Patent Number: 
Section: claims

1. A package for transporting and/or storing radioactive materials such as nuclear fuel assemblies, comprising:an outer wall element, anda cooling element which is attached to the outer wall element, wherein the cooling element comprises a base and at least one fin which is integral with or fixed to the base, wherein the fin projects outwardly from the outer wall element and outwardly from the package,wherein the base extends on either side of the fin respectively towards two opposite side ends of the base, wherein each of the side ends is attached to the outer wall element via a weld. 2. The package according to claim 1, wherein the outer surface of the outer wall element comprises a recess forming a housing for the base, wherein at least one of the side ends of the base is connected to at least one side edge of the housing via a weld. 3. The package according to claim 2, wherein the base is housed in the housing so as to be flush with the surface of the outer wall element at least at one edge of the housing. 4. The package according to claim 2, wherein the housing has a width between its side edges which is at most equal to the sum of the width of the base and the width of the welds. 5. The package according to claim 1, wherein the height of the base along at least one of the side ends is higher than or equal to half the mean thickness of the fin. 6. The package according to claim 1, wherein the outer wall element, the base and/or the fin comprise copper. 7. The package according to claim 1, wherein the base and the fin are integrally formed as a single piece. 8. The package according to claim 1, comprising:a neutron shield block andat least one heat conducting inner element,wherein the outer wall element is integral with or fixed to the heat conducting inner element, wherein the heat conducting inner element is in contact with a ferrule of the package,wherein the ferrule, the heat conducting inner element and the outer wall element surround at least partially the neutron shield block. 9. The package according to claim 1, wherein the cooling element comprises at least two fins and a base which is common to the fins,wherein the base extends on either side of the fin towards two opposite side ends of the base, wherein each of the ends is attached to the outer wall element via a weld. 10. The package according to claim 1, comprising a second cooling element which is attached to the outer wall element,wherein the second cooling element comprises at least one fin which is integral with or fixed to the base,wherein the distance between the cooling elements is lower than the height of at least one of the fins. 11. A heat conducting element for a package for transporting and/or storing radioactive materials, comprising:a heat conducting inner element,at least one cooling element, andan outer wall element for forming an outer shell portion of the package, wherein the heat conducting inner element and the cooling element are located on either side of the outer wall element, wherein the outer wall element mechanically and thermally connects the heat conducting inner element to the cooling element,wherein the cooling element comprises a base and at least one fin which is integral with or fixed to the base,wherein the base extends on either side of the fin respectively towards two side ends opposite to the base, wherein each of the side ends is attached to the outer wall element via a weld. 12. A method for manufacturing a package for transporting and/or storing radioactive materials according to claim 1,comprising a step of welding each of the two opposite side ends of the base to the outer wall element. 13. The manufacturing method according to claim 12, wherein the width of the base between its two side ends is higher than or equal to twice the mean thickness of the fin. 14. The manufacturing method according to claim 12, wherein the base is welded to the outer wall element by electron beam or by laser beam welding. 15. The manufacturing method according to claim 12, wherein the base is arranged in a housing provided in the outer wall element, wherein the base is welded in the housing along a thermal contact interface, wherein the thermal contact interface is tilted at an angle between 0° to 30° with respect to the height direction of the fin. 16. The manufacturing method according to claim 12, comprising a step of making notches in a plate to form fins of the cooling element, wherein the notches are spaced from each other along the longitudinal direction of the plate. 17. The manufacturing method according to claim 16, wherein the plate comprises the base of the cooling element,wherein the step of welding the side ends of the base along the longitudinal direction of the plate occurs after the step of making the notches. 18. The manufacturing method according to claim 16, wherein the method comprises a step of twisting the fins about their longitudinal axis after the welding step.