Note: Descriptions are shown in the official language in which they were submitted.
3;5 3
MELrrING F[~RNACE FOR RADIOACTIVE WASTES
Background of the Invention
_ __ _
1 Field o~ the Invention
___ . ___
. This invention relates to a furnace for melt-
ing radioactive wastes arising from establishments for
handling radioactive materials such as atomic power
plants for the purpose of volume reducing treatment
thereof.
2. Description of the Prior Art
The radioactive wastes emit radioactivity
therefrom and thus they are dangerous, and in addition,
elaborate operation is hard to be carried out. Accordingly,
in prior arts, when these radioactive wastes are melted,
they have been indiscriminately charged into aknown melting
furnace withoùt predividing them into heavy wastes and
light-weighted.wastes. I~owever, if the wastes are melted
in this way, the wastes are partly caught in the furnace
when they are charged into the furnace or the wastes fall
down the edge within the furnace thus failing to achieve
good melting. Or, if the heavy wastes are charged, an
intensive shock is transmitted to the furnace body to pose
a problem of danger in damaging the furnace body.
y__f the Invention
_ __
. It is an object oE the present invention to
provide a melting furnace which can melt radioactive wastes
to volume-reduce the wastes.
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353
It is a further object of the present inventiOn
to provide a melting fu~nace in which even if a radioactive
waste is dangerous and hard to be handled as described above,
- when the wastes are charged into the furnace in order to
melt them, such charging operation can he done in a simple
procedure.
That is, in the melting furnace of the present
invention, a guide cylinder is provided to introduce the
radioactive wastes to a predetermined place within the
furnace, that is, a place where the wastes are melted.
Accordingly, the radioactive wastes may be merely put into
the guide cylinder so that the wastes reach the predetermilled
place within the furnace.
It is another o~ject of the present invention
to provide a melting furnace which when the wastes are melted,
can efficiently transmit heat to and rapidly melt massive
wastes in the form of large bulk or slender wastes such as
wires in the form of a small bulk or even inorganic wastes
having a high melting point such as heat insulating materials.
That is, in the melting furnace of the present
invention, the wastes introduced into the furnace are immersed
in a high temperature liquid melt present in the furnace.
Accordingly, the wastes irrespective of their ~ul~, large
or small, all touch the high temperature liquid melt.
Further, the wastes not only touch the melt with an outer
surface thereof but tne liquid melt is moved round along
the recessed portions and inner port:ions o~ the wastes and
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353
thus, any partsof the wastes touch the melt. In -this
way, the wastes touch the high tempera-ture melt over
the wide contact area. For these reasons, heat is
always transmitted effic:iently to the wastes irrespective
of their shape and melting is rapidly carried out.
It is yet ano-ther object of the present
invention to provide a melting furnace in which this
furnace is the melting ~urnace for radioactive wastes and
is designed so that said wastes are charged into the
furnace through a guide cylinder, whereby irregular
heavy and light-weight wastes such as wire materials,
columnar material and die steel materials are indiscrimi-
nately charged into the guide cylinder and even if
extremely heavy wastes are possibly fallen heavily in-to
~S the furnace through the guide cylinder at times it is
possible to prevent a part of the furnace body rom being
damaged as a result of a great shock directly received
because of said falling, thus extending the service life
of the Eurnace ~ody.
It is still another object of the present
invention to prevent the need of operation for replacing
refrac-tory and heat insulating materials which have been
consumed within a short period of time~ and to prevent
generation of the secondary waste.s (the residue from the
above-mentioned refractory and heat insulating materials)
resulting from such operation fo~ replacement.
Thus and in accordance with the broad concept
of the invention, there is provided and claimed herein
a melting furnace for radioactive wastes comprising:
a hollow furnace body; a buffer layer interiorly dispo-
sed on the bottom of the furnace body; a recessed
portion, in order to store a melt of the radioactive
wastes, formed in the upper surface of the buffer layer;
a guide cylinder arranged in a state which in the
furnace body, extends through a portion positioned
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.
; .
