Top end support for water displacement rod guides of pressurized water reactor

A top end support for rod guides disposed in closely spaced, parallel axial relationship within an inner barrel assembly of a pressurized water reactor vessel includes, in telescoping relationship, a generally cylindrical support having an end closure with a central aperture therein for receiving a downwardly depending extension from a lower calandria plate and a sleeve having an outer periphery corresponding in cross-section to that of said rod guide and affixed thereto at its lower end, the sleeve having an interior, generally cylindrical surface for receiving the cylindrical support in close engagement therein. The telescopingly engaged, generally cylindrical surfaces of the cylindrical support and the sleeve provide substantial area to function as a long-life wear couple. Both the end closure and the cylindrical sidewalls of the fixed cylindrical support and the interior surface of the sleeve are configured so as to correspond to the perimeter of flow holes disposed in a symmetrical array about the associated depending extension, to permit unimpeded passage therethrough of the core outlet flow.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to pressurized water reactors and, more 
particularly, to a top end support for the water displacement rod guides 
positioned within the inner barrel assembly of a pressurized water 
reactor. 
2. State of the Prior Art 
Certain advanced designs of nuclear reactors incorporate at successively 
higher, axially aligned elevations within the reactor vessel, a lower 
barrel assembly, an inner barrel assembly, and a calandria, each of 
generally cylindrical configuration, and an upper closure dome. The lower 
barrel assembly may be conventional, having mounted therein, in parallel 
axial relationship, a plurality of fuel rod assemblies which are supported 
at the lower and upper ends thereof, respectively, by corresponding lower 
and upper core plates. Within the inner barrel assembly there is provided 
a large number of rod guides disposed in closely spaced relationship, in 
an array extending substantially throughout the cross-sectional area of 
the inner barrel assembly. The rod guides are of first and second types, 
respectively housing therewithin reactor control rod clusters (RCC) and 
water displacer rodlet clusters (WDRC); these clusters, as received within 
their respectively associated guides, generally are aligned with the fuel 
rod assemblies. 
The calandria includes a lower calandria plate and an upper calandria 
plate. The rod guides are secured in position at the lower and upper ends 
thereof, respectively, to the upper core plate and the lower calandria 
plate. The inner barrel assembly thus is defined in axial height between a 
first plate of a lower elevation comprising the upper core plate and a 
second plate of a higher elevation comprising the lower calandria plate. 
Within the calandria and extending between the lower and upper plates 
thereof is mounted a plurality of calandria tubes in parallel axial 
relationship and respectively aligned with the rod guides. A number of 
flow holes are provided in remaining portions of the calandria plates, 
intermediate the calandria tubes, through which passes the the reactor 
core outlet flow as it exits from its passage through the inner barrel 
assembly. 
In similar parallel axial and aligned relationship, the calandria tubes are 
joined to corresponding flow shrouds which extend to a predetermined 
elevation within the dome, and which in turn are connected to 
corresponding head extensions which pass through the structural wall of 
the dome and carry, on their free ends at the exterior of and vertically 
above the dome, corresponding adjustment mechanisms. The adjustment 
mechanisms have corresponding control lines which extend through the 
respective head extensions, flow shrouds, and calandria tubes and are 
connected to the respectively associated clusters of RCC rods and WDRC 
rods, and serve to adjist their elevational positions within the inner 
barrel assembly and, particularly, the level to which same are lowered 
into the lower barrel assembly and thus into association with the fuel rod 
assemblies therein, thereby to control the activity within the core. 
