Note: Descriptions are shown in the official language in which they were submitted.
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Machines for dismantling decommissioned nuclear reactors.
This invention relates to the decommissioning of
nuclear reactors which are considered to have completed
her operational life, and in particular, to machines
for effecting dismantling of the reactor structure in a
controlled and safe manner.
hen a nuclear reactor has reached the end of its
planned operational fife, the alternatives, after removal
of the nuclear fuel and reactor coolant, are to cover the
whole structure with adequate shielding, such as a mound
of soil 9 and take precautions for the covered reactor to
be preserved BY shielded for all time as a permanent
'memorial', or to dismantle the structure of the reactor
and dispose of the dismantled material in small amounts
in conventional safe storage facilities, and as a
result, restore the reactor site to its rebuilding
state. The latter course is Jo be preferred, especially
in view of doubts concerning the practicability of
preserving the shielding integrity of the whole reactor
structure over the period of thousands of years necessary
before biologically unsafe amounts of radioactivity will
have decayed away.
To put the present invention into context, consider
a conventional gss-cooled, graphite moderated, nuclear
reactor which has within a pressure vessel a core
I including the moderator and the fuel elements, the
' latter being capable of being charged and discharged by a
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ruffling machine, and surrounding the core, heat
exchangers which remove heat from coolant heated by
circulation through the core and employ the removed heat
to generate electricity for example employing steam and
turbine. When such a reactor has completed its
operational lifetime, let it be assumed that a decision
has been reached to dismantle the reactor and restore the
site. After normal discharge of the fuel elements and
blow-down of the coolant gas it is considered acceptable
from a safety point of view to employ conventional
dismantling techniques for removal of the turbines, heat
exchangers, refueling machine and, with adequate
temporary shielding, the top dome of the pressure vessel
80 as to expose the core. In order to dismantle and
remove the pressure vessel and to unload and transfer to
a disposal facility the graphite moderator (which it in
discrete block form) and other vessel internal, a
machine is required which will perform these operation
safely and expeditiously, and it it an object of the
present invention to provide such a machine.
According to the invention, a machine for
dismantling, unloading and transferring to a disposal
facility, nuclear reactor structure including components
which have been irradiated during operation of the
reactor, comprises a vertically extending mast of
adjustable longitudinal extent, means supporting the mast
from a rigid undismantled part of the reactor whereby
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the mast extends into a pressure vessel of the reactor
located beneath the supporting means, means for moving
the mast transversely of its longitudinal axis whereby
the mast can be moved into different positions within the
interior of the pressure vessel, a manipulator mounted on
the mast for movement relative thereto and for supporting
and operating a variety of tool for effecting
dismantling of the structure, a movable beam mounted
beneath the supporting mean and above the pressure
vessel, the beam extending transversely of the mast and
being movable angularly in a horizontal plane over an
area encompassing the range of the transverse movement of
the mast, hoist means mounted for traverse along the beam
and extendible into the pressure vessel for lifting parts
of the pressure vessel after such parts have been
prepared for disentailing by the tool-supporting
manipulator, and at least one fixed beam mounted in the
same horizontal plane as the movable beam for
registration with the movable beam when the latter is in
a predetermined angular orientation, the fixed beam when
a registered forming a continuation of the movable beam
whereby the hoist can be transferred from the movable
beam onto the fixed beam and traversed to an unloading
station. Preferably, all the features of the machine are
controllable remotely. The movable beam may be mounted
on & ring girder secured to the reactor structure to
enable the movable beam to be rotated about the center
ire of the pressure vessel. The movable beam may be
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mounted on the mast The supporting means may include
structure rotatable about a vertical axis whereby the
mast can be moved along an arc-shaped path within the
pressure vessel. The machine may include a radiation
S shield mounted for rotation above the movable beam, the
radiation shield including an eccentrically-disposed
entry opening through which the mast and the tool-
carrying manipulator pass when the mast is extended into
the pressure vessel, the mast being retractable in its
entirety through the opening together with the
manipulator, and the radiation shield including a
removable section for insertion into the entry opening
when the mast is 80 retracted. The mast may comprise an
assembly of sections arranged so that sections can be
added to and removed from the assembly to extend and
retract the mast respectively. The mast may be of
telescopic construction.
