Patent Number: 
Section: claims

1. A pump-less nuclear steam supply system with natural gravity-driven primary coolant circulation, the system comprising:a containment vessel comprising a cylindrical sidewall and a horizontal partition wall dividing an interior space of the containment vessel into an upper portion and a lower portion;a vertically-oriented reactor vessel extending through the partition wall, the reactor vessel including an upper part in the upper portion of the containment vessel above the partition wall, and a lower part in the lower portion of the containment vessel below the partition wall;the reactor vessel comprising an elongated cylindrical shell defining a first vertical axis and an internal cavity configured for containing primary coolant;a nuclear fuel core arranged in the reactor vessel to heat the primary coolant;an annular support flange attached to the upper part of the reactor vessel and supporting the reactor vessel from the horizontal partition wall;a vertically-oriented steam generating vessel comprising an elongated cylindrical shell, a top tubesheet, a bottom tubesheet, and a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets;a support skirt having a top end coupled to the bottom tubesheet, the support skirt extending downwards from the bottom tubesheet and having a bottom end seated on the horizontal partition wall to support the steam generating vessel;a vertical riser pipe extending vertically between the top and bottom tubesheets; anda combined inlet-outlet primary coolant fluid coupling comprising a pair of concentrically arranged flow conduits including an outer inlet nozzle and inner outlet nozzle;the primary coolant fluid coupling configured to form bi-directional exchange of primary coolant between the steam generating vessel and reactor vessel;wherein a closed primary coolant loop is formed in which primary coolant flows from the reactor vessel internally through the fluid coupling into the steam generator vessel and returns from the steam generating vessel to the reactor vessel internally through the same fluid coupling. 2. The system according to claim 1, wherein the riser pipe includes an extension which extends internally through the fluid coupling and is fluidly coupled to the reactor vessel for flowing primary coolant from the reactor vessel to the steam generating vessel. 3. The system according to claim 2, wherein the primary coolant flows from the reactor vessel upwards through the riser pipe to the top tubesheet of the steam generator vessel at a first temperature, reverses direction, and flows downward through the tubes and bottom tubesheet into the fluid coupling at a second temperature lower than the first temperature. 4. The system according to claim 2, further comprising an annular bottom collection plenum formed inside the fluid coupling between the riser pipe extension and the outer inlet nozzle, the bottom collection plenum being in fluid communication with a tube side of the steam generating vessel to collect primary coolant flowing outwards from the tubes through the bottom tubesheet and returning the primary coolant to the reactor vessel. 5. The system according to claim 1, wherein the outer inlet nozzle is physically connected to the bottom tubesheet of the steam generating vessel at a first end and physically connected to the upper part of the reactor vessel at a second end. 6. The system according to claim 1, wherein the outer inlet nozzle of the fluid coupling comprises a flat inclined outer wall obliquely angled to the vertical centerline of the steam generating vessel and an opposing straight inner wall oriented parallel to the vertical centerline of the steam generating vessel thereby defining an eccentric cone. 7. The system according to claim 6, wherein the eccentric cone forms a 90 degree flow transition for primary coolant flow between the steam generator vessel and the reactor vessel. 8. The system according to claim 7, wherein the outer inlet nozzle of the fluid coupling further includes a horizontally oriented stub pipe section fluidly connecting the eccentric cone to the reactor vessel, the stub pipe section being joined to the eccentric cone via an angled miter joint. 9. The system according to claim 7, wherein the eccentric cone provides a total horizontal length of inlet-outlet primary coolant fluid coupling between the reactor vessel and steam generating vessel is less than or equal to a diameter of the reactor vessel to eliminate long runs of large coolant piping between the reactor and steam generating vessels. 10. The system according to claim 1, wherein the fluid coupling forms a 90 degree flow transition for primary coolant flow between the steam generator vessel and the reactor vessel. 11. The system according to claim 1, wherein the reactor vessel is supported by the annular support flange in a suspended manner in which a bottom of the reactor vessel is not supported underneath by a support structure thereby allowing the reactor vessel to freely grow in length when heated by the fuel core. 12. The system according to claim 1, wherein the fluid coupling between the steam generating vessel and reactor vessel is a mitered 90 degree elbow such that the vertical centerline of the steam generating vessel is less than two steam generator diameters apart horizontally from the vertical centerline of the reactor vessel. 13. The system according to claim 1, wherein the vertical centerline of the steam generating vessel is parallel to and horizontal offset from the vertical centerline of the reactor vessel. 14. The system according to claim 1, wherein a majority of a length of the reactor vessel is below the horizontal partition wall. 15. The system according to claim 14, wherein the containment vessel comprises an upper section joined to a lower section at a flanged joint. 16. The system according to claim 14, wherein the upper section is above grade and the lower section is below grade. 17. The system according to claim 14, wherein an entirety of the reactor vessel is located in the lower section of the containment vessel. 18. A pump-less nuclear steam supply system with natural gravity-driven primary coolant circulation, the system comprising:a containment vessel horizontally split into an upper section joined to a lower section at a flanged joint, and a horizontal partition wall dividing an interior space of the containment vessel into an upper portion and a lower portion;a vertically-oriented reactor vessel extending through the partition wall, the reactor vessel including an upper part in the upper portion of the containment vessel above the partition wall, and a lower part in the lower portion of the containment vessel below the partition wall;the reactor vessel comprising an elongated cylindrical shell defining a first vertical axis and an internal cavity configured for containing primary coolant;a nuclear fuel core arranged in the reactor vessel to heat the primary coolant;an annular support flange attached to the upper part of the reactor vessel and supporting the reactor vessel from the horizontal partition wall;a vertically-oriented steam generating vessel comprising an elongated cylindrical shell, a top tubesheet, a bottom tubesheet, and a plurality of heat transfer tubes extending vertically between the top and bottom tubesheets;a vertical riser pipe extending vertically between the top and bottom tubesheets; anda 90 degree combined inlet-outlet primary coolant fluid coupling comprising a pair of concentrically arranged flow conduits including an outer inlet nozzle and inner outlet nozzle;the primary coolant fluid coupling configured to form bi-directional exchange of primary coolant between the steam generating vessel and reactor vessel;wherein a closed primary coolant loop is formed in which primary coolant flows from the reactor vessel internally through the fluid coupling into the steam generator vessel and returns from the steam generating vessel to the reactor vessel internally through the same fluid coupling. 19. The system according to claim 18, wherein the outer inlet nozzle of the fluid coupling between the steam generating vessel and reactor vessel is a mitered 90 degree elbow such that the vertical centerline of the steam generating vessel is less than two steam generator diameters apart horizontally from the vertical centerline of the reactor vessel. 20. The system according to claim 19, wherein the outer inlet nozzle is physically connected to the bottom tubesheet of the steam generating vessel at a first end and physically connected to the upper part of the reactor vessel at a second end.