Patent Number: 
Section: claims

1. A reactor pressure vessel comprising:a substantially cylindrical shaped wall including an upper reactor pressure vessel region and a lower reactor pressure vessel region;a plate having a substantially circular shape and attached to and extending completely across a cylindrical inside surface of the wall of the reactor pressure vessel, wherein the plate separates the upper reactor pressure vessel region from the lower reactor pressure vessel region, and creates a thermal barrier between a pressurized volume located within the upper reactor pressure vessel region and primary coolant located within the lower reactor pressure vessel region; andone or more plenums including multiple holes extending through the plate, and a dome extending up from the plate and over the multiple holes in the upper reactor pressure vessel region and connecting around an opening in the wall of the reactor pressure vessel, the multiple holes receiving a plurality of heat transfer tubes that pass through the plate and through the opening in the wall of the reactor pressure vessel. 2. The system of claim 1, wherein the upper reactor pressure vessel region contains at least a portion of either one or both of a chemical volume control system or an emergency core cooling system, and wherein the lower reactor pressure vessel region contains a reactor core submerged in the primary coolant. 3. The system of claim 1, wherein the one or more plenums are attached to the plate, and wherein the plurality of heat transfer tubes are connected to the plate below the one or more plenum. 4. The system of claim 1, wherein the plate comprises a substantially horizontal plate attached to the wall of the reactor pressure vessel, and wherein the plurality of heat transfer tubes pass through a number of through-holes located in the horizontal plate. 5. The system of claim 1, wherein the plate comprises an upper flange that mounts to the upper reactor pressure vessel region and a lower flange that mounts to the lower reactor pressure vessel region. 6. The system of claim 5, wherein the plate separates a pressurized fluid located above the plate in the upper reactor pressure vessel region from reactor coolant system fluid located below the plate in the lower reactor pressure vessel region. 7. The system of claim 5, wherein the upper flange forms a portion of the wall of the reactor pressure vessel intermediate the upper reactor pressure vessel region and the lower reactor pressure vessel region. 8. The system of claim 5, wherein a side wall of the upper flange extends from the plate to a height which is above the one or more plenum. 9. The system of claim 8, wherein a lower portion of the one or more plenums is welded to the plate, and wherein a side of the one or more plenums is welded to the side wall of the upper flange. 10. The system of claim 5, wherein the upper reactor pressure vessel region is welded to a top surface of the upper flange; and wherein the lower reactor pressure vessel region is welded to a bottom surface of the lower flange. 11. The system of claim 1, wherein the plate comprises a number of orifices that are configured to controllably allow the primary coolant to pass through the plate into the upper reactor pressure vessel region and to re-circulate back into the lower reactor pressure vessel region. 12. The system of claim 11, wherein the orifices when closed prohibit the primary coolant from passing through the plate. 13. The system of claim 11, wherein the heat transfer tubes are configured to allow a secondary coolant from a steam generation system to pass through the plate and into the lower reactor pressure vessel region. 14. The system of claim 13, wherein both the primary coolant and the secondary coolant pass through the plate without becoming comingled. 15. The system of claim 1, wherein the one or more plenums comprise a substantially vertical plate attached to the wall of the reactor pressure vessel, and wherein the plurality of heat transfer tubes pass through a number of through-holes located in the vertical plate. 16. The system of claim 15, wherein the vertical plate forms a portion of the wall of the reactor pressure vessel. 17. The system of claim 1, further comprising a containment vessel configured to house the reactor pressure vessel, wherein an outer diameter of an upper portion of the containment vessel located above the plate is smaller than an outer diameter of a lower portion of the containment vessel. 18. The system of claim 17, wherein the outer diameter of the upper portion of the containment vessel is less than one-half as large as the outer diameter of the lower portion of the containment vessel. 19. The system of claim 17, further comprising a plurality of control rods which are suspended from the upper portion of the containment vessel and pass through the plate into the lower reactor pressure vessel region located within the lower portion of the containment vessel. 20. The system of claim 17, wherein the upper portion of the containment vessel forms a nipple-shaped dome on a cylindrical-shaped lower portion of the containment vessel.