Patent Number: 
Section: claims

1. An autonomous self-powered system for cooling radioactive materials, the system comprising:a pool at least partially filled with a liquid and radioactive materials immersed in the liquid;a closed-loop fluid circuit comprising a working fluid having a boiling temperature that is less than a boiling temperature of the liquid, the closed-loop fluid circuit comprising, in an operable fluid coupling, an evaporative heat exchanger at least partially immersed in the liquid, a turbogenerator, and a condenser;one or more forced flow units operably coupled to the closed-loop fluid circuit to induce flow of the working fluid through the closed-loop fluid circuit; andthe closed-loop fluid circuit converting thermal energy extracted from the liquid of the pool into electrical energy that powers the one or more forced flow units;wherein the evaporative heat exchanger comprises:a top header, a bottom header, a downcomer tube defining a first passageway between the top and bottom headers, and a plurality of heat exchange tubes each forming a second passageway between the top and bottom headers, each of the plurality of heat exchange tubes comprising an outer surface, and wherein an entirety of the outer surface of the heat exchange tubes are in direct contact with the liquid of the pool;a working fluid inlet extending into the downcomer tube for introducing a liquid phase of the working fluid into the first passageway; anda working fluid outlet for allowing a vapor phase of the working fluid to exit the evaporative heat exchanger. 2. The autonomous self-powered system of claim 1 wherein the downcomer tube and the heat exchange tubes of the evaporative heat exchanger are arranged in a substantially vertical orientation and the downcomer tube is circumferentially surrounded by the heat exchange tubes. 3. The autonomous self-powered system of claim 1 wherein the downcomer tube comprises a thermal insulating layer. 4. The autonomous self-powered system of claim 1 wherein the first passageway has a first width and the each of the second passageways have a second width, the first width being greater than the second width. 5. The autonomous self-powered system of claim 1 wherein the downcomer tube has a first effective coefficient of thermal conductivity and the heat exchange tubes have a second effective coefficient of thermal conductivity, the first effective coefficient of thermal conductivity being less than the second effective coefficient of thermal conductivity. 6. The autonomous self-powered system of claim 1 wherein the evaporative heat exchanger is configured to achieve an internal thermosiphon flow of the liquid phase of the working fluid within the evaporative heat exchanger. 7. The autonomous self-powered system of claim 1 further comprising:the evaporative heat exchanger converting the working fluid from the liquid phase to the vapor phase by transferring the thermal energy from the liquid in the pool to the working fluid;the turbogenerator receiving the vapor phase of the working fluid from the evaporative heat exchanger, the turbogenerator generating the electrical energy by extracting energy from the vapor phase of the working fluid flowing through the turbogenerator;the condenser receiving the vapor phase of the working fluid from the turbogenerator and converting the vapor phase of the working fluid flowing through the condenser back into the liquid phase of the working fluid by removing thermal energy from the working fluid; andthe at least one forced flow unit electrically coupled to the turbogenerator so as to be powered by the electrical energy generated by the turbogenerator. 8. The autonomous self-powered system of claim 1 wherein the one or more forced flow units comprises a hydraulic pump, the closed-loop fluid circuit comprising the hydraulic pump, the hydraulic pump forcing the liquid phase of the working fluid into the evaporative heat exchanger. 9. The autonomous self-powered system of claim 1 wherein the liquid in the pool is at a first pressure and the working fluid within the evaporative heat exchanger is at a second pressure that is greater than the first pressure, the boiling temperature of the working fluid at the second pressure being less than the boiling temperature of the liquid in the pool at the first pressure. 10. The autonomous self-powered system of claim 1 wherein the liquid in the pool is water and the working fluid is a refrigerant or a hydrocarbon. 11. The autonomous self-powered system of claim 1 wherein the evaporative heat exchanger is fully immersed in the liquid in the pool and located at a top portion of the pool. 12. The autonomous self-powered system of claim 1 wherein the autonomous self-powered system operates free of electrical energy generated outside of the closed-loop fluid circuit. 13. A vertical evaporative heat exchanger for immersion in a heated fluid comprising:a tubeside fluid circuit comprising:a top header;a bottom header;a core tube forming a downcomer passageway between the top header and the bottom header, the core tube having a first effective coefficient of thermal conductivity;a plurality of heat exchange tubes forming passageways between the bottom header and the top header, the plurality of the heat exchange tubes having a second effective coefficient of thermal conductivity that is greater than the first effective coefficient of thermal conductivity;a working fluid in the tubeside fluid circuit;a conduit extending through the top header of the tubeside fluid circuit, the conduit comprising:a working fluid inlet in a first end of the conduit for introducing a liquid phase of the working fluid into the tubeside fluid circuit; anda working fluid outlet in a second end of the conduit that is located within the downcomer passageway so that the working fluid flows directly into the downcomer passageway;at least one vapor outlet for allowing a vapor phase of the working fluid to exit the top header; andwherein transfer of heat from the heated fluid to the working fluid induces a thermosiphon flow of the liquid phase of the working fluid within the tubeside fluid circuit. 14. The vertical evaporative heat exchanger of claim 13 further comprising a plurality of the vapor outlets, and wherein the working fluid inlet of the conduit is surrounded by the vapor outlets. 15. The vertical evaporative heat exchanger of claim 14 further comprising a longitudinal axis, and wherein the conduit extends along the longitudinal axis. 16. The autonomous self-powered system of claim 1 wherein the evaporative heat exchanger further comprises a conduit extending through the top header of the evaporative heat exchanger and into the downcomer tube, the conduit comprising the working fluid inlet in a first end of the conduit and a working fluid outlet in a second end of the conduit, the second end of the conduit being located within the downcomer tube to ensure that the liquid phase of the working fluid is introduced directly into the downcomer tube to isolate the working fluid being introduced into the evaporative heat exchanger via the conduit from the working fluid already circulating within the evaporative heat exchanger. 17. The autonomous self-powered system of claim 1 wherein the downcomer tube extends from a first end to a second end and each of the heat exchange tubes extends from a first end to a second end, and wherein the first end of the downcomer tube is aligned with the first end of each of the heat exchange tubes and wherein the second end of the downcomer tube is aligned with the second end of each of the heat exchange tubes. 18. The autonomous self-powered system of claim 17 wherein the top header comprises a top tube sheet and the bottom header comprises a bottom tube sheet, the first end of each of the heat exchange tubes and the downcomer tube terminating at the top tube sheet and the second end of each of the heat exchange tubes and the downcomer tube terminating at the bottom tube sheet. 19. The autonomous self-powered system of claim 1 wherein the heat exchange tubes are not enclosed within a housing such that the outer surface of outermost ones of the heat exchange tubes form a portion of an outer surface of the evaporative heat exchanger. 20. The autonomous self-powered system of claim 1 wherein each of the heat exchange tubes extends from a first end that is connected to the top header to a second end that is connected to the bottom header, the heat exchange tubes having a length measured from the first end to the second and, and wherein the outer surfaces of the heat exchange tubes are in direct contact with the liquid in the pool along an entirety of the length of the heat exchange tubes.