FR2970328A1 - ASSEMBLY FOR ASSAYING AT LEAST ONE POWDER MATERIAL - Google Patents

Abstract

Dosing plant for a powder material comprising at least one hopper (TC), a conveyor (2) having a container (6) provided with a filling opening below said hopper (TC), a filling system weighing (4) able to weigh at least said container (6), means (20) able to move the weighing system (4) and the container (6) so as to move the container (6) away from the conveyor (2) and so that in at least one remote position the weighing system (4) weighs only the container (6) and its contents, said weighing system (4) having a first scale (8) supporting the container (6) and a second scale (10) on which the first scale (8) rests. Said installation may comprise individual hoppers (T1, T2, T3) upstream of the hopper (TC), making it possible to produce powder mixtures.

Description

TECHNICAL FIELD AND PRIOR ART The present invention relates to a metering device for a powder material and an installation for manufacturing mixtures of at least two materials in one or more materials. powder, particularly suitable for the manufacture of powder mixtures in the field of the manufacture of nuclear fuels. The manufacture of nuclear fuels, for example in the form of pellets intended to be stacked in sheaths to form pencils, requires great precision in the determination of the various mixed materials. For example, for the production of pellets of MOX (mixture of uranium oxide and plutonium oxide), a mixture of uranium oxide, plutonium oxide and chamotte is produced. Each component is weighed carefully. As a precaution, two weighings by two different weighing systems are performed. The mixture that will eventually be pressed into pellets is obtained in two stages.

In a first step, plutonium oxide, uranium oxide and chamotte are mixed in powder form, constituting a so-called primary mixture. In a second step, uranium oxide is added to this primary mixture in order to obtain the precise content required. This final mixture is called secondary mixture, and will be pelleted by means of a press, and then sintered. In order to perform each of these steps, the manufacturing plant comprises hoppers fed with the powder materials to be mixed and a collecting hopper in which the contents of each of the hoppers are discharged. The contents of the collecting hopper pour, meanwhile, into a jar.

In order to control the composition of the mixture, each of the hoppers is equipped with a scale to measure the amount of powder that flows into the collecting hopper. In addition, the jar rests on a scale in order to carry out the second weighing. With each flow of material in the jar, the mass of it is weighed and is compared with that measured with the scale associated with each hopper. This installation is satisfactory and provides the required dosages. However, it requires significant maintenance. Indeed, the load cells on the hoppers are subject to significant mechanical stress and repeated, especially because of the presence of vibrating corridors out of the hoppers for conveying the powder to the collecting hopper. In addition, each hopper is surrounded by biological protection. It is possible that powder falls between the individual hopper and the biological protection and disturbs the weighing.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a metering facility of at least one powdered material of improved operation and simplified maintenance. The previously stated purpose is achieved by a dosing installation of one or more powder materials having a first balance and a second balance resting on the first balance, the second balance being intended to directly support the jar. According to the invention, the two weighings are carried out by means of two superimposed scales. It is then no longer necessary to use the weighers on the hoppers to perform a second check. The problem of mechanical stressing of the load cells does not arise anymore. In addition, the double weighing system has a small footprint, which simplifies its handling in case of maintenance.

The powder metering system is particularly suitable for the manufacture of powder mixtures, and in particular in the nuclear field, since it offers high precision and robustness of operation, reduced bulk and simplified maintenance. The subject of the present invention is therefore a metering installation of at least one powder material comprising at least one hopper, a conveyor intended to have a container provided with a filling opening below said hopper, a weighing system capable of weighing at least said container, means 3 4 able to move the weighing system and the container so as to move the container away from the conveyor and so that, in at least one position apart, the weighing system can weigh only the container and its contents, said weighing system comprising a first balance intended to support the container and a second scale on which the first balance rests, the second balance resting on the means of displacement.

