linear reduction leading to a truncated pyramid u to a non linear for example quadratic reduction t making it possible to correct large misalignments over short lengths and to contribute towards releasing dust and chips as a result of the change in relative orientation of the pellets with one another as for the two circular cross sections of 48 and 49 the two bores d y and d z are cut respectively with the diameters of the pellets d ynom dpell max 0 02 mm for example and the claddings d znom dcas max 0 01 mm for example with a concentricity of 0 01 mm and diametral tolerances of u2212 0 0 01 mm this introduction component can also be provided fig3 b with various gas injection apertures or plugture apertures for trapping collecting or forcing back the dust and chips adhering to or conveyed by the pellets longitudinal and or transverse grooves can also be machined in the component 14 in order to contribute towards trapping the chips and dust it should be noted that in other possible embodiments of the invention the upper part of the channel 42 can have a shape other than an inverted v it should also be noted that the introduction device 14 can be used for direct introduction of the pellets into the cladding and for centring and alignment of the pellets in any intermediate device provided before the cladding during loading of the columns of.