A method for sealing in a leak-proof manner a filling orifice formed on a wall of a secondary cell container using a stopper arrangement, said stopper arrangement comprising: - a tubular member, said tubular member being provided at one of its ends with a flange having an upper face adapted to receive a nosepiece of a riveting tool and a lower face adapted to cover the orifice, and - a mandrel provided with a stem terminating with a head, the stem being housed inside the tubular member and the head being located at one end of the mandrel, opposite the flange, said mandrel head having a cross section that is comprised between the inside cross section (s30 int) and the outer cross section (s30 ext) of the tubular member, the material constituting the stem having a hardness that is equal to or greater than three times the hardness of the material constituting the tubular member, said method comprising the steps of: - introducing the stopper arrangement into the orifice, the cross section of the orifice being greater than the outer cross section (s30 ext) of the tubular member so as to intentionally define a gap (m) between the wall of the orifice and the outer wall of the tubular member, - bringing the nosepiece of the riveting tool into abutment with the upper face of the flange of the stopper arrangement, - actuating the riveting tool so as to exert a tensile force on the stem of the mandrel, the nosepiece of the riveting tool maintaining the tubular member in the orifice, the method being characterized in that the riveting tool is operated such as to: • bring about expansion of the tubular member against the wall of the orifice by the entrance and advance of the head of the mandrel inside the tubular member and, • close the gap (m) between the wall of the orifice and the outer wall of the tubular member by the advance and maintenance of the head of the mandrel inside the tubular member at the wall of the secondary cell container, the material constituting the secondary cell container wall having a hardness greater than or equal to 1.3 times that of the tubular member, - a tubular member, said tubular member being provided at one of its ends with a flange having an upper face adapted to receive a nosepiece of a riveting tool and a lower face adapted to cover the orifice, and - a mandrel provided with a stem terminating with a head, the stem being housed inside the tubular member and the head being located at one end of the mandrel, opposite the flange, said mandrel head having a cross section that is comprised between the inside cross section (s30 int) and the outer cross section (s30 ext) of the tubular member, the material constituting the stem having a hardness that is equal to or greater than three times the hardness of the material constituting the tubular member, - introducing the stopper arrangement into the orifice, the cross section of the orifice being greater than the outer cross section (s30 ext) of the tubular member so as to intentionally define a gap (m) between the wall of the orifice and the outer wall of the tubular member, - bringing the nosepiece of the riveting tool into abutment with the upper face of the flange of the stopper arrangement, - actuating the riveting tool so as to exert a tensile force on the stem of the mandrel, the nosepiece of the riveting tool maintaining the tubular member in the orifice, • bring about expansion of the tubular member against the wall of the orifice by the entrance and advance of the head of the mandrel inside the tubular member and, • close the gap (m) between the wall of the orifice and the outer wall of the tubular member by the advance and maintenance of the head of the mandrel inside the tubular member at the wall of the secondary cell container,