Self-operation type control rod drive

Purpose: To generate a reliable scram signal by ensuring the contact OFF operation. Constitution: A detection portion is prepared by charging liquid metal to the lower portion of a tightly closed vessel, charging gases in the upper space and incorporating electrical contacts so as to dipped in the liquid metal in the normal state. Bellows are disposed by way of a conduit pipe to the lower portion of the tightly closed vessel. When abnormality should occur in the reactor to elevate the temperature, gases are expanded to increase the inner pressure thereby depress the liquid metal downwardly and the bellows are extended to absorb the pressure. Accordingly, the contacts are exposed to open the circuit for the control rod drives and deactivate the electromagnet, by which the control rod is released and fallen spontaneously to shutdown the reactor. (Sekiya, K.)