2353
upwardly of the recessed portion, the guide cylinder
having an ope~ing at the upper end thereof positioned
externally of the furnace body and an opening at the
lowe,r end thereof opposed to the recessed portion, the
radioactive wastes thrown into the opening at -the upper
end being guided toward the recessed portion; and a
heating means mounted on the furnace body to heat the
melt of the radioactive wastes stored in the recessed
portion.
Other objects and advantages of the invention
will become apparent during the following description
of a preferred embodiment havin~ reerence to the
accompanying drawings.
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353
Brief Description of the Drawings
FIGS. 1 and 2 are respectively perspective views
of a volume reducing system;
FIG. 3 is a longitudinal sectional view of a
melting furnace and a pulverizing device;
FIG. 4 is a sectional view taken along line IV-IV
of FIG. 3;
FIG. 5 is a longitudinal sectional view of a
solidifying devicei and
FIG. 6 is a longitudinal sectional view showing
another embodiment of the solidifying device.
Description of the Preferred Embodiments
FIGS. 1 and 2 show the entire volume reducing
system for wastes such as radioactive materials. In FIGS, 1
and 2, the wastes such as various filter, pipes, steels
and other radioactive materials, which are packed into a
container 1 (for example, a drum can of 200 Q), are carried
into a processing room by means of a transport means 3 such
as a roller conveyor through an inlet 2 of the processing
room. A cover la of the thus carried container 1 is removed
by means of a cover-removing device 4. This cover-removing
device 4 comprises an expansible arm 5 and an attracting
device 6 mounted on the end of the arm 5, the c~ver la
being attracted and removed by the attracting device 6.
The container with the cover la removed is then
fed to a laterally turning device i by means of the transport
means 3. The laterally turning device 7 comprises a turn
table 8, two support~posts 9, 9 and a container holder 10
.
s~
journalled on bo-th support posts 9, 9. The container holder
10 may be tilted in a direction of allow lla with the
container held thereon. Then, wastes 13 within the container
are discharged onto a hed 14. After the wastes 13 have been
discharged, the holder 10 is returned in a direction of
arrow llb. Next, the turn table 8 is rotated through
90 in a direction of arrow 12a. After rotated, the emptied
container is a transferred on a transport means 15 such as
a roller conveyor, and is carried out of an outlet 16.
L,arge wastesl~a out of those discharged onto the
bed 14 are carried through a power manipulator 17 to a cut-
ting device 18 where the wastes are cut into small wastes.
This miniaturization means that the wastes are formed into
sizes enough to be charged into a processing container
described later. The power manipulator 17 is movable in a
horizontal plane as constructed in the ~ollowing. That is,
two rails 19 (one of which is not shown) disposed in parallel
have a movable frame 20 mounted movably in a direction of
arrow 21, and the manipulator 17 is provided movably in a
direction of arrow 22 with respect to the movable frame 20.
The manipulator 17 comprises a body 2~, a vertically moving
rod 24 designed movably up and down with respect to the body
23, a plurality of links 25 connected to the lower end of
the vertically movin~ rod 24, and a grip member 26 mounted
on the end of the link 25. Thus, the grip member 26 can
grip the waste 13a which can be carried to a suitable
place oE a three dimensional space. The cutting device 18
~23~;3
comprises a fixing device 27 and a plasma cutter 28. The
plasma cutter ~8 is designed so tha~ it may be m~ved towards
the arrow. The large waste 13a carried by the manipulator
17 is secured by means of the fixing device 27 and cut by
the plasma cutter 28 into small sizes. The thus miniaturized
wastes are returned onto the bed 14 by the manipulator 17.
It is noted that closed wastes, which are possibly exploded
when heated, are bored by -the aforesaid plasma cutter 28.
In this cutting device 18, a suitable cutting mechanism
can be used in place of the plasma cutter 28.
The wastes miniaturized or bored as described
above and originally small wastes are charged into a
processing container 32 through a charging chute 31 disposed
on the end of the bed 14 by operation of the manipulator 17.
The processing container 32 is in the form of a cylinder
as shown. The container 32 has its dimension, for example,
outer diameter 390 mm, inner diameter 381, outer height 51
mm, inner height 487 mm, and capacity 50 Q. The container
32 is formed of materiàls such as metal plates such as iron
or metal plates bored with numerous holes or netting.
