Patent Number: 
Section: claims

1. A nuclear power plant, comprising:a nuclear steam supply system;a containment system comprising a containment enclosure for hermetically housing the nuclear steam supply system;an annulus adjacent an exterior surface of the containment enclosure;a reservoir comprising water, wherein the reservoir is housed within or within proximity of the containment enclosure;spent nuclear fuel submerged within the reservoir and cooled by the water; anda thermosiphon extending from within the reservoir to an exterior of the containment enclosure for transferring heat in the reservoir to air outside of the containment enclosure, wherein the thermosiphon comprises:a first heat exchanger at least partially submerged in the water, anda second heat exchanger thermally coupled to the first heat exchanger, wherein the second heat exchanger comprises an air-cooled heat exchanger positioned within the annulus. 2. The nuclear power plant of claim 1 wherein:the second heat exchanger is at a higher elevation than the first heat exchanger;the water on a first side of the first heat exchanger is in thermal communication with a working fluid on a second side of the first heat exchanger;the second side of the first heat exchanger is in fluid communication with a first side of the second heat exchanger through a closed loop in which the working fluid circulates; andthe working fluid on the first side of the second heat exchanger is in thermal communication with ambient air outside the containment enclosure on a second side of the second heat exchanger. 3. The nuclear power plant of claim 2 wherein the working fluid is a refrigerant. 4. The nuclear power plant of claim 3 wherein the refrigerant is 245fa. 5. The nuclear power plant of claim 2 wherein a portion of the closed loop outside the containment enclosure comprises a finned tube. 6. The nuclear power plant of claim 2 wherein the containment enclosure comprises a steel shell having substantially vertical walls that extend from a lower portion of the containment system to an upper portion of the containment system. 7. The nuclear power plant of claim 6 including an air baffle extending substantially around and spaced from the vertical walls of the containment enclosure with an air inlet at a lower elevation of the air baffle and an air outlet at an upper elevation of the air baffle, the second heat exchanger being supported within an annulus between the vertical wall of the containment enclosure and the air baffle. 8. The nuclear power plant of claim 7 wherein the second heat exchanger is supported in a lower portion of the annulus or outside the containment. 9. The nuclear power plant of claim 2 wherein the first heat exchanger includes a plurality of first heat exchangers, the second heat exchanger includes a plurality of second heat exchangers and the closed loop includes a plurality of closed loops operating in parallel with each of the closed loops having at least one of the first heat exchangers and at least one of the second heat exchangers. 10. The nuclear power plant of claim 9 wherein each of the second heat exchangers are spaced around the outside of the containment. 11. The nuclear power plant of claim 2 wherein the closed loop includes a valve for cutting off circulation of the working fluid. 12. The nuclear power plant of claim 1 wherein the reservoir is a refueling water storage tank within the containment and the first heat exchanger is within the containment and the second heat exchanger is outside the containment. 13. The nuclear power plant of claim 1 wherein the reservoir is a spent fuel pool outside of and within proximity of the containment enclosure.