Patent Number: 
Section: claims

1. A passively-cooled spent nuclear fuel pool system, the system comprising:a containment vessel comprising a thermally-conductive cylindrical shell formed of metal;an annular reservoir surrounding the cylindrical shell of the containment vessel, the annular reservoir holding a coolant that defines a heat sink;a spent fuel pool disposed in the containment vessel, the fuel pool comprising:a floor and a peripheral sidewall extending upwards from the floor that collectively define an interior cavity;a body of water disposed in the interior cavity and having a surface level, at least one spent nuclear fuel rod submerged in the body of water that heats the water to form water vapor via evaporation; anda removable lid covering the spent fuel pool to form a sealed vapor space between the surface level of the body of water and the lid;a passive heat exchange sub-system comprising an assembly of:a primary riser section fluidly coupled to the vapor space;at least one downcomer fluidly coupled to the primary riser section for receiving the water vapor from the primary riser section, the water vapor condensing within the at least one downcomer to form a condensed water vapor; andat least one return conduit fluidly coupled to the at least one downcomer, the at least one return conduit having an outlet located within the body of liquid water for returning the condensed water vapor to the body of liquid water;wherein the peripheral sidewall of the fuel pool is formed by a portion of the cylindrical shell of the containment vessel adjacent to the spent fuel pool which defines a shared heat transfer wall, the heat transfer wall operable to transfer heat from the body of water in the spent fuel pool to the heat sink for cooling the body of water. 2. The system according to claim 1, wherein the at least one downcomer is attached to the cylindrical shell of the containment vessel for transferring heat to the heat sink. 3. The system according to claim 1, wherein the annular reservoir contains water as the liquid coolant having a lower temperature than the body of water in the fuel pool. 4. The system according to claim 1, wherein the heat transfer wall has an arcuate shape in top plan view. 5. The system according to claim 1, further comprising a vertically oriented flow partition plate disposed at least in a portion of the annular reservoir adjacent the heat transfer wall, the flow partition plate spaced radially apart from the heat transfer wall and configured to define a convective flow path that induces natural gravity circulation of the liquid coolant in the annular reservoir. 6. The system according to claim 5, wherein the flow partition plate includes a bottom spaced above a base mat of the annular reservoir and a top spaced apart below a top end of the annular reservoir such that a liquid coolant circulation flow path is formed over and under the flow partition plate. 7. The system according to claim 5, further comprising a plurality of heat exchange fins extending radially outwards from cylindrical shell of the containment vessel into the annular reservoir, and wherein the flow partition plate is supported by the heat exchange fins. 8. The system according to claim 7, wherein the flow partition plate is comprised of a plurality of segments each attached between a pair of heat exchange fins. 9. The system according to claim 1, further comprising a vertically oriented flow partition wall disposed in the fuel pool between a spent fuel rack storage area on the floor and the heat transfer wall, the flow partition wall configured to define a convective flow path that induces natural gravity circulation of the body of water in the fuel pool. 10. The system according to claim 1, wherein the heat transfer wall has an arcuate shape in top plan view. 11. The system according to claim 1, wherein the annular reservoir is vented to atmosphere for cooling the liquid coolant via evaporative loss.