Two milestone tests were conducted in the Experimental Breeder Reactor II (EBR-II), demonstrating some of the inherent safety features of a liquid-metal reactor. The first test was a loss of flow without scram and the second was a loss of heat sink without scram. Both tests were initiated from 100% power, and in both tests the reactor was shut down passively-by natural processes, principally thermal expansion—without automatic scram, operator intervention, or the help of special incore devices. The temperature transients during the tests were mild, as predicted, and there was no damage to the core or reactor plant structures. The tests plus analysis demonstrated the feasibility of inherent passive shutdown for undercooling accidents and identified the more important features necessary for inherent shutdown and passive cooling. The results provide a technical basis for future experiments in EBR-II to investigate inherent safety for transient overpower accidents and to provide additional data for validation of computer codes used for design and safety analysis of inherently safe reactor plants.