Patent Number: 06233302&
Section: claims

1. A method of fueling a nuclear reactor comprising: loading a first group of fresh unburnt MOX fuel rod assemblies into a first set of predetermined positions in a core of the reactor, in accordance with a predetermined location schedule;  loading a second group of MOX fuel rod assemblies which have been burned once, into a second set of predetermined positions which are selectively arranged in the core with respect to the first set of predetermined positions, in accordance with the predetermined location schedule; and  loading a third group of MOX fuel rod assemblies which have been burned twice, into a third set of predetermined positions which are selectively arranged in the core with respect to the first and second set of predetermined positions, in accordance with the predetermined location schedule  wherein upon completion of loading the core, the core consists essentially of said first, second and third groups, and burnable absorber rods containing urania-erbia.  a first group of fresh MOX fuel rod assemblies which are unburnt and which are loaded into a first set of predetermined positions in the core, in accordance with a predetermined location schedule;  a second group of MOX fuel rod assemblies which have been burned once, and which are loaded into a second set of predetermined positions which are selectively arranged in the core with respect to the first set of predetermined positions, in accordance with the predetermined location schedule;  a third group of MOX fuel rod assemblies which have been burned twice, and which are loaded into a third set of predetermined positions which are selectively arranged in the core with respect to the first and second set of predetermined positions, in accordance with the predetermined location schedule and  burnable absorber rods containing urania-erbia. 2. A method of fueling as set forth in claim 1, further comprising the step of selecting the first group of fuel rod assemblies so as to comprise one or more of a plurality of predetermined octantly symmetrical assembly designs which each contain different amounts of plutonium, and so that an equilibrium cycle for the core exhibits a predetermined relationship with a predetermined equilibrium cycle produced using urania fuel. 3. A method of fueling as set forth in claim 2, further comprising the step of distributing the amount of plutonium, which is contained in the fuel rods of each of the plurality of octantly symmetrical assembly designs, in accordance with a plurality of predetermined distribution schedules. 4. A nuclear reactor core consisting essentially of: 5. A nuclear reactor core as set forth in claim 4, wherein the first group of fuel rod assemblies comprise one or more of a plurality of predetermined octantly symmetrical assembly designs which each contain different amounts of plutonium, and are so configured that an equilibrium cycle for the core exhibits a predetermined relationship with a predetermined equilibrium cycle produced using urania fuel. 6. A nuclear reactor as set forth in claim 5, wherein the amount of plutonium which is contained in the fuel rods of each of the plurality of octantly symmetrical assembly designs, is distributed in accordance with a respective plurality of predetermined distribution schedules.