Steam generator supplied with secondary water from the bottom part

Steam generator comprising a vertically axed outer envelope, a horizontal tube plate tightly fixed to the interior of the outer envelope, a bundle of inverted U-tubes, each having two ends fixed to the tube plate and issuing below the tube plate, respectively into an admission collector and into a discharge collector for the primary fluid, an inner envelope covering the tube bundle and having a lower edge spaced from the tube plate and forming with the outer envelope an annular recirculation space, secondary water supply means incorporating a main supply collector and secondary steam extraction means through upper parts of the inner and outer envelopes, wherein the main supply collector is disposed in the bottom part of the annular recirculation space and has holes ensuring a substantially vertical mean flow of the secondary water into said annular space, said holes having a maximum size smaller than a minimum distance separating the tubes of the bundle.