In one exemplary embodiment, one of the scales has a higher precision than the other, the scale having the highest precision, for example of +/- 6g, used to adjust the powder dosage and the balance presenting the lowest accuracy, for example +/- 25 g, used to check if the amount of powder corresponds substantially to that expected. The weighing system comprises for example support elements projecting from a plate of the first scale, intended to come into contact with the bottom of the container to lift it. The support elements may be formed by at least three vertical rods fixed by a first longitudinal end to the surface of the plate of the first balance and a second longitudinal end is intended to come into contact with the bottom of the container to lift it. The conveyor may have openings above and aligned with the support members to allow their passage and their contact with the bottom of the container. For example, the conveyor comprises rollers, the support elements passing between the rollers. Advantageously, the support elements have an adjustable height. The dosing system of at least one powder material advantageously comprises a leaktight connection between a discharge end of the hopper and the filling opening of the container. The displacement means may have a vertical stroke sufficient to ensure the contact of the connection and the container. The dosing installation of at least one powder material may also comprise means for indexing the position of the container relative to the weighing system. For example, the indexing means comprise a movable pin vertically and able to penetrate into a fixed housing relative to the container, when the container is in a given position above the weighing system. Preferably, the portion of the conveyor located above the weighing system is at least partially removable, and the weighing system is such that it can be removed by the area left free by the at least partial withdrawal of the weighing system. The connection may comprise a bellows whose first end is connected to the hopper and whose second end is intended to come into sealing contact with the contour of the opening of the container. In an exemplary embodiment, the installation is disposed in a confinement enclosure. For example, the hopper is a hopper 6, said manufacturing facility comprising at least two individual hoppers upstream of the collecting hopper, the contents of the individual hoppers pouring into said collecting hopper. The installation may comprise at least one system for measuring the quantity delivered by each individual hopper, for example of the weighing type. The installation may also include a vibrating channel disposed between each individual hopper and the inlet of the collecting hopper. For example, the facility for manufacturing a powder mixture may be intended for the manufacture of a mixture for the manufacture of nuclear fuel, for example MOX. The individual hoppers are then preferably equipped with biological protections and the container is surrounded laterally and at the bottom by a biological protection, the bottom of said biological protection being equipped with openings for the passage of the support elements. The pin of the indexing means can then enter a housing made in the biological protection, aligning the openings of the bottom of the biological protection with the support elements of the weighing system Said metering installation may comprise three individual hoppers, the first being intended to deliver plutonium oxide, the second being intended to deliver the chamotte and the third to deliver uranium oxide. The present invention also relates to a process for the metering of at least one powdered material by means of a metering device according to the present invention comprising the steps of: a) placing the container below and above the weighing system of the hopper by means of the conveyor, b) lifting in a first position of the container and weighing thereof, c) docking between the container and the connection with the hopper, d) weighing the assembly formed by the container and connection, e) loading of at least one powder material, f) end of the docking between the container and the connection, g) weighing of the container and its contents in said first position. For example, docking is achieved by vertically moving the vessel from the first position to a second position greater than the first position. Several materials can be assayed, steps c) to g) are then repeated for each material. The present invention will be better understood from the following description and drawings in which:

FIG. 1 is a diagrammatic front view of a metering installation according to the present invention; FIG. 2 is a front perspective view of the weighing system according to the invention used in the installation of FIG. 1, shown in a confinement chamber, FIGS. 3A and 3B are sectional views of the weighing system of FIG. 2 respectively in the weighing position and in the rest position, FIG. 4 is a side view of the system. in the position of FIG. 3B; FIG. 5A is a perspective view from above of the weighing system in the position of FIG. 3A; FIG. 5B is a perspective view from above of the weighing system; The rollers of the conveyors being only partially shown, FIG. 6A is a detailed perspective view of the weighing system of FIG. 2. FIG. 6B is a cross-sectional view at one of the vertical guide rails. from the fork of the f FIG. 6C is a perspective view of the fork supporting the weighing means, the latter having been omitted, having guide means different from those of FIGS. 6B; FIG. 7 is a rear view of the system. Figure 8 is a longitudinal sectional view of an example of a docking cuff 9 between the collecting hopper and the jar, in contact with the jar. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS The present invention will be described more particularly in its application to the manufacture of a mixture of powder materials, specifically a primary mixture for producing MOX. The present invention also applies to the production of secondary mixtures, and more generally to the production of any powder mixtures. In addition, the installation is not limited to the dosages of several materials, for example two or three materials, but can be implemented to dose a single powder material.

