Abstract: In a nuclear fuel reactor well, storage pool or the like, a lightweight, removable pneumatic action sealing means is disclosed for providing a leak-tight seal between the walls of said well and an access gate. The sealing means comprises a lightweight metallic beam structure removably supported by the gate and arranged between the gate and portions of the adjacent wall. Inflatable sealing members are mounted on the lightweight beam structure and are operable when the gate is in a locked position to expand between the gate and wall, thereby forming a leak-tight seal. The beam structure includes connector flanges so that a hoisting apparatus may be attached to the lightweight structure to lift the entire sealing means from the gate for repair, maintenance or replacement.