[en] A detailed characterization of the corrosion products found on portions of the recirculation loop bypass lines and a flange from the recirculation line of Millstone-1 is described. A duplex structure is identified for the corrosion scale. This structure consists mainly of a loosely adherent outer layer of α--Fe₂O₃ and a tightly adherent inner layer to which a spinel structure can be assigned. The distribution profile of several elements across the inner layer determined by ion microprobe analysis is discussed. A model for crud growth that accounts for the present fidings is proposed