Note: Descriptions are shown in the official language in which they were submitted.
CA 2766440 2017-03-17
Attorney Docket No. 027813-9029-CA
FEEDER PLATFORM FOR NUCLEAR REACTOR
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No.
61/432,960, filed January 14, 2011.
BACKGROUND
[0002] The present invention relates to nuclear reactors. More
particularly, the invention
relates to systems used in maintenance or refurbishment (e.g., a full retube)
of a nuclear reactor.
SUMMARY
[0003] In one aspect, the invention provides a feeder platform system for
installation in a
reactor vault adjacent an end of a CANDUTM reactor core for accessing a feeder
cabinet and
feeder tubes therein during a retube process. The feeder platform system
includes front and rear
platforms. The front platform is movable between a variety of heights in a
first vertical space
adjacent the reactor core. The rear platform is movable between a variety of
heights in a second
vertical space adjacent the first vertical space. The front and rear platforms
define respective
lengths parallel to and spaced from the end of the reactor core. At least one
of the lengths can be
increased with a plurality of extensions releasably connectable with at least
one of the front and
rear platforms. Lifting mechanisms are coupled to each of the front and rear
platforms and
configured to raise and lower the front and rear platforms independently
within the respective
first and second vertical spaces.
[0004] In another aspect, the invention provides a method of using a feeder
platform system
in a reactor vault to access and service a feeder cabinet of a CANDUTM
reactor. A reactor vault
is provided adjacent a reactor core of the CANDUTM reactor, the reactor vault
including a feeder
cabinet, a plurality of feeder tubes positioned inside the feeder cabinet, a
pair of fueling machine
bridge columns, and a column support adjacent an upper end of each of the
fueling machine
bridge columns, the column supports supporting an overhead gantry crane having
a bridge beam
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spanning the column supports. A platform is positioned on a floor of the
reactor vault adjacent
the reactor core, the platform defining a width measured away from the reactor
core and a length
measured perpendicular to the width, the length being less than a spacing
distance between the
column supports. The platform is lifted between the column supports to a first
height above the
column supports and below a top of the gantry crane bridge beam. From the
platform, with the
platform at the first height, a portion of the feeder cabinet is removed to at
least partially expose
the plurality of feeder tubes. The length of the platform is extended with at
least one releasably
connectable extension to a length exceeding the spacing distance between the
column supports
while the platform is at the first height. The platform is lifted to a second
height above the
column supports and above the top of the gantry crane bridge beam. From the
platform, with the
platform at the second height, the feeder tubes are serviced.
[0005] In yet
another aspect, the invention provides CANDUTm-type nuclear reactor site. A
reactor core includes a calandria having an end. A vault encloses the
calandria end. A pair of
fueling machine bridge columns are positioned in a first vertical space
adjacent the reactor core,
each of the fueling machine bridge columns being secured to the vault with a
corresponding
column support, the column supports further supporting an overhead gantry
crane movable along
the column supports. A front platform is movable between a variety of heights
in the first
vertical space. The front platform defmes a first length measured parallel to
the calandria end,
the first length being less than a spacing distance between the column
supports. A rear platform
is movable between a variety of heights in a second vertical space adjacent
the first vertical
space. The second platform defines a second length measured parallel to the
calandria end, the
second length being less than the spacing distance between the column
supports. Lifting
mechanisms are coupled to each of the front and rear platforms and configured
to raise and lower
the front and rear platforms independently within the respective first and
second vertical spaces.
A plurality of extensions are releasably connectable with at least one of the
front and rear
platforms to increase at least one of the first and second lengths to a length
greater than the
spacing distance between the column supports when the at least one of the
front and rear
platforms is raised above the column supports by the lifting mechanisms.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Fig. 1 is a perspective view of a reactor core.
[0007] Fig. 2 is a cut-away view of a fuel channel assembly of the reactor
core of Fig. 1.
[0008] Fig. 3 is a side view of a feeder cabinet on the end of the reactor
core of Fig. 1.
[0009] Fig. 4 is a perspective view of a front feeder platform section,
assembled and ready
for hoisting.
