[acidburnNSA]

The Experimental Breeder Reactor 2 on what is now the Idaho National Lab was the first reactor to demonstrate full passive safety in 2 related tests in 1986. In the first, they turned off all primary pumps and did not insert the control rods. The reactor shut itself down and established natural circulation decay-heat removal. This class of event (unprotected loss of flow) would melt the core of almost any other kind of reactor. Then they did a unprotected loss of heat sink to the same result. My dissertation advisor was there, and said that it was glorious. They knew that they had finally achieved truly safe, socially acceptable nuclear energy. Less than a month later Chernobyl happened and the advanced breeder reactors with their inherent safety have still not been developed commercially.

Breeders use low-pressure coolants with very high heat capacity, thermal conductivity, and boiling points so they can go to natural circulation easily at decay heat levels.

https://en.wikipedia.org/wiki/Experimental_Breeder_Reactor_I...