Patent Publication Number: US-6666003-B1

Title: Method and device for filling drums containing dangerous waste

Description:
TECHNICAL FIELD 
     The invention relates to a process making it possible to ensure the filling of drums containing dangerous wastes, such as very low level radioactive waste, previously processed and compacted to form “flat cakes” piled on top of each other inside the drum. 
     Another object of the invention is an installation for operating this process. 
     STATE OF THE ART 
     In nuclear installations, low level technological wastes are first of all processed in cylindrical metallic containers. The volume of these containers is, for example, 120 litres. 
     The containers holding the wastes are then compacted using a press, to obtain “cakes” greatly reduced in volume, height-wise relative to the containers. 
     During a later stage, these cakes are piled in cylindrical metal drums. As a general rule, five cakes, for example, are piled in each of the drums. 
     During a following operation called “blocking” the drums are placed on a vibrating table and filled with a blocking material such as a cement plaster or grout. 
     When a drum has been filled with blocking material, it is then closed by means of a crimped lid. 
     Finally, when the blocking material is dry, the drums are transported to a long-term surface storage site. 
     More precisely, the invention concerns the blocking operation, during which the drums containing the cakes are filled with a blocking material. 
     At the time of this operation, which is carried out in a workshop, the contaminated air contained in the drum escapes into the workshop and tends, in particular, to contaminate the external wall of the drum as well as the close surroundings. In fact, a volume of contaminated air equivalent to that of the blocking material injected into the drum escapes from it to the outside. 
     In prior art, no known technical solution exists for this problem. 
     DESCRIPTION OF THE INVENTION 
     The object of the invention is precisely a process for filling a drum containing dangerous wastes, making it possible to avoid any dispersion of contamination into the atmosphere of the room, and in particular onto the external wall of the drum, due to the contaminated air ejected from the drum during the blocking operation. 
     According to the invention, this result is obtained by means of a process for filling drums containing dangerous wastes, characterised in that it comprises the following stages: 
     assembly of an intermediary lid on a drum, said lid comprising an opening closed in a sealed fashion by a cap; 
     perforation of the cap by a toothed crown carried by a containment hood overhanging an end of the drum closed by the intermediary lid; 
     injection of a blocking material into the drum, by means of an injection tube located inside the toothed crown; 
     negative pressure application to the drum and the containment hood, as soon as the drum is set in place and during perforation and injection. 
     In the process described above, the intermediary lid provided with its cap ensures the sealed containment of the drum before perforation of the cap. After perforation, dynamic containment is ensured by negative pressure application to the drum and containment hood. Thus, the contaminated air contained in the drum is sucked out as the drum is filled with the blocking material, without this air being dispersed into the atmosphere of the workshop. Thus one avoids in particular, any contamination of the external walls of the drum. 
     According to a preferred embodiment of the invention, the end of the filling of the drum by blocking material is detected, in such a way as to stop injection of this material. 
     Detection of the end of filling of the drum can in particular be ensured by at least one bubble tube opening into the interior of the toothed crown. 
     In this case, in order that the level of filling can be controlled with precision, advantageously the end of the bubble tube is positioned at a predetermined level below the cap, after perforation of the latter. To do this, one can in particular use a laser detector mounted on the containment hood and able to measure the distance between the latter and the intermediary lid. 
     Preferably, the cap is equipped with ballast means to ensure, through gravity, the evacuation into the drum of the disc cut out in the cap by the toothed crown, in order to avoid total or partial closing of the orifice of the injection tube through a suction effect on the cap. 
     The perforation of the cap can in particular be carried out by displacing the drum upwards relative to the fixed containment hood. Advantageously, lifting means such as a jack can be used for this. Preferably, these lifting means are associated with means capable of making the drum they support vibrate, during filling, so as to improve the penetration of the blocking material in the drum, around the radioactive waste. 
     As a variant, the perforation of the cap can also be obtained by displacing the toothed crown or the hood downwards. 
     In order to avoid in particular the blocking material setting before being injected into the drum, advantageously this material is made to circulate continuously in a closed circuit, during the period preceding this injection. 
     Moreover, after injection of the blocking material into the drum, it is preferable to carry out a cleaning of the means of injection, that is to say of the closed circuit and the nozzle through which the material is injected into the drum. 
     Finally, after injection of the blocking material into the drum, the latter is separated from the containment hood and an external lid is placed on the drum, above the intermediary lid. The drum then passes into a crimping machine which crimps the external lid. Then the drum is in a condition ready for storage, before being transported to a site prepared for very long-term storage. 