[0010] Fig. 5 is a perspective view of the front feeder platform section
raised to a first height
above a pair of fueling machine bridge column supports and having extensions
attached.
[0011] Fig. 6 is a perspective view of a front wall of a lower feeder
cabinet removed with the
front feeder platform section at the first height.
[0012] Fig. 7 is a perspective view of the front feeder platform section
raised to a second
height above a vault crane with feeder cabinet side panels removed, and a rear
feeder platform
section, assembled and ready for hoisting.
[0013] Figs. 8-9 are a perspective view and a side view of the rear feeder
platform section
raised to the first height above the fueling machine bridge column supports
and having
extensions attached. A front portion of the feeder cabinet soffit panels are
removed, and a rear
portion of the feeder cabinet soffit panels are being removed.
[0014] Figs. 10-11 are perspective views of the front and rear feeder
platform sections raised
to the second height above the vault crane with rear wall panels of the feeder
cabinet removed.
[0015] Fig. 12 is a perspective view of the front feeder platform in a
first configuration.
[0016] Fig. 13 is a perspective view of the rear feeder platform in a first
configuration.
[0017] Fig. 14 is a perspective view of the front feeder platform with
extensions attached.
[0018] Fig. 15 is a perspective view of the rear feeder platform with
extensions attached.
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DETAILED DESCRIPTION
[0019] Before any embodiments of the invention are explained in detail, it
is to be
understood that the invention is not limited in its application to the details
of construction and the
arrangement of components set forth in the following description or
illustrated in the following
drawings. The invention is capable of other embodiments and of being practiced
or of being
carried out in various ways.
[0020] FIG. 1 is a perspective of a reactor core of a CANDUTm-type reactor
6. The reactor
core is typically contained within a vault that is sealed with an air lock for
radiation control and
shielding. A generally cylindrical vessel, known as a calandria 10, contains a
heavy-water
moderator. The calandria 10 has an annular shell 14 and a tube sheet 18 at a
first end 22 and a
second end 24. The tube sheets 18 include a plurality of bores that accept a
fuel channel
assembly 28. As shown in FIG. 1, a number of fuel channel assemblies 28 pass
through the tube
sheets 18 of calandria 10 from the first end 22 to the second end 24. The fuel
channel assemblies
28 are generally arranged in a horizontal and vertical grid on the end faces
of the reactor
core. Feeder tubes 59 communicate with the fuel channel assemblies 28 to
provide heavy-water
to the fuel channel assemblies 28 during operation of the reactor. Each feeder
tube 59 includes
an upper feeder tube section or "upper feeder tube" 59A, and a lower feeder
tube section or
"lower feeder tube" 59B. The upper feeder tubes 59A extend from headers H
toward the reactor
6, and the lower feeder tubes 59B extend along the end of the reactor 6 to the
corresponding fuel
channel assembly 28. The upper and lower feeder tubes 59A, 59B are joined at a
"field weld
location" adjacent a bend in the upper feeder tubes 59A as shown in Fig. 9.
[0021] FIG. 2 is a cut-away view of the fuel channel assembly 28. As
illustrated in FIG. 2,
each fuel channel assembly 28 is surrounded by a calandria tube ("CT") 32. The
CT 32 forms a
first boundary between the heavy water moderator of the calandria 10 and the
fuel bundles or
assemblies 40. The CTs 32 are positioned in the bores on the tube sheet 18. A
CT rolled joint
insert 34 within each bore is used to secure the CT 32 to the tube sheet 18.
[0022] A pressure tube ("PT") 36 forms an inner wall of the fuel channel
assembly 28. The
PT 36 provides a conduit for reactor coolant and the fuel bundles or
assemblies 40. The PT 36,
for example, generally holds two or more fuel assemblies 40 and acts as a
conduit for reactor
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coolant that passes through each fuel assembly 40. An annulus space 44 is
defined by a gap
between the PT 36 and the CT 32. The annulus space 44 is normally filled with
a circulating
gas, such as dry carbon dioxide, helium, nitrogen, air, or mixtures thereof.
The annulus space 44
and gas are part of an annulus gas system. The annulus gas system has two
primary functions.
