Patent Number: 
Section: claims

1. An apparatus comprising:a nuclear core comprising a fissile material;a vertically oriented cylindrical pressure vessel containing the nuclear core immersed in primary coolant water;a cylindrical riser oriented coaxially inside the pressure vessel, the pressure vessel and the central riser defining a downcomer annulus;a plurality of turbo pumps disposed in the pressure vessel to provide active circulation of primary coolant water in the pressure vessel wherein each turbo pump includes a turbine operatively connected with an impeller to drive the impeller;a manifold plenum chamber including an annular housing, the manifold plenum chamber being disposed in the pressure vessel so that the annular housing surrounds the central riser and is in fluid communication with inlets of the turbines of the plurality of turbo pumps; andan electrically driven pump operatively connected with the manifold plenum chamber to pressurize the manifold plenum chamber with primary coolant water. 2. The apparatus of claim 1, wherein the electrically driven pump includes an inlet arranged to receive primary coolant water from the pressure vessel and an outlet operatively connected with the manifold plenum chamber to pressurize the manifold plenum chamber with primary coolant water. 3. The apparatus of claim 1, wherein the turbo pumps are disposed in openings passing through the manifold plenum chamber such that the turbo pumps and the manifold plenum chamber define a reactor coolant pump (RCP) assembly having a suction side and a discharge side separated from the suction side by the RCP assembly, the turbo pumps being arranged to pump primary coolant water from the suction side to the discharge side. 4. The apparatus of claim 3, wherein each turbo pump is secured in the respective opening of the manifold plenum chamber by fasteners at an installation side selected from the suction side and the discharge side such that the turbo pump can be removed from the manifold plenum chamber at the installation side by disengaging the fasteners and withdrawing the turbo pump from the manifold plenum chamber at the installation side. 5. The apparatus of claim 3, wherein each turbo pump is secured in its respective opening of the manifold plenum chamber by fasteners at one of the suction side and the discharge side and by a compression seal ring at the other of the suction side and the discharge side. 6. The apparatus of claim 3, further comprising:flow distribution headers disposed in the manifold plenum chamber at respective openings in which the turbo pumps are installed, each flow distribution header including an area-reducing nozzle aligned with the inlet of the turbine of the respective turbo pump to inject primary coolant water from the manifold plenum chamber into the turbine. 7. The apparatus of claim 3, wherein the outlets of the turbines of the turbo pumps are arranged to discharge at the discharge side of the RCP assembly. 8. The apparatus of claim 3, wherein the inlets of the turbines of the turbo pumps are enclosed by the manifold plenum chamber. 9. The apparatus of claim 1, wherein the manifold plenum chamber is separate from and not welded to the pressure vessel. 10. The apparatus of claim 1, wherein the turbo pumps and the manifold plenum chamber define a reactor coolant pump (RCP) assembly having a suction side above the RCP assembly and a discharge side below the RCP assembly. 11. The apparatus of claim 10, wherein each turbo pump is secured in an opening of the manifold plenum chamber by fasteners on the suction side such that the turbo pump can be removed from the manifold plenum chamber by disengaging the fasteners and lifting the turbo pump upward away from the manifold plenum chamber. 12. The apparatus of claim 11, wherein each turbo pump is sealed at the discharge side by a compression seal ring but not by fasteners. 13. The apparatus of claim 10, wherein the turbines of the turbo pumps are configured to discharge into the downcomer annulus at the discharge side of the RCP assembly. 14. The apparatus of claim 1, wherein the nuclear core and the pressure vessel are configured as a pressurized water reactor (PWR) in which the primary coolant water in the pressure vessel does not boil. 15. The apparatus of claim 1, further comprising:a coaxial pipe including an inner passage surrounded by an outer annulus, the coaxial pipe connecting the electrically driven pump with the pressure vessel,wherein one of the inner passage and the outer annulus conveys primary coolant water from the pressure vessel to the electrically driven pump, andwherein the other of the inner passage and the outer annulus conveys primary coolant water pressurized by the electrically driven pump from the electrically driven pump to the pressure vessel. 16. The apparatus of claim 15, wherein:the inner passage conveys primary coolant water from the pressure vessel to the electrically driven pump, andthe outer annulus conveys primary coolant water pressurized by the electrically driven pump from the electrically driven pump to the pressure vessel. 17. An apparatus comprising:a nuclear core comprising a fissile material;a vertically oriented cylindrical pressure vessel containing the nuclear core immersed in primary coolant water;a cylindrical riser oriented coaxially inside the pressure vessel so that a downcomer annulus is defined therebetween;a plurality of turbo pumps disposed in the pressure vessel to provide active circulation of primary coolant water in the pressure vessel wherein each turbo pump includes a turbine operatively connected with an impeller to drive the impeller;an annular manifold plenum chamber disposed in the downcomer annulus and in fluid communication with inlets of the turbines of the plurality of turbo pumps;a riser manifold plenum chamber disposed inside the cylindrical riser; andan electrically driven pump operatively connected with the manifold plenum chamber to pressurize the manifold plenum chamber with primary coolant water,wherein the annular manifold plenum chamber and the turbo pumps in fluid communication with the annular manifold plenum chamber define a downcomer reactor coolant pump (RCP) assembly having a suction side in the downcomer annulus above the downcomer RCP assembly and a discharge side in the downcomer annulus below the downcomer RCP assembly, andthe riser manifold plenum chamber and the turbo pumps in fluid communication with the riser manifold plenum chamber define a riser reactor coolant pump (RCP) assembly having a suction side inside the riser below the riser RCP assembly and a discharge side inside the riser above the riser RCP assembly.