The Molten Salt Reactor Experiment has been refueled with an enriching salt concentrate,7LiFUF4(73 to 27 mole%). Sixty-three kilograms of this was prepared in a shielded cell in the Thorium-Uranium Recycle Facility at Oak Ridge National Laboratory. The preparation process involved reducing233UO3to UO2by treatment with hydrogen, converting the233UO2to233UF4by hydrofluorination, and fusing the233UF4with LiF. Its preparation in a shielded cell was required because of the high232U content (222 ppm) of the233U.The product salt, containing 39 kg of uranium (91.4%233U), was low in oxide content (50 ppm) and the concentration of the corrosion products, chromium, iron, and nickel, was minimal at less than (0.05%) total.