First, a gas boundary between the CT 32 and PT 36 provides thermal insulation
between hot
reactor coolant and fuel within the PTs 36 and the relatively cool CTs 32.
Second, the annulus
gas system provides an indication of a leaking CT 32 or PT 36 via the presence
of moisture,
deuterium, or both in the annulus gas.
[0023] An annulus spacer or garter spring 48 is disposed between the CT 32
and PT 36. The
annulus spacer 48 maintains the gap between the PT 36 and the corresponding CT
32, while
allowing the passage of the annulus gas through and around the annulus spacer
48. Maintaining
the gap helps ensure safe and efficient long-term operation of the reactor 6.
[0024] As also shown in FIG. 2, an end fitting 50 is attached around the
fuel channel
assembly 28 outside of the tube sheet 18 at each end 22, 24. At the front of
each end fitting 50 is
a closure plug 52. Each end fitting 50 also includes a feeder assembly 54. The
feeder assemblies
54 feed reactor coolant into or remove reactor coolant from the PTs 36. In
particular, for a single
fuel channel assembly 28, the feeder assembly 54 on one end of the fuel
channel assembly 28
acts as an inlet feeder, and the feeder assembly 54 on the opposite end of the
fuel channel
assembly 28 acts as an outlet feeder. As shown in FIG. 2, the feeder
assemblies 54 can be
attached to the end fitting 50 using a coupling assembly 56 including a number
of screws,
washers, seals, and/or other types of connectors.
[0025] Coolant from the inlet feeder assembly flows along a perimeter
channel of the end
fitting 50 until it reaches a shield plug 58. The shield plug 58 is contained
inside the end fitting
50 and provides radiation shielding. The shield plug 58 also includes a number
of openings that
allow the coolant provided by the inlet feeder assembly to enter an end of a
PT 36. A shield plug
58 located within the end fitting 50 at the other end of the fuel channel
assembly 28 includes
similar openings that allow coolant passing through the PT 36 to exit the PT
36 and flow to the
outlet feeder assembly 54 through a perimeter channel of another end fitting
50 at the opposite
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face of the reactor 6. As shown in FIG. 1, feeder tubes 59 are connected to
the feeder assemblies
54 that carry coolant to or away from the reactor 6.
[0026] The feeder tubes 59 are substantially enclosed in a feeder cabinet
104 that extends
along the end face of the reactor core, upward and away from the reactor core
as shown in Fig. 3.
Access to the feeder tubes 59 is provide by a series of removable panels 106
of the feeder cabinet
104, which can include a front face panel 106A, side panels 106B adjacent the
front face panel
106A, a soffit panel 106C, a rear wall panel 106D, and side panels 106E
adjacent the soffit and
rear wall panels 106C, 106D. Any or all of the panels can be formed in
multiple pieces. The
front face panel 106A and adjacent side panels 106B generally enclose the
lower feeder tubes
59B and form a "lower feeder cabinet". The upper feeder tubes 59A are
generally enclosed in an
"upper feeder cabinet" formed at least in part by the soffit panel 106C, the
rear wall panel 106D,
and the adjacent side panels 106E. The headers H are also generally enclosed
within the upper
feeder cabinet.
[0027] Returning to FIG. 2, a positioning hardware assembly 60 and bellows
62 are also
coupled to each end fitting 50. The bellows 62 allows the fuel channel
assemblies 28 to move
axially. The positioning hardware assemblies 60 are used to set an end of a
fuel channel
assembly 28 in either a locked or unlocked position. In a locked position, the
end of the fuel
channel assembly 28 is held stationary. In an unlocked position, the end of
the fuel channel
assembly 28 is allowed to move. A tool can be used with the positioning
hardware assemblies
60 to switch the position of a particular fuel channel assembly 28.
[0028] The positioning hardware assemblies 60 are also coupled to an end
shield 64. The
end shields 64 provide additional radiation shielding. Positioned between the
tube sheet 18 and
the end shield 64 is a lattice sleeve or tube 65. The lattice tube 65 encases
the connection
between the end fitting 50 and the PT 36 containing the fuel assemblies 40.
Shielding ball
bearings 66 and cooling water surround the exterior the lattice tubes 65,
which provides
additional radiation shielding.
