We fscking had it back in 1968 and we stopped developing it because none of the components went Ka-Boom. In 1968, we wanted Ka-Boom and we did not want to pay for separate development paths for ordnance and power generation.
From Frank Munger's Atomic City Underground:
Glenn Seaborg and the startup of Molten Salt (1968)
The date is Oct. 10, 1968, and Atomic Energy Commission Chairman Glenn Seaborg is at the controls for the startup of the U-233-fueled Molten Salt Reactor Experiment at Oak Ridge National Laboratory. (Department of Energy archives/Frank Hoffman photo)
Uranium 233 is an isotope and a product of the transmutation (Neutron enrichment) of Thorium (Atomic weight of 232) (Much more detail here, here and here.)
These reactors can also burn spent nuclear waste from conventional reactors and when the fuel is eventually consumed, the waste needs to be sequestered for only a few hundred years, not tens of thousands. The fact that the reactor is intrinsically safe is just gravy.
There is a wonderful resurgence of these designs for electrical power generation and medical isotopes. The only problem is that it is happening in China and India and not here where it was invented...