Note: Descriptions are shown in the official language in which they were submitted.
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PRESSURE TUBE-TO-END FITTING COUPLING AND
METHOD OF ASSEMBLING NUCLEAR REACTOR FUEL CHANNEL ASSEMBLY
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from US Provisional Patent
Application No.
62/524,267 filed on June 23, 2017, the contents of which are hereby
incorporated by
reference.
FIELD
[0002] This relates to methods and systems for coupling a pressure tube
to an
end fitting in a nuclear reactor fuel channel assembly.
BACKGROUND
[0003] A nuclear reactor has a limited life of operation. For example,
second
generation CANDUTm-type reactors ("CANada Deuterium Uranium") are designed to
operate for approximately 25 to 30 years. After this time, the existing fuel
channels can
be removed and new fuel channels can be installed. Performing this "retubing"
process
can extend the life of a reactor significantly, as an alternative to
decommissioning the
reactor. Nuclear reactor retubing processes include removal of a large number
of
reactor components and include various other activities, such as shutting down
the
reactor, preparing the vault, and installing material handling equipment and
various
platforms and equipment supports. The removal process can also include
removing
closure plugs and positioning hardware assemblies, disconnecting feeder
assemblies,
severing bellows, removing end fittings, releasing and removing calandria tube
inserts,
and severing and removing pressure tubes and calandria tubes.
[0004] After the removal process is complete, an inspection and
installation
process is typically performed. For example, tube sheets positioned at each
end of the
reactor may include a plurality of bores. Each of the plurality of bores
supports a fuel
channel assembly that spans between the tube sheets. When a fuel channel
assembly
is removed, each tube sheet bore is inspected to ensure that the removal of
the fuel
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channel assembly has not damaged the tube sheet bore and that the tube sheet
bore is
ready for insertion of a new fuel channel assembly.
[0005] After the tube sheets are confirmed to be in suitable condition,
the
calandria tubes, pressure tubes, end fittings, and other components can be re-
installed
into the bores. For each fuel channel assembly, part of this process involves
inserting a
sub-assembly consisting of an end fitting and pressure tube that has been
rolled on one
side of the reactor (for example, in an assembly area), inserting an end
fitting body into
the opposite side lattice tube, rolling the end of the pressure tube into the
end fitting
body, and inserting an end fitting liner into the end fitting.
[0006] Accordingly, there is a need for improved systems and methods for
coupling a pressure tube to the end fitting of a fuel channel assembly without
damaging
the end fitting or end fitting liner.
SUMMARY
[0007] The present provides a nuclear reactor core comprising a calandria
vessel
having a shell and a tube sheet on an end of the shell and defining an
aperture, a
calandria tube coupled to the tube sheet (e.g., using a calandria insert) and
extending
into the annular shell, a lattice tube coupled to the tube sheet (e.g.,
integrally) and
extending toward an exterior of the reactor core, an end fitting body
positioned at least
partially in the lattice tube, a pressure tube positioned at least partially
in the calandria
tube and have an end secured to the end fitting body, and an end fitting liner
positioned
at least partially in the end fitting body coaxial with the pressure tube. An
end of the end
fitting liner adjacent the pressure tube includes a first inner surface having
a roller
clearance counter bore.
[0008] The present also provides a method of securing a pressure tube to
an end
fitting body in a nuclear reactor core including a calandria vessel having a
shell and a
tube sheet on an end of the shell, a calandria tube coupled to the tube sheet
and
extending into the annular shell, a lattice tube coupled to the tube sheet and
extending
outwardly away from the reactor core, and an end fitting body positioned at
least
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partially in the lattice tube. The method comprises inserting an inner end of
an end
fitting liner into an end fitting body, positioning the pressure tube inside
the calandria
tube with an end of the pressure tube axially overlapped with a portion of the
end fitting
body, introducing a rolling tool into the end fitting liner until a roller of
the rolling tool is
axially overlapped with the pressure tube, deforming the end of the pressure
tube into
the end fitting body by rotating the rolling tool and moving the roller
radially outward into
contact with the pressure tube, and axially overlapping (i.e., positioning to
establish
common axial position(s)) the roller with the inner end of the end fitting
liner during the
deforming step. In one embodiment, the inner surface of the inner end of the
end fitting
liner includes a counter bore, and the step of axially overlapping includes
positioning at
least a portion of the roller in the counter bore. In some embodiments, the
end fitting
liner includes a latch, and the step of introducing a rolling tool includes
moving the latch
to an unlatched position, such as by axial movement of the rolling tool.
