Self-actuated reactor shutdown system using a curie temperature electromagnet

A Self-Actuated Shutdown System (SASS) has been under development at Westinghouse for several years as part of the U.S. LMFBR Safety/Development Program. This shutdown system uses the temperature dependent magnetic properties of a nickel-iron alloy, exposed to the outlet coolant of core fuel pins, to control the holding force of an electromagnet which supports a neutron absorber assembly. If core temperatures rise above normal, the temperature dependent alloy inherently reduces the electromagnet holding force below the weight of the assembly, releasing the absorber into the core. This design has reached an advanced stage of development, in which many of the key features have been fully verified. One key element in the design is the combined thermal-magnetic system performance, as it affects the accident response time. The related phenomena have been investigated through both an analytic and experiment program, and results indicate that the response time necessary to insure inherent termination of applicable accident events is readily achievable