The container 32 has its size determined in accordance with
the succeeding melting furnace. The container 32 is to be
pre-transported by the transport means 33 such ~s a roller
conve~or to a position below the chute 31.
The container 32 with the wastes packed therein
. is further carried by the transport means 33 and transferred
onto a roller portion 33' mounted on a truck 35. The truck
.
~Z3~3
35 may be reciprocated along rails 36 and 36 to feed the
container 32 into an introducing device 38. The introducing
device 38 comprises a cylindrical body 39 and a door 40
free to open and close disposed at an inlet thereof. When
the door 40 is opened, the truck 35 moves forward towards
the inlet of the body 39 to transfer the container 32
onto transfer means 41 such as a roller conveyor disposed
within the body 39. After transfer, the truck 35 is with-
dra~n and the door is closed. The container 32 is carried
by the transfer means 41 and held by means of a holdinq
frame ~2. A vertically moving device 43 is located above
the holding frame 42. The vertically moving device 43 has
a vertically moving rod 44 at the lower end of which is
mounted a gripping device 45. When the container 32 is
gripped by the gripping device 45, the holding frame 92 is
withdrawn and a slide door 46 is opened. Then, the verti-
cally moving rod 44 is moved down to charge the container
32 wi'th the wastes packed therein into a melting furnace 50.
In the melting furnace 50, the thus charged
container 32 is melted by means of a heating torch 52
disposed within the furnacè body 51. A melt 53 obtained
therefrom is taken out from a take-out hole 54 in the
furnace body 51 through a take-out device 55 and fed into
a pulverizing device 57. The aforesaid melt 53 is thrown
into water ~ithin the body 58 and formed into particles 60.
- The particles 60 stay in the bottom of the body 58. When
a bottom cover 59 is opened, the particles stayed in the
2~3
bottom of the body enter a bucket 61 together with water.
Since the bucket 61 has its bottom 62 in the form of a
netting (a porous plate can be used), only the water is
discharged.
The bucket 61 is fed to a next station by means
of a truck 64 which is moved along rails 63. In the
midst during movement of the bucket, the particles
within the bucket 61 are dried by means of a dryer 65.
When a charging device 66 at the lower end of the buc~et
is opened, the dried particles are ~acked into a storing
container 67, which is then carried out by means of
transport means 6~ such as aroller conveyor for storage.
For the storing container 67, a drum can, for exarrlple,
of 200 Q may be used.
Next, the above-mentioned melting furnace 50 and
the pulverizing device will be.further described in detail
with reference to FIGS. 3 and 4 in addition to the preceding
drawings. The furnace body 51 comprises a recessed water-
cooled hearth 71 and an upper ~rame 72 covered thereon.
The water-cooled hearth 71 has its internal surfac~ coated
with heat insulating materials 73 and 74. The heat insulat-
ing material 73 used inclildes graphitic oxide (which is
composed of 10 to 30 % of graphite and the remainder
compris.ing a].umina or magnesia) also called the carbonaceous
brick. This is used to enable energization between the
hearth 71 and the melt 53 because a plasma torch is used
as the heating torch 52, which will be described in detail
-- 8 --
:
.
~Z3~
later. Known refractorles may be used for the heat
insulating material 7~ The heat insulating materials 73,
74 has a buffer layer 75 disposed internally thereof.
This buffer layer 75 is provided to prevent the heat ¦1
S insulating materials 73, 74 from being dama~ed as a result
of direct touch of the melt 53 with the ~eat insulating
materials 73, 74. The buffer layer 75 comprises a ballast
layer 75a and a solid layer 75b positioned thereon. The
ballast layer 75a is designed so that a number of massive
buffer materials are disposed at random in a state where
cleararlces are formed therebetween and they may be moved
one another. For the buffer material, scrap-icon of the
size about pebbles and cobble stones may be used, for
example. The solid layer 75~ has its upper surface in the
form of a recess which forms a reservoir 76 of the melt 53.