[0009] According to an aspect, there is provided a nuclear reactor core
comprising: a calandria vessel having a shell and a tube sheet on an end of
the shell
and the tube sheet defining an aperture; a calandria tube coupled to the tube
sheet and
extending into the annular shell; a lattice tube coupled to the tube sheet and
extending
outwardly away from the reactor core; an end fitting body positioned at least
partially in
the lattice tube; a pressure tube positioned at least partially in the
calandria tube and
having an end secured to the end fitting body; and an end fitting liner
positioned at least
partially in the end fitting body coaxial with the pressure tube, wherein an
end of the end
fitting liner adjacent the pressure tube includes a first inner surface having
a counter
bore.
[0010] According to another aspect, there is provided a method of
securing a
pressure tube to an end fitting body in a nuclear reactor core including a
calandria
vessel having a shell and a tube sheet on an end of the shell, a calandria
tube coupled
to the tube sheet and extending into the annular shell, a lattice tube coupled
to the tube
sheet and extending outwardly away from the reactor core, and an end fitting
body
positioned at least partially in the lattice tube, the method comprising:
inserting an inner
end of an end fitting liner into the end fitting body; positioning the
pressure tube inside
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the calandria tube with an end of the pressure tube axially overlapped with a
portion of
the end fitting body; introducing a rolling tool into the end fitting liner
until a roller of the
rolling tool is axially aligned with the pressure tube; deforming the end of
the pressure
tube into the end fitting body by rotating the rolling tool to move the roller
radially
outward into contact with the pressure tube; and axially aligning the roller
with the inner
end of the end fitting liner during the deforming.
[0011] Other features will become apparent from the drawings in
conjunction with
the following description.
BRIEF DESCRIPTION OF DRAWINGS
[0012] In the figures which illustrate example embodiments:
[0013] FIG. 1 is a perspective view of a CANDUTm-type reactor.
[0014] FIG. 2 is a cutaway perspective view of a CANDUTm-type nuclear
reactor
fuel channel assembly, according to an embodiment.
[0015] FIG. 3 is a cross-sectional view along lines I-I of a portion of
the fuel
channel assembly shown in FIG. 2 immediately outboard of the tube sheet at the
bottom
of FIG. 2, according to an embodiment.
[0016] FIG. 4A is a cross-sectional view of the portion of the fuel
channel
assembly of FIG. 3, shown without a fuel bundle and with a joint rolling tool
axially
inserted into the fuel channel assembly to a first axial working position with
rollers of the
joint rolling tool in a retracted position, according to an embodiment.
[0017] FIG. 4B is a cross-sectional view of the portion of the fuel
channel
assembly of FIG. 3, shown without a fuel bundle and with a joint rolling tool
axially
inserted into the fuel channel assembly to a second axial working position
with rollers of
the joint rolling tool in an extended position, according to an embodiment.
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DETAILED DESCRIPTION
[0018] FIG. 1 is a perspective view of a reactor core of a CANDUTm-type
Pressurized Heavy Water Reactor (PHWR) 6. In some embodiments, the PHWR may
be a 100-300 MW CANDUTM reactor, a 600MW CANDUTM reactor, a 900MW CANDU TM
reactor, or a 1000 MW CANDUTM reactor. The reactor core is typically contained
within
a vault that is sealed with an air lock for radiation control and shielding.
Although
aspects of the disclosure are described with particular reference to the
CANDUTm-type
reactor 6 for convenience, the disclosure is not limited to CANDUTm-type
reactors, and
may be useful outside this particular field as well. In use, the reactor core
is typically
contained within a vault that is sealed with an air lock for radiation control
and shielding.
[0019] A generally cylindrical vessel, known as calandria vessel 10 of
the
CANDUTm-type reactor 6, contains a heavy-water moderator. In some embodiments,
calandria vessel 10 has an annular shell 14 and a tube sheet 18 at a first end
22 and a
second end 24. Tube sheets 18 include a plurality of apertures 19 (referred to
herein as
"bores" 19) that each accept a fuel channel assembly 28. As shown in FIG. 1, a
number
of fuel channel assemblies 28 pass through tube sheets 18 of calandria vessel
10 from
first end 22 to second end 24.