In Figure 1, we can see a schematic representation of an example of a powder mixing plant according to the present invention, suitable for mixing three powder materials. In the case of the manufacture of a mixture of materials for the production of nuclear fuel, the installation is confined in a sealed enclosure type BG glove box, the latter being partially shown in Figure 2. The enclosure comprises means of 3 waterproof access, round type of glove and round bag. In the example shown, the installation comprises three individual hoppers T1, T2, T3 downstream of tanks connected to each of the individual hoppers, a collecting hopper TC disposed downstream of the individual hoppers T1, T2, T3, a conveyor 2 of jar under the collecting hopper Tc and a weighing system 4. Each of the individual hoppers T1, T2, T3 is intended to ensure the flow of a given amount of powder from a reservoir not shown to the collecting hopper TC. For example, the T1 hopper assures the plutonium oxide dosage, the T2 hopper assures the measurement of the chamotte, and the T3 hopper assures the uranium oxide dosage. Each hopper is equipped with a valve to control the flow of the powder material to the collecting hopper TC. Advantageously, vibrating corridors (not shown) are provided between the output of the individual hoppers T1, T2, T3 and the inlet of the collecting hopper TC for conveying the powder to the collecting hopper TC. The collecting hopper TC ensures the transfer of the powder from each individual hopper T1, T2, T3 to a jar 6. In Figure 3A, we can see an example of jar 6 in longitudinal section. The jar has a neck 6.1 surrounding a filling and emptying opening 6.2. The conveyor 2 ensures the placement of the empty jar 6 below the flow end of the collecting hopper TC and the discharge of the jar 6 when it contains the required mixture. The conveyor 2 is preferably a roller conveyor 7, as will be seen in the following description. The weighing system 4 is arranged under the conveyor 2, and is such that it makes it possible to measure the mass of powder in the jar. The weighing system comprises a first scale 8 and a second scale 10, the first scale 8 resting on the second scale 10. The second scale 10 comprises a weighing plate 12 on which the feet 14 of the first scale 8 rest (see FIG. 6A) and the first balance 8 comprises a weighing plate 16 provided with vertical rods 18 projecting whose free end 18.1 (particularly visible in Figure 3A) is intended to support the jar forming a support for the bottom of it this. In FIG. 6A, the two scales 8, 10 can be partially seen. The vertical rods 18 are arranged relative to the conveyor 2 so that they pass between the rollers 7. The free end 18.1 of the rods projects from the conveyor to support the jar, as can be seen in Figure 5, in the absence of jar. Advantageously, the rods 18 have an adjustable length. In the example shown and particularly visible in FIG. 3A, they comprise machined screws 18.2 screwed into hollow and threaded evacuators. The rods may be replaced by support elements projecting from the plate of the first scale having other shapes, for example by two cleats transversely arranged on the plate, substantially parallel to the rollers and passing each between a pair of rollers, the cleats. having a sufficient height, these being advantageously adjustable.

The use of three rods has the advantage of ensuring a stable support between the weighing system 4 and the jar 6. In addition, the installation comprises means 20 for vertical displacements of the jar 6, to move closer or away the jar and the free ends 18.1 of the rods 18 to perform, respectively interrupt the weighing. As will be seen in the description of the operation, the rods can take at least two positions: - a low position in which they are not in contact with the jar, the jar resting on the conveyor, - an intermediate position corresponding to the weighing , in which they are in contact with the jar, which is lifted from the conveyor. This position can also form a docking position with the hopper seal when the connection is lowered.

In the case where the jar comes docking the connection to the collecting hopper, the rods 18 take a high position corresponding to this docking. When the connection lowers, it can be expected that the rods also take a high position. Preferably, the conveyor 2 comprises rollers 7, which allows the rods 18 to pass easily through the conveyor. But this achievement is by no means limiting. It would be possible, in a variant, to provide a treadmill-like conveyor upstream and downstream of the weighing zone and to keep the rollers at the weighing zone, or to provide that the belt is formed of several parallel strips, providing for them passages for the stems 18.

In the example shown, the means 20 for vertically moving the weighing means 4 comprise a fixed frame 19, a fork 22 on which the lateral feet of the second balance 10 rest. The fork 22 is movable vertically along the frame 19. Alternatively, the fork 22 may be replaced by a tray. In the example shown in FIG. 1, the vertical displacement means also comprise a jack 21, particularly visible in FIG. 6C. Other means are conceivable, for example rack-and-pinion systems or sprocket and chain. The jack is equipped with an encoder formed in the example represented by a pinion and rack assembly visible in FIG.

