cylinder, or skirt, 154 which is welded at its upper and lower edges to the upper and lower calandria plates 54 and 52, respectively. The lower connecting cylinder, or skirt, 154 includes an opening 154a aligned with each of the outlet nozzles 13 such that the axial core outlet flow received within the calandria 52 through the openings 52a in the lower calandria plate 52 may turn through 90.degree. and exit radially from within the calandria 52 through the opening 154a to the outlet nozzle 13. The annular flange 50a which is received on the flange 26a to support the calandria assembly 50 on the mounting ledge 12e. Plural, parallel axial calandria tubes 56 and 57 are positioned in alignment with corresponding apertures in the lower and upper calandria plates 53 and 54, to which the calandria tubes 56 and 57 are mounted at their respective, opposite ends. Extending upwardly beyond the upper calandria plate 54 and, more particularly, within the head assembly 12a of the vessel 12, there are provided plural flow shrouds 60 and 61 respectively aligned with and connected to the plural calandria tubes 56 and 57. A corresponding plurality of head extensions 62 and 63 is aligned with the plurality of flow shrouds 60, 61, the respective lower ends 62a and 63a being flared, or bell-shaped, so as to facilitate assembly procedures and, particularly, to guide the drive rods (not shown in FIG. 1) into the head extensions 62, 63 as the head assembly 12a is lowered onto the mating annular end surface 12d of the vessel sidewall 12b. The flared ends 62a, 63a also receive therein the corresponding upper ends 60a, 61a of the flow shrouds 60, 61 in the completed assembly, as seen in FIG. 1. The head extensions 62, 63 pass through the upper wall portion of the head assembly 12a and are sealed thereto. Control rod cluster (RCC) displacement mechanisms 64 and water displacement rod cluster (WDRC) displacement mechanisms 66 are associated with the respective head extensions 62, 63 flow shrouds 60, 61 and calandria tubes 56, 57 which, in turn, are associated with respective clusters of radiation control rods 30 and water displacement rods 34. The RCC displacement mechanisms (CRDM's) 64 may be of well known type, as are and have been employed with conventional reactor vessels. The displacer mechanisms (DRDM's) 66 for the water displacer rod clusters (WDRC's) 34 may be in accordance with the disclosure of U.S. Letters Pat. No. 4,439,054-Veronesi, assigned to the common assignee hereof. The respective drive rods (not shown in FIGS. 1A and 1B) associated with the CRDM's 64 and the DRDM's 66 are structurally and functionally the equivalent of elongated, rigid rods extending from the respective CRDM's 64 and DRDM's 66 to the respective clusters of radiation control rods (RCC's) 30 and water displacement rods (WDRC's) 34 and are connected at their lower ends to the spiders 100 and 120. Apertures 58 and 59 in the lower calandria plate accommodate the corresponding drive rods. The CRDM's and DRDM's 64 and 66 thus function through the corresponding drive rods to control the respective vertical positions of, and particularly, selectively to lower and/or raise, the RCC's 30 and the WDRC's 34 through corresponding openings (not shown) provided therefore in the upper core plate 19, telescopingly into or out of surrounding relationship with the respectively associated fuel rod assemblies 20. In this regard, the interior height D.sub.1 of the lower barrel assembly 16 is approximately 178 inches, and the active length D.sub.2 of the fuel rod assemblies 20 is approximately 153 inches. The interior, axial height D.sub.3 is approximately 176 inches, and the extent of travel, D.sub.4, of the rod clusters 30 and 34 is approximately 149 inches. It follows that the extent of travel of the corresponding CRDM and DRDM drive rods is likewise approximately 149 inches. While the particular control function is not relevant to the present invention, insofar as the specific control over the reaction within the core is effected by the selective positioning of the respective rod clusters 30 and 34, it is believed that those skilled in the art will appreciate that moderation or control of the reaction is accomplished in accordance with the extent to which the control rod clusters 30 are inserted into or withdrawn from the core and with the effective water displacement which is achieved by selective positioning of the water displacement rod clusters 34. The flow of the reactor coolant fluid, or water, through the vessel 10 proceeds, generally, radially inwardly through a plurality of inlet nozzles 11, one of which is seen in FIG. 1, and downwardly through the annular chamber 15 which is defined by the generally cylindrical interior surface of the cylindrical side wall 12b of the vessel 12 and the generally cylindrical surface exterior surface of the sidewall 17 of the lower barrel assembly 16. The flow then reverses direction and passes axially