     Another object of the invention is an installation for filling drums containing dangerous wastes, characterised in that it comprises: 
     an intermediary lid able to be mounted on a drum, said lid comprising an opening closed in a sealed fashion by a cap; 
     a containment hood able to overhang an end of the drum closed by the intermediary lid, said hood having a toothed crown able to perforate the cap; 
     means of injection of a blocking material, opening inside the toothed crown; and 
     means of negative pressure application for the drum and the containment hood. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     A preferred embodiment of the invention is described below, as a non-limiting example, referring to the attached drawings, in which: 
     FIG. 1 is a vertical section illustrating the filling of a drum containing radioactive wastes by means of a filling installation according to the invention; 
     FIG. 2 is a view in perspective and cut-away, showing in more detail the intermediary lid placed on the drum, as well as its cap; and 
     FIG. 3 shows diagrammatically the means of injection of the blocking material used in the filling installation according to the invention. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION 
     In FIG. 1, reference  10  refers to a cylindrical metallic drum in which nuclear waste of very low radioactivity is placed beforehand. More precisely, these nuclear wastes are in the form of flat cakes  12 , piled one on top of the other inside the drum  10 . Each of these flat cakes  12  is constituted of a cylindrical metallic packaging filled with nuclear waste of very low activity, then compacted inside a press. 
     As indicated above, the invention concerns a process and an installation making it possible to carry out a blocking operation, during which a blocking material  14  such as cement plaster is injected successively into each drum  10 , to immobilise the flat cakes  12  there by filling as far as possible the free space inside the drum  10 . According to the invention, the process and installation are designed in such a way that the blocking operation is carried out while avoiding any dispersion of the contaminated air initially contained in the drum  10  into the atmosphere of the processing workshop and in particular on the external wall of the drum. 
     The installation according to the invention comprises an intermediary lid  16 , which is mounted on the open upper end of the drum  10  as soon as the cakes have been placed in it. The intermediary lid  16  is then crimped. 
     As shown more clearly in FIG. 2, the intermediary lid is fixed in a sealed fashion to the upper part of the drum  10 . In order to do this, it can in particular be fitted into an annular sealing joint  18  which covers the curl  10 a forming the upper end of the drum  10 , and then crimped. 
     The intermediary lid  16 , made out of sheet metal, comprises at its centre a circular opening  20 . The diameter of this opening is, for example, 164 mm in the case of a drum  10  of 570 mm diameter. 
     The circular central opening  20  of the intermediary lid  16  is initially closed in a sealed fashion by a metallic cap  22 , for example in aluminum, glued on the upper face or external to the intermediary lid  16 . The metallic cap  22  is constituted of a temporary closing pellet for the drum. At its centre, on its lower surface turned towards the inside of the drum  10 , it is provided with a ballast domino  24  constituting ballast means whose function will be made clear below. As a non-limiting example, the mass of the ballast domino  24  can be about 50 gm. 
     On its lower face turned towards the interior of the drum  10 , the intermediary lid  16  comprises at least one anti-float organ such as three lugs  26  soldered on the lid  16  and arranged at 120° one after the other around a circle centered on the axis of the intermediary lid  16 . As a non-limiting example, the circle around which the lugs  26  are arranged can have a diameter of 350 mm. The lugs  26  stick out downwards inside the drum  10 , of a determined length, for example 45 mm. Thus they maintain a minimum free space of the same height between the intermediary lid  16  and the top of the pile of cakes  12  placed in the drum  10 . This space favors later flow of the blocking material  14  when it is injected into the drum. 
     The installation according to the invention also comprises a dynamic containment hood  28  (FIG. 1) under which is placed the upper part of the drum  10  closed by the intermediary lid  16 , when the blocking operation is carried out. In the embodiment represented, the dynamic containment hood  28  is fixed. More precisely, it is fixed under a horizontal partition  30  equipping the processing workshop. 
     The setting of the upper part of the drum  10  under the dynamic containment hood  28  is obtained by placing the drum  10  on the upper plate of a jack  32  comprising lifting means. When lifting of the drum  10  is completed, its upper end is received inside the dynamic containment hood  28 , as illustrated in FIG.  1 . 
     In order to improve filling of the drum  10  by the blocking material  14  during the blocking operation, means  34  (FIG. 3) able to make the drum  10  vibrate are associated with the jack  32 . In other terms, the latter is a vibrating jack. 
     In FIG. 1, lines of dots and dashes represent diagrammatically an anti-fall system constituted of fingers  35  linked by arms  37  to the horizontal partition  30 . When the drum  10  is in the upper position, the fingers  35  arrive under the upper plate of the jack and ensure that it is maintained in this position, even in the case of failure of the jack  32 . 
     As shown diagrammatically in FIG. 3, the drums  10  are moved one after the other above the jack  32  by a conveyor belt  36 , to be submitted to the blocking operation. They are then moved on from this post by the same conveyor belt  36 . 
