Patent Number: 
Section: claims

1. An apparatus comprising:a cylindrical pressure vessel including an upper vessel section, a lower vessel section, and a mid-flange, the upper vessel section and the lower vessel section being joined by the mid-flange;a cylindrical central riser disposed concentrically inside the cylindrical pressure vessel and including an upper riser section disposed in the upper vessel section and a lower riser section disposed in the lower vessel section;a reactor core comprising fissile material disposed inside the cylindrical pressure vessel in the lower vessel section;control rod drive mechanism (CRDM) units controlling control rod insertion actively into the reactor core, the CRDM units being disposed inside the cylindrical pressure vessel above the reactor core and in the lower vessel section with no vertical overlap between the upper vessel section and the CRDM units;a riser transition section disposed between the upper riser section and the lower riser section, the riser transition section being connected to the mid-flange by gussets having first ends welded to the mid-flange and second ends welded to the riser transition section, the gussets being angled downward such that the riser transition section is disposed below the mid-flange;a CRDM support plate disposed below the riser transition section and supporting the CRDM units; andtie rods suspending the CRDM support plate from the mid-flange. 2. The apparatus of claim 1, further comprising:steam generators disposed inside the cylindrical pressure vessel and entirely in the upper vessel section. 3. The apparatus of claim 2, wherein the steam generators are secured to the upper vessel section such that the upper vessel section and the steam generators can be lifted as a unit. 4. The apparatus of claim 1, wherein upper ends of the tie rods connect with the riser transition section to suspend the CRDM support plate from the mid-flange via the riser transition section and the gussets. 5. The apparatus of claim 1, further comprising:guide frames disposed between the CRDM units and the reactor core and guiding control rods into the reactor core;a lower hanger plate supporting the guide frames; andlower tie rods suspending the lower hanger plate from the CRDM support plate. 6. The apparatus of claim 1, further comprising:guide frames disposed between the CRDM units and the reactor core and guiding control rods into the reactor core; anda lower hanger plate supporting the guide frames; andwherein the tie rods further connect with the lower hanger plate such that the lower hanger plate is also suspended from the mid-flange by the tie rods. 7. The apparatus of claim 1, further comprising:power delivery cabling including at least one of:(1) a plurality of electrical feedthroughs passing through the mid-flange and mineral insulated (MI) cables extending from the electrical feedthroughs to the CRDM units to conduct electrical power to the CRDM units; and(2) a plurality of hydraulic feedthroughs passing through the mid-flange and hydraulic cables extending from the hydraulic feedthroughs to the CRDM units to conduct hydraulic power to the CRDM units. 8. The apparatus of claim 7, wherein at least one of MI cables and hydraulic cables of the power delivery cabling are embedded in or secured to the CRDM support plate such that the CRDM support plate is a power distribution plate. 9. The apparatus of claim 1, further comprising:an annular pump plate having an outer circular perimeter connecting with the mid-flange and an inner circular perimeter connected with the riser transition section; andreactor coolant pumps disposed entirely inside the cylindrical pressure vessel and mounted on the annular pump plate. 10. The apparatus of claim 1, further comprising:reactor coolant pumps mounted on the upper vessel section. 11. An apparatus comprising:a cylindrical pressure vessel including an upper vessel section, a lower vessel section, and a mid-flange, the upper vessel section and the lower vessel section being joined by the mid-flange;a cylindrical central riser disposed concentrically inside the cylindrical pressure vessel and including an upper riser section disposed in the upper vessel section, a lower riser section disposed in the lower vessel section, and a riser transition section disposed between the upper riser section and the lower riser section, the riser transition section being connected to the mid-flange;a reactor core comprising fissile material disposed inside the cylindrical pressure vessel in the lower vessel section;control rod drive mechanism (CRDM) units controlling control rod insertion actively into the reactor core, the CRDM units being disposed inside the cylindrical pressure vessel above the reactor core and in the lower vessel section with no vertical overlap between the upper vessel section and the CRDM units;a CRDM support plate disposed below the riser transition section and supporting the CRDM units; andtie rods suspending the CRDM support plate from the mid-flange. 12. The apparatus of claim 11, further comprising:steam generators disposed inside the cylindrical pressure vessel and entirely in the upper vessel section. 13. The apparatus of claim 12, wherein the steam generators are secured to the upper vessel section such that the upper vessel section and the steam generators can be lifted as a unit. 14. The apparatus of claim 11, further comprising:gussets connecting the riser transition section to the mid-flange, the gussets having first ends welded to the mid-flange and second ends welded to the riser transition section. 15. The apparatus of claim 14, wherein the gussets connecting the riser transition section to the mid-flange are angled downward such that the riser transition section is disposed below the mid-flange. 16. The apparatus of claim 11, wherein upper ends of the tie rods connect with the riser transition section to suspend the CRDM support plate from the mid-flange via the riser transition section and the gussets. 17. The apparatus of claim 11, further comprising:guide frames disposed between the CRDM units and the reactor core and guiding control rods into the reactor core;a lower hanger plate supporting the guide frames; andlower tie rods suspending the lower hanger plate from the CRDM support plate. 18. The apparatus of claim 11, further comprising:guide frames disposed between the CRDM units and the reactor core and guiding control rods into the reactor core; anda lower hanger plate supporting the guide frames; andwherein the tie rods further connect with the lower hanger plate such that the lower hanger plate is also suspended from the mid-flange by the tie rods. 19. The apparatus of claim 11, further comprising:an annular pump plate having an outer circular perimeter connecting with the mid-flange and an inner circular perimeter connected with the riser transition section; andreactor coolant pumps disposed entirely inside the cylindrical pressure vessel and mounted on the annular pump plate. 20. The apparatus of claim 11, further comprising:reactor coolant pumps mounted on the upper vessel section.