It will be noted that the solid layer 75b results from a
mixture of the melted buffer material and the melt 53, said
mixture being solidified.
A guide cylinder 80 is suspended from the middle
portion of a top plate 72a of the upper frame 72. This guide
cylinder 80 is of the water-cooled construction. The upper
end of the guide cylinder 80 is in communication with the
.
interior of the body 39 in the introducing device 38 through
a cornmunicating pipe 81. Around the communicating pipe 81
in the top plate 72a of the upper frame 72, there are dis-
posed vertically moving devices 82 at positions where the
whole circumference is divided into three or four sections.
3~j3
Each of these vertically moving devices 82 has a vertically
moving rod 83. The heating torch 52 is mounted on the lower
end of the vertically moving rod 83. In the illustrated
embodiment, an annular plasma torch is used for the heating
torch 52. This heating -torch 52 is annually formed coaxial
with the center axis of the guide cylinder 80 and has an
annular arc discharge opening 84. The arc discharge opening
84 is directed in a direction in which the plasma arc at a
temperature above 10000K is discharged toward the neigh-
bourhood of the lower end of a ~ortion exposed from the meltand toward the upper surface of the melt 53 within the
container 32. The vertically moving rod 83 is internally
provided with a passage for supply of electrie power and gas
to the torch 52, said passage having one end connected to
the torch 52 while the other end being eonnected to a DC
power source 85 and an operating gas souree 86. A eoil 87
positioned in the outer periphery of the upper frame 72 is
provided to apply the magnetie field to the annular are
discharge opening 84 to rotate the arc along the diseharge
opening, the magnetie field being adapted to discharge the
arc from the entire zone of the arc discharge opening 84
in the toreh 82. It is noted that the aforesaid heating
torch 52 may be replaced by a plurality of normal torches
(for exarnpel, toreh 100 deseribed later) widely used or a
gas burner or an oil burner. In this ease, the aforesaid
coil 87 cannot be required. The upper frame 72 is partly
formed with a gas outlet 88. ~nnecessary gases in the
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~Z~3~3
furnace body 51 are delivered to a duct 89 through the
outlet 88 and then discharged into atmosphere through a
heat exchanger 90, a filter 91 for removing dusts con-
taminated by the radioactive materials,blower 92 and
stack 93.
In a part of the furnace body 51 positioned
sideward the reservoir 7~ of the melt, the take-out hole
5~ is formed extending through the water-cooled hearth 71
and heat insulating material 73. In the water-cooled
hearth 71, a forced cooling pipe 95 is provided, which is
illustrated as forced cooling means, of which inner side
forms a take-out hole. The forced cooling pipe 95 is of
the dual cylinder, between which cooling water flows. Gases
such as air or nitrogen may be used in place of water.
A take-out devicè 55 is connected to the forced
cooling pipe 95. This take-out device 55 comprises a body
96 formed of metal (generally, iron) and a heat insulating
material 97 lined on the internal surface thereof. The
heat insulating material 97 is similar to the above-
described heat insulating material 73. The take-out device
55 has at its lower part an outflow opening 98 through
which the melt from the take-out hole 5g is fed into the
device in next stage. The route from a port in communication
with the ta~e-out hole 54 to the outflow opening 98 forms
a down-flow passage 99 (surface of the heat insulating
material 97) of the melt 53. The take-out device 55 further
comprises first and second plasma torches 100, 101,
~ 11 --
.
.
'
respectively mounted on the body 96. The first plasma torch
100 is directed so as to irradiate the plasma arc into the
take-out hole 54. The second plasma torch 101 is directed
so as to i~radiate the plasma arc toward the outflow opening
98 and the do~m-flow passage 99. These plasma torches 100,
101 are also connected to a DC power sources 102, 103 and
an operating gas source 86 similarly to the aforementioned
torch 52. The take-out device 55 further has a gas outlet
104. Unnecessary gases are delivered to the duct 89 through
'the outlet 104. The body 58 of the pulverizing device 57
is connected to the body 96 of the take-out device 55
through a connecting member 107, the body 96 having an
inlet 108 communicated with the outflow opening 98. In the
pulverizing device 57, the inlet 10~ has a water pipe 109.