     According to the invention, the dynamic containment hood  28  supports in its centre the collar  39 , terminated at its lower part by a toothed crown  38  (FIG.  1 ). This toothed crown  38  is placed along the axis of the opening  20  formed at the centre of the intermediary lid  16  and its diameter is slightly smaller than that of this opening. The toothed crown  38  is provided around the length of its boundary with pointed and long saw-teeth directed downwards. These saw-teeth ensure the perforation of the cap  22  at the end of the lifting of the drum  10  under the dynamic containment hood  28 , just before the beginning of injection of the blocking material  14 . 
     Holes  37  are pierced all around the cylindrical support of the toothed crown  38 , at such a level that they are below the intermediary lid  16 , at the end of the piercing operation of the cap  22 . These holes  37  avoid negative pressure application to the cap  22  after piercing and allow good air circulation. 
     When perforation is carried out, the ballast domino  24  placed at the centre of the cap  22  drags downwards, by gravity, the disc cut out in the cap by the toothed crown  38 . The ballast domino  24  ensures that the disc falls in the drum and thus prevents this disc remaining inside the toothed crown  38  and closing the piping opening inside the crown. It also avoids the risk of it floating on the surface of the blocking material  14 . 
     The installation according to the invention also comprises means  40 , for injecting the blocking material  14  in the drum  10 . These means of injection  40 , which will be described in more detail below with reference to FIG. 3, comprise in particular an injection nozzle  42  which opens inside the toothed crown  38 , as shown in FIG.  1 . The injection nozzle  42  is oriented downwards and is preferably arranged along the axis of the toothed crown. When the cap  22  has been perforated by the toothed crown  38 , the operation of the means of injection  40  makes it possible to inject blocking material  14  directly inside the drum  10  without rupture of the containment of the latter. 
     The installation according to the invention also comprises means  44  of negative pressure application onto the drum  10  and the interior of the dynamic containment hood  28 . These means for negative pressure application  44  comprise in particular one or several air suction tubes  46 , which open inside the collar  39  carrying the toothed crown  38 . The air suction tube or tubes  46  are linked to suction means  47  able to extract the contaminated air pushed out of the drum  10 , while blocking material  14  is injected, still maintaining negative pressure in the drum and inside the dynamic containment hood  28 , compared to the outside environment. As a non-limiting illustration, the depression produced by the negative pressure application means  44  is, for example, about 2660 Pa. 
     The negative pressure application means  44  also comprise very high efficiency filters  49  able to retain the totality of the contaminated dusts contained in the air sucked out. 
     Advantageously, the means of suction  47  are doubled, in order to avoid any loss of containment in the event of deterioration of the main suction system or a loss of electricity supply. 
     Advantageously and as shown schematically in FIG. 1, a deflector  48  is placed inside the toothed crown  38 , immediately below the injection head  42 , so as to direct the blocking material  14  towards the periphery of the drum  10 . Thus any risk of clogging, even temporary, is avoided for the air suction tubes  46 . In fact, in the absence of a deflector, a bank of blocking material could be formed on the top of the pile of cakes  12 . 
     Outside the collar  39  carrying the toothed crown  38 , the upper wall of the dynamic containment hood  28  supports a laser detector  50  directed towards the intermediary lid  16 . The laser detector  50  makes it possible to measure the distance separating the containment hood  28  from the intermediary lid  16 . Linked to a control circuit (not shown) of the lifting jack  32 , the laser detector  50  thus forms means for positioning the lower end of at least one bubble tube  52  at a predetermined level below the cap  22 , after perforation of the latter (preferably, two bubble tubes  52  are used, as shown in FIG.  1 ). In other terms, when the distance measured by the laser detector  50  reaches a predetermined value, the upward movement of the drum  10  assured by the lifting jack  32  is stopped. The lower ends of the bubble tubes  52  are then at a predetermined level below the intermediary lid  16 . The control of this positioning makes it possible to pilot precisely the filling level of the drum  10  with the blocking material  14 , by using the bubble tubes  52 . 
     For this, the lower parts of the bubble tubes  52  (FIG. 1) are placed inside the collar  39  carrying the toothed crown  38 . The level of the lower ends of the bubble tubes  52  is such that, when the lifting of the drum  10  has been stopped in response to the measurement made by the laser detector  50 , these ends are situated at a level slightly lower than that of the intermediary lid  16 . As an example, the lower ends of the bubble tubes  52  can be at 4 mm below the level of the intermediary lid  16 . The bubble tubes  52  thus constitute means for detecting the filling of the drum  10 . In other terms, when the bubble tubes  52  are closed by the blocking material  14  at the end of filling, one is sure that the drum is completely filled. The filling of the drum is thus stopped. 
     When two bubble tubes  52  are used as shown in FIG. 1, advantageously they are placed in positions diametrically opposite each other relative to the vertical axis of the dynamic containment hood  28 . Thus they ensure redundancy of detection. 
