A method to reduce the gap between cladding tube and fuel of nuclear reactor fuel rods

To reduce the gap between the cladding tube and the fuel charge, e.g., of fuel pellets, the cladding tube is hydraulically forced onto the charge and strained in the process. For this purpose, the fuel rod is moved step by step through a compression unit consisting of a disk-shaped pressure resistant housing with an annular pressure chamber. This pressure chamber is sealed against the cladding tube by a ring seal which at the same time acts as a pressure cushion. The annular space behind the ring seal is filled with high pressure oil pressurized by means of a plunger actuated electromagnetically. The fuel rod is advanced by a collet actuated by an eccentric unit. After strainig the cladding tube has no folds. (DG)