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A BWR fuel assembly includes an outer hollow tubular flow channel, a water cross and a plurality of mini-bundles of fuel rods. The outer channel provides an enclosure for directing the flow of coolant/moderator fluid through the fuel assembly. The water cross extends through the outer channel and ha

A BWR fuel assembly includes an outer hollow tubular flow channel, a water cross and a plurality of mini-bundles of fuel rods. The outer channel provides an enclosure for directing the flow of coolant/moderator fluid through the fuel assembly. The water cross extends through the outer channel and has a plurality of radially extending members attached along the interior of the outer channel which divide it into a plurality of separate compartments. One mini-bundle of elongated fuel rods is located in each compartment between the interior of the outer flow channel and exterior of the radially extending members of the water cross. Each fuel rod mini-bundle is comprised of an interior array of fuel rods with each fuel rod being of a first predetermined diameter size, and a peripheral array of fuel rods with each fuel rod being of a second predetermined diameter size greater than the first diameter size. The interior array of fuel rods forms an inner, centrally-located, generally squared pattern, whereas the peripheral array of fuel rods forms an outer, peripherally-located, generally squared annular pattern which surrounds the interior array. The fuel rods in both arrays are aligned with one another in columns and rows. The fuel rods of the interior array are ten to twelve percent less in diameter size compared to the fuel rods of the peripheral array.

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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 sai

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.