[en] The invention relates to the improvement of the seal of a conduit flexibly attached to the housing of a heat exchanger. When these heat exchangers are used as steam generators for nuclear power plants, they must meet high thermal and mechanical requirements. It is proposed to use a labyrinth seal with several annular disks surrounding the conduit instead of the metal bellows customarily applied so far. The annular disks are positioned one beside the other with the sides facing each other pointing in the direction of the axis of the conduit, while the faces extending at right angles to this direction alternately abut against the conduit or the housing. They have different thicknesses. The labyrinth seal may additionally be enclosed in a jacket. (UWI)