This device is intended to be used in a working station where ceramic fuel pellets are sorted according to appearance criteria, such as the presence of superficial defects or local material deficiencies and where precise geometrical measurements are carried out, such as the measurement of the diameter or height of said fuel pellets. This metrology and this appearance sorting are generally automated and are then embodied by methods using lasers. Now, the presence of dust on these fuel pellets generates aberrant or deviant defects which ought to be eliminated. Accordingly, it is desirable to dedust these pellets.
In addition, if special precautions are not taken when introducing the fuel pellets into their casing tube, the dust adhering to the outer surface of the pellets risks entering and being suspended in the ambient atmosphere and contaminating the outside of the tube or the immediate vicinity of the feed orifice.
The prior art discloses a number of dedusting devices.
According to the document FR-A-2 379 886, a sealed confinement system is described for a nuclear reactor and able to assemble nuclear fuel elements and in particular fill the latter with fuel pellets. This system includes a plurality of stations for assembling fuel elements, that is in particular a device for loading the pellets inside fuel elements, a station for inserting plugs and a device for welding these plugs. In addition, this device includes transport means connecting together the various assembling stations. Finally, these assembling stations are disposed along a sealed closing body and opening inside the latter. Furthermore, the extremities of the fuel elements also open into this sealed closing body, the latter including an electrostatic sealing device.
According to this invention, this electrostatic sealing device includes an electrostatic field dedusting device. This dedusting device includes a chamber inside which the fuel element circulates, said chamber being provided with two precipitation cells placed on both sides of the path of the fuel element. Each of these precipitation cells is a rectangular box including a set of metallic bars constituting a protective shield, an electrode being placed behind said shield. Continuous high voltage is applied to this electrode so as to create a corona effect discharge. All the material particles carried into the air circulating around the fuel element are then electrostatically charged and attracted towards the precipitation cells. Owing to this, they are removed from the main air current.
However, this device does have several drawbacks. In particular, it requires that high voltage is present in the confinement chambers, which proves to be harmful as there is a risk of creating electric arcs.
Furthermore, it is able to solely remove fine electrically charged particles.
In addition, there also exists a nuclear fuel pellet dedusting device commercialized by the BELGONUCLEAIRE company using first of all a system of forced air jet directed perpendicular to the cylindrical peripheral wall of the pellet, and secondly a suction system applied to a train of pellets moving inside a helical spring situated in a chamber kept in a partial vacuum.
This device is unsatisfactory and is unable to obtain correct dedusting. In fact, it tends to clad a certain amount of dust against the surface of the pellet rather then remove it.