Nuclear fuel bundle packaging apparatus

In a nuclear reactor fuel bundle packaging apparatus including a hollow cylindrical cask (22) and a basket liner assembly (23) receivable within the cask, the basket liner assembly including a plurality of laterally spaced disks (26) rigidly held by a plurality of tie rods (28), and a plurality of elongated hollow basket liners (33) extending through and fixed to the plurality of disks, each hollow basket liner (33) holding a nuclear fuel bundle assembly (10) having an upper tie plate (14), a lower tie plate (16) and a plurality of fuel rods (12) arranged in a substantially square array, extending between the upper and lower tie plates, the improvement comprising an oversized hollow fuel bundle channel (68) received over the fuel bundle assembly, the channel (68) having the same cross sectional shape as the basket liner (33) but sized to fit within the basket liner, the basket liner having at least one slot (74) formed in at least one side thereof at each disk, and at least one spring (72) mounted on the basket liner (33) spanning the slot (74) with one surface of the spring engaging the disk (26) and another surface of the spring engaging an adjacent surface of the oversized hollow fuel bundle channel (68).

TECHNICAL FIELD 
This invention relates generally to the field of nuclear reactors and, 
specifically, to the safe shipment of new or used fuel bundles employed in 
such reactors. 
BACKGROUND 
Nuclear fuel bundle assemblies are highly engineered and costly 
manufactured products. While they are rugged in use, they must be 
protected from damage during shipping not only after initial manufacture, 
but particularly after use. 
There is a conventional shipping container or cask assembly used 
specifically for the shipment of nuclear reactor fuel bundles. This 
container or cask assembly essentially comprises a cylinder closed at one 
end in combination with a "basket liner assembly" slidably receivable 
within the cask. This basket liner assembly is formed by a plurality of 
horizontally spaced disks held together by tie rods extending between the 
first and last of such disks. Each disk is also provided with, for 
example, seventeen square openings arranged in a uniform array and aligned 
with similar openings in the adjacent disks. Each set of aligned openings 
receives an elongated hollow tube, also known as a "basket liner". The 
basket liner has a substantially square cross sectional shape 
corresponding generally to (but larger than) the cross-sectional shape of 
the fuel bundle assemblies, and is welded in place at the various disks. 
New unchanneled fuel bundles, or used channeled fuel bundles are 
receivable within the various basket liners. After the bundles are 
installed in the basket liners, the open end of the cask is sealed shut 
and the cask is ready for shipping. 
DISCLOSURE OF THE INVENTION 
It is the principal purpose of this invention to provide an improved 
packaging system that can be remotely installed and removed, and that will 
better protect nuclear fuel bundle assemblies from damaging shocks and 
vibration during shipping. 
The packaging system in accordance with this invention adds five additional 
components to the conventional cask assembly as described above. A first 
of the new components is referred to herein as a "clustered fuel rod 
separator unit" (or simply as a "separator unit"). For a typical fuel 
bundle assembly, sixty-four (64) such separator units will be utilized. 
Each separator unit comprises three basic parts. First, there is a 
substantially U-shaped holder which fits around one haft of the 
substantially square cross section of the fuel bundle. This holder 
captures a number of substantially parallel planar leaf elements (the 
second part) which extend from the base of the holder and substantially 
parallel to the sides thereof. A third part comprises one or more leaf 
elements specially designed to allow for the shape and size of water rods 
which may be used in the fuel bundle assembly. In use, one separator unit 
is inserted into the bundle such that the planar leaf elements extend 
between the rows of the bundle. These leaf elements increase the rigidity 
of the fuel bundle by allowing each fuel rod to support any other fuel 
rods surrounding it. Another cluster separator unit of the same design is 
inserted into the remaining half of the cross section of the bundle so 
that two such separator units provide full support through the array of a 
selected axial location along the bundle length. An adjacent pair of 
separator units are inserted into the bundle but rotated 90.degree. to the 
first pair so that the fuel rods are supported both horizontally and 
vertically. This alternating arrangement of separator unit pairs is 
repeated along the length of the bundle, with four pairs of separator 
units installed between the conventional fuel rod spacer elements 
(typically, seven such spacers are used in a typical bundle). 
