Sealing system for the engagement of a container beneath a melting furnace

A sealing system for the engagement of a container (24) beneath a melting pot containing a molten material, comprising a shell (30) surrounding a nozzle (40), the nozzle being located in the axis of the neck of the container and permitting the pouring of the material from the melting pot into the container. The shell (30) has tight connection means with the nozzle (40), a base (32) having a bearing surface for the reception of a corresponding bearing surface on the container neck and at least one bellows (33, 34) surrounding the nozzle and connecting the tight connection means to said base, the bellows being able to render the shell retractable along the nozzle axis, means for introducing a gas flow between said bearing surfaces being provided in order to permit the circulation of part of said flow towards the nozzle.

The present invention relates to a sealing system for the engagement of a 
container beneath a melting furnace. It more particularly applies to the 
pouring of molten radioactive glass into a container. 
The reprocessing of nuclear fuels permits the separation of uranium, 
plutonium and fission products present in the fuel elements which have 
spent a time in a reactor. 
A process has been developed which is known as vitrification for the 
inclusion of a certain number of radioactive elements and in particular 
fission products in a vitreous matrix. 
The melting furnace is constituted by a metal container, known as a melting 
pot and which is heated by induction. Melting takes place at the same time 
in the melting pot of a glass frit and calcinates of fission products in 
order to obtain a glass, which is poured into stainless steel containers. 
This process has become necessary because it permits the storage over a 
long period and with very great safety of highly radioactive products. 
This operating procedure is widely used, described and demonstrated, 
particularly at the Marcoule nuclear centre (vitrification works) and more 
recently in reprocessing plants in La Hague. 
In a more general manner, the installation has two levels separated by a 
slab. At the upper level the melting pot is placed in a furnace. At the 
lower level the container is positioned vertically with respect to the 
tapping hole of the pot. An opening in the slab permits pouring or 
tapping. 
The installation must make it possible to strictly confine the molten 
glass, so that there is no spread of radioactivity, particularly at the 
time of pouring, into the ambient air and onto the outer wall of the 
container. It must permit the collection of all the gases, dust and 
particles given off. It must also permit the expansion of the container 
under the effect of the temperature rise occurring between the instant 
when the container is empty and the instant when it is filled with very 
hot glass. 
To this end FR-A-2 616 000 proposed an apparatus permitting the pouring of 
molten radioactive glass into a container. This apparatus has a static or 
material seal between the various elements of the apparatus and a dynamic 
confinement by the extraction of air or gas around the molten glass being 
poured or tapped. This apparatus, shown in FIG. 1, leaves between the 
container neck and the pouring nozzle, an annular area opening onto the 
outside and by which the tapping gases and dust can leak to the outside. 
This leak is in principle fought by an air extraction. However, if said 
air extraction is not sufficiently effective, there can be a leak of 
radioactive dust and gases to the outside contaminating the outer wall of 
the container. The dynamic sealing apparatus according to the present 
invention obviates this disadvantage. 
Thus, the present invention relates to a dynamic sealing apparatus for the 
engagement of a container beneath a melting pot containing a molten 
material, comprising a shell surrounding a nozzle, the nozzle being 
located in the axis of the container neck and permitting the pouring of 
material from the melting pot into the container, characterized in that 
the shell comprises means for tight connection to the nozzle, a base 
having a bearing surface for receiving a corresponding bearing surface on 
the container neck, and at least one bellows surrounding the nozzle and 
connecting the tight connection means to said base, the bellows making it 
possible to retract the shell along the axis of the nozzle, means for 
introducing a gas flow between said bearing surfaces being provided in 
order to permit the circulation of part of said flow towards the nozzle. 
The gas flow introduction means can include at least one groove forming a 
labyrinth seal. Advantageously, the pressure drop in the leakage flow to 
the nozzle creates in the labyrinth seal an overpressure opposing the 
leakage to the outside of tapping gases.