In addition, the fork 22 is slidably mounted on two vertical rails 23.1, 23.2 along which it is guided by rollers 25 on each rail 23.1, 23.2. In FIG. 6C and preferably, the guiding along the rail 23.1 is carried out by four pairs of rollers 25 on each rail 23.1, 14 23.2, only three pairs of rollers 25 are visible, the fourth pair being located behind the forks. Alternatively, as shown in Figure 6B, the guide along the rail 23.1 is obtained by means of two rollers 25 opposite to the rail 23.1 and another roller 25 on the rail 23.1. In FIG. 3B, the weighing means can be seen in an inactive position, the jar 6 resting on the rollers 7 of the conveyor 2. In FIG. 3A, the weighing system is in the active position, the jar then resting on the rods 18 and is removed from the conveyor. In the example shown and preferably, the rods 18 are three in number.

Preferably, the jar 6 is surrounded by a biological protection 24 as can be seen in Figures 2, 3A and 3B. The biological protection comprises a bottom 24.1 and a side wall 24.2 of a shape corresponding to that of the jar; in the example shown, it has the shape of a cylinder of revolution. The protection 24 has an upper opening corresponding to the internal cross section of the side wall to allow the establishment of the jar and its vertical movement during filling. The height of the biological protection is such that it surrounds the jar substantially over its entire height, regardless of the position of the jar between a low position on the conveyor and a high filling position.

In Figure 5A, we can see the rods 18 passing between the rollers 7 of the conveyor. The installation also preferably comprises indexing means 28 for the position of the jar provided with its biological protection with respect to the weighing system and more particularly to the rods 18. This indexing in position makes it possible to ensure the alignment of the rods 18 with the passages made in the bottom 24.1 of the biological protection 24. In the example shown, more particularly in Figure 7, the indexing means in position 28 comprise a pin 30 movable vertically and intended to enter a housing (not visible) of the biological protection and means for moving the pin 30. The displacement means are for example formed by an electric jack 32 of horizontal displacement and a yoke 34 articulated on the jack 32 and the pin 30, transforming the horizontal movement of the jack in a vertical movement of the pin 30. Thus when the pin 30 has penetrated into the housing of the biological protection 24, it is a The alignment of the bottom passages 24.1 of the biological protection 24 and the rods 18 is achieved. The displacement means have the advantage of integrating into the architecture of the installation without increasing its size. In addition, these mechanical indexing means 28 are very robust and very simple, and are not very sensitive to pollution caused by the powder. Any other means of displacement of the indexing pin 30 is conceivable. Any other means of mechanical indexing is also conceivable. One can even consider electronic sensors, 16 optical type, detecting the position of the biological protection 24 relative to the pin 30. We will describe in more detail the first 8 and second 10 scales.

Preferably, but not limited to, the first scale 8 has a weighing accuracy greater than that of the second scale 10. The first scale 8 serves to adjust the dosage, ie to measure very precisely the amount of powder that has fallen into the jar. For example, in the application of MOX, the accuracy of the first scale is +/- 6g. While the second scale 10 is intended to verify if the amount of powder corresponds substantially to that expected. For example, in the application of MOX, the accuracy of the second scale is +/- 25 g. By using a second scale 10 offering less precision, it is possible to realize a simpler and less cumbersome scale. For example, it may comprise strain gauges and a lever arm, which are sufficient for the desired accuracy and which make it possible to obtain a relatively thin balance. The size is reduced, the implementation of two superimposed scales does not impose any significant changes to the installation. We could consider that the second scale is more accurate than the first scale. Both scales could also have the same high accuracy.