The separator units in accordance with this invention have been provided 
with specially shaped notches to facilitate insertion and removal with an 
automated machine, and these operations can be carried out under water if 
required. 
A second of the five new components in accordance with the invention is an 
oversized protective channel. With the separator units described above 
inserted within the bundle, the standard fuel bundle channel is unable to 
fit over the bundle. The oversized protective channel in accordance with 
this invention is sized to be slidably received over the bundle and to 
hold the separator units in place. This oversized channel provides 
additional rigidity and protection to the fuel bundle. If installed over 
used irradiated fuel, the oversized protective channel is designed to 
replace the existing channel and to use similar hardware to fit the 
existing upper and lower tie plates. If installed over new fuel, which is 
typically shipped separately from its channel (in a channel-like shipping 
container), the separate shipping container can be eliminated. 
A third component of the packaging system in accordance with this invention 
comprises a flat leaf spring, a plurality of which are used to hold the 
(oversized) channeled fuel bundles within the basket liners in a 
resiliently biased fashion. 
A fourth component of the packaging system is a specially designed bottom 
spring used at the bottom of the basket liner to cushion the fuel bundle 
assembly, and to minimize undesirable accelerations and loads on the 
bundle during shipping, or when the shipping container is raised to an 
upright position. 
A fifth packaging component relates to polyethylene spacers utilized to 
occupy excess space between a spacer plate in the top of the shipping 
container or cask and the top of the fuel bundle within the cask. In the 
exemplary embodiment, spacer pads secured to the spacer plate of the cask 
at locations aligned with each basket liner, are covered with polyethylene 
sheets to prevent metal-to-metal contact between upper tie plate handles 
(which protrude beyond the individual basket liners) and the end plate 
pads. This also serves to reduce the axial space or play between the 
individual bundles and the cask ends. This is done to minimize the 
distance the fuel bundle can slide or drop during handling or shipping 
which, in turn, minimizes undesirable accelerations and loads on the fuel 
bundle assembly. 
Accordingly, in one aspect, the present invention relates to a nuclear 
reactor fuel bundle packaging apparatus including a hollow cylindrical 
cask and a basket liner assembly receivable within the cask, the basket 
liner assembly including a plurality of laterally spaced disks rigidly 
held by a plurality of tie rods, and a plurality of elongated hollow 
basket liners extending through and fixed to the plurality of disks, each 
hollow basket liner holding a nuclear fuel bundle assembly having an upper 
tie plate, a lower tie plate and a plurality of fuel rods arranged in a 
substantially square array, extending between said upper and lower tie 
plates, the improvement comprising an oversized hollow fuel bundle channel 
received over the fuel bundle assembly, the channel having the same cross 
sectional shape as the basket liner member but sized to fit within the 
basket liner member, the basket liner having at least one slot formed in 
at least one side thereof at each disk, and a spring mounted on the basket 
liner spanning the slot with one surface of the spring engaging the disk 
and another surface of the spring engaging an adjacent surface of the 
oversized protective channel. 
In another aspect, the invention relates to a nuclear reactor fuel bundle 
packaging apparatus including a hollow cylindrical cask and a basket liner 
assembly receivable within the cask, the basket liner assembly including a 
plurality of laterally spaced disks rigidly held by a plurality of tie 
rods, and a plurality of elongated hollow basket liners extending through 
and fixed to the plurality of disks, each hollow basket liner holding a 
nuclear fuel bundle assembly having an upper tie plate, a lower tie plate 
and a plurality of fuel rods arranged in a substantially square array, 
extending between the upper and lower tie plates, the improvement 
comprising first means for keeping the fuel rods in the array separated 
from each other; second means for resiliently laterally biasing the fuel 
bundle within the basket liner; third and fourth means for preventing 
substantial axial movement of the fuel bundle within the basket liner, the 
third and fourth means located at opposite ends, respectively, of the 
basket liner member. 
