Patent Number: 
Section: claims

1. A method of making a nuclear fuel duct, comprising:forming a first hollow structure having a first cross-sectional geometry by extruding or pilgering;forming a second hollow structure having a second cross-sectional geometry different from the first cross-sectional geometry by extruding or pilgering; anddisposing the first hollow structure interior to the second hollow structure to form a nuclear fuel duct;joining a side of the first hollow structure to a corner of the second hollow structure via a structural member;wherein the first hollow structure is configured to expand in at least one dimension under stress and cause at least portion of the first hollow structure to contact the second hollow structure; andwherein the second hollow structure is configured to distribute at least a portion of the stress of the first hollow structure therethrough. 2. The method of claim 1, wherein extruding comprises extruding a metal sheet, forming the metal sheet into a polygonal shape and closing the polygonal shape. 3. The method of claim 1, wherein extruding comprises extruding the first cross-sectional geometry of the first hollow structure. 4. The method of claim 1, wherein extruding comprises extruding the second cross-sectional geometry of the second hollow structure. 5. The method of claim 1, further comprising joining a side of the first hollow structure to a side of the second hollow structure. 6. The method of claim 1, further comprising compartmentalizing axially an interior of the first hollow structure. 7. A method of making a nuclear fuel duct, comprising:providing a first hollow structure having a first cross-sectional geometry configured to expand in at least one dimension under stress, the first hollow structure configured to contain a plurality of nuclear fuel elements located therein;providing a second hollow structure having a second cross-sectional geometry defining sides and corners, the second cross-sectional geometry different than the first cross-sectional geometry;placing the second hollow structure external to and around the first hollow structure to form a nuclear fuel duct such that a space is defined between the first hollow structure and the corners of the second hollow structure; andjoining a side of the first hollow structure to a corner of the second hollow structure via a structural member. 8. The method of claim 7, wherein providing the first hollow structure includes forming metal sheets into a polygonal shape and closing the polygonal shape by welding a seam, riveting, forming a seam and tack welding, forming a seam and isostatically compressing the seam, or diffusion bonding. 9. The method of claim 7, wherein providing the first hollow structure includes forming by extruding or pilgering. 10. The method of claim 9, wherein extruding comprises extruding a metal sheet, forming the metal sheet into a polygonal shape and closing the polygonal shape. 11. The method of claim 9, wherein extruding comprises extruding the first cross-sectional geometry of the first hollow structure. 12. The method of claim 7, wherein providing the second hollow structure comprises extruding the second cross-sectional geometry of the second hollow structure. 13. The method of claim 7, further comprising coupling the first hollow structure to the second hollow structure with at least one structural member. 14. A method of making a nuclear fuel duct, comprising:providing a first hollow structure having a first polygonal cross-sectional geometry configured to contain a plurality of nuclear fuel elements therein;providing a second hollow structure having a second polygonal cross-sectional geometry different than the first polygonal cross-sectional geometry; andplacing the first hollow structure internal to the second hollow structure with a portion of the first hollow structure in physical contact with the second hollow structure in order for the second hollow structure to distribute therethrough at least a portion of stress caused by expansion of the first hollow structure;wherein placing the first hollow structure internal to the second hollow structure with a portion of the first hollow structure in physical contact with the second hollow structure comprising placing a structural member connecting a side wall of the first hollow structure with a corner of the second hollow structure. 15. The method of claim 14, wherein providing a first hollow structure comprises extruding or pilgering the first hollow structure. 16. The method of claim 14, wherein providing a second hollow structure comprises extruding or pilgering the second hollow structure. 17. The method of claim 14, wherein placing the first hollow structure internal to the second hollow structure with a portion of the first hollow structure in physical contact with the second hollow structure comprising contacting a side wall of the first hollow structure with a side wall of the second hollow structure. 18. The method of claim 14, wherein providing the first hollow structure includes forming metal sheets into a polygonal shape and closing the polygonal shape along a seam. 19. The method of claim 14, further comprising axially compartmentalizing an interior of the first hollow structure.