Abstract: A steam generator for a nuclear reactor cooled with liquid metal, comprising a bundle consisting of double-walled tubes (20) arranged inside an enclosure in which the liquid metal circulates. The tubes (20) which are substantially straight and directed in the axial direction of the steam generator enclosure are each formed by at least two successive sections (20a and 20b) in the axial direction. Each section (20a or 20b) comprises an outer tube (27a or 27b) welded at one of its ends to at least one leakage collecting chamber (25) arranged wholly inside the enclosure. The adjacent sections of the outer tubes (27a, 27b) are not joined together. Each section also comprises an inner tube (28a or 28b) welded to the adjacent inner tube, inside the chamber (25). The leakage space between the tubes (27 and 28) communicates solely with the inner space of at least one collecting chamber (25). The invention applies in particular to fast neutron nuclear reactors cooled with liquid sodium.