[en] Power Reactor and Nuclear Fuel Development Corporation (PNC) and Japan Atomic Power Company (JAPC, supported by the Japanese ten electric utility companies) are jointly developing the self actuating shutdown system (SASS) for liquid metal fast breeder reactors. A synthetic program was made and put into practice to investigate the feasibility of temperature sensitive electromagnet (TSEM) type self actuated shutdown system to the Demonstration Fast Breeder Reactor whose construction is expected to start in late 1990s. As of the end of 1988, fundamental function and properties of the system have been obtained, which suggest that the shutdown system with the TSEM would meet the severer safety requirement of fast reactors. Successive studies are under progress to examine the performance and availability of the system. A potential demonstration test of the SASS in actual reactor condition is being studied. (author). 4 refs, 9 figs, 2 tabs