| 摘要 |
A fuel assembly to be charged in a reactor core comprises a channel box extending vertically in the core and having a substantially square cross section, a number of fuel rods arranged in the channel box in the form of a lattice in cross sections thereof, the fuel rods extending vertically in the channel box with spaces between each other, a plurality of spacers for supporting the fuel rods in the channel box so as to maintain axial spaces between the fuel rods and upper and lower tie plates for supporting upper and lower end portions of the fuel rods. The fuel rods include first type fuel rods arranged at and near four corner portions of the channel box, each of the first type fuel rods being composed of upper and lower areas, except for extreme upper and lower ends, in which a fuel enrichment of the upper area is made lower than that of the lower area. Furthermore, the fuel rods further include other type fuel rods being arranged at portions other than the first type fuel rods and including second type fuel rods, each of said second type fuel rods being composed of upper and lower areas, except for extreme upper and lower ends, in which a fuel enrichment of the upper area is made higher than that of the lower area. The boundary portions between the first and second type fuel rods are disposed in substantially the same level or different levels.
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