[0020] As shown in FIG. 2, in some embodiments the reactor core is
provided
with two walls at each end 22, 24 of the reactor core: an inner wall defined
by tube
sheet 18 at each end 22, 24 of the reactor core, and an outer wall 64 (often
referred to
as a "end shield") located a distance outboard from tube sheet 18 at each end
22, 24 of
the reactor core. A lattice tube 65 spans the distance between tube sheet 18
and end
shield 64 at each pair of bores 19 (i.e., in the tube sheet 18 and the end
shield 64,
respectively). In the embodiment illustrated in FIG. 2, the lattice tube 65 is
formed
integrally with the tube sheet 18, but in some embodiments could be formed as
a
separate part.
[0021] FIG. 2 illustrates a cutaway view of one fuel channel assembly 28
of the
reactor core illustrated in FIG. 1. As illustrated in FIG. 2, each fuel
channel assembly 28
includes a calandria tube ("CT") 32 surrounding other components of the fuel
channel
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assembly 28. Calandria tubes 32 each span the distance between tube sheets 18
from
first end 22 to second end 24. Also, the opposite ends of each calandria tube
32 are
received within and sealed to respective bores in the tube sheets 18. In some
embodiments, a rolled joint insert such as a calandria insert 70 is used to
secure each
calandria tube 32 to tube sheet 18 within a bore 19. A pressure tube ("PT") 36
forms an
inner wall of fuel channel assembly 28. Pressure tube 36 provides a conduit
for reactor
coolant and fuel bundles or assemblies 40. Pressure tube 36, for example,
generally
holds two or more fuel assemblies 40, and acts as a conduit for reactor
coolant that
passes through each fuel assembly 40. An annulus space 44 is defined by a gap
between each pressure tube 36 and its corresponding calandria tube 32.
[0022] Annulus space 44 is normally filled with a circulating gas, such
as dry
carbon dioxide, helium, nitrogen, air, or mixtures thereof. One or more
annulus spacers
or garter springs 48 are disposed between calandria tube 32 and pressure tube
36.
Annulus spacers 48 maintain the gap between pressure tube 36 and corresponding
calandria tube 32, while allowing passage of annulus gas through and around
annulus
spacers 48.
[0023] As also shown in FIG. 2, each end of each fuel channel assembly 28
is
provided with an end fitting assembly 50 located outside of corresponding tube
sheet
18. Each end fitting assembly 50 includes an end fitting body 57 and an end
fitting liner
59. At the terminal end of each end fitting assembly 50 is a closure plug 52.
Each end
fitting assembly 50 also includes a feeder assembly 54.
[0024] Feeder assemblies 54 feed reactor coolant into or remove reactor
coolant
from the PTs 36 via feeder tubes. In particular, for a single fuel channel
assembly 28, a
feeder assembly 54 on one end of the fuel channel assembly 28 acts as an inlet
feeder,
and a feeder assembly 54 on the opposite end of the fuel channel assembly 28
acts as
an outlet feeder.
[0025] As shown in FIG. 2, feeder assemblies 54 can be attached to the
end
fitting assemblies 50 using a coupling assembly 56 including a number of
screws,
washers, seals, and/or other types of connectors. Lattice tube 65 (described
above)
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encases the connection between the end fitting assembly 50 and the pressure
tube 36
containing the fuel assemblies 40. Shielding ball bearings 66 and cooling
water
surround the exterior of the lattice tubes 65, which may provide additional
radiation
shielding.
[0026] A positioning hardware assembly 60 and bellows 62 are also coupled
to
each end fitting assembly 50. Bellows 62 allows the fuel channel assemblies 28
to move
axially ¨ a capability that can be important where fuel channel assemblies 28
experience changes in length over time, which is common in many reactors.
Positioning
hardware assemblies 60 may be used to set an end of a fuel channel assembly 28
in
either a locked configuration that fixes the axial position or an unlocked
configuration.
Positioning hardware assemblies 60 are also coupled to the end shield 64. The
illustrated positioning hardware assemblies 60 each include a rod having an
end that is
received in a bore of the respective end shield 64. In some embodiments, the
rod end
and the bore in end shield 64 are threaded. Again, it should be understood
that although
a CANDUTm-type reactor is illustrated in FIGS. 1-2, in other embodiments, the
features
described may also apply to other types of reactors, including reactors having
components that are similar to those illustrated in FIGS. 1-2.
[0027] Referring to FIGS. 3 and 4A, 4B, calandria tube 32 includes ends
positioned in corresponding openings in tube sheet 18. Each end includes a
calandria
insert 70 that is rolled radially outwardly to secure the calandria tube 32 to
the tube
sheet 18. The pressure tube 36 is then inserted into the calandria tube 32 and
held
concentrically within and with respect to calandria tube 32 by annular spacers
48 (see
FIG. 2).