     In FIG. 3, a diagram is shown of means of level detection  54  to which the bubble tubes  52  are connected. These means of level detection  54  pilot the automatic closing of two level-detection valves  56   a  and  56   b , placed in a circuit for feeding the nozzle  42  with blocking material  14 . This supply circuit constitutes, with the injection nozzle  42 , the injections means  40 . A third valve  56   c , located immediately above the injection nozzle  42 , serves as a safety valve and enables piloting of the rinsing of the supply circuit. It is controlled from the operations room, by an on-off control. 
     As shown in FIG. 3, the supply circuit for the nozzle  42  comprises a closed circuit  58  connected to the injection nozzle  42  by a pipe  60  in which the valves  56   b  and  56   c  are placed. 
     The closed circuit  58  comprises a hopper  62  for filling and storing the blocking material  14 . The capacity of the hopper  62  is designed to allow at least one drum  10  to be filled. The hopper  62  is filled with the desired volume of blocking material, from a mixer (not shown), let in through a pipe  64  through a valve  66 . The closed circuit  58  allows the blocking material  14  to circulate continuously in a loop, to avoid it all setting, to increase its lifetime and to limit the effects of clogging the tubing, until this material is injected into the drum  10 . For this, it is equipped with pumping means such as a peristaltic pump  68 . The valve  56   a  piloted by the level detection system  54  is placed in the closed circuit  58 , immediately below the branch linking the circuit  58  to the injection nozzle  42  through the pipe  60 . 
     A pipe  74 , provided with a valve  76 , links the water distribution network to the pipe  60  between the two valves  56   b  and  56   c  placed on it. This pipe  74  makes it possible, by injecting water under pressure, to carry out the rinsing of the central and lower parts of the injection nozzle  42  when the drum which has just been filled has been emptied. It is set in action before the following drum arrives underneath the dynamic containment hood  28 . The recuperation of rinsing effluents is carried out by a retractable plate (not shown) which comes into place against the dynamic containment hood  28 , in place of the drum. The effluents are then directed towards a specialised installation for treating polluted water. 
     Other valves  82  are set in different locations around the closed circuit  58 . In addition, a pipeline  84  provided with a valve  86  opens into the circuit  58 , near the suction of the pumping means  68 . This pipeline makes it possible to ensure the cleaning of the whole circuit, in particular by introducing a foam ball, through the piping  84 , thus ensuring evacuation of the residual blocking material through emptying tubing  87 , provided with a stop valve  88 . The final rinsing of the closed circuit is carried out by injecting clean water into the hopper  62  (with pumping means  68  in operation) and recuperating the effluents in the retractable plate then set in place under the hood  28 . 
     Only a part of the closed circuit  58  is inside the processing workshop in which the filling of the drums  10  is carried out. A portion of the containment partition  88  defining this workshop is shown diagrammatically in FIG.  3 . The part of the circuit  58  located outside the processing workshop includes in particular the hopper  62  and the pumping means  68 . 
     Advantageously, the whole of the installation is piloted by automatic control-command means (not shown). 
     When a drum  10  is brought up to the filling post in which the blocking operation is carried out according to the invention, it contains cakes  12  and its upper end is closed in a sealed fashion by the intermediary crimped lid  16  whose central opening  20  is closed by the cap  22 . As soon as the drum  10  is set on the lifting jack  32  by the conveyor belt  36 , its horizontal displacement is stopped and the drum is lifted up to the position shown in FIG.  1 . In this position, controlled by laser detectors  50 , the cap  22  is perforated by the toothed crown  38 . The disc cut out in the cap falls immediately onto the pile of cakes  12 , by gravity, because of the mass of the ballast domino  24 . 
     Despite this perforation, the containment of the drum  10  remains intact, until the end of filling, by the dynamic containment hood  28  under negative pressure application by means  44  for negative pressure application. 
     The injection of the filling material  14  into the drum then begins under the action of the pumping means  68 , after opening valves  56   a  and  56   c  placed in the piping  60 . Simultaneously, the drum is made to vibrate by means  34  for creating vibration, associated with the jack  32 . 
     The injection of the filling material  14  continues until the bubble tubes  52  detect the arrival of the free level of the blocking material immediately next to the intermediary lid  16 . The level detection means  54  then automatically close the valves  56   a  and  56   b  and the injection is stopped. 
     Next, the jack  32  is once again activated to re-lower the drum  10  onto the conveyor belt and to carry it to the following post where an external lid (not shown) is set in place. More precisely, the external lid is set on the drum above the intermediary lid  16  and crimped on the curl  10   a  of the drum. 
     The process and installation which have just been described make it possible to carry out the blocking operation while still ensuring complete control of containment. Any dispersion of contamination into the atmosphere of the workshop, and in particular any contamination of the external wall of the drum is thus avoided.