Abstract: A steam generator includes: an annular member (21) that surrounds a U-bent portion (18) obtained by collectively disposing bent portions of a plurality of heat transfer tubes and is provided between an outer peripheral portion of the U-bent portion (18) and a tube bundle shroud (3) surrounding the outer peripheral portion so as to have a predetermined gap with respect to the U-bent portion (18); a second support member (22) that is provided between the annular member (21) and the tube bundle shroud (3); and a third support member (23) that is attached to a cylinder portion (2) accommodating a plurality of heat transfer tubes and supports the second support member (22).

Abstract: The steam generator includes: a water supply channel for supplying a secondary coolant to a tube bundle outer casing with the secondary coolant being isolated from the recirculating secondary coolant; a recirculating secondary coolant injection section for injecting the recirculating secondary coolant toward a high temperature-side heat transfer tube bundle; and a supplied secondary coolant injection section for injecting the secondary coolant supplied from the water supply channel toward a low temperature-side heat transfer tube bundle. The recirculating secondary coolant injection section and the supplied secondary coolant injection section being disposed in the tube bundle outer casing on the side toward the tube plate. The recirculating secondary coolant injection section and the supplied secondary coolant injection section are defined such that, of the secondary coolant and the recirculating secondary coolant, the coolant having a higher relative flow rate than the other flows at a lower velocity.