Abstract: The invention relates to an apparatus for automatic or remotely operated welding of the cover and/or the bottom of the walls of a container for receiving and storing radioactive fuel elements and wastes in a hot cell by employing the narrow joint welding technique, comprising at least one sensor sensing the course of the weld line between the container wall and the container cover and/or bottom effective to assist at least one three-dimensionally movable welding head controlled by control means utilizing signals supplied by the sensor to guide it along the joint for producing a continuous welding seam consisting of a plurality of super-imposed and offset weld beads or passes, respectively.