upwardly through flow holes 18a in the lower core plate 18 and into the lower barrel assembly 16, from which it exits through a plurality of flow holes 19a in the upper core plate 19 to pass into the inner barrel assembly 24, continuing in parallel axial flow therethrough and finally exiting upwardly through flow holes 52a in the lower calandria plate 52. Thus, parallel axial flow conditions are maintained through both the lower and inner barrel assemblies 16 and 24. Within the calandria 50, the flow in general turns through 90.degree. to exit radially from a plurality of outlet nozzles 13 (one of which is shown in FIG. 1). The inlet coolant flow also proceeds into the interior region of the head assembly 12a through perimeter bypass passageways in the mounting flanges received on the ledge 12e. Particularly, a plurality of holes 170, angularly spaced and at a common radius, are formed in the flange 17a and provide axially-directed flow paths from the annular chamber 15 into the annular space 172 intermediate the spring 27 and the interior surfaces of the sidewalls of the vessel 12; further, a plurality of aligned holes 174 and 176 extend through the flanges 26a and 50a, the holes 174 being angularly oriented, to complete the flow paths from the annular space 172 to the interior of the head assembly 12a. The flow of coolant proceeds from the head region through annular downcomer flow paths defined interiorly of certain of the flow shrouds 60, 61 and calandria tubes 56, 57, as later described, from which the head coolant flow exits into the top region of the inner barrel assembly 24, just below the lower calandria plate 52, to mix with the core outlet flow and pass through the calandria 50, exiting from the outlet nozzles 13. A first plurality of calandria extensions 58 project downwardly from the calandria tubes 56 and connect to corresponding mounting means, or top end supports, 36 for the upper ends, or tops, of the RCC rod guides 28. The top end supports 36 may be in accordance with the structure disclosed in the concurrently filed patent application entitled LATERAL SUPPORT FOR CANTILEVER-MOUNTED ROD GUIDES OF A PRESSURIZED WATER REACTOR Ser. No. 936,301,filed 11-3-86or, alternatively, in the pending patent application entitled FLEXIBLE ROD GUIDE SUPPORT STRUCTURE FOR INNER BARREL ASSEMBLY OF PRESSURIZED WATER REACTOR Ser. No. 798,220 filed 11-14-85 ), both assigned to the common assignee hereof. A second plurality of calandria extensions 59, in interleaved relationship with the plurality of extensions 58, projects downwardly from the respectively corresponding calandria tubes 56, each extension 59 telescopingly connecting to a corresponding, frictionally loaded top end support mounting means 38 for a WDRC rod guide 32 in accordance with the present invention. As before briefly noted, each of the mounting means 38 for the WDRC rod guides in accordance with the present invention provides a frictionally loaded, telescoping interconnection between the lower calandria plate 52 and the respectively associated WDRC rod guide 32, thereby not only affording axial alignment and lateral support of the top end of the associated, individual WDRC rod guide 32, but also preventing vibration of the rod guide 32 and the upper core plate 19. The calandria extensions 59, moreover, function, in cooperation with and in response to the frictionally loaded mounting means 38, to react seismic forces from the rod guides 32 into the calandria, while accommodating axial height variations arising from structural tolerances and thermal stresses at the interface of the upper ends of the rod guides 32 and the lower calandria plate 52. FIG. 1C is a schematic, top plan view of the calandria plate 52 indicating in hidden lines the general, outer peripheral configuration of the RCC rod guides 28 and the WDRC rod guides 32. As later explained, threaded holes 87 provide for engaging the top end supports for the WDRC rod guides to the calandria plate 52. Holes 56 and 57 respectively labelled "C" and "D" identify the corresponding holes through the lower calandria plate 52 through which pass the RCC and the WDRC drive rods 56 and 57. Holes 52A are flow holes through the lower calandria plate 52, as likewise seen in FIG. 1A. FIG. 1C serves to illustrate the dense packing of the RCC and WDRC rod clusters and the geometrically interspersed arrays thereof within the upper internals 24 and, as well, the complexity of the structure within the calandria assembly 50. The frictionally loaded top end support for cantilever-mounted water displacement rod guides of a pressurized water reactor in accordance with the present invention will be explained with concurrent reference to FIGS. 2, 3 and 4. FIG. 2 is an elevational view of the mounting means 38 comprising the frictionally loaded top end support for a WDRC rod guide 32. FIG. 3 is a cross-sectional view of the mounting means 38 taken along the line 3--3 in FIG. 2. FIG. 4 is