A critical design criterion of such reactors is to minimize wear of the 
rodlets in the rod guides, and thus to reduce or eliminate the factors 
which produce wear, such as flow induced vibration. Because of the 
relatively dense packing of the rod guides within the inner barrel 
assembly, it is critical to maintain substantially uniform distribution of 
the outlet flow from the reactor core, and an axial direction of that flow 
through the upper barrel assembly. Even if a uniform, axial flow of the 
core outlet is achieved, the effects of differential pressure and 
temperature across the array of rod guides or an individual rod guide can 
produce significant reaction loads at the support points, or support 
connections, for the rod guides. These reaction loads, coupled with the 
flow induced vibration, create a high potential for wear at the support 
points for the rod guides as well as the rodlets. Additionally, the 
provision of the calandria, and particularly the lower plate thereof, 
presents an interface with the top end of the rod guides which does not 
exist in conventional pressurized water reactors. That interface must be 
capable of accommodating differential thermal expansions between the lower 
calandria plate and the inner barrel in order to prevent large thermal 
stresses from developing. Furthermore, the lower calandria plate and the 
upper core plate are essentially structurally independent; therefore, 
vibration of the internals can result in significant relative movement 
between the supporting connections of the rod guides at their lower and 
upper ends to the respective upper core plate and the bottom calandria 
plate. The wear potential under these circumstances is great. 
Thus, split, or two-pin connections of conventional types are inappropriate 
for use as the supporting connections for the top ends of the rod guides 
since they have too much torsional stiffness. If used, they would wear 
rapidly, with the result that the top ends of the rod guides would become 
loose. Rod guides having such loose top end connections are unacceptable 
because of the rapid rate of wear of the rodlets which would result. Other 
known mounting devices as well are inappropriate. For example, leaf 
springs cannot be used to support all of the rod guides because sufficient 
space is not available within the inner barrel assembly to provide leaf 
springs of the proper size for the large number of rod guides which are 
present, even if high strength material is used for the leaf springs. 
Beyond the unsuitability of existing, known structural support 
arrangements, further factors must be taken into account in the 
consideration of possible designs for the support of the top end of the 
rod guides within the inner barrel assembly. For example, both the RCC and 
the WDRC rod clusters should be removable without requiring that the 
guides be disassembled. This requirement imposes a severe space limitation 
in view of the dense packing of the guides and their associated rod 
clusters within the inner barrel assembly. For example, in one such 
reactor design, over 2,800 rods are mounted in 185 clusters, the latter 
being received within a corresponding 185 guides. The space limitation is 
further compounded by the requirement that unimpeded flow holes must be 
provided in the calandria plates for the core outlet flow. While these 
foregoing factors severly restrict the available space envelope in the 
horizontal cross-sectional dimension of the inner barrel assembly, axial 
or vertical limitations on this space envelope must also be considered. 
For example, the presence of the support members should not require any 
increase in the height of the vessel. From a maintenance standpoint, the 
support members should be replaceable without undue effort. Additionally, 
the assembly of the calandria must be accomplished without access to the 
support region. 
While the supports for the rod guides must therefore satisfy a wide range 
of structural and functional requirements relating to, or imposed by, the 
inner barrel assembly itself, a further critical requirement is that the 
wear potential of the support structure itself must be minimized. This is 
a critical requirement in view of the potential for intense vibration 
arising out of the core outlet flow and the development of contact forces 
due to differential pressure and steady state and transient temperature 
conditions across the array of rod guides and the individual rod guides. 
Conventional reactor designs do not present the support problems attendant 
the dense packing of rod guides and associated rod clusters in advanced 
reactor designs of the type herein contemplated. Thus, there is no known 
solution to the problems of adequately supporting the rod guides, 
consistent with the requirements and taking into account the environmental 
factors which exist in operation of such reactors as hereinabove set 
forth. 
SUMMARY OF THE INVENTION 
A pressurized water nuclear reactor, of the type with which the top end 
supports for water displacement rod guides of the present invention are 
intended for use, as before noted employs a large number of reactor 
control rods, or rodlets, typically arranged in what are termed reactor 
control rod clusters (RCC) and, additionally, a large number of water 
displacer rods, or rodlets, similarly arranged in water displacer rod 
clusters (WDRC). For example, in one such reactor, an array of 185 such 
clusters containing a total of 2800 rodlets (i.e., the total of reactor 
control rods and water displacer rods) are mounted in parallel axial 
relationship within the inner barrel assembly. Each of these clusters, 
moreover, is received within a corresponding rod guide structure. In 
operation, it is desired to maintain the core outlet flow in an axial flow 
condition and in a substantially uniform distribution throughout the 
cross-sectional area of the inner barrel assembly, as it passes through 
the inner barrel assembly, and thus to prevent cross-flow conditions 
(i.e., core flow in a direction transverse of the rod guides). This is a 
critical requirement in reactors of such advanced designs in which the 
inner barrel is densely loaded with rodlets, as before noted. 
