Patent Number: 055984509
Section: claims

1. In a fuel bundle for a boiling water nuclear reactor comprising a plurality of fuel rods secured within an array and extending between upper and lower tie plates, and including at least one additional fuel rod extending from said lower tie plate but terminating short of said upper tie plate, the improvement comprising a removable extension rod secured to said at least one additional fuel rod and extending substantially to said upper tie plate. 2. The fuel bundle of claim 1 wherein a plurality of spacers are provided at axially spaced locations along said bundle and wherein said at least one additional rod terminates adjacent and above an upper edge of one of said spacers. 3. The fuel bundle of claim 1 wherein said extension rod is secured to the top of said at least one additional rod such that said extension rod and said at least one additional rod are substantially co-linear. 4. The fuel bundle of claim 1 wherein said extension rod is hollow and filled substantially with single phase water to increase reactivity. 5. The fuel bundle of claim 1 wherein said extension rod is substantially devoid of any hydrogen bearing material. 6. The fuel bundle of claim 5 wherein said extension rod is formed of solid Zircaloy material. 7. The fuel bundle of claim 5 wherein said extension rod is formed of Zircaloy material in tubular form, and wherein gadolinium is added to further reduce reactivity. 8. In a fuel bundle for a nuclear reactor having fuel rods secured with an array and extending generally axially between upper and lower tie plates, and a plurality of spacers at axially spaced locations along said bundle holding said fuel rods in the array, said fuel rods including a first plurality of full length rods secured at lower ends thereof to the lower tie plate and at upper ends thereof to the upper tie plate, and a second plurality of partial length rods secured at lower ends thereof to the lower tie plate, with upper ends thereof terminating above and adjacent one or more of said spacers, the improvement comprising fuel rod extension members removably attached to at least some of the plurality of partial length fuel rods such that said at least some of the plurality of partial length fuel rods extend substantially to said upper tie plate, and such that said fuel rod extension members can be removed from the bundle independently of the partial length fuel rods to which they are attached. 9. The fuel bundle of claim 8 wherein said fuel rod extension members are formed of solid Zircaloy material. 10. The fuel bundle of claim 8 wherein said fuel rod extension members are formed as hollow tubes. 11. The fuel bundle of claim 10 wherein said fuel rod extension members contain single phase water. 12. The fuel bundle of claim 10 wherein said fuel rod extension members contain gadolinium. 13. In a fuel bundle for a nuclear reactor having fuel rods secured within an array and extending generally axially between upper and lower tie plates, and a plurality of spacers at axially spaced locations along said bundle holding said fuel rods in the array, said fuel rods including a first plurality of full length rods secured at lower ends thereof to the lower tie plate and at upper ends thereof to the upper tie plate, and a second plurality of partial length rods secured at lower ends thereof to the lower tie plate, with upper ends thereof terminating above and adjacent one of said spacers, the improvement comprising means for causing all of said fuel rods to behave similarly relative to coolant flow pressure drop in the channel, and associated means for varying reactivity of the second plurality of partial length rods.