Also in accordance with the invention, a machine for
dismantling, unloading and transferring to a disposal
facility, nuclear reactor structure, including
components which have been irradiated during operation of
the reactor comprises a gantry, means mounting the
gantry on a rigid, undismantled part of the reactor, a
carriage mounted on the gantry for rotation about a
vertical axis, a platform mounted on the carriage for
movement diametrally thereof, a vertically extending mast
of adjustable longitudinal extent supported by the
platform whereby the mast extends into a pressure vessel
aye
of the reactor located beneath the gantry, the gantry,
carriage and platform serving to move the mast
transversely of its longitudinal axis whereby the mast
can be moved into different positions within the interior
of the pressure vessel, a manipulator mounted on the mast
for movement relative thereto and for supporting and
operating a variety of tools for effecting dismantling of
the structure, a radiation shield mounted for rotation
beneath the carriage and platform, the shield including
an eccentrically disposed entry opening through which the
mast passes when extended into the pressure vessel, the
mast being retractable in its entirety through the
opening together with the manipulator, and the shield
including a removable closure section for insertion into
the opening when the mast is a retracted, a movable beam
mounted beneath the radiation shield and above the
pressure vessel, the beam extending transversely of the
mast and being movable angularly in a horizontal plane
over an area encompassing the range of the transverse
movement of the mast, hoist means mounted for traverse
along the beam and extendible into the pressure vesflel
for lifting parts of the pressure vessel after such part
have been prepared for dismantling by said tool-
supporting manipulator, and at least one fixed beam
mounted in the same horizontal plane as the movable beam
for registration with the movable beam when the latter
it in a predetermined angular orientation, the fixed beam
Lyle
when 80 registered forming a continuation of the movable
beam whereby the hoist can be transferred from the
movable beam onto the fixed beam and traversed to an
unloading station
Constructional examples of machine according to the
invention will now be described with reference to the
accompanying diagrammatic drawings, wherein:-
Figure 1 is a side view in section and
Figure 2 a plan view of a nuclear reactor which it
0 it intended to dismantle with the aid of
one of the machines shown in Figures 3 lo
Figure 3 is a side view,
Figure a plan view and
Figure 5 a perspective view of one construction of
-machine in operative position,
Figure 6 is a side view,
Figure 7 a plan view and
Figure 8 a perspective view of another construction
of machine in operative positlon9
I Figure 9 1B a side view and
Figure 10 a plan view of a modification.
like reference numerals in the drawings illustrate
like parts.
Referring firstly to Figures 1 and I these Figures
show in diagrammatic form the gas-cooled, graphite
moderated, nucleate reactor known as the Wind scale
Advanced Gas-Cooled Reactor (WAR), which has now
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completed it useful life and it to be dismantled. The
reactor core (not shown), which includes the graphite
moderator and fuel element channels, and other internals
such as core support (not shown), hot box 1 and
refueling standplpe~ 2, are contained in a pressure
vessel 3, the upper dome and the upper parts of the
atandpipes 2 of which are shown removed. The volume
which the upper dome occupied 18 intended to be employed
for a dismantling, unloading and transferring machine,
lo arch as one of those subsequently described heroin and
referred to hereinafter inclusively a a 'handling
motion The reactor also ha four heat exchanger
housings 4, from which the heat exchangers have been
dismantled and removed by conventional means with
shielding precautions, since the radioactivity level of
these structures is such as to permit such operations.
One of the buildings 4 (when emptied) it employed as a
temporary repository 5 for dismantled material, in which
sorting and designation for packaging in a communicating
building 6 18 carried out, small sloe material which can
be disposed of in bulk being dropped into a waste
container 7 beneath the temporary repository I The
outer containment of the reactor is retained end helps
to retain integrity during dismantling and related
operations. The packaging building 6 is outside the
containment a and communicates via an air lock (not
shown).
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The ruffling floor level it designated 9 in Figure
1, and it provided with rails 10 for the reactor
refueling machine (already removed to run on.
Figures 3-5 show the reactor with a handling machine
11 in poaltlon. The machine 11 consists of a gantry 12
with wheel 13 funning on the acid rails 10, and a
carriage I able to move angularly relative to the gantry
12 on a rail 15 on the gantry 12 (see particular Figures
4 and 5). The carriage 14 carries on a platform 14'
movable linearly on the carriage 14 a mast 16 able to be
extended and made shorter relative to the carriage 14 in
a direction parallel to the axis of the reactor pressure
vessel 3. There is a manipulator 17 mounted on the lower
end of the mast 16 and movable in an angular and linear
manner relative thereto, the manipulator 17 being capable
of carrying cutting and the like tools 18 by mean of
which the pressure vessel 3 and vessel internals may be
dismantled prior to transfer for packaging. The mast 16
can be extended or made shorter by adding or taking away
separate auctions provided with appropriate secure
fastening expedients (not shown) of conventional kind.
