Patent Number: 
Section: claims

1. A passive reactor cooling system usable after a loss-of-coolant accident, the system comprising:a containment vessel in thermal communication with a heat sink;a reactor well disposed in the containment vessel;a reactor vessel disposed at least partially in the reactorwell, the reactor vessel containing a nuclear fuel core which heats primary coolant in the reactorvessel;a steam generator disposed in the containment vessel in fluid communication with the reactor vessel, the primary coolant circulating between the reactor vessel and steam generator via a primary coolant flow loop;a water storage tank disposed in the containment vessel and in fluid communication with the reactor well, the tank containing an inventory of cooling water which is supplied directly to the reactor well;a heat exchanger disposed in the containment vessel, the heat exchanger in fluid communication with the reactor well via a closed flow loop in which the flow is driven via gravity;wherein following a loss of primary coolant, the tank is configured to flood the reactor well to contact and cool the exterior of the reactor vessel with the cooling water which is converted into steam by heat from the fuel core and which steam flows through the closed flow loop to the heat exchanger;wherein the closed flow loop is fluidly isolated from the primary coolant; and further comprisingan insulating liner assembly disposed on an outside surface of the reactor vessel, the liner assembly comprising a plurality of spaced apart metal liners having air gaps formed between the liners;a top flow-hole node disposed at the outside surface of reactor vessel which is in fluid communication with the air gaps formed between the liners and the reactor well,wherein the top flow-hole nozzle is configured to evacuate steam produced within the liner assembly and discharge the steam to the reactor well. 2. The system according to claim 1, wherein the steam condenses in the heat exchanger forming condensate, and the condensate flows via gravity back to the reactor well. 3. The system according to claim 1, wherein the heat exchanger comprises an array of heat dissipater ducts integrally attached to the containment vessel. 4. The system according to claim 1, wherein the heat sink comprises an annular reservoir holding water that surrounds the containment vessel. 5. The system according to claim 4, wherein the water in the annular reservoir has a temperature lower than the temperature of the steam which condenses the steam. 6. The system according to claim 4, wherein the annular reservoir is formed between the containment vessel and an outer containment enclosure structure. 7. The system according to claim 2, wherein the closed flow loop includes:inlet steam piping fluidly coupling a top portion of the reactor well and heat exchanger, andoutlet condensate piping fluidly coupling the heat exchanger and water storage tank. 8. The system according to claim 1, wherein the reactor well and water storage tank are formed in a concrete monolith disposed in the containment vessel. 9. The system according to claim 1, wherein the water storage tank is fluidly coupled to the reactor well by at least one flow conduit having a dump valve disposed therein, the dump valve configured to control the flow of cooling water to the reactor well by moving from a closed position to an open position. 10. The system according to claim 1, wherein the top flow-hole nozzle includes a flap configured to cover the nozzle, the flap being pivotably movable between an open position and a closed position. 11. The system according to claim 1, further comprising a bottom flow-hole node disposed at the outside surface of a bottom head of the reactor vessel which is in fluid communication with the air gaps formed between the liners and the reactor well,wherein the bottom flow-hole nozzle is configured to admit cooling water in the reactor well into the liner assembly. 12. The system according to claim 11, wherein the bottom flow-hole nozzle includes a flap configured to cover the nozzle, the flap being pivotably movable between an open position and a closed position. 13. A passive reactor cooling system usable after a loss-of-coolant accident, the system comprising:a containment vessel in thermal communication with a heat sink;a reactor well disposed in the containment vessel;a reactor vessel disposed at least partially in the reactor well, the reactorvessel containing a nuclear fuel core and primary coolant heated by the fuel core;a steam generator disposed in the containment vessel in fluid communication with the reactor vessel, the primary coolant circulating between the reactor vessel and steam generator via a primary coolant flow loop;a water storage tank disposed in the containment vessel and in fluid communication with the reactor well, the tank containing an inventory of cooling water which is supplied directly to the reactor well; anda heat exchanger disposed in the containment vessel, the heat exchanger in fluid communication with the reactor well via an atmospheric pressure closed flow loop;wherein following a loss of primary coolant, the tank is configured to flood the reactor well with cooling water which contacts and cools the exterior of the reactor vessel;wherein the cooling water in the flooded reactor well is heated by the fuel core and converted into steam, the steam flows through the closed flow loop to the heat exchanger and condenses forming condensate, and the condensate flows via gravity back to the reactorwell;wherein the closed flow loop is fluidly isolated from the primary coolant; and further comprising:an insulating liner assembly disposed on an outside surface of the reactor vessel, the liner assembly comprising a plurality of spaced apart metal liners having air gaps formed between the liners;a top flow-hole nozzle disposed at the outside surface of reactor vessel which is in fluid communication with the air gaps formed between the liners and the reactorwell, the top flow-hole note being configured to evacuate steam produced within the liner assembly and discharge the steam to the reactor well; anda bottom flow-hole nozzle disposed at the outside surface of a bottom head of the reactor vessel which is in fluid communication with the air gaps formed between the liners and the reactor well, the bottom flow-hole nozzle being configured to admit cooling water in the reactor well into the liner assembly;wherein the cooling water enters the liner assembly through the bottom flow-hole node and is converted to steam by heat from the reactor fuel core, and the steam exits the liner assembly and flows into the reactor well through the top flow-hole nozzle. 14. The system according to claim 13, wherein the heat exchanger comprises an array of heat dissipater ducts integrally attached to the containment vessel. 15. The system according to claim 13, wherein the heat sink comprises an annular reservoir holding water that surrounds the containment vessel. 16. The system according to claim 13, wherein the reactor well and water storage tank are formed in a concrete monolith disposed in the containment vessel. 17. The system according to claim 13, wherein the water storage tank is fluidly coupled to the reactor well by at least one flow conduit having a dump valve disposed therein, the dump valve configured to control the flow of cooling water to the reactor well by moving from a closed position to an open position. 18. The system according to claim 13, wherein the top and bottom flow-hole nozzles each include a closure flap configured to cover the nozzle, the flaps being pivotably movable between an open position and a closed position.