Yes, one of the reason I like that reactor design. They basically put something in the fluoride that is basically designed to corrode so that the actual reactor vessel doesn't. If I understand correctly.

Their design doesn't require the 7 year swap cycle most MSR do.

Right! They've got the same thing going that ordinary LWRs do: the neutrons lose their energy in a surround liquid rather than in a solid moderator or solid structural materials other than the fuel rods (which are designed to be replaced often anyway). The design even adds some hafnium to the coolant salt (substituting for zirconium, which is the sacrificial metal you refer to there); hafnium serves to shield the reactor walls from thermalized neutrons.

One additional advantage of separating the fuel salt from the coolant salt is that the coolant salt volume can be increased as desired, making the thermal inertia of the reactor as large as one likes independent of reactor power or size of the fuel load.

> One additional advantage

The problem with that is that you would likely require a different design and go threw full licensing. So in practice this will likely not be used.

Presumably it would happen at design time and a large, high thermal inertia design would be the one licensed.