Patent Number: 
Section: claims

1. A fuel bundle for a nuclear reactor core, said fuel bundle comprising:a plurality of rods including at least one of fuel rods and isotope production rods, each rod including a plurality of axially adjacent interconnected rod segments with at least a first rod segment and a second rod segment, each of the rod segments having a first end portion, a second end portion, and a central body portion between the first end portion and the second end portion, the central body portion including an internal cavity, the first and second rod segments having different outside diameters;a rod spacer grid securely retained between each pair of axially adjacent interconnected rod segments to form an array of substantially equally spaced rods; andan elongate tubular channel in which the arrayed rods are housed,whereineach of the rod spacer grids includes a plurality of annular disks, at least one of the plurality of annular disks securely retained between the first rod segment and the second rod segment, the at least one annular disk having a top horizontal surface and a bottom horizontal surface,the central body portion of the first rod segment has an outer diameter of D1 and the first end portion of the first rod segment includes a first horizontal surface contacting the bottom horizontal surface of the at least one annular disk, and the first end portion of the first rod segment has a length Y defined as a distance from the first horizontal surface to the central body portion of the first rod segment,the central body portion of the second rod segment has an outer diameter of D2 and the second end portion of the second rod segment includes a second horizontal surface contacting the top horizontal surface of the at least one annular disk, and the second end portion of the second rod segment has a length N defined as a distance from the second horizontal surface to the central body portion of the second rod segment, andlength N>length Y and diameter D1>diameter D2. 2. The fuel bundle of claim 1, wherein the internal cavity is for retaining one of nuclear fuel and a plurality of isotope production targets such that each rod segment has a respective enrichment value and at least two of the rod segments of at least one rod have different enrichment values. 3. The fuel bundle of claim 1, wherein each rod segment has a respective axial length and at least two of the rod segments of at least one rod have different axial lengths. 4. The fuel bundle of claim 1, wherein the first end portion is a solid first end portion and the second end portion is a partially solid second end portion, and the first and second end portions are mateable to interconnect axially adjacent rod segments such that a respective one of the spacer grids is fixedly retained there between. 5. The fuel bundle of claim 4, wherein the first and second end portions are fabricated from one of zirconium. zircaloy-2, and zircaloy-4. 6. The fuel bundle of claim 4, wherein the first end portion comprises a male connector and the second end portion comprises a female receptacle structured to securely mate with a male connector of an axially adjacent rod segment to interconnect axially adjacent rod segments. 7. The fuel bundle of claim 6, wherein each spacer grid includes a plurality of interconnected annular disks, each annular disk including an aperture sized to receive the male connector such that each respective annular disk can be securely retained between axially adjacent, interconnected rod segments. 8. The fuel bundle of claim 7, wherein each annular disk is structured to have an outside diameter that is substantially equal to, or less than, the outside diameter of the respective rod segment interconnected below each respective annular disk, with respect to orientation within the reactor core. 9. The fuel bundle of claim 4, wherein the solid first end and the partially solid second end portions are mateable such that each interconnection of axially adjacent rod segments comprises:a first section of solid material adjacent a first side of the respective spacer grid, the first section of solid material having an axial length sufficient to prevent rupturing the internal cavity of the respective central body due to fretting damage by debris entrapped and the interconnection of the respective axially adjacent rod segments; anda second section of solid material adjacent an opposing second side of the respective spacer grid, the second section of solid material having an axial length sufficient to prevent rupturing the internal cavity of the respective central body due to fretting damage by debris entrapped and the interconnection of the respective axially adjacent rod segments. 10. The fuel bundle of claim 9, wherein, with respect to orientation within the reactor core, the first section of solid material is located above the respective spacer grid and has an axial length greater than the axial length of the second section of solid material located below the respective spacer grid. 11. A fuel bundle for a nuclear reactor core, said fuel bundle comprising:a plurality of rods comprised of at least one of fuel rods and isotope production rods, each rod including a plurality of axially adjacent interconnected rod segments, at least two of the rod segments having at least one of,different outside diameters, the outside diameters being outside diameters of central body portions of the at least two rods, and the larger of the outside diameters is substantially equal to an outside diameter of an annular disk that is secured between two axially adjacent interconnected rod segments and configured to provide lateral and axial support to the two axially adjacent interconnected rod segments, anddifferent axial lengths; anda rod spacer grid securely retained between each pair of axially adjacent interconnected rod segments to form an array of