FIG. 1 illustrates the prior art, as disclosed by FR-A-2 616 000. It 
permits the transfer of molten glass between two superimposed cells 
separated by a dismantlable dome 13. The upper or vitrification cell 1 
contains the melting pot 2. The lower or pouring cell 3 contains the 
container 4 in which it is wished to pour the molten radioactive glass 
coming from said melting pot. A horizontal concrete slab 5 beneath the 
melting pot has an opening 6. The complete melting pot 2, opening 6 and 
container 4 is organized about a vertical axis 7 known as the pouring 
axis. 
The radioactive glass is in the liquid state in the melting pot 2 and is 
kept in the latter by set glass obstructing the pot neck 8. An inductor 9 
is placed around the neck so that, at the chosen instant, it softens the 
set glass forming a plug, so as to enable the molten glass contained in 
the melting pot to flow out through the neck. The inductor 9 is connected 
by not shown connections to a medium frequency energy source permitting 
the heating of the neck 8 and the set glass. An insulating plate 10 
insulates the melting pot 2 with respect to the concrete slab 5. 
Beneath the concrete slab, to the right of the slab opening 6, is 
positioned the casting apparatus which is successively constituted from 
top to bottom by a retractable shell 11, a dismantlable shell 12 and the 
dismantlable dome 13. 
The retractable shell 11 is formed by two interpenetrating boxes or cans, 
which slide in one another, the lower can entering the upper can. The two 
cans are interconnected by a metal bellows integral therewith. A not shown 
linkage system makes it possible to move the two cans together and the 
retractable shell is fixed by its upper can beneath the concrete slab. 
The dismantlable shell 12 is fitted to the lower face of the retractable 
shell 11. It is put into place and retained by using the dismantlable dome 
13. It is connected to a tapping gas suction system 14. The central part 
of the dismantlable shell is extended downwards in order to form a molten 
glass discharge nozzle. 
The dismantlable dome is traversed by an internal chamber forming a coil 
for receiving a circulation of water for the cooling thereof. It also has 
a second chamber provided with a tube 44 permitting the entry of air into 
said chamber. 
This apparatus ensures the sealing between the melting pot 2 and the bottom 
of the dismantlable shell 12. However, between the neck 47 of the 
container 4, the dismantlable shell 12 and the dismantlable dome 13 there 
is an annular area by which the tapping gases and dust can diffuse to the 
outside. If the air suction by the suction system 14 is not sufficiently 
effective, there can be a leakage of gases and dust at this location. 
FIG. 2 shows a container 24 in the pouring cell 23. In diagrammatic manner 
is shown the lower part of the retractable shell 50 and the dismantlable 
dome 60. 
In this application example of the invention, the nozzle 40 is a metal part 
revolving about an axis along which pouring or tapping takes place. Its 
upper part is constituted by a disk 43, which rests on a shoulder 41 of 
the central orifice 61 of the dismantlable dome 60 and which is extended 
by a tube 45. The not shown melting pot has a pouring tube communicating 
with the nozzle 40 by the duct constituted by the retractable shell 50. 
The upper orifice of the nozzle 40 is widened in truncated cone-shaped 
manner in order to receive the lower face of the retractable shell 50. The 
contacting of the spherical cap portion forming the lower face of the 
retractable shell 50 with the truncated cone of the upper orifice of the 
nozzle prevents leaks with the vitrification cell. 
According to the invention, the tube 45 of the nozzle 40 is surrounded by a 
shell 30 formed by an upper disk 31, a lower disk 32 and two bellows 
concentric to the nozzle, namely an inner bellows 33 and an outer bellows 
34. 
The shell 30 is tightly connected to the nozzle 40 by fixing the upper disk 
31 beneath the nozzle disk 43. Thus, the upper disk 31 is located in the 
hole 61. 
The lower disk 32 surrounds the nozzle tube 45 with a certain clearance. 
The lower face of said disk 32 is contacted with the rim 28 of the neck of 
the container 24, contacting occurring along a plane. The lower face of 
the disk 32 is grooved in order to form a labyrinth seal 35 extending over 
the entire surface of said face. 
The blowing in of gas, e.g. air, takes place by means of various holes made 
in the disk 43 of the nozzle 40, in the upper disk 31 and in the lower 
disk 32 of the shell. As shown in FIG. 2, the hole 46 of the disk 43 
communicates with the hole 36 of the disk 31, said hole 36 issuing into 
the annular space between the bellows 33 and 34. At least one hole 37 made 
in the lower disk 32 roughly midway between the internal radius and the 
external radius of the disk and between the two bellows 33 and 34, 
communicates with the groove or grooves forming the labyrinth seal 35. 
Compressed air blown in from the hole 46 then circulates between the two 
bellows 33, 34, passes through the hole 37 of the lower disk 32 and 
arrives at the labyrinth seal 35. Part of the blown in air flow is 
directed towards the pouring axis and rises via the interior of the nozzle 
where it is extracted with the pouring or tapping gases by means of the 
duct 35 connected to the nozzle 40 and to a gas extraction apparatus. The 
other part of the air flow escapes to the outside. There is a slight 
overpressure due to the pressure drops in the labyrinth seal within the 
annular chamber and the flow is distributed so as to prevent any leak to 
the outside of the tapping gases. 
Compressed air (or some other scavenging gas) can also be blown in between 
the inner bellows 33 and the nozzle in order to prevent any contamination 
rise in this area. As shown in FIG. 2, the hole 48 made in the nozzle disk 
43 close to the tube 45, permits the injection of said compressed air. It 
communicates with the hole 38 made in the upper disk 31 of the shell 30. 
The blown in air then passes into the annular area located between the 
inner bellows 33 and the nozzle, after which it penetrates the neck of the 
container 34 as a result of the clearance existing between the lower disk 
32 of the shell and the tube 45 of the nozzle. 
The tapping gases, the air blown in for supplying the labyrinth seal and 
possibly the scavenging air around the nozzle 40 are sucked in by means of 
the duct 53, filtered and then treated by an appropriate equipment. 
According to the variant of FIG. 3, the shell 30' only has a single 
bellows, the inner bellows 33. The air blown in on the bearing plane 
between the lower disk 32 and the rim 28 of the neck of the container 24 
is then supplied by a flexible pipe 55 connected to the hole 37 made in 
the lower disk 32. 
Thus, the sealing system according to the invention effectively fulfils the 
three following functions: 
formation of a bearing surface of the container beneath the melting pot, 
dynamic sealing at the bearing area of the container, 
extraction of the tapping or pouring gases to the gas treatment unit.