I suppose one problem might be selecting an appropriate coolant that doesn't dissolve the salt on contact. Presumably water would, but google says that salt doesn't dissolve in oil so maybe that's an option.
Ideally you wouldn't need to expend energy to keep the coolant cold enough; rather, you'd use the coolant to boil water to run your steam generator.
“Vessel built out of nothing but heat transfer interface and freeze plug". Do some of the materials problems get easier while it's only touching the salt in frozen state?
Ideally you wouldn't need to expend energy to keep the coolant cold enough; rather, you'd use the coolant to boil water to run your steam generator.