In still another aspect, the invention relates to a nuclear reactor fuel 
bundle packaging apparatus including a hollow cylindrical cask and a 
basket liner assembly receivable within the cask, the basket liner 
assembly including a plurality of laterally spaced disks rigidly held by a 
plurality of tie rods, and a plurality of elongated hollow basket liners 
extending through and fixed to the plurality of disks, each hollow basket 
liner holding a nuclear fuel bundle assembly having an upper tie plate, a 
lower tie plate and a plurality of fuel rods arranged in a substantially 
square array, extending between the upper and lower tie plates, the 
improvement comprising means for resiliently holding the fuel bundle 
assembly within the basket liner, the means capable of exerting resilient 
biasing forces on the fuel bundle assembly in at least two mutually 
perpendicular directions. 
Additional objects and advantages of the subject invention will become 
apparent from the detailed description which follows.

BEST MODE FOR CARRYING OUT THE INVENTION 
With reference to FIG. 1, a conventional fuel bundle assembly 10 comprises 
generally a plurality of fuel elements or rods 12 supported between an 
upper tie plate 14 and a lower tie plate 16. The fuel rods 12 pass through 
a plurality of fuel rod spacers 18 which provide intermediate support to 
retain the elongated rods 12 in spaced relation, and to restrain them from 
lateral vibration. These spacers 18 are located at axially spaced 
positions along the length of the bundle, and in a typical bundle, seven 
such spacers 18 may be employed. Within the fuel rod bundle 10, certain of 
the rods about the periphery of the bundle are tie rods rigidly connecting 
the upper tie plate 14 and lower tie plate 16. In addition, two rods 
within the interior foursome of each bundle may comprise water rods 
adapted to introduce moderating material within the bundle interior. One 
of the water rods also serves as the spacer capture rod which is 
mechanically locked to each of the seven fuel rod spacers 18. In the 
conventional assembly shown, the fuel bundle contains 64 rods (including 
the water rods) spaced and supported in a square, 8.times.8 array. The 
fuel bundle 10 as illustrated in FIG. 1 is enclosed within a bundle 
channel 20 which comprises a substantially square-shaped tubular member 
extending between the upper tie plate 14 and the lower tie plate 16. 
The rods in the bundle may be between 13 and 14 feet in length with a 
diameter of less than 0.5 inch OD, and a wall thickness of 32 mils. It 
will be appreciated that these rods must be well protected during shipment 
and handling prior to use and after use. 
Before describing in detail the individual fuel bundle assembly packaging 
components of this invention, however, a conventional cask and related 
hardware for shipping fuel rod bundles will be reviewed briefly. 
With reference to FIGS. 2 and 3, a conventional outer cask 22 (shown in 
simplified fashion for ease of understanding) is essentially a hollow 
cylinder of relatively thick wall construction, with one closed end and 
one open end adapted to be closed and sealed by an end cap (not shown). 
The interior volume of the cask is also cylindrical in shape, as defined 
by the interior wall surface 24. The cask itself forms no part of this 
invention, and the drawings here illustrate generally only the cylindrical 
side wall of a commercially available cask, known as the Shoreham IF300 
fuel cask assembly. Several fuel bundles, seventeen (17) in the example 
shown and described here, may be supported within the cask 22, each bundle 
received within a hollow "basket liner" (described below) which, in turn, 
is supported in a basket liner frame or holder 23. 
The basket liner frame or holder 23 for the cask consists of a series of 
axially spaced disks 26, held together by four tie rods 28 as shown in 
FIG. 4. The disks 26 are substantially identical, and as best seen in FIG. 
5, each disk 26 in this particular assembly is formed with seventeen (17) 
substantially square openings 30, along with four round openings 31. The 
latter are designed to receive the tie rods 28 while the former are sized 
and arranged to receive individual fuel bundle basket liners 33. Each 
basket liner 33 is an elongated, hollow tube of substantially square 
cross-section, which is adapted to be received in an aligned group of 
square openings 30 in disks 26. One such basket liner 33 is shown in place 
in FIG. 4 and 5, the remaining basket liners having been omitted for the 
sake of clarity. It will be appreciated that the basket liner holder can 
hold up to seventeen basket liners, each supported by the nine axially 
spaced disks 26. Each basket liner 33 is welded preferably at least to the 
disks 26 at opposite ends of the holder, but may be welded to additional 
disks 26 as well. The basket liner holder assembly as described above is 
of conventional construction, with the exception of modifications 
described herein. 
The invention here relates to the manner in which the individual fuel 
bundle assemblies are packaged and supported within the individual basket 
liners and within the cask assembly as a whole. 