[0028] End fitting assembly 50 (see FIG. 2), including end fitting body
57 and end
fitting liner 59, is then inserted into lattice tube 65 such that an inner end
of the end
fitting assembly 50 receives the end of pressure tube 36, as shown in FIG. 3.
End fitting
body 57 can include a series of annular grooves 72 adapted to facilitate
securing the
pressure tube 36 to the end fitting assembly 50 and creating a fluid-tight
seal
therebetween, as described below in more detail. After the end fitting
assembly 50 is
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inserted into lattice tube 65, annular grooves 72 will be axially overlapped
with the end
of pressure tube 36.
[0029] End fitting liner 59 includes an inner support surface 73 that can
support
an end of a fuel bundle 40 during insertion into fuel channel assembly 28, and
in some
embodiments during operation of the nuclear reactor. It can be seen that the
inner end
of end fitting liner 59 also includes a counter bore 74 defining an inner
counter bore
surface with an inner diameter that is larger than support surface 73. In some
embodiments, a counter bore region of end fitting body 57 may also have an
inner
diameter that is greater than a surface of the remaining end fitting body 57.
[0030] The end fitting liner 59 illustrated in FIG. 3 also includes a
pivotable latch
76 that is biased toward the latched position.
[0031] In some embodiments, latch 76 has a hinge (not shown) at a first
end of
arm 92. Latch 76 rotates about axis A by way of hinge . At a second end,
opposing the
first end of arm 92, latch 76 may have a ramp 94 leading to a ledge 96. Ledge
96 may
form a right angle. Latch 76 may be formed of metal, for example, spring
steel, and
operatively connected to the wall of end fitting liner 59. Latch 76 may be
spring-loaded
to bias into a latched position, for example as shown in FIG. 3.
[0032] Latch 76 is designed to retain the fuel bundle 40 in the pressure
tube 36.
Latch 76 may inhibit axial movement of fuel bundle 40 once fuel bundle 40
engages
with ledge 96 of latch 76. In other embodiments, no such latch 76 is provided.
[0033] In order to secure pressure tube 36 to end fitting assembly 50,
the end of
pressure tube 36 is roll-formed radially outwardly such that the end of the
pressure tube
36 is deformed into annular grooves 72 on the inside surface of end fitting
body 57, as
shown in FIG. 3. This rolling operation may be accomplished using a rolling
tool 78,
such as PT Rolled Joint Expander Part No. RT38-17000-010 manufactured by
Commonwealth Manufacturing, Mississauga, Ontario, Canada.
[0034] As shown in FIGS. 4A and 4B, in some embodiments rolling tool 78
has a
leading end 82. Axis D extends through the center of rolling tool 78. In some
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embodiments, rolling tool 78 includes a cage 84. Cage 84 may be generally
cylindrical,
with a hollow center extending axially from leading end 82 to an opposing end.
Cage 84
also includes apertures extending radially around the curved surface of cage
84, in
which rollers 80 are retained.
[0035] In some embodiments, cage 84 may be integrally formed or attached
to a
collar 88 and a body 89. Collar 88 and body 89 may be generally cylindrical,
with a
hollow center extending radially along axis D.
[0036] A mandrel 86 extends through the hollow center of cage 84, collar
88 and
body 89. Mandrel 86 may be tapered, with the smaller diameter end of mandrel
86
adjacent leading end 82 of rolling tool 78, and mandrel 86 may be operable to
move
axially within the hollow center of cage 84 to make contact and apply radial
force on
rollers 80 to move rollers 80 radially with reference to axis D.
[0037] A rolling operation to secure pressure tube 36 to end fitting
assembly 50
will now be described in more detail.
[0038] A rolling operation may be initiated by inserting rolling tool 78
through end
fitting liner 59 in direction B.
[0039] Prior to inserting rolling tool 78 through end fitting liner 59, a
protective
sleeve 79 may be inserted in end fitting liner 59. In some embodiments,
protective
sleeve 79 may be cylindrical in shape with an outer diameter sized to fit
within end fitting
liner 59 and an inner diameter sized to provide clearance for rolling tool 78.
Protective
sleeve 79 may be formed of metal, or other suitable material as would be known
by a
person skilled in the art. Protective sleeve 79 may prevent rolling tool 78
from directly
contacting end fitting liner 59, and thus may prevent rolling tool 78 from
damaging end
fitting liner 59, as the mass and lubricant of rolling tool 78 may scratch end
fitting liner
59 if it comes into contact with it. In some embodiments, protective sleeve 79
remains in
fuel assembly 40 for the duration of use of rolling tool 78, and is removed
from fuel
channel assembly 40 during operation of reactor 6.