a vertical cross-sectional view of the mounting means 38 taken along the lines 4--4 in each of FIGS. 2 and 3. The WDRC rod guide 32, throughout substantially its entire axial length, comprises a relatively thin metal sidewall 70 of generally square cross-sectional configuration which carries, at its upper extremity, a reinforced, generally coaxial sleeve 72 having a generally square cross-sectional configuration corresponding to the outer perimeter of the thin sidewall 70 and which is permanently joined at its bottom end to the top end of the latter at their common outer perimeters, as illustrated by weld bead 74. The sleeve 72 receives in telescoping relationship therein a generally cylindrical, fixed support 80 comprising a cylindrical sidewall 81 and an end closure 82. The end closure 82 includes a central, annular projection 83 which is received within a corresponding annular recess 53 in the lower calandria plate 52, thereby interlocking the support 80 with the lower calandria plate 52 against lateral displacement. A central aperture 82' in the cylindrical support 80 is of a diameter corresponding to, and is aligned with, the aperture 52' in the lower calandria plate 52. A calandria extension 59 is received through the apertures 52', 82' and may extend downwardly through the aperture 82', serving to further stabilize the support 80 to the lower calandria plate 52. Typically, the calandria extension 59 is permanently secured to the lower calandria plate 52, as indicated by weld bead 59'. Flow holes 100 are disposed in a symmetrical array about the axis of the calandria extension 59 associated with the WDRC rod guide 32 and its associated top end support 38, which must be unobstructed so as to permit unimpeded passage of the core output flow axially therethrough and into the calandria assembly 50. Accordingly, the end closure 82 includes a number of arcuate indentations, or recesses, 82" corresponding to the inner perimeter portions of the flow holes 100 adjacent the calandria extension 59. The cylindrical sidewall 81 of the fixed support 80 correspondingly is segmented, i.e., is discontinuous, and terminates at the corresponding perimeters of the flow holes 100 and thus comprises a plurality of arcuate segments 81', defining a plurality of arcuate flanges 84 (best seen in FIG. 3), each bounded at its opposite ends by the corresponding perimeters of the adjacent flow holes 100. The arcuate flanges 84 comprise the frictional load bearing components of the frictionally loaded top end support of the invention, as will be described. The end closure 82 furthermore includes a number of countersunk bores 85 through which bolts 86 are received and secured in tightly threaded engagement within the corresponding threaded bores 87 in the calandria lower plate 52. Inner cylindrical bores 88a and outer cylindrical bores 88b are optionally formed in the support 80 for a purpose to be described. As best seen in FIG. 3, the outer bores 88b may be centered at a radius slightly greater than the inner surface of the arcuate flanges 84. The rod guide sleeve 72, as before noted, has an outer periphery of a predetermined geometric configuration corresponding substantially to that of the thin metal sidewall 70; particularly, it is of a eight-sided configuration, comprising two pairs of opposed major faces 72a and two pairs of opposed minor faces 72b. A leaf spring 110 is formed in each of the major faces 72a, in a central portion 113 which integrally connects an upper, continuous annular collar portion 112 and a lower, continuous annular base portion 114. Each leaf-spring 110 is machined so as to have a planar, interior surface 111a which is angled relative to the vertical outer surface and defines a tapered integral shank portion extending upwardly from the annular base portion 114, and an integral arcuate segment lip portion 111b. The arcuate segment lip portions 111b normally extend radially inwardly of the continuous annular collar portion 112. In the telescopingly assembled relationship with the fixed cylindrical support 80, the interior arcuate surface 72' of the sleeve 72 is annularly spaced from the exterior surfaces of the arcuate segments 81' of the cylindrical sidewall 81 of the fixed cylindrical support 80, whereas the arcuate segment lip portions 111b are frictionally loaded onto the annular flange extensions 84. The rod guide sleeve 72 furthermore is machined so as to define an interior surface configuration which is in mating and complementary relationship with the exterior surface configuration of the cylindrical sidewall 81. As best seen in FIG. 3, the rod guide sleeve 72 includes plural interior arcuate surfaces 72' in mating relationship with the corresponding exterior surfaces of the arcuate segments 81' of the cylindrical sidewall 81, and generally arcuate recesses 72" conforming to the corresponding outer perimeter portions of the flow holes 100 and complementing the arcuate recesses 