Patent Number: 054405980
Section: claims

1. A nuclear fuel bundle comprising: a plurality of fuel rods arranged in a generally square array, each of said rods having a predetermined concentration of fissile material with at least a majority of said rods including plutonium;  a predetermined number of said rods having a concentration of a material for absorbing neutrons, said predetermined number of rods constituting an interior array thereof, all of which predetermined number of rods be within a surrounding exterior array of fuel rods of said plurality thereof;  said predetermined number of rods in said interior array thereof having said concentration of material for absorbing neutrons being in excess of 20% of the total number of said plurality of rods in said fuel bundle.  a plurality of fuel rods arranged in said bundle, each of said rods having a predetermined concentration of fissile material with at least a majority of said rods including plutonium, a predetermined number of said rods having a concentration of a material for absorbing neutrons, said fuel bundle having a reactivity curve substantially corresponding to the reactivity curve illustrated in FIG. 4c of the drawings. 2. A nuclear fuel bundle according to claim 1 wherein said fissile material includes enriched uranium and plutonium and said neutron absorbing material comprises gadolinium. 3. A nuclear fuel bundle according to claim 1 wherein said exterior array of fuel rods is void of a burnable poison. 4. A nuclear fuel bundle according to claim 3 wherein said interior array of rods having said concentration of material for absorbing neutrons is arranged geometrically symmetrically about a central axis of the fuel bundle parallel to said rods. 5. A nuclear fuel bundle according to claim 4 wherein said interior array of rods having said concentration of material for absorbing neutrons constitutes all of the fuel rods within said bundle except said surrounding exterior array of said rods. 6. A nuclear fuel bundle according to claim 2 wherein said interior array of rods having gadolinium constitutes all of the fuel rods within said bundle except said surrounding exterior array of said rods. 7. A nuclear fuel bundle according to claim 1 wherein each of said rods includes a predetermined concentration of plutonium. 8. A nuclear fuel bundle according to claim 1 wherein each of said majority of said rods including plutonium has a percentage concentration of fissile plutonium in excess of a percentage concentration of any other fissile material in said rods. 9. A nuclear fuel bundle according to claim 1 wherein said fissile material includes enriched uranium and plutonium and said neutron absorbing material comprises gadolinium, said exterior array of fuel rods being void of a material for absorbing neutrons. 10. A nuclear fuel bundle according to claim 9 wherein said interior array of rods having gadolinium constitutes all of the fuel rods within said bundle except said surrounding exterior array of said rods, each of said rods including a predetermined concentration of plutonium. 11. A nuclear fuel bundle according to claim 10 wherein each of said majority of said rods including plutonium has a percentage concentration of fissile plutonium in excess of a percentage concentration of any other fissile material in said rods. 12. A nuclear fuel bundle according to claim 1 having a reactivity curve substantially corresponding to the reactivity curve illustrated in FIG. 4c of the drawings. 13. A nuclear fuel bundle according to claim 1 wherein said fissile material includes enriched uranium and plutonium and said neutron absorbing material comprises gadolinium, each of said interior array of rods having a percentage concentration of gadolinium, plutonium and enriched uranium. 14. A nuclear fuel bundle according to claim 13 wherein each of said rods includes a predetermined concentration of plutonium, said fuel bundle having a reactivity curve substantially corresponding to the reactivity curve illustrated in FIG. 4c of the drawings. 15. A nuclear fuel bundle comprising: 16. A nuclear fuel bundle according to claim 15 wherein said fissile material includes enriched uranium and plutonium and said neutron absorbing material comprises gadolinium. 17. A nuclear fuel bundle according to claim 15 wherein said rods are arranged in said fuel bundle in interior and exterior arrays thereof with said exterior array surrounding said interior array, only the rods of said interior array thereof having said neutron absorbing material, said exterior array of rods being void of said neutron absorbing material. 18. A nuclear fuel bundle according to claim 17 wherein said fissile material includes a concentration of enriched uranium and said neutron absorbing material comprises gadolinium. 19. A nuclear fuel bundle according to claim 18 wherein each of said rods in said fuel bundle includes at least concentrations of plutonium and enriched uranium. 20. In a nuclear reactor core having a plurality of fuel bundles, at least a first bundle of said plurality thereof containing a plurality of fuel rods having a concentration of enriched uranium with certain of said rods thereof having a concentration of a burnable poison, said first bundle having a reactivity curve substantially corresponding to a reactivity curve illustrated in FIG. 2c of the drawings and at least a second bundle of said plurality thereof containing a plurality of fuel rods each having a concentration of enriched uranium and plutonium and certain of said rods of said second bundle forming an interior array thereof having a concentration of burnable poison surrounded by an exterior array of rods void of the burnable poison, said second bundle having a reactivity curve substantially corresponding to the reactivity curve of FIG. 4c of the drawings, the reactivity curves of FIGS. 2c and 4c substantially corresponding to one another. 21. In a nuclear reactor core having a plurality of fuel bundles, at least a first bundle of said plurality thereof containing a plurality of fuel rods having a concentration of enriched uranium with certain of said rods thereof having a concentration of a burnable poison, said first bundle having a reactivity curve showing reactivity as a function of fuel exposure, at least a second bundle of said plurality thereof containing a plurality of fuel rods each having a concentration of enriched uranium and plutonium and certain of said rods of said second bundle forming an interior array thereof having a concentration of burnable poison surrounded by an exterior array of rods void of the burnable poison, said certain of said rods forming said interior array thereof being in excess of 20% of the total number of said plurality of rods in said second bundle, said second bundle having a reactivity curve showing full reactivity as a function of fuel exposure and substantially corresponding to the reactivity curve of said first bundle.