[Layman, but I've read up quite a bit on thorium and molten salt reactor designs]
The 1959 Sodium Reactor experiment was to demonstrate the feasibility of a sodium-cooled reactor as the heat source for a commercial power reactor to produce electricity. It used fuel rods similar to rods used in reactors in operation today.
Conversely the The Molten Salt Reactor experiment[1] used uranium fuel dissolved into a salt as both fuel and coolant for the reactor - this design enables significant advantages over traditional reactors powered by solid fuel.
[1] https://www.etec.energy.gov/Operations/Major_Operations/SRE....