1535940 Inflatable sealing rings for stoppers LE JOINT FRANCAIS 15 Dec 1975 [19 Dec 1974] 51333/75 Heading B8T [Also in Division F2] A stopper 4 in a vessel containing a radioactive gas is sealed by means of two gas-filled Hollow seal rings 5, 6, located in grooves in the vessel wall, the ring being pressurized via conduits 7 and 8. The outer layer 13 may be of a silicon elastomer, and the inner layer 14 of butyl-rubber, ethylene and propylene copolymer or vinylidene fluoride and hexachloropropylene copolymer. The stopper may be connected to the vessel by a bayonet connection.