The water pipe 109 is partly formed with a flow-down opening
110, and water from the flow-down opening 110 flows down
along the inclined surface 111 for pulverization and stays
in the lower part of the body 58. The thus stayed water
'flows out of a water outlet 112 and is cooled by the heat
exchanger 113, dusts ~such as particles or grains mixed
into water) are removed by means of a filter 114, and water
is then fed by a pump 115 to t'ne water pipe 109 for reuse.
The abode-described structure operate~ as follows:
The container with the wastes packed therein is charged
into the guide cylinder 80 in the melting furnace 50 from
..... .the aforementioned in~roducing device 38. The containers
may be suitably charged into the guide cylinder in a state
~2~:~5~
where a plurality of containers are stacked or one by one.
The thus charged container 32 together with the wastes is
immersed in the melt 53 of which lower part is already
melted. Thus, heat of the arc released from the torch 52
is not only transmit-ted directly to the containers 32 but
transmitted to these containers 32 or wastes 13 even through
the melt 53, ~hereby the containers and wastes may be heated
in an extremely smooth manner. Because of this, the
containers 32 and the wastes 13 may be melted rapidly
into melt. Since the plasma arc emitted from the torch 52
is maintained at a temperature above lOOOOOK, electric
power to the torch 52 may be regulated so that the melt 53
may assume a suitable high temperature. In this way, metal
as well as wastes composed of inorganic material having a
high melting point may be formed into a melt.
In charging these containers 32, even if they
are violently lowered, the provision of the buffer layer
75 prevents the heat insulating materials 73, 7~ and
water-cooled hearth 71 from being damaged. That is, even
if the container 32 is heavily fallen down to produce a
shock which is locally applied to a part of the solid
layer 75b, the shock is dispersed into a wide region in
the lower surface of the solid layer 75b and the shock
transmitted to parts of the ballast layer 75a becomes -
weak. Furthermore, the weak shock applied to the ballast
layer 75a i5 absorbed by the ballast layer 75d itself and
thus the shock transmitted to the heat insulating materials
73, 74 is very weak.
- 13 -
~1~23~
~ t the time of meltinq as described above, heating
by means of the torch 52 and cooling by means of the water-
cooled hearth 71 are simultaneously carried out. However~
since the heat insulating materlals 73, 74 are provided
between.the buffer layer 75 and the water-cooled hearth 71,
these heat insulating materials serve as walls for control-
ling ~ransfer of heat to prevent heat applied from the
torch 52 from being excessively taken away by the water-
cooled hearth 71 or conversely to prevent the buffer layer
75 from being excessively melted by the heat from the
torch 52. Conversely, the provision of the buffer layer 75
can prevent the heat insulating material from being overheated
or from coming into direct contact with the melt, thus
preventing consumption of the heat insulating material.
As for example, temperatures in normal state in the case of
the foregoing are l,500C for the melt 53 in the vicinity
of the center of the reservoir 76, 1300 - 1400C for the
solid layer 75b, 700 - 1200C for the ballast layer 75a
(the temperature in a portion c].oser to the solid layer
75b is high whereas the temperature in a portion closer
to the heat insulating materials 73, 74 is low), and 610C
for the heat insulating materials 73, 74.
The melt 53 formed by melting the con~ainers 32
and the wastes 13 is taken out of the take-out hole 54 and
drop out of the outflow opening 98 via the down-flow
passage 99 of the take-out device 55. The dropping dew
falls down on the pulverizing inclined surface 111 through
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.
.
~23~3
the inlet 108 of the pulveri~ing device 57, and the melt is
then rapidly cooled by water into particles 60, which stay
in the bottom of the body 58.
Next, where the melt 53 is stopped to be taken
out, coolant such as cooling water is supplied to the
forced cooling pipe 95. Then the melt present inside,
that is, present in the take-out hole 54 is solidified
and the solidified melt is formed into a plug which stops
outflow of the melt 53.
