Ironically, the EBR-II reactor in Idaho was the first to demonstrate true passive shutdown and cooling in 1986. It first operated in 1964, 55 years ago! Unfortunately, we shut this reactor and the research surrounding it down in '94. [1]

[1] https://en.wikipedia.org/wiki/Experimental_Breeder_Reactor_I...

Very fascinating, why was it shut down tho?

Breeders were based on unrealistic projections of there being a thousand reactors in the US by the year 2000. Under such extreme growth, uranium would be getting scarce, so breeding would be needed.

But that didn't happen, and, absent uranium shortages, breeder reactors are more expensive than ordinary thermal reactors. There's also the small problem of fast breeders being potentially subject to prompt fast supercriticality during a meltdown. That's one of the few ways to make an accident worse than Chernobyl.

Basically because we as a nation had largely given up on nuclear energy back then. Almost all research on advanced reactors was canned by Clinton at this time. The people who worked on it were mortified: "Doesn't the country know what of has here?" they wondered.

Probably a combination of the bullet points in https://en.wikipedia.org/wiki/Breeder_reactor#Discussion

> "Nuclear power is weird—it exists to produce electricity, and at the same time it can’t exist without electricity.

This is a problem for a lot of power plants, although most non-nuclear ones can safely survive a sudden shutdown. Starting up after a total shutdown is known as "black start" and an important part of contingency planning: https://www.drax.com/technology/black-start-important-back-p...