82" of the end closure 82 of the fixed support 80. Within each of the arcuate recesses 72" there additionally are formed axially extending grooves 75, for a purpose to be explained. FIG. 5 is a simplified, schematic plan view of the WDRC rod cluster 34, which more particularly comprises a spider 90 having a plurality of radially extending arms 92 connected to a central hub 93; further, alternate ones of the arms 92 include transverse cross-arms 92a. A plurality of WDRC rods 94 are appropriately connected to the arms 92 and the cross-arms 92a and depend therefrom in parallel axial relationship. With concurrent reference to FIGS. 2 to 5, the grooves 75 and bores 88a, 88b are designed to accommodate respective, individual WDRC rods 94 when the cluster 34 is raised to a refueling position, as shown in phantom lines in FIG. 4. As shown by phantom lines as well in FIG. 3, the grooves 75 formed in the interior arcuate surface 72" corresponding to a given flow hole 100 receive the respective rods 94 of an outer pair mounted on an outermost cross-bar 92, whereas the radially inner and outer bores 88a and 88b in the fixed support 80 accommodate the corresponding, radially inner and outer rods 94 mounted on the single radial arms 92. As shown by phantom lines in FIG. 4, a drive rod or drive shaft 95 is connected to the hub 93 of the spider 90 and extends upwardly through the calandria extension 59, as previously described, for raising or lowering the WDRC rod cluster 34 within its associated rod guide 32. The grooves 75 and the bores 88a and 88b avoid the necessity of increasing the height of the inner barrel assembly 24 in the event that adequate axial height is not available for permitting the cluster 34 to be raised to the required height during refueling. Where adequate vertical space is available, the grooves 75 and the bores 88a and 88b are not required, and accordingly are optional. In accordance with the WDRC top end support 38 afforded by the present invention, during normal reactor operation, the radial load provided by the four leaf springs 110 prevents vibration of the sleeve 72 in a radial, or lateral, direction and thus maintains the spaced, concentric relationship of the sleeve 72 and the mount 80 and Specifically the nominal spacing of the respective, opposed arcuate surfaces 72' and 81' so as to avoid frictional wear therebetween. The axial friction load produced by the radial load, furthermore, prevents axial vibration of the rod guide 32 and, through the plurality of rod guides 32, vertical vibration of the core plate 19, as well. During abnormal load conditions, such as seismic and LOCA, in which the loading, or force, of the springs 110 is exceeded, the fixed cylindrical support 80 functions as a rigid abutment stop to the continuous annular collar portion 112 of the sleeve 72, and reacts any such abnormal load directly into the lower calandria plate 52. The frictional loaded top end support of the present invention therefore substantially eliminates any continuous frictional wear between the contiguous but nominally spaced surfaces of the sleeve 72 and the support 80, affording long life and reduced maintenance. Nevertheless, the support of the invention maintains the desirable feature of a telescoping interconnection of the sleeves 72 and the corresponding fixed cylindrical supports 80, which permits the calandria 50 to be raised and withdrawn for gaining access to the rod clusters 34 within the respective guides 32, for normal maintenance purposes, and thereafter re-installed, simply by being lowered into position with the fixed mount and respective sleeves 72 axially aligned. To facilitate the installation, the inner upper edges 78 of the collar portion 112 are outwardly bevelled and the lower outer edge of the flanges 84 of the fixed support 80 are inwardly bevelled to facilitate the telescoping assembly; likewise, the arcuate segment lips 111b of the leaf springs 110 have arcuate cross-sectional configurations in a vertical plane passing therethrough, as shown in FIG. 4, for facilitating the telescoping interconnection during assembly. In an actual pressurized water reactor of the advanced design herein contemplated and incorporating the present invention, the thin wall section 70 of the rod guide 32 is formed of sheet metal of approximately 1/8 inch thickness. The rod guide 32 is approximately 12 inches wide, in both dimensions of its generally square cross-section, and approximately 174" (14-1/2 feet) in height. The rod guide sleeve 72 has an outer periphery, in cross-section, corresponding to that of the rod guide 70, and may have a diagonal dimension between the opposed minor faces 72b of 14.8 inches and a transverse dimension between the opposed major faces 72a of 12.3 inches. The axial height of the sleeve 72 may be 9.0 inches, that of the collar portion 112 being somewhat over 2 inches, that of the leaf spring 110 being somewhat less than 5 inches and that of