A sealing bolt for sealing a container (e.g. for fissile materials), the sealing bolt adapted to cooperate, in use, with a locking device for locking a container lid to a container body of the container. The sealing bolt includes an upper part (i.e. adapted to be manipulated by an operator using a tool), a lower part (cooperating with the locking device 46) and an axial rod connecting the upper and lower parts, the upper part, lower part and axial rod being arranged coaxially about an axis. An integrity element is disposed in the upper part and a release arrangement (a detachable conical end-piece 24 retained by a ball 34 and recess 32 arrangement) is disposed so as to be releasably attached to the lower part. The sealing bolt is movable, through a first operator actuation of the upper part, from a first state, in which the integrity element is intact, to a second state, in which the integrity element of the sealing bolt is visibly broken. The sealing bolt is movable, through a second operator actuation of the upper part, from the second state to a third state, in which the release arrangement is released, thereby enabling disengagement of the locking device and removal of the lid from the container body. A locking system for a container, a method of releasably sealing a container, and a method of unsealing a container, are also disclosed.