Abstract: A tool for remotely installing a plug in a steam line of a reactor vessel. The tool has a strongback assembly on which a plug is securely mounted, a collapsible structure (e.g., a scissors jack assembly) which supports the strongback assembly and is movable between an extended state and a collapsed state, a hanging bracket assembly for hanging the collapsible structure inside the reactor vessel, and a rotatable actuating screw coupled to the collapsible structure. The collapsible structure moves between the extended and collapsed states in response to rotation of the actuating screw. During this operation, the plug is carried from a retracted position outside and aligned with the steam line nozzle to an inserted position inside the nozzle.