The geometry of the reactor vessel itself introduces a structural anomaly 
which is contrary to maintaining the desired, substantially uniform axial 
flow condition. Particularly, the circular configuration of the reactor 
vessel, including the inner barrel assembly, is geometrically incompatible 
with the generally rectangular or square cross-sectional configuration of 
the individual rod guides, and correspondingly of an array thereof as 
stacked in closely adjacent relationship within the inner barrel assembly. 
Thus, in the peripheral regions between the inside diameter of the 
cylindrical inner barrel assembly and the outer periphery of the array of 
rod guides, no rodlets are present, resulting in a non-uniform flow 
distribution and presenting at least the potential of turbulence and 
cross-flow conditions with attendant problems of vibration. A related 
application of a common one of the co-inventors herein, entitled "Modular 
Former For Inner Barrel Assembly Of Pressurized Water Reactor," Gillett et 
al., Ser. No. 798,195, filed Nov. 14, 1985, and assigned to the common 
assignee hereof, discloses an invention relating to modular formers which 
are configured to be mounted in these peripheral regions, to provide 
hydraulic resistance and thereby to maintain a primarily axial direction, 
and substantially uniform distribution, of the core outlet flow, 
throughout the length of the rod guides within the inner barrel assembly. 
Thus while the state of the art, in the design of the inner barrel assembly 
of such advanced types of pressurized water reactors, has addressed the 
problem of attempting to maintain relatively stable conditions by 
minimizing cross-flow, e.g. substantially uniform distribution and axial 
direction of the core output flow throughout the inner barrel assembly, 
there remains the critical problem of properly supporting the rod guides 
within the inner barrel, because of remaining excitation forces from 
internals vibration and axial flow turbulence. 
The present invention addresses the problem of the top end support for rod 
guides which house so-called water displacement rods or rodlets, also 
referred to as water displacer rodlet clusters (WDRC), which terms are 
used synomonously herein. Basically, the WDRC rod guide top end support of 
the invention provides for a telescoping interconnection between the lower 
calandria plate and the top end of each WDRC rod guide. Each of the rod 
guide top end supports of the invention maximizes the area of the wear 
surface of the telescoping interconnection with the associated rod guide, 
thereby to resist wear during normal operation, while permitting access to 
the rod cluster received in each such rod guide to facilitate the 
performance of routine maintenance functions. Additionally, the top end 
support of the present invention accommodates the requisite flow path to 
the calandria for the core output flow during operation of the reactor. 
More specifically, the top end support for the WDRC rod guides comprises a 
fixed cylindrical support having a closed end with a central aperture 
which is received over a depending calandria extension on the lower 
surface of the lower calandria plate and is bolted thereto, the support 
having a cylindrical sidewall extending downwardly from the lower 
calandria plate, the outer circumferential surface of which comprising a 
wear surface of substantial area. An axially extending sleeve having an 
outer periphery corresponding in cross-section to that of the rod guide is 
affixed at its lower end to the rod guide and has an inner circumferential 
surface of generally cylindrical cross-section for receiving the integral 
sidewall of the fixed cylindrical support in telescoping relationship 
therewith, the sleeve having an axial length such that the upper end 
thereof is disposed closely adjacent to but displaced from the lower 
surface of the lower calandria plate when in assembled relationship with 
the cylindrical support. Each of the fixed cylindrical supports, including 
the end closure thereof and the depending cylindrical sidewall, and the 
interior portion of the sleeve include mating recesses therein 
corresponding to flow holes typically symetrically disposed about the 
depending extension of a given top end support to afford unimpeded passage 
therethrough of the core outlet flow. As a concomitant advantage of 
affording maximum area of the wear surface through maximizing the interior 
diameter of the sleeve, adequate space thereby is afforded for axially 
withdrawing a rod cluster from within the rod guide and associated sleeve, 
such as is required for maintenance purposes. Preferably, a lower axial 
portion of the interior diameter of the cylindrical sidewall furthermore 
is machined to define receiving channels for clearance in axially raising 
the rod cluster for accommodating the upper end thereof, as is required 
during control of the reactor through adjustment of the height of the rod 
cluster, thereby permitting use of a reactor vessel of shorter axial 
height, where axial height limitations are of concern. 