There are essentially five packaging components in accordance with this 
invention which together provide for enhanced packaging of the fuel bundle 
assemblies: 1) clustered fuel rod separators; 2) oversize protective 
channels; 3) basket liner leaf springs; 4) bottom cushioning 
spacers/springs; and 5) improved top spacers. Each will be described in 
detail below. 
Clustered Fuel Rod Separators 
With reference now to FIGS. 6-11, a clustered fuel rod packaging separator 
unit 32 in accordance with this invention includes an elongated, 
substantially U-shaped and relatively rigid holder 34 comprised of a base 
wall 36 and a pair of perpendicularly extending end walls 38 and 40. 
Within this substantially U-shaped enclosure, a plurality of substantially 
planar, relatively flexible separator leaves 42 are secured to the base 
wall 36 and extend in a direction perpendicular to the base wall and 
substantially parallel to the end walls 38, 40. The separator leaves 42 
are spaced within the holder to correspond substantially to the spacing 
between the fuel rods 12. These leaves 42 are secured to the base wall 36 
of the separator holder 34 by means of a plurality of integral leaf 
anchoring pins 44 which serve to hold the leaves substantially 
perpendicular to the holder base wall 36 when assembled, despite the 
relative thin cross-section of the holder. 
As best seen in FIGS. 8 and 9, each pin 44 is substantially cylindrical in 
shape, with a tapered end 46 joined to the leaf 42, and an enlarged head 
48 projecting beyond the leaf. The head 48 is split by a slot or groove 50 
to facilitate insertion into counterbored holes 52 (see FIG. 11) provided 
in the base wall 36. It will be appreciated that during insertion, the 
head 46 will compress inwardly and then spring outwardly as it passes into 
the larger diameter portion of the counterbored holes 52. This arrangement 
not only insures easy assembly of the separator leaves 42 within the 
holder 34, but also makes it difficult (but not impossible) to remove the 
separator leaves 42 from the holder 34. 
With reference specifically to FIG. 10, each leaf 42 is provided with a 
plurality of ribs or ridges 54 (six in the exemplary embodiment) which 
extend longitudinally between the edges 56, 58 of the leaf, in 
substantially parallel relationship with each other. These ridges or ribs 
54 project alternately from opposite sides of the separator leaf (as best 
seen in FIG. 12), and are designed to reduce frictional contact with the 
fuel rods 12 and thereby also reduce the potential of fretting of the rods 
from the spacer springs during shipment. Ribs 54 also minimize the forces 
exerted on the fuel rods by the clustered separator units as a whole. The 
leaf construction described above provides maximum protection for the fuel 
rods 12 and also allows for easy insertion and removal relative to the 
fuel bundle. In the exemplary embodiment shown, the separator unit 32 is 
designed for use with a 7.times.7 array of fuel rods. It will be 
understood, however, that the separator unit (and indeed the invention as 
a whole) may be configured for use with various fuel bundle 
configurations. 
The end walls 38, 40, of the holder 34 are each provided with a pair of 
aligned recesses 60 adjacent the base wall 36, as well as a pair of 
aligned cut-out notches 62 at their free ends remote from the base wall 
36, as shown in FIG. 7. Recesses 60 are adapted for engagement with 
automated and remote installation equipment while notches 62 are designed 
to facilitate manual insertion and removal of the separator units 
vis-a-vis the bundle. 
The interior or inside surfaces of the holder 34 may be molded to include a 
waffle pattern of ribs 64 (as on the inside base wall shown in FIG. 11), 
and/or elongated, parallel ribs 66 (as on the inside surfaces of the 
respective end portions also shown in FIG. 11). This insures a relatively 
rigid holder which will maintain the overall shape of the unit in use. 
Turning now to FIG. 13, a pair of clustered separator units 32 are shown at 
"A", inserted between the fuel rods from opposite sides until the ends 36, 
38 approximately abut each other. An adjacent pair of clustered separator 
units 32 are inserted at "B" between the fuel bundle rods, but rotated 
90.degree. from the first set of separator units. By so alternating 
adjacent pairs of the separator units, (as shown at C, D, etc.) support 
and protection are provided to the fuel rods in both vertical and 
horizontal modes of oscillations. In the exemplary embodiment, four pair 
of alternately rotated clustered separator units 32 may be installed 
between each adjacent pair of spacers 18. Thus, in an exemplary embodiment 
where seven spacers 18 are employed along the length of the fuel bundle, 
sixty-four (64) such separator units 32 will be utilized to protect the 
fuel rods during shipment. 
