STUDIES OF GRAPHITE FOR FUEL ELEMENTS

Improved graphites for use in fuel elements were developed from artificial graphites and phenolic resins. These materials are particularly well suited for fuelelement preparation. The resins do not soften during baking, so bodies hold their shape and show good dimensional uniformity. The physical properties of graphite were obtained without heating at "graphitizing" temperatures, which would be detrimental to UO/sub 2/ or other inclusions of nuclear fuel. High densities and bending strengths, viz., 1.80 g/cm/sup 3/ and 15,000 psi, were obtained directly without the usual impregnation of the baked product with pitch and rebaking. At 2770 deg F, one of the experimental bodies had a tensile strength of 8250 psi as compared to 4700 psi for Type ECA, a commercial graphite of irterest for fuel ele ments. UO/sub 2/-bearing bodies were prepared by using the improved graphites as matrices. The UO/sub 2/ was added during primary fabrication of the bodies by several different methods which produced a wide range of particle sizes. Consideration of the qualitative effects of UO/sub 2/ particle size and of some of the experimental results indicates that the use of UO/sub 2/ nodules between 100 and 800 microns in diameter may have three important advantages: (1) less fission damage to the graphite, (2) less diffusion and loss of U, and (3) better retention of fission products by the fuel element. (auth