Patent Number: 039717321
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of an apparatus for fixing radioactive and/or toxic waste may find application in a bituminization system illustrated schematically in FIG. 1. In a storage tank 1 having a volume of approximately 20 m.sup.3, bitumen is heated to 140.degree.C by means of a heat exchanger 2. The heat exchanger 2 is connected by means of a reducing valve 3 to a heating vapor conduit 4. The heating vapor is, in the conduit 4, brought from 16 atm. gauge and 203.degree.C to 8 atm. gauge and 175.degree.C by means of the reducing valve 3. A bitumen metering pump 5 supplies the liquid bitumen through a conduit 6 provided with a heater 7 to a dual-shaft extruder 8. In the mixing chamber of the extruder 8 there are disposed parallel-spaced shafts 9 and 10 on which there are arranged respective screw conveyors 11 and 12 of different length and pitch. The turns of the two screw conveyors are in an interleaving relationship with one another and rotate in the same direction, thereby mixing together the radioactive concentrate and the bitumen and at the same time, advancing the mixture in an axial direction. The screw conveyors are supported in 11 housing parts flanged to one another; the housing parts are combined into housing pairs, each defining a vapor-heated heating zone. Each heating zone is provided with a vapor outlet device constituted by a tubular vapor exhaust coupling 13 and a condenser 14. Each heating zone has a temperature-regulating device. The screw conveyors are rotated with a speed of up to 300 rpm by a 60 kW D.C. motor 15 with the intermediary of a drive gearing 16. A concentrate metering pump 17 feeds the extruder 8 with a concentrate consisting of liquid radioactive waste from a storage container 18 which, in turn, is charged by means of a further pump 19 from a larger storage vessel 20. The storage container 18 is shielded by lead walls 21 through which, while observing safety regulations, samples may be withdrawn into a specimen box 22. The vapor generated in the extruder 8 upon introduction of the concentrate into the bitumen, is precipitated in five condensers 14 and the distillate, for removing the bitumen particles still being carried, is passed through a tar filter 23 and introduced into a distillate accumulator 24 provided with a cooling device 25. A distillate pump 26 advances the distillate into an evaporator 27 for further purification. In the zone of the outlet or discharge spout 28 of the extruder 8 there is provided a loading device, constituted by a charging cabin 30 provided with lead walls 29 forming a radiation shield. In the cabin 30 there is disposed a mechanically driven rotary disc 31 which is movable in either direction and on which there are disposed, for example six barrels 32 (only two shown). A portion of the lateral wall and the ceiling of the cabin 30 constitute a slideable angle door 33 which may be shifted to provide an opening through which the barrels 32 may be moved by means of an overhead hoist 34 and a barrel gripper 35. The charging cabin 30 is ventilated by means of a ventilating system isolated from the other spaces. The mixed material emerges from the discharge spout 28 of the extruder 8 in a continuous manner. As soon as the barrel 32 positioned under the discharge spout 28 is filled, an interrupter bowl 37 is brought under the spout 28 by means of an externally operable actuating lever 36 and, by rotating the disc 31, an empty barrel 32 is moved under the extrusion nipple 28 to begin the filling thereof subsequent to pivoting away the interrupter bowl 37. The interrupter bowl 37 which is made, for example, of pressed sheet metal, catches approximately 2 liters of material and is filled approximately after four or five barrel changes. After such filling, the interrupter bowl 37 is dropped into the barrel below, so that the surface of the barrel will not be contaminated and an elimination of the filled interrupter bowl can be effected in a simple manner. For this purpose, the diameter of the interrupter bowl 37 is smaller than that of the filler opening provided in each barrel 32. A closure locking device 38 places, with a gripper 39, a closure 40 on the filler opening of the barrel 32, presses the closure 40 into the opening and deforms the closure edge by the four jaws of the gripper 39, so that a crimped closure lock is obtained. Turning now to FIG. 2, there is illustrated a vapor exhaust coupling 13 of the dual-shaft extruder 8. To a flange 41 there is attached the conduit 6 for introducing the liquid bitumen, and to a flange 42 there is connected the concentrate conduit leading from the concentrate metering pump 17. By arranging the couplings for the bitumen conduit and the concentrate conduit above the shafts 9 and 10, a plug formation in the bitumen conduit is prevented. Between a flange 43 at the upper end of the vapor exhaust coupling 13 and a flange 44 of an adjoining tube 45 provided with a window 46, there is fixedly secured an intermediate ring 47 by means of tension screws 48. The ring 47 has the same internal diameter as the tubular coupling 13 and is contiguous therewith. Internally of the intermediate ring 47 there is arranged an annular tubular conduit (distributor) 49 which is connected to a steam supply conduit 50 passing through the ring 47 and supported thereby. From the underside of the distributor 49 there extend six tubes (vapor lances) 52 (only three shown) which have at their ends outlet nozzles 51 oriented towards the inner wall of the vapor exhaust coupling 13 at a distance of up to approximately 20 centimeters from the upper edge of the screw conveyors 11, 12. By means of the vapor lances 52 deposits of radioactive salts are removed from the inner wall of the exhaust coupling 13 in a simple manner whenever necessary, without interrupting the operation of the apparatus. The removed salt deposits are then mixed into the bitumen by the screw conveyors 11, 12. For cleaning the observation window 46, there is provided a further steam supply conduit 53 which passes through the intermediate ring 47 and is supported thereby. The steam conduit 53 has a nozzle terminal 54 projecting into the space defined by the ring 47. The nozzle 54 is directed towards the window 46, so that deposits which adversely affect the transparency of the glass may be removed in a simple manner. In case of a relatively large-area observation window 46, it is expedient to connect at the end of the steam conduit 53 a U-shaped or comb-shaped tube member, the free ends of which each carry a nozzle 54 oriented towards the observation window 46. FIG. 3 illustrates one of the vertically oriented tar filters 23. It comprises two transparent (glass) tubes 55 which have, at each of their end zones, a radially outwardly projecting conical collar 56 for attachment with a flange 57 with the interposition of a sealing ring 58. The glass tubes 55 are connected to one another by means of two flanges 57, an intermediate flange 59 and seals 60. Across the central bore 61 of the intermediate flange 59 there extends a first sieve 62. The lower end of the tar filter 23 is closed by a second sieve 62, a flange 57 with a sealing ring 58 and a flange 63 with a seal 60. The upper end of the tar filter 23 is closed in a similar manner, but has no sieve. The space 64 between the sieves 62 is filled with an oil-absorbing substance. The distillate is introduced from the condenser 14 through the upper conduit coupling 65 into the filter 23. At the first sieve 62, the bitumen particles carried by the material are retained and they are collected in the space 66. After the separation of the oil contained in the distillate in the space 64, the purified distillate leaves the filter 23 through the conduit nipple 67 and is admitted -- as it may be observed in FIG. 1 -- to the distillate accumulator 24. Of the two identical filters 23 shown in FIG. 1, during operation one always constitutes the active (operating) filter, while the other is the reserve filter. The distillate stream is switched over from the active filter to the reserve filter when the space 66 of the operative filter 23 is filled with bitumen particles or, as the case may be, when the absorption capabilities of the oil-absorbing substance are exhausted or when the accumulated activity makes a replacement necessary. Each filter may be easily replaced with the aid of rapid couplings. It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.