Hitachi, Ltd.

Shiro Nakamura

Mikio Sakurai

Yuichiro Yoshimoto

Takao Igarashi

Koki Yamauchi

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.

Nuclear reactor

System for preventing erroneous operation of control rods for securing a safety control of a nuclear reactor. The erroneous operation preventing system is comprised of a control rod objective position setting means for setting an objective position of a control rod, a control rod position detector for detecting a position of the control rod, and an operation means which operates a difference between the objective position set up and the detected position of the control rod being operated and produces a signal for blocking the control rod operation when the control rod is operated so that the difference goes away from zero. The erroneous operation blocking system stops the control rod at the first possible control rod stopping position. The erroneous operation preventing system includes a return operation commanding unit for compensating for erroneous operation of the control rod when the control rod is erroneously operated.

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Hitachi, Japan

Shiro Nakamura