Abstract: An end closure for a nuclear fuel flask in which the gate, which is movable between open and closed positions across an end of the flask, has first and second portions which are urged apart, conveniently by spring-loaded means. A door has upper and lower wedge-shaped members mounted on and releasably connected to the respective gate portions. In use, a displacement of the gate into or out of its fully closed position effects movement of one only of the gate portions and its associated door member. As the door members are wedge-shaped the other door member is urged into or out of sealing engagement with the end of the fuel flask.