1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing nuclear fuel rods by introducing elongated fuel pellets into cladding tubes.
2. Description of the Prior Art
The fuel for nuclear reactors generally is in the form of cylindrical sintered uranium pellets. Groups of such pellets are disposed in elongated cladding tubes designed to prevent coolant from making direct contact with the radioactive fuel. This is to prevent the scattering of radioactive material with the coolant. A particular fuel rod may contain up to 500 individual pellets each having a diameter of about 10 millimeters and a length of about 11 millimeters. The cladding tube itself will thus often have a length of up to about 5000 millimeters. In such fuel rods it is desirable to have a very small clearance in the order of a few hundredths of a millimeter between the outer diameter of the pellets and the inner diameter of the tube.
The introduction of the pellets into the cladding tubes has in the past been very difficult and time consuming because of the small clearances involved. Ordinarily strings of pellets have been inserted into horizontally positioned tubes and it has been found that if the end surfaces of the pellets are not absolutely perpendicular to the longitudinal axis of the tube, the string of pellets will become disoriented during insertion whereby the friction between the pellets and the inside surfaces of the tube is increased and a cutting phenomena may even result. Moreover, large insertion forces have often been required in the past due to the high density of the pellets.