substantially equally spaced rods,whereineach rod segment comprises a central body having a respective internal cavity, a solid first end portion having a first horizontal surface configured to contact a lower horizontal surface of a respective one of the rod spacer grids and a length Y defined as a distance from the first horizontal surface to the internal cavity of the rod segment and, a partially solid second end portion having a second horizontal surface configured to contact an upper horizontal surface of a respective one of the rod spacer grids and a length N defined as a distance from the second horizontal surface to the internal cavity of the rod segment, and the first and second end portions are mateable to interconnect axially adjacent rod segments such that the respective spacer grids are fixedly retained there between,the first end portion comprises a male connector and the second end portion comprises a female receptacle configured to securely mate with a male connector to interconnect axially adjacent rod segments,each spacer grid includes a plurality of interconnected annular disks, each annular disk including an aperture sized to receive the male connector such that each respective annular disk can be securely retained between axially adjacent interconnected rod segments, andtwo rod segments securely retaining one of the spacer grids have different diameters and the length N of one of the two rod segments is greater than the length Y of the other of the two rod segments. 12. The fuel bundle of claim 11, wherein the first and second end portions are fabricated from one of zirconium, zircaloy-2, zircaloy-4. 13. The fuel bundle of claim 11 wherein each interconnected annular disk is structured to have an outside diameter that is substantially equal to, or less than, the outside diameter of the respective rod segment interconnected below each respective annular disk, with respect to orientation within the reactor core. 14. The fuel bundle of claim 11, wherein the solid first end and the partially solid second end portions are mateable such that each interconnection of axially adjacent rod segments comprises:a first section of solid material adjacent a first side of the respective spacer grid, the first section of solid material having an axial length sufficient to prevent rupturing the internal cavity of the respective central body due to fretting damage by debris entrapped and the interconnection of the respective axially adjacent rod segments; anda second section of solid material adjacent an opposing second side of the respective spacer grid, the second section of solid material having an axial length sufficient to prevent rupturing the internal cavity of the respective central body due to fretting damage by debris entrapped and the interconnection of the respective axially adjacent rod segments. 15. The fuel bundle of claim 14, wherein, with respect to orientation within the reactor core, the first section of solid material is located above the respective spacer grid and has an axial length greater than the axial length of the second section of solid material located below the respective spacer grid. 16. A rod for a fuel bundle for a nuclear reactor core, said rod comprising:one of a fuel rod and an isotope production rod;a plurality of axially adjacent interconnected rod segments, each rod segment including,a central body portion with an internal cavity for retaining one of nuclear fuel and a plurality of isotope production targets,a solid first end portion having a first horizontal surface configured to contact a lower surface of a spacer grid and an axial length N sufficient to prevent rupturing the internal cavity due to fretting damage by debris entrapped at the interconnection of the respective axially adjacent rod segments, the axial length N being defined as a distance from the first horizontal surface to the central body portion, anda partially solid second end portion having a second horizontal surface configured to contact an upper surface of a spacer grid and an axial length Y sufficient to prevent rupturing the internal cavity of the respective central body due to fretting damage by debris entrapped at the interconnection of the respective axially adjacent rod segments, the axial length Y being defined as a distance from the second horizontal surface to the central body portion, wherein a solid end portion of one rod segment is configured to attach to a partially solid second end portion of another rod segment such that a spacer grid between the one rod segment and the another rod segment is restrained;at least two of the rod segments havecentral body portions with different outside diameters and the N of one of the at least two rod segments having the smaller diameter is greater than the Y of the other of the at least two rod segments and the spacer grid includes a plurality of annular disks, at least one of the plurality of annular disks having an outer diameter substantially equal to the larger of the outside diameters, andat least one of,different axial lengths;different nuclear fuel enrichment values; anddifferent isotope targets. 17. The rod for a fuel bundle for a nuclear reactor core according to claim 16, wherein the axial length of the partially solid second end portion of the one rod segment is longer than an axial length of a solid first end portion of the another rod segment configured to connect to the second end portion of the one rod segment. 18. The fuel bundle for a nuclear reactor core of claim 11, wherein at least two of the rod segments have at least one of different nuclear fuel enrichment values and different isotope targets. 19. The fuel bundle of claim 1, wherein each rod includes more than two axially adjacent interconnected rod segments. 20. The fuel bundle of claim 11, wherein each rod includes more than two axially adjacent interconnected rod segments.