Patent Number: 048184780
Section: claims

1. A mini-bundle of fuel rods for use in each of a plurality of separate compartments of a BWR fuel assembly, said compartments being formed by an outer hollow tubular flow channel for directing the flow of coolant/moderator fluid through the fuel assembly and a hollow water cross extending through said channel and attached along the interior of said channel so as to provide a central hollow channel for flow of coolant/moderator fluid through the fuel assembly and to divide said outer channel into said separate compartments, said mini-bundle of fuel rods comprising: (a) an interior array of fuel rods in said mini-bundle thereof, each of said fuel rods in said interior array being of a first predetermined diameter size; and  (b) a peripheral array of fuel rods in said mini-bundle thereof, each of said fuel rods in said peripheral array being of a second predetermined diameter size greater than said first diameter size.  (a) an interior array of fuel rods in said mini-bundle, each of said fuel rods in said interior array thereof being of a first predetermined diameter size; and  (b) a peripheral array of fuel rods in said mini-bundle, each of said fuel rods in said peripheral array thereof being of a second predetermined diameter size greater than said first diameter size.  (a) a bundle of spaced fuel rods;  (b) an outer hollow tubular flow channel surrounding said fuel rods so as to direct flow of coolant/moderator fluid therealong; and  (c) a water cross extending through said channel and having a plurality of radially extending panels dividing said bundle of fuel rods into a plurality of separate fuel rod mini-bundles;  (d) each of said fuel rod mini-bundles having an interior array of fuel rods of a first predetermined diameter size;  (e) each of said fuel rod mini-bundles having a peripheral array of fuel rods of a second predetermined diameter size greater than said first diameter size. 2. The fuel rod mini-bundle as recited in claim 1, wherein said interior array of fuel rods forms an inner, centrally-located, generally squared pattern. 3. The fuel rod mini-bundle as recited in claim 2, wherein the only fuel rods present in said inner squared pattern are said fuel rods of said first diameter size. 4. The fuel rod mini-bundle as recited in claim 1, wherein said peripheral array of fuel rods forms an outer, peripherally-located, generally squared annular pattern which surrounds said interior array. 5. The fuel rod mini-bundle as recited in claim 4, wherein the only fuel rods present in said outer squared pattern are said fuel rods of said second diameter size. 6. The fuel rod mini-bundle as recited in claim 1, wherein said interior and peripheral arrays of fuel rods together comprise a squared array in which said fuel rods of each array are aligned with one another in columns and rows. 7. The fuel rod mini-bundle as recited in claim 1, wherein said fuel rods of said interior array are ten to twelve percent less in diameter size compared to said fuel rods of said peripheral array. 8. In a nuclear fuel assembly including an outer hollow tubular flow channel providing an enclosure for directing the flow of coolant/moderator fluid through the fuel assembly and a water cross extending through said channel and having a plurality of radially extending members attached along the interior of said channel and dividing it into a plurality of separate compartments, a mini-bundle of elongated fuel rods located in each compartment between the interior of said outer flow channel and exterior of said radially extending members of said water cross, said fuel rod mini-bundle comprising: 9. The fuel assembly as recited in claim 8, wherein said interior array of fuel rods forms an inner, centrally-located, generally squared pattern. 10. The fuel assembly as recited in claim 9, wherein the only fuel rods present in said inner squared pattern are said fuel rods of said first diameter size. 11. The fuel assembly as recited in claim 8, wherein said peripheral array of fuel rods forms an outer, peripherally-located, generally squared annular pattern which surrounds said interior array. 12. The fuel assembly as recited in claim 11, wherein the only fuel rods present in said outer squared pattern are said fuel rods of said second diameter size. 13. The fuel assembly as recited in claim 8, wherein said interior and peripheral arrays of fuel rods together comprise a squared array in which said fuel rods of each array are aligned with one another in columns and rows. 14. The fuel assembly as recited in claim 8, wherein said fuel rods of said interior array are ten to twelve percent less in diameter size compared to said fuel rods of said peripheral array. 15. In a fuel assembly, the combination comprising: 16. The fuel assembly as recited in claim 15, wherein said interior array of fuel rods forms an inner, centrally-located, generally squared pattern. 17. The fuel assembly as recited in claim 16, wherein the only fuel rods present in said inner squared pattern are said fuel rods of said first diameter size. 18. The fuel assembly as recited in claim 15, wherein said peripheral array of fuel rods forms an outer, peripherally-located, generally squared annular pattern which surrounds said interior array. 19. The fuel assembly as recited in claim 18, wherein the only fuel rods present in said outer squared pattern are said fuel rods of said second diameter size. 20. The fuel assembly as recited in claim 15, wherein said interior and peripheral arrays of fuel rods together comprise a squared array in which said fuel rods of each array are aligned with one another in columns and rows. 21. The fuel assembly as recited in claim 15, wherein said fuel rods of said interior array are ten to twelve percent less in diameter size compared to said fuel rods of said peripheral array.