The entire clustered separator unit 32 may be constructed of low-density 
polyethylene or other suitable plastic or metal material. 
It is also contemplated that the separator material be impregnated with (or 
otherwise contain) neutron absorbing or moderating materials, or materials 
which can attenuate the gamma or neutron radiation, i.e., a neutron poison 
such as boron compounds, alloys or mixtures. By incorporating a neutron 
poison in the separator material, criticality control is enhanced and 
thus, cask capacity and overall system efficiency can be significantly 
improved. Traditionally, the spent fuel shipping cask is the component 
that contains the neutron poison for criticality control purposes. 
However, it has now been recognized that for some fuel, the neutron poison 
may be separate from the cask or canister. In other words, the poison may 
be incorporated into the fuel rod matrix so as to further reduce the 
overall reactivity of the bundle. As a result, spacing between bundles can 
be reduced, thereby enabling more bundles to be packed into a single given 
size cask. Alternatively, larger casks with greater numbers of bundles can 
be utilized in light of the reduction in reactivity afforded by the use of 
poison impregnated separators. In addition, when the bundles have finally 
reached their place of storage, the fuel bundle assemblies can be stored 
closer together, thereby resulting in even further efficiency. 
Oversize Protective Channel 
With reference to FIGS. 13, 14 and 15, the fuel bundle assembly with its 
clustered fuel rod separators 32 installed as shown in FIG. 13, is 
inserted into a square section, oversized protective channel 68 (FIG. 14) 
which holds the clustered fuel rod separators 32 in place, and provides 
additional rigidity and protection to the fuel bundle. This protective 
channel 68, if installed over irradiated fuel, is designed to replace the 
existing channel 20, and uses similar hardware to fit the existing upper 
and lower tie plates 14, 16, respectively. 
For new fuel, the oversized channel 68 replaces the separate shipping 
channel now usually employed in the shipment of fuel bundles (the bundle 
channel 20 is typically shipped in a separate container). 
It will be appreciated, however, that if the clustered fuel rod separators 
32 were made thin enough so as to allow the bundle channel 20 to slide 
over the bundle, then the oversized channel 68 would not be needed. For 
purposes of discussion here, however, it will be assumed that the 
oversized channel 68 is part of the packaging system. 
The oversized channel 68 optionally may be provided with a series of 
axially spaced slots 70 which permit visual inspection of the bundles, and 
particularly the clustered fuel rod separators 32, so that their proper 
location and alignment of the latter relative to the bundle can be 
confirmed. 
Basket liner Leaf Springs 
Individual leaf springs 72 in accordance with this invention are utilized 
to hold the channeled fuel bundle (with the standard or oversized channel) 
firmly against a wall of the basket liner 33 in which the channeled bundle 
is inserted. To this end, elongated slots 74 are formed in the basket 
liner, as best seen in FIGS. 4, 18 and 19. These slots 74 are shown in one 
side wall surface of the basket liner 33, running parallel to the axis of 
the basket liner but offset from one another. In the preferred 
arrangement, the slots 74 are located only on one horizontal side surface 
of the basket liner, one slot 74 for each disk 26. It will be appreciated 
however, that the number and placement of slots (and associated leaf 
springs) may vary depending on weight and specific configuration of the 
bundle. Each slot 74 is bordered by clips 76, 78 welded to the basket 
liner 33 adjacent axial ends of the slots. Each pair of clips 76, 78 is 
designed to hold a single leaf spring, as described below, centered 
relative to respective slot 74. 
With reference now to FIGS. 16 and 17, a leaf spring 72 is illustrated 
which includes an elongated metal strip (preferably made of Inconel) and 
appropriately hardened or otherwise heat treated. The metal strip is 
formed to include a pair of co-planar end portions 80, 82 connected by 
angled center portion 84. The latter is connected to the end portions 80, 
82 by similarly angled (i.e., substantially parallel) connecting portions 
86, 88. To insure proper orientation, one side of the spring may be 
labelled "This Side Up" (or similar message). 