Also preferably used for the first scale is a scale having a small footprint. Preferably, the transverse dimensions of the two scales are chosen so that they can be lifted between the two amounts of the conveyor after removal of the rollers and loaded on the conveyor for transport, for example for maintenance. This considerably reduces the working time to move the scales. In the state-of-the-art installations, the intervention times are very long because they require an important decontamination operation. The operation can take on the order of 15 to 20 positions. Thanks to the two balances, the intervention time is reduced to three or even two positions. Advantageously, the installation comprises weighing means (not shown) at each of the individual hoppers T1, T2, T3, for example formed by load cells, to control the filling of each of the individual hoppers and thus detect a anomaly upstream, for example a plugging. A low accuracy of the scales is no longer problematic, the double verification being done elsewhere. The installation also comprises a connection between the collecting hopper TC and the neck of the jar 6, also called docking cuff 26 connected to the outlet of the collecting hopper and opening above the opening of the jar. This cuff can be of several types. The sleeve 26 may be of the static type, it is then the opening of the jar which comes dock the downstream end of the sleeve 26. In Figure 8, 18 can be seen an example of such a cuff. The docking is preferably sealed, the seal being obtained for example by a seal carried by the downstream end of the sleeve and intended to bear against the neck of the jar. This type of sleeve has the advantage of being of simple construction. In addition, an actuator at the docking cuff may be omitted. The sleeve comprises for example a bellows whose free end forms the downstream end of the sleeve. Preferably, a position sensor is provided to detect the contact between the sleeve and the jar. Means for generating vibrations within the cuff may be provided to prevent powder sticking into the cuff. A vent duct is also preferably provided to ensure a good flow of the powder in the jar, this duct being advantageously connected to a powder recovery system. The static docking sleeve as shown in FIG. 8 comprises a support ring 38 mounted to slide sealingly around the collecting hopper TC and a sealing ring 40 forming the downstream end of the sleeve, the sealing ring. 40 being intended to come into sealing contact with the contour of the filling orifice of the jar 6. The sealing ring 40 and the support ring 38 are connected by sealed and flexible means 42. In the example shown and in a preferred manner, it is a sealed bellows providing mechanical decoupling between the collecting hopper TC and the sealing ring 40. The sealing ring comprises, for example, a lip seal 44 intended to come into contact with the neck collar 6. The sleeve 26 preferably comprises means 44 for limiting the movement away from the sealing ring 40 relative to the support ring 38, avoiding a request tension ion of the bellows 42 in the rest state. These means are then active when the sealing ring 40 is not in contact with the contour of the filling orifice of the jar 6 and are inactive when the sealing ring 40 is in contact with the contour of the filling port.

These limiting means comprise radial fingers 46 and a shoulder 48 upstream of the fingers so that, when the sealing ring 40 comes into contact with the contour of the filling orifice and is raised by the jar 6 the shoulder 48 and the fingers 46 move apart. When the sealing ring 40 is no longer supported by the jar 6 the fingers 46 rest on the shoulder 48. The vertical displacement means of the jar are such that they raise the jar in a high position ensuring the l distance of the fingers 46 from the shoulder 48. Alternatively, the sleeve 26 may be of the dynamic type. In this case, one or more actuators move the downstream end of the sleeve so that it comes close to the opening of the jar. Preferably, the downstream end of the sleeve 20 does not come into contact with the jar, the seal is then obtained dynamically by circulation of a gas. The dynamic sleeve is equipped with a docking check sensor.

Preferably, the vertical displacement of the jar is obtained only by means of the rods through the conveyor rollers. This simplifies the realization of the conveyor. Indeed, it is not necessary to provide that the conveyor has a portion that can rise, avoiding the implementation of complex gears systems to follow the movement. However, an installation in which the conveyor, and more particularly the conveyor portion located above the weighing system, can be raised, is not outside the scope of the present invention. We will now describe the development of the manufacture of a mixture of powders for the manufacture of MOX pellets with the installation. We consider that the installation has a static filling collar. Tanks directly feeding individual hoppers T1, T2 and T3 are filled respectively with plutonium oxide, chamotte, and uranium oxide. The jar 6 inside its biological protection is brought under the collection hopper TC by means of the conveyor 2. Its position relative to the rods 18 is fixed by the indexing means 28, the pin 30 penetrating into the housing of the biological protection 24. First weighing of the empty jar 6 is carried out. For this purpose, the vertical displacement means 28 causes the scales 8, 10 and rods 18 to rise, which come into contact with the bottom of the jar 6 through the biological protection 24, and away from the rollers 7 of the conveyor 2. The jar 6 is then only supported by the rods 18 and the first balance 8, as shown in Figure 3B.

