Hitachi, Ltd.

Koki Yamauchi

Yasunori Bessho

Mikio Sakurai

Takao Igarashi

Sadayuki Izutsu

Shiro Nakamura

A plurality of fuel rods containing fissile material are arranged in triangle lattices. A plurality of water rods groups are arranged among the fuel rods. Each of the water rods groups includes no fuel rod but a plurality of water rods which are arranged adjacently each other in triangle lattices having substantially same pitch as the fuel rods. The water rods groups are arranged not adjacently each other, and are surrounded with the fuel rods. the outer diameter of the water rod is smaller than the pitch. The fuel assembly is able to suppress increment of pressure loss because of formation of coolant path among adjacent water rods. Further, void reactivity coefficient is able to be small.

Fuel assembly

A nuclear reactor having a reactor vessel adapted to be supplied with a coolant, a reactor core disposed in the reactor vessel and including a plurality of fuel assemblies, a plurality of control rods adapted to be inserted into the reactor core and a plurality of control rod driving devices for driving the control rods into and out of the reactor core. A plurality of tubular coolant passage members are disposed above the fuel assemblies so as to receive the heated coolant discharged from the fuel assemblies, so that the heated coolant flows upwardly through the tubular coolant passage members. The tubular coolant passage members provide a chimney effect which enhances the upward flow of the coolant and, hence, increases the flow rate of coolant flowing through the reactor core. In consequence, a greater cooling effect is obtained and the range of power controllable by the control rods is widened. In consequence, the construction of the reactor is simplified and the size is decreased due to elimination of coolant recycling system in the reactor vessel.

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Hitachi, Japan

Koki Yamauchi