Hitachi-ge Nuclear Energy, Ltd.

Doryokuro Kakunenryo Kaihatsu Jigyodan

Kiyoshi Harada

Toshihiro Kodama

Hirokazu Akatsuka

Takahiro Tsuchiya

Yuuichi Matsushita

Tomonori Soga

A control rod drive mechanism includes an outer tube, a guide tube disposed inside the outer tube, a ball tube, a hollow piston, and an electric motor. A gap between a ball traveling side of the screw shaft and the traveling balls and a gap between the traveling balls and a ball traveling side of the ball nut, having the gap coefficient (A) is given by: A=((2&#xd7;R&#x2212;L)&#x2212;D)&#xf7;(2&#xd7;R&#x2212;L). The diameter of the traveling balls is determined to satisfy the expression given by A, in which A has the value of more than 0.03 and less than 0.17.

Gap expanding method of ball screw and fine motion control rod drive mechanism incorporating gap expanded ball screw

It is an object of the present invention to provide a gap expanding method of a ball screw for preventing an increase in torque relative to an electric motor due to a protruding bulge caused by generation of a scar on the traveling side of the screw shaft of the ball screw, and to provide a control rod drive mechanism incorporating the gap expanded ball screw. In a ball screw disposed in a control rod drive mechanism, the ball screw has a screw shaft and a ball nut engaged with the screw shaft via travelling balls, and the balls are each configured to have a diameter smaller than that of the existing ball, thereby expanding a gap between a ball traveling side of the screw shaft and the ball and a gap between the ball and a ball traveling side of the ball nut.

A diving bell type control rod of sodium bond type. The control rod including a plurality of control elements each comprising a pellet chamber for packing B.sub.4 C pellets and disposed in a cladding tube, an intermediate plug disposed above the pellet chamber, an upper chamber formed above the intermediate plug, a vent tube allowing the pellet chamber to communicate with the upper chamber while penetrating through the intermediate plug, upper and lower vent holes formed in upper and lower two stages in the cladding tube at the upper chamber, a sodium inflow port opening to the upper surface of the intermediate plug, and a sodium introduction tube extending from the sodium inflow port to a position below the lower end surface of the intermediate plug while penetrating through the intermediate plug.

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Hitachi, Japan

Kiyoshi Harada