Patent Number: 
Section: claims

1. A system for removing thermal energy generated by radioactive materials comprising:an air-cooled heat exchanger;a heat rejection closed-loop fluid circuit comprising a tube-side fluid path of the air-cooled heat exchanger, a coolant fluid flowing through the heat rejection closed-loop fluid circuit, the heat rejection closed-loop fluid circuit thermally coupled to the radioactive materials so that thermal energy generated by the radioactive materials is transferred to the coolant fluid; andthe air-cooled heat exchanger comprising a shell-side fluid path having a first air inlet, a second air inlet and an air outlet, the first air inlet located at a first elevation, the second air inlet located at a second elevation, and the air outlet located at a third elevation, the second elevation greater than the first elevation and the third elevation greater than the second elevation, the air-cooled heat exchanger transferring thermal energy from the coolant fluid flowing through the tube-side fluid path to air flowing through the shell-side fluid path;the tube-side fluid path comprising internal cavities of a plurality of heat exchange tubes, the plurality of heat exchange tubes located within the shell-side fluid path;wherein the shell-side fluid path comprises a first venturi located at an elevation between the second air inlet and the air outlet, the first venturi created by fins of the plurality of heat exchange tubes;wherein the shell-side fluid path comprises a second venturi located at an elevation between the first air inlet and the second air inlet, the second venturi created by fins of the plurality of heat exchange tubes;wherein the fins are discontinuous in structure such that the plurality of heat exchange tubes between the first venturi and second venturi at the second air inlet do not have fins. 2. The system of claim 1 wherein the plurality of heat exchange tubes form a tube bundle having a longitudinal axis, and wherein each of the fins of the plurality of heat exchange tubes comprise opposing surfaces that extend substantially parallel to the longitudinal axis. 3. The system of claim 1 wherein the shell-side fluid path comprises a first free transverse cross-sectional area at the second elevation and a second free transverse cross-sectional area at an elevation between the second air inlet and the air outlet, the second free transverse cross-sectional area being less than the first free transverse cross-sectional area. 4. The system of claim 3 wherein the shell-side fluid path comprises a third free transverse cross-sectional area at the third elevation, the third free transverse cross-sectional area being greater than the second free transverse cross-sectional area. 5. The system of claim 1 further comprising:an intermediate heat exchanger;an intermediate closed-loop fluid circuit comprising, in operable fluid coupling, a pool of a liquid and a first fluid path of the intermediate heat exchanger, the radioactive materials immersed in the pool of the liquid, the liquid flowing through the intermediate closed-loop fluid circuit; andthe heat rejection closed-loop fluid circuit further comprising a second fluid path of the intermediate heat exchanger, the intermediate heat exchanger transferring thermal energy from the liquid flowing through the first fluid path to the coolant fluid flowing through the second fluid path. 6. The system of claim 5 wherein the pool of the liquid and the intermediate heat exchanger are contained within a containment structure. 7. The system of claim 1, wherein the plurality of heat exchange tubes are arranged in a substantially vertical orientation. 8. The system of claim 7 wherein the plurality of heat exchange tubes collectively form a tube bundle that extends along a longitudinal axis, and the tube bundle comprising finned tube sections and a non-finned tube section arranged in axial alignment, the second air inlet transversely aligned with the non-finned tube section between the finned tube sections. 9. The system of claim 8 wherein the finned tube sections and the non-finned tube section alternate along the longitudinal axis. 10. The system of claim 8 further comprising a plurality of the non-finned tube sections, each of the first air inlet, the second air inlet and the air outlet transversely aligned with one of the non-finned tube sections. 11. The system of claim 8 further comprising:the air-cooled heat exchanger comprising a top tube sheet and a bottom tube sheet, the plurality of heat exchange tubes extending from the top tube sheet to the bottom tube sheet, the first air inlet located adjacent the bottom tube sheet and the air outlet located adjacent the top tube sheet; andthe tube-side fluid path of the air-cooled heat exchanger comprising a coolant fluid inlet header and a coolant fluid outlet header, the internal cavities of the plurality of heat exchange tubes forming passageways between the coolant fluid inlet header and the coolant fluid outlet header. 12. The system of claim 1 wherein the air-cooled heat exchanger comprises a shell, each of the first air inlet, the second air inlet and the air outlet formed in the shell. 13. The system of claim 12 further comprising:a shroud forming a shroud cavity, the air-cooled heat exchanger located within the shroud cavity, the shroud cavity comprising a shroud outlet plenum circumferentially surrounding the air-cooled heat exchanger, the air outlet of the shell located within the shroud outlet plenum; anda chimney forming a passageway from the shroud outlet plenum to an ambient environment. 14. The system of claim 1 further comprising a blower for inducing air flow through the shell-side fluid path. 15. A system for removing thermal energy generated by radioactive materials comprising:an air-cooled shell-and-tube heat exchanger comprising a shell and plurality of heat exchange tubes arranged in a substantially vertical orientation within the shell, the plurality of heat exchange tubes comprising interior cavities that collectively form a tube-side fluid path, the shell forming a shell-side fluid path that extends from an air inlet of the shell to an air outlet of the shell, the first air inlet located at a lower elevation than the air outlet and the plurality of heat exchange tubes located within the shell-side fluid path;the shell comprising a second air inlet located at an elevation between the first air inlet and the air outlet;a heat rejection closed-loop fluid circuit comprising the tube-side fluid path of the air-cooled heat exchanger, a coolant fluid flowing through the heat rejection closed-loop fluid circuit, the heat rejection closed-loop fluid circuit thermally coupled to the radioactive materials so that thermal energy generated by the radioactive materials is transferred to the coolant fluid; andthe air-cooled shell-and-tube heat exchanger transferring thermal energy from the coolant fluid flowing through the tube-side fluid path to air flowing through the shell-side fluid path;wherein the shell-side fluid path comprises a first venturi located at an elevation between the second air inlet and the air outlet, the first venturi created by fins of the plurality of heat exchange tubes;wherein the shell-side fluid path comprises a second venturi located at an elevation between the first air inlet and the second air inlet, the second venturi created by fins of the plurality of heat exchange tubes;wherein the fins are discontinuous in structure such that the plurality of heat exchange tubes between the first venturi and second venturi at the second air inlet do not have fins. 16. The system of claim 15 further comprising a pool of a liquid, the radioactive materials immersed in the pool of the liquid, wherein thermal energy generated by the radioactive materials is transferred to the liquid of the pool prior to being transferred to the coolant fluid. 17. The system of claim 15 further comprising:a shroud forming a shroud cavity, the shell of the shell-and-tube air-cooled heat exchanger located within the shroud cavity, the shroud cavity comprising a shroud outlet plenum circumferentially surrounding the shell-and-tube air-cooled heat exchanger, the air outlet of the shell located within the shroud outlet plenum; anda chimney forming a passageway from the shroud outlet plenum to an ambient environment. 18. The system of claim 15 further comprising a blower for inducing air flow through the shell-side fluid path. 19. The system of claim 15 wherein the plurality of heat exchange tubes collectively form a tube bundle that extends along a longitudinal axis, and the tube bundle comprising finned tube sections and non-finned tube sections arranged in alternating axial alignment.