In use, each spring 72 is located such that end portions 80, 82 are held in 
the pair of clips 76, 78, respectively, with the angled centered portion 
84 passing through the associated slot 74, as best seen in FIGS. 18 and 
19. It will be seen that the oppositely facing surfaces along which the 
angled center portion 84 meets the connecting portions 86, 88 bear on the 
adjacent disk 26 outside the basket liner, and the oversized channel 68 
inside the basket liner, as best seen in FIG. 17. As indicated above, 
these springs are located along one side surface 90 of the basket liner 
33, recognizing that the cask 22 is oriented horizontally when shipped. 
Thus, the individual fuel bundles, lying horizontally within the 
cask/basket liner assembly, are biased towards the opposite, interior side 
surface of the basket liner by leaf springs 72. It will also be 
appreciated that, during insertion of the bundles into the basket liner, 
the springs 72 will flex sufficiently to allow complete axial insertion. 
The arrangement and number of leaf springs 72 is not limited by the 
arrangement described above, and may vary in accordance with particular 
applications of the invention. 
The Bottom Spring 
With reference now to FIGS. 20 and 21, a bottom spring 92 is designed to be 
placed at the bottom of the basket liner, i.e., between the lower tie 
plate and nozzle of the fuel bundle and the closed end of the cask. The 
spring 92 includes a flat base 94 and a substantially cylindrical spring 
body 96 provided with peripheral slots 98 through the full thickness of 
the body 96. Four slots are formed at a given axial location, connected by 
webs 100. 
In the illustrated embodiment, three groups of slots 98, 98A and 98B are 
formed at three axial positions along the body 96. The upper and lower 
groups of slots 98 and 98B (as viewed in FIG. 20) are substantially 
vertically aligned whereas the intermediate group of slots 98A are offset 
by substantially 90.degree.. This arrangement allows the cylindrical body 
96 to resiliently compress and expand in the nature of a spring. 
In use, a spring 92 is placed in the bottom of each basket liner 33, before 
insertion of the respective fuel bundle. The spring cushions the bundle 
when it is in an upright position (i.e., under the weight of the bundle), 
and minimizes undesirable accelerations and loads on the bundle during 
shipment. 
The Top Plate Spacer 
In the current cask construction, a spacer disk 102 is located between the 
cask assembly top plate or end disk 26- and the cask end (not shown). This 
spacer disk 102, as shown in FIG. 22 is essentially a round disk with a 
plurality of openings 104 corresponding in number and location with the 
seventeen basket liners 33 in the basket liner assembly. Over each opening 
104 there is bolted a square spacer plate 106, fixed at opposite diagonal 
ends by suitable fasteners 108, 110 to the surface of the plate 102 which 
faces the cask interior, i.e., the basket liner assembly. These metal 
spacer plates 106 are axially aligned with each basket liner and serve to 
reduce the axial clearance between the upper end of the fuel bundle 
assembly (and particularly the handle 112 on the upper tie plate) and the 
spacer plate. In order to prevent metal-to-metal rubbing action between 
the handles 112 and the spacer plates 106, there are provided additional 
spacer plates 114 constructed (preferably) of polyethylene (or other 
suitable material) and applied over the existing spacer plates 106. The 
plastic spacer plates 114 are secured via bolts or screws (countersunk) 
107, 109 to the existing plates as shown in FIGS. 20 and 21. The plastic 
spacers, which may be 1/4 to 3/8 inch thick, serve to further reduce axial 
clearance, thus further minimizing the axial distance the fuel bundle 
assembly can slide or drop during handling and shipping. This, in turn, 
minimizes undesirable acceleration and loads on the fuel bundle. 
From the above description, it will be appreciated that the above described 
components, both individually and collectively, improve the existing cask 
assembly by providing increased protection for nuclear fuel bundles during 
shipment. It should also be noted that all of the above components can be 
installed remotely with automated machines, and can be installed and/or 
removed underwater where required. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiment, it is to be 
understood that the invention is not to be limited to the disclosed 
embodiment, but on the contrary, is intended to cover various 
modifications and equivalent arrangements included within the spirit and 
scope of the appended claims.