Weighing can take place by the first 8 and the second scale. Then, in the case of a static sleeve 26, the vertical displacement means 20 further raise the jar 6 to reach a high position of docking of the sleeve 26, which is the position shown in Figure 8. A weighing of the assembly formed by the jar 6 and the sleeve 26 is made. The filling is then carried out with a given quantity of chamotte by controlling the valve of the individual hopper T2 and the vibrating passage. The quantity delivered is measured by the scale dedicated to the hopper T2, and is weighed simultaneously by the first scale 8 and the second scale 10. The consistency check between the respective weighings of the two scales 8, 10 is triggered at each static weighing. system: weighing empty jar, weighing the chamotte, weighing the plutonium oxide and the chamotte, weighing the plutonium oxide, the chamotte and the uranium oxide.

Then, a weighing step is carried out when the chamotte filling is completed. For this, the jar 6 is spaced from the sleeve 26 by lowering the rods 18 to be in the intermediate weighing position. A weighing of the jar 6 containing the chamotte takes place. If the mass of fireclay corresponds to the desired value, it goes to filling with the PuO2 and UO2r otherwise we adjust the mass of chamotte, putting the jar 6 in place in contact with the sleeve 26. The filling steps with the PuO2 and UO2 are similar to those for filling with chamotte by operating the individual hopper valves T1 and T3 respectively. Their descriptions will not be repeated. When the three desired quantities have been poured into the jar 6, the jar 6 is lowered to the lower position, it rests again on the conveyor 2. The jar 6 can then be evacuated to another manufacturing station. As mentioned above, the conveying of the powders from their individual hopper to the connecting device is generally achieved by means of vibrating corridors. In order to respect the filling rates while ensuring dosing accuracy, the vibrating channels are controlled at high speed, to deliver a mass of powder M '= M - A, M being the desired mass of powder and A being a low mass missing powder.

When the scales detect that the mass M 'is reached, the corridor control system reduces the speed which passes at an average speed, then at a low speed until the scales detect that the mass M is reached. At this point, the vibrating corridor is stopped. This cycle of control of a vibrating corridor is similar for each vibrating corridor connecting the chamotte, PuO2 and UO2 hoppers to the collecting hopper. In the case of a dynamic cuff, it is lowered at least in part to come dock the neck of the jar, the remaining jar for example in the intermediate position, or by taking a higher position, the jar and the cuff each making part of the berthing race. In case of maintenance on the first and / or second scale, the rollers located above the scales and below the collecting hopper, are removed, the scales 8 and 10 are hoisted for example by means of a hoist system above the conveyor 2 and deposited on the rollers located downstream of the removed rollers, then are discharged to a maintenance area by operating the conveyor 2. These manipulations merge through the glove rings 3 provided in the wall of the enclosure. As mentioned above, the dosing system is not limited to the manufacture of nuclear fuels, but it can be used in all areas where it is desired to perform assays and mixtures. In the case of handling materials which do not require special confinement and / or protection against irradiation, the enclosure and / or biological protection may be omitted.

Claims (24)