A ring girder 19 carried by the reactor concrete
structure 20 provides a track for a slew beam 21 to be
rotated about the vessel center line and in one angular
po~ltlon to be aligned and reglatered with fixed beams
22, 23. The beam 22 is an intermediate between the beam
21 and another slew beam 24 rotatable about the center
by
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fine of that heat exchanger housing 4 which is used as
the temporary repository 5. The beam 23 it a fixed beam
extending into another heat exchanger housing 4,
designated 25 and employed as a maintenance cell. There
are for example two hoists 26, 27 movable along the
beams 21, 22, 23, 24, the hoist 26 operating normally
over the vessel 3 and movable into the cell 25, and the
hoist 21 being normally situated over the repository 5
and on the clew beam 24 but being movable from the beam
lo 24 to the beam 21 via the beam 22 and vice versa for
transfer of material between the area of vessel 3 and the
repository 5. There it soother fixed beam 28 with which
beam 24 can be aligned and registered and which extends
between repository 5 and another of the empty heat
exchanger housings 4, this being designated 29 and
employed for temporary waste storage. The hoist 27 can
be made to travel from beam 24 to beam 28 and vice versa.
There 18 remotely controlled mechanism provided (not
shown) for controlling and rotating the beams 21, I and
for moving and operating the hoists 26, 27.
It 18 envisaged that the manipulator 17 and tools 18
are to be employed to cut the material of the pressure
vessel into manageably-sized pieces, and that the hoist
26 with the aid of conventional gripping or possibly
magnetic ].iftlng means on the end of the hoist cable
(none shown), be used to transfer the pieces when cut to
the repository 5 and thence to the packaging building 6
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or to the temporary storage area 29. Furthermore, the
hoist 26 would be used to pick up and transfer dismantled
moderator blocks piecemeal to 5, 6 or 29.
In order to permit short-term access to the gantry
S 12, carriage 14 and the upper area occupied by these
components, and to obviate undue exposure of the
component to radiation from vessel 3 and the vessel
internals, rotatable shielding 30 with an
eccentrically deposed removable shield circle 31 is
provided to span the ring girder 20 (see Figures 3 and
4), the mast 16 being extendible, and the hoist 26 being
operable, through the hole provided in the shielding 30
suitably rotated, when the circle 31 it removed. Figure
5 shows the mast 16 in its extended position with the
manipulator 17 and tool I in position for attacking the
material of vessel 3, whereas Figure 3 shows the mast 16,
manipulator 17 and tool 18 in retracted position.
In an alternstlve construction, illustrated in
Figures 6, 7 and 8, the handling machine if' has a
20 gantry 12 similar to the gantry 12 of the Figures 3-5
construction, with wheels 13 able to run on the existing
falls 10 on the reactor charge face 9. A carriage 32 is
mounted on the gantry 12 for cross-tra~el thereon.
mat 16 similar to the mat 16 of the Figures 3-5
construction is mounted on the carriage 32 and carries,
a in the Figure 3-5 construction, a manipulator 17
capable of holding a tool 18.
AYE
isle
11 -
The main difference from the Figures 3-S
construction 18 that there 18 a beam 33 radially mounted
on a collar 34 rotatable on the mast 16. The beam 33 can
be rotated by remote control of the collar 34 and can be
made to align and register with an intermediate beam 22
or with a fixed beam 23, as was the beam 21 in the
Figures 3-5 construction, except that, in this cave,
alternative but not simultaneous registration 19 only
possible. There is a slew beam 24 and fixed beam 28 as
in the Figures 3-5 construction, and a hoist 27 operates
between vessel 3 space and repository 5 or storage I
hoist 26 operates on beam 33 and can move on to
beam 23 to operate in maintenance cell 25 or on to beam
24 via beam 22 to operate in cell 5. As in the Figures
3-5 construction, the mast 16 can be extended and
shortened by adding or subtracting section.
The construction shown in Figures 9 and 10 provides
a handling machine 11' which combines the slew beam 21
construction shown in Figures 3-5 with the gantry 12 and
cross-travel carriage 32 of the Figures 6-8 construction,
but is varied by having a telescopic mast 35 mounted on a
platform 36 on the carriage 32 and having equipment,
diagrammatically indicated as a windlass 37 and cable 38,
for controlling the telescoping and untelescoping of the
sections 39 of the mast 35.
In a modification, not illustrated, the slew beam 21
of the Figures 3-5 construction can, instead of being
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mounted on the separate ring girder 20 on the reactor
building, be suspended rigidly from the rotatable
carriage 14 of that construction, and be rotatable
by virtue of the controlled rotation of that carriage 14
on the gantry 12, the beam corresponding to slew beam 21
thereby having its loading transferred to the falls 10
via the wheels 13 of gantry 12.
In another modification, not illustrated, the mast
may be a rigid structure, and the elevation of the
manipulator and tooting mounted thereon can be varied by
providing means, operable remotely, for raising and
towering the carriage relative to the gantry, whose
elevation 18 fixed by being mounted on the said rails.
If desired, the manipulator may be mounted on an
elevatable platform.
It will be appreciated that suitable biological
shielding may be installed as and where necessary. For
example, as floor mounted retractable shielding, and on
the gantry itself, and for a maintenance cell beneath the
gantry.
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