[0029] During a retube of the reactor 6, many of the major components of
the reactor core
are removed and replaced. Other components are inspected and/or repaired. In
addition to
reactor core components such as the fuel channel end fittings 50, the
calandria tube inserts 34,
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the calandria tubes 32, the pressure tubes 36, and the associated annulus
spacers 48 (e.g., garter
springs), the feeder tubes 59 may be inspected, and potentially removed and
replaced. In order
to accommodate personnel, tooling, and materials to service the feeder tubes
59, a feeder
platform system 100 is provided adjacent each end of the reactor core. One
exemplary feeder
platform system 100 is shown in the drawings, with the understanding that a
substantially similar
feeder platform system can be provided in the vault on the opposite end of the
reactor core.
Therefore, it will be understood that the below description relates to the
illustrated feeder
platform assembly 100, but multiple feeder platform assemblies 100 would
typically be provided
to enable servicing the feeder tubes on both ends of the reactor core
simultaneously.
[0030] Feeder installation is generally comprised of four distinct mini-
series: (1) header
nozzle inspection and preparation, (2) feeder pipe inspection and preparation,
(3) upper feeder
installation, and (4) lower feeder installation. However, in at least one
method of use, feeder
installation is carried-out as part of a retubing process for the nuclear
reactor 6, as opposed to
during construction of a new nuclear reactor. During retubing, the upper
feeders 59A are
removed leaving a stub (several inches long) of feeder pipe attached to the
corresponding header
H. As described in further detail below, one or more feeder platforms 110 are
positioned
adjacent each end face of the nuclear reactor 6 at desired working elevations,
and can be moved
to various working elevations throughout different stages of feeder tube
servicing during
retubing of the reactor 6. The feeder platform(s) 110 are used with a lifting
mechanism to
provide a height-adjustable feeder platform system 100 to maximize efficiency
of the feeder tube
servicing.
[0031] The feeder platform(s) 110 are installed to provide a safe work
surface providing
access to remove the upper feeder cabinet (panels 106C, 106D, 106E), upper
feeders 59A,
resistance temperature detectors (RTDs, not shown) and other tubing, which may
occur during
the course of a retubing process of the reactor 6. The feeder platform 110 can
also be used to
perform inspection on any of the components in the feeder cabinet 104,
including header nozzles,
and can also be used for upper feeder installation and installation of the
upper portion of the
feeder cabinet 104. As described below, the feeder platform 110 may be
provided in separate
sections, such as front and rear sections, referred to herein simply as the
front feeder platform
110F (Figs. 12 and 14) and the rear feeder platform 11OR (Figs. 13 and 15).
The front and rear
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feeder platforms 110F, 11OR can be independent platforms usable separately,
but may also be
releasably connectable to each other as described in further detail below.
[0032] A lifting mechanism is coupled to each of the feeder platforms 110F,
110R. The
lifting mechanism can be any type of device or system providing elevation
control. In one
construction, a plurality of wire ropes or cables 114 are coupled to each
feeder platform 110F,
110R, and a corresponding plurality of strand jacks 115 (Figs. 12-15) are
provided to engage the
plurality of cables 114 and enable each of the feeder platforms 110F, 11OR to
move up and down
within the vault. Each cable 114 can be secured to a fixed structure within
the vault, which can
include concrete vault walls, structural (e.2., steel) attachment points on
the vault walls, or the
structural frame 116 of the upper feeder cabinet as shown in Fig. 9. The
strand jacks 115 can be
positioned at the upper ends of the cables 114 as shown, or alternately, can
be positioned on each
feeder platform 110F, 110R. The strand jacks 115 can be installed at pre-
determined locations in
the upper feeder cabinet. At these locations, the cables 114 are affixed and
dropped through
corresponding holes formed in the feeder cabinet. In other constructions, the
feeder platform
lifting mechanism can include one or more of screw drives, scissor lifts,
chains, straps, pulleys,
etc.
[0033] With continued reference to Figs. 12-15, each of the feeder
platforms 110F, 11OR is
generally constructed of a structural frame 120, a decking 122 of one or more
panels forming a
work surface, and handrails 124 positioned adjacent at least a portion of the
perimeter. The
handrails 124 can be removably coupled to the frame 120 and the decking 122,
and may be
rearranged in a plurality of configurations to suit various operational needs.