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[0040] During insertion of rolling tool 78 through end fitting liner 59,
leading end
82 of rolling tool 78 may engage the latch 76 (if present), and pivot the
latch 76 to an
unlatched position (see FIGS. 4A and 4B) to provide the needed clearance for
further
insertion of rolling tool 78. Upon sufficient axial insertion of rolling tool
78 towards
pressure tube 36 (i.e., in direction B as shown in FIGS. 4A and 4B), leading
end 82 of
rolling tool 78 engages ramp 94 of latch 76. As leading end 82 of rolling tool
78 is
moved toward pressure tube 36, rolling tool 78 (e.g., leading end 82 of
rolling tool 78)
cams against ramp 94 of latch 76 to pivot latch 76, rotating latch 76 in a
counter-
clockwise direction C about axis A, toward an unlatched position. With
continued
movement of rolling tool 78 in direction B, latch 76 is pivoted sufficiently
in direction C
about axis A to enable rolling tool 78 to continue to pass latch 76.
[0041] In some embodiments, protective sleeve 79 may be inserted in end
fitting
liner 59 prior to inserting rolling tool 78 through end fitting liner 59, such
that with axial
insertion of protective sleeve 79 in direction B as shown in FIGS. 4A and 4B,
protective
sleeve 79 engages ramp 94 of latch 76, in a similar manner to that described
above.
Latch 76 may then move to an unlatched position, to enable protective sleeve
79 to
continue to pass latch 76 to the position illustrated in FIGS. 4A and 4B.
Rolling tool 78
may then be inserted into protective sleeve 79.
[0042] Rolling tool 78 is inserted until its rollers 80 are axially
overlapped with the
end of pressure tube 36 adjacent annular grooves 72 of end fitting body 57
into a
working position, as shown in FIGS. 4A and 4B.
[0043] FIG. 4A is a cross-sectional view of the portion of the fuel
channel
assembly of FIG. 3, shown without a fuel bundle and with rolling tool 78
axially inserted
into fuel channel assembly 28 to a first axial working position with rollers
80 of rolling
tool 78 in a retracted and starting position, according to an embodiment. FIG.
4B is a
cross-sectional view of the portion of the fuel channel assembly of FIG. 3,
shown
without a fuel bundle and with rolling tool 78 axially inserted into the fuel
channel
assembly 28 to a second axial working position with rollers 80 of rolling tool
78 in an
extended position, according to an embodiment.
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[0044] In the first axial working position shown in FIG. 4A, rollers 80
of rolling tool
78 are axially aligned and overlapped with counter bore 74 of end fitting
liner 59. Rolling
tool 78 can then be rolled about the axis of rolling tool 78, and rollers 80
can be moved
radially and outwardly away from axis D and at least part of rolling tool 78
may move
axially in direction B, to the second axial working position shown in FIG. 4B.
In the first
axial working position, rollers 80 of rolling tool 78 may be in a starting
position that is
approximately one inch outboard of the second axial working position shown in
FIG. 4B,
in which rollers 80 are in a final roller position.
[0045] Rollers 80 may be actuated radially, for example, by rotating a
ball screw
(not shown) that is operatively connected to mandrel 86. As mandrel 86
actuates axially
in direction B, the diameter of the tapered mandrel 86 that contacts rollers
80 increases,
thus pushing rollers 80 radially outwardly.
[0046] Radial outward movement of rollers 80 may deform the end of
pressure
tube 36 into annular grooves 72 of end fitting body 57, thereby creating a
fluid-tight joint
between pressure tube 36 and end fitting body 57 as shown in FIG. 4B.
[0047] During this operation, counter bore 74 has a large enough inner
diameter
such that contact between rolling tool 78 and end fitting liner 59 may be
avoided, for
example, in the first axial working position shown in FIG. 4A, and even as
rollers 80 of
rolling tool 78 expand until the rolled joint has been completed. In this
manner,
deformation (and in some embodiments, even contact) between rolling tool 78
and end
fitting liner 59 may be avoided altogether. Such deformation or contact may be
undesirable, as damage to end fitting liner 59 may result. Similarly, in some
embodiments, a counter bore region of end fitting body 57 may also have an
inner
diameter that is large enough such that contact between rolling tool 78 and
end fitting
body 57 may be avoided when rolling tool 78 and rollers 80 are in a retracted
and
starting position, for example, in the first axial working position shown in
FIG. 4A, or in
the second axial working position shown in FIG. 4B.
