The MSRE went critical on June 1, 1965 and operated for 4.5 years until it was shut down in December 1969. The MSRE was the first (and probably only) reactor to operate on all three fissile fuels: U-233, U-235, and Pu-239. During its operation, uranium was completely removed from the salt through fluorination by bubbling gaseous fluorine through the salt. The fluorine caused the uranium tetrafluoride to convert to uranium hexafluoride, which is gaseous, and could then be removed. In 4 days, 218 kg of uranium was separated from the intensely radioactive fission products and its activity was reduced by a billionfold. The reactor was then loaded with U-233 that had been made by early runs of thorium fuel at the Indian Point reactor in New York.