Patent Number: 
Section: claims

1. A spent nuclear fuel assembly storage container comprising:a metal cask which stores a spent nuclear fuel assembly therein;a container body which stores the metal cask and has a substantially hexagonal tubular shape; anda concave portion which is formed on an outer surface of the container body having the substantially hexagonal tubular shape, is recessed inward, and extends in a longitudinal direction,wherein the concave portion forms an external cooling passage for a cooling gas when an outer surface of the container body is joined to an outer surface of another container body. 2. The spent nuclear fuel assembly storage container according to claim 1,wherein an inner surface of the container body is provided with a stopper which prevents vibration of the metal cask. 3. The spent nuclear fuel assembly storage container according to claim 1,wherein an upper surface of the container body is provided with a tapered chimney. 4. The spent nuclear fuel assembly storage container according to claim 1,wherein the container body is made of heavy-weight concrete having a specific gravity of 3.5 or more. 5. A spent nuclear fuel assembly storage container comprising:a metal cask which stores a spent nuclear fuel assembly;a container body which stores the metal cask and has a substantially hexagonal tubular shape; andan internal cooling passage which is provided between the metal cask and an inner surface of the container body and is provided with a cooling gas supply passage and an exhaust passage communicating with external air at upper and lower portions thereof. 6. The spent nuclear fuel assembly storage container according to claim 5,wherein an inner surface of the container body is provided with a stopper which prevents vibration of the metal cask. 7. The spent nuclear fuel assembly storage container according to claim 5,wherein an upper surface of the container body is provided with a tapered chimney. 8. The spent nuclear fuel assembly storage container according to claim 5,wherein the container body is made of heavy-weight concrete having a specific gravity of 3.5 or more. 9. A spent nuclear fuel assembly storage container comprising:a metal cask which stores a spent nuclear fuel assembly; anda container body which stores the metal cask and has a substantially hexagonal tubular shape,wherein the container body is made of neutron shielding concrete including an aggregate mainly including colemanite and/or hilgardite collected from an ore of an evaporation type sedimentary deposit and a cement which is a consolidating material and is manufactured by mixing the cement with the colemanite and/or hilgardite as an aggregate excluding ulexite and sassolite contained in the ore of the evaporation type sedimentary deposit. 10. An assembly of spent nuclear fuel assembly storage containers in which spent nuclear fuel assembly storage containers each including a metal cask storing a spent nuclear fuel assembly and a container body storing the metal cask and having a substantially hexagonal tubular outer surface are arranged,wherein the container bodies are arranged to have a honeycomb structure while the outer surfaces are brought into contact with each other, andwherein a space without the spent nuclear fuel assembly storage container is provided in such a manner that at least one outer surface of the bodies contacts external air. 11. An assembly of spent nuclear fuel assembly storage containers in which spent nuclear fuel assembly storage containers each including a metal cask storing a spent nuclear fuel assembly and a container body storing the metal cask and having a substantially hexagonal tubular outer surface are arranged,wherein the container bodies are arranged to have a honeycomb structure while the outer surfaces are brought into contact with each other, andwherein container bodies not storing the metal casks are arranged at a further outside of spent nuclear fuel assembly storage containers arranged at an outside of the spent nuclear fuel assembly storage containers.