You're thinking of sodium. This reactor uses salt, which is very stable, just like the salt on your kitchen table.
The lack of any sort of driver for chemical explosions is one of the advantages of molten salt reactors over light water reactors, in which the water can split into oxygen and hydrogen and cause explosions (as we saw at Fukushima).
That's pretty cool but the guy's conclusion is that it's not a chemical explosion, it's just from the water turning to steam. But I'll concede that we shouldn't drop a molten salt reactor in a lake.
I was indeed thinking about the NaK (sodium+potassium) alloy (which is used in some molten salt reactors, but not this one). And indeed this reactor design uses LiF (Lithiumfluoride). However, LiF-based salts have the obvious drawback of their high melting points (pure LiF 840 °C, FLiBe 460 °C).
Do you have any examples of liquid-fueled reactors using NaK?
Some MSR companies are working on fast reactors using chloride salts, including Moltex, Elysium, and Terrapower (in a project separate from their better-known sodium-cooled fast reactor).
High temperature is a property of all MSRs I know of and does have some advantages, including better thermodynamic efficiency and usefulness for process heat.
The lack of any sort of driver for chemical explosions is one of the advantages of molten salt reactors over light water reactors, in which the water can split into oxygen and hydrogen and cause explosions (as we saw at Fukushima).