[thackney]

Fermi wasn’t the same type. It was cooled by salt (sodium), but it was a fast breeder. The fuel wasn’t mixed into the salt . This design is very different.

[867V309]

This design is very different.

I never said it wasn't.

But in the nuke power business, it's always the unexpected that bites you in the butt. Why anyone would put their faith in the devastatingly horrific potential of a nuke when we can't even secure government computers is totally beyond me.

[Zathras]

Actually Fermi was liquid sodium metal.
Few elements make great moderators (slowing neutrons), are liquid or gases at fairly low temp and do NOT absorb neutrons.

Typical Moderators
Hydrogen
Helium
Carbon
Sodium Metal
Heavy Water (presence of Hydrogen)
Distilled Water (presence of Hydrogen)

Sodium is difficult to work with as refueling is done blind.
No way to see where the fuel bundles are.
You need a minimal amount of heat to get pumps flowing.
Also goes BadaBOOM in presence of any water.