Arrangement for installing a nuclear reactor block in a vessel

An assembly for installing a nuclear reactor block in a vessel, said vessel being built in at least two prefabricated parts which are then assembled end to end, one of the parts including a chamber in which said block may be inserted before said parts are assembled by a substantially horizontal translation movement of said block from a barge by rolling or sliding onto a temporary support situated in said chamber, the improvement wherein said assembly includes hoisting means composed of a plurality of guide columns borne by said one part for guiding the block in a vertical translation movement, jacks provided to the tops of said columns, cables for suspending said block, said cables allowing said block to be raised momentarily to remove the temporary support and to be lowered to make it rest in its final position in said chamber.