Further, where the melt 53 is again taken out,
the plasma arc is irradiated toward the aforesaid soli-
dified material plugged in the take-out hole 54 from the
plasma torch 100. Then the solidified material is melted
and the melt 53 again flows out of the reservoir 76
through the take-out hole 54. In this case, where the
melt previously moved out of the take-out hole 54 becomes
solidified when it flows down through the down-flow
passage 99 or the melt at the time of previous taking-out
becomes solidified at the down-flow passage 99 so that the
solidified material possibly impedes the flow-down of the
melt which comes later or the solidified melt blocks the
outlet 98, the plasma arc is irradiated toward the down-flow
passage 99 or the outlet 98 from the plasma torch 101
disposed upwardly of the outlet 9~ to melt even those
solidified and adhered thereto, thus effecting the smooth
- flow-down of the aforementioned melt. For the above-described
pulverizing device, there can be used/ for examp~e, a device
- 15 -
~4~
of the construction in which a melt drops on the rotary
disk to scatter it in the form of a melted drop, and other
devices.
Next, FIG. 5 shows a different embodiment of
a device for Fosteriorly treating the melt 53 formed by
melting the wastes 13 within the melting furnace 50.
This post-treating device is the solidifying device in
which the melt 53 is solidified by a water-cooled mold
121, and the device is used in place of the above-described
pulverizing device 57. The body 122 of the solidifying
device is connected below the connecting member 107. A
vertically moving bed 123 on which the water-cooled mold
121 is placed is moved up and down by means of a lift
not shown, and in its up position, the bed blocks a lcwer
opening of the body 122 and positions the water-cooled
mold 121 at a predetermined position to receive the melt 53.
The body 122 is provided with a gas outlet 124 through
which exhaust gas is delivered toward the duct 89. Cooling
water within a water tank 127 is circulated by means of
pump 128 in the water-cooled mold 121 through cooling
water pipes 125 and 126.
The melt within the melting furnace 50 is fed
into the water-cooled mold 121 through the take out device
55 and solidified therein. In this case, if those not
melted are present within the water-cooled mnld 121 or
include an inflation of solidiEied material resulting
from occluded gas at the solidification, the plasma arc
- - 16 -
35~3
from the plasma torch 101 is irradiated toward the unmelted
material within the water-cooled mold 1 1 through the
outflow opening 98 to melt it.
FIG. 6 shows another solidifying device. In
this device, in place of the aforementioned water-cooled
mold there is provided a graphite crucible 132 interiorly
of a storing container 131. The body 133 and vertically
moving bed 134 are constructed equall~ to those of the
aforementioned solidifying device. The body 133 has a
plurality of cooling pipes 135 disposed therein. These
cooling pipes 135 blow cooling gases, which are fed therein,
against the container 131 from a number of nozzles to cool
and protect the container 131. ~he gases ~at a high
temperature) within the body 133 are moved out of the ~as
outlet 136, after which the gases are cooled by means of
a heat exchanger 1`37, and dusts are removed by means of a
filter 138, the gases being compressed by means of a
compressor 139 and fe;d into the cooling pipe 135. Surplus
gases are moved out of the compressor 139, and thereafter
the dusts are again removed by another filter 14~ and
released into the atmosphere through a stack 141.
With the arrangement as described above, the
melt fed into the crucible 132 is solidified therein.
When the crucible 132 is filled with the melt, the crucible
132 together with the container is carried out from the
solidifying device. After carried out, a clearance 142
between the container 131 and the crucible 132 is filled
~'23~3
with concrete, and the solidified material within the
crucible 132 together with the crucible 132 is sealed
into the concrete and a cover is placed thereon.
It should be noted when the rnelt is put into
the crucible 132 that the plasma arc from the plasma
torch 101 is pre-irradiated ayainst the crucible 132 to
preheat the crucible 132 so that all the melt introduced
into the crucible 132 m~y be solidified in the form of a
lump.
It should be also noted when concrete need not
be sealed, the clearance 142 can be prefilled with heat
insulating material such as magnesia particles.
As many apparently widely different embodiments
of this invention may be made without departing from the
spirit and scope thereof, it is to be understood that the
invention is not limited to the specific embodiments
thereof except as defined in the appended claims.
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