Hitachi, Ltd.

Hitachi Engineering Co., Ltd.

Toshiro Yoshioka

Takaaki Mochida

Michihiro Ozawa

Junichi Yamashita

Junichi Koyama

Katsumasa Haikawa

Akihiro Yamanaka

Mitsunari Nakamura

Takao Igarashi

Yoshihiri Iwashita

Hiroko Haraguchi

In an initial core constituted by various kinds of fuel assemblies having a different average enrichment of uranium 235 four fuel assemblies having the lowest average enrichment constitute a square shaped cell. Three fuel assemblies having the highest average enrichment constitute an L-shaped cell, and the L-shaped cell is arranged at corners of the square shaped cells, whereby each assembly of the L-shaped cell adjoins a square shaped cell. The ratio of the number of assemblies of the L-shaped cell to the total number of fuel assemblies in the core is 10% or more.

Initial core of nuclear power plant

A fuel assembly including a channel box, upper and lower tie plates, fuel rods inserted in the channel box and held at upper and lower end portions by the upper and lower tie plates, a water rod disposed among the fuel rods and spacers for keeping the fuel rods and the water rod spaced from one another. The water rod has a diameter larger than that of each of the fuel rods and the upper end of the water rod has a height substantially as high as an upper end of an effective enriched fuel section of each fuel rod.

Fuel assembly

A nuclear fuel assembly has a plurality of fuel rods each containing a multiplicity of fuel pellets. The fuel rods include a plurality of first fuel rods and a plurality of second fuel rods. Each of the first fuel rods contains a burnable poison over substantially the entire axial length thereof. The first fuel rod also has a greater means enrichment in the upper axial region thereof than that in the lower axial region thereof. Each of the second fuel rods contains no burnable poison and has a uniform enrichment distribution over substantially the entire axial length thereof. In each cross-section of the fuel assembly perpendicular to the axis thereof, the outer peripheral portion has a greater mean enrichment than the central portion. The first fuel rods are disposed in the peripheral portion except the outermost peripheral portion of the cross-section of the fuel assembly.

Nuclear fuel assembly

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Hitachi, Japan

Toshiro Yoshioka