Apologies for linking to the physics aggregate equivalent of 4Chan.
Oscar Wildcat Molten salts are amazing stuff. Unlike a molten metal, the salts are ionic when molten. All kinds of shit dissolves in them, and reactions take place with available energies far in excess of anything you're used to in aqueous solutions.
Frankly, I'm amazed the project went as well as it did. From the wiki I gather that radioactive tellurium was causing intergranular cracking in the hastelloy. If that's all the corrosion that happened, that's pretty remarkable. The only thing I've ever found that can handle the material is carbon. Even then, you end up with a lot of carbon dissolved in the salts.
Another fun fact: putting something in the molten salt with even the merest hint of moisture will cause a steam explosion spattering the molten salt like hot oil. I once poured a crucible of the stuff into a pan to cool that I forgot to dry out with a torch. All the of salt ended up outside the pan from the explosion. I wasn't hurt but suitably chastened.
That guy One of the cross beams has gone out of skew on the treadle.