[0048] In some embodiments, roller(s) 80 of the rolling tool 78 are
positioned in
counter bore 74 during the rolling operation. The final inner diameter of the
rolled
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portion of pressure tube 36 may be smaller than the diameter of counter bore
74 in the
end of end fitting liner 59.
[0049] As described above, rolling tool 78 begins its rolling operation
in an axial
position in which at least one roller 80 of rolling tool 78 overlaps (i.e.,
shares one or
more common axial locations with) end fitting liner 59. In those embodiments
(such as
the illustrated embodiment) in which pressure tube 36 and end fitting liner 59
are
spaced from one another by a gap, at least one roller 80 therefore also spans
the gap
when the rolling operation begins.
[0050] In some embodiments, the entire pressure tube-to-end fitting
rolling
operation takes place without significant axial movement of rolling tool 78.
In other
words, rollers 80 of rolling tool 78 expand outwardly to create the rolled
joint as
described above without any needed axial movement of rolling tool 78.
[0051] However, in other embodiments, the rolling operation begins with
at least
one roller 80 in the position described above (i.e., overlapping a portion of
end fitting
liner 59 and pressure tube 36 and expanded to the rolling position), but
rolling tool 78 is
moved axially toward tube sheet 18 as the rolling operation continues in a
"propulsive
rolling" process.
[0052] In some embodiments (i.e., those including axial movement of the
rolling
operation), the "propulsive rolling" process may continue until a
predetermined axial
position of rolling tool 78 is reached, such as a set axial stop position of
rolling tool 78.
Once this end rolling position is reached, roller(s) 80 of rolling tool 78 can
be retracted
to complete the rolling operation, and rolling tool 78 can be axially
withdrawn from fuel
channel assembly 28.
[0053] In propulsive rolling operations, the axial range of positions of
the roller(s)
when performing their rolling operations are greater than in those rolling
operations in
which rolling tool 78 is stationary during the rolling operation. Therefore,
counter bore
74 of end fitting liner 59 may provide additional axial room for the
propulsive rolling
operation and may avoid damage to end fitting liner 59 as described above.
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Furthermore, the greater inner diameter of counter bore 74 may only extend the
axial
distance needed for operation of rolling tool 78, thus the remainder of end
fitting liner 59
may be kept at a desired thickness to maintain structural integrity of end
fitting liner 59.
Thus, a rolling operation of pressure tube 36 to end fitting body 57 may be
allowed with
end fitting liner 59 in place within fuel assembly 28.
[0054] In some embodiments, a rolling operation can begin without the
roller(s)
80 sharing ("overlapping" or in axial alignment with) the same axial position
of some or
any of annular grooves 72 described above (i.e., instead being positioned so
that
roller(s) 80 are positioned axially outboard, or to the right as illustrated
in FIGS. 4A and
4B, of some or all of annular grooves 72, depending at least in part upon the
dimensions of the rolling tool, pressure tube 36, and end fitting body 57).
[0055] The initial phase of the rolling operation, where the rollers
travel axially
inboard, for example, from the first axial working position shown in FIG. 4A,
is referred
to as rolling to "nip up", "nip up" being the state where all of the initial
clearances
between pressure tube 36 and end fitting body 57 have been taken up. By
beginning
rolling operation with rolling tool 78 axially overlapping with end fitting
liner 59 and in
particular, with rolling tool 78 axially overlapping with counter bore 74 of
end fitting liner
59, (for example, as shown in the first axial working position of FIG. 4A)
during rolling to
nip up, rollers 80 may be rolling less surface area of pressure tube 36 and
therefore less
force may be applied to pressure tube 36 and the tooling that is holding
pressure tube
36 and end fitting body 57 in place. This may avoid pressure tube 36 and end
fitting
body 57 shifting out of position, and rolling with less force may reduce the
risk of the
components (such as pressure tube 36 and end fitting body 57) moving. After
nip up,
pressure tube 36 and end fitting body 57 may be solidly connected and the high
force
portion of the rolling operation may occur, with rollers 80 extending radially
outwardly to
complete the formation of a rolled joint of pressure tube 36 and end fitting
body 57.
[0056] Of course, the above described embodiments are intended to be
illustrative only and in no way limiting. The described embodiments are
susceptible to
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many modifications of form, arrangement of parts, details and order of
operation. This is
intended to encompass all such modification within its scope, as defined by
the claims.
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