Fail-free fuel bundle assembly

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, and
• different axial lengths;
• and
• a rod spacer grid securely retained between each pair of axially adjacent interconnected rod segments to form an array of substantially equally spaced rods,
• wherein
• each 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, and
• two 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.

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, and
• a 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 have
• central 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, and
• at least one of,
• different axial lengths;
• different nuclear fuel enrichment values;
• and
• different isotope targets.