PROGRESS ON THE DEVELOPMENT OF URANIUM CARBIDE-TYPE FUELS. Final Report on the AEC Fuel-Cycle Program

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Abstract
A 2 1/2-year study of uranium monocarbide is concluded. The skull arc- melting equipment and process were developed to produce 6-kg castings with a carbon content predictable within plus or minus 0.05 wt%. The preparation of a homogenous skull is important in obtaining this control, and may be accomplished by melting pre-alloyed uranium carbide in a water-cooled copper crucible. Once a homogeneous skull is prepared, this compositional control can be maintained even with elemental charges. Erosion of the graphite electrode is minimized by using outgassed TSF graphite and is compensated for by adding small amounts of elemental uranium. The highest quality material is produced by vacuum melting and casting procedures. Hot hardness, dilation, and resistivity measurements to about 1600 deg C were performed. A change in state of UC/sub 2/ at about 870 deg C was indicated. As-cast mixtures of UC and UC/sub 2/ containing 7.0 wt% carbon were found to transform to U/sub 2/C/sub 3/ on reheating by a sluggish reaction between ll00 and 1700 deg C. Rates of self-diffusion of carbon in uranium monocarbide were about l000 times the rates of self-diffusion of uranium in uranium monocarbide between l200 and 2200 deg C. Below 700 deg C, uraniummore » monocarbide showed no gross dimensional changes as a function of irradiation to a burnup of 0.7 at.% of the uranium. Resistivity and lattice strain of uranium monocarbide showed significant changes at a burnup of only 0.004 at.% of the uranium. No further significant change occurred as a function of additional burnup. A portion of this effect was annealed out in irradiation at 700 deg C. Uranium sesquicarbide showed no gross dimensional changes under irradiation to a burnup of 0.56 at.% of the uranium at about 700 deg C. Metastable uranium dicarbide structures which began to precipitate graphite were not compatible with NaK. (auth) « less

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