To enhance the airtightness, simplify the structure at low cost, and improve and uniform the mechanical strength by screwing a drum part to a lid part, and fixing them together by pressure welding.

In the bonding of a cylinder part 1 to a lid part 2, the connecting surfaces of the both are degreased by trichlene or acetone in order to remove the dust, fat and oil, and oxide film or the like adhered to the connecting surface which arrests pressure welding, and then polished with a wire puff made of stainless steel stranded wire. Then, an irradiation sample (fuel) is house in the cylinder part 1, and the male screw 5 of the lid part 2 is screwed to the female screw 4 of the cylinder part 1, whereby the both are screwed together. The mechanical strength of the cylinder part 1 and the lid part 2 is increased by this screwing. By preliminary confirming the strength of the screw part, it is nit necessary to perform a strength test every individual vessel after pressure welding, and the mechanical strength can be uniformed.