RECOVERY OF URANIUM AND THORIUM FROM GRAPHITE FUELS. I. LABORATORY DEVELOPMENT OF A GRIND-LEACH PROCESS

摘要

A grind-leach method is presented for the recovery of uranium from uranium-graphite fuel elements. With unirradiated graphitized high-density reimpregnated fuel ground to -200 mesh containing 5.5-14 wt ％ uranium and less than 0.4％ iron, 99.9％ or more of the uranium was recovered with two leaches of boiling 15.8 M HNO3 and thorough washing of the graphite residue. Yields were 0.1-0.2％ lower when the fuel was ground to only -4 +8 mesh. Uranium recovery decreased rapidly with decreasing uranium concentration in the fuel, rendering the grind-leach method unsuitable for fuels containing less than 3％ uranium. The gases evolved during leaching were a mixture of nitrogen oxides. No volatile carbon-containing gas was found. Preliminary data indicated that about 3.2 moles of nitric acid was consumed per mole of metal when oxygen was excluded from the system, suggesting that, in fuel specimens which had been exposed to the laboratory atmosphere for months, the uranium was present as U02 rather than UC2O.