Patent Number: 
Section: claims

1. A ventilated cask for transporting and/or storing radioactive materials comprising: a vertically elongated overpack body comprising a longitudinal axis, an outer shell defining an outer surface, an inner shell defining an inner surface, a gap extending radially between the inner and outer shells, and an internal cavity configured for holding a nuclear fuel canister;a base enclosing a bottom end of the cavity;a lid enclosing a top end of the cavity;a plurality of outlet ducts each forming an air outlet passageway from a top portion of the cavity to an external atmosphere;a plurality of arcuately curved structures forming air inlet ducts extending radially between the outer and inner surfaces at a bottom portion of the overpack body, the air inlet ducts configured for admitting ambient cooling air into a lower portion of the cavity;the air inlet ducts spaced circumferentially apart around the longitudinal axis and the bottom portion of the overpack body in a symmetric arrangement;a plurality of wall segments comprising a radiation shielding material filled in the gap between each pair of air inlet ducts, each wall segment comprising a circumferentially projecting convex portion and an opposing circumferentially recessed concave portion. 2. The ventilated cask according to claim 1, wherein each of the wall segments has a convex outer wall that adjoins the outer shell of the overpack body and a concave inner wall that adjoins the inner shell of the overpack body. 3. The ventilated cask according to claim 2, wherein each of the wall segments is a singular uninterrupted monolithic structure. 4. The ventilated cask according to claim 3, wherein each wall segment is separated from every other wall segment by the air inlet ducts. 5. The ventilated cask according to claim 2, wherein the wall segments are arranged in an intermeshing configuration such that the convex portion of each wall segment is at least partially nested within the concave portion of an adjacent wall segment. 6. The ventilated cask according to claim 5, wherein each air inlet duct is interspersed between the convex and concave portions of adjacent wall segments. 7. The ventilated cask according to claim 5, wherein the wall segments are formed of poured concrete mass. 8. The ventilated cask according to claim 7, wherein the concrete mass is a monolithic mass extending from a top of the gap between the inner and outer shells to a bottom of the gap between the air inlet ducts. 9. The ventilated cask according to claim 1, wherein a straight line of sight does not exist from the cavity to the external atmosphere through each of the air inlet ducts. 10. The ventilated cask according to claim 5, wherein each air inlet duct includes a radially straight outer section, a radially straight inner section, and a curved section extending therebetween. 11. The ventilated cask according to claim 5, wherein each air inlet duct includes a vertically elongated outer opening formed in the outer surface of the outer shell of the overpack body, and a vertically elongated inner opening formed in the inner surface of the inner shell of the overpack body. 12. The ventilated cask according to claim 11, wherein the outer and inner openings have a rectangular configuration. 13. The ventilated cask according to claim 1, wherein each air inlet duct is defined by a pair of metal inter-shell connectors, each pair of inter-shell connectors extending between an outer opening formed in the outer surface of the outer shell of the overpack body, and an inner opening formed in the inner surface of the outer shell of the overpack body. 14. The ventilated cask according to claim 13, wherein the inter-shell connectors in each pair are complementary configured and spaced circumferentially apart, and a roof extends between tops of and covers each pair of inter-shell connectors to form one of the air inlet ducts. 15. The ventilated cask according to claim 1, wherein each of the air inlet ducts comprises a first radial section extending inwards from the outer shell into the gap, a second radial section extending outwards from the inner shell into the gap, and an arcuately curved section extending between the first and second radial sections. 16. The ventilated cask according to claim 1, wherein the air inlet ducts are C-shaped. 17. The ventilated cask according to claim 1, wherein each of the air inlet ducts are vertically elongated slots having a height and a width, and wherein a ratio of height to width is at least 10:1. 18. The ventilated cask according to claim 1, wherein for each segment, the convex portion comprises an arcuately curved first end wall adjoining a first air inlet duct, and the concave portion comprises an arcuately curved second end wall adjoining a second air inlet duct. 19. The ventilated cask according to claim 18, wherein the first end wall further comprises a first angled shoulder on an outer end adjacent to the outer shell of the overpack body, and a second angle shoulder on an inner end adjacent to the inner shell of the overpack body. 20. A ventilated cask for transporting and/or storing radioactive materials comprising:a vertically elongated overpack body comprising a longitudinal axis, an outer shell defining an outer surface, an inner shell defining an inner surface, a gap extending radially between the inner and outer shells, and an internal cavity configured for holding a nuclear fuel canister;a base enclosing a bottom end of the cavity;a lid enclosing a top end of the cavity;a plurality of outlet ducts each forming an air outlet passageway from a top portion of the cavity to an external atmosphere;a plurality of arcuately curved metallic air inlet ducts extending radially between the outer and inner surfaces at a bottom portion of the overpack body, the air inlet ducts configured for admitting ambient cooling air into a lower portion of the cavity;the air inlet ducts spaced circumferentially apart around the longitudinal axis and the bottom portion of the overpack body; anda plurality of wall segments comprising a radiation shielding material filled in the gap between each pair of air inlet ducts, each wall segment comprising a circumferentially projecting convex portion at one end extending into a concavity formed by a first one of the air inlet ducts, and a circumferentially recessed concave portion at an opposite end receiving a convexity of a second one of the air inlet ducts.