REVENDICATIONS1. Dosing plant for at least one powder material comprising at least one hopper (TC), a conveyor (2) for disposing a container (6) having a filling opening below said hopper (TC), a weighing system (4) able to weigh at least said container (6), means (20) able to move the weighing system (4) and the container (6) so as to move the container (6) away from the conveyor ( 2) and so that, in at least one spaced apart position, the weighing system (4) can weigh only the container (6) and its contents, said weighing system (4) having a first scale (8) for supporting the container (6) and a second scale (10) on which the first scale (8) rests, the second scale (10) resting on the displacement means (20). A dosing device of at least one powder material according to claim 1, wherein one of the scales (8) has a higher precision than the other, the balance (8) having the highest accuracy, for example +/- 6g, used to adjust the dosage of powder and scale (10) having the lowest precision, for example +/- 25 g, to check if the amount of powder corresponds substantially to that expected .30 26 A dosing device of at least one powder material according to claim 1 or 2, wherein the weighing system (4) comprises support elements (18) projecting from a plate of the first scale (8), intended to come into contact with the bottom of the container (6) to lift it. 4. dosing plant of at least one powder material according to claim 3, wherein the support elements are formed by at least three vertical rods (18) fixed by a first longitudinal end to the surface of the plate of the first scale ( 8) and a second longitudinal end (18.1) is intended to come into contact with the bottom of the container (6) to lift it. 5. dosing plant of at least one powder material according to claim 3 or 4, wherein the conveyor (2) has openings above and aligned with the support elements (18) to allow their passage and their implementation. contact with the bottom of the container (6). 6. dosing plant of at least one powder material according to one of claims 3 to 5, wherein the conveyor (2) comprises rollers (7), the support elements (18) passing between the rollers (7). .30 27 7. dosing installation of at least one powder material according to one of claims 3 to 6, wherein the support elements (18) have an adjustable height. 8. dosing plant of at least one powder material according to one of claims 1 to 7, comprising a connection (26) sealed between a discharge end of the hopper (TC) and the filling port of the container (6). 9. dosing installation of at least one powder material according to claim 8, wherein the displacement means (20) have a vertical stroke sufficient to ensure the contacting of the connection (26) and the container (6). . 10. dosing installation of at least one powder material according to one of claims 1 to 9, comprising indexing means (28) of the position of the container (6) relative to the weighing system (4). 11. dosing installation of at least one powder material according to claim 10, wherein the indexing means (28) comprise a pin (30) movable vertically and able to penetrate into a fixed housing relative to the container (6). ), when the container (6) is in a given position above the weighing system (4). 12. Dosing plant of at least one powder material according to one of claims 1 to 11, wherein the portion of the conveyor (2) above the weighing system (4) is at least partially removable, and the weighing system (4) is such that it can be removed by the area left free by the at least partial withdrawal of the weighing system (4). 13. dosing plant of at least one powder material according to one of claims 1 to 12 in combination with claim 8 or 9, wherein the connection (26) comprises a bellows having a first end connected to the hopper. (TC) and a second end of which is intended to come into sealing contact with the contour of the opening of the container (6). 14. Dosage installation of at least one powder material according to one of claims 1 to 13, being disposed in a confinement chamber. 15. Installation for manufacturing a mixture of at least two powder materials, comprising a metering installation according to one of claims 1 to 14, wherein the hopper (TC) is a collecting hopper, said manufacturing facility comprising at least two individual hoppers (T1, T2, T3) upstream of the collecting hopper (TC), the contents of the individual hoppers (T1, T2, T3) flowing into said collecting hopper (TC). 29 16. Installation for manufacturing a mixture of at least two powder materials according to claim 15, comprising at least one system for measuring the quantity delivered by each individual hopper, for example weighing type. 17. Installation for manufacturing a mixture of at least two powder materials according to claim 15 or 16, comprising a vibrating corridor disposed between each individual hopper (T1, T2, T3) and the inlet of the collecting hopper (TC ). 18. Installation for manufacturing a powder mixture according to one of claims 15 to 17 for the manufacture of a mixture for the manufacture of nuclear fuel, for example MOX. Powder material mixture manufacturing plant according to Claim 18, in which the individual hoppers (T1, T2, T3) are equipped with biological protections and in which the container (6) is surrounded laterally and at the level of the container. bottom by a biological protection (24), the bottom of said biological protection (24) being provided with openings for the passage of the support elements (18). 20. A powder material mixture manufacturing plant according to claim 18 or 20 in combination with claim 10 or 11, wherein the pin (30) of the indexing means (28) enters a housing made of in the biological protection (24), aligning the bottom openings of the biological protection (24) with the supporting elements (18) of the weighing system (4). Apparatus for manufacturing a mixture of powdered materials for the manufacture of MOX according to claim 18, 19 or 20, wherein said metering device comprises three individual hoppers (T1, T2, T3), the first one (T1 ) being intended to deliver plutonium oxide, the second (T2) being intended to deliver the chamotte and the third (T3) to deliver uranium oxide. 22. A method of dosing at least one powdered material by means of a metering device according to one of claims 1 to 14, comprising the steps of: a) placing the container (6) below and above above the hopper weighing system (TC) by means of the conveyor (2), b) lifting in a first position of the container (6) and weighing thereof, c) docking between the container (6) and the connection (26) with the hopper (TC), d) weighing the assembly formed by the container (6) and the connection (26), e) loading at least one powder material, f) end of berthing between the container (6) and the connection (26), g) weighing the container (6) and its contents in said first position. 23. The method of claim 22, wherein the docking is obtained by a vertical displacement of the container (6) from the first position to a second position greater than the first position. 24. The method of claim 22 or 23, wherein a plurality of materials are metered, steps c) to g) being repeated for each material.