Patent Number: 050733346
Section: abstract

A self-actuated nuclear reactor shutdown system includes a control rod, a temperature sensitive electromagnet disposed above the control rod for causing the control rod to latch thereto and unlatch therefrom, and a control rod insertion portion around which a plurality of wrapper tubes each accommodating a fuel assembly are arranged. The present invention is characterized in that the upper part of the wrapper tube or an extension tube connected to the upper end of the wrapper tube is made of a temperature-sensitive magnetic material having a characteristic by which the saturation flux density thereof will be reduced at the time of an extraordinary rise in the temperature of a coolant flowing through the fuel assembly. The temperature sensitive magnetic material constitutes a part of a magnetic circuit of the electromagnet. When the coolant at a high temperature raises the temperature of the temperature-sensitive magnetic material, the magnetic circuit of the electromagnet is broken, and the control rod is released from the electromagnet and drops into the reactor core to shut down the reactor.