Steam generator for nuclear steam supply system

A steam generator for a nuclear steam supply system, the steam generator comprising:

• a vertically-oriented steam generating vessel comprising an elongated cylindrical shell defining an internal cavity configured for containing secondary coolant, a top tubesheet, a secondary coolant outlet nozzle proximate to the top tubesheet, a bottom tubesheet, and a secondary coolant inlet nozzle proximate to the bottom tubesheet;
• a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets, the tubes including a preheater section, a steam generator section, and a superheater section, wherein secondary coolant in a liquid state enters a shell side of the preheater section via the inlet nozzle and flows upward to the steam generator section where a portion of the secondary coolant boils to produce steam which in turn flows upward into the superheater section and exits the steam generating vessel through the outlet nozzle;
• and
• a vertical riser pipe extending vertically between the top and bottom tubesheets, the riser pipe in fluid communication with the tubes and configured for fluid coupling to a reactor vessel containing primary coolant;
• a double-walled fluid coupling forming a flow conduit for exchanging primary coolant between the steam generating vessel and reactor vessel, the fluid coupling configured so that primary coolant from the reactor vessel flows through the fluid coupling into the steam generator riser pipe and returns from the steam generating vessel to the reactor vessel through the fluid coupling;
• a bottom collection plenum formed below the bottom tubesheet by the fluid coupling and configured for fluid coupling to the reactor vessel, the collection plenum in fluid communication with the tubes;
• a top distribution plenum formed above the top tubesheet, the distribution plenum in fluid communication with the riser pipe and tubes;
• and
• a tubular recirculation shroud surrounding the tubes in the steam generator section, the shroud configured to recirculate a portion of the liquid secondary coolant in the steam generator section back to the preheater section.