The RCC rod guides may be connected to the calandria by any desired support 
structure, such as that shown in the concurrently filed application 
entitled FLEXIBLE ROD GUIDE SUPPORT STRUCTURE FOR INNER BARREL ASSEMBLY OF 
PRESSURIZED WATER REACTOR Gillett et al., Ser. No. 798,220, filed Nov. 14, 
1985, and which is assigned to the common assignee hereof. 
The top end support of the present invention thus provides overall support 
and alignment between the calandria and the associated rod guides, loads 
exerted on the associated rod guides being reacted into the calandria. The 
telescoping interconnection between the fixed cylindrical supports and the 
associated rod guide sleeves, on the other hand, provides compensation for 
thermal stresses and accommodates tolerances in the axial spacing between 
the lower calandria plate and the upper core plate and the vibrations 
encountered during operation, while facilitating removal and reassembly of 
the calandria with the rod guides for routine maintenance. Moreover, the 
configuration of the top end support maximizes the area of the associated 
wear surfaces, affording a long-life device. Significantly, the top end 
support is configured to provide the requisite flow paths through the 
lower calandria plate for the core outlet flow. 
These and other advantages of the top end support for rod guides in 
accordance with the present invention will become more apparent from the 
following detailed description and drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is an elevational view, partly in cross-section, of a pressurized 
water reactor 10 comprising a vessel 12 of generally conventional 
configuration including an upper dome 12a, cylindrical sidewalls 12b, and 
a bottom closure 12c comprising the base of the reactor 10. Within the 
bottom closure 12c, as schematically indicated, is so-called base-mounted 
instrumentation 14. The lower barrel assembly 16 comprises a generally 
cylindrical sidewall 17 affixed at its lower and upper ends to respective 
lower and upper core plates 18 and 19. Fuel rod assemblies 20 are 
positioned in generally vertically oriented, parallel axial relationship 
within the lower barrel assembly 16. A radiation reflection shield 21 is 
mounted interiorly of the cylindrical sidewalls 17, in conventional 
fashion. 
The inner barrel assembly 24 includes a cylindrical sidewall 26 within 
which 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 of 
radiation control rods 30 (RCC) and a rod guie 32 housing a cluster of 
water displacement rods 34 (WDRC). Mounting means 36 and 37 are provided 
at the respective upper and lower ends of the rod guide 28 and, 
correspondingly, mounting means 38 and 39 are provided at the respective 
upper and lower ends of the rod guide 32, the lower end mounting means 37 
and 39 mounting the respective rod guides 28 and 32 to the upper core 
plate 19, and the upper mounting means 36 and 38 mounting the respective 
rod guides 28 and 32 to a calandria assembly 50, and more particularly to 
the lower caladria plate 52. The inner barrel assembly 24 thus is defined 
to extend, in axial height, from a first plate of lower elevation 
comprising the upper core plate 19 to a second plate of higher elevation 
comprising the lower calandria plate 52. 
