Integral reactor pressure vessel tube sheet

A nuclear reactor system comprising:

• a reactor pressure vessel;
• a plate including:
• an upper flange mounted to an upper head of the reactor pressure vessel;
• and
• a lower flange welded to a lower portion of the reactor pressure vessel, the upper head being spaced apart from the lower portion of the reactor pressure vessel by the upper flange and the lower flange, the plate being attached to a wall of the reactor pressure vessel and dividing the reactor pressure vessel into an upper reactor pressure vessel region and a lower reactor pressure vessel region, the plate being positioned to re-direct an upward flow of a primary fluid exiting a riser within the reactor pressure vessel downwardly in the reactor pressure vessel, the plate including a tube sheet portion;
• heat transfer tubes connected to the plate at the tube sheet portion and extending into the lower reactor pressure vessel region;
• and
• a plenum positioned in the upper reactor pressure vessel region, the plenum enclosing the tube sheet portion and in fluid communication with an exterior of the reactor pressure vessel to transfer a secondary fluid between the heat transfer tubes and a region outside the reactor pressure vessel.