the lower annular base portion 114 being approximately 2 inches. To achieve the desired uniform spring deflection/loading force characteristics, the leaf spring 110 is tapered in its planar dimensions as seen in FIG. 2 from a base width of 6 inches to a width of somewhat over 4 inches at the lip portion 111b. An annular clearance of a nominal 0.007 inches is sufficient for the spacing between the cylindrical surface 81' of the fixed support 80 and the interior, mating surfaces 72' of the collar portion 112, the surfaces 72' lying on a diameter of approximately 11 inches. It furthermore is believed sufficient, to achieve the requisite radial loading of the springs 110, that the interior surfaces of the arcuate lip portions 111b lie on a diameter, in their nondeflected positions, which is at most several thousandths of an inch less than the diameter of the fixed cylindrical support 80. Further, it has been determined to be sufficient that the annular flanges 84 extend approximately 1 inch beyond the lower surface of the end closure 82 of the support 80 which in turn may be approximately 2.5 inches in axial height, or thickness. Further, the annular extension 83 and correspondingly the annular recess 53 may be of approximately 0.25 inches. FIG. 6 is a plan view of the reinforced sleeve for the RCC mounting means, or top end support 36, illustrating in hidden lines the corresponding configuration of the thin metal wall rod guide 28; FIG. 7 is a cross-sectional, elevational view taken in a plane through the line 7,8--7,8 in FIG. 6; and FIG. 8 is a cross-sectional view as in FIG. 7, of the assembled top end support 36 comprising the reinforced sleeve 172 with the calandria extension 58 received therein, the calandria extension 58 moreover being secured to the lower calandria plate 52. Reference is had concurrently thereto in the following. The reinforced sleeve 172 is of a generally X-shaped cross-sectional configuration, as best seen in the plan view of FIG. 6, and is slightly larger in its lateral dimensions than the corresponding dimensions of the thin metal sidewall 170 of the RCC rod guide 28. The sleeve 172 thus has generally 90.degree. displaced, radially oriented arms 172a defining therebetween an interior, or included vertex of truncated configuration defined by the short, interior face 172b. As seen in FIG. 1C, each interior vertex of sleeve 172 receives a corresponding exterior vertex of an adjacent WDRC sleeve 72, the interior face 172b being contiguous the corresponding minor face 72b, when in assembled relationship. The sleeve 172 is joined to the metal sidewall 170 for the rod guide 28 by a weld bead 174 (FIGS. 7 and 8). The lower end 173 of the sleeve 172 comprises an annular base portion of fixed inner and outer diameters, the sidewalls tapering slightly in the axial upward direction to the upper end 177; further, annular flange 175 extends inwardly from the base portion 173 and defines an opening of an interior diameter sufficient to receive coaxially therethrough a drive rod 145 connected to a spider 147 to which the rods of the RCC rod cluster 30 are secured, the latter in conventional fashion. The upper end 177 of the sleeve 172 forms a continuous annular and non-yielding collar, the interior surface 177a comprising a load pick-up surface, as later described. Leaf springs 210 are symmetrically disposed about the center axis of the support 172; in the preferred embodiment illustrated, four such leaf springs 210 are disposed at 90.degree. displaced positions about the axis. The base portion 213 of each spring 210 has an inner, flat surface 213a and an outer, arcuate segment surface 213b which conforms to the generally cylindrical interior surface 173a of the lower portion 173 of sleeve 172, as best seen in the cut-away view of the topmost spring 210 in FIG. 6. Shank portion 215 of the spring 210 is joined through a compound curved and integral section 214 to the base portion 213 and thereafter is of tapered and rectangular cross-sectional configuration in the generally axial direction, in accordance with proper design for stress efficiency of a leaf spring. Integral neck portion 216 (the opposite edges of which are seen in the hidden lines in FIG. 6') joins shank 215 to an arcuate segment lip portion 217 (best seen in FIGS. 6 and 7). Bolts 220, 221 and 222 are received through corresponding apertures in the base portion 173 of the sleeve 172 and engaged in respective, threaded bores in the base portion 213 of the spring 210. A clearance bore 217a is formed in the lip portion 2I7, in alignment with and for receiving therein a retaining pin 219 which extends radially through hole 218 of the collar portion 177 of the sleeve 172 and is secured in position by a weld bead 219a. With reference to the elevational and cross-sectional assembly drawing of FIG. 8, the RCC sleeve 172 is axially aligned with and receives therein the downwardly extending calandria extension 58. Flange 