Closed vessel for radioactive substance, seal-welding method for closed vessel, and exhaust system used for seal-welding method

摘要

A primary lid is set in a top opening of a vessel body that contains radioactive substance, and closes the top opening. The peripheral edge portion of the primary lid is welded to the inner peripheral surface of the vessel body. As the primary lid is welded, steam in the vessel body is discharged to the outside through a discharge hole in the primary lid, and a shield gas is filled into or run through a space in the outer peripheral portion of the primary lid, so as to prevent the steam from flowing into the welding portion.