The front feeder
platform 110F defines a length Li and a width WI, and the rear feeder platform
11OR defines a
length L2 and a width W2. The lengths Ll , L2 are measured parallel to the
reactor face, and the
widths WI, W2 are measured away from the reactor face (i.e., perpendicular to
the lengths Ll,
L2). The lengths Li, L2 of the front and rear feeder platforms 110F, 11OR can
be substantially
equal in some constructions, each providing access to a majority of the width
of the feeder
cabinet 104. The lengths Ll, L2 are slightly smaller than a spacing distance D
(Fig. 4) between a
pair of opposed column supports 128 coupled to the upper ends of the fueling
machine bridge
columns 130 to laterally brace the columns 130 against the vault walls. In the
illustrated
construction, the column supports 128 also serve as crane rails supportinu,
the vault crane C (e.g.,
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an overhead gantry crane). The frame 120 and decking 122 of the front feeder
platform 110F are
configured to provide recesses 132 at the lateral sides, which are at the ends
of the length
direction. Each recess 132 is configured to at least partially receive one of
the fueling machine
bridge columns 130 as shown in Fig. 4. Thus, the front feeder platform 110F is
configured to at
least partially wrap around the fueling machine bridge columns 130.
[0034] As shown in Figs. 14 and 15, the front and rear feeder platforms
110F, 11OR can be
reconfigured to extended lengths L3, L4 with extensions 136 at each lateral
end. The extended
lengths L3, L4 can be equivalent, but need not be, and can be configured to
provide full access to
the feeder cabinet 104 and the feeder tubes 59 therein. Each of the extended
lengths L3, L4 is
greater than the spacing distance D between the column supports 128. Each of
the extensions
136 can be an additional platform section, constructed substantially similarly
to the main portion
of the platforms 110F, 11OR (i.e., of a frame 120 and decking 122), and
releasably coupled to the
frames 120 of the pre-assembled platforms 110F, 110R. Although not
illustrated, the handrails
124 can be reconfigured and/or additional handrails 124 added to at least
partially encompass the
ends of the extensions 136 when attached. As shown in Fig. 14, connection of
the extensions
136 on the front feeder platform 110F creates a unitary working surface with
pair of apertures
140. The apertures 140 are partially formed by the recesses 132, and are
enclosed by the
addition of the extensions 136. Each aperture 140 is configured to receive one
of the fueling
machine bridge columns 130 with minimal clearance, allowing the front feeder
platform 110F to
travel up and down in a vertical space VS1 (Fig. 3) adjacent the reactor core
that includes the
fueling machine bridge columns 130, while avoiding interference. Use of the
extensions 136 is
discussed in further detail below with regard to the method of using the
platforms 110F, 110R.
100351 Before any feeder platforms 110 are installed, the reactor face
and end fitting
insulation are removed, and the vault crane C is parked at its furthest
location from the reactor 6
(Fig. 4). A lower majority of the front face panel 106A of the lower feeder
cabinet is removed as
shown in Fig. 4. This can be accomplished with one or more scissor lifts, boom
lifts, or similar
devices. Adjacent side panels 106B of the lower feeder cabinet may or may not
be removed at
this time.
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[0036] With
the lower feeder cabinet at least partially removed as shown in Fig. 4, the
front
feeder platform 110F is positioned on the vault floor or on a retube platform
RTP (Fig. 11)
provided adjacent the calandria 10 for the retubing. The front feeder platform
110F can be
assembled from a small number of pre-assembled modules to minimize assembly
time. Once
assembled, the front feeder platform 110F is hoisted to a first height (Fig.
