RECOVERY OF URANIUM AND THORIUM FROM GRAPHITE FUELS. I. LABORATORY DEVELOPMENT OF A GRIND-LEACH PROCESS
A grind-leach method is presented for the recovery of U from uranium- graphite fuel elements. With unirradiated graphitized high-density reimpregnated fuel ground to -200 mesh containing 5.5 to 14 wt.% U and less than 0.4% Fe, 99.9% or more of the U was recovered with two leaches of boiling 15.8 M HNO/sub 3/ and thorough washing of the graphite residue. Yields were 0.1 to 0.2% lower when the fuel was ground to only -4 + 8 mesh. Recovery of U decreased rapidly with decreasing U concentration in the fuel, rendering the grind-leach method unsuitable for fuels containing less than 3% U. 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 O was excluded from the system, suggesting that, in fuel specimens which had been exposed to the laboratory atmosphere for months, the U was present as UO/sub 2/ rather than UO/sub 2/. Leaching of -200 mesh samples of 1.5% U-7.2% Thgraphite fuel with boiling 15.8 M HNO/sub 3/ resulted in maximum U and Th recoveries of about 90%. Leaching with 15.8 M HNO/sub 3/-0.04 M NaF-0.04 M Al(NO/sub 3/)/sub 3/ offered no advantages. Combustion of the fuel followed by dissolution of the U and thorium oxide products in boiling 13 M HNO/ sub 3/0.04 M NaF-0.04 M Al(NO/sub 3/)/sub 3/ resulted in essentially quantitative recovery of the metals. A survey of processing methods indicated that combustion and digestion or particle size disintegration and leaching are the better possibllities for graphite fuels. (auth)
- Research Organization:
- Oak Ridge National Lab., Tenn.
- DOE Contract Number:
- W-7405-ENG-26
- NSA Number:
- NSA-14-010530
- OSTI ID:
- 4156760
- Report Number(s):
- ORNL-2761
- Country of Publication:
- United States
- Language:
- English
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