58a is received in an annular recess 152 in the lower calandria plate 52 and secured in position by weld bead 153. Tapered end surface 58b of the calandria extension 58 facilitates the alignment and telescoping insertion thereof into the generally axially aligned, cylindrical boundary defined by the interior surfaces 217b of the lip portions 217 of the springs 210. It will be understood that the annular gap between the calandria extension 58 and the load pick-up surface 177a of the collar portion 177 of sleeve 172 is slightly greater than the radial depth of the intervening lip portions 177, and that the latter normally exert a lateral, radially inward resilient force, produced by flexible shank 215, against the exterior surface of the calandria extension 58. The lateral force of the leaf springs 210 serves to stabilize and maintain alignment of the sleeve 172 and thereby the RCC rod guide 28, as against the influences of flow-induced lateral loading during normal reactor operation, the frictional, axially oriented loading force as well serving to stabilize the RCC rod guide 28 against vertical displacement and in turn stabilizing the spaced relationship between the upper core plate 19 and the lower calandria plate 52. Excessive lateral forces acting on the RCC rod guide 28, as may occur during normal operating conditions or as a result of accident situations (seismic or LOCA) and which exceed the center biasing effect of the leaf springs 210, are transferred to the non-yielding, load pick-up surface 177a of the continuous annular collar portion 177 and directly through the intervening lip portion 217 of the correspondingly positioned leaf spring 210 to the calandria extension 58 and into the lower calandria plate 52. As best seen in FIG. 6, and taken in conjunction with the broken-away and hidden view of the RCC rod cluster 30 in FIG. 8, the sleeve 172 is configured internally to permit telescoping passage therethrough of the RCC rod cluster 30 including the RCC spider 147 which is connected to drive rod 145 and the associated RCC control rods; more particularly, the sleeve 172 includes passageways 224 extending radially from the axis and centrally of the arms 172a, having rounded openings 225 and 226 respectively corresponding to the vanes 147c and 147d and the mounting hubs 147a and 147b for the respective, radially displaced RCC rods 30a and 30b, the vanes being connected to a central hub 147e of the RCC spider 147 mounted on the drive rod 145. Thus, when the calandria 50 is removed from an engaged position with the sleeve 172, the corresponding RCC cluster 30 may be withdrawn vertically and in sliding, telescoping relationship relatively to the RCC rod guide 28 and through the sleeve 172, without requiring any disassembly of the latter. As noted, the RCC top end supports 36 are less massive than the WDRC top end supports 38, as is permissible in view of the smaller lateral forces which must be reacted thereby. On the other hand, the smaller spatial envelope presents alternative design constraints. By way of comparison, the height of the RCC sleeve 172 may be approximately 7.25 inches and the cross-sectional width of the central portion, as seen in cross-section in FIG. 8, approximately 4.75 inches. The width of the arms 172a may be 1.75 inches and the radial length thereof, from the central axis, 6.25 inches. The leaf springs 210 may have a height of approximately 6.6 inches, the shank portion 215 tapering from 0.45 inches to approximately 0.20 inches adjacent the arcuate lip portion 217. The sidewall of the sleeve 172 tapers outwardly from an interior diameter of approximately 3.5 inches at the bottom to 4 inches at the top, thereby affording the clearance gap relative to the calandria extension 58, the latter having an outer diameter of approximately 3 inches, within which gap the arcuate segment lip portions 217 of the leaf spring are received. The specific configuration and structural dimensions of the WDRC and RCC top end supports as provided hereinabove are significant, in that they establish the capability of achieving a practical implementation in accordance with the design configurations as set forth herein, despite the extremely limited spatial envelope available therefor within the reactor internals, taking further into account the necessity of accommodating the requisite flow passages and the like. While of relatively low size, they afford the necessary structural strength for reacting both axial and transverse loading forces and yet are compliant for ease of performing assembly and disassembly operations. Nevertheless, they are of reduced complexity, affording reduced costs of manufacture and installation. Numerous modifications and adaptations of the present invention will be apparent to those of skill in the art and thus it is intended by the appended claims to cover all such modifications and adaptations as fall within the true spirit and scope of the invention.