5) above the column
supports 128 that brace the fueling machine bridge columns 130. The first
height can be just far
enough above the column supports 128 to ensure clearance (e.g., 0.5 inch to 6
inches). The
height of the front feeder platform 110F can be configured to substantially
fill the vertical space
between the column supports 128 and the upper feeder cabinet. At the first
height, the front
feeder platform 110F is extended to maximum length L3 by releasably coupling
the extensions
136 to the assembled portion of the platform frame 120. The extensions 136 are
positioned over
top of the obstructing column supports 128. In this configuration, the front
feeder platform 110F
can provide access to the entirety of the feeder cabinet. The remaining top
portion of the front
face panel 106A of the lower feeder cabinet is removed from the front feeder
platform 110F (at
the first height) along with the front portion of the soffit panel 106C and
the side panels 106E or
the upper feeder cabinet (Fig. 6). The front feeder platform 110F is then
further raised to a
second height (Fig. 7), which may be a maximum working elevation. At the
second height, the
bottom of the front feeder platform 110F is above an upper bridge beam 144 of
the vault crane C,
so that the vault crane C is operational and can move freely back and forth
underneath the front
feeder platform 110F. At the second height, the front feeder platform can be
secured relative to
the vault (e.g., with one or more braces 148 between the frame 120 and a fixed
vault structure
150 such as a concrete vault wall, fixed structural steel beam, or other
attachment point) as
shown in Fig. 11, and the vault crane C is moved forward underneath the front
feeder platform
110F. Securing the front feeder platform 110F to the vault provides lateral
bracing that prevents
any swinging of the platform during the ensuing work operations. When secured,
the front
feeder platform 110F is ready to provide a working surface for servicing the
upper feeder tubes
59A, excluding those toward the rear portion of the upper feeder cabinet. Some
or all of the
handrails 124 may be removed before raising the front feeder platform 110F to
the second height
to avoid interference, and alternate fall prevention is provided.
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[0037] Two-stage assembly and lifting of the rear feeder platform 11OR is
carried out
substantially similar to that of the front feeder platform 110F described
above. However, the
rear feeder platform 11OR is positioned and made operable in a second vertical
space VS2 (Fig.
3) that is adjacent to the rear or non-reactor-facing side of the front feeder
platform 110F and its
vertical space VS1, and is spaced away from the reactor core. The rear feeder
platform 11OR is
assembled on the vault floor (Fig. 7) or retube platform and is raised to the
first height just above
the column supports 128, and the extensions 136 are attached when the rear
feeder platform
11OR is positioned at the first height (Figs. 8 and 9). At the first height,
the rear feeder platform
110R is used to remove the remaining (rear) portion of the soffit panel 106C
and the rear wall
panel 106D of the upper feeder cabinet.
[0038] After the extensions are added, the rear portion of the feeder
platform is hoisted to the
second height to match the height of the front feeder platform 110F as shown
in Figs. 10 and 11.
When both platforms 110F, 11OR are at the second height, they are directly
adjacent to one
another and can be fastened together with one or more braces between the
frames 120, such that
the two sections 110F, 110R form a single rigid, conjoined feeder platform
110. Redundant
and/or interfering handrails 124 may be removed to optimize the environment
for removal of the
upper feeder tubes 59A.
[0039] The feeder platform 110 remains in this configuration for the
duration of the servicing
of the upper feeder assembly (e.g., upper feeder tube removal, nozzle
inspection, weld
preparation and upper feeder tube installation processes). When the vault is
ready for installation
of the lower feeder tubes 59B, the feeder platform 110 (or only the front
feeder platform 110F,
detached from the rear feeder platform 110R) is lowered below the second
height to a convenient
elevation at or above the first height to provide a working surface adjacent
the field weld location
between the upper and lower feeder tubes 59A. 59B to facilitate field weld fit-
up, welding and
non-destructive examination (NDE). At this height, the platform 110 (or 110F)
may interfere
with the operation of the crane C, so movement to this height is limited to
the specific operation
requiring it, and proper planning can be used to minimize disturbance to any
operations requiring
crane operation.
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[0040] After servicing is completed, re-installation of the feeder cabinet
104 is performed by
reversing the removal sequence described above, including disassembling
portions of the front
and rear feeder platforms 110F, 11OR as required.
[0041] In some constructions, the feeder platforms may offer at least one
feature or
advantage such as: saving time in feeder removal, maintenance and/or
installation, offering a
high level of safety, providing a particularly low radiation dose for work
tasks on the feeders,
and enabling a high quality of work to be performed on the feeders.
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