The calandria assembly 50 includes a lower calandria plate 52, an upper 
calandria plate 54, and a plurality of parallel axial calandria tubes 56 
which are positioned in alignment with corresponding apertures in the 
lower and upper calandria plates 52 and 54 and to which the calandria 
tubes 56 are mounted at their respective, opposite ends. Extending 
upwardly beyond the upper calandria plate 54 and, more particularly, 
within the dome 12a of the vessel 12, there is provided a plurality of 
flow shrouds 60 respectively aligned with the calandria tubes 56. A 
corresponding plurality of head extensions 62 is aligned with the 
plurality of flow shrouds 60, with respective adjacent ends thereof in 
generally overlapping relationship. Control rod cluster (RCC) displacement 
mechanisms 64 and water displacement rod cluster (WDRC) displacement 
mechanisms 66 are associated with the respective head extensions 62, flow 
shrouds 60 and calandria tubes 56 which, in turn, are respectively 
associated with the respective clusters of radiation control rods 30 and 
water displacment rods 34. Particularly, the RCC and WDRC displacement 
mechanisms 64 and 66 connect through corresponding lines to the respective 
clusters of radiation control rods and water displacement rods 30 and 34, 
to control the respective vertical positions thereof and, particularly, to 
selectively lower same through corresponding openings (not shown) provided 
therefore in the upper core plate 19 into surrounding relationship with 
respectively associated fuel rod assemblies 20. While the particular 
control function is not relevant to the present invention, insofar as the 
control over the reaction within the core is effected by the selective 
positions 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 the core and with the effective 
water displacement adjustment which is achieved by selective positioning 
of the water displacement rods 34. 
A first matrix of calandria extensions 58 project downwardly from the 
calandria tubes 56 and connect to corresponding mounting means 36 for the 
upper ends, or tops, of the RCC rod guides 28. As before noted, the top 
end support for the RCC rod guides 28 may be in accordance with the 
structure disclosed in a concurrently filed application of one of the 
named co-inventors herein, entitled FLEXIBLE ROD GUIDE SUPPORT STRUCTURE 
FOR INNER BARREL ASSEMBLY OF PRESSURIZED WATER REACTOR, Gillett et al., 
Ser. No. 798,220, filed Nov. 14, 1985, assigned to the common assignee 
herewith. 
A second matrix of calandria extensions 59, in interleaved relationship 
with the matrix of extensions 58, projects downwardly from the 
respectively corresponding calandria tubes 56, each extension 59 
connecting to a corresponding 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 provides a telescoping 
interconnection between the lower calandria plate 52 and the respectively 
associated WDRC rod guide 32, thereby affording axial alignment and 
lateral support of the associated, individual WDRC rod guide 32. The 
calandria extensions 59 function to react seismic forces from the rod 
guides 32 into the calandria, while accommodating axial height tolerances 
and thermal stresses at the interface of the upper ends of the rod guides 
32 and the lower calandria plate 52. 
FIG. 2 is a plan view of the top end support in accordance with the present 
invention, taken along the line 2--2 in FIG. 1 and thus showing an upper 
end portion o a WDRC rod guide 32 in cross-section, and a bottom plan view 
of the associated top end support 38. The top end support 38 furthermore 
will be described with concurrent reference to FIGS. 3 and 4, which 
respectively comprise cross-sectional elevational views taken along the 
lines 3--3 and 4--4 in FIG. 2. 
The WDRC rod guide, 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 is one component of a pair of wear couple 
components which axially align and laterally support the rod guide with 
respect to the lower calandria plate 52. 
The second component of the top end support 38 comprises a fixed 
cylindrical support 80 having a generally cylindrical sidewall 81 and an 
end closure 82. The end closure 82 includes a central aperture 82' for 
receiving therethrough the calandria extension 59 in closely engaged, 
coaxial relationship. 
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 cylindrical sidewall 81 is 
discontinuous, or terminates, at the corresponding perimeters of the flow 
holes 100 and thus comprises a plurality of arcuate segments 81' (best 
seen in FIG. 2), each bounded at its opposite ends by the corresponding 
perimeters of the adjacent flow holes 100. The end closure 82 
correspondingly is configured to accommodate the flow holes 100 and thus 
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. 
As best seen in FIG. 4, the calandria extension 59 is rigidly secured to 
the lower calandria plate 52 by a weld bead 59' which extends about the 
entire circumference of the extension 59, the calandria extension 59 being 
of sufficient axial length such that its lower end 59" is flush with the 
lower surface of the end closure 82. The end closure 82 furthermore 
includes a number of countersunk bores 85 through which bolts 86 are 
received and secured in tightly threaded engagement with the corresponding 
threaded bores 87 in the calandria lower plate 52. The interior surfaces 
of the arcuate segments 81' include axially extending grooves 88, for a 
purpose to be explained. 
The rod guide sleeve 72 is machined so as to include an inner surface 
having a configuration which accommodates the flow holes 100, and defines 
a mating, wear surface with the outer circumferences of the arcuate 
segments 81' of the cylindrical sidewall 81. More specifically, as best 
seen in FIG. 2, the rod guide sleeve 72 includes plural interior arcuate 
surfaces 72' in precise conformity and 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. Within 
each of the arcuate recesses 72" there additionally are formed axially 
extending grooves 75, for a purpose to be explained. 
As best seen in FIGS. 3 and 4, the fixed cylindrical support 80 and the rod 
guide sleeve 72 are assembled in coaxial, concentric and telescoping 
relationship, permitting axial movement therebetween while restraining any 
lateral movement such that forces acting on the rod guide 32 are reacted 
through the top end support 38 and into the lower calandria plate 52. To 
facilitate the telescoping assemblage, the sleeve 72 includes an outward 
bevel 78, and the cylindrical support 80 includes an inward bevel 89. 
FIG. 5 comprises a simplified, schematic plan view of the WDRC rod cluster 
34, more particularly comprising 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 88 are 
designed to accommodate the outer pair of rods 94 on the outermost 
cross-bars 92, and the rods 94 at the extremities of the single radial 
arms 92, respectively, so that a given cluster 34 may be raised to the 
extent necessary within the inner barrel assembly and particularly within 
its associated rod guide 32 for the aforementioned control purposes. The 
provision of the grooves 75 and 88 more particularly avoids 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. Where adequate vertical space is available, 
the groove 75 and 88 are not required, and accordingly are optional. 
In accordance with the foregoing, it will be understood that secure 
mounting of the top ends of the WDRC rod guides is afforded, while 
permitting the required vertical displacement of the associated WDRC rod 
clusters. Further, the telescoping interconnections of the sleeves 72 and 
the corresponding fixed cylindrical supports 80 permit the calandria 50 to 
be raised and withdrawn, affording access to the rod clusters 34 within 
the respective guides 32 for normal maintenance purposes. 
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" (141/2 feet) in height. The rod guide sleeve 72 has an outer 
periphery, in cross-section, corresponding to that of the rod guide 70, as 
aforenoted, and defines an inner circumferential support/wear surface of 
approximately 11.20 inches in diameter. The fixed cylindrical support 80 
has a corresponding outer diameter of approximately 11.14 inches thereby 
to afford a nominal 0.030 inch radial clearance to permit the telescoping 
interconnection of the wear surfaces of the cylindrical support 80 and the 
sleeve 72. The end closure 82 of the cylindrical support 80 has a 
thickness as measured in the vertical axial direction of approximately 
1.10 inches. The axial height of the sleeve 72 is approximately 4.0 inches 
whereas the axial length of the cylindrical support 80 is approximately 
4.60 inches in axial height, resulting in a clearance between the upper 
end of the sleeve 72 and the lower surface of the lower calandria plate 52 
of approximately 0.60 inches. The bevels 80 and 89 are each of 
approximately 0.625 inches, resulting in an axial length of the engaged, 
wear surfaces of the inner circumference of the sleeve 72 and the outer 
circumference of the cylindrical support 80 of approximately 2.75 inches. 
The substantial wear surface area thus afforded provides for long life of 
the top end support of the present invention, as before noted. 
Further enhancement of the effective life of the top end support of the 
invention may be achieved by appropriate selection of the materials used 
in fabricating the cylindrical support 80 and the sleeve 72, on at least 
the engaged, wear surfaces thereof. Various weld overlay materials are 
suitable for this purpose. An electro-spark deposited coating having 
particularly desirable characteristics for this purpose, in view of the 
reduced amount of cobalt contained therein, is disclosed in an application 
entitled WEAR RESISTANT ZIRCONIUM BASE ALLOY ARTICLE FOR WATER REACTORS, 
Ser. No. 798,193, filed Nov. 14, 1985 assigned to the common assignee 
herewith. 
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 adapations as fall 
within the true spirit and scope of the invention.