Hitachi, Ltd.

Yoko Yuchi

Motoo Aoyama

Junichi Yamashita

Katsumasa Haikawa

Akihiro Yamanaka

Akiko Kanda

Junichi Koyama

Takaaki Mochida

In an arrangement of an initial core, the core is loaded with 572 high enrichment fuel assemblies H with 4.2 wt % average enrichment and 300 low enrichment fuel assemblies L with 1.5 wt % average enrichment. The average enrichment of the core is about 3.3 wt %. In this core, only the low enrichment fuel assemblies are loaded into the most outer position of the core and the high enrichment fuel assemblies are loaded into an area other than the most outer position. In this arrangement, the average enrichment of reload fuel assemblies is 3.7 wt %.

Initial core

In an initial core of the present invention, a low enrichment fuel assembly having the lowest average enrichment factor and three fuel assemblies having a higher average enrichment factor than that of the low enrichment fuel assembly are arranged in a square shape, control rods of a cross shape are arranged at each of four corners of the square shape to constitute a unit loading pattern, and a plurality of the unit loading patterns are provided in the central region of the core, the fuel assemblies having the higher average enrichment factor are divided by a diagonal line into a first region of the side of the control rods and a second region of the side opposite to the control rods, and the number of the gadolinia-containing fuel rods is greater in the second region by at least two than in the first region. The initial core having an enhanced average enrichment factor for accomplishing a high exposure, makes it possible to maintain thermal margin, to suitably suppress the excess reactivity and to improve fuel economy.

Initial core and fuel assembly